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A Time-resolved Spectroscopic Comparison of the Photoisomerization of Small beta-Turn-forming Thioxopeptides


Bregy, H; Heimgartner, H; Helbing, J (2009). A Time-resolved Spectroscopic Comparison of the Photoisomerization of Small beta-Turn-forming Thioxopeptides. Journal of Physical Chemistry. B, 113(6):1756-1762.

Abstract

The monosubstituted thioxopeptide Boe-Ala-Pro-psi(SC-NH)-Aib-Ala-OMe is investigated by time-resolved UV-pump/IR-probe and IR-pump/IR-probe spectroscopy, steady-state FTIR-spectroscopy, and NMR-techniques. The compound has a high propensity to adopt a i --> i + 3 hydrogen-bonded conformation. Time-resolved infrared measurements reveal the opening of this beta-turn structure upon trans --> cis photo isomerization of the thioamide bond. Comparison is made with three protected tripeptides containing the -SC-NH-Aib- moiety with different thio-substituted residues. Very similar photo isomerization dynamics and comparable quantum efficiencies are found. Differences are seen for the thermally activated cis --> trans relaxation in the electronic ground state, where thioxopeptides with larger residues next to the thioamide moiety exhibit subsecond isomerization times. Anisotropy measurements indicate a very rigid Aib-containing core structure for all four thioxopeptides in acetonitrile solution.

Abstract

The monosubstituted thioxopeptide Boe-Ala-Pro-psi(SC-NH)-Aib-Ala-OMe is investigated by time-resolved UV-pump/IR-probe and IR-pump/IR-probe spectroscopy, steady-state FTIR-spectroscopy, and NMR-techniques. The compound has a high propensity to adopt a i --> i + 3 hydrogen-bonded conformation. Time-resolved infrared measurements reveal the opening of this beta-turn structure upon trans --> cis photo isomerization of the thioamide bond. Comparison is made with three protected tripeptides containing the -SC-NH-Aib- moiety with different thio-substituted residues. Very similar photo isomerization dynamics and comparable quantum efficiencies are found. Differences are seen for the thermally activated cis --> trans relaxation in the electronic ground state, where thioxopeptides with larger residues next to the thioamide moiety exhibit subsecond isomerization times. Anisotropy measurements indicate a very rigid Aib-containing core structure for all four thioxopeptides in acetonitrile solution.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Date:12 February 2009
Deposited On:24 Jun 2009 13:36
Last Modified:05 Apr 2016 13:16
Publisher:American Chemical Society
ISSN:1520-5207
Funders:Swiss National Science Foundation (SNF)
Publisher DOI:https://doi.org/10.1021/jp8089402

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