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.     

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     

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.     

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.     

Blends of poly(n-vinyl-2-pyrrolidone)/poly(monoitaconates) II. The coefficient of linear expansion

Blends of poly(monoitaconates)^b) containing different side chain structures with poly(N-vinyl-2-pyrrolidone) (PVP) of three different weight-average molecular weights (M̄_w) were studied by thermomechanical analysis. Blends containing PVP of M̄_w =10000 shows a monotonous variation of the coefficient of linear expansion α against composition but PVP samples of higher molecular weights present a minimum which is attributed to polymer-polymer complex due to strong specific interactions.     

非离子聚(N-乙烯基-2-吡咯烷酮)凝胶在线型聚(丙烯酸)溶液中的溶胀特性

研究了在线型聚 (丙烯酸 ) (PAA)溶液中链长、pH、离子强度和水 /二甲亚砜混合溶剂组成对非离子聚 (N-乙烯基 - 2 -吡咯烷酮 ) (PVP)水凝胶溶胀特性的影响 .发现聚酸浓度的变化引起凝胶显著的体积相变 ,这是因为凝胶和聚合物通过氢键形成了大分子间凝胶 -聚合物复合物 .凝胶的溶胀特性取决于聚酸的链长而不是离子强度 .随着pH值和水 /二甲亚砜混合溶剂组成的变化 ,凝胶的溶胀率 (SR)发生变化     

Colloidal metal dispersions as catalysts for selective surface hydrogenation of biomembranes, 1. Preparation and characterization of palladium catalysts

Paliadium sols containing largely uniform, nanosize metallic, particles stabilized by poly(N-vinyl-2-pyrrolidone) were found to be active microheterogeneous catalysts for hydrogenation of water soluble olefinic substrates as well as of unsaturated lipid dispersions. The same metallic particles were supported on the surface of crosslinked insoluble poly(N-vinyl-2-pyrrolidone) and served as easily removable macroheterogeneous hydrogenation catalysts.     

Pretreatment of Polymer-Supported Pd-Co and Its Catalytic Activity

l/or if llctcrogclleous catalyst, it is c('lllllloll that dillbrcnt 1llcthods of preparation result ina dillbrcllcc ill tile catalytic activity, altllotlgll its composition is the same. For atriltlitiotlill if')lllogctlcolls catalyst witll ljxc(l c(f)lllpositioll, its catalytic activity usuallydt)es hot cllallgc Witll tile llletllod elf l,l'cl,arutioll. I'olylller-supported catalysts are calledtile lletcrogcllizc(1 llolllogcllcolls catalysts that colllbille the nlcrits of h()1llogcncous andllc…     

Binding methyl orange and hydrophobic fluorescent probes by poly(2-dimethylaminoethyl methacrylate) and copolymers of 2-dimethylaminoethyl methacrylate and N-vinyl-2-pyrrolidone: pH dependence of the binding and fluorescence intensity

The 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-1,3,5-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.     

Styryl-Telechelic Polyisobutylenes. II. Amphiphilic Sequential Copolymers of Styryl-Telechelic Polyisobutylenes with Vinyl Acetate or N-Vinyl-2-pyrrolidone

Styryl-telechelic polyisobutylenes (i.e., linear and three-arm star polyisobutylenes capped with polymerizable p-styryl endgroups St-PIB-St and St-PIB-St) have been copolymerized with vinyl ace State VAc or N-vinyl-2-pyrrolidone VP by conventional free radical techniques. The products obtained with St-PIB-St/VAc systems were soluble, most likely branched block copolymers of isobutylene IB and VAc, whereas those prepared with St-PIB-St/VP or St-PIB-St/VP Stcombinations were networks consisting of PIB and poly(N-vinyl-2-pyrrolidone) PVP sequences. That the copolymerization of St-PIB-St with VAc results in soluble products and that with VP yields networks is due to the very different reactivities of styrene with VAc and with VP. Hydrolysis of VAc units in PID-PV Ac block copolymers gave vinyl alcohol V A units, i.e., these products are branched block copolymers consistion of random VAc/VA composition of these soluble aphiphilic materials was determined from conversion and molecular weight data and by ¹H-NMR soectroscopy; their mechanical properties were examined by stress - strain measurements. The composition of amphiphilic PVP-PIB networks was calculated from conversion and elemental analysis data. These gels were founds to bind both water -soludle dyes (methyl orange) and hydrocarbons (benzene). The first binding constant K¹ that characterizes the binding of methyl orange by these PVP-PIB networks is one order of magnitude larger than that characteristic of the binding of this dye by cross - linked PVP or by serum albumin.     

