Can Raman optical activity separate axial from local chirality? A theoretical study of helical deca-alanine.
Motivated by experimental work on the distinction of protein secondary structure motifs by Raman optical activity (ROA) spectroscopy, we demonstrate using density functional theory that axial chirality in structures with different local chirality can be filtered out by ROA spectroscopy. To this purpose, two diastereomers of right-handed helical deca-alanine, the (all-S) and the (R,S,R,S,R,S,R,S,R,S) form, are compared. Furthermore, we suggest to interpret calculated ROA spectra of large molecules in terms of vibrational bands rather than individual peaks. This is due to the non-homogeneous effect of the harmonic approximation as well as of the chosen electronic structure method onto the vibrational frequencies, which in a dense region of many vibrations will strongly determine the shape of the spectrum. In addition, the calculated ROA spectrum of (all-S)-deca-alanine is compared to the experimental spectrum of poly-(L)-alanine in solution.
Herrmann
Carmen
C
Laboratorium für Physikalische Chemie, ETH Zürich Hönggerberg Campus, Wolfgang-Pauli-Str. 10, 8093 Zürich, Switzerland.
Ruud
Kenneth
K
Reiher
Markus
M
D000409:Alanine / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013237:Stereoisomerism; D014732:Vibration
D009842:Oligopeptides; D010455:Peptides; C019529:polyalanine; D000409:Alanine