Circular dichroism of amino acid films in UV-VUV region.

Circular dichroism (CD) spectra of sublimated films of alanine and alanine dipeptide were measured in UV-VUV region. When a film has some linear anisotropy, the apparent CD signal is known to be strongly distributed by linear anisotropy. In order to obtain the true CD spectra, we examined this disturbance for L-alanine films. We measured linear dichroism spectra and CD spectra as a function of the sample rotation angle, turning the sample over. On the basis of these measurements, we concluded that the linear anisotropy contribution to CD was sufficiently small for carefully prepared films. In addition, we revealed that it is essential for accurate measurement to prepare thin film of which thickness is smaller than 100 nm for the case of alanine films. CD of amino acid films was compared with that of aqueous solution. Sign of CD signal of solid films was observed to be the same for aspartic acid, but it was reversed from that of aqueous solution for alanine and alanine dipeptide.