{{Short description|Atomic, molecular, and optical physics}} 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. In a wavelength region where the light is absorbed, the absolute magnitude of the optical rotation at first varies rapidly with wavelength, crosses zero at absorption maxima and then again varies rapidly with wavelength but in the opposite direction. 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.<ref>{{cite book |author-link1=Ernest L. Eliel |first1=Ernest L. |last1=Eliel |first2=Samuel H. |last2=Wilen |first3=Lewis N. |last3=Mander|title=Stereochemistry of Organic Compounds |publisher=Wiley |date=1994 |page=1000 |isbn=0-471-01670-5 |url={{GBurl|OAUPEAAAQBAJ|pg=PR5}}}}</ref> A protein structure such as a beta sheet shows a negative Cotton effect.<ref>{{cite journal |last1=Iizuka |first1=E. |last2=Yang |first2=J. T. |year=1966 |title=Optical rotatory dispersion and circular dichroism of the beta-form of silk fibroin in solution |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=55 |issue=5 |pages=1175–1182 |doi=10.1073/pnas.55.5.1175 |pmid=5225514 |pmc=224296 |bibcode=1966PNAS...55.1175I |doi-access=free }}</ref>
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Category:Polarization (waves) Category:Atomic, molecular, and optical physics
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