Circular dichroism From Wikipedia, the free encyclopedia Circular dichroism (CD) refers to the differential absorption of left and right circularly polarized light . [1] [2] This phenomenon was discovered by Jean- Baptiste Biot , Augustin Fresnel , and Aimé Cotton in the first half of the 19th century. [3] It is exhibited in the absorption bands of optically active chiral molecules. CD spectroscopy has a wide range of applications in many different fields. Most notably, UV CD is used to investigate the secondary structure of proteins. [4] UV/Vis CD is used to investigate charge-transfer transitions . [5] Near-infrared CD is used to investigate geometric and electronic structure by probing metal d →d transitions. [2] Vibrational circular dichroism , which uses light from the infrared energy region, is used for structural studies of small organic molecules, and most recently proteins and DNA. [4] Contents [hide ] 1 Physical principles o 1.1 Circular polarization of light o 1.2 Interaction of circularly polarized light with matter 1.2.1 Delta absorbance 1.2.2 Molar circular dichroism 1.2.3 Extrinsic effects on circular dichroism 1.2.4 Molar ellipticity 1.2.5 Mean residue ellipticity 2 Application to biological molecules 3 Experimental limitations 4 See also 5 References 6 External links [edit ]Physical principles
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Circular dichroismFrom Wikipedia, the free encyclopedia
Circular dichroism (CD) refers to the differential absorption of left and right circularly polarized light.[1]
[2] This phenomenon was discovered by Jean-Baptiste Biot, Augustin Fresnel , and Aimé Cotton in the first
half of the 19th century.[3] It is exhibited in the absorption bands of optically active chiral molecules.
CD spectroscopy has a wide range of applications in many different fields. Most notably, UVCD is used to
investigate the secondary structure of proteins.[4] UV/Vis CD is used to investigate charge-transfer
transitions.[5] Near-infrared CD is used to investigate geometric and electronic structureby
probing metal d→d transitions.[2] Vibrational circular dichroism , which uses light from the infrared energy
region, is used for structural studies of small organic molecules, and most recently proteins and DNA. [4]
Contents
[hide]
1 Physical principles
o 1.1 Circular polarization of light
o 1.2 Interaction of circularly polarized light with matter
1.2.1 Delta absorbance
1.2.2 Molar circular dichroism
1.2.3 Extrinsic effects on circular dichroism
1.2.4 Molar ellipticity
1.2.5 Mean residue ellipticity
2 Application to biological molecules
3 Experimental limitations
4 See also
5 References
6 External links
[edit]Physical principles
[edit]Circular polarization of light
Main article: Circular polarization
Electromagnetic radiation consists of an electric and magnetic field that oscillate perpendicular to one
another and to the propagating direction. [6] While linearly polarized light occurs when the electric field
vector oscillates only in one plane and changes in magnitude, circularly polarized light occurs when the
electric field vector rotates about its propagation direction and retains constant magnitude. For left
circularly polarized light (LCP) with propagation towards the observer, the electric vector rotates
counterclockwise.[2] For right circularly polarized light (RCP), the electric vector rotates clockwise.
[edit]Interaction of circularly polarized light with matter
When circularly polarized light passes through an absorbing optically active medium, the speeds between
right and left polarizations differ (cL ≠ cR) as well as their wavelength (λL ≠ λR) and the extent to which
they are absorbed (εL≠εR). Circular dichroism is the difference Δε ≡ εL- εR.[4] The electric field of a light
beam causes a linear displacement of charge when interacting with a molecule (electric dipole), whereas
the magnetic field of it causes a circulation of charge (magnetic dipole). These two motions combined
cause an excitation of an electron in a helical motion, which includes translationand rotation and their
associated operators. The experimentally determined relationship between the rotational strength (R) of a