Аннотация:The volume phase transition of a hydrogel of the polyampholyte network N-isopropylacrylamide (6000) - N-(3-
aminopropylmethacrylamide) (120) - Acrylic acid (120) - N,N′-Methylenebisacrylamide (40) was investigated by
high-sensitivity differential scanning calorimetry in relation to pH, concentrations of NaCl and two oppositely
charged drug ligands (ibuprofen and propranolol). The transition temperature, enthalpy, heat capacity increment
and width against these thermodynamic variables were determined. The experimental data were used for
calculation of the excess free energy functions of the phase transition which are measures of the relative stability
of the dense (collapsed) state of the polyampholyte network under different conditions. By analogy with globular
proteins, the stability of the network dense state is maximal at the isoelectric point of the polyampholyte and is
increased by the kosmotropic salt and specific ligands. We demonstrate that the polyampholyte hydrogel consists
of independent cooperative domains. The sizes of these domains in the hydrogel (9–15 kDa) are comparable with
those in globular proteins.