Search results for "Equilibrium constant"
showing 10 items of 79 documents
Ion-exchange fibers and drugs: a transient study.
2003
The objective of this study was to theoretically model and experimentally measure the kinetics and extent of drug release from different ion-exchange materials using an in-house-designed flow-cell. Ion-exchange fibers (staple fibers and fiber cloth) were compared with commercially available ion-exchange materials (resins and gels). The functional ion-exchange groups in all the materials were weak -COOH or strong -SO3H groups. The rate and extent of drug release from the fibers (staple fiber>fiber cloth) was much higher than that from the resin or the gel. An increase in the hydrophilicity of the model drugs resulted in markedly higher rates of drug release from the fibers (nadolol>metoprolo…
Equilibria in the anionic polymerization of methyl methacrylate, 1. Chain-length dependence of the rate and equilibrium constants
1986
The rate constants of polymerization and cyclization and the equilibrium constants of polymerization are calculated from kinetic data of the anionic oligomerization of methyl methacrylate initiated by methyl α-lithioisobutyrate in THF at 25°C, and of the “disproportionation” of living oligomers. The numeric method reported earlier was improved. The rate constants of cyclization decrease with chain-length, due to increasing steric hindrance. The rate constants of polymerization depend on the concentration of active centres, due to the formation of associates. Rate and equilibrium constants of polymerization decrease with chain-length. This is discussed in terms of intramolecular coordination…
Immunochemical method for penthiopyrad detection through thermodynamic and kinetic characterization of monoclonal antibodies.
2021
Immunoassays are nowadays being employed for rapid contaminant analysis in clinical, environmental, and agrochemical samples. A thorough characterization of the antibody‒antigen interaction can bring light to the immunoreagent selection process in order to develop sensitive and robust tests. Thus, determination of equilibrium and reaction rate constants is usually recommendable. However, this can be quite tricky for low molecular weight compounds, and competitive strategies are commonly followed to estimate apparent affinity values. In the present study, a collection of monoclonal antibodies to penthiopyrad was raised for the first time, and apparent equilibrium constants were assessed by t…
Adducts of 1,4-diazabutadienes with group IIB metal halides
1981
Abstract The reactions of 1,4-diazabutadienes (or α-diimines) RNC(R′)C(R″)NR, DAB, (R = p -C 6 H 4 OMe, R′ = R″ = H, DAB I ; R = p -C 6 H 4 OMe,R′ = H, R″ = Me, DAB II ; R = p -C 6 H 4 OMe, R′= R″ = Me; DAB III ; R = CMe 3 , R′ = R″ = H, DAB IV ) with MX 2 M = Zn, Cd, Hg; X = CI, Br) yield in general 1/1 adducts. These species are assigned a monomeric configuration with a σ,σ′-N,N′, chelating DAB ligand for M = Zn, Hg, whereas the CdCl 2 adducts have polymeric structures with terminal and/or bridging chlorides. In the reactions of CdCl 2 with DAB I or DAB IV polymeric species [(CdCl 2 ) 2 (DAB)] x are obtained in which all chlorides are bridging. Spectrophotometric dissociation equilib…
The heat of transfer in a chemical reaction at equilibrium.
