Chemistry's Evil Twin

In the American-English spoken language, there are many metaphors for that member of the family that seems just a little bit more different from the others–the black sheep, the odd duck, the bad apple, for example. One often heard specifically with twins is that of an "evil twin." The idea of an evil twin is ancient and based in some of the oldest mythologies that folklore still knows of, including Native American creation myths and those from the Mandika people of southern Mali, but for the most part it has always been more of a fictional tool than a reflection of reality. The one major exception (because there's always one) is in chemistry.

An approximate visualization of what the glucose molecule looks like.
PC: Jessica Noviello

Every chemical has a chemical formula that shows how much of every element is in it. For example, the formula for glucose, a basic sugar created by cells for energy, is C6H12O6. This formula tells me, a definitive non-chemist, that there are 6 atoms of carbon (C), 12 atoms of hydrogen (H), and 6 atoms of oxygen (O) in every molecule of glucose. Unfortunately, this is only half of the story when talking about chemistry.

As small as atoms are, they are still three dimensional, which means the molecules they create are also three dimensional. Every molecule has a specific structure of how the atoms are arranged that give it a particular shape. It's hard to see in the two dimensional approximation of the glucose molecule that I made (above), but glucose has a slight twist in the molecule, and the loosely connected carbon to the top-right is more underneath the rest of the molecule than I've shown here

There are many different molecular structures. Some shapes look like a triangular pyramid (tetrahedral), a starfish (seesaw), and even two x's merged together (octahedral), but these are only some of the many shapes that molecules can have. Sometimes the only thing that's different between two molecules is the shape. The same chemical formula but a different molecular shape means that the two molecules are totally different. In special cases, the molecules are the same in both formula and are almost identical in structure, but they are mirror images of each other. These molecules are called enantiomers.

To visualize how enantiomers look, just look down at your hands. They each have five digits, palms, and fingernails. They both do the same thing (more or less) and allow you pick things up, move things around, write, type, hold, and touch. Even though they look very similar, you have a distinct left and a distinct right hand, and they are not the same. They are mirror images of each other, and though you may try to put one on top of the other, it will never be a perfect fit.

These "two" pictures are actually only a single picture! I took a
picture of my left hand, copied it, and flipped the image. It looks
pretty much like my actual right hand! PC: Jessica Noviello.

Chemical enantiomers are the same way, and chemists even refer to them as "right" or "left" handed molecules. Another word for this is chirality. There are many known chiral pairs in chemistry, and the differences in chemical effects between the two members of the pairs range from relatively harmless, such as things smelling different, to downright dangerous.

Oranges smell like oranges because of + limonene, but
its cousin would make them smell like lemons!
PC: Wikipedia, used under the Creative Commons license.

On the harmless side, there are plenty of good examples in the food world. One chemical, limonene, smells different depending on the handedness of the molecules being smelled. The right-handed (+) limonene molecule smells like orange, but its left-handed (-) counterpart smells like, as you may have guessed from the name, lemon. Another example, and one that we had at our November Science on Main table just a couple of weeks ago, is that of another chemical called carvone. L-carvone (-) smells like spearmint and is often used in essential oils products, and its counterpart D-carvone (+) smells like caraway seeds or rye.

A pack of thalidomide capsules. PC: Steven C. Dickson.
Used under the Creative Commons license.

On the more dangerous side, the best example is also a tragic one, a true chemical evil twin. Before chirality and enantiomers were understood, pharmaceutical companies and scientists didn't know that the almost-identical chemicals could produce very different outcomes. In the late 1950s, many doctors in Europe prescribed pregnant women a drug called thalidomide to ease morning sickness, anxiety, and trouble sleeping. It really did a great job doing all of that, but it also caused serious birth defects in babies whose mothers used the drug. 40% of these babies died at birth.

Doctors made the connection between thalidomide and the birth defects in 1961, and the drug was immediately pulled from the market. It turns out that one of the enantiomers caused the beneficial effects of a sedative that relieved the symptoms of pregnancy, but the other caused the birth defects, and both were present in the medicine prescribed. Once chemists figured this out, they also figured out how to isolate the helpful molecule from the dangerous one. Today, thalidomide is still used to manage and treat serious illnesses such as cancer, tuberculosis, leprosy, and HIV/AIDS. It is a drug with a terrible history and still is risky to take, but it is significantly safer than what it was in 1961.

This Thanksgiving, be thankful that your family isn't as bad as chemistry's evil twin!

Arizona's Copper History

Pure copper, element #29 on the periodic table.
PC: Jonathan Zander 2009, used under the Creative
Commons license CC BY-SA 3.0.

One of the most important exports of Arizona is the element copper. As of 2007, Arizona was the leading copper-producing state in the U.S. and accounted for 60% of the total for the entire country. According to the University of Arizona's Geological Survey, prospecting and mining in Arizona begin as far back as 1583, though their targets were gold and silver rather than copper. In the 1850s, shortly after the land that became Arizona was acquired by the U.S. in the signing of the Treaty of Guadalupe Hidalgo, hardrock mining in the area helped build up the local economies, towns, and cities, many of which still exist today. By the time that Arizona became a state in 1912, "there were 445 active mines, 72 concentrating facilities, and 11 smelters with a gross value of nearly $67 million," an amount equivalent to $1.76 billion in 2018 dollars. Not too shabby for the 29th element!

Copper mining is part of Arizona's recent history, and its roots in the community stretch deep. In November 2018, the magma smelter of Resolution Copper in Superior, AZ was demolished as part of a larger effort to reduce the environmental impact of mining and to remove toxins from the area. The smelter is named after the old Magma Copper Co., which began mining the area around Superior in 1911. The smelter was opened in 1924 and immediately got to melting down ore to extract the valuable copper. In 1971 Magma Copper started to use another smelter, and this one was left in honor of its standing as a literal pillar of the community. Eventually it became too dangerous and unstable to keep it, and the choice was made to demolish it safely. It crashed down on November 10, 2018.

PC: Mark Henle/The Republic, c/o the Arizona Republic.

On a larger scale, what is it about Arizona that makes it so wonderful for copper mining? To answer this I first need to explain where the copper comes from. Copper needs to be extracted from copper-rich ores, or the natural materials that contains valuable metals or minerals. Copper-bearing rocks usually have a blue or green hue. When the copper-rich rocks interact with weathering agents such as water and Earth's atmosphere, the copper reacts with the other chemicals and can form other minerals. For example, if there is a lot of carbonate (a salt component of carbon and oxygen) in the water that touches the rocks, then other famous Arizona minerals such as malachite and azurite can form. Chrysocolla is another ore of copper. Though it is generally thought of as a phosphate-rich mineral, turquoise also contains copper and is found in Arizona and New Mexico.

The rocks that are richest in copper in Arizona are igneous rocks, meaning they formed either when a volcano erupted and deposited lava or ash on Earth's surface, or deep under the ground in a magma chamber. The rocks around Superior are a type of volcanic rock called tuff (specifically the Apache Leap Tuff). Tuff is formed from solidified ash that erupted from a vent during a volcanic eruption. The Apache Leap tuff is estimated to have formed 20 million years ago, plenty of time to interact with groundwater and form copper-rich minerals. Other volcanic rocks in the Superior area are rhyolite, a silica-rich igneous rock, and porphyry, a general term for rocks that have large crystals in them.

The copper rich minerals azurite (blue) and malachite
(green). PC: BYU Geology Dept.

Eastern and southeastern Arizona between 55 and 5 million years ago was an incredibly volcanically active place. A major geologic event called orogeny, or mountain building, was developing as the ancient Farallon tectonic plate was slowly moving underneath the larger North American plate. This subduction led to major eruptions that spread enormous amounts of ash all over what later became Arizona. The ash eventually solidified and became tuff, a rock we're already familiar with. These tuff rocks formed large mountain ranges like the Superstitions, Galiuros, Chiricahuas and Tumacacoris. This tuff reacted with groundwater and formed the copper-bearing minerals and ores that are mined today.

All of the volcanic deposits in Arizona make it a rich environment for copper mining. The unique geology here is the reason for why this state is the most copper-rich in the country, which has important economic implications for the state's continued success.
From a science perspective, studying and understanding the environments where certain minerals form is an important step in learning more about Earth's history.

Resources: 
http://azgs.arizona.edu/minerals/mining-arizona


https://www.azcentral.com/story/news/local/pinal/2018/11/10/cheers-tears-historic-copper-smelter-superior-demolished/1808363002/


USGS Geologic map of the Superior, AZ quadrangle: https://ngmdb.usgs.gov/Prodesc/proddesc_2120.htm

https://en.wikipedia.org/wiki/Copper_mining_in_Arizona