BCHM 313 Chapter Notes - Chapter 2: Circular Polarization, Circular Dichroism, Peptide
20 Apr 2016
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Chiral molecules may respond differently to left- or right-circularly polarized light. In particular there may be slight differences in absorbance of uv/visible light. Circular dichroism is measured as the difference in absorbance between left and right circularly polarized light: Where al and ar refer to the absorbance of the sample at a particular wavelength for left- or right- circularly polarized light. This can be expressed in terms of differences in molar extinction coefficients, which for historical reasons is often converted to ellipticity, . Proteins are made up of amino acids which are (with the exception of glycine) intrinsically chiral. In addition, secondary structure elements such as a-helix and b-sheet impose additional chirality on the polypeptide chain. This gives rise to cd effects in the far uv(190 240nm) arising mainly from the peptide backbone groups which are characteristic of the overall secondary structure of the protein.
