SynopsisThe pH dependence of the interaction of poly(2-dimethylaminoethyl methacrylate) and copolymers of 2-dimethylaminoethyl methacrylate and N-vinyl-2-pyrrolidone with methyl orange, 2-p-toluidinylnaphthalene-6-sulfonate (TNS), and 1,6-diphenyl-l,3,5-hexatriene (DHT) was studied by equilibrium dialysis and fluorescence measurements at pH's 7-10. The first binding constant accompanying the binding of methyl orange and TNS by the polymers, in particular the homopolymer, shows a maximum around pH 8 and maximal fluorescence intensity of TNS is obtained around pH 8.5 in the presence of the polymers. To elucidate these observations the pH-induced conformational changes of the homopolymer were examined by potentiometric titration and viscosity measurements and the thermodynamic parameters that accompany-the binding were calculated. The polymer was found to change from an extended coil at lower pH to a compact coil at higher pH. The electrostatic attraction between the sulfonate group of the small molecule and the protonated nitrogen atoms on the polymer is increased at lower pH and the hydrophobic interaction between the hydrophobic moieties of the polymer and the small molecule is enhanced at higher pH. The results obtained for the dye binding and fluorescence intensity were discussed in terms of the electrostatic and hydrophobic interactions.

The copolymers of methyl quaternized 2‐dimethylaminoethyl acrylate and styrene, 2‐vinyl naphthalene, acrylic acid iso‐octyl ester, or acrylic acid n‐butyl ester have been prepared. Studies were made of the binding of a “binding probe,” methyl orange, by the copolymers in aqueous solution. The first binding constants and the thermodynamic parameters in the course of the binding were evaluated. Furthermore, the intensity of fluorescence of a hydrophobic fluorescent probe, 2‐p‐toluidinylnaphthalene‐6‐sulfonate, in the presence of these polymers was investigated. In addition, the fluorescence spectra of monomer and excimer emissions of the polymers with aromatic residues were measured. The excimer/monomer fluorescence intensity ratio was studied in the presence of various additives such as methyl orange, urea, methanol, and NaCl to gain an insight into the nature of microdomains in the polymer. The nature and phenomena of dye binding and hydrophobic fluorescent probe binding with the polymers are discussed. © 1993 John Wiley & Sons, Inc.

The temperature dependence of the binding of butyl orange by a homopolymer of 2‐dimethylaminoethyl methacrylate (DMAEMA) and copolymers of DMAEMA and N‐vinyl‐2‐pyrrolidone (VPy) has been examined at various pH's. The binding is very much dependent upon the temperature of the system, the pH of the binding medium, and the DMAEMA content in the polymer. In this case maximal binding is obtained at approximately 15–25° in the temperature range measured, although in most cases which have been examined, the degree of binding increases steadily with increasing temperature. This peculiar temperature dependence of the binding becomes more pronounced as the pH and the DMAEMA content are increased. The appearance of the peculiarity is discussed in terms of the pH‐induced conformational changes of the polymer and the hydrophobicity of the polymer.

The copolymers of N‐vinyl‐2‐pyrrolidone and 2‐dimethylaminoethyl methacrylate, 2‐diethylaminoethyl methacrylate, 2‐dimethylaminoethyl acrylate, or 2‐dimethylaminopropyl acrylamide have been prepared. Studies were made of the binding of a “binding probe,” methyl orange, by the copolymers in aqueous solution. The first binding constants accompanying the binding were evaluated. Furthermore, the intensity of fluorescence of a hydrophobic fluorescent probe, 2‐p‐toluidinylnaphthalene‐6‐sulfonate, in the presence of these polymers was investigated. The nature and phenomena of dye binding and hydrophobic fluorescent probe binding with the polymers are discussed.

Synopsis2-Chethylaminoethyl methacrylate (DEAEMA) N-vinyl-2-pyrrolidone (VPy) copolymers of various compositions have bcwn synthesized. The resultant copol3mers were examined for their ability to hind methyl orange and its homologs, in particular hutyl orange. a t 5, 15, 25, arid 3 5 O ( : in aqueous solutions. T h e amount of binding of hutyl orange is much higher with the copolymcrs than with polyvinylpyrrolidone or with 2-hydroxyethyl methacrylate-N-vinq.l-2-pyrrolidorlr copolymers. Introduction of only 3% of the hydrophobic IIEAEMA residue increases niarkedly t h e binding affinity toward the cosolute. Maximal binding is obtained at Iso(: iri the terrperaturc range measured. This peculiar temperature dependence of t h e extent of binding is explicable on the basis of hydrophobic effects involved in this binding. The peculiar temperature dependence disappeared in aqueous solution of N&CN which acts as a water-structure breaker: the extent of binding changes regularly with temperature. This is interpretable only in ternis of reduction of hydrophobic contribution to the binding. With propyl orange, which is a less hydrophot)ic. cosolute than butyl orange, the peculiarity of the binding was not detected.