Making Sense of Milk by Frankie Wood-Black the Array of Milk Options on Store Shelves Can Be Overwhelming

February/March 2019

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DEPARTMENTS 2 Connecting Chemistry and Art 4 Open for Discussion: Unpacking the Paleo Diet 19 Profile: Chancée Lundy Catalyzes Change

FEATURES 5 Making Sense of Milk By Frankie Wood-Black The array of milk options on store shelves can be overwhelming. Breaking down their differences will help you choose which ones to try.

8 What’s Sunless Tanner? By Tien M. Nguyen With that summer glow still a few months away, you might be interested in a faux glow. Here’s a primer on how tanning products work.

11 The Periodic Table Turns 150 By David Warmflash That iconic chart of elements in Clean, Green Chemistry your classroom turns 150 this year! Celebrate with a look at its past and p. 15 a peek into its intriguing future. Spanish translation available online!

15 Clean, Green Chemistry By XiaoZhi Lim High school students from around the U.S. try their hand at green chemistry, an approach that prioritizes the planet and people’s health.

ON THE COVER: THINKSTOCK

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ChemMatters | www.acs.org/chemmatters 3 OPEN FOR DISCUSSION

Should We Eat Like Our Stone-Age Ancestors? By Michael Tinnesand n 2014, as word of the paleo diet allows us to break down lactose (Fig. 1), would spread, one columnist predicted its shut off—and toddlers would lose the ability to quick demise. Many dieticians said digest milk. Ithere was no evidence that the life- But as humans began domesticating cows style trend was beneficial. But today, and goats, milk from these animals became proponents continue to promote it. a source of nutrition. Adults still had a hard time digesting the animal milk, but turning Paleo’s adherents suggest that we it into cheese reduced the lactose content, should eat like early humans did which made it easier to digest. Milk became an easier-to-drink option when a random DNA about 3.3 million to 10,000 years ago. mutation in some people allowed the lactase This was the era of hunter-gatherers, gene to stay active into adulthood. before the development of agriculture. Stone Age diets consisted of wild fish, THE MILK ADVANTAGE game, fruits, nuts, and roots. It did not Figure 1. Enzymes are biological catalysts that speed up reactions. Lactase, for example, enables the breakdown of include animal milk or dairy products, Incorporating animal milk in a person’s diet lactose into simple sugars. legumes, modern grains, or any pro- turned out to be an advantage. Genetics cessed foods. researchers have reported that between 5,000 and 10,000 years ago, lactose-tolerant people But over the years, our diets have changed in some parts of the world, including North- profoundly due to advances in agriculture and We’ve bred animals to be fast growing and ern Europe, reproduced at a higher rate than technology. Paleo proponents argue that our provide large amounts meat. We’ve favored lactose-intolerant individuals. Two-thirds of bodies are still similar to the bodies of our the biggest, hardiest and plumpest varieties of the global population are still lactose intolerant ancestors and therefore out of sync with the fruits and vegetables, so they bear little resem- as adults. But the fact that one-third of us can modern diet. So, should we eat like hunter- blance to their plant predecessors. Tomatoes drink milk without running to the bathroom gatherers? in the Stone Age, for example, were the size of afterwards shows how well we can adapt—and berries. benefit from—dietary changes. REALITY CHECK At the same time, humans’ bodies have also As the saying goes: You can’t go home again— First, let’s consider if it’s even possible to find changed. The ability to digest milk sugar, and perhaps that is true with our diets as well. food that resembles meats and produce from called lactose, is a prime example. In Paleolith- If we could time-travel and sit down for dinner the Paleolithic era. Nearly all the foods we ic times, infants were nourished by their moth- with a family of cave-dwellers, it would be buy today have been significantly modified by er’s milk. But after about two years of age, the an interesting meal. But whether it would be selective breeding over the past 10,000 years. gene that produces the enzyme lactase, which healthier is open for discussion.

4 ChemMatters | FEBRUARY/MARCH 2019 ILLUSTRATION: THINKSTOCK Making Sense Looking for an alternative to cow’s milk? Here’s what you need to know. of Milk By Frankie Wood-Black o to the dairy section of any grocery store, and you’ll find a variety of milks made from soy, nuts, or rice in addition to good ol’ cow’s milk. Plant-based beverages aren’t necessarily new (almond milk has been around for centuries), but their production has boomed in recent years. G If you’re looking to replace cow’s milk, how do you know what to choose?

To understand the difference be- Given the differences in how milks tween plant milk and animal milk, are produced, let’s see how the let’s first turn to biology. Animal nutritional profiles compare. milk is a complex fluid produced by the mammary glands of female mammals to feed their young. In What’s in dairy milk some ways, the nutritional purpose You probably already know that of animal milk resembles that cow’s milk is a good source of of nuts and seeds (technically, calcium. But it’s also a source what we usually call nuts, such as of many vitamins, minerals, and almonds and walnuts, are seeds). lipids—or fats. Additionally, it Seeds contain nutrients that em- contains sugars, hormones and bryonic plants use to develop into proteins, such as casein, immuno- seedlings. globins, cytokines, and enzymes. (The latter three types of proteins Of course, a new plant’s nutritional help nursing animals grow and needs are distinct from what a develop their immune systems, but nursing animal requires. And the wouldn’t necessarily have the same process of getting milk from seeds effect on you.) is completely different from milking an animal. “Milking” seeds involves This mixture is also complex from soaking them, blending them with a physical standpoint. Milk is pri- water, and straining them. marily water with sugars, minerals,

