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Preresonance Raman single-crystal measurements of electronic transition moment orientations in N-acetylglycinamide

Pajcini, V and Asher, SA (1999) Preresonance Raman single-crystal measurements of electronic transition moment orientations in N-acetylglycinamide. Journal of the American Chemical Society, 121 (47). 10942 - 10954. ISSN 0002-7863

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We have examined electronic coupling between the two amide electronic transitions in a dipeptide and have found strong excitonic interactions in a case where the amide planes are almost perpendicular. We compared the absorption and resonance Raman spectra of N-methylacetamide (NMA) and acetamide (AM) to that of the dipeptide N-acetylglycinamide (NAGA), which is composed of linked primary and secondary amides. We measured the transition moment magnitudes of each of these species and also determined the orientation of the preresonance Raman tensor of NAGA in a single crystal. From these single-crystal tensor values, we calculated the NAGA diagonal Raman tensor orientations and compared them to those expected for unperturbed primary and secondary amides oriented as in the NAGA crystal. Because the primary and secondary amide III vibrations are vibrationally uncoupled and nonoverlapping, we can use their intensities to determine the contributions to their resonance enhancement from the coupled NAGA electronic transitions. The Raman tensor major axes of the primary and secondary amide III and amide I vibrations do not lie in their corresponding amide planes, indicating excitonically coupled states which mix the primary and secondary amide transitions. These results are relevant to the understanding of amide coupling in peptides and proteins; the NAGA crystal conformation is similar to that of a type 1 β-turn in peptides and proteins, with the amide planes nearly perpendicular to each other (dihedral angle 85°).


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Item Type: Article
Status: Published
CreatorsEmailPitt UsernameORCID
Pajcini, V
Asher, SAasher@pitt.eduASHER
Date: 1 December 1999
Date Type: Publication
Journal or Publication Title: Journal of the American Chemical Society
Volume: 121
Number: 47
Page Range: 10942 - 10954
DOI or Unique Handle: 10.1021/ja990429u
Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
Refereed: Yes
ISSN: 0002-7863
Date Deposited: 20 Mar 2013 16:41
Last Modified: 02 Feb 2019 16:55


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