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UV resonance raman investigation of electronic transitions in α-helical and polyproline II-like conformations

Sharma, B and Bykov, SV and Asher, SA (2008) UV resonance raman investigation of electronic transitions in α-helical and polyproline II-like conformations. Journal of Physical Chemistry B, 112 (37). 11762 - 11769. ISSN 1520-6106

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UV resonance Raman (UVRR) excitation profiles and Raman depolarization ratios were measured for a 21-residue predominantly alanine peptide, AAAAA(AAARA)3A (AP), excited between 194 and 218 nm. Excitation within the π→π* electronic transitions of the amide group results in UVRR spectra dominated by amide vibrations. The Raman cross sections and excitation profiles provide information about the nature of the electronic transitions of the α-helix and polyproline II (PPII)-like peptide conformations. AP is known to be predominantly a-helical at low temperatures and to take on a PPII helix-like conformation at high temperatures. The PPII-like and a-helix conformations show distinctly different Raman excitation profiles. The PPII-like conformation cross sections are approximately twice those of the a-helix. This is due to hypochromism that results from excitonic interactions between the NV1 transition of one amide group with higher energy electronic transitions of other amide groups, which decreases the α-helical NV1 (π→π*) oscillator strengths. Excitation profiles of the α-helix and PPII-like conformations indicate that the highest signal-to-noise Raman spectra of a-helix and PPII-like conformations are obtained at excitation wavelengths of 194 and 198 nm, respectively. We also see evidence of at least two electronic transitions underlying the Raman excitation profiles of both the a-helical and the PPII-like conformations. In addition to the well-known ∼190 nm π→π* transitions, the Raman excitation profiles and Raman depolarization ratio measurements show features between 205-207 nm, which in the a-helix likely results from the parallel excitonic component. The PPII-like helix appears to also undergo excitonic splitting of its π→π* transition which leads to a 207 nm feature. © 2008 American Chemical Society.


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Item Type: Article
Status: Published
CreatorsEmailPitt UsernameORCID
Sharma, B
Bykov, SV
Asher, SAasher@pitt.eduASHER
Date: 18 September 2008
Date Type: Publication
Journal or Publication Title: Journal of Physical Chemistry B
Volume: 112
Number: 37
Page Range: 11762 - 11769
DOI or Unique Handle: 10.1021/jp801110q
Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
Refereed: Yes
ISSN: 1520-6106
MeSH Headings: Electrons; Peptide Fragments--chemistry; Peptides--chemistry; Protein Structure, Secondary; Spectrophotometry, Ultraviolet; Spectrum Analysis, Raman; Temperature
Other ID: NLM NIHMS239056, NLM PMC2958432
PubMed Central ID: PMC2958432
PubMed ID: 18712913
Date Deposited: 08 Feb 2013 21:05
Last Modified: 22 Jun 2021 12:56


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