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Explainer: What are chemical bonds?
Imagine a glass jar holding 118 types of building blocks. Every type is a slightly different color, size and shape. And each represents an atom of a different element on the periodic table. With enough jars, you can use the blocks to build anything — as long as you follow a few simple rules. A combination of blocks is a compound. Within the compound, bonds are what “glue” each of the blocks together. Additional, weaker types of bonds can attract one compound to another.
These bonds are quite important. Essential, really. Quite simply, they hold our universe together. They also determine the structure — and therefore the properties — of all substances. To know if a material dissolves in water, for instance, we look to its bonds. Those bonds also will determine if a substance conducts electricity. Can we use a material as a lubricant? Once again, check out its bonds.
Chemical bonds broadly fall into two categories. Those that hold one building block to another inside a compound are known as intra bonds. (Intra means within.) Those that attract one compound to another are known as inter bonds. (Inter means between.)
Intra- and inter-bonding are further divided into different types. But electrons control all bonds, no matter what type.
Electrons are of one the three primary sub-atomic particles that make up atoms. (Positively charged protons and electrically neutral neutrons are the others.) Electrons carry a negative charge. How they behave will control the properties of a bond. Atoms can give up electrons to a neighboring atom. Other times, they might jointly share the electrons with that neighbor. Or electrons can shift around inside a molecule. When the electrons move or shift, they create electrically positive and negative areas. Negative areas attract a positive area and vice versa.
Bonds are what we call those attractions between negative and positive areas.
Intra-bond type 1: Ionic
Electrons can be passed between atoms just like money can be handed from one person to another. The atoms of metallic elements tend to lose electrons easily. When that happens, they become positively charged. Non-metal atoms tend to gain the electrons that the metals lose. When this happens, the non-metals become negatively charged.
This is an artist’s depiction of the lattice structure that makes up table salt. Each sodium ion (Na+) is held in place by its attraction to chloride ions (Cl-) and vice-versa, through ionic bonds. jack0m/DigitalVision Vectors/Getty Images
Such charged particles are known as ions. Opposite charges attract one another. The attraction of a positive ion to a negative ion forms an ionic (Eye-ON-ik) bond. The resulting substance is called an ionic compound.
An example of an ionic compound is sodium chloride, better known as table salt. Within it are positive sodium ions and negative chloride ions. All of the attractions between the ions are strong. A lot of energy is required to pull these ions apart. This trait means sodium chloride has a high melting point and a high boiling point. Those charges also mean that when salt is dissolved in water or melted, it becomes a good conductor of electricity.
One tiny grain of salt has billions and billions of these tiny ions attracted to one another in a giant, 3-D arrangement called a lattice. Just a few grams of salt could contain more than a septillion sodium and chloride ions. How big a number is that? It’s a quadrillion times a billion (or 1,000,000,000,000,000,000,000,000).
Intra-bond type 2: Covalent
A second type of bond doesn’t transfer an electron from one atom to another. Instead, it shares two electrons. Such a shared pair of electrons is called a covalent (Koh-VAY-lunt) bond. Imagine a handshake between one hand (an electron) each from two people (atoms).
Water is an example of a compound formed by covalent bonds. Two hydrogen atoms each join up with an oxygen atom (H2O) and shake hands, or share two electrons. As long as the handshake holds, it glues the atoms together. Sometimes an atom will share more than one pair of electrons. In these cases, a double or triple bond forms. The small groups of atoms bonded together in this way are called molecules. H2O represents one molecule of water.
This drawing depicts the covalent bonds that hold together a water molecule. The two hydrogen atoms are each attached to the oxygen atom through a pair of shared electrons (the smaller, darker blue balls). ttsz/iStock/Getty Images Plus
But why do bonds form?
Imagine standing on the very edge of the top step of a huge flight of stairs. You might feel unstable there. Now imagine standing at the bottom of the staircase. Much better. You feel more secure. This is why intra-bonds form. Whenever atoms can create a more energetically stable situation they do so. Forming one or more chemical bonds with other atoms gives the starting atom more stability.
Inter-bonding
Once covalent molecules form, inter-bonding can attract one molecule to another. Because these attractions are between molecules — never inside them — they are called intermolecular forces (IMFs). But first, a word about something related: electronegativity (Ee-LEK-troh-neg-ah-TIV-ih-tee).
This mouthful of a term refers to the ability of an atom within a covalent bond to attract electrons. Remember, a covalent bond is a shared pair of electrons. Imagine a molecule where atom A shares a pair of electrons with atom B. If B is more electronegative than A, then the electrons in its covalent bond will be shifted towards atom B. This gives B a tiny negative charge. We mark this using the lowercase Greek letter delta together with a minus sign (or δ-). The lowercase delta denotes a small or partial charge. Because negative electrons have moved away from atom A, the charge it develops is written δ+.
The shifting of electrons to create these positive and negative areas results in a separation of electrical charge. Chemists refer to this as a dipole (DY-pohl). As its name suggests, a dipole has two poles. One end is positive; the other negatively charged. The IMF is what develops between the positive pole of one molecule and the negative pole of another. Chemists call this a dipole-dipole attraction.
When hydrogen atoms bond covalently to very electronegative atoms, such as nitrogen, oxygen or fluorine, an especially large dipole develops. The intermolecular dipole attraction is the same as described above but is given a special name. It is called a hydrogen bond.
Electrons sometimes move around within bonds for reasons other than differences in electronegativity. For example, when one molecule approaches another one, the electrons within the covalent bonds of the two molecules repel one another. This creates the same type of δ+ and δ- charges as described above. And the same attractions occur between the δ+ and δ- parts. This type of IMF gets a different name: a London dispersion force.
No matter how electrons are moved to create the δ charges, the results are similar. Opposite δ+ and δ- charges attract to create IMFs between molecules.
Chemical changes, physical changes and bonds
Sometimes a chemical undergoes a phase change. Ice may melt into water or vaporize as steam. In such changes, the chemical — in this case, H2O — remains the same. It is still water: frozen water, liquid water or gaseous water. It’s the forces of attraction between the water molecules — the inter-bonds — that are broken.
Other times, chemicals may transform into a new substance. To get there, intra-bonds break and then new ones form. It’s like dismantling the building blocks from which you had made a racecar or a castle. Now you use their pieces to build a house or a table.
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New recycling technologies could keep more plastic out of landfills
It feels good to recycle. When you sort soda bottles and plastic bags from the rest of your garbage, it seems like you’re helping the planet. The more plastic you put in the blue bin, the more you’re keeping out of landfills, right?
Wrong. No matter how much plastic you try to recycle, most ends up in the trash heap.
Take flexible food packages. Those films contain several layers, each made of a different type of plastic. Because each type must be recycled separately, those films are not recyclable. Even some items made from only one kind of plastic are not recyclable. Yogurt cups, for instance, contain a plastic called polypropylene (Pah-lee-PROH-puh-leen). When this gets recycled, it turns into a gross, dark, smelly material. So most recycling plants don’t bother with it.
Only two kinds of plastic are commonly recycled in the United States. One is the type used in soda bottles. That’s called PET, short for polyethylene terephthalate (Pah-lee-ETH-uh-leen TAIR-eh-THAAL-ayt). The other is the plastic in milk jugs and detergent containers. That’s high-density polyethylene, or HDPE. Together, those plastics make up only a small fraction of plastic trash. In 2018 alone, the United States landfilled 27 million tons of plastic, according to the U.S. Environmental Protection Agency. A mere 3 million tons was recycled.
Low recycling rates aren’t just a problem in the United States. Only 9 percent of all the world’s plastic trash has ever been recycled. Twelve percent was burned. Seventy-nine percent has piled up on land or in waterways. Researchers reported those estimates in 2017 in Science Advances.
Good news/bad news
The amount of plastic recycled in the United States has increased over the last few decades. However, those levels still pale in comparison with the amount of plastic that goes into landfills.
Plastic waste management, 1960–2018
E. Otwell
E. Otwell
Source: EPA
Even when plastic does get recycled, it isn’t good for much. Recycling changes the consistency of a plastic. So recycled plastics have to be mixed with brand-new material to make sturdy products. What’s more, recycling a bunch of different colored plastic together creates a dark mixture. That means a lot of recycled plastic can only be used to make items whose color doesn’t matter, such as benches and dumpsters.
Plastic recycling clearly has a lot of room for improvement. And with plastic piling up everywhere from mountaintops to the seafloor, there is an urgent need for better recycling. Luckily, chemists around the world are on the case. Some are trying to make it easier to recycle more types of plastic. Others are trying to turn recycled plastic into more useful products. Both strategies could cut how much plastic winds up in landfills or oceans.
