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April 19, 2013 at 8:00 AMComments: 0 Faves: 0

The ABCs of Chemistry: Part 4

By Lydia from SLN More Blogs by This AuthorFrom the Science Bits in a World of Bytes Blog Series

I took two semesters of organic chemistry to learn about the many structures carbon can form and how we can probe them.  I learned about chelation in inorganic chemistry and stability diagrams in geochemistry. Physical chemistry made me confront thermodynamics in detail my first semester and quantum chemistry in my second. This broad exposure has made me interested in a variety of applications, some more of which I will explore and explain below.

L is for Luminol

Luminol Molecule

With a name like that, it has to have something to do with light! This molecule has been popularized due to its use in forensic chemistry to detect blood. The molecule was first synthesized in Germany in 1902, but its interaction with blood was not noted until 1928. It did not receive its current moniker until 1934. Its luminescence stems from a reaction with a peroxide (-O-O- group) and hydroxide (-OH) salt. A dianion (two separate negative charges) is formed, which reacts with oxygen to form an unstable peroxide species. The electrons of the unstable species give off light to settle down to the ground state, and we see this as an eerie blue glow.Luminol glows blue when it contacts blood because the iron in blood catalyzes  the reaction (makes it go faster). The glow is intense because the amount of catalyst needed is small. Other substances, such as copper-containing compounds, bleach, and feces also cause luminescence, leading to false positives.

This chemical has found use in the biology lab as a detector or copper, iron, and cyanide in cellular assays. Luminol is also used to track activity of white blood cells, the part of your blood that eats invaders. White blood cells (technical name: leukocytes) emit light when consuming something else.  Quantifying this activity helps to determine the overall activity of the cell while it eats. Researchers have found that adding luminol makes the measurement more sensitive, so only tens of thousands of cells are needed rather than tens of millions. This is a boon for patients who have low white blood cell counts. In addition, this technique is sensitive to other factors, so the rate of pathogen consumption can be measured.

M is for Melanin

Eumelanin

Melanin is the only pigment found in the human body. It is a polymer that comes in two varieties. The first is eumelanin that gives a brown or black tint to skin and hair. Pheomelanin gives a reddish tint and is found in higher concentration in redheads, the lips, nipples, and certain genital parts. The precursor to both is the amino acid tyrosine, which is converted to L-dopa and then dopaquinone. Dopaquinone is converted to leucodopachrome and then follows one of two pathways to become eumelanin. When dopaquinone combines with the amino acid cysteine, it can follow one of two pathways to become pheomelanin.

We use melanin as protection from the sun, albeit a poor one, since its SPF is only 1 or 2. Eumelanin uses the oxygen atoms on the benzene ring to interact with oxygen radicals (one unpaired electron) to convert them to harmless species. It can bind a wide variety of molecules, such as cations, anions, and amines. Pheomelanin also reacts with reactive oxygen species (ROS), but it binds tightly to proteins and has the ability to grab on to drugs and other chemicals. Pheomelanin can produce ROS like hydroxyl radicals and so can be considered carcinogenic. Really? Don’t we get enough of that from the sun?

During my senior year of college, I attended a chemistry seminar about melanin.  The topic was different but fascinating; I learned more about melanin in that hour than I had before or since. I was surprised to hear that it could do something harmful, like produce carcinogenic species. When the spekaer explained its affinity for grabbing stuff, I was not surprised that drugs can be detected in hair. The main thrust of his research, though, was water filtration. We have great water filtration, but it’s too large and expensive to put in a poor village in Africa. However, where you have people, you have hair and therefore melanin (usually). His tests showed that melanin filters were good at binding pollutants like lead and arsenic (done more by pheomelanin) and, overall, make excellent first-step water filters.

N is for Nylon

Nylon 66

Nylon is a trade name for polyamides. The amide bonds have a carbon double-bonded to an oxygen and single-bonded to nitrogen. The body uses this type of bond in making proteins, so the bond is also known as a peptide bond. Wallace Carothers first prepared polyamides while at Du Pont by combining a diamine (NH2 on each end) and a diacid (-COOH on each end). Alternatively, nylon can be made from a single molecule with an amine at one end and acid at the other. Nylons are named according to the number of carbon atoms in the diamine and the number of carbon atoms in the diacid. For example, Nylon 66 has six atoms of carbon in both the diamine and diacid. Nylon 6 is made from a six-carbon chain with an amine at one end and an amine at the other.

Commercial use of the fiber expanded soon after its invention due to many desirable properties of the molecule. When at a temperature below its melting point, a nylon fiber has rigid areas that make it strong and amorphous areas that give it flexibility.  Hydrogen bonding between parallel strands contributes to the strength of the bulk material. Nylon can be made to different specifications for different uses. For example, because it is tough enough to withstand mechanical, chemical, and thermal stress, it has found extensive use in the automotive industry. It can, however, be extruded to a fine enough fiber that it can be made into hosiery.   It is an ideal fiber because fabric made from it is easily washed, dries fast, does not need much ironing, and does not shrink or stretch. The end groups enhance the dyeability of the molecule.

Although Nylon is a tough, useful fiber, it can break down under certain conditions. The peptide bonds are susceptible to attack by water at high temperatures, which snips the bond between the carbonyl (C=O) carbon and the nitrogen. A strong acid, like sulfuric acid (H2SO4), will also hydrolyze the bond. Light, especially UV wavelengths, will degrade the polymer. The degradation is very slow, however, so concerns have arisen over its disposal. Some recycling of nylon is done; during WWII, women’s worn-out nylons were recycled into parachutes. A research group found that certain fungi broke down nylon when starved for carbon or nitrogen.

I had the privilege of taking a tour of Alticor/Amway headquarters in high school. I saw different steps from formulation to packaging in the production of various products, such as detergents. There was a room full of appliances from different areas of the world to test formulations. The next room had sinks used to test dish soaps. That cemented in my mind my desire to pursue a career in chemistry, as have numerous college seminars and courses like geochemistry. What’s your inspiration?

Belitsky, Jason. "Melanin Molecular Recognition." Hope College. Michigan, Holland. 11 Nov 2011. Lecture.

Deguchi, Tetsuya, Masaaki Kakezawa, and Tomoaki Nishida. "Nylon Biodegradation by Lignin-Degrading Fungi." Applied and Environmental Microbiology. 63.1 (1997): 329-331. Web. 27 Mar. 2013.

Hegde, Raghavendra, Atul Dahiya, and et al. "Nylon Fibers." . University of Tennessee, n.d. Web. 27 Mar 2013.

Slominki, Andrzej, Desmond Tobin, et al. "Melanin Pigmentation in Mammalian Skin and Its Hormonal Regulation." Physiological Reviews. 84.4 (2004): 1155-1228. Web. 27 Mar. 2013.

Stevens, P, DJ Winston, et al. "In Vitro Evaluation of Opsonic and Cellular Granulocyte Function by Luminol-Dependent Chemiluminescence: Utility in Patients with Severe Neutropenia and Cellular Deficiency States." Infection and Immunity. 22.1 (1978): 41-51. Web. 27 Mar. 2013.

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