A time-resolved spectroscopic comparison of the photoisomerization of small beta-turn-forming thioxopeptides.
The monosubstituted thioxopeptide Boc-Ala-Pro-psi(SCNH)-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 -SCNH-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.
Bregy
H
H
Physikalisch-Chemisches Institut and Organisch-Chemisches Institut, Universitat Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Heimgartner
H
H
Helbing
J
J
D006860:Hydrogen Bonding; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D009842:Oligopeptides / Q000737:chemistry*; D055668:Photochemical Processes; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013997:Time Factors
D009842:Oligopeptides; D013438:Sulfhydryl Compounds