%0 Journal Article
%@ 1520-6106
%A Sharma, B
%A Asher, SA
%D 2010
%F pittir:17247
%J Journal of Physical Chemistry B
%N 19
%P 6661 - 6668
%T UV resonance Raman investigation of the conformations and lowest energy allowed electronic excited states of tri- and tetraalanine: Charge transfer transitions
%U http://d-scholarship-dev.library.pitt.edu/17247/
%V 114
%X UV resonance Raman excitation profiles and Raman depolarization ratios were measured for trialanine and tetraalanine between 198 and 210 nm. Excitation within the π → π* electronic transitions of the peptide bond results in UVRR spectra dominated by amide peptide bond vibrations. In addition to the resonance enhancement of the normal amide vibrations, we find enhancement of the symmetric terminal COO- vibration. The Ala3 UVRR AmIII3 band frequencies indicate that poly-proline II and 2.5 1 helix conformations and type II turns are present in solution. We also find that the conformation of the interior peptide bond of Ala4 is predominantly poly-proline-II-like. The Raman excitation profiles of both Ala3 and Ala4 reveal a charge transfer electronic transition at 202 nm, where electron transfer occurs from the terminal nonbonding carboxylate orbital to the adjacent peptide bond π* orbital. Raman depolarization ratio measurements support this assignment. An additional electronic transition is found in Ala4 at 206 nm. © 2010 American Chemical Society.