Influence of concentration and temperature on the dynamics of water in the hydrophobic hydration shell of tetramethylurea.
We study the influence of the amphipilic compound tetramethylurea (TMU) on the dynamical properties of water, using dielectric relaxation spectroscopy in the regime between 0.2 GHz and 2 THz. This technique is capable of resolving different water species, their relative fractions, and their corresponding reorientation dynamics. We find that the reorientation dynamics of water molecules in the hydration shell of the hydrophobic groups of TMU is between 3 (at low concentrations) and 10 (at higher concentrations) times slower than the dynamics of bulk water. The data indicate that the effect of hydrophobic groups on water is strong but relatively short-ranged. With increasing temperature, the fraction of water contained in the hydrophobic hydration shell decreases, which implies that the overall effect of hydrophobic groups on water becomes smaller.
FOM Institute Amolf, Science Park 104 1098 XG Amsterdam, The Netherlands.
Klaas-Jan
KJ
Tielrooij
Johannes
J
Hunger
Richard
R
Buchner
Mischa
M
Bonn
Huib J
HJ
Bakker
D057927:Hydrophobic and Hydrophilic Interactions; D008782:Methylurea Compounds / Q000737:chemistry*; D013696:Temperature; D014867:Water / Q000737:chemistry*
D008782:Methylurea Compounds; D014867:Water; C004168:1,1,3,3-tetramethylurea