期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2003
卷号：100
期号：10
页码：5601-5606
DOI：10.1073/pnas.0931292100
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The structure fluctuations of the peptide bond interacting with solvent are examined through the coupling and correlations of the frequency distributions of amide I and amide II transitions. The fluctuations of the two modes are anticorrelated as a result of the solvent-induced changes in the mixing of the dominant valence-bond structures of the peptide. Significant anharmonic coupling of the two modes is seen. The results are the application of a new approach to two-dimensional infrared (2D-IR) spectroscopy in which the pulse sequences used to produce the vibrational echoes incorporate two frequencies. This dual-frequency arrangement greatly extends the capabilities of 2D-IR spectroscopy by allowing the coupling between widely separated modes to be characterized in analogy with heteronuclear NMR. The experiment exposes the cross peaks, representing the mode coupling, free of the interference of the strong diagonal peaks that typically dominate 2D-IR spectroscopy. The alignment and dephasing of coupled transitions, in this example the amide I and amide II transition dipoles, is also determined by these experiments.