PHOTO: PIXABAY ChemMatters | www.acs.org/chemmatters 5 PHOTO: THINKSTOCK From Farm to Store lipids, and proteins blended together. The sugars and miner- Have you heard the expression: Cream rises to the top—as in the brightest people als remain dissolved in the watery solution, while lipids form or ideas will naturally succeed? You can probably guess why we’re bringing it up small clumps of fat that stay suspended in store-bought milk. here: The saying comes from the chemistry of milk. Casein proteins, which comprise about 80% of cow-milk proteins, are also suspended in milk. They are too large to be Milk is an emulsion, a suspension of droplets of one liquid in another liquid, not a soluble in water, and instead form droplets called micelles. solution in which a solute dissolves in a solvent to create a uniform mixture. If you The micelles are spherical particles with the hydrophilic, or let raw cow’s milk sit for a bit, the fats in the milk will rise to the top because they “water-loving,” side of casein facing outward. The protein’s are less dense than water, a major component of milk. The fat layer can be easily hydrophobic, or “water-hating,” side gets tucked inside separated from the rest of the milk. the droplets along with clusters of calcium phosphate. The suspension and dispersion of droplets of fat and protein But you don’t see separation in store-bought milk. The milk has been homogenized, make milk a colloid—more specifically, an emulsified colloid which involves a mechanical process that breaks up the fats into smaller sizes to because the mixture components are all in liquid form. allow them to stay suspended in the watery mixture. Botanical beverages abound Today, many people are choosing not to drink cow’s milk for several reasons. Some people are allergic to milk proteins. Others are lactose intolerant. Cultural, personal, and environmental considerations provide additional reasons for some people to avoid cow’s milk.

The most widely available plant-based milk alternatives in the United States are derived from soy, rice, almond, and coconut. Also available are milk beverages made from peas, oats, cashews, potatoes, flax, hemp, sesame, and peanuts.

Like store-bought cow’s milk, plant-based milks are a suspension of ingredients. But from a nutritional standpoint, how do plant-based alternatives compare to cow’s milk?

The short answer is: It depends. The nutritional value varies from product to product, and it might or might not provide the equivalent nutritional value of traditional cow’s milk. To make sense of the varieties, first consider what your body ILLUSTRATION: KELSEY CASSELBURY needs. 6 ChemMatters | FEBRUARY/MARCH 2019 6 ChemMatters |FEBRUARY 2019 | www.acs.org/chemmatters Types of Milk and Milk Alternatives

The current U.S. dietary guidelines rec- COW’S MILK ommend that we consume dairy products, Positives: High in protein, calcium, vitamin D, and phosphorus including milk, yogurt, and cheese, which Negatives: Contains lactose and saturated fat are excellent sources of calcium, potassium, phosphorus, vitamin D, and protein. PIXABAY PHOTO:

Calcium, potassium, phosphorus, and vitamin D are essential for bone health. Calcium is also SOY MILK important for the development of strong teeth. Positives: High in protein, often fortified so its nutritional And diets rich in potassium can help maintain profile is close to cow’s milk healthy blood pressure, while proteins contrib- Negatives: Can cause allergic reaction ute to building muscle. PHOTO: PIXABAY PHOTO: Additionally, proteins provide amino acids ALMOND MILK that our bodies need. So, when nutritionists Positives: Low calorie, high in vitamin E and can be fortified; look at protein quality, they are looking at the no saturated fats amino-acid composition, digestibility, and bio- Negatives: Low in protein availability—that is, how much of the protein PIXABAY PHOTO: your body can use.

Cow’s milk typically has better protein quality than that of plant-based milks because the RICE MILK proteins are made with a wider array of amino Positives: Suggested for individuals with multiple allergies acids and are easier for our bodies to use. Negatives: Low in protein; high in carbohydrates

The one plant-based exception is soy. Soy contains the nine essential amino acids that THINKSTOCK PHOTO: the human body can’t synthesize—so like COCONUT MILK cow’s milk, soy is considered a “complete” Positives: Contains potassium, iron, and fiber protein source. As for nutrients, such as Negatives: Low in protein, more saturated fat than other calcium, potassium, and vitamin D, they can plant milks

be added to make soy-milk nutrition closer to THINKSTOCK PHOTO: cow’s milk. Because of this and its complete protein content, fortified soy milk is the one plant-based milk the U.S. dietary guidelines list under the dairy recommendations. antioxidants in addition to vitamin E that can But as with milk proteins, nut or soy proteins The bottom line guard against cellular damage. Coconut milk contains lauric acid, which some research can cause allergic reactions in some people, Curious to learn more about the potential suggests promotes brain development and so products with these ingredients aren’t right health effects of increasingly popular milk helps boost the immune system. for everyone. Additionally, if you’re looking for alternatives, researchers have done some a source of phosphorus, zinc, thiamin, vitamin investigating and found that plant-based bev- The bottom line: Botanical milks differ con- B6, vitamin E, vitamin K, and folate, cow’s milk erages could have benefits beyond providing siderably from cow’s milk. And knowing the has these nutrients, but they are not always proteins, vitamins, and minerals. differences can help you make more informed found in plant-based alternatives. So, while decisions about your drink—or drinks—of For example, soy milk contains isoflavones nut and seed milks provide some benefits, choice. that some research suggests can protect they do not have the same nutritional value as against cardiovascular disease and osteopo- Frankie Wood-Black is a science writer based cow’s milk (see chart). rosis. Peanut milk and almond milk contain in Tonkawa, Oklahoma.

Selected References Abou-Dorbara, M. I. et al. Chemical Composition, Senso- Bridges, M. Moo-ve Over, Cow’s Milk: The Rise of Plant- Haug, A. et al. Bovine Milk in Human Nutrition–a ry Evaluation and Stater Activity in Cow, Soy, Peanut, and Based Dairy Alternatives. Practical Gastroenterology, Jan Review. Lipids in Health and Disease, Sept 25, 2007: Rice Milk. Journal of Nutritional Health & Food Engineer- 2018: https://med.virginia.edu/ginutrition/wp-content/ https://lipidworld.biomedcentral.com/track/pd- ing, Nov 28, 2016: https://medcraveonline.com/JNHFE/ uploads/sites/199/2014/06/January-18-Milk-Alternatives. f/10.1186/1476-511X-6-25 [accessed Dec 2018]. JNHFE-05-00175.pdf [accessed Dec 2018]. pdf [accessed Dec 2018].

