Urea's match in the hydrogen-bond network? A high pressure THz study.

Authors :: Vondracek H
Alfarano S
Hoberg C
Kolling I
Novelli F
Sebastiani F
Brubach JB
Roy P
Schwaab G
Havenith M
Source :: Biophysical chemistry [Biophys Chem] 2019 Nov; Vol. 254, pp. 106240. Date of Electronic Publication: 2019 Aug 06.
Publication Year :: 2019
Abstract: We present results of the measurement of the low frequency spectrum of solvated urea. The study revealed a blue shift of the intramolecular mode of urea centered at 150 cm <superscript>-1</superscript> of Δν= 17 cm <superscript>-1</superscript> upon increasing the pressure up to 10 kbar. The blue shift scaled linearly with the increase in density and was attributed to a stiffening of the water-urea intermolecular potential. We deduced an increase in the number of affected water molecules from 1 to 2 up to 5-7, which corresponds to the sterical coordination number of urea. The increase in hydration number can be explained by an suppression of the NH <subscript>2</subscript> inversion and the hydrogen bond switching around the NH <subscript>2</subscript> group. Pressure induced sterical constraints are proposed to hinder the rapid switching of hydrogen bond partners and make the water around urea less bulk-like than under ambient conditions.<br /> (Copyright © 2019 Elsevier B.V. All rights reserved.)