Tag Archives: chemistry

Food and science: Why are peppers hot?

Chili peppers, such as jalapeños and serranos and habañeros, are hot because they contain a chemical called capsaicin, which is an irritant to humans.

Why capsaicin?

If it is advantageous to plants to spread their seeds, why do the fruits (peppers) contain a chemical that repels animals? It turns out that birds are not sensitive to the effects of capsaicin. Thus, capsaicin repels animals whose chewing action may destroy the seed while not repelling birds. Additionally, capsaicin may function as a antifungal.

What does capsaicin do, chemically?

Capsaicin binds to receptors for heat and pain called vanilloid receptors. Capsaicin causes the receptor’s neuron to fire, which normally occurs at higher temperatures; thus, the brain interprets this neuron signal as sensing heat.

Capsaicin is just one kind of vanilloid compound; vanilla is another member of the vanilloid family, with a similar structure, but it does not act on vanilloid receptors. Now I wonder if peppers taste at all like vanilla to birds. A mystery for the ages.

Capsaicin in peppers

As you may have noticed, some peppers are hotter than others. This is because some contain more capsaicin and related chemicals than others. The relative hotness of peppers is measured by the Scoville scale. According to this scale, habañeros are a few times hotter than ají peppers which are a few times hotter than chipotle peppers. Bell peppers actually don’t contain capsaicin due to a recessive trait.

Contrary to what I learned growing up, the seeds don’t contain capsaicin. However, the pith that surrounds the seeds has the highest concentration. This may be why the hottest peppers look like wrinkly sphinx cats; they are just packed with pith (such as the Carolina Reaper pepper, bottom). You can reduce the hotness of a pepper for cooking by preferentially removing the white spines, which is the pith.

Habañero peppers have a Scoville rating of roughly 500,000. Pure capsaicin has a rating of 16 million. Some chemical called resiniferatoxin found in Moroccan cacti has a rating of 16 billion (1,000 times higher!). 40 grams of the stuff can kill a person.

So, there’s your overview of peppers for this Friday. Don’t consider this a challenge to go find that Moroccan cactus, but when your lips tingle after eating salsa, perhaps think of capsaicin.

Carolina reaper peppers, one of the hottest according to the Scoville Scale. Just look at the wrinkles! (Wikipedia)

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Food and Science: Caramelization and the Maillard Reaction

When we cook food, we want it to be as flavorful as possible. Two types of chemical reactions contribute to browning; both of these reactions create hundreds or thousands of other molecules, which then add aroma and flavor. The higher temperature reaction you may be familiar with: caramelization is the breakdown and reaction of sugars. The Maillard reaction occurs at slightly lower temperatures (still usually above the boiling point of water); this reaction occurs between the amino acids of proteins and sugars.

Both of these reactions are so complex that scientists don’t know everything that occurs during them. We understand the basic nature of each reaction, but any plant or animal food contains literally thousands of different molecules that can all react together. Fortunately, we can still implement the process without a full understanding (and we have been for millennia), and a lot of very nice foods undergo either or both reactions.

The Maillard reaction and caramelization often occur at the same time, and produce similar results visually, so they can be tough to separate. If something contains both proteins and sugars, both reactions can occur with heat. Fortunately, they both taste good. They’re also easy to do at home. If you want to brown your food, get a skillet nice and hot. Make sure you’ve patted the food dry (this allows the surface to get hotter than the boiling point of water, thus allowing the reactions to occur), and sear away.

Fun science: the smell of lavender

This weekend, I visited a lavender farm, and thus smelled a lot of lavender. The sense of smell is really an amazing thing. Our vision processes light waves, our hearing processes sound waves– but smell processes many kinds of molecules at concentrations down to parts per billion. We tend to think of smell as a less important sense, but from a scientific standpoint, it’s amazing.

How does smell work?

The short answer is, we don’t fully know. We know receptors recognize different parts of molecules like ketones, alcohols and aldehydes. We don’t know how the brain assembles all the information from the various receptors. Some studies suggest that groups of neurons synchronize in different ways for different scents, while other studies suggest that the locations of receptors that fire create a spatial pattern for each smell. You can find further reading here, but fair warning, it’s tough material.

How sensitive is smell?

We can detect methyl mercaptan, the scent added to natural gas so that we can smell leaks (also the smell of asparagus pee!), down to parts per billion (ppb).