ChemMatters | www.acs.org/chemmatters 7 What’s Sunless Tanner? One simple molecule holds the key to keeping a tan year-round. By Tien M. Nguyen/C&EN

hen physician Eva Wittgenstein discovered a chemical that could W bronze skin rapidly, cosmetics and sunless tanners were probably the last thing on her mind.

It was the mid-1950s, and Wittgenstein was conducting research at Children’s Hospital at PHOTO: THINKSTOCK tastiest transformations, called the Maillard reaction, responsi- the University of Cincinnati. She was studying ble for the browned appearance of fried bacon and roasted cof- children who had a rare metabolic disease fee. In the Maillard reaction, sugars and amino acids react when and examining the effects of treating them heated to form a multitude of molecules, including some with a brownish hue. Similarly, the reaction that turns skin tan at room with dihydroxyacetone (C3H6O3), which is a temperature occurs when dihydroxyacetone reacts with amino simple, plant-derived, sugar-like molecule. acids like arginine, lysine, and histidine found in the outer layer of skin to produce yellowish-brown pigments called melanoidins.

Her small patients took big doses of the stuff—up to 1 Creating a faux glow gram (g) of C3H6O3 per 1 kilogram (kg) of body weight— sometimes causing the kids to spit up on themselves, Word of dihydroxyacetone’s browning abilities spread quickly which, if not cleaned up right away, left strange brown to the cosmetic industry. By 1960, according to one newspaper spots on their skin. Their clothes, however, remained report, at least a dozen sunless tanning products based on the unstained. molecule—with names like Man-Tan, Magic Tan, Tansation, and Tanorama—had been introduced to bronze the public. Intrigued, Wittgenstein poured a solution of dihydroxyacetone onto her own skin and confirmed its color-changing The products’ appeal grew as people recognized that sunbathing effects. She found that unlike makeup, which lies inert on caused skin damage, though their understanding was flawed. At top of skin, dihydroxyacetone reacts with it. the time, many people thought that “good” ultraviolet-A (UV-A) radiation gave healthy-looking tans, while “bad” ultraviolet-B (UV- The reaction, it turns out, is related to one of chemistry’s B) radiation caused burns and, in extreme cases, cancer, says

This article was adapted from “What’s Sunless Tanner, and How Does It Impart That Faux Glow?” It first appeared inChemical & Engineering News on Jan. 22, 2018.

8 ChemMatters | FEBRUARY/MARCH 2019 ILLUSTRATION: THINKSTOCK

x A molecule of glycerol (top), the starting material WHAT’S AN ENZYMATIC PROCESS? in the enzymatic process used in the production w of dihydroxyacetone, shares some structural An enzymatic process is a reaction in the body that a type of similarities with a dihydroxyacetone (DHA) molecule protein called an enzyme, speeds up, or catalyzes. (bottom). Dihydroxyacetone (C3H6O3) has dominated the sunless tanning industry since its browning abilities were accidentally discovered in vomit. additives, lowering the pH of the mixture for circulated in the late 1980s. The supply of better stability, and obtaining purer sources of the pills was eventually seized and destroyed dihydroxyacetone. Germany-based Merck KGaA, by U.S. marshals. Ads in muscle magazines David C. Steinberg, a chemist and regulatory a science, healthcare, and technology company, claimed that the tablets, which contained expert on the cosmetics industry. has produced pure dihydroxyacetone—via an concentrated amounts of the food additive and enzymatic process with glycerol as the starting pigment canthaxanthin rather than dihydroxy- But the idea of safe UV exposure was a myth. material—for self-tanning products almost since acetone, could give people golden tans within In 2015, the U.S. Centers for Disease Control the sunless-tanning industry’s start. three weeks. What the ads didn’t mention was and Prevention reported that more than 90% that, along with coloring users’ skins, it could of melanomas, the most dangerous type of In 2013, Merck KGaA launched a non-dihy- also accumulate in their eyes, depositing yellow, skin cancer, are caused by both types of UV droxyacetone-based self-tanning product, called sight-interfering crystals inside the retina. The radiation. RonaCare Bronzyl, that works by enhancing effect reversed on its own, although eye crystals a person’s melanin production. Melanin is a were detected in some people for up to seven By 2017, sunless-tanning products were pro- pigment that occurs naturally in people’s skin, years after they stopped taking the pills. jected to bring in just over $1 billion in revenue irises, and hair. In skin, its production is trig- worldwide. A national phone survey in 2004 gered by ultraviolet light and results in tanning. Sunless-tanning pills can still be found online, estimated that 11% of adolescents in the U.S. but these usually contain compounds like had used such products in the past year, though RonaCare Bronzyl’s active ingredient is a β-carotene, found in fruits and vegetables like some reports suggest that figure could be clos- compound called dihydroxy methylchromonyl carrots, that can turn skin an orangey shade. er to 35% for young men and women. palmitate. Bronzyl is more expensive than other existing sunless tanners, and the results Dihydroxyacetone has been approved for Color correction it yields are subtler and appear after about five external use by the U.S. Food and Drug to 10 days versus the typical two to six hours. Administration (FDA) for decades. But it hasn’t As a high school student in the early days of The new tanner may offer safety advantages been cleared for use inside the body. A 2004 self-tanning, Steinberg recalls one classmate’s because it promotes the production of melanin, FDA study, however, showed that as much as unforgettable experience with a sunless-tanning which dissipates UV light. 11% of the dihydroxyacetone applied to skin product. “She was yellow!” he says. Today’s penetrates into living skin, and 0.5% could get tanners still use the same main ingredient, Is sunless tanning safe? into the bloodstream. What that could mean for dihydroxyacetone, but the hues have been much a user’s health remains uncertain. improved. Sunless tanning is a much safer alternative to UV-powered sunbathing or sunlamp tanning, Unknown risks These chromatic advances come from changes but it isn’t without risks. in the formulation of dihydroxyacetone, which is With the advent of spray-tanning salons, where unstable. Cosmetic companies have improved Take, for example, the dangerous sunless-tan- customers are showered with a mist of sun- the products by using different solvents and ning pills called French Bronze Tablets, which less-tanning products, people can be exposed ChemMatters | www.acs.org/chemmatters 9 SIMULATING SUNSCREEN How Sunblock Works

