Proline Zwitterion Dynamics in Solution, Glass, and Crystalline State
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- 作者：Josef Kapitá ; n ; Vladimí ; r Baumruk ; Vladimí ; r Kopeck
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- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：October 18, 2006
- 年：2006
- 卷：128
- 期：41
- 页码：13451 - 13462
- 全文大小：807K
- 年卷期：v.128,no.41(October 18, 2006)
- ISSN：1520-5126
文摘
Raman and Raman optical activity spectra of L- and D-proline zwitterionic (PROZW) forms wererecorded for H2O and D2O solutions in a wide frequency range and analyzed with respect to the motion ofthe proline ring and rotation of the carbonyl group. The solution spectra were additionally compared toRaman scattering of glass and crystalline powder proline. Solution and glass spectral band broadeningsare similar and reveal information about the extent of internal molecular motion. Two distinct but equallypopulated flexible forms were found in the glass and the solution. The equal population is consistent withNMR data, temperature, and concentration dependencies. The molecular flexibility is reduced significantlyin the crystal, however, where only one conformer is present. Consequently, the crystal bands are narrowand exhibit minor frequency shifts. The spectra were interpreted with the aid of density functional theorycomputations involving both continuum and explicit solvent. A two-dimensional potential energy surfacepertaining to the five-member ring puckering coordinates was constructed and used for dynamical averagingof spectral properties. Comparison of the computed and experimental bandwidths suggests that thepuckering is strongly correlated with the carbonyl rotation. An averaging over these two motions producessimilar results. The interpretation of the Raman experiments with the aid of the simulation techniques alsoindicates that the environment modulates properties of the hydrophobic part of the molecule indirectly byinteracting with the ionic group. Such behavior may be important for the reactivity and biological activity ofproline-containing peptides and proteins.