Differential scanning calorimetry studies of NaCl effect on the inverse temperature transition of some elastin-based polytetra-, polypenta-, and polynonapeptides

Differential scanning calorimetry studies of the effect of NaCl on protein-based polymer self-assembly has been carried out on six elastin-based synthetic sequential polypeptides- i.e., the polypentapeptide (L-Val¹-L- Pro²-Gly³-L-Val⁴-Gly⁵)(n) and its more hydrophobic analogues (L-Leu¹-L- Pro²-Gly³-L-Val⁴-Gly⁵)(n) and (L-Val¹-L-Pro²-L-Ala³-L-Val⁴-Gly⁵)(n); the polytetrapeptide (L-Val¹-L-Pro²-Gly³-Gly⁴)(n) and its more hydrophobic analogue (L-Ile¹-L-Pro²-Gly³-Gly⁴)(n); and the polynonapeptide (a pentatetra hybrid), (L-Val¹-L-Pro²-Gly³-L-Val⁴-Gly⁵- L-Val⁶-L-Pro⁷-Gly⁸-Gly⁹)(n). Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order of the polypentapeptide, as the temperature is raised from below to above that of the transition, has been repeatedly observed using different physical characterizations. In the present experiments, it is observed that the transition temperatures of the polypeptides studied are linearly dependent on NaCl concentration. The molar effectiveness of NaCl in shifting the transition temperature ΔT(m)/[N], is about 14°C/[N], with the dependence on peptide hydrophobicity being fairly small. Interestingly, however, the δΔQ/[N] does depend on the hydrophobicity of a polypeptide.