Whether you opt for a sunless tan, a suntan, or prefer none at all, you should protect yourself from the sun’s rays. To do so, you can cover up with long sleeves, pants, and hats, or slather on the sunblock. There are two types of sunblock: chemical and mineral. They differ in how they block UV rays (Fig. 1). Chemical sunscreens have a chemical compound capable of absorbing UV rays. When the molecule absorbs the UV rays, it rearranges its electrons to form a higher-energy (excited) state, which then relaxes back to its original form, dissipating the energy of the UV light harmlessly as heat. ABOVE: When light is absorbed by sunblock particles on the skin, the energy is Mineral sunblock contains particles that are so small, they are measured in transferred to electrons in lower-energy levels, which are then excited and move into nanometers (nm) (a human hair is about 75,000 nm wide). These mineral higher-energy levels (photon absorption). Electrons later lose this excess energy and relax back into their original energy levels, releasing heat into their surroundings nanoparticles, such as zinc oxide and titanium oxide, protect your skin by (heat loss). reflecting UV rays. Just how small should the nanoparticles be? Check out this simulation to find out: https://bit.ly/2DjzRbN. For more on the Maillard reaction, watch this ACS Reactions video: You will see a drawing of skin with a coating of mineral sunscreen and UV rays shining down. Explore how the size of zinc oxide nanoparticles affects https://youtu.be/rs1JLYXROVU UV-ray deflection by changing the diameters of the nanoparticles in the sunblock. Before you begin, make a prediction: Will smaller particles be to aerosolized dihydroxyacetone. And these tiny droplets could be better UV blockers than larger particles? Click on the Nanoscopic View for a inhaled without the proper protection. close-up of UV rays headed toward the skin. Ashlee J. Howarth, a chemistry professor at Concordia University, So, what size nanoparticles would you like your sunblock to have? describes receiving a home spray tan in preparation for a wed- ding. The technician who sprayed the members of the bridal party —Emily Abbott didn’t offer any protective face or nose guards and didn’t wear any herself. As a chemist, Howarth was wary of exposure and found herself checking the bottle label. “I held my breath just in case,” she says.

“There’s really a lack of information about sunless-tanning products,” says Natalie R. Gassman, a professor of oncologic sciences at the University of South Alabama Mitchell Cancer Institute.

Gassman and others have studied the effects of dihydroxyacetone on healthy cells called melanocytes and keratinocytes, found under the dead outer layer of skin, as well as on cancerous melanoma cells. The experiments have shown that dihydroxyacetone is toxic to all three types of cells at dosage levels that people could potentially encounter through normal use. But estimating exposure levels is difficult because of poorly understood factors such as the amount of sunless tanner applied and how long it stays active on the skin, Gassman says.

When it comes to sunless-tanning products, “No one can definitive- ly say that they’re bad for you,” she says, adding that on the other x FIGURE 1. Mineral sunscreen (left) deflects UV rays, and chemical sunscreen hand, these products can help move people away from outdoor or (right) absorbs them. sunlamp tanning, practices that are certainly unhealthy. But if we’re asking people to switch over to these products, Gassman says, we ILLUSTRATIONS: INCHEMISTRY/AMERICAN CHEMISTRY SOCIETY should understand any risks that exposure to them might pose.

Tien M. Nguyen is an assistant editor at Chemical & Engineering News. 10 ChemMatters | FEBRUARY/MARCH 2019

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HISTORY INSTITUTE HISTORY PHOTO: COURTESY OF SCIENCE SCIENCE OF COURTESY PHOTO:

PHOTO: INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY

PUBLIC DOMAIN PHOTO: WIKIMEDIA COMMONS/

The he periodic table of elements is one of the PeriodIC T most recognizable icons of science. You probably have one hanging on your chemistry classroom wall. If you google Table turns it, you’ll see versions in rainbow colors, or with tiny photos in every box representing each element. There’s even a periodic table of moles! You could almost call the table mundane, except really, it’s any- thing but. The periodic table has been perhaps as foundational to chemistry as the discovery of DNA 150 has been to biology. It is 150 years old this year and is holding up Is the best yet to come? well under the test of time—and By David Warmflash science.

ChemMatters | www.acs.org/chemmatters 11 In celebration of the table, the United Nations proclaimed 2019 as the International Year of the Periodic Table of Chemical Elements. Time to break out the helium balloons, iron-based sparklers, and calcium-rich ice cream!

And whom do we have to thank for the exqui- site arrangement of elements? While many scientists contributed to the formation of the table, Russian chemist Dmitri Mendeleev is most often credited for the periodic table’s creation. He found that there was a periodicity to their organization, a repetition of particular chemical properties at regular intervals as atomic weight increased.

