title: Hydration and self-aggregation of a neutral cosolute from dielectric relaxation spectroscopy and MD simulations: the case of 1,3-dimethylurea.
abstract: The influence of the amphiphile 1,3-dimethylurea (1,3-DMU) on the dynamic properties of water was studied using dielectric relaxation spectroscopy. The experiment provided evidence for substantial retardation of water reorientation in the hydration shell of 1,3-DMU, leading to a separate slow-water relaxation in addition to contributions from bulk-like and fast water as well as from the solute. From the amplitudes of the resolved water modes effective hydration numbers were calculated, showing that each 1,3-DMU molecule effectively freezes the reorientation of 1-2 water molecules. Additionally, a significant amount of solvent molecules, decreasing from ∼39 at infinite dilution to ∼3 close to the solubility limit, is retarded by a factor of ∼1.4 to 2.3, depending on concentration. The marked increase of the solute amplitude indicates pronounced parallel dipole alignment between 1,3-DMU and its strongly bound H2O molecules. Molecular dynamics (MD) simulations of selected solutions revealed a notable slowdown of water rotation for those solvent molecules surrounding the methyl groups of 1,3-DMU and strong binding of ∼2H2O by the hydrophilic carbonyl group, corroborating thus the experimental results. Additionally, the simulations revealed 1,3-DMU self-aggregates of substantial lifetime.
authors.affiliation: Department of Physical Chemistry, Kazan Federal University, 420008 Kazan, Russia and Department of Inorganic Chemistry, Chemical Faculty, V. N. Karazin Kharkiv National University, 4 Svobody sq., 61022 Kharkiv, Ukraine.
authors.forename: Vira
authors.identifier: http://orcid.org/0000-0002-9398-1666
authors.initials: V
authors.lastname: Agieienko
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Regensburg, D-93040 Regensburg, Germany. Dominik.Horinek@ur.de Richard.Buchner@ur.de.
authors.forename: Dominik
authors.initials: D
authors.lastname: Horinek
authors.affiliation: Institut für Physikalische und Theoretische Chemie, Universität Regensburg, D-93040 Regensburg, Germany. Dominik.Horinek@ur.de Richard.Buchner@ur.de.
authors.forename: Richard
authors.identifier: http://orcid.org/0000-0003-3029-1278
authors.initials: R
authors.lastname: Buchner