Binding of 1-anilinonaphthalene-8-sulphonate to poly (N-vinyl-2-pyrrolidone)

The binding of 1-anilinonaphthalene-8-sulphonate (ANS) to poly(N-vinyl-2-pyrrolidone) (PVP) of molecular weight grades k30 (molecular weight 40,000) and k90 (360,000) was studied by a dialysis technique in 0·05 M phosphate buffer, pH 7·1, at different temperatures. The intrinsic binding constant,K, was determined. The binding was favoured by negative enthalpy and positive entropy in both the systems indicating respectively that energetic forces and hydrophobic interactions were contributing to the binding affinity. The effects of addition of urea and palmitic acid on binding were investigated by dialysis and fluorescence techniques. The results showed that the binding of ANS to PVP was dependent on the nature and microenvironment of the binding sites and thereby pointed out the importance of the iceberg structure of water in the binding system.     

Preirradiation grafting of N-vinyl-2-pyrrolidone onto poly(tetrafluoroethylene) and poly(tetrafluoroethylene-hexafluoropropylene) films

Preirradiation grafting of N-vinylpyrrolidone (NVP) onto poly(tetrafluoroethylene) (PTFE) and poly(tetrafluoroethylene-hexafluoropropylene) (FEP) films was investigated. The influence of grafting parameters such as preirradiation dose, monomer concentration, and grafting temperature on the rate and grafting yield was studied. Different solvents were used for diluting the monomer and it was found that the aqueous monomer solution at a concentration of 80 wt% was suitable for this grafting system. However, the graft polymerization of NVP in benzene terminated within a short time without significant grafting yield. The dependence of the grafting rate on preirradiation dose and monomer concentration was 1.2 and 1.07 order, respectively, for grafting onto PTFE films and 1.1 and 1.2 order, respectively, for grafting onto FEP films. Arrhenius plots for grafting onto PTFE films showed a breaking point at ca. 35°C and the overall activation energies were calculated as 23.6 and 9.0 Kcal/mol below and above 35°C, respectively. For grafting onto FEP films, however, no break was observed in the Arrhenius plots; the overall activation energy was 11.9 Kcal/mol. The swelling behavior and electric resistance of the grafted materials were investigated.     

Graft copolymerization of N-vinyl-2-pyrrolidone onto pre-irradiated poly(vinylidene fluoride) powder

Graft copolymerization of N-vinyl-2-pyrrolidone (NVP) onto ⁶⁰Co γ-ray pre-irradiated poly (vinylidene fluoride) (PVDF) powder was investigated to find out the relationship between the degree of grafting (DG) and various factors, including monomer concentration, irradiation dose, reaction time, catalyst and so on. The DG can be calculated by comparing the amount of nitrogen element in the resulting copolymer (PVDF-g-PVP) powder with that in PVP on the basis of element analysis. The presence of PVP in the resulting PVDF powder was confirmed by the comparative studies of pristine PVDF and grafted PVDF powder through Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), thermo gravimetric analyzer (TGA) and differential scanning calorimetry (DSC), respectively. When the reaction was performed at the monomer concentration of 20% (vol.) and the absorbed dose of 40 kGy for 3 h in water, the max. DG of 17.7% was obtained.     

Binding studies of sodium dodecyl benzene sulphonate with poly(N-vinyl-2-pyrrolidone)

The binding of sodium dodecyl benzene sulphonate (SDBS) with poly(N-vinyl-2-pyrrolidone) (PVP) has been investigated at 303.15 and 313.15 K using equilibrium dialysis, surface tension, viscosity, ultrasound velocity and ultrasound absorption techniques. From each of these studies four distinct regions of SDBS-PVP interactions were observed. Interaction of SDBS with PVP was found to involve the binding of surfactant dimers with the polymer molecule followed by usual micellization. The binding data has been analyzed in terms of various models of polymer-surfactant interaction.     

