Dependence of Glycine CH2 Stretching Frequencies on Conformation, Ionization State, and Hydrogen Bonding

摘要: We experimentally and theoretically examined the conformation, pH, temperature dependence of CH2 stretching frequencies glycine (gly) in solution crystalline state. To separate effects amine carboxyl groups on we Raman spectra 2,2,2-d3-ethylamine (CD3-CH2-NH2) 3,3,3-d3-propionic acid (CD3-CH2-COOH) D2O. The symmetric (nusCH2) asymmetric (nuasCH2) show a significant gly conformation. quantified relation between frequency splitting (Delta = nuasCH2-nusCH2) xi angle which determines conformational geometry. This allows us to determine conformation directly from spectral frequencies. observe large nusCH2 nuasCH2 ionization state group, demonstrate results negative hyperconjugation nitrogen lone pair C-H antibonding orbitals. magnitude this effect is maximized for bonds trans pair. In contrast, small group arises delocalization electron density oxygen bonding According our experimental observations theoretical calculations due change hydrogen-bonding strength amine/carboxyl water.