Evidence of a structural defect in Ice VII and the side-chain-dependent response of small model peptides to increased pressure.

The effect of high pressure on the OH stretch of dilute HOD in D(2)O was examined using high-pressure Fourier transform infrared (FT-IR) spectroscopy. It was found that at pressures directly above the ice VI to ice VII transition, ice VII displays a splitting in the OH absorption indicative of differing hydrogen bonding environments. This result is contrary to published structures of ice VII in which each OH oscillator should experience an identical electronic environment. The anomalous band was found to decrease in absorbance and finally disappear at ∼43.0 kbar. In addition, the pressure response of the amide I' and II' bands of three small model peptides was examined. Analysis of these bands' response to increased pressure indicates significant side-chain dependence of their structural rearrangement, which may play a role in the composition of full length proteins of barophilic organisms.