SynopsisTo model the compact structures of globular proteins and the processes of their breakdown, the local compact structures have been investigated in the nonionized (or weakly ionized) molecules of polymethacrylic acid (PMA) in aqueous solutions. The potentiometric titration curves differ markedly from the analogous curves for polyacrylic acid (PAA) and show the existence of the cooperative breakdown of the local compact structures in a definite region of the ionization degree. The presence of the local compact structures in the PMA molecules is also manifested in sharp differences between the luminescent characteristics of the dyes (auramine and acridine orange) in aqueous solutions with PMA and the same characteristics in aqueous solutions with PAA. In a certain range (which coincides with the interval of the breakdown of local compact structures) these differences disappear. This permits us to interpret them as the result of the dye molecules binding on the structurized parts of PMA. The assumption has been made that the local compact structures in the PMA molecules in aqueous solutions are stabilized by the hydrophobic interactions of methyl groups. This assumption explains the abnormal temperature dependencies of the properties of the aqueous solutions of PMA and the absence of the local compact structures in the PMA molecules in methanol as well as in the P AA molecules in any solvents. To check this assumption we have. investigated the breakdown of the local compact structures in the PMA molecules when aliphatic alcohols are added to the aqueous PMA solution. It was shown that the transition of dye molecules from the bound state to the free one (which is the evidence of the breakdown of the local compact structures) takes place in the narrow range of alcohol concentrations decreasing in the series methanol-ethanol-propanol-butanol. It means that alcohol destroys compact structures the better, the more hydrophobic groups it possesses.The investigations of intrinsic viscosity of PMA in the water-methanol mixtures have shown that the addition of alcohol leads not only to the breakdown of the local compact structures, but also the unfolding of the macromolecule as a whole. The analogy between the local compact structures in PMA molecules and the compact structures of globular proteins has been discussed.

The photophysical properties of poly 2,2' (1 dodecyl carbazole 4,7 yl) 6,6' (oxy) bis (4 phe nylquinoline) in a solution, as a film, and in a poly(methyl methacrylate) or poly N vinylcarbazole host matrix have been studied. Considerable positive solvatochromism in the photoluminescence spectra, com pared with solvatochromism in the absorption spectra, indicates that the dipole moment of the donor-accep tor complex increases in the excited state. Calculations show that the dipole moments of the complex in the ground and excited states differ by more than an order of magnitude. Upon transition to films, photolumi nescence is observed in the entire visible spectral range (white luminescence). The intensity of the white lumi nescence grows by an order of magnitude when the polymer is dispersed in a poly(methyl methacrylate) matrix. The integrated photosensitivity and parameters of the photogeneration process (quantum yield of carrier photogeneration, quantum yield of free carrier formation, and thermalization radii) have been determined.

No abstract

No abstract

No abstract