Picking plastics apart
One big challenge to recycling is that every type of plastic must get processed separately. “Most plastics are like oil and water,” says Geoffrey Coates. He’s a chemist at Cornell University in Ithaca, N.Y. Plastics just don’t mix, he says. Take, for example, a detergent container. The jug may be HDPE plastic, but its cap is polypropylene. What would happen if a recycling plant melted those two plastics together and tried to make a new jug from the blend? “It would basically crack down the side,” Coates says. “It’s crazy brittle. Totally worthless.”
That’s why all the plastic in the recycling bin first goes to a material recovery facility. There, people and machines sort trash. Sorted plastics are then washed, shredded, melted and remolded. The system works well for simple items like soda bottles and milk jugs. But it doesn’t work for items like deodorant containers. A deodorant bottle, cap and crank could all be different plastics.
Food packaging films made of different plastic layers are even harder to take apart. Every year, 100 million tons of these films are made worldwide. Those films all go to landfills, says George Huber. He’s a chemical engineer at the University of Wisconsin–Madison.
Huber and his colleagues came up with a way to sort these pesky mixes of plastics. The researchers use different liquids to dissolve different plastic parts off an item. The trick is choosing the right liquids to dissolve only one plastic at a time, Huber says. This strategy was described last November 18 in Science Advances.
False advertising
Many plastic products are labeled with a number inside a triangle that symbolizes recycling. Yet, only plastics with 1 (polyethylene terephthalate) or 2 (high-density polyethylene) are widely recycled in the United States. The rest typically get buried in landfills.
PET
Water and soft drink bottles, salad domes, cookie trays, salad dressing and peanut butter containers
HDPE
Milk and juice bottles, freezer bags, shampoo and detergent bottles
PVC
Cosmetic containers, commercial cling wrap
LDPE
Squeeze bottles, cling wrap, trash bags
PP
Microwave dishes, ice cream tubs, yogurt containers, detergent bottle caps
PS
CD cases, plastic disposable cups, plastic cutlery, video cases
EPS
Foam polystyrene hot drink cups, food takeaway trays, protective packaging for fragile items
Other
Water cooler bottles, flexible films, multimaterial packaging
Source: Ellen MacArthur Foundation 2017
Huber’s team tested the technique on a food-packaging film. The film contained three plastics: polyethylene, PET and ethylene vinyl alcohol, or EVOH. The researchers first stirred the film into a liquid called toluene (TAHL-you-een). That dissolved the polyethylene layer. Then, Huber’s team dunked the film in another chemical to strip off the EVOH. The researchers plucked out the remaining PET film and set it aside. To recover the other two plastics from the liquids, the researchers mixed in “antisolvent” chemicals. These chemicals caused the plastic molecules drifting in the liquids to clump together so that they could later be fished out.
Making plastics mix
There may be shortcuts to recycling unsorted mixes of plastics. Chemicals called “compatibilizers” help different plastics blend. There is no chemical that allows every type of plastic to mix. But Coates’ team has made one to combine polyethylene and polypropylene. That could make recycling much easier. Those two plastics make up the bulk of the world’s plastic trash.
The new compatibilizer contains specially designed molecules. Each molecule has four pieces. Two pieces of polyethylene alternate with two pieces of polypropylene. Those segments latch on to plastic molecules of the same kind in a mixture. It’s as if polyethylene were made of Legos, and polypropylene were made of Duplos. The compatibilizer molecule is like a connector that fits both types of blocks. That helps polyethylene and polypropylene molecules link up. The researchers reported this work in 2017 in Science.
The first test of this compatibilizer involved using it as a glue. Coates’ team spread a layer of the chemical between a strip of polyethylene and a strip of polypropylene. Then, the researchers tried to peel the plastics apart. The two plastics would normally separate easily. But with the glue between them, the plastic strips broke before the seal.
The researchers also mixed their compatibilizer into a melted blend of the two plastics. Adding just 1 percent of the new chemical created a tough plastic product.
Good as new
Making it easier to recycle plastic isn’t enough. To reuse the same material over and over, recycled plastic needs to be as good as new. Right now, it’s second-rate.
One problem is all the extra chemicals in plastic trash. Plastic items often contain dyes, flame retardants and other additives. Current recycling cannot get rid of those contaminants. As a result, recycled plastic comes with lots of impurities. Few manufacturers can use plastic with a random mishmash of properties to make something new.
Explainer: What are chemical bonds?
Plus, recycling breaks some of the chemical bonds in plastic molecules. That affects the strength and consistency of the material. Recycling plastic is sort of like reheating pizza in the microwave. You get out pretty much what you put in, just not as good. That limits the number of times plastic can be recycled.
The solution to both problems could be a new type of recycling, called chemical recycling. This process takes plastic apart at the molecular level. And it could make pure new plastic an infinite number of times.
The molecules that make up plastics are called polymers. Those polymers, in turn, consist of smaller building blocks called monomers. Heat and chemicals can break polymers down into monomers. Those monomers can then be separated from dyes and other contaminants. Piecing pure monomers back together creates plastic that’s good as new.
Explainer: What are polymers?
“Chemical recycling has really started to emerge as a force … within the last three or four years,” says Eric Beckman. He’s a chemical engineer at the University of Pittsburgh in Pennsylvania. But most chemical recycling requires a whole lot of energy. “It’s not ready for prime time,” he says.
Some plastics are easier to chemically recycle than others. “The one that’s farthest along is PET,” Beckman says. That’s the plastic in water and soft-drink bottles. “That polymer happens to be easy to take apart.” Several companies are trying to chemically recycle PET. One is a French company called Carbios.
Carbios breaks down PET using a molecule called an enzyme. Microbes in compost naturally produce this enzyme to decompose the waxy coating on leaves. But the enzyme is also good at breaking apart PET. “The enzyme is like a molecular scissor,” says Alain Marty. He is the chief scientific officer at Carbios in Saint-Beauzire, France. The enzyme snips PET polymers into their two monomers. One is ethylene glycol. The other is terephthalic acid.
Explainer: What are acids and bases?
Because this enzyme evolved to decompose leaves, not plastic, it’s not perfect. But Marty’s team improved it by redesigning its “active site.” That’s where the enzyme latches onto PET. The redesign involved swapping out some amino acids at the active site for others. Marty and his colleagues reported how they did this April 8, 2020 in Nature.
The researchers tested their upgraded enzyme on plastic flakes from colored PET bottles. About 90 percent of the plastic broke down in about 10 hours. The team purified the PET monomers and used them to make new clear plastic bottles. Those bottles were just as strong as the originals. Carbios is now building a plant in France to chemically recycle PET.
Microbial help
In one study, an enzyme naturally produced by microbes broke down about 50 percent of polyethylene terephthalate, or PET (blue line). A tweaked version of the enzyme broke down more than 80 percent of the plastic (black dotted line). Increasing the amount of the enzyme from 1 milligram per gram of PET to 3 milligrams made it even more efficient — breaking down about 90 percent of the plastic.
PET breakdown by an enzyme
E. Otwell
E. Otwell
Source: V. Tournier et al/Nature 2020
Milder conditions
PET is a special case for chemical recycling. Other plastics are much harder to break down. Taking apart polyethylene, for instance, requires temperatures over 400° Celsius (750° Fahrenheit). At such high heat, the chemistry is chaotic. Plastic molecules break down randomly. The result is jumble of different compounds. Those molecules can be burned as fuel but not used to make new plastic.
Susannah Scott proposes a better way to recycle polyethylene. A chemist, Scott works at the University of California, Santa Barbara. Her idea is to break the plastic down under milder conditions. That more-controlled breakdown could produce ingredients for soaps and other products. These ingredients are called alkylaromatic (AL-kyl-air-oh-MAT-ik) compounds.
To make these, Scott placed polyethylene inside a chemical-reaction chamber. Then she heated it up to 280 °C (540 °F). Her team cooked the plastic with a powder that contained tiny platinum particles for 24 hours. The platinum helps break the carbon-hydrogen bonds in the polyethylene. That process releases hydrogen. The hydrogen then helps break the plastic’s carbon-carbon bonds. This chops the plastic molecules up into smaller pieces. Each piece is about 30 carbon atoms long. Those fragments arrange themselves into rings. Then voilà — alkylaromatic compounds.
Scott and her colleagues tested this technique on a plastic bag and a bottle cap. Both were made of polyethylene. About 69 percent of the plastic bag became liquid containing alkylaromatic compounds. About 55 percent of the bottle cap was converted. Scott’s team reported these results last October 23 in Science. Transforming the polyethylene also produced gases like methane. Those gases could be burned as fuel to heat the reaction chamber.