Polymer-ligand interaction studies. Part I. Binding of some drugs to poly(N-vinyl-2-pyrrolidone)

A physico-chemical investigation on the binding of some nonsteroidal anti-inflammatory drugs, Naproxen (NP) and Ketoprofen (KP) and a drug model compound, salicylic acid (SA) to poly(N-vinyl-2-pyrrolidone) (PVP, molecular weight = 360,000), was performed at pH 7.1 by the fluorescence competition method employing 1-anilinonaphthalene-8-sulphonate (ANS) as the fluorescent probe. The binding affinities of these substrates to PVP are in the order KP < SA < NP which has been explained on the basis of their structural features and the consequent effect on the interacting forces. Theπ-π interaction between the carbonyl group of PVP and theπ-ring system of the substrate molecule seems to be crucial in deciding the binding affinities of the substrates     

Interaction of 1-anilinonaphthalene-8-sulphonate with cross-linked poly (N-vinyl-2-pyrrolidone)

The interaction of 1-anilinonaphthalene-8-sulphonate (ANS) with cross-linked poly(N-vinyl-2-pyrrolidone) (CPVP) was studied by the adsorption technique at different temperatures and at two different pH values. Analysis by the Scatchard method and the study made in the presence of urea showed that the iceberg structure of water affects the sorption of ANS to CPVP, leading to cooperativity. The observed Giles sorption isotherms at both the pH values were of theL-type which indicated the interaction of ANS in flat configuration with the binding site in CPVP. The sorption of ANS to CPVP was enhanced considerably at acidic pH due to some structural factors which also resulted in multilayer sorption at this pH. Comparison of binding of ANS to CPVP and to linear poly(N-vinyl-2-pyrrolidone) demonstrated the greater contribution of hydrophobic interaction in CPVP than in the linear polymer.     

Size-dependent interaction of the poly(N-vinyl-2-pyrrolidone) capping ligand with Pd nanocrystals

Pd nanocrystals were prepared by the reduction of a H(2)PdCl(4) aqueous solution with C(2)H(4) in the presence of different amounts of poly(N-vinyl-2-pyrrolidone) (PVP). Their average size decreases monotonically as the PVP monomer/Pd molar ratio increases up to 1.0 and then does not vary much at higher PVP monomer/Pd molar ratios. Infrared spectroscopy and X-ray photoelectron spectroscopy results reveal the interesting size-dependent interaction of PVP molecules with Pd nanocrystals. For fine Pd nanocrystals capped with a large number of PVP molecules, each PVP molecule chemisorbs with its oxygen atom in the ring; for large Pd nanocrystals capped by a small number of PVP molecules, each PVP molecule chemisorbs with both the oxygen atom and nitrogen atom in the ring, which obviously affects the structure of chemisorbed PVP molecules and even results in the breaking of involved C-N bonds of some chemisorbed PVP molecules. Charge transfer always occurs from a chemisorbed PVP ligand to Pd nanocrystals. These results provide novel insights into the PVP-metal nanocrystal interaction, which are of great importance in the fundamental understanding of surface-mediated properties of PVP-capped metal nanocrystals.     

Single-chain mechanical property of poly(N-vinyl-2-pyrrolidone) and interaction with small molecules

The single-chain nanomechanical properties of poly(N-vinyl-2-pyrrolidone) (PVPr) and povidone-iodine (PVPr-I2) under different solution conditions have been investigated by using an atomic force microscopy based technique-single-molecule force spectroscopy. The force-extension curve (force curve) of PVPr in water is markedly deviated from that obtained in ethanol or tetrahydrofuran, suggesting a different interaction between PVPr and the solvents. Moreover, we have comparatively studied the force signals of PVPr-I2 and PVPr in an aqueous solution of KI or KI3 and found that only KI3 influences the elastic property of PVPr dramatically. These experimental results indicate that there exists a specific interaction between PVPr and KI3, which is also supported by Fourier transform infrared data. By the integration of the deviated area between the force curve and the modified freely jointed chain fitting curve, we estimate that the energy needed to destroy the interaction between PVPr and water is 5.3 kT and between PVPr and KI3 is 3.6 kT per repeating unit, respectively.     

