Role of water in structural changes of poly(AVGVP) and poly(GVGVP) studied by FTIR and Raman spectroscopy and ab initio calculations

Two elastin-like poly(pentapeptides), poly(AV(1)GV(2)P) and poly(G(1)V(1)G(2)V(2)P), have been studied in water and in solid state by ATR FTIR and Raman spectroscopy in combination with model ab initio calculations. In aqueous solutions below the transition temperature T-t a part of the amide groups and of the methyl groups of both polypentapeptides interacts with neighboring water molecules, whereas the other part of amide groups mutually interacts forming a beta-sheetlike structure. Below T-t, poly(AV(1)GV(2)P) is dissolved more perfectly, and the water shells around the polymer chains are more closely structured. The suspension of poly(AV(1)GV(2)P) formed above T-t is more compact and, on cooling, resists more to the reverse dissolution, whereas the suspension of poly(G(1)V(1)G(2)V(2)P) contains more water molecules bound to the carbonyl of amide groups and on backward cooling dissolves fairly reversibly. The measured poly(pentapeptides) tend to form P-turns due to the conformational transition on the residue between P and V-1.