Built to last
Plastics were never designed to be used more than once. That’s why recycling them is so hard. But some researchers are now asking, “What does the next generation of materials look like? How do you design a material specifically so that it never has to go into a landfill?” Beckman asks. The new goal, he says, is to design a plastic “that falls apart on command.”
A new generation of plastics called PDKs may be infinitely recyclable. PDKs, short for poly(diketoenamine)s, were first described in Nature Chemistry in 2019.
“PDKs have the ability to break their bonds under relatively mild conditions,” says Brett Helms. He’s a chemist at the Lawrence Berkeley National Laboratory in California. Simply dunking a PDK in acid breaks it into its monomers.
The plastic must be dunked in a very acidic liquid to decompose. Say, a pH of 1 or 2. “Materials don’t usually encounter a pH that’s that low,” he notes. “It’s not like if you put PDKs in vinegar, the polymer is going to start breaking down.” But it could make for easy recycling. PDK monomers could then be used to make pristine new plastic, again and again.
The plastics used today are so cheap that it would be hard for any new plastic to compete solely on cost, Beckman says. For now, infinitely recyclable plastic is just a scientific curiosity. But someday, plastics made to be recyclable from the get-go may help solve the world’s plastic waste problem.
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Explainer: What are chemical bonds?
Imagine a glass jar holding 118 types of building blocks. Every type is a slightly different color, size and shape. And each represents an atom of a different element on the periodic table. With enough jars, you can use the blocks to build anything — as long as you follow a few simple rules. A combination of blocks is a compound. Within the compound, bonds are what “glue” each of the blocks together. Additional, weaker types of bonds can attract one compound to another.
These bonds are quite important. Essential, really. Quite simply, they hold our universe together. They also determine the structure — and therefore the properties — of all substances. To know if a material dissolves in water, for instance, we look to its bonds. Those bonds also will determine if a substance conducts electricity. Can we use a material as a lubricant? Once again, check out its bonds.
Chemical bonds broadly fall into two categories. Those that hold one building block to another inside a compound are known as intra bonds. (Intra means within.) Those that attract one compound to another are known as inter bonds. (Inter means between.)
Intra- and inter-bonding are further divided into different types. But electrons control all bonds, no matter what type.
Electrons are of one the three primary sub-atomic particles that make up atoms. (Positively charged protons and electrically neutral neutrons are the others.) Electrons carry a negative charge. How they behave will control the properties of a bond. Atoms can give up electrons to a neighboring atom. Other times, they might jointly share the electrons with that neighbor. Or electrons can shift around inside a molecule. When the electrons move or shift, they create electrically positive and negative areas. Negative areas attract a positive area and vice versa.
Bonds are what we call those attractions between negative and positive areas.
Intra-bond type 1: Ionic
Electrons can be passed between atoms just like money can be handed from one person to another. The atoms of metallic elements tend to lose electrons easily. When that happens, they become positively charged. Non-metal atoms tend to gain the electrons that the metals lose. When this happens, the non-metals become negatively charged.
This is an artist’s depiction of the lattice structure that makes up table salt. Each sodium ion (Na+) is held in place by its attraction to chloride ions (Cl-) and vice-versa, through ionic bonds. jack0m/DigitalVision Vectors/Getty Images
Such charged particles are known as ions. Opposite charges attract one another. The attraction of a positive ion to a negative ion forms an ionic (Eye-ON-ik) bond. The resulting substance is called an ionic compound.
An example of an ionic compound is sodium chloride, better known as table salt. Within it are positive sodium ions and negative chloride ions. All of the attractions between the ions are strong. A lot of energy is required to pull these ions apart. This trait means sodium chloride has a high melting point and a high boiling point. Those charges also mean that when salt is dissolved in water or melted, it becomes a good conductor of electricity.
One tiny grain of salt has billions and billions of these tiny ions attracted to one another in a giant, 3-D arrangement called a lattice. Just a few grams of salt could contain more than a septillion sodium and chloride ions. How big a number is that? It’s a quadrillion times a billion (or 1,000,000,000,000,000,000,000,000).
Intra-bond type 2: Covalent
A second type of bond doesn’t transfer an electron from one atom to another. Instead, it shares two electrons. Such a shared pair of electrons is called a covalent (Koh-VAY-lunt) bond. Imagine a handshake between one hand (an electron) each from two people (atoms).
Water is an example of a compound formed by covalent bonds. Two hydrogen atoms each join up with an oxygen atom (H2O) and shake hands, or share two electrons. As long as the handshake holds, it glues the atoms together. Sometimes an atom will share more than one pair of electrons. In these cases, a double or triple bond forms. The small groups of atoms bonded together in this way are called molecules. H2O represents one molecule of water.
This drawing depicts the covalent bonds that hold together a water molecule. The two hydrogen atoms are each attached to the oxygen atom through a pair of shared electrons (the smaller, darker blue balls). ttsz/iStock/Getty Images Plus
But why do bonds form?
Imagine standing on the very edge of the top step of a huge flight of stairs. You might feel unstable there. Now imagine standing at the bottom of the staircase. Much better. You feel more secure. This is why intra-bonds form. Whenever atoms can create a more energetically stable situation they do so. Forming one or more chemical bonds with other atoms gives the starting atom more stability.
Inter-bonding
Once covalent molecules form, inter-bonding can attract one molecule to another. Because these attractions are between molecules — never inside them — they are called intermolecular forces (IMFs). But first, a word about something related: electronegativity (Ee-LEK-troh-neg-ah-TIV-ih-tee).
This mouthful of a term refers to the ability of an atom within a covalent bond to attract electrons. Remember, a covalent bond is a shared pair of electrons. Imagine a molecule where atom A shares a pair of electrons with atom B. If B is more electronegative than A, then the electrons in its covalent bond will be shifted towards atom B. This gives B a tiny negative charge. We mark this using the lowercase Greek letter delta together with a minus sign (or δ-). The lowercase delta denotes a small or partial charge. Because negative electrons have moved away from atom A, the charge it develops is written δ+.
The shifting of electrons to create these positive and negative areas results in a separation of electrical charge. Chemists refer to this as a dipole (DY-pohl). As its name suggests, a dipole has two poles. One end is positive; the other negatively charged. The IMF is what develops between the positive pole of one molecule and the negative pole of another. Chemists call this a dipole-dipole attraction.
When hydrogen atoms bond covalently to very electronegative atoms, such as nitrogen, oxygen or fluorine, an especially large dipole develops. The intermolecular dipole attraction is the same as described above but is given a special name. It is called a hydrogen bond.
Electrons sometimes move around within bonds for reasons other than differences in electronegativity. For example, when one molecule approaches another one, the electrons within the covalent bonds of the two molecules repel one another. This creates the same type of δ+ and δ- charges as described above. And the same attractions occur between the δ+ and δ- parts. This type of IMF gets a different name: a London dispersion force.
No matter how electrons are moved to create the δ charges, the results are similar. Opposite δ+ and δ- charges attract to create IMFs between molecules.
Chemical changes, physical changes and bonds
Sometimes a chemical undergoes a phase change. Ice may melt into water or vaporize as steam. In such changes, the chemical — in this case, H2O — remains the same. It is still water: frozen water, liquid water or gaseous water. It’s the forces of attraction between the water molecules — the inter-bonds — that are broken.
Other times, chemicals may transform into a new substance. To get there, intra-bonds break and then new ones form. It’s like dismantling the building blocks from which you had made a racecar or a castle. Now you use their pieces to build a house or a table.
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New recycling technologies could keep more plastic out of landfills
It feels good to recycle. When you sort soda bottles and plastic bags from the rest of your garbage, it seems like you’re helping the planet. The more plastic you put in the blue bin, the more you’re keeping out of landfills, right?
Wrong. No matter how much plastic you try to recycle, most ends up in the trash heap.
Take flexible food packages. Those films contain several layers, each made of a different type of plastic. Because each type must be recycled separately, those films are not recyclable. Even some items made from only one kind of plastic are not recyclable. Yogurt cups, for instance, contain a plastic called polypropylene (Pah-lee-PROH-puh-leen). When this gets recycled, it turns into a gross, dark, smelly material. So most recycling plants don’t bother with it.
Only two kinds of plastic are commonly recycled in the United States. One is the type used in soda bottles. That’s called PET, short for polyethylene terephthalate (Pah-lee-ETH-uh-leen TAIR-eh-THAAL-ayt). The other is the plastic in milk jugs and detergent containers. That’s high-density polyethylene, or HDPE. Together, those plastics make up only a small fraction of plastic trash. In 2018 alone, the United States landfilled 27 million tons of plastic, according to the U.S. Environmental Protection Agency. A mere 3 million tons was recycled.
