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UV Resonance Raman Investigation of the Conformations and Lowest Energy Allowed Electronic Excited States of Tri-and Tetraalanine: Charge Transfer Transitions
 

Summary: UV Resonance Raman Investigation of the Conformations and Lowest Energy Allowed
Electronic Excited States of Tri- and Tetraalanine: Charge Transfer Transitions
Bhavya Sharma and Sanford A. Asher*
Department of Chemistry, UniVersity of Pittsburgh, 219 Parkman AVenue, Pittsburgh, PennsylVania 15260
ReceiVed: January 15, 2010; ReVised Manuscript ReceiVed: March 16, 2010
UV resonance Raman excitation profiles and Raman depolarization ratios were measured for trialanine and
tetraalanine between 198 and 210 nm. Excitation within the f * 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 2.51 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 * orbital. Raman depolarization ratio measurements support this
assignment. An additional electronic transition is found in Ala4 at 206 nm.
Introduction
UV resonance Raman (UVRR) spectroscopy is recognized
as a powerful technique for probing peptide and protein
secondary structure.1-14

  

Source: Asher, Sanford A. - Department of Chemistry, University of Pittsburgh

 

Collections: Materials Science; Chemistry