Monitoring the Tanford transition in β‐lactoglobulin by 8‐anilino‐1‐naphthalene sulfonate and mass spectrometry

The fluorescent dye 8‐anilino‐1‐naphthalene sulfonate (ANS) is known to interact with proteins by conformation‐specific hydrophobic interactions and rather nonspecific electrostatic interactions. To which category the complexes detectable by mass spectrometry (MS) belong is still the subject of debate. Here, the Tanford transition in β‐lactoglobulin (BLG) is exploited as an experimental device to expose hydrophobic binding sites by an increase in pH, rather than, as usually done, by lowering the pH. Complex formation is monitored by electrospray ionization (ESI)‐MS and fluorescence spectroscopy. Both techniques reveal stronger ANS binding to BLG at pH 7.9 than at pH 5.9, suggesting that dye binding inside the calyx, which is known to be hydrophobically driven in solution, can contribute to the complexes detected by ESI‐MS. Electrostatic interactions between the protein and the ANS sulfonate group can only be weaker at pH 7.9 than at pH 5.9, supporting the interpretation of the results by the protein conformational change. Lysozyme is used as a negative control, which shows no variation in the interaction with ANS in the same range of pH, in the absence of conformational changes. However, comparison of MS and fluorescence data at variable pH for BLG and myoglobin (Mb) suggests that conformation‐specific ANS binding to proteins is detectable by ESI‐MS only inside well‐structured cavities of folded structures, like the BLG calyx and apoMb heme pocket. Indeed, ANS interactions with highly dynamic structures or molten globules, although detectable in solution, are easily lost in the gas phase. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

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.     

Superdispersible PVP-coated Fe3O4 nanocrystals prepared by a "one-pot" reaction

Poly( N-vinyl-2-pyrrolidone) (PVP)-coated Fe3O4 nanocrystals were prepared by a "one-pot" synthesis through the pyrolysis of ferric triacetylacetonate (Fe(acac)3) in N-vinyl-2-pyrrolidone (NVP). The polymerization of NVP was followed by measuring the shear viscosity of the reaction mixture. The PVP molecules formed in the reaction mixture was investigated by gel permeation chromatography. As the resultant Fe3O4 nanocrystals presented superdispersibility in 10 different types of organic solvents and aqueous solutions with different pH, including 0.01 M phosphate-buffered saline buffer, their hydrodynamic properties in both organic and aqueous systems were investigated by dynamic light-scattering. The results indicated that the PVP-coated Fe3O4 nanocrystals can completely be dispersed forming stable colloidal solutions in both organic solvents and water. Fourier transform infrared spectroscopy results suggested that PVP interacted with Fe3O4 via its carbonyl groups. Further surface analysis by X-ray photoelectron spectroscopy revealed that there were both coordinating and noncoordinating segments of PVP on the particle surface; the molar ratio between them was of 1:2.6.     

Synthesis of silver nanoprisms in formamide

Polygonal (mainly triangular) silver nanoprisms were prepared by reducing silver perchlorate in formamide in the presence of polyethylene glycol (PEG) at room temperature. The reduction of silver ions by formamide leads to the deposition of arrays of triangular shaped silver nanoparticles on the glass walls of the container, accompanied by evolution of CO2 gas. In the presence of poly(N-vinyl-2-pyrrolidone) (PVP) and PEG (1:1), both nanospheres and nanoprisms are formed.     

