As a chemist of over 15 years experience (post Ph.D.), I’m very familiar with the concept of a review article. Non-scientists may not understand the sheer volume of papers that are published every single day in the various chemical journals that exist. It’s absolutely impossible to read them all – they’re literally coming out faster than you can read. About the best a scientists like myself can do is to become specialized in a field and then try to collect all the relevant articles in that sub-specialty. For me, the topic is conjugated organic materials. I find them absolutely fascinating. A conjugated material is one that has an extended system of “pi electrons” that overlap and become dissociated.
The pi-system of conjugated electrons makes them ideal candidates for dyes. Organic chemistry has an intimate association with dyes, as the field originated with German dye companies in the early 1800’s. The synthesis of dyes started it all, with the drive to replace natural dyes with synthetic counterparts driving the scientists to develop synthetic methods and large scale production. The dyes that exist are almost entirely comprised of conjugated organics. Because the electrons can shuttle back and forth over the molecule using the pi system of orbitals, the materials become very skilled at absorbing light. This manifests itself as a highly colored appearance that is then granted to whatever material is exposed to the dye. Just about any color imaginable is now possible with a variety of dyes, all of which have the extended / overlapping pi system in the molecule. Dyes are very common in every day life. One of the most fascinating applications of dyes (from a chemists point of view) are the use of these materials to dye hair.
Human hair is primarily a protein. Proteins are large molecules comprised of amino acids, all linked end to end to make the keratin molecule. Because the amino acids in keratin are all highly polar and charged with electrons, they are very “polar” and stick to the highly polar organic dyes. Most modern technology is based on a chemical called 4-phenylenediamine. This molecule darkens when exposed to light, as the dye oxidizes and the conjugated organics begin to lose their overlapping pi system. However, this molecule is toxic, and scientists are searching for a safer replacement. I’ve done quite a lot of work in the cosmetics industry, and have developed a patent pending technology for hair dyeing that is safe and nontoxic. It’s a difficult goal, because the keratin molecule can’t really be chemically altered; you have to design a molecule to infiltrate the protein and impart it’s color. Since I’ve done so much work in the field, it was satisfying to read a recent article published in the American Chemical Society journal Chemical Reviews. This journal publishes nothing but review articles. Review articles do all the work of gathering relevant articles for you, and compile them all into one paper. They’re useful for a scientist like myself, because you can “catch up” by just reading one paper.
This particular paper was a great read. It included recent work to make nanometer sized dyes, which can more easily penetrate the hair fiber. Also discussed was gene therapy which can assist the patient in producing more nature melanin, which is responsible for hair color. It was exciting for me to read all the recent work in hair dyeing. It’s a process that most people take for granted. However, as an organic chemist, it’s fantastic to see how my specialty has progressed from 1800’s shop factories to modern biochemical approaches to hair dyeing. It’s an opportunity for organic chemists to develop a new technology. I came away from the article with several new ideas, and I’m eager to get into the lab and put them to test.
The source of this article can be found at:
Olivier, J., et al. “Current trends in the chemistry of permanent hair dyeing”. Chem. Rev. 2011, 111, 2537-2561.