Low recycling rates aren’t just a problem in the United States. Only 9 percent of all the world’s plastic trash has ever been recycled. Twelve percent was burned. Seventy-nine percent has piled up on land or in waterways. Researchers reported those estimates in 2017 in Science Advances.
Good news/bad news
The amount of plastic recycled in the United States has increased over the last few decades. However, those levels still pale in comparison with the amount of plastic that goes into landfills.
Plastic waste management, 1960–2018
E. Otwell
E. Otwell
Source: EPA
Even when plastic does get recycled, it isn’t good for much. Recycling changes the consistency of a plastic. So recycled plastics have to be mixed with brand-new material to make sturdy products. What’s more, recycling a bunch of different colored plastic together creates a dark mixture. That means a lot of recycled plastic can only be used to make items whose color doesn’t matter, such as benches and dumpsters.
Plastic recycling clearly has a lot of room for improvement. And with plastic piling up everywhere from mountaintops to the seafloor, there is an urgent need for better recycling. Luckily, chemists around the world are on the case. Some are trying to make it easier to recycle more types of plastic. Others are trying to turn recycled plastic into more useful products. Both strategies could cut how much plastic winds up in landfills or oceans.
Picking plastics apart
One big challenge to recycling is that every type of plastic must get processed separately. “Most plastics are like oil and water,” says Geoffrey Coates. He’s a chemist at Cornell University in Ithaca, N.Y. Plastics just don’t mix, he says. Take, for example, a detergent container. The jug may be HDPE plastic, but its cap is polypropylene. What would happen if a recycling plant melted those two plastics together and tried to make a new jug from the blend? “It would basically crack down the side,” Coates says. “It’s crazy brittle. Totally worthless.”
That’s why all the plastic in the recycling bin first goes to a material recovery facility. There, people and machines sort trash. Sorted plastics are then washed, shredded, melted and remolded. The system works well for simple items like soda bottles and milk jugs. But it doesn’t work for items like deodorant containers. A deodorant bottle, cap and crank could all be different plastics.
Food packaging films made of different plastic layers are even harder to take apart. Every year, 100 million tons of these films are made worldwide. Those films all go to landfills, says George Huber. He’s a chemical engineer at the University of Wisconsin–Madison.
Huber and his colleagues came up with a way to sort these pesky mixes of plastics. The researchers use different liquids to dissolve different plastic parts off an item. The trick is choosing the right liquids to dissolve only one plastic at a time, Huber says. This strategy was described last November 18 in Science Advances.
False advertising
Many plastic products are labeled with a number inside a triangle that symbolizes recycling. Yet, only plastics with 1 (polyethylene terephthalate) or 2 (high-density polyethylene) are widely recycled in the United States. The rest typically get buried in landfills.
PET
Water and soft drink bottles, salad domes, cookie trays, salad dressing and peanut butter containers
HDPE
Milk and juice bottles, freezer bags, shampoo and detergent bottles
PVC
Cosmetic containers, commercial cling wrap
LDPE
Squeeze bottles, cling wrap, trash bags
PP
Microwave dishes, ice cream tubs, yogurt containers, detergent bottle caps
PS
CD cases, plastic disposable cups, plastic cutlery, video cases
EPS
Foam polystyrene hot drink cups, food takeaway trays, protective packaging for fragile items
Other
Water cooler bottles, flexible films, multimaterial packaging
Source: Ellen MacArthur Foundation 2017
Huber’s team tested the technique on a food-packaging film. The film contained three plastics: polyethylene, PET and ethylene vinyl alcohol, or EVOH. The researchers first stirred the film into a liquid called toluene (TAHL-you-een). That dissolved the polyethylene layer. Then, Huber’s team dunked the film in another chemical to strip off the EVOH. The researchers plucked out the remaining PET film and set it aside. To recover the other two plastics from the liquids, the researchers mixed in “antisolvent” chemicals. These chemicals caused the plastic molecules drifting in the liquids to clump together so that they could later be fished out.
Making plastics mix
There may be shortcuts to recycling unsorted mixes of plastics. Chemicals called “compatibilizers” help different plastics blend. There is no chemical that allows every type of plastic to mix. But Coates’ team has made one to combine polyethylene and polypropylene. That could make recycling much easier. Those two plastics make up the bulk of the world’s plastic trash.
The new compatibilizer contains specially designed molecules. Each molecule has four pieces. Two pieces of polyethylene alternate with two pieces of polypropylene. Those segments latch on to plastic molecules of the same kind in a mixture. It’s as if polyethylene were made of Legos, and polypropylene were made of Duplos. The compatibilizer molecule is like a connector that fits both types of blocks. That helps polyethylene and polypropylene molecules link up. The researchers reported this work in 2017 in Science.
The first test of this compatibilizer involved using it as a glue. Coates’ team spread a layer of the chemical between a strip of polyethylene and a strip of polypropylene. Then, the researchers tried to peel the plastics apart. The two plastics would normally separate easily. But with the glue between them, the plastic strips broke before the seal.
The researchers also mixed their compatibilizer into a melted blend of the two plastics. Adding just 1 percent of the new chemical created a tough plastic product.
Good as new
Making it easier to recycle plastic isn’t enough. To reuse the same material over and over, recycled plastic needs to be as good as new. Right now, it’s second-rate.
One problem is all the extra chemicals in plastic trash. Plastic items often contain dyes, flame retardants and other additives. Current recycling cannot get rid of those contaminants. As a result, recycled plastic comes with lots of impurities. Few manufacturers can use plastic with a random mishmash of properties to make something new.
Explainer: What are chemical bonds?
Plus, recycling breaks some of the chemical bonds in plastic molecules. That affects the strength and consistency of the material. Recycling plastic is sort of like reheating pizza in the microwave. You get out pretty much what you put in, just not as good. That limits the number of times plastic can be recycled.
The solution to both problems could be a new type of recycling, called chemical recycling. This process takes plastic apart at the molecular level. And it could make pure new plastic an infinite number of times.
The molecules that make up plastics are called polymers. Those polymers, in turn, consist of smaller building blocks called monomers. Heat and chemicals can break polymers down into monomers. Those monomers can then be separated from dyes and other contaminants. Piecing pure monomers back together creates plastic that’s good as new.
Explainer: What are polymers?
“Chemical recycling has really started to emerge as a force … within the last three or four years,” says Eric Beckman. He’s a chemical engineer at the University of Pittsburgh in Pennsylvania. But most chemical recycling requires a whole lot of energy. “It’s not ready for prime time,” he says.
Some plastics are easier to chemically recycle than others. “The one that’s farthest along is PET,” Beckman says. That’s the plastic in water and soft-drink bottles. “That polymer happens to be easy to take apart.” Several companies are trying to chemically recycle PET. One is a French company called Carbios.
Carbios breaks down PET using a molecule called an enzyme. Microbes in compost naturally produce this enzyme to decompose the waxy coating on leaves. But the enzyme is also good at breaking apart PET. “The enzyme is like a molecular scissor,” says Alain Marty. He is the chief scientific officer at Carbios in Saint-Beauzire, France. The enzyme snips PET polymers into their two monomers. One is ethylene glycol. The other is terephthalic acid.
Explainer: What are acids and bases?
Because this enzyme evolved to decompose leaves, not plastic, it’s not perfect. But Marty’s team improved it by redesigning its “active site.” That’s where the enzyme latches onto PET. The redesign involved swapping out some amino acids at the active site for others. Marty and his colleagues reported how they did this April 8, 2020 in Nature.
The researchers tested their upgraded enzyme on plastic flakes from colored PET bottles. About 90 percent of the plastic broke down in about 10 hours. The team purified the PET monomers and used them to make new clear plastic bottles. Those bottles were just as strong as the originals. Carbios is now building a plant in France to chemically recycle PET.
Microbial help
In one study, an enzyme naturally produced by microbes broke down about 50 percent of polyethylene terephthalate, or PET (blue line). A tweaked version of the enzyme broke down more than 80 percent of the plastic (black dotted line). Increasing the amount of the enzyme from 1 milligram per gram of PET to 3 milligrams made it even more efficient — breaking down about 90 percent of the plastic.
PET breakdown by an enzyme
E. Otwell
E. Otwell
Source: V. Tournier et al/Nature 2020
Milder conditions
PET is a special case for chemical recycling. Other plastics are much harder to break down. Taking apart polyethylene, for instance, requires temperatures over 400° Celsius (750° Fahrenheit). At such high heat, the chemistry is chaotic. Plastic molecules break down randomly. The result is jumble of different compounds. Those molecules can be burned as fuel but not used to make new plastic.