We can also tell the difference between very similar compounds. Linalool, the primary component of lavender oil, exists in two configurations called enantiomers. Both contain the same elements linked in the same way, but the two are mirror images. The left-handed linalool is the primary component of coriander seed and sweet orange flowers. The right-handed linalool is the primary component of lavender and sweet basil. (L)-linalool is sweeter and detectable to 7.4 ppb while (R)-linalool is woodier and detectable to 0.8 ppb.

Left:Left-handed linalool, the primary smell of coriander seed. Right: right-handed linalool, the primary smell of lavender oil. Image from Wikimedia commons.

Smell and Emotions

Studies suggest that the smell of lavender relieves anxiety and can promote sleep. Smell is strongly tied to emotions; the same parts of the brain that process smell store emotional memories.

I wonder if this connection is partially why we discount smell; smell is at its basic core tied to emotions rather than logic. It’s hard to put a smell into words, and science understands our others senses far better. I stood in the room full of lavender, remembering my last visit to a lavender farm with my family, and thought about how amazingly complex our response to little molecules can be.

Fun science: more crystals!

Months ago, I posted about the collection of crystals and minerals at the Smithsonian Natural History Museum. Well, I went again, this time armed with a nicer (and heavier!) camera, and below are a few of the finds.SONY DSC

Quartz: quartz is a very common type of type of mineral (the second most common after feldspar), made up of silicon and oxygen. This variation is called agate. I used to buy agate slices as a kid, but the Smithsonian’s are slightly fancier.

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Another example of quartz. This one arose in a piece of petrified wood. I like this one because it looks like a painting of a setting sun behind a row of pine trees–almost Japanese.

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Malachite with azurite: both malachite and azurite are compounds of copper with oxygen, carbon, and hydrogen. The two differ only in the ratios. By geological standards, this rock formed somewhat quickly. We can tell this because the crystals are numerous and small. Single, large crystals form more slowly. This is why you should make ice cream at low temperatures, because when you freeze it quickly, many tiny crystals form, producing a better texture.

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Pyrite: As you may see, pyrite, or fool’s gold, has a cubic crystalline structure. Pyrite is composed of iron and sulfur.

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Calcite with duftite inclusions: Calcite is known for its optical properties such as birefringence. It was used as a material for gun sights in World War 2. Duftite is a compound of lead, copper, and arsenic. It is the duftite that gives the distinctive green color. I think of this as the kiwi mineral, as it even has the seeds.

Fun Science: The Element Lithium

Lithium is the third element on the periodic table, after hydrogen and helium. It is the lightest metal, and you probably use it every day. The batteries in your phones and laptops and most rechargeable batteries you use are lithium ion batteries.

Lithium is used in batteries because it has the highest electrochemical potential of any element. It is so high that it will split water into hydrogen and oxygen (and violently!). This means there is a lot of energy available to exploit. This is also why laptop batteries can sometimes explode; the batteries are sealed very tightly, but if the seal is broken, air and water vapor will come in contact with the lithium and this is unsafe. 10-15 years ago, there weren’t as many lithium batteries in use, but now they are everywhere. Science has made great strides in improving the configurations of the batteries to give more energy, such as increasing the surface area of the lithium portion. Each time you cycle your battery, the lithium undergoes an electrochemical reaction on the draining and again on the charging of the battery. This is also why batteries become shorter lived over time; the high surface areas of new batteries aren’t thermodynamically favorable, and the lithium will become lower surface area with time. Less available surface area means less available energy.

Lithium ion (Li+) has another, very different use. It is used as a mood stabilizer. It is particularly useful at combatting mania. The linked wikipedia page contains its fascinating medical history. It was first used in the 1870’s as a mood stabilizer. Eventually LiCl was marketed as an alternative to table salt (NaCl), to avoid high blood pressure, and its mood properties were forgotten. Early versions of 7 Up contained lithium. Excessive lithium use was found to be deadly, and it was banned as an additive in the 1940s. Then in Australia, it was again discovered to have mood-stabilizing properties. Its therapeutic dose is quite close to its toxic dose, which is maybe why it took a while to gain approval in the US. Studies suggest that water supplies containing lithium may promote longevity and reduce the occurrence of suicide.

Lithium salts also have another really nifty use: cleansing the air in spaceships and submarines.  Not only does human breathing consume oxygen; it also produces carbon dioxide, which is toxic when present in high amounts. Several lithium salts can remove carbon dioxide from the air. One even adds oxygen to the air when it removes carbon dioxide.

