Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9588682 | Journal of Molecular Liquids | 2005 | 6 Pages |
Abstract
The complex dielectric permittivity spectra, É*(ν), of aqueous glycine solutions at 25 °C were determined in the frequency range of 0.1â¤Î½/GHzâ¤89 using TDR and wave-guide interferometry. The concentration range covered amino acid mole fractions of 0â¤Xâ¤0.05, corresponding to molar concentrations of 0â¤c/Mâ¤2.6. For all samples, a superposition of three Debye relaxation processes was required for a consistent description of É*(ν). The low-frequency dispersion (j=1) of relaxation time Ï1â¼40 ps, assigned to the rotational diffusion of the zwitterionic amino acid molecule, exhibits a linearly increasing amplitude, ÎÉ1(c) from which an effective dipole moment of μeff=11.9 D was deduced for the glycine zwitterion. This value agrees well with the result (11.4 D) of MOPAC calculations for the isolated molecule using the semiempirical AM1 force field, indicating that dipole-dipole correlations among glycine molecules are negligible even in concentrated solutions where direct contacts of the hydrated solute molecules are likely. This is corroborated by the analysis of the glycine relaxation times. The intermediate (j=2; Ï2â¼8-9 ps) and the fast (j=3; Ï3â¼1-2 ps) dispersions originate from the contribution of water, assigned to the cooperative dynamics of bulk water and a fast localized motion of “free water” molecules, respectively. From the solvent amplitude an effective hydration number of Zib(0)=4.2 was determined for glycine at infinite dilution.
Related Topics
Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
Takaaki Sato, Richard Buchner, Å arka Fernandez, Akio Chiba, Werner Kunz,