Susannah Scott proposes a better way to recycle polyethylene. A chemist, Scott works at the University of California, Santa Barbara. Her idea is to break the plastic down under milder conditions. That more-controlled breakdown could produce ingredients for soaps and other products. These ingredients are called alkylaromatic (AL-kyl-air-oh-MAT-ik) compounds.
To make these, Scott placed polyethylene inside a chemical-reaction chamber. Then she heated it up to 280 °C (540 °F). Her team cooked the plastic with a powder that contained tiny platinum particles for 24 hours. The platinum helps break the carbon-hydrogen bonds in the polyethylene. That process releases hydrogen. The hydrogen then helps break the plastic’s carbon-carbon bonds. This chops the plastic molecules up into smaller pieces. Each piece is about 30 carbon atoms long. Those fragments arrange themselves into rings. Then voilà — alkylaromatic compounds.
Scott and her colleagues tested this technique on a plastic bag and a bottle cap. Both were made of polyethylene. About 69 percent of the plastic bag became liquid containing alkylaromatic compounds. About 55 percent of the bottle cap was converted. Scott’s team reported these results last October 23 in Science. Transforming the polyethylene also produced gases like methane. Those gases could be burned as fuel to heat the reaction chamber.
Built to last
Plastics were never designed to be used more than once. That’s why recycling them is so hard. But some researchers are now asking, “What does the next generation of materials look like? How do you design a material specifically so that it never has to go into a landfill?” Beckman asks. The new goal, he says, is to design a plastic “that falls apart on command.”
A new generation of plastics called PDKs may be infinitely recyclable. PDKs, short for poly(diketoenamine)s, were first described in Nature Chemistry in 2019.
“PDKs have the ability to break their bonds under relatively mild conditions,” says Brett Helms. He’s a chemist at the Lawrence Berkeley National Laboratory in California. Simply dunking a PDK in acid breaks it into its monomers.
The plastic must be dunked in a very acidic liquid to decompose. Say, a pH of 1 or 2. “Materials don’t usually encounter a pH that’s that low,” he notes. “It’s not like if you put PDKs in vinegar, the polymer is going to start breaking down.” But it could make for easy recycling. PDK monomers could then be used to make pristine new plastic, again and again.
The plastics used today are so cheap that it would be hard for any new plastic to compete solely on cost, Beckman says. For now, infinitely recyclable plastic is just a scientific curiosity. But someday, plastics made to be recyclable from the get-go may help solve the world’s plastic waste problem.
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Transcriptomic alterations in malignant pleural mesothelioma cells in response to long‑term treatment with bullfrog sialic acid‑binding lectin
Molecular Medicine Reports 2021 June [Link]
Takeo Tatsuta, Arisu Nakasato, Shigeki Sugawara, Masahiro Hosono
Abstract
Malignant pleural mesothelioma (MPM) is a universally lethal type of cancer that is increasing in incidence worldwide; therefore, the development of new drugs for MPM is an urgent task. Bullfrog sialic acid‑binding lectin (cSBL) is a multifunctional protein that has carbohydrate‑binding and ribonuclease activities. cSBL exerts marked antitumor activity against numerous types of cancer cells, with low toxicity to normal cells. Although in vitro and in vivo studies revealed that cSBL was effective against MPM, the mechanism by which cSBL exerts antitumor effects is not fully understood. To further understand the mechanism of action of cSBL, the present study aimed to identify the key molecules whose expression was affected by cSBL. The present study established cSBL‑resistant MPM cells. Microarray analyses revealed that there were significant pleiotropic changes in the expression profiles of several genes, including multiple genes involved in metabolic pathways in cSBL‑resistant cells. Furthermore, the expression of some members of the aldo‑keto reductase family was revealed to be markedly downregulated in these cells. Among these, it was particularly interesting that cSBL action reduced the level of AKR1B10, which has been reported as a biomarker candidate for MPM prognosis. These findings revealed novel aspects of the effect of cSBL, which may contribute to the development of new therapeutic strategies for MPM.
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Transcriptomic alterations in malignant pleural mesothelioma cells in response to long‑term treatment with bullfrog sialic acid‑binding lectin
Molecular Medicine Reports 2021 June [Link]
Takeo Tatsuta, Arisu Nakasato, Shigeki Sugawara, Masahiro Hosono
Abstract
Malignant pleural mesothelioma (MPM) is a universally lethal type of cancer that is increasing in incidence worldwide; therefore, the development of new drugs for MPM is an urgent task. Bullfrog sialic acid‑binding lectin (cSBL) is a multifunctional protein that has carbohydrate‑binding and ribonuclease activities. cSBL exerts marked antitumor activity against numerous types of cancer cells, with low toxicity to normal cells. Although in vitro and in vivo studies revealed that cSBL was effective against MPM, the mechanism by which cSBL exerts antitumor effects is not fully understood. To further understand the mechanism of action of cSBL, the present study aimed to identify the key molecules whose expression was affected by cSBL. The present study established cSBL‑resistant MPM cells. Microarray analyses revealed that there were significant pleiotropic changes in the expression profiles of several genes, including multiple genes involved in metabolic pathways in cSBL‑resistant cells. Furthermore, the expression of some members of the aldo‑keto reductase family was revealed to be markedly downregulated in these cells. Among these, it was particularly interesting that cSBL action reduced the level of AKR1B10, which has been reported as a biomarker candidate for MPM prognosis. These findings revealed novel aspects of the effect of cSBL, which may contribute to the development of new therapeutic strategies for MPM.
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Here’s why people picked certain stars as constellations
The Big Dipper’s stars are a celestial landmark. Visible in the Northern Hemisphere’s night sky, the stars draw out a shape like a scoop with a handle. Beginner stargazers can easily pick it out. Now, scientists have shown that three factors can explain why certain groups of stars form such recognizable patterns. One is how bright the stars are. Another is how far apart they are. And a third has to do with how human eyes move.
The Big Dipper is part of the constellation Ursa Major. That’s one of many star groupings that people in the past selected for their shapes. Some shapes were said to depict animals, people or objects. Sophia David wondered why people selected these star groupings. She is a high school student at Friends’ Central School in Wynnewood, Penn.
“Ancient people from various cultures connected similar groupings of stars independently of each other,” said David. That suggests that different people were perceiving the stars in the same way. So David teamed up with scientists at the University of Pennsylvania in Philadelphia. She presented their work March 18 at an online meeting of the American Physical Society.
The researchers thought about how the eyes travel across this night sky. Human eyes tend to move in discrete jumps, called saccades (Seh-KAADS). That’s when both eyes quickly shift from one point of interest to another. The team created a computer simulation based on the distribution of saccade lengths. They also included two basic details of the night sky as seen from Earth. The first was how far apart different stars appear from one another in the sky. The second was how bright various stars are.
The technique could pick out single constellations. One constellation it picked out was the star grouping known as Dorado, the dolphinfish. The researchers also used the technique to map the whole sky. It generated groups of stars. The scientists compared those groups to the 88 modern constellations. Those are groups of stars recognized by the International Astronomical Union. The two sets of star groups mostly matched. That confirmed the method worked to explain how the constellations came to be.
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Here’s why people picked certain stars as constellations
The Big Dipper’s stars are a celestial landmark. Visible in the Northern Hemisphere’s night sky, the stars draw out a shape like a scoop with a handle. Beginner stargazers can easily pick it out. Now, scientists have shown that three factors can explain why certain groups of stars form such recognizable patterns. One is how bright the stars are. Another is how far apart they are. And a third has to do with how human eyes move.
The Big Dipper is part of the constellation Ursa Major. That’s one of many star groupings that people in the past selected for their shapes. Some shapes were said to depict animals, people or objects. Sophia David wondered why people selected these star groupings. She is a high school student at Friends’ Central School in Wynnewood, Penn.
“Ancient people from various cultures connected similar groupings of stars independently of each other,” said David. That suggests that different people were perceiving the stars in the same way. So David teamed up with scientists at the University of Pennsylvania in Philadelphia. She presented their work March 18 at an online meeting of the American Physical Society.
The researchers thought about how the eyes travel across this night sky. Human eyes tend to move in discrete jumps, called saccades (Seh-KAADS). That’s when both eyes quickly shift from one point of interest to another. The team created a computer simulation based on the distribution of saccade lengths. They also included two basic details of the night sky as seen from Earth. The first was how far apart different stars appear from one another in the sky. The second was how bright various stars are.