Elemental lithium is highly reactive, and is a member of the alkali metal group (all of whom react very impressively with water). Below is a video of lithium reacting with water. It bursts into bright red flame:

Another video shows more lithium action:

The people who made the second video have a great youtube channel with videos about all the elements done in a university laboratory environment. Most of them have good footage of reactions as well. I just spent an hour watching their videos, they are very entertaining for people with little knowledge, or a lot. If you have a little time to kill, the videos of sodium and potassium are also good, flammable fun.

100 posts, 100 fun facts

This list making business is slow stuff, and too interesting, so I decided to split it into two 50-fact posts. Happy memorial day, and happy 100 posts to me! Here are your first 50 factoids!

1. People from different cultures differ in what colors they perceive. As a simple example, english speakers deem pink as a different color than red. Russian speakers don’t, but they have a fundamentally different word for dark and light blue. In chinese, red and pink are red and pastel red, and likewise with blue.

2. Corrosion occurs preferentially where you can’t see it, such as under the head of a bolt or a foot or two under sea water. This is due to small concentration differences which cause a charge differential, which leads to corrosion. This is one reason trying to detect corrosion is very hard.

3. The biggest silicon wafers made are 45 cm or 17.7″, though they aren’t yet in production. The silicon is 99.9999999% pure, and monocrystaline.

4. Glass doesn’t have a set crystal structure; this is why it can cut so badly, because shards can be arbitrarily sharp. Auto glass is laminated with plastic to help hold it in place.

5. Many of the scenes in engineering in “Star Trek” and “Star Trek: Into Darkness” are filmed at the Anheuser-Busch brewery in Los Angeles. Look for the green labels reading “VF##”– these are vertical fermenters. In another part of the movie, Chekhov slides past some really shiny tanks on a red floor– these are horizontal fermenters. I used to work at an AB brewery, so I got really excited when I first noticed this.

6. A neutron star is so-called because all the electrons and protons are forced by immense gravitational pressure to combine. The whole star is nearly as dense as a nucleus, or 5.9×10^14 times denser than water. This is equivalent to the weight of a 747 in the space of a grain of sand.

7. Have you ever tried dividing by zero on a calculator? A black hole is remarkably similar to dividing by zero in space.

8. Near a black hole, forces called “tidal forces” (which are felt everywhere, but are crazy strong near a black hole) can be very strong over short distances, ripping anything apart. This is called “spaghettification” (no joke).

9.  After the death of Ivan the Terrible in Russia, three men claimed to be his lost son, Dimitri. They are collectively referred to as the false Dimitris. The first successfully became Czar for ten months, after which his was killed and cremated. His ashes were loaded into a cannon and shot towards Poland, as he was believed to be a Polish spy.

10. The word “defenestration” means “the act of being thrown from a window”. The need for such a word was precipitated by two such events in Prague.

11. The 1904 World’s Fair and Olympics were held in St. Louis. In the marathon, the man who finished first hitched a ride in a car, one favorite made himself sick eating apples, and another favorite was run off course by an angry dog.

12. Toasted ravioli, or breaded deep-fried ravioli, are a culinary delight in St. Louis. Also popular is provel, a cheese used almost exclusively in St. Louis (giving a hilarious Wikipedia by someone who seems unimpressed).

13. The Cahokia mounds are a set of artificial hills in Southern Illinois. They may look unimpressive, but they are about a thousand years old, built by a native culture which later abandoned them. An old nickname of nearby St. Louis is “mound city”, because similar mounds used to be found in the city.

14. Peter the Great of Russia was 6′ 7″. In his early adulthood, he traveled to Europe to learn about shipbuilding, a passion of his. He tried to pass off as a member of the company, but his great height continuously gave him away. The little shack where he lived in Holland still stands near Amsterdam.

15. Over 100,000 serfs died building St. Petersburg, Russia. Peter the Great commissioned the city because the only Russian port at the time, Archangel, was occluded by ice 6 months of the year.

16. 5 people died building the Empire State Building.

17.  The first electric light bulb and dynamo west of the Mississippi was on the campus of the University of Missouri at Academic Hall. The building caught fire and burned to the ground, leaving only the front columns of the building. They remain standing today.

