Search results for "Equilibrium"

Complexation of phosphine ligands with peracetylated β-cyclodextrin in supercritical carbon dioxide: Effect of temperature and cosolvent on the equil…

2009

Abstract The interaction between peracetylated-β-cyclodextrin and tert-butyl and adamantyl functionalized triphenylphosphine derivatives was studied in supercritical carbon dioxide (scCO 2 ) based solvent media by UV–vis spectroscopy. The equilibrium constant for a 1:1 complexation reaction was obtained from titration spectra both in pure carbon dioxide and in the presence of methanol as a cosolvent in the temperature range 308–323 K to estimate the internal energy and entropy of the inclusion equilibrium. The values of the equilibrium constants were found significantly smaller than those obtained in aqueous solution with analogous phosphines and substantially independent of the nature of t…

Thermodynamic Properties of Sodium n-Alkanecarboxylates in Water and in Water + Cyclodextrins Mixtures

1998

Densities and heat capacities of water−substrate, water−cyclodextrin, and water−substrate−cyclodextrin systems were determined at 298 K. The substrates studied are sodium n-alkanecarboxylates (CnCOONa) (from sodium acetate to sodium decanoate) and the cyclodextrins are hydroxypropyl-α-cyclodextrin (HP-α-CD), hydroxypropyl-β-cyclodextrin, (HP-β-CD), hydroxypropyl-γ-cyclodextrin (HP-γ-CD) and β-cyclodextrin (β-CD). The apparent molar volumes and heat capacities of CnCOONa in water were calculated as functions of concentration. The standard partial molar properties agree with those obtained by using the additivity rule. HP-β-CD essentially does not affect the thermodynamic properties of C1COON…

Calorimetric investigation of the complex formation between surfactants and α-, β- and γ-cyclodextrins

1992

Abstract A calorimetric technique has been used to study complex formation between α-, β- and γ-cyclodextrins (αCD, βCD and γCD) and some surfactants (sodium dodecylsulphate (SDS), hexadecyl trimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl) phenoxypoly(oxyethyleneglycol) (Triton X-100)). The experimental data indicate that some complexes (SDS-αCD, SDS-βCD and CTAB-αCD) are very stable and allow direct determination of their stoichiometry and molar enthalpy of complex formation. Those for other complexes closely fit a model based on an equilibrium reaction between surfactant, cyclodextrin and a single complex. According to the model, data analysis allows determination of the …

1990

The determination of average molecular weights and the characterization of molecular weight distributions by the ratio of the weight- to number-average molecular weights Mw/Mn from sedimentation equilibrium in the ultracentrifuge are described. The essential measurement of the density profile of the mixed solvent is conducted according to Munk (Macromolecules15, 500 (1982)). Special evaluation of the polymer band in the equilibrium allowed to deduce from the observed concentration profile Mw and Mn of a series of poly(methyl methacrylate) samples and thus to characterize the molecular weight distribution of the samples.

Study of the interaction of [Cu(bipy)]2+ with oxalate and squarate in aqueous solution

1988

A study of the formation of complexes between [Cu(bipy)]2+ and ox2− and sq2− in aqueous solution, (bipy being 2,2′-bipyridine and ox2− and sq2− the dianions of ethanedioic acid and 3,4-dihydroxy-3-cyclobutene-1,2-dione, respectively), has been carried out with the aim of comparing the coordinating properties of these related ligands. The constants of the equilibria (i) and (ii) $$[Cu(bipy)]^{2 + } + ox^{2 - } \rightleftharpoons [Cu(bipy)ox]$$ (i) $$[Cu(bipy)]^{2 + } + sq^{2 - } \rightleftharpoons [Cu(bipy)sq]$$ (ii) have been determined by potentiometry and spectrophotometry at 25.0°C and 0.1 M NaNO3:logβ=5.78(2) and 2.16(2) for the oxalato- and squarato-complex, respectively. Such differen…

A Novel Gas Chromatographic Method to Measure Sorption of Dense Gases into Polymers

2006

A novel experimental approach to determine the solubility of gaseous compounds inside polymers is here described. The method is based on the gas chromatographic determination of the composition of the fluid phase at equilibrium with the polymer. To take into account the effect of the volume swelling on the measurement a suitable probe, nonabsorbable by the polymer, was added to the fluid phase. Under the adopted configuration the apparatus can operate up to 35 MPa and 80°C. This experimental technique has been used to determine the solubility of carbon dioxide in poly(vinylidene fluoride) using argon as a probe. The latter was chosen because it is negligibly absorbed by the polymer and does…

Cyclic voltammetric analysis of pH-dependent complex formation equilibria in anion coordination chemistry

1995

A procedure to analyze pH-dependent complex formation equilibria from cyclic voltammetry is described. Application to adduct formation equilibria between [Fe(CN)(6)](4-) and [Fe(CN)(6)](3-) with different polyammonium receptors is discussed. Extension to the interaction of substrates such as ATP, NAD(+), NADP(+), and carboxylate ions with these receptors by means of competitive interaction with hexacyanoferrate(II) ion is presented.

Stopped-Flow and DFT Studies of Proton Transfer and Isomerization of 5-Amino-3-imino-1,2,6,7-tetracyano-3H-pyrrolizine and Its Related Base 2-(5-Amin…

2001

International audience; A complete kinetic study of pH-dependent isomerization of 5-amino-3-imino-1,2,6,7-tetracyano-3H-pyrrolizine (HL) and 2-(5-amino-3,4-dicyano-2H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide (L‘-) in the pH range from −0.5 to +13 in aqueous solution, which spans over 7 orders of magnitude for the pseudo-first-order rates (log k from −4.8 to +2.5), has revealed for the first time the existence of the corresponding conjugate species L- and HL‘. The study has allowed the determination of the acid dissociation constants of HL (pKa) and HL‘ (pKa‘), as well as all of the individual forward and reverse isomerization rates of the acidic (HL/HL‘) and basic (L-/L‘-) forms. Although L…

Forces Between Solid Surfaces Across Polymer Melts as Revealed by Atomic Force Microscopy

2007

Forces between solid surfaces across polymer melts are poorly understood despite their fundamental importance and their relevance for making composite materials. Such force measurements reveal information on the structure of polymers at surfaces and of confined polymers. Experiments with the atomic force microscope and polyisoprene (PI) confirmed theoretical predictions that no long‐range force should be present in thermodynamic equilibrium. In poly(dimethyl siloxane) (PDMS) repulsive forces are observed at high molar mass. We attribute this to the formation of an immobilized layer caused by a slow release of adsorbed segments enhanced by entanglement. In low molar mass PDMS attractive forc…

Connectivity defects enhance chain dynamics in supramolecular polymer model-network gels

2016

Supramolecular polymer networks exhibit twofold dynamics: that of their polymer chains and that of the transient bonds between them, which is further complexed when irregular network structures lead to local variation of both. A typical irregularity is imperfect network-chain connectivity. To assess the impact of that, we study the diffusion of three different types of tracer polymers in supramolecular model networks of four-arm star-shaped poly(ethylene glycol). First, we focus on tracers that carry three stickers and one fluorescent label at their four arms, thereby creating an inherent network connectivity defect in their vicinity. Second, we embed tracers that carry four stickers and fo…