FORMATION AND DISSOCIATION KINETICS OF THE STRONTIUM(II) COMPLEX OF CRYPT AND C222 IN BINARY DIMETHYLSULFOXIDE-ACETONITRILE MIXTURES

Abstract

The dissociation and the formation rates of the Sr ²⁺ - C222 cryptate in different dimethylsulf-oxide-acetonitrile mixtures have been studied spectrophotometrically using murexide as a metallochromic indicator. In all solvent mixtures used, the ratio of the rate constants for dissociation and formation of the cryptate was found to be in agreement with the formation constants obtained by an independent equilibrium spectrophotometric technique. The activation parameters E _a, δH ^? and δS ^? for the formation and dissociation of the cryptate were determined from the temperature dependence of the corresponding rate constants, and found to be strongly solvent dependent. There is a linear relationship between the logarithm of the formation constant as well as the activation parameters and the mol fraction of acetonitrile in the mixed solvent.     

Chromatographic study of four sesquiterpenoids in volatile oil of Curcumae Rhizoma on reverse phase stationary phase with methyl-β-cyclodextrin as mobile additive

Abstract

The elution behavior of four sesquiterpenoids in volatile oil of Curcumae Rhizoma on reverse-phase high-performance liquid chromatography with methyl-β-cyclodextrin as mobile phase additive was studied, including germacrone, curzerene, furanodiene, and β-elemene. Stoichiometric ratio and apparent formation constants of inclusion complex formed by methyl-β-cyclodextrin and each analyte were calculated by varying the concentration of the additive in the mobile phase composed of methanol and water (90:10, v/v), in which the association constant for inclusion complex formed by the organic modifier methanol and methyl-β-cyclodextrin was also determined. Results showed that the stoichiometric ratio of all the inclusion complex was 1:1 when 0–9?mmol L^?1 of methyl-β-cyclodextrin was added in the mobile phase. Unusual retention behavior of the analyte germacrone was found, which was further investigated by the calculation of thermodynamic parameters. Meanwhile, enthalpy and entropy of the inclusion complexes and solute-stationary phase interactions were determined by linear van’t Hoff plots.     

Study of protein association and micelle formation in surfactants by microcolumn exclusion chromatography

The application of microcolumn exclusion chromatography to the determination of equilibrium and kinetic association constants for proteins is described. