The Cotton effect in physics, is the characteristic change in optical rotatory dispersion and/or circular dichroism in the vicinity of an absorption band of a substance.
This phenomenon was discovered in 1895 by the French physicist Aimé Cotton (1869–1951).
The Cotton effect is called positive if the optical rotation first increases as the wavelength decreases (as first observed by Cotton), and negative if the rotation first decreases.
[1] A protein structure such as a beta sheet shows a negative Cotton effect.
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