PRESSURE EFFECT ON INVERSE TEMPERATURE TRANSITIONS - BIOLOGICAL IMPLICATIONS

Elastic protein-based polymers of the form poly[f(x)(VPGXG),f(v)(VPGVG)], where f(x) and f(v) are mole fractions with f(x) + f(v) = 1, exhibit inverse temperature transitions in the form of a phase separation in which folding and aggregation of polymer chains into more-ordered states of the condensed (coacervate) phase occurs on raising the temperature. When X = Trp, Phe or Tyr, an increase in pressure causes a substantial increase in the temperature of the transition. The data are interpreted to indicate that water molecules surrounding the aromatic side chains of Trp(W), Phe(F) or Tyr(Y) occupy less volume than water molecules in bulk water. The calculated volume change for poly[0.8(GVGVP), 0.2(GFGVP)], for example, on going from coacervate phase, where hydrophobic associations have largely eliminated waters of hydrophobic hydration, to be dispersed in water where the hydrophobic moieties are surrounded by water is 80 cm3/mol of mean pentamers or some 400 cm3/mol of (GFGVP). The results provide an understanding of the source of pressure effects in biological systems and for the capacity to design materials capable of exhibiting baromechanical transduction.