Pressure-induced changes in the nuclear magnetic resonance spectra of a biopolymer in aqueous solution.
High resolution proton nuclear magnetic resonance spectra of the poly(amino acid)poly[N5-(3-hydroxypropyl)-L-glutamine], of degrees of polymerization 685 and 137, were measured in a mixed D2O and H2O solvent, at pressures from 1.03 to 1968.5 kg/cm2, and at temperatures of 2 and 10 degrees C. Increasing the pressure appeared to cause an increased mobility of the side chain hydrocarbon residues, and also of the alpha-hydrocarbon residue of the polymer chain. This is interpreted to imply the occurrence of a volume decrease on unfolding of the polymer from a helix to a random coli, with subsequent exposure of hydrophobic groups to the solvent.