In 1815, the same year as the Battle of Waterloo, French scientist Jean-Baptiste Biot discovered he could make up solutions of organic chemicals that rotated the plane of polarized light to the left or right.
He proposed a remarkable cause for the phenomenon.
He proposed that molecules of the same compound could exist in different forms. He called these the left-handed and right-handed forms. These molecules were described as optically active because of their effect on light.
Three decades later, Biot’s remarkable observation was developed further by his compatriot Louis Pasteur.
Jean Baptiste Biot in about 1855 and Louis Pasteur in about 1880.
Pasteur demonstrated that the light rotation Biot saw is linked to the physical shape of the molecules.
He further showed that optically active molecules were not symmetrical.
Left and Right Handed Molecules: although the molecules above appear very similar, they differ in the way your right hand differs from your left hand. One molecule is a mirror image of the other. They cannot be superimposed on one another. They affect light differently.
The Molecules of Life are Left Handed
The left hand and right hand versions of molecules have identical physical and chemical properties. However, they differ in reactions with other handed molecules.
In fact, life on earth is built largely on left-handed amino acids, while all of the sugars made by plants are right-handed. The left-handed molecules in our bodies cannot recognize left-handed sugars. We would starve if we only had left-handed sugars to eat, so it’s just as well plants make right-handed sugars!
Scientists still can’t agree on the reasons for the handed preferences of the biological world, because when scientists synthesize these molecules in a test-tube, they get equal numbers of left and right handed molecules.
Interesting Facts about Optically Active Molecules
Thalidomide, morning sickness, and birth defects
Thalidomide has two optically active forms, shown below. The molecule on the left is useful for treating morning sickness. The molecule on the right causes abnormalities in developing fetuses.
In the 1950s and 1960s thousands of children died and suffered serious birth defects as a result of thalidomide being prescribed as a mixture of the two optically active forms to their pregnant mothers.
Ethambutol, tuberculosis and blindness
The right handed version of ethambutol, known as d-ethambutol, can be used to treat you if you contract tuberculosis. If you are unfortunate enough to take the left-handed l-ethambutol, it would make you to go blind.
Naproxen, arthritis pain and liver poisoning
Naproxen is a nonsteroidal anti-inflammatory drug (NSAID) similar to ibuprofen. The form shown on the left below is used to treat arthritis pain, fever and swelling.
Its mirror image, shown on the right, causes liver poisoning.
Biot’s discovery 200 years ago may yet be proven to lie at the heart of the mystery of life on Earth. Even if it does not, it has certainly changed lives.
Author of this page: The Doc
Images of scientists digitally enhanced and colorized by this website.
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