Conformational change of poly(L‐lysine) by formation of complexes with poly(styrene sulfonate)

Abstract

AbstractCircular dichroic studies were made on the conformational change of poly(L‐lysine) (PLL) by complex formation with sulfonated polystyrenes (PSS) as functions of pH, temperature and polymer compositions in comparison with the complexes of PLL with sulfated poly(vinyl alcohol) (PVS). The coil‐to‐helix transition of PLL by complex formation at neutral and acidic pHs, which took place in the PLL/PVS (with high degrees of sulfation) complexes, was prevented in the PLL/PSS complexes due to the less chain flexibility of PSS than PVS. Above pH 11, the α‐helix of PLL was partially broken into random coil by complex formation with PSS. The drastic decrease in the solution viscosity by the complex formation revealed a large contraction of PSS chain and subsequently a large strain of the α‐helical PLL chain so as to give the breakdown of the α‐helix. This is denoted a strain‐induced conformational change of PLL. It was found that the α‐helix of PLL was thermally stabilized by the complex formation with PSS as in the case of PLL/PVS complexes. A β‐to‐α transition of PLL by the complex formation with PSS was also found, while the β‐form was maintained in the PLL/PVS (with high degrees of sulfation) complexes.