2007
International audience; We study a reacting mixture (2F $ F2) in a temperature gradient. We had previously used boundary-driven non-equilibrium molecular dynamics (NEMD) simulations to study this system, and found that the reaction was close to local chemical equilibrium in temperature gradients up to 1012 K/m. Using the condition of local chemical equilibrium, we show that the heat of transfer of the reacting mixture is equal to minus the enthalpy of the reaction. The fact that the sign of the heat of transfer is determined by the type of reaction adds insight to the discussion of the origin of the sign
Copolymer−Cyclodextrin Inclusion Complexes in Water and in the Solid State. A Physico-Chemical Study
2008
The formation of inclusion complexes (ICs) composed of cyclodextrins (CDs) and poly(ethylene oxides)-poly(propylene oxides)-poly(ethylene oxides) (PEO-PPO-PEO) was studied. To this purpose, native and hydroxypropyl cyclodextrins with different cavity size were chosen. The PEO-PPO-PEO copolymers were selected to study the role of the molecular weight, keeping constant the hydrophilic/hydrophobic ratio, and the hydrophilicity. The volumetric studies at 25 degrees C allowed to determine the equilibrium constant and the volume change for the IC formation in water as well as the IC stoichiometry. Surface tension experiments evidenced that the copolymer and the CD interfacial behavior is controll…
Assignment of complex species by affinity capillary electrophoresis: The case of Th(IV)‐desferrioxamine B
2020
International audience; The electrophoretic mobility change of desferrioxamine B (DFO) was monitored by UV absorption spectrophotometry upon increasing the thorium(IV) concentration in the background electrolyte at two acidities ([HClO4]Tot = 0.0316 and 0.0100 M). These data enabled to assess the speciation model and to determine the equilibrium constant of [Th(DFO)H2]3+ at fixed ionic strength (I = 0.1 M (H,Na)ClO4). Affinity capillary electrophoresis (ACE) turned out to be most helpful in identifying the complexed species by ascertaining its charge and protonation state. The assignment of the correct stoichiometry relied on the reliable estimation of the electrophoretic mobility by assumi…
The azide/tetrazole equilibrium: an investigation in the series of furo- and thieno[2,3-e]tetrazolo[3,2-d]pyrimidine derivatives
2016
Abstract Starting from 7(8)-chlorofuro(thieno)[3,2- d ]pyrimidines 1 , the corresponding 7(8)-hydrazinofuro(thieno)[3,2- d ]pyrimidines 2 were obtained by reaction with hydrazine. By treatment with nitrous acid, compounds 2 gave fused furo- and thieno[2,3- e ]tetrazolo[1,5- c ]pyrimidines 3 T and 4 T in excellent yields, which in solution exist in equilibrium with 7(8)-azidofuro(thieno)[3,2- d ]pyrimidines 3 A and 4 A . Compounds 3 T / 3 A and 4 T / 4 A represent useful substrates for investigating the azide/tetrazole equilibrium: it has been examined as a function of solvent, temperature, and their structure. We have observed that, in solution, in both 3 and 4 the equilibrium was strongly …
Thermodynamics of competing oxidation reactions of allyl methyl disulfide by hydrogen peroxide: a first principle molecular computational study on th…
2008
Allyl methyl disulfide, a peroxide scavenger, was studied together with three isomeric (two sulfoxides and one epoxide) forms of its mono-oxidized products. After a full conformational study of the reactant and three isomeric oxidized forms, the geometries were optimized at B3LYP/6-31G (d) level of theory. The epoxide form turned and to be more stable than either one of the two isomeric sulfoxides. Changes for Thermodynamic functions of oxidation reactions were calculated and from the δGreaction values the equilibrium constant for the interconversions of the oxidized products were estimated. Bader-type AIM analyses were performed on the electron density, computed at the B3LYP/6-311++G (d,p)…
Ion Pairing in the Analysis of Voltammetric Data at the ITIES: RbTPB and RbTPBCl in 1,2-dichloroethane
1995
The association of rubidium-tetraphenylborate (RbTPB) and rubidium-tetrakis(-chlorophenyl)borate (RbTPBCl) ion pairs in the organic solvent 1,2-dichloroethane (DCE) have been obtained from condutivity and voltammetric data. Conductivity measurements given K RbTPBCl =43 100 M -1 and yield a lower bound for K RbTPB (K RbTPB > 70000 M -1 ). The latter association constant is at variance with the previously accepted value. A method for analysing voltammetric data which allows for the determination of the association constants is presented. The positive polarization limit where the transfer of Rb + takes place is shifted by ca. 200 mV when changing the anion of the organic base electrolyte from …