DEVELOPING AND DESIGNING NEW CHEMICALS AND MATERIALS - Chemistry: Notable Research and Discoveries - page 17

sheets of carbon are only weakly bonded; in carbon composites, the car-
bon is twisted into threads, which are held together with strong bonds.
When these thin carbon fibers are glued into a piece of plastic, the result
is a relatively lightweight material of exceptional strength.
Structure is also essential in complex biological molecules. A lot
of medicines used for psychiatric illnesses such as depression rely on
their ability to interact with certain proteins in the brain. For instance,
a class of antidepressants—medications that alleviate the symptoms of
depression—act on proteins involved with the collection (reuptake) of
the chemical serotonin, and they are known as selective serotonin reup-
take inhibitors (SSRIs). This class of antidepressants includes Prozac
and Zoloft. Earlier medications were also effective and are still some-
times used though they produce a number of side effects, such as dietary
problems. Although an SSRI can also generate potentially dangerous
side effects, psychiatrists tend to observe these effects less often. (Brain
chemistry is the subject of chapter 3.)
Finding and developing new materials, whether they are organic —
complex biological molecules with carbon backbones—or inorganic,
requires a series of chemical reactions. The experimentation necessary
to find the right reactions is time consuming. As with cooks who oper-
ate without a recipe, the trial-and-error process with a chemist usually
leaves time for the production and testing of only a few hundred com-
pounds. Although this number may seem like a lot, most of the effort
is wasted—the product is too sticky, not strong enough, too brittle, too
easily damaged by other chemicals, not flexible enough, or has some
other fault for which it fails to suit its intended purpose.
But a new technique, beginning in the 1990s, has accelerated the
process of generating compounds to be tested. The idea is to start with
a chemical or small group of chemicals that the experimenter believes
is important—perhaps these chemicals have formed some of the most
promising compounds in previous efforts, or they are components of
related materials. In the past, chemists needed to mix the chemicals
along with other reactants under the proper conditions of temperature,
pressure, and so forth, and then use various methods such as distilla-
tion or chromatography to extract the reaction product. To get another
product, the experiment must plod through the same steps. But in a
technique known as combinatorial chemistry, the chemicals are mixed
in a parallel fashion, so that many reactions proceed at the same time.