18. Thomas Jefferson has two tombstones: one at his home of Monticello, and one at the University of Missouri. The University of the Missouri is the first land-grant university in the Louisiana Purchase, and many aspects of the university were modeled after Jefferson’s University of Virginia.

19. Cape Hatteras on the Outer Banks has had over 600 recorded shipwrecks. The most recent occurred during Hurricane Sandy in 2012.

20. In November 1956, the USSR invaded Hungary. The Hungarian water polo team fled the country after watching the invasion from nearby mountains. On December 4, the Russian and Hungarian teams met in the gold medal qualifying game of the 1956 Olympics. The game is called the “Blood in the Water” game, due to its violence. The story is told in a documentary called “Freedom’s Fury.”

21. The shortest player in the history of baseball was Eddie Gaedel, who batted for the St. Louis Browns on August 19, 1951. He stood 3’7″ tall, and wore the number”1/8″. Because he had such a small strike zone, he was walked. His contract was voided by baseball the next day.

22. Mercury is a toxic metal that used to be used in thermometers due to its consistent thermal expansion. The mad hatter concept owes to mercury poisoning in old hat makers. A researcher at Duke died in 1997 after a few drops of methyl mercury fell on her glove; organic mercury is incredibly toxic.

23. Humans now have 46 chromosomes in 23 pairs, but at some point in history, they had 48 chromosomes, the same as chimpanzees. Scientists theorize that the number changed when the human population dwindled at one point in history.

24. Splenda is chemically identical to sugar, but it is the mirror image “left-handed” sugar. The left-handed sugar tastes the same as sugar, but it can’t be digested, because the human body only handles right-handed molecules. However, brain scans of people eating sugar or splenda show that the brain registers more reward sensation with sugar. The body can be clever! (I tried to find this study; unfortunately, searching about splenda turns up a lot of nonsense to wade through.)

25. Cuttlefish can change the color of their skin for communication or for camouflage. They can make complex, varying patterns, or they can match a stationary one. Check out this video of a cuttlefish matching a chessboard.

26. Women generally have a better sense of smell than men. in particular, they are better at smelling something they’ve smelled before, where men show less improvement.

27. The Marianas Trench, the deepest ocean trench, is 6.8 miles deep at its deepest point. We still know very little about our deep oceans.

28. Giant squids have been written about since ancient times, but we took our first picture of one in 2004.

29. Only two elements are liquid at standard room temperature: mercury and bromine.

30. The world’s deepest hand dug well in is Greensburg, Kansas. Greensburg was decimated by an EF5 tornado in 2007. It has since started rebuilding, and aims to be the first LEEDS certified green city in the US.

31. Hurricane Camille came over land in Louisiana in 1969 as a category 5 hurricane. Of the 259 deaths caused, 123 were in the mountains of Virginia, in Nelson County (over 1% of the population). The storm dropped 27 inches of rain in a few hours. 133 bridges were washed out, and birds drowned in the trees.

32. Many of Thomas Jefferson’s inventions still reside at Monticello in Charlottesville, VA. There is a clock that tells the day of the week, a dumb-waiter, and a device for writing on two pieces of paper at once.

33. Blue eyes are caused by the presence of less pigment in the eye, resulting in a different light scattering pattern. Blue-eyed baseball players sometimes have much lower daytime hitting averages, because blue eyes filter out less glare.

34. Albinism is principally defined by eye defects caused by the lack of pigment during the formation of the eye. Without pigment in the iris, the eye doesn’t properly focus light, leading to numerous vision problems. It is possible to be albino while still having normally pigmented skin.

35. Catgut is prepared from animal intestine, and was used historically to make strings for instruments. Its name is probably a shortening from cattle gut, for those of us who like kitties.

36. Paper didn’t make its way to Europe until after the year 1000. It was made from old fabric and clothes. Old paper doesn’t yellow and age the same way as 1900’s paperbacks because it tended to be acid-free. Books can last centuries if the paper and ink are acid free.

37. Organisms around deep sea vents metabolize hydrogen sulfide from the vents to survive. 300 new species have been discovered around such vents; because exploration there is so hard, there are likely many more.

38. Hydrogen Fluoride is considered a weak acid, because hydrogen and fluoride bond strongly as resist dissociation. However, HF will go after just about anything including glass. HF is very dangerous to work with, because it does not hurt immediately. It seeps through the skin and begins to dissolve the bone.

39. Phosgene was used in chemical warfare in World War 1. The Japanese also used it extensively in World War 2. It smells like freshly cut grass.

