Circular dichroism of the alkyl amino acids in the vacuum ultraviolet

The circular dichroism and absorption for five alkyl amino acids as zwitterions has now been measured to 160 nm. Two bands are found, the nπ* at long wavelengths and ππ* at short wavelengths. In an effort to extract conformal information from the circular dichroism measurmenths, the circular dichroism spectra for these molecules is calculated using an independent systems apporach. It is found that the signs calculated using these methods are quite reliable, but that reliable magnitudes must await more accurate data to use in the calculations. Comparing the signs for both the measured and calculated circular dichriosm it if possible to determine the region inhabited by the carboxylate anion chromophore of these amino acid zwitterions. The greatest failure of the calculations is that thay are unable to explain the sigmoidal shape of the nπ* transition in proline. The problems facing workers trying to make calculations to relate circular dichroism measurements to conformation are discussed.