Hydrophobicity‐induced pK shifts in elastin protein‐based polymers

Three polypentapeptides—poly[0.8(GVGVP), 0.2(GEGVP)], poly[0.8(GVGIP), 0.2‐(GEGIP)], and poly[0.75(GFGVP), 0.25(GEGVP)]—all analogues of the polypenta‐peptide of elastin—(Val 1 ‐Pro 2 ‐Gly 3 ‐Val 4 ‐Gly 5 ) n or poly(VPGVG)—have been prepared to determine the effect of changing the hydrophobicity, i.e., Val 1 → Ile 1 (I) and Val 4 → Phe 4 (F), on the pK a and the temperature dependence of pK a of the Glu (E) residue. Shifts in pK a as large as 1.7 units are observed and the temperature dependence is much steeper for the structure‐dependent proximity of the more hydrophobic Ile 1 residues to the Glu 4 residue. Even though this system is dominated by the inverse temperature transition of hydrophobically driven folding on raising the temperature, the effect of adding 0.15 N NaCl is to suppress the hydrophobicity‐induced pK a shift.