In 1869, Mendeleev published his vision in an early form of the periodic table. It included the 63 elements that were known at the time, with holes to account for elements that hadn’t yet PHOTO: THINKSTOCK been discovered. And while the table has been fleshed out over the past century and a half— Before Mendeleev came along with his 2 Li(s) + H2(g) a 2 LiH(s) including the addition of four new elements approach, other scientists were attempting to in 2016—the essence of Mendeleev’s original organize the elements. As early as 1789, French In contrast, the next element by weight, idea remains. But who knows, future discover- chemist Antoine Lavoisier had categorized beryllium (Be), formed the hydride BeH2. ies could lead to materials that even Mendeleev elements into metals, nonmetals, “earths,” and a couldn’t have dreamed of. gases, based on their physical and chemical Be(s) + H2(g) BeH2(s) characteristics. By 1829, German chemist Each successively heavier element formed Getting organized Johann Döbereiner had noticed patterns among different kinds of hydrides until he got to triplets of elements. In 1865, British chemist To understand how Mendeleev created the sodium (Na). Sodium behaved like lithium in its John Newlands noticed the periodicity of reactions with hydrogen, forming NaH. table in the first place, you have to go back in chemical properties and likened the phenom- time and erase what you’ve learned about the enon to musical octaves, in which the same 2 Na(s) + H (g) a 2 NaH(s) table. Imagine for a moment that the distinctive tone repeats after an increase or decrease of 2 shape of the present-day periodic table with its eight notes. In Germany, chemist Julius Lothar Thus, a pattern started to emerge. neat columns and rows doesn’t exist. You don’t Meyer was developing his own periodic table yet know about protons and therefore atomic that was published in 1870. But Mendeleev But Mendeleev’s most numbers, which, for the most part, convenient- beat Meyer to the punch a year earlier. insightful decision was ly run in order from one to 118 from left to to let properties some- right and top to bottom of the table. What sort of chemical properties did Mende- times trump atomic leev have in mind when he developed his table? weight when he placed All you know about the elements identified at To get a better idea of the patterns he noticed, elements. For example, the time is how they interact with each other, let’s start with the metal lithium (Li). Mendeleev if you look at the peri- their physical properties, and their relative knew the hydride—a compound of hydrogen odic table, you’ll notice atomic weights. And you want to categorize with another element—that Li formed had the that nickel follows them. formula LiH. cobalt in the fourth row

The Periodic Table Timeline: Scientists’ Contributions

French chemist Antoine Lavoisier categorized German chemist Johann Döbereiner British chemist John Newlands elements into metals, nonmetals, “earths,” noticed that triplets of elements likened the periodicity of and gases. shared chemical behaviors. chemical properties to musical octaves. 1789 1829 1865

PHOTO: THINKSTOCK 12 ChemMatters | FEBRUARY/MARCH 2019 The Hydrogen Puzzle even though nickel is lighter. Mendeleev placed them this way because nickel’s properties We often see hydrogen atop group 1 although aligned with palladium’s (on the next row, same hydrogen is very different from the other elements column) and cobalt’s with rhodium. in the column. Unlike group 1 elements, hydrogen is not a metal, it’s a gas at room temperature, This approach allowed him to skip slots in the and it bonds covalently most of the time. Group 1 table that corresponded to chemical properties elements are metals, solid at room temperature, and atomic mass ranges that did not match any and form only ionic bonds. elements known at the time. For each open slot, Mendeleev predicted the existence of a yet-to-be So, why is hydrogen grouped with these metals? discovered element. Today, we know that hydrogen has a single He turned out to be right most of the time. For electron in its electron shell, defined as a set of example, Mendeleev had left spaces for yet-to- electrons with similar energies in an atom. This be discovered elements that he called eka-alu- shell contains one subshell, which consists of one minum, eka-manganese, and eka-silicon—eka orbital. An orbital is a region of high probability of is the Sanskrit word for “one.” These spots were The sun is more than 70% hydrogen by mass. ultimately taken by gallium, technetium, and finding an electron. Each orbital can hold up to two germanium. electrons. That’s not to say Mendeleev’s table was perfect Since hydrogen has only one electron total, its Because of this shared trait, hydrogen forms from the beginning, or even the only way to electron is in the outermost—or valence—shell. some compounds in ways that are similar to how Valence shell electrons account for how an element organize elements. He himself revised it within alkali metals form compounds. Reactions between reacts chemically. Other group 1 elements have two years of introducing it. Mendeleev’s 1869 hydrogen and chlorine, and between sodium and periodic table had the elements with increasing more than one electron, but like hydrogen, they mass moving down in columns, while elements have only a single electron in their valence shells. chlorine provide an example of this: with similar chemical properties lined up hori- H (g) + Cl (g) a 2 HCl(g) zontally in rows. In 1871, however, he reversed 2 2 this idea. He lined up elements with similar 2 Na(s) + Cl (g) a 2 NaCl(s) properties vertically, and the periods appeared 2 in horizontal rows. But in other ways, hydrogen resembles elements in group 17, the halogens, which are nonmetals The discovery of protons like hydrogen. Halogens’ valence shells have seven It wasn’t until more than 40 years later in 1913 electrons, and need just one more for these shells that British physicist Henry Moseley used a to be full. Hydrogen’s valence shell also needs just technique called X-ray spectroscopy to count one more electron to fill its valence shell and form the numbers of positive charges in the atom- an anion. ic nucleus. Moseley then developed the first modern periodic table, basing the element se- H(g) + e- a H-(g) quence directly on these charges. In 1920, New Zealand-born British physicist Ernest identified F(g) + e- a F-(g) the charge as the atomic number, or the proton number. Remarkably, organizing the table this After 150 years, some scientists still debate way validated Mendeleev’s original approach PHOTOS: COURTESY OF NASA where this unique element fits best. (Continued on next page) On Earth, hydrogen is mainly found in water.

Russian chemist Dmitri Mendeleev published an German chemist Julius Lothar Meyer published a Mendeleev revised his early form of what would become the modern different version of the periodic table. table. periodic table. 1871 1869 1870 (Continued on page 14)

ChemMatters | www.acs.org/chemmatters 13 The Race to Invent the Periodic Table Additional findings further fleshed out the table.

By this point, for instance, noble gases had been discovered. Initially, they were placed to the left of group 1 metals. But further study https://youtu.be/-ojcm3IIf98 justified moving them to the far-right side of the table where they reside now.

