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The thermotropic collapse of the hydrogel of copolymer N-isopropylacrylamide with acrylic acid (NIPA−AAc) upon heating has been studied by high-sensitivity differential scanning calorimetry. Curves of the polymer partial heat capacity have been measured at different pH (from pH 2 to 11) and different concentrations of cationic ligands: CaCl2, dodecyltrimethylammonium bromide (DTAB), and cetyltrimethylammonium bromide (CTAB). Dependencies of the main thermodynamic parameters of the gel collapsetemperature, enthalpy, and width of the transition on pH and ligand concentrationhave been obtained. It has been found that the collapse is characterized by a negative value of the heat capacity increment Δtcp. Its average value determined over all variables studied is Δtcp = −0.62 ± 0.02 J/(g K). This result is in accordance with the observed correlation between the transition enthalpy and temperature of the NIPA−AAc gel. The free energy of the collapse has been calculated as a function of pH and concentration of C...

We report the data on concurrent multiple point adsorption of two oppositely charged species of “target molecules” (aluminum ions and 1,3,6,8-pyrenetetrasulfonic sodium salt (Py-4)) by a polyampholyte gel of N-isopropylacrylamide (NIPA, 6 M) with methacrylic acid (MAA, 80 mM) and methacrylamidopropyl trimethylammonium chloride (MAPTAC, 80 mM). The goal of this study is to test the mutual frustrations created by adsorption of one species on the adsorption of the other. Understanding these frustrations is an important step toward elucidating the memory of conformations in heteropolymer systems. We found that in the absence of aluminum, the adsorption of Py-4 was suppressed by gel collapse, presumably because of an increase in MAA/MAPTAC ionic pairs that prevents the formation of potential adsorbing centers. Adding a moderate amount of aluminum significantly enhances adsorption of Py-4 by the collapsed gel, indicating that aluminum ions compete for bonds with MAA and help release vacant MAPTAC centers. Final...

Weakly cross-linked heteropolymer gels that memorize molecular pairs have been designed and synthesized. The polymer consists of a main monomer component responsible for volume phase transition, methacrylic acid that adsorbs one divalent ion as a pair, and cross-links. The memory of pairing of methacrylic acids within the gels was encoded in the primary sequence of main monomers, methacrylic acids and cross-links within the gels, which was achieved by “imprinting”, namely, by synthesizing gels while methacrylic monomers were paired prior to polymerization. The control gels, where methacrylic monomers were randomly distributed, showed frustration in forming pairs, whereas such frustration was completely diminished in the imprinted gels allowing the memory of pair formation.

The photochemistry of ethylindium(III) tetraphenylporphyrin, C/sub 2/H/sub 5/In/sup III/TPP, in benzene solutions was studied by steady light and laser flash photolysis. From the analysis of the products, the C/sub 2/H/sub 5/-In bond in C/sub 2/H/sub 5/In/sup III/TPP was confirmed to be photodissociated. The quantum yields for the photodecomposition of C/sub 2/H/sub 5/In/sup III/TPP were found to be diminished by the addition of ferrocene. However, 2,4,7-trinitro-9-fluorenone, a strong electron acceptor, was found to increase the quantum yields. The laser photolysis studies revealed that the photoreaction of C/sub 7/H/sub 5/In/sup III/TPP occurs via the triplet state originating from the porphyrin ligand.