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Modern Spectroscopy Lab

Circular Dichroism Spectroscopy

Circular dichroism spectroscopy (CD) is a technique that measures the differential absorption of left handed and right handed circular polarized light.  CD can be measured in the ultraviolet (UV), visible (Vis), near infrared (NIR) and infrared (IR) regions of the electromagnetic spectrum.  Left and right-hand circular polarized light represent two possible spin angular momentum states for a photon, so circular dichroism may be thought of as a measure of the difference in two states of spin angular momentum. Because CD is a manifestation of optical activity it is evident in the absorption bands of optically active molecules.  Such molecules are those that have the ability to rotate the plane of plane-polarized light; and only chiral structures have this ability.  (A chiral molecule is one whose mirror image cannot be superimpose on itself.)  


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.  Information related to alpha helix and parallel/antiparallel beta sheet content is readily obtained, as is information related to turns in abnormally folded proteins.  UV and Vis CD is used to investigate charge-transfer transitions. NIR CD has been used to investigate geometric and electronic structure by probing atomic orbital transitions in metals.  However, recently both NIR and IR CD have been found useful in the study of both protein and nucleic acid secondary structure.  Abnormally folded proteins, such as the amyloids are increasingly being studied in these longer wavelengths.


We have one of two modern CD spectrometers in Utah, and we have found it to be particularly helpful in the characterization of the effects of our novel compounds on Aβ oligomer size, secondary structure, turns and other information.  We employ vibrational (NIR and IR) regions of the electromagnetic spectrum, in addition to the UV frequency domain, to maximize the yield of information obtainable using this valuable spectroscopic tool.  Using an expanded array of sample handling accessories we are able to study sample volumes as low as 10 microliters, in a temperature controlled environment.

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