Also, beginning with period 4, which starts with Some scientists have hypothesized that period potassium (K), the table expanded like an accor- 7 might not be the last one in the table. A dion to hold 10 additional groups. The addition proposed superactinide series could get us to of these transition elements gave the table a element 157! shape more like you see in today’s version. How is that possible? Well, during the 1950s, And what about the two rows that sit below chemists had developed a model of the nucleus the main table? These are the lanthanide and in which protons and neutrons are not simply actinide series. The first elements in these rows clumped together, but rather arranged in rings. were discovered as early as the 1700s, but they Based on the idea that each nuclear ring could weren’t organized in their own section until the become full, U.S. chemist and Nobel Laureate PHOTOS: LAWRENCE BERKELEY NATIONAL LABORATORY 1900s. Although they look separate from the Glenn Seaborg proposed something called an U.S. chemist and Nobel Laureate Glenn Seaborg rest of the table, they really belong to periods “island of stability.” He suggested that when a 6 and 7, respectively, and in between groups 2 ring becomes full with a particular number of with element 126. Both these elements would and 3. protons and neutrons, a super-heavy element belong to Seaborg’s superactinide series, but would be stable for long periods of time. only a particular number of neutrons would allow them to stick around. Filling in the blanks Take flerovium (Fl) as an example. It’s a Changes to the periodic table continue to super-heavy element that was first discov- If such stable elements could be created at this day and will likely keep surprising us in ered in 1998 and is only stable for about 2.6 some point in the future, there would be more the future. As recently as 2016, the four final seconds. The island of stability theory predicts at stake than just creating and filling period gaps in period 7—elements 113, 115, 117, that if Fl could be created with 184 neutrons, 8, because stability is the key to practicality. and 118—were officially filled. In order of it would be stable. So far, it has only been Such elements could be used to make special increasing atomic number, these elements are observed with a maximum of 176 neutrons. materials with properties that we cannot even named nihonium, moscovium, tennessine, and begin to imagine. Or maybe we can. Vibranium, oganesson. Moving to even heavier elements, the next anyone? island of stability in Seaborg’s hypothesis is the So, it would seem that the periodic table is yet-to-be created element 120, which would be David Warmflash is a science writer based in complete with period 7 filled in. Now what? in period 8 on an extended periodic table, along Portland, Oregon.

Selected References United Nations Educational, Scientific, and Cultural Institute, Jan 8, 2018: https://www.sciencehistory.org/ Poliakoff, M.; Tang, S. The Periodic Table: Icon and Inspi- Organization. 2019 International Year of the Periodic historical-profile/glenn-theodore-seaborg [accessed Dec ration. Philosophical Transactions of the Royal Society Table of Chemical Elements: https://www.iypt2019.org 2018]. A: Mathematical, Physical, and Engineering Sciences, [accessed Dec 2018]. March 13, 2015: http://rsta.royalsocietypublishing.org/ content/373/2037/20140211.long [accessed Dec 2018]. Biography: Glenn Theodore Seaborg.Science History

The Periodic Table Timeline: Scientists’ Contributions

British physicist Henry Moseley developed New Zealand-born British The official addition of four new the modern periodic table, basing the physicist Ernest Rutherford elements completed the seventh sequence of elements on atomic number. discovered protons. row of the periodic table. 1913 1919 2016

14 ChemMatters | FEBRUARY/MARCH 2019 Student Keirsi Birch learns how to extract essential oils from citrus zests using carbon dioxide (CO2) in a chemistry lab at Beyond Benign, a non-profit organization in Wilmington, Massachusetts. PHOTO: XIAOZHI LIM

Clean Green& Saving the planet is an enormous task. Here’s how chemistry can help. By XiaoZhi Lim

iara Johnson zests an orange, while her partner K Keirsi Birch pounds away at chunks of dry ice. “Plink, plink, plink!” The chemistry lab around them quickly fills with citrus smells and smashing sounds. Together with 11 other classmates, Kiara and Keirsi are on a day trip visiting Beyond Benign, a nonprofit organization in Wilmington, Massachu- setts, that is devoted to promoting green chemistry education. The students are learning how to extract essential oils using carbon dioxide

(CO2), which in solid form is called dry ice.

ChemMatters | www.acs.org/chemmatters 15 So, You Want to be a Green Chemist For those of you who want to explore green chemistry further, here’s what you can do: Take a toxicology class in college. Most chemistry classes teach us what molecules can do and how to make those molecules. But what happens when they interact with our bodies? This is a completely different field, known as toxicology, and many professional chemists do not receive training in this subject. Learn about alternative solvents, or even better, learn how to avoid using solvents. Many solvents, such as acetone, hexane, or dichloro- methane are volatile, hazardous, and become waste after a reaction is complete. Disposal of these solvents becomes an environmental problem. Start thinking about waste as a resource. We throw away all sorts of materials: plastic waste, electronic waste, agricultural waste,

sewage, and CO2. Imagine if we could convert all that waste into raw materials. This would help us avoid digging up even more fossil fuels and metals than we’ve already used, A small drop of yellow oil is found at and keep waste from piling up in our landfills. the bottom of the tube after students Find a green chemistry program. Learn more successfully extracted it from citrus zest.

about university programs that have a green PHOTO: XIAOZHI LIM chemistry focus at: www.acs.org/gci

The high school freshmen came from various places in the country: Kiara from Texas, Keirsi from Essential Oil Kentucky. It was their last week attending Math and Science for Minority Students, or (MS)2, a program Extraction at Phillips Academy in nearby Andover, Massa- chusetts. It was also the first time any of them As the warm water causes tried their hand at green chemistry—an approach the dry ice (CO ) to turn 2 to designing chemicals, chemical processes, and into gas, the pressure in consumer products that aims to avoid harm to the the tube rises and forces environment and human health. some of the CO2 to turn into a liquid, which penetrates Working in pairs, the students’ goal is to obtain the zest and brings out the essential oil from various citrus zests. Kiara twists essential oils. a wire into a coil basket that will fit inside a plastic centrifuge tube and hold the orange zest. Keirsi

crushes the dry ice—the solid form of CO2—until it resembles fine salt. Then, she holds the tube steady with a gloved hand while Kiara carefully scoops the dry ice until it fills up the rest of the tube. The girls cap the tube tightly and immerse it in a bottle of warm water.

