Two-Dimensional Infrared Investigation of N-Acetyl Tryptophan Methyl Amide in Solution

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• 作者：Sayan Bagchi ; Yung Sam Kim ; Adam K. Charnley ; Amos B. Smith ; III ; Robin M. Hochstrasser
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：March 22, 2007
• 年：2007
• 卷：111
• 期：11
• 页码：3010 - 3018
• 全文大小：532K
• 年卷期：v.111,no.11(March 22, 2007)
• ISSN：1520-5207

文摘

The linear infrared and two-dimensional infrared (2D IR) spectra in the amide-I region of N-acetyl tryptophanmethyl amide (NATMA) in solvents of varying polarity are reported. The two amide-I transitions have beenassigned unambiguously by using ¹³C isotopic substitution of the carbonyl group. The amide unit at theamino end shows a lower transition frequency in CH₂Cl₂ and methanol, while the acetyl end has a lowertransition frequency in D₂O. Multiple conformers exist in CH₂Cl₂ and methanol, but only one conformer isevident in D₂O. The 2D IR cross peaks from the intermode coupling yield off-diagonal anharmonicities 2.5± 0.5, 3.25 ± 0.5, and 3.0 ± 0.5 cm^-1 in CH₂Cl₂, methanol, and D₂O, respectively, which by simple matrixdiagonalization yield the coupling constants 8.0 ± 0.5, 8.0 ± 1.0, and 5.5 ± 1.0 cm^-1. The major conformerin CH₂Cl₂ corresponds to a C₇ structure, in agreement with that found in the gas phase [Dian, B. C.; Longarte,A.; Mercier, S.; Evans, D. A.; Wales, D. J.; Zwier, T. S. J. Chem. Phys. 2002, 117, 10688-10702] withintramolecular hydrogen bonding between the acetyl end C=O and the amino end N-H. The backbone dihedralangles (, ) are determined to be in the ranges of (-55 ± 5, 30 ± 5), (120 ± 10, -20 ± 10), and(±160 ± 10, ±75 ± 10) in CH₂Cl₂, methanol, and D₂O, respectively.