Binding of benzopurpurin 4B to poly(N-vinyl-2-pyrrolidone): A spectral study on the mechanism of dye binding

The binding mechanism of benzopurpurin 4B to poly(N-vinyl-2-pyrrolidone) was studied by a spectrophotometric absorbance change method at pH 7.1 in 0.05 mol dm^–3 phosphate buffer. The results were analyzed by Scatchard, Hill, and Schwarz methods. The different shapes of the Scatchard plots indicated the varying degrees of cooperativity which depended on the percent saturation of binding sites. The Hill method elucidated the pairwise binding of the dye to polymer at the intermediate saturation and multimolecular binding both at the low and high saturations. The Schwarz method confirmed the interaction between bound dye molecules which led to cooperativity. The difference spectra of the polymer-dye complex evidenced the elucidated binding mechanism.     

Surfactant--polymer aggregates formed by sodium dodecyl sulfate, poly(N-vinyl-2-pyrrolidone), and poly(ethylene glycol)

The interaction of sodium dodecyl sulfate (SDS) in aqueous solution with poly(N-vinyl-2-pyrrolidone) (M(w) = 55,000 g/mol) in the presence of poly(ethylene glycol) (M(w) = 8000 g/mol) is investigated by electrical conductivity, zeta potential measurements, viscosity measurements, fluorescence spectroscopy, and small-angle X-ray scattering (SAXS). The results indicate that SDS-polymer interaction occurs at low surfactant concentration, and its critical aggregation concentration is fairly dependent on polymer composition. The polymer-supported micelles have average aggregation numbers dependent on surfactant concentration, are highly dissociated when compared with aqueous SDS micelles, and have zeta potentials that increase linearly with the fraction of PVP at constant SDS concentration. The analysis of the SAXS measurements indicated that the PVP/PEG/SDS system forms surface-charged aggregates of a cylindrical shape with an anisometry (length to cross-section dimension ratio) of about 3.0.     

Direct synthesis of fct-structured FePt nanoparticles at low temperature with assistance of poly(N-vinyl-2-pyrrolidone)

Direct synthesis of fct-structured FePt nanoparticles was successfully achieved by using poly(N-vinyl-2-pyrrolidone) as a protective reagent at lower temperature than the case using low molecular weight ligands as a protective reagent. Experimental data suggest that a transformation of FePt nanoparticles from face-centered cubic to face-centered tetragonal (fct) structure takes place at reaction temperature of 261 degrees C. The results of XRD and the magnetic properties exhibit that the FePt nanoparticles synthesized at 261 degrees C have partially ordered fct-structure and a ferromagnetic behavior at room temperature.     

One-step synthesis of gold and silver hydrosols using poly(N-vinyl-2-pyrrolidone) as a reducing agent

Synthesis of gold and silver hydrosols was carried out in a one-step process by reduction of aqueous solutions of metal salts using poly(N-vinyl-2-pyrrolidone) (PVP). Both kinds of metal nanoparticles were obtained without the addition of any other reducing agent, at low temperatures and using water as the synthesis solvent. Shape, size, and optical properties of the particles could be tuned by changing the employed PVP/metal salt ratio. It is proposed that PVP acts as the reducing agent suffering a partial degradation during the nanoparticles synthesis. Two possible mechanisms are proposed to explain the reduction step: direct hydrogen abstraction induced by the metal ion and/or reducing action of macroradicals formed during degradation of the polymer. Initial formation of the macroradicals might be associated with the metal-accelerated decomposition of low amounts of peroxides present in the commercial polymer.     

Binding of butyl orange by poly(2-dimethylaminoethyl methacrylate) and copolymers of 2-dimethylaminoethyl methacrylate and N-vinyl-2-pyrrolidone: Peculiar temperature dependence of the binding

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.