Almost immediately, there is a faint fizzing sound, and tiny bubbles emerge from under the cap. The

ILLUSTRATION: KELSEY CASSELBURY warm water causes the dry ice to sublime—turn

16 ChemMatters | FEBRUARY/MARCH 2019 CO2 Extraction

from solid directly into gas. When this happens, the pressure in the tube rises and forces some of the CO2 to turn into a liquid, which penetrates the zest and brings the essential oils out.

“It happened really fast,” says Kiara.

When all the dry ice is gone, they remove the tube from the water bath. There is a small drop of yellowish oil at the very bottom.

“It’s fun,” says Keirsi. “It’s really fun.” The green shift

Essential oils are a big part of our lives. We ILLUSTRATION: KELSEY CASSELBURY FIGURE 1: The extraction of essential oils using CO takes place at lower temperatures than steam distillation, find them in soaps and perfumes, and in flavor 2 making it an alternative method with the potential to do less environmental harm. extracts such as vanilla or lemon. What makes them so fragrant is their chemical makeup. They are complex mixtures that contain some compounds which are quite volatile—that is, CO ’s use in extraction recycles waste from in- and other private initiatives, promote green they evaporate easily. 2 dustry (see Carbon Dioxide: A Green Chemical? chemistry, which include minimizing energy Essential oils are natural and generally thought page 18). use, avoiding waste, and designing non-toxic, of as environmentally friendly. But getting them safe chemicals. After the lab and a short break, “I really enjoyed [the experience],” says Sabrina 2 out of plants can require a lot of energy. Global the (MS) students get ready for a tour of WBI, Marte from Massachusetts. “It showed me a which is right next door to Beyond Benign. energy production and use is the largest source different perspective on what we can do as of greenhouse gas emissions, according to the scientists in order to help the environment.” “Industry is all about green chemistry if it saves International Energy Agency. So lowering the them money,” says Kate Anderson, who leads amount of energy required to make essen- From idea to invention K–12 education at Beyond Benign. Green chem- tial oils would reduce the products’ carbon istry is not just about making things that are footprint. The term green chemistry was coined in the better for the environment and human health. It 1990s when a group of U.S. Environmental In industry, essential oils are commonly ob- must also be cheaper and perform equally well, Protection Agency (EPA) scientists, includ- tained by steam distillation. The process blasts if not better, she adds. ing Paul Anastas, John Warner, and Joseph hot steam at more than 100 °C (212 °F) through Breen, began advocating for the prevention of “We usually talk about three criteria—cost, plant material, vaporizing its essential oils and unintended pollution. At the time, the agency safety, and performance,” says Anderson. “If carrying them away from the source. Then, the was focused more on cleaning up pollution you buy a green cleaner and it doesn’t clean, vaporized oils are cooled back into liquids in after it had already been released. But wouldn’t that’s ‘greenwashing.’” Greenwashing refers to a separate container from the plant material. it be better to, for example, create plastics that a product or service that is presented as good Because the technique takes place at high heat, degrade harmlessly in water and sunlight than it requires a lot of energy. for the environment but really isn’t. have them accumulate in the ocean? Beyond Benign is walking the students through The scientists at WBI invent new green an alternative method that has the potential Anastas and Warner came up with the guiding products or synthetic technologies. They also find solutions for chemical companies seeking to do less environmental harm (Fig. 1). CO2 principles to define green chemistry practices. extraction of essential oils usually takes place After retiring from the EPA, Breen went on to to phase out certain chemicals that could be at temperatures below 60 °C (140 °F). The co-found the American Chemical Society Green damaging or bad for human health. lower temperatures for this method reduces Chemistry Institute (ACS GCI) in 1997 (ACS “No chemist set out to design a molecule that the amount of energy required for the process, also publishes this magazine). In 2007, Warner which is one of the goals of green chemistry. co-founded a company called the Warner was going to cause harm to the environment,” Babcock Institute (WBI) for Green Chemis- says Anderson to the students. “But what was Additionally, the initial supply of CO for indus- 2 try. He also started Beyond Benign, a related not understood in the past was how some trial-scale extraction isn’t produced specifically non-profit. molecules would interact with the environment for this purpose. It often comes from other and the human body. And so this is where green processes that release CO2 as a byproduct. So These organizations, along with academic chemistry comes in.”

ChemMatters | www.acs.org/chemmatters 17 Carbon Dioxide: A Green Chemical?

Carbon dioxide (CO2) has a bad reputation. It’s known as a villain in climate change and ocean acidification. It is produced whenever we burn fuels such as gasoline in large quantities. But it’s also abundant and can be a good resource. What can we do with CO2?

We already use CO2 to make drinks fizzy and as dry ice to keep things cold or to get that smoky effect during stage performances.

CO2 can also be a clean solvent, particularly as a supercritical fluid—a state of matter that has properties of both liquids and gases. Supercritical CO2 can dissolve materials like a liquid, but fills containers like a gas. It reaches this state at temperatures above 31 °C (88 °F) and at pressures above 73 atm. In industrial processes, unlike in the Beyond ILLUSTRATION: KELSEY CASSELBURY

Benign classroom experiment, special equipment keeps CO2 As temperatures rise past the sublimation point, CO transitions directly from solid to gas. At the triple point, at high pressures. 2 all three phases of CO2 can exist in equilibrium. Above the critical point, CO2 exists as a supercritical fluid.

In addition to essential oil extraction, supercritical CO2 is used to decaffeinate coffee and tea, and in dry cleaning. Although technologies to capture CO2 from methods. But perhaps one day, there will be a power plants and the air exist, most companies stronger push to capture and make new products Unfortunately, the demand for CO2 is much too small to make a dent in global carbon emissions. have little incentive to invest in carbon-reducing out of CO2 .