40. The kite buggy was invented in China in the 1300s. It is a cart drawn by wind power. It seems hard.

41. Capillary action in trees helps fluid rise in trees. This is how tree several hundred feet tall supply water to the leaves.

42. The Negro Leagues baseball museum is in Kansas City, Missouri. Many of the negro leagues teams were fairly successful, and drew enthusiastic crowds. The exclusion of blacks from baseball was shameful, but they made something great in spite of it. You can learn about Satchel Paige or Buck O’Neal, as well as the various negro leagues teams.

43. The Eads bridge in St. Louis was the longest of its kind when it was built, over a mile wide. The supports are some of the deepest ever sunk, and 15 workers died due to decompression sickness.

44. The Anheuser-Busch brewery in St. Louis is the biggest brewery in the world. It outputs 25 million barrels per year. You can visit for free and get some complimentary beer.

45. The international rose test garden in is Portland, Oregon. It is free to visit and they have over 550 varieties.

47. The male paradise whydah grows out a foot-long feather during mating time to impress the female paradise whydah. The paradise whydah is a parasitic species that uses the nest of the melba finch.The male whydah imitates the melba finches song. In captivity, the whydah cannot reproduce without the melba finch also present.

48. The carrion flower is an enormous bloom that stinks of rotting flesh. It can be up to nine feet tall.

49. Blue is a rare color for organic molecules. This may be because the color is associated with alkaline conditions, which are relatively rare in organisms.

50. Monarch butterflies can sense the earth’s magnetic field. They use it to complete their 2000 mile migration.

Come back Thursday for 50 more interesting factoids! Happy 100 posts!

Fun Science: Why’s platinum so special?

In science, we tend only to learn about a small subset of the elements that populate our world. This is not unreasonable, since 96% of our bodies are composed of just hydrogen, water, carbon, and nitrogen. But there are over a hundred more elements, and they often influence life outside our bodies in ways we don’t hear about. So in today’s post I will talk about platinum.

Platinum is one of the rarest metals in the Earth’s crust. Only 192 tonnes of it are mined annually, where 2700 tonnes of gold are mined annually. When the economy is doing well, platinum can be twice as expensive as gold. So what’s so valuable about it?

Platinum is used a lot in jewelry. Platinum has the appearance of silver, but it doesn’t oxidize and become tarnished like silver. It’s harder than gold, and its rarity can be appealing.

But it’s the chemical properties of platinum that set it apart. Platinum is a great catalyst. This means that platinum facilitates chemical reactions, but is not consumed as the reaction proceeds. The catalytic converter in your car is a platinum catalyst. The catalytic converter helps eliminate a variety of undesirable compounds such as carbon monoxide, nitrous oxides, and incompletely combusted hydrocarbons. Platinum is also a critical part of current hydrogen fuel cells; it splits hydrogen into protons and electrons.

Platinum doesn’t force reactions to occur, but it makes them easier by reducing the energy required. The image below shows the reaction of carbon monoxide (CO) to carbon dioxide (CO2). The chart at the bottom shows the potential energy before, during and after the reaction. Imagine a ball rolling along the red curve (with platinum) and the black curve (without platinum). The ball on the black curve will need more speed to get over the hump. Any given ball is more likely to get over the red hump. Likewise, the presence of platinum lets CO get over the hump to become CO2. Platinum does this for all kinds of reactions.

activation energy

The reaction takes less energy because once a molecule bonds to the surface of platinum, the bonds within the molecule are a little weaker. Molecules like O-O and H-H can split into singletons, something they would never do off the surface. Below I show an example reaction for CO to COon platinum. This diagram is meant to be illustrative, a possible mechanism for the reaction and to show how platinum helps out. In reality these reactions occur very quickly, and careers can be spent figuring out exact reaction mechanisms.

catalysis

 

Platinum is a bit like velcro. Molecules become hooked to the surface, do their reaction, and unstick. If molecules stick and then refuse to unstick, this is called catalyst poisoning, and it’s a big issue in fuel cells. Like velcro, once the hooks are occupied, they can’t do anything else. Platinum is a good catalyst because a lot of things (like hydrocarbons) want to stick to it, but they don’t stick too hard. Other metals either are not attractive enough, or they are too attractive. Platinum is so valuable because, besides being rare, its properties happen to be balanced just right for the reactions we want.