The technique could pick out single constellations. One constellation it picked out was the star grouping known as Dorado, the dolphinfish. The researchers also used the technique to map the whole sky. It generated groups of stars. The scientists compared those groups to the 88 modern constellations. Those are groups of stars recognized by the International Astronomical Union. The two sets of star groups mostly matched. That confirmed the method worked to explain how the constellations came to be.
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Effect of IL-15 addition on asbestos-induced suppression of human cytotoxic T lymphocyte induction
Environmental Health and Preventive Medicine 2021 [Link]
Naoko Kumagai-Takei, Yasumitsu Nishimura, Hidenori Matsuzaki, Suni Lee, Kei Yoshitome, Tatsuo Ito, Takemi Otsuki
Abstract
Background: Asbestos fibers possess tumorigenicity and are thought to cause mesothelioma. We have previously reported that exposure to asbestos fibers causes a reduction in antitumor immunity. Asbestos exposure in the mixed lymphocyte reaction (MLR) showed suppressed induction of cytotoxic T lymphocytes (CTLs), accompanied by a decrease in proliferation of CD8+ T cells. Recently, we reported that asbestos-induced suppression of CTL induction is not due to insufficient levels of interleukin-2 (IL-2). In this study, we continue to investigate the mechanism responsible for the effect of asbestos fibers on the differentiation of CTLs and focus on interleukin-15 (IL-15) which is known to be a regulator of T lymphocyte proliferation.
Methods: For MLR, human peripheral blood mononuclear cells (PBMCs) were cultured with irradiated allogenic PBMCs upon exposure to chrysotile B asbestos at 5 μg/ml for 7 days. After 2 days of culture, IL-15 was added at 1 ng/ml. After 7 days of MLR, PBMCs were collected and analyzed for phenotypic and functional markers of CD8+ T cells with fluorescence-labeled anti-CD3, anti-CD8, anti-CD45RA, anti-CD45RO, anti-CD25, and anti-granzyme B antibodies using flow cytometry. To examine the effect of IL-15 on the expression level of intracellular granzyme B in proliferating and non-proliferating CD8+ lymphocytes, PBMCs were stained using carboxyfluorescein diacetate succinimidyl ester (CFSE) and then washed and used for the MLR.
Results: IL-15 addition partially reversed the decrease in CD3+CD8+ cell numbers and facilitated complete recovery of granzyme B+ cell percentages. IL-15 completely reversed the asbestos-induced decrease in percentage of granzyme B+ cells in both non-proliferating CFSE-positive and proliferating CFSE-negative CD8+ cells. The asbestos-induced decrease in the percentage of CD25+ and CD45RO+ cells in CD8+ lymphocytes was not reversed by IL-15.
Conclusion: These findings indicate that CTLs induced upon exposure to asbestos possess dysfunctional machinery that can be partly compensated by IL-15 supplementation, and that IL-15 is more effective in the recovery of proliferation and granzyme B levels from asbestos-induced suppression of CTL induction compared with IL-2.
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Effect of IL-15 addition on asbestos-induced suppression of human cytotoxic T lymphocyte induction
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Effect of IL-15 addition on asbestos-induced suppression of human cytotoxic T lymphocyte induction
Environmental Health and Preventive Medicine 2021 [Link]
Naoko Kumagai-Takei, Yasumitsu Nishimura, Hidenori Matsuzaki, Suni Lee, Kei Yoshitome, Tatsuo Ito, Takemi Otsuki
Abstract
Background: Asbestos fibers possess tumorigenicity and are thought to cause mesothelioma. We have previously reported that exposure to asbestos fibers causes a reduction in antitumor immunity. Asbestos exposure in the mixed lymphocyte reaction (MLR) showed suppressed induction of cytotoxic T lymphocytes (CTLs), accompanied by a decrease in proliferation of CD8+ T cells. Recently, we reported that asbestos-induced suppression of CTL induction is not due to insufficient levels of interleukin-2 (IL-2). In this study, we continue to investigate the mechanism responsible for the effect of asbestos fibers on the differentiation of CTLs and focus on interleukin-15 (IL-15) which is known to be a regulator of T lymphocyte proliferation.
Methods: For MLR, human peripheral blood mononuclear cells (PBMCs) were cultured with irradiated allogenic PBMCs upon exposure to chrysotile B asbestos at 5 μg/ml for 7 days. After 2 days of culture, IL-15 was added at 1 ng/ml. After 7 days of MLR, PBMCs were collected and analyzed for phenotypic and functional markers of CD8+ T cells with fluorescence-labeled anti-CD3, anti-CD8, anti-CD45RA, anti-CD45RO, anti-CD25, and anti-granzyme B antibodies using flow cytometry. To examine the effect of IL-15 on the expression level of intracellular granzyme B in proliferating and non-proliferating CD8+ lymphocytes, PBMCs were stained using carboxyfluorescein diacetate succinimidyl ester (CFSE) and then washed and used for the MLR.
Results: IL-15 addition partially reversed the decrease in CD3+CD8+ cell numbers and facilitated complete recovery of granzyme B+ cell percentages. IL-15 completely reversed the asbestos-induced decrease in percentage of granzyme B+ cells in both non-proliferating CFSE-positive and proliferating CFSE-negative CD8+ cells. The asbestos-induced decrease in the percentage of CD25+ and CD45RO+ cells in CD8+ lymphocytes was not reversed by IL-15.
Conclusion: These findings indicate that CTLs induced upon exposure to asbestos possess dysfunctional machinery that can be partly compensated by IL-15 supplementation, and that IL-15 is more effective in the recovery of proliferation and granzyme B levels from asbestos-induced suppression of CTL induction compared with IL-2.
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Patterns in brain activity can identify who will struggle to read
Reading involves several different areas of the brain. A new study finds that connections between these regions can predict how well someone reads. Surprisingly, new data show that the connections that develop while doing mental math computations also predict reading ability.
Chris McNorgan works at the University at Buffalo in New York. As a cognitive neuroscientist, he studies how brain regions interact while we do various tasks. For the new study, he looked at which parts of the brain link up as we read. “Reading involves connecting words that you see on a page with sounds that you hear in your head,” he says. That requires connections between the systems that process vision and hearing, he explains. But making those connections doesn’t come easily for all.
People with dyslexia, for instance, often struggle with reading. This learning disorder makes it hard for the brain to link written letters or numbers to the sounds they represent. The condition does not reflect intelligence. Even bright people who suffer from it may confuse the order of letters and sounds such that they mix up words or their spelling. McNorgan wanted to know what brain connections were behind this.
Investigating links between brain regions is hard. “The whole brain is always doing something,” McNorgan says. As it works, the brain briefly connects different regions. Some links form while thinking. Others connect while reading. Still others form while listening to a teacher or watching a video.
As we mentally shift from one thing to another, some connections break as others form. McNorgan used computers to hunt those links down. He used artificial intelligence systems known as machine learning models. People train them using large data sets. The models learn which features within the data point to something of interest. Here, McNorgan wanted to find out which connections predicted reading ability.
Scientists Say: MRI
McNorgan trained his model using data from another lab. Those data came from kids ages 8 to 13 as they read a real word or fake word while lying in an MRI machine. That machine scanned their brains to show which areas were active as they read. McNorgan identified the strongest and weakest readers from the group based on test scores. He then used those students’ brain scans to train his machine-learning model.
It found one set of connections in the brains of strong readers. A different set emerged in the brains of kids with dyslexia. Strong readers used the left side of their brains when reading. That’s the side associated with language, McNorgan explains.
“We don’t know why,” he says, but readers who struggled made more use of the brain’s right side. McNorgan says the brain of poor readers may use this side to compensate — “to help get up to speed.”
Surprising link
It’s possible a model will work for one set of data and not another, McNorgan explains. If that happens, it can suggest any signal seen with the training data may just be due to noise. That’s why after training a machine-learning model, researchers test it with a new set of data.
Explainer: What is a computer model?
To test his model, McNorgan turned to a second study from the MRI lab. It had asked students do simple multiplication problems in their heads. The same kids also performed some reading tasks. McNorgan used scans for these kids to see if his model could predict which were strong or weak readers.
On a whim, he also decided to test the model with the scans made when the students had been multiplying numbers instead of reading. He didn’t expect the model to find anything. After all, math and reading are very different skills. To his surprise, however, the model identified strong and weak readers with almost perfect accuracy.
“Whatever is going on in that reading network also is showing up while they’re doing another task,” McNorgan now reports. It’s hard to say exactly what strong and weak readers are doing differently when they do multiplication in their head, he notes.
He reported his findings February 12 in Frontiers in Computational Neuroscience.
