Louis Pasteur (idea)

Louis Pasteur was obviously a genius. He lived from 1822 to 1895. He lives on now. In 1848 he established the principle of chirality using kitchen tools and a whole lot of genius. What is chirality? Basically chirality is the chemical principle that chemically the same compound can have right and left handed configurations. A left handed glove can not be superimposed on a right handed glove, and that demonstrates the principle of chirality. Right and left handed molecules are called dextrorotatory and levorotatory and this pertains to the way light is polarized as it passes through solutions of the substance. Interestingly most optically active molecules in human biochemistry are dextrorotatory (eg fructose, glucose, mannose and glucosamine -check out hexokinase.

eg : (from the online Glossary of Chemical Terms)

1. Dextrorotatory: A compound that rotates plane-polarized light to the right (clockwise) when viewed in the direction of the light source.
2. Levorotatory: Describes compounds that rotate plane-polarized light to the left (counterclockwise) when viewed in the direction of the light source.

Pure solutions of either left or right handed molecules are said to be optically active which means they rotate the plane of polarization of light. That is hard to explain but when you realize that we can buy and wear polarizing sunglasses it is not so far out. Try rotating two such lenses over one another while observing the brightness or darkness of light passing through and you will see what I mean.

Well what of this genius Pasteur. In 1848 Pasteur took optically inactive tartaric acid salt and dissolved it and grew crystals from it. He found, by actually seeing the crystals, the symmettry of the crystals came in two forms, one left handed and the other right handed. He later proposed that this meant the molecules had left handed and right handed forms figuring that the observable crystal forms were due to the form of the molecular building blocks. His observation could be used to explain optical activity and thus Pasteur in 1848 established with a simple experimental apparatus and a great deal of perspicacity the principle of chirality.

see also chiral