Synthesis of 4% Glu-containing Val1 and Ile1-polypentapeptides: model protein systems for demonstrating mechanochemical coupling.

The synthesis of 4% Glu-polypentapeptide (PPP) (i.e., 4 Glu residues per 100 amino acid residues) and 4% Glu-Ile1-PPP, in which Val1 is substituted by a more hydrophobic Ile residue, is carried out by copolymerizing the p-nitrophenyl-active esters of GE(OMe)GVP and GE(OMe)GIP with their parent pentamers GVGVP and GVGIP in 1:4 ratios, respectively. After removal of the methyl ester on the side chain of Glu, these polymers exhibited a remarkable pH dependence of the temperature for their inverse temperature transitions, which are followed as turbidity development at 300 nm. On gamma-irradiation crosslinking, the elastomeric bands obtained exhibited a pH-mediated contraction and relaxation. Thus, for the first time, mechanochemical coupling is demonstrated in a synthetic polypeptide system. That the basic mechanism involves the hydrophobic effect (chemical modulation of an inverse temperature transition) and not ion-ion electrostatic repulsion is also discussed.