Computer models identified brain connections involved with reading and math. Red lines point to connections between areas used to read words. Blue lines show connections used to read fake words and to multiply numbers.Chris McNorgan/Univ. at Buffalo (CC BY 4.0)
More questions
Although the brain uses some of the same connections in reading and math, this doesn’t mean someone is going to be good — or bad — at both. “Being a good reader and being good at math are disconnected,” he says. “In fact, you can be a poor reader and be fantastic at math.” But in kids who struggle with both reading and math, McNorgan hopes his research will be the first step in helping to understand why.
Marc Joanisse finds the new study on brain linkages “a unique step forward in how we think about brain differences in children with learning disabilities.” Joanisse, who was not involved with the study, is a psychologist at the University of Western Ontario in Canada. The new findings show that learning disabilities are much less specific than we usually assume, he notes.
“The technique has tremendous promise,” Joanisse says. It can be used to better understand “many different aspects of how the brain works.” He says it may even identify the source of disorders in the brain.
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Level up your demonstration: Make it an experiment
Science demonstrations can be real crowd pleasers. In fact, Camille Schrier won the 2020 Miss America crown after performing a science demonstration during the talent portion of the competition. On stage, she mixed common chemicals to create massive mountains of steaming foam — a trick often called “elephant toothpaste.” It wowed the judges. But as she said when she performed it, this was a demonstration. It wasn’t an experiment. But you can turn that, or any demonstration, into an experiment.
Start by finding a hypothesis. This a statement that you can test. How do you find a hypothesis? You can begin by learning more about how a specific scientific demonstration works. By breaking it down into its parts, you might be able to find a statement to test. And from there, you can design your experiment.
youtube
Camille Schrier demonstrates elephant toothpaste. Limited time on stage meant there probably wasn’t time for an experiment.
Elephant toothpaste explained
Let’s look at the elephant toothpaste demonstration. There are four ingredients: hydrogen peroxide, dish soap, food coloring and a catalyst. Hydrogen peroxide (H2O2) is a chemical people can use to clean wounds or surfaces and bleach them. It slowly breaks down when exposed to light, forming water and oxygen
This is where the catalyst comes in. A catalyst is something that speeds up a chemical reaction. In the elephant toothpaste experiment, yeast or potassium iodide can be used as a catalyst. Either will cause the hydrogen peroxide to break down very quickly.
The dish soap and food coloring aren’t needed for the reaction. But they create the show. As hydrogen peroxide breaks down into water and oxygen, the dish soap will catch the liquid and gas to form bubbles. It’s the source of the foam. The food coloring gives the foam its bright color.
Now that we know what’s happening, we can start asking questions. How much hydrogen peroxide should you use? How much catalyst? How much dish soap? Those are all good questions. In fact, they’re each the beginning of a hypothesis.
Let’s focus on hydrogen peroxide. If the hydrogen peroxide breaks down into the water and oxygen that power the foam, then perhaps more hydrogen peroxide would produce more foam. That gives us a hypothesis: More hydrogen peroxide will produce more foam.
Demo to experiment
We can now design an experiment to test that hypothesis. First, identify the variable that you will be testing. Here, our hypothesis is about hydrogen peroxide. So the experiment needs to change the proportion of hydrogen peroxide in the elephant toothpaste.
An experiment also needs a control — a part of the experiment where nothing changes. The control could be no hydrogen peroxide (and no foam). The experiment could then test different amounts of hydrogen peroxide to see which produces the most foam.
You will have to measure the outcome of any experiment. For elephant toothpaste, you might measure the height of the foam using video recordings. Or you could measure the mass of your container before and after the reaction, to see how much foam exploded out. This would be different for every experiment. For an experiment involving plants, you could measure plant height or the size of any fruit. When growing rock candy, you could weigh the final product.
Running the experiment just once isn’t enough. You need to repeat it many times, step by step, over and over. Any single result could have been due to some accident. Repeating the experiment again and again cuts the chance you will see a difference by mistake. Write down all the results very carefully. It helps to keep a lab notebook.
Finally, you will want to compare results. This may mean running statistical tests on your data. These are mathematical tests that can help you interpret your findings. They might show you that more hydrogen peroxide does indeed produce more elephant toothpaste. Or the results might show something else. Maybe there’s just the right amount of hydrogen peroxide, and too much doesn’t produce any more foam.
If you want to find out, though, don’t do a demonstration. Test it through an experiment.
For more ideas, check out our experiments collection. We’ve made experiments out of the five-second rule, baking soda volcanoes, sneezing out snot and much more.
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Patterns in brain activity can identify who will struggle to read
Reading involves several different areas of the brain. A new study finds that connections between these regions can predict how well someone reads. Surprisingly, new data show that the connections that develop while doing mental math computations also predict reading ability.
Chris McNorgan works at the University at Buffalo in New York. As a cognitive neuroscientist, he studies how brain regions interact while we do various tasks. For the new study, he looked at which parts of the brain link up as we read. “Reading involves connecting words that you see on a page with sounds that you hear in your head,” he says. That requires connections between the systems that process vision and hearing, he explains. But making those connections doesn’t come easily for all.
People with dyslexia, for instance, often struggle with reading. This learning disorder makes it hard for the brain to link written letters or numbers to the sounds they represent. The condition does not reflect intelligence. Even bright people who suffer from it may confuse the order of letters and sounds such that they mix up words or their spelling. McNorgan wanted to know what brain connections were behind this.
Investigating links between brain regions is hard. “The whole brain is always doing something,” McNorgan says. As it works, the brain briefly connects different regions. Some links form while thinking. Others connect while reading. Still others form while listening to a teacher or watching a video.
As we mentally shift from one thing to another, some connections break as others form. McNorgan used computers to hunt those links down. He used artificial intelligence systems known as machine learning models. People train them using large data sets. The models learn which features within the data point to something of interest. Here, McNorgan wanted to find out which connections predicted reading ability.
Scientists Say: MRI
McNorgan trained his model using data from another lab. Those data came from kids ages 8 to 13 as they read a real word or fake word while lying in an MRI machine. That machine scanned their brains to show which areas were active as they read. McNorgan identified the strongest and weakest readers from the group based on test scores. He then used those students’ brain scans to train his machine-learning model.
It found one set of connections in the brains of strong readers. A different set emerged in the brains of kids with dyslexia. Strong readers used the left side of their brains when reading. That’s the side associated with language, McNorgan explains.
“We don’t know why,” he says, but readers who struggled made more use of the brain’s right side. McNorgan says the brain of poor readers may use this side to compensate — “to help get up to speed.”
Surprising link
It’s possible a model will work for one set of data and not another, McNorgan explains. If that happens, it can suggest any signal seen with the training data may just be due to noise. That’s why after training a machine-learning model, researchers test it with a new set of data.
Explainer: What is a computer model?
To test his model, McNorgan turned to a second study from the MRI lab. It had asked students do simple multiplication problems in their heads. The same kids also performed some reading tasks. McNorgan used scans for these kids to see if his model could predict which were strong or weak readers.
On a whim, he also decided to test the model with the scans made when the students had been multiplying numbers instead of reading. He didn’t expect the model to find anything. After all, math and reading are very different skills. To his surprise, however, the model identified strong and weak readers with almost perfect accuracy.
“Whatever is going on in that reading network also is showing up while they’re doing another task,” McNorgan now reports. It’s hard to say exactly what strong and weak readers are doing differently when they do multiplication in their head, he notes.
He reported his findings February 12 in Frontiers in Computational Neuroscience.
Computer models identified brain connections involved with reading and math. Red lines point to connections between areas used to read words. Blue lines show connections used to read fake words and to multiply numbers.Chris McNorgan/Univ. at Buffalo (CC BY 4.0)
More questions
Although the brain uses some of the same connections in reading and math, this doesn’t mean someone is going to be good — or bad — at both. “Being a good reader and being good at math are disconnected,” he says. “In fact, you can be a poor reader and be fantastic at math.” But in kids who struggle with both reading and math, McNorgan hopes his research will be the first step in helping to understand why.
Marc Joanisse finds the new study on brain linkages “a unique step forward in how we think about brain differences in children with learning disabilities.” Joanisse, who was not involved with the study, is a psychologist at the University of Western Ontario in Canada. The new findings show that learning disabilities are much less specific than we usually assume, he notes.
“The technique has tremendous promise,” Joanisse says. It can be used to better understand “many different aspects of how the brain works.” He says it may even identify the source of disorders in the brain.
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Level up your demonstration: Make it an experiment
Science demonstrations can be real crowd pleasers. In fact, Camille Schrier won the 2020 Miss America crown after performing a science demonstration during the talent portion of the competition. On stage, she mixed common chemicals to create massive mountains of steaming foam — a trick often called “elephant toothpaste.” It wowed the judges. But as she said when she performed it, this was a demonstration. It wasn’t an experiment. But you can turn that, or any demonstration, into an experiment.
Start by finding a hypothesis. This a statement that you can test. How do you find a hypothesis? You can begin by learning more about how a specific scientific demonstration works. By breaking it down into its parts, you might be able to find a statement to test. And from there, you can design your experiment.
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Camille Schrier demonstrates elephant toothpaste. Limited time on stage meant there probably wasn’t time for an experiment.
Elephant toothpaste explained
Let’s look at the elephant toothpaste demonstration. There are four ingredients: hydrogen peroxide, dish soap, food coloring and a catalyst. Hydrogen peroxide (H2O2) is a chemical people can use to clean wounds or surfaces and bleach them. It slowly breaks down when exposed to light, forming water and oxygen
This is where the catalyst comes in. A catalyst is something that speeds up a chemical reaction. In the elephant toothpaste experiment, yeast or potassium iodide can be used as a catalyst. Either will cause the hydrogen peroxide to break down very quickly.
The dish soap and food coloring aren’t needed for the reaction. But they create the show. As hydrogen peroxide breaks down into water and oxygen, the dish soap will catch the liquid and gas to form bubbles. It’s the source of the foam. The food coloring gives the foam its bright color.
Now that we know what’s happening, we can start asking questions. How much hydrogen peroxide should you use? How much catalyst? How much dish soap? Those are all good questions. In fact, they’re each the beginning of a hypothesis.
Let’s focus on hydrogen peroxide. If the hydrogen peroxide breaks down into the water and oxygen that power the foam, then perhaps more hydrogen peroxide would produce more foam. That gives us a hypothesis: More hydrogen peroxide will produce more foam.
Demo to experiment
We can now design an experiment to test that hypothesis. First, identify the variable that you will be testing. Here, our hypothesis is about hydrogen peroxide. So the experiment needs to change the proportion of hydrogen peroxide in the elephant toothpaste.
An experiment also needs a control — a part of the experiment where nothing changes. The control could be no hydrogen peroxide (and no foam). The experiment could then test different amounts of hydrogen peroxide to see which produces the most foam.
You will have to measure the outcome of any experiment. For elephant toothpaste, you might measure the height of the foam using video recordings. Or you could measure the mass of your container before and after the reaction, to see how much foam exploded out. This would be different for every experiment. For an experiment involving plants, you could measure plant height or the size of any fruit. When growing rock candy, you could weigh the final product.
Running the experiment just once isn’t enough. You need to repeat it many times, step by step, over and over. Any single result could have been due to some accident. Repeating the experiment again and again cuts the chance you will see a difference by mistake. Write down all the results very carefully. It helps to keep a lab notebook.
Finally, you will want to compare results. This may mean running statistical tests on your data. These are mathematical tests that can help you interpret your findings. They might show you that more hydrogen peroxide does indeed produce more elephant toothpaste. Or the results might show something else. Maybe there’s just the right amount of hydrogen peroxide, and too much doesn’t produce any more foam.
If you want to find out, though, don’t do a demonstration. Test it through an experiment.
For more ideas, check out our experiments collection. We’ve made experiments out of the five-second rule, baking soda volcanoes, sneezing out snot and much more.
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Sulforaphane inhibits PRMT5 and MEP50 function to suppress the mesothelioma cancer cell phenotype
Molecular Carcinogenesis 2021 April 19 [Link]
Geraldine Ezeka, Gautam Adhikary, Sivaveera Kandasamy, Joseph S Friedberg, Richard L Eckert
Abstract
Mesothelioma is a highly aggressive cancer of the mesothelial lining that is caused by exposure to asbestos. Surgical resection followed by chemotherapy is the current treatment strategy, but this is marginally successful and leads to drug-resistant disease. We are interested in factors that maintain the aggressive mesothelioma cancer phenotype as therapy targets. Protein arginine methyltransferase 5 (PRMT5) functions in concert with the methylosome protein 50 (MEP50) cofactor to catalyze symmetric dimethylation of key arginine resides in histones 3 and 4 which modifies the chromatin environment to alter tumor suppressor and oncogene expression and enhance cancer cell survival. Our studies show that PRMT5 or MEP50 loss reduces H4R3me2s formation and that this is associated with reduced cancer cell spheroid formation, invasion, and migration. Treatment with sulforaphane (SFN), a diet-derived anticancer agent, reduces PRMT5/MEP50 level and H4R3me2s formation and suppresses the cancer phenotype. We further show that SFN treatment reduces PRMT5 and MEP50 levels and that this reduction is required for SFN suppression of the cancer phenotype. SFN treatment also reduces tumor formation which is associated with reduced PRMT5/MEP50 expression and activity. These findings suggest that SFN may be a useful mesothelioma treatment agent that operates, at least in part, via suppression of PRMT5/MEP50 function.
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Sulforaphane inhibits PRMT5 and MEP50 function to suppress the mesothelioma cancer cell phenotype
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Sulforaphane inhibits PRMT5 and MEP50 function to suppress the mesothelioma cancer cell phenotype
Molecular Carcinogenesis 2021 April 19 [Link]
Geraldine Ezeka, Gautam Adhikary, Sivaveera Kandasamy, Joseph S Friedberg, Richard L Eckert
Abstract
Mesothelioma is a highly aggressive cancer of the mesothelial lining that is caused by exposure to asbestos. Surgical resection followed by chemotherapy is the current treatment strategy, but this is marginally successful and leads to drug-resistant disease. We are interested in factors that maintain the aggressive mesothelioma cancer phenotype as therapy targets. Protein arginine methyltransferase 5 (PRMT5) functions in concert with the methylosome protein 50 (MEP50) cofactor to catalyze symmetric dimethylation of key arginine resides in histones 3 and 4 which modifies the chromatin environment to alter tumor suppressor and oncogene expression and enhance cancer cell survival. Our studies show that PRMT5 or MEP50 loss reduces H4R3me2s formation and that this is associated with reduced cancer cell spheroid formation, invasion, and migration. Treatment with sulforaphane (SFN), a diet-derived anticancer agent, reduces PRMT5/MEP50 level and H4R3me2s formation and suppresses the cancer phenotype. We further show that SFN treatment reduces PRMT5 and MEP50 levels and that this reduction is required for SFN suppression of the cancer phenotype. SFN treatment also reduces tumor formation which is associated with reduced PRMT5/MEP50 expression and activity. These findings suggest that SFN may be a useful mesothelioma treatment agent that operates, at least in part, via suppression of PRMT5/MEP50 function.
The post Sulforaphane inhibits PRMT5 and MEP50 function to suppress the mesothelioma cancer cell phenotype appeared first on Mesothelioma Line.
Sulforaphane inhibits PRMT5 and MEP50 function to suppress the mesothelioma cancer cell phenotype
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Scientists Say: Pi
Pi (noun “pye”)
This is a mathematical constant — a number whose value never changes. Symbolized by Greek letter π, pi is the ratio of a circle’s circumference — the distance around the outer edge — to its diameter, the length across its center. That ratio is always pi to one. The number pi is often shortened to 3.14 or 3.14159. But this number is actually infinite. One number cruncher calculated pi out to 50 trillion digits. The digits after the decimal place, though, go on forever, into infinity.
Mathematicians can use pi to determine a circle’s circumference from its diameter. A circle one meter in diameter, for instance, will have a circumference of 3.14159 meters. If it measures two meters in diameter, the circumference will be 6.28318 meters.
Pi also can be used to calculate the area of a circle. The radius of a circle is one half its diameter. The area is equal to pi times the radius squared. That one-meter-diameter circle, then, has an area of 0.79 square meter. Scientists might use this equation to determine the size of craters on the moon, for example, or to calculate where a spacecraft travels.
But some mathematicians think that pi is too confusing. Instead, they would like to use tau — or τ. Tau is the ratio between a circle’s circumference and its radius. Tau is equal to 2π. Like pi, tau is also a constant and infinite.
Mathematicians like tau because it is easier to use to calculate a circle’s radians — the unit for measuring angles — like the angle at the tip of a slice of pizza. If they succeed in replacing pi, then instead of celebrating pi day on March 14 (3/14), people might instead celebrate tau day on June 28 (6/28). But there might not be as many tasty baked goods.
In a sentence
Scientists gave an exoplanet the nickname “Pi Earth” because it orbits around its star once every 3.14 days.
Check out the full list of Scientists Say.
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