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.     

Fluorescence studies on the interaction of hydrophobic ligands with Momordica charantia (bitter gourd) seed lectin

The interaction of Momordica charantia (bitter gourd) seed lectin (MCL) with several nucleic acid bases has been investigated by monitoring changes induced in the protein fluorescence by ligand binding. Values of the binding constant, K_a were obtained as 1.1 × 10⁴, 1.56 × 10⁴ and 2.2 × 10³ M^?1 for adenine, cytosine and uracil, respectively. In addition, binding of 8-anilinonaphthalene 1-sulfonate (ANS) with MCL was investigated by fluorescence spectroscopy. Interaction with MCL at low pH results in a large enhancement of the fluorescence intensity of ANS with a concomitant blue shift in the emission λ_max, whereas at neutral and basic pH changes in both fluorescence intensity and emission maximum were very small, clearly suggesting that the MCL–ANS interaction is stronger at lower pH values. When excited at 295 nm in the presence of ANS, the protein fluorescence decreased with a concomitant increase in the emission intensity of ANS, suggesting resonance energy transfer from the tryptophan residues of MCL to ANS. Gel filtration profiles of MCL at pH values 2.0 and 7.4 are similar indicating that the tetrameric nature of MCL is retained even at low pH. Addition of lactose or adenine to MCL–ANS mixture did not alter the change in ANS fluorescence suggesting that lactose, adenine and ANS bind to MCL at independent and non-interacting sites. These results are relevant to understanding the functional role of MCL in the parent tissue.     

Synthesis of PVP-stabilized ruthenium colloids with low boiling point alcohols

A route to the preparation of poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium colloids by refluxing ruthenium(III) chloride in low boiling point alcohols was developed. Deep purple colloids with shuttle-like ruthenium particles were also synthesized. XPS measurement verified the nanoparticles were in the metallic state. The morphology of metal nanoparticles was characterized by UV-visible absorption spectrophotometry, TEM and XRD.     

Dehalogenation of Aryl Halides Catalyzed by Montmorillonite Immobilized Bimetal Catalyst in Aqueous System

A novel bisupported bimetal catalyst PVP-PdCl2-FeSO4/Al-Mont-PEG600 was prepared by immobilization of PVP (poly (N-vinyl-2-pyrrolidone)) supported bimetallic catalyst using alumina pillared inartificial montmorillonite as the carrier. This catalyst has good dehalogenation activity and selectivity to aryl halides-o-chlorotoluene in aqueous system in the presence of phase transfer catalyst (PEG) and sodium formate as hydrogen source. The catalyst also shows good reusability.     

Aggregation properties of oligo(methacrylic acid)-shelled dendrimer and its microenvironment in aqueous solutions

A third-generation poly(amido amine) dendrimer having poly(methacrylic acid) segments on the periphery (G3-PMAA) was newly synthesized. A xanthate-modified dendrimer (G3-X) was first prepared by condensation of the terminal amino groups of the poly(amido amine) dendrimer with an activated-ester xanthate. G3-PMAA was then synthesized by polymerization of methacrylic acid initiated with G3-X. The number-average degree of polymerization of PMAA segment was estimated to be 10. The pK_a value for G3-PMAA was evaluated to be 7.3 that is somewhat higher than that (6.8) of the corresponding linear PMAA with the same segment length, indicating the interaction of PMAA segments caused by assembling them at the dendrimer surface. When the diameter of G3-PMAA in aqueous solution at various pHs was measured by a dynamic light scattering, G3-PMAA was found to self-aggregate in a pH region, where the PMAA segment took a hydrophobic, compact coil conformation. Subsequently, the interaction of a fluorescent probe (1-anilino-8-naphthalenesulfonic acid ammonium salt (ANS)) with G3-PMAA was examined by means of fluorescence spectroscopy. As a result, ANS was found to bind to the hydrophobic site of G3-PMAA aggregates at lower pH, and to be released into water phase at higher pH.