  We use systematic 8 ns ab initio molecular dynamics (AIMD) to study the
structure and dynamics of water in bulk, and close to both hydrophobic and
hydrophilic (carbonyl) groups of tetramethylurea (TMU). We observe crossovers
in the dynamical behavior around the hydrophobic group at $T_X = 256 \pm 4$K
and another one at $265 \pm 5$K related to the relative strength of water-water
and water-carbonyl hydrogen bonds (HBs). For bulk water, the temperature of the
apparent divergence in relaxation times is located at $T_c = 210 \pm 10$K. To
better identify the effects arising from the hydrophilic carbonyl group,
systems of water with a methane molecule were used as references. These
findings are related to the structural and thermodynamic transitions reported
for proteins in solution and may also play a role in the mechanism of cold
denaturation of proteins.
