title: Proline zwitterion dynamics in solution, glass, and crystalline state.
abstract: Raman and Raman optical activity spectra of L- and D-proline zwitterionic (PROZW) forms were recorded for H(2)O and D(2)O solutions in a wide frequency range and analyzed with respect to the motion of the proline ring and rotation of the carbonyl group. The solution spectra were additionally compared to Raman scattering of glass and crystalline powder proline. Solution and glass spectral band broadenings are similar and reveal information about the extent of internal molecular motion. Two distinct but equally populated flexible forms were found in the glass and the solution. The equal population is consistent with NMR data, temperature, and concentration dependencies. The molecular flexibility is reduced significantly in the crystal, however, where only one conformer is present. Consequently, the crystal bands are narrow and exhibit minor frequency shifts. The spectra were interpreted with the aid of density functional theory computations involving both continuum and explicit solvent. A two-dimensional potential energy surface pertaining to the five-member ring puckering coordinates was constructed and used for dynamical averaging of spectral properties. Comparison of the computed and experimental bandwidths suggests that the puckering is strongly correlated with the carbonyl rotation. An averaging over these two motions produces similar results. The interpretation of the Raman experiments with the aid of the simulation techniques also indicates that the environment modulates properties of the hydrophobic part of the molecule indirectly by interacting with the ionic group. Such behavior may be important for the reactivity and biological activity of proline-containing peptides and proteins.
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences, Flemingovo nam. 2, 16610, Prague 6, Czech Republic.
authors.forename: Josef
authors.initials: J
authors.lastname: Kapitán
authors.forename: Vladimír
authors.initials: V
authors.lastname: Baumruk
authors.forename: Vladimír
authors.initials: V
authors.lastname: Kopecký
authors.forename: Radek
authors.initials: R
authors.lastname: Pohl
authors.forename: Petr
authors.initials: P
authors.lastname: Bour
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D003460:Crystallization; D003903:Deuterium / Q000737:chemistry; D005898:Glass / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry; D011392:Proline / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D013499:Surface Properties; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D007477:Ions; D010455:Peptides; D011506:Proteins; D012996:Solutions; D012997:Solvents; D014867:Water; D011392:Proline; D003903:Deuterium