Three Types of Induced Tryptophan Optical Activity Compared in Model Dipeptides: Theory and Experiment

0383282 - ÚOCHB 2013 RIV DE eng J - Journal Article
Hudecová, Jana - Horníček, Jan - Buděšínský, Miloš - Šebestík, Jaroslav - Šafařík, Martin - Zhang, G. - Keiderling, T. A. - Bouř, Petr
Three Types of Induced Tryptophan Optical Activity Compared in Model Dipeptides: Theory and Experiment.
ChemPhysChem. Roč. 13, č. 11 (2012), s. 2748-2760. ISSN 1439-4235. E-ISSN 1439-7641
R&D Projects: GA ČR GAP208/11/0105; GA MŠMT(CZ) LH11033
Grant - others:GA UK(CZ) 126310
Institutional research plan: CEZ:AV0Z40550506
Keywords : circular dichroism * conformation analysis * density functional calculations * Raman spectroscopy * peptides
Subject RIV: CF - Physical ; Theoretical Chemistry
Impact factor: 3.349, year: 2012

The tryptophan (Trp) aromatic residue in chiral matrices often exhibits a large optical activity and thus provides valuable structural information. However, it can also obscure spectral contributions from other peptide parts. To better understand the induced chirality, electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and Raman optical activity (ROA) spectra of Trp-containing cyclic dipeptides c-(Trp-X) (where X=Gly, Ala, Trp, Leu, nLeu, and Pro) are analyzed on the basis of experimental spectra and density functional theory (DFT) computations. The results provide valuable insight into the molecular conformational and spectroscopic behavior of Trp. Whereas the ECD is dominated by Trp pi-pi transitions, VCD is dominated by the amide modes, well separated from minor Trp contributions. The ROA signal is the most complex. However, an ROA marker band at 1554 cm-1 indicates the local chi2 angle value in this residue, in accordance with previous theoretical predictions. The spectra and computations also indicate that the peptide ring is nonplanar, with a shallow potential so that the nonplanarity is primarily induced by the side chains. Dispersion-corrected DFT calculations provide better results than plain DFT, but comparison with experiment suggests that they overestimate the stability of the folded conformers. Molecular dynamics simulations and NMR results also confirm a limited accuracy of the dispersion-DFT model in nonaqueous solvents. Combination of chiral spectroscopies with theoretical analysis thus significantly enhances the information that can be obtained from the induced chirality of the Trp aromatic residue.
Permanent Link: http://hdl.handle.net/11104/0213270