Meeting green demands Interested? Be influential! For aspiring chemists, green chemistry training is now prized. The efforts are not all scientist-led. Students have also exercised their in- fluence by talking to their professors about green chemistry. For example, “Companies get it,” says Warner. Many companies, not just chemical 12 years ago, Gordon College professor Irv Levy resisted when a student companies but also manufacturers such as Unilever and Johnson & at the time, Laura Hamel, wanted to write a paper on green chemistry. Johnson, are embracing green chemistry. In contrast, universities are lagging behind, he says. “I rolled my eyes, and said c’mon, pick another topic,” he recalls. He didn’t think she would find enough material on the subject for a term “Unfortunately, if you look at the training in academia, we’re not meeting paper. “But she came back with a whole file of references on green chem- that need as well as we could,” says Warner. istry,” he says. He had no choice but to let her do it.

But efforts are afoot to change that from the elementary-school level That same year, he noticed that ACS had a meeting about green chemis- through college. Beyond Benign was set up to advance green chemistry try. Thanks to Hamel’s paper, he attended, and heard Warner and Anastas education. Led by Amy Cannon, Beyond Benign’s staff creates free, explain what green chemistry was all about. Now, Levy is a dedicated online lesson plans for K–12 classrooms. For example, there are lessons green chemist, and Gordon College was one of the first to sign on to the that teach students about recycling polylactic acid plastic cups and how Green Chemistry Commitment. to make their own biodiesel. Hamel went on to become the first green chemistry intern at Pfizer, and At the university level, ACS GCI coordinates efforts to integrate green today, her term paper is framed in Levy’s office. “That paper changed my chemistry concepts into the undergraduate chemistry curriculum. Many entire career,” he says. universities have started their own programs or added classes dedicated to green chemistry approaches. Green chemists are counting on a growing number of students and sci- Beyond Benign also created a program for universities called the Green entists to make a similar pivot to help reduce our impact on the environ- Chemistry Commitment. These commitments require faculty members to ment. include environmental health sciences in general chemistry courses and teach green chemistry practices in labs. XiaoZhi Lim is a freelance science writer based in Boston.

Selected References Anastas, P. T.; Warner, J. C. The 12 Principles of Green Capuzo, A. et al. Supercritical Fluid Extraction of Plant Kenis, P. J. A. et al. Carbon Dioxide Utilization Coming Chemistry: https://www.acs.org/content/dam/acsorg/ Flavors and Fragrances. Molecules, June 19, 2013: of Age. ChemPhysChem, Nov 10, 2017: https://on- greenchemistry/resources/the-12-principles-of-green- https://www.mdpi.com/1420-3049/18/6/7194 [accessed linelibrary.wiley.com/doi/full/10.1002/cphc.201701204 chemistry-pocket-guide.pdf. [accessed Dec 2018]. Dec 2018]. [accessed Dec 2018].

18 ChemMatters | FEBRUARY/MARCH 2019 Profile with Chancée Lundy, Co-founder of Nspiregreen Helping Communities with Chemistry or Chancée Lundy, high school was more Perhaps it’s no coincidence that Lundy than a place to learn: It served as a refuge. attended a school intimately familiar with F “It provided an escape from what I saw as activism—Selma High School, which formed a neighborhood that I didn’t necessarily during the civil rights movement in response want to hang out in,” she says. to court-ordered integration.

Fortunately, she loved school—and chem- Lundy wanted to help communities bridge istry, in particular. At the same time, her the technical knowledge gap, so she studied involvement with community organizations environmental science with a minor in chem- introduced her to the concept of environ- istry at Alabama A&M University. She went on mental racism, a web of local policies and to earn a master’s degree in civil engineering practices that results in people of color being at Florida State University. After that, she disproportionately affected by pollution in a worked in the private sector, ensuring that her particular neighborhood. employers were being good stewards of the environment. “A lot of what I saw in communities is that people [affected by pollution] would be advo- Wanting to circle back to her passion for com- cating for change, and they would know which PHOTO: COURTESY OF CHANCEE LUNDY munity-based environmental justice, she and policy they were against,” Lundy says. But, she adds, the communities often didn’t have fellow engineer Veronica Davis co-founded an company today, helping communities reduce the technical expertise that could environmental consulting firm called Nspire- pollution and its ill effects. help them interpret data and make green in 2009. The duo continues a case for change. to lead the Washington, D.C.-based — Christine Suh “ Q&A ” Q.What did you like about chemistry in that the company I worked for was being a good high school? neighbor. I helped come up with programs to reduce greenhouse-gas emissions. A.I think I was a sophomore in high school when I took general chemistry Q.How did you make the transition from corporate and really loved it. I don’t know if it was employee to the co-founder of your own business? just balancing equations or what it was, but I liked chemistry. I liked doing the A.When Veronica and I started our company, it was experiments. 2009 at the height of the recession. So, I think a bit of youth and naivety was tied into the decision. But we just wanted to offer something a little different Q.How did you become interested in to the marketplace, and we believed that we could the intersection between science and do it. policy? What need did you identify that your company A. I wanted to help people. Back then, Q. could fill? people were talking about environmental racism, the relationship between A.We started our company to do public outreach toxic chemicals in the air and water for environmental and transportation-related near manufacturing areas, and how projects. That is low-hanging fruit on most projects. they related to cancer clusters. I was looking at For us, the differentiator would be that we are not PHOTOS: JENNIFER BOYER (TOP), ERIC VANCE (BOTTOM) chemistry to determine if there were better ways a public relations or marketing firm. We know the of manufacturing that would reduce the need for technical side, and we know how to communicate it. these chemicals and reduce the amount of pollution from these processes. Q.What advice would you give to high school chemistry students?

We just wanted to offer something Q.After you got your engineering master’s degree, A.Whether you want to be a public speaker, an a little different to the marketplace, what did you do? entertainer, or in a scientific field, think about how and we believed that we could do it. chemistry fits in. For me, I wanted to pursue envi- A.I went to work in corporate America as an ronmental and social justice, so I figured out how air-quality engineer. I was trying to make sure chemistry fit into that.

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