Journal of Physical Chemistry A, Vol.114, No.44, 11928-11932, 2010
Chiroptical Study of alpha-Aliphatic Amino Acid Films in the Vacuum Ultraviolet Region
A series of mutual circular dichroism (CD) and absorption spectra for films of alpha-aliphatic amino acids such as alanine, aminobutyric acid, norvaline, norleucine, valine, leucine. and isoleucine-in the Vaccum ultraviolet (VUV) region were observed with the-absolute values of optical constants at the undulator-based CD beamline TERAS BL5 Preliminary predictions or some CD spectra were also performed, based on quantum-chemical calculations using the crystal structure. Although the absorption spectra show similar features to each other, significant differences between the CD spectra wet e found, especially in the 7-8 eV region. The CD spectra of aliphatic amino acids with branched alkyl groups in the side-chain such as valine, leucme, and isoleueme-exhibit strong negative CD peaks in this energy region In contrast. the corresponding CD peaks were weak oi absent in the spectra or amino acids with straight alkyl groups Our simple calculation, and the absorption spectra of alkalies. suggest that this difference: partly originates from the contribution of the alkyl group Clear discrepancies between the CD spectra of these amino acids in solutions and those in the solid state were also observed this is caused by the different molecular structures in each state Our results clearly indicated that CD spectra in the VUV region were very sensitive to the conformations of chiral molecules