ИСТИНА

It was shown that nanoscale inhomogeneities exist in solutions of PNIPAM and albumin. The structure of these inhomogeneities in protein and polymer solutions is different. At protein concentrations of ~10%, the formation of inhomogeneities in solution was observed already at 273–295 K. Addition of BSA to a PNIPAM solution leads to an increase in the proportion of probe molecules located in polymer-protein inhomogeneities along compared to a protein-free solution. The use of a paramagnetic label covalently attached to the polymer chain makes it possible to determine the dynamics of the polymer chain itself. It was shown that the EPR signal of spin-labeled PNIPAM is close to the hard limit of rotation of the nitroxide radical with an average rotational correlation time of about 0.1 μs. It was also shown by EPR spectroscopy using spin-labeled PNIPAM that the collapse of the polymer chain at 305 K occurs faster when BSA is added: the fraction of slowly rotating label particles in the globule increases with increasing protein concentration. Apparently, albumin contributes to the formation of inhomogeneities in PNIPAM solutions during the coil to globule phase transition, but does not affect the structure of the globule core.