Zusammenfassung
The intermol. interactions and dynamics of aq. 1,1-dimethyurea (1,1-DMU) solns. were studied by examg. the concn. dependence of the solvent and solute relaxations detected by dielec. spectroscopy. Mol. dynamics simulations were carried out to facilitate interpretation of the dielec. data and to get a deeper insight into the behavior of the system components at the microscopic level. In ...
Zusammenfassung
The intermol. interactions and dynamics of aq. 1,1-dimethyurea (1,1-DMU) solns. were studied by examg. the concn. dependence of the solvent and solute relaxations detected by dielec. spectroscopy. Mol. dynamics simulations were carried out to facilitate interpretation of the dielec. data and to get a deeper insight into the behavior of the system components at the microscopic level. In particular, the simulations allowed for explaining the main differences between the dielec. spectra of aq. solns. of 1,1-DMU and of its structural isomer 1,3-DMU. Similar to the previously studied compds. urea and 1,3-DMU, 1,1-DMU forms rather stable hydrates. This is evidenced by an effective solute dipole moment that significantly exceeds the value of a neat 1,1-DMU mol., indicating pronounced parallel alignment of the solute dipole with two to three H2O moments. The MD simulations revealed that the involved water mols. form strong hydrogen bonds with the carbonyl group. However, in contrast to 1,3-DMU, it was not possible to resolve a "slow-water" mode in the dielec. spectra, suggesting rather different hydration-shell dynamics for 1,1-DMU as confirmed by the simulations. In contrast to aq. urea and 1,3-DMU, addn. of 1,1-DMU to water leads to a weak decrease of the static permittivity. This is explained by the emergence of antiparallel dipole-dipole correlations among 1,1-DMU hydrates with rising concn.
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