Wednesday, May 30, 2012

Chemistry and Chemicals – a Brief Tutorial for the non-Chemist

I have been a professional chemist for well over 30 years. I know a bit about organic and medicinal chemistry, some about biochemistry, and enough about toxicology, pharmacology, and metabolism to discuss them with reasonable accuracy. My area of specialization is natural products chemistry, which is the study of biologically active chemicals from plants and bacteria. I am planning a post on pesticides and organic farming, but I thought I would first put up a post on chemistry for the non-chemist.

A chemical is the form of physical matter with which we interact directly. Chemicals are the components of everything you see, smell, touch and taste. The oxygen you breathe is a chemical, as is the water you drink. There are simple chemicals such as sodium chloride, there are complex chemicals such as sucrose, which is a dimer of glucose and fructose, themselves complex organic molecules made up of carbon, hydrogen, and oxygen. There are exceptionally large and even more complex chemicals such as DNA or proteins. Absolutely everything that physically exists in our world is made of chemicals. The only thing that is absolutely chemical free is a pure vacuum. Those two words, chemical and free, when put together, construct the most ridiculous non sequitur in existence.

  • Organic Chemicals
Chemists divide chemicals into two classes: organic and inorganic. Organic chemicals are compounds containing carbon such as plastics, cotton, sugar, vitamins, proteins, and natural gas (methane). All of the foodstuffs we eat, with exceptions of ingredients such as salt, baking soda, etc., are made of organic chemicals. Inorganic chemicals are everything else, chemicals such as those that make-up sand, glass, concrete, and marble, and the metals in things such as copper wire, aluminum foil, steel beams, and the rust on those beams. Organic simply means that the chemical is carbon-based.

  • Toxic Chemicals
All chemicals are toxic to a greater or lesser degree. If you inject water directly into a vein of a rat at the level of 90 g/kg of body weight, the rat has a 50% chance of dying. If you eat a big pile of salt, you will die. Try breathing chemically inert argon gas for a while and see what happens (actually, please don't do this). Toxicity is generally expressed as the dose of a given chemical that will kill 50% of an exposed population of organisms. This value is known as the LD50 (lethal dose 50%). Potassium chloride has an LD50 of about 30 mg/kg body weight in humans when administered intravenously. That is the same potassium you need to keep your heart working. Too much potassium, and your heart stops beating. At the extreme end of the toxicity spectrum is tetanospasmin, the neurotoxin produced by the bacterium Clostridium tetani that causes tetanus. It has an LD50 of 1 ng/kg body weight, or 0.000000001 g/kg. One gram (0.035 ounces) of this chemical would be enough to kill every person in the United States. Luckily you can be vaccinated against this disease.

  • Synthetic vs. Natural
A broad division has been made in the minds of most people between synthetic and natural. Interestingly, this division surrounded one of the earliest controversies in chemistry. In 1828, the German chemist Friedrich Wöhler was the first person to synthesize an organic chemical that was produced by a living animal. Wöhler synthesized urea, which is excreted in the feces of birds and reptiles to get rid of excess nitrogen in their systems. Wöhler's synthetic urea was absolutely identical to natural urea. At that time in history, it was considered impossible to synthesize an organic compound because molecules that came from living beings were thought to possess a vital force that could not be replicated by chemists in the lab. Today we know this to be false.

Synthetic and natural versions of a chemical are indistinguishable. When an organic chemist synthesizes a chemical originally produced by a living organism (e.g., penicillin, glucose, or estrogen) the definition of success is whether the synthetic chemical is identical in absolutely all respects with the natural compound. I have done this quite a number of times, and the true test of whether one has achieved the synthesis is whether the synthetic and natural version of the chemical are completely identical. If I were to prepare synthetic limonene, which is the principal flavoring chemical in lemons, the synthetic limonene would be indistinguishable in all respects from natural limonene isolated directly from lemons. There is absolutely no difference whatsoever between the synthetic and natural version of a chemical.

Natural chemicals can be toxic. Examples include strychnine, which occurs naturally in the nuts of a tree native to India, palytoxin, a chemical produced by a coral native to Hawaii, or digitalis, which is produced by the common foxglove, grown in many gardens. Strychnine, palytoxin and digitalis are 100% natural, yet are deadly toxins. Natural is not always good.

One surprising aspect of this denigration of synthetic chemicals is that people who make a false distinction in their minds between natural = good/synthetic = bad are likely to get up in the morning and take some ibuprophen or Lipitor or Zoloft. These are synthetic chemicals, yet little thought is given by most to taking a (synthetic) pharmaceutical agent prescribed by a doctor. Synthetic is not always bad. Society would lose an enormous number of benefits without synthetic chemicals.

  • Chlorinated Hydrocarbons

Molecules containing the element chlorine have a particularly bad reputation as environmental pollutants, and Greenpeace has ludicrously proposed an across-the-board ban on chlorine and chlorinated molecules. Some chlorinated chemicals are persistent in the environment and do show long term effects and toxicity in animals, but not all chlorinated chemicals share these problems. Some chlorine-containing molecules such as tetracycline are life-saving. A number of the most highly prescribed synthetic drugs in the U.S. contain chlorine, drugs such as clopidogrel (Plavix) that helps people with heart problems or amlodipine (Norvasc) that helps people with high blood pressure or bupropion (Wellbutrin) that helps people with depression.

When one thinks of instances of synthetic chlorine-containing chemicals such as DDT that have wreaked havoc in nature, is it not the over-zealous use of the chemical that was the actual problem? DDT plays an important role even today in controlling malaria, saving countless lives by killing the malaria-carrying mosquitoes, but in the 1950's, it was sprayed everywhere. Trucks drove down the street spraying DDT into the air so people could sit outside and not be bitten by mosquitoes. Planes flew over cities and indiscriminately sprayed DDT on everything, houses, gardens, animals, people in an attempt to control gypsy-moths. It was ill-advised over-use by misguided government agencies that was the problem. Judicious, careful, and warranted use of DDT is a completely different scenario.

Generalization of good versus bad chemicals because of the atoms present in them is a poor way to fix a problem. If chlorinated molecules are environmentally persistent, then the solution to the problem is not to ban them, but to stop using them in ways that are polluting. Society certainly managed to do just this with ozone-destructive chlorofluorocarbons (CFCs).

  • Chemophobia

Fear of chemicals is a misplaced phobia. There is little to say about this, given that everything is a chemical. Chemophobia is solely caused by the lack of education some people have on the subject of chemistry.

  • Processed Food

First of all, we must define the word "process" as it applies to food. Given that the word "process" is defined as "a systematic series of actions directed to some end," then washing, peeling and slicing an apple to make apple pie is a process, and the apple slices have been processed. This is perhaps one end of the spectrum of processing food. At the other end of the spectrum, the extreme end, is pink slime. This disgusting "food" product consists of finely ground beef scraps, fat, and connective tissue, which is mechanically separated from residual fat using a heated centrifuge (i.e., rendered). The residue, so to speak, is further processed by heating and treatment with either ammonia or citric acid to kill all the Salmonella and E. coli that have managed to latch on to "scraps" of meat. (I am unsure how the beef industry defines "scraps," but I am absolutely certain I don't want to know what they are or where they've been to become so contaminated with bacteria.) Finally, the disinfected product is finely ground and pressed into solid blocks for transport and use. The USDA allows ground beef to contain up to 15% of "lean, fine textured beef," as it is known inside the industry, without labeling it as such. I cannot understand why people in the beef industry object to this wonderful product being labeled with such a cute name. I mean, look what Victoria's Secret has done with "Pink." /sarcasm

Another example of a processed food is sugar (sucrose). It is actually one of the most pure chemicals available to consumers. It is produced by either sugar cane or sugar beet plants, and is 100% natural. Related to this process is molasses, which is what is left over after all the sucrose has been crystallized out of the cane or beet juice. In this sense, molasses is not processed to any significant extent.

The point at which I object to processing is when the result can no longer be called by its original name; when so many artificial and non-natural ingredients have been added that they outnumber the original ingredients. Processed cheese food comes to mind. It certainly isn't cheese, and it is highly questionable whether it should be considered food. However, cheese is actually processed milk and butter is processed cream, although neither process involves adulteration of the product with additives, preservatives, and other ingredients, nor chemicals to alter the consistency, palatability, or shelf-life (except salt). Ground beef is clearly processed beef, however minimally, but I personally prefer to know what sort of beef went into the grinder. Our local butcher grinds the beef right in front of your eyes and it is 100% meat, nothing added. It is the extent of the processing and to what extent the product is adulterated that is really the issue.

  • Words and Their Definitions

I find it objectionable when a word is perverted to mean something other than its real true definition. Take the word "perverted" as a prototype. The primary definition of the word when used as an adjective is "deviating greatly from what is regarded as right; distorted" or "changed to or being of an unnatural or abnormal kind." However, "perverted" is now a perverted word, because it can no longer be used without the negative connotation of some unacceptable sexual deviation. Another good example is "liberal." The meaning of this word is "favorable to progress or reform", but the word has been co-opted to mean something different, as has "conservative". One of the antonyms of the word "liberal" is "niggardly," a word loaded with racial connotations despite originating from the Swedish word "nygg," which means stingy. "Segregated" is yet another example. We segregate all the time, when we wash laundry we segregate whites from colors, we segregate vegetables to the vegetable drawer in the refrigerator, etc. Many people have a "meat and poultry only" segregated cutting board. The word was used correctly to describe racial segregation, but now it is rarely used outside of this context.

Thus, we have the perversion of the word "chemical" as something bad and unnatural, when, in fact, every physical thing is made of chemicals. Our bodies use chemicals like glucose to obtain energy, our bodies metabolize chemicals like cholesterol to obtain other chemicals such as estrogen, we take chemicals to cure infections and to reduce pain, the nerve impulses from your eyes to your brain that are being transmitted as you read this are controlled by chemicals called neurotransmitters, as is the control of the beating of your heart and contraction of your muscles. Everything you eat, absolutely everything, is a chemical.

  • Chemical Free

This brings me to the close of this post. For anything to be "chemical free" is impossible. Period.


  1. You can usually distinguish between a molecule synthesized in the lab and one that has been synthesized biologically. The caveat is that you (typically) use starting materials in the lab that are oil-derived while biologically synthesized materials are derived from atmospheric CO2. Oil contains virtually no 14C, while atmospheric CO2 has a measurable quantity.

  2. I left that little detail out of my discussion. I didn't think the non-Ph.D. chemist would appreciate such a fine point. Based on the source of the starting materials, there can also be a variation in the 12C/13C isotope ratios, just as water carries a 16O/18O isotope ratio as a signature of its source. If you measure this ratio in rain, the proportion of 18O increases as temperature increases. When I was writing this post, I wondered if anyone would catch the discrepancy between what I said and the absence of 14C in most synthetic compounds.

  3. We agree completely about the general message you are putting out here. I only commented because of your emphasis on "indistinguishable". Companies are marketing products as bio-based, even though it has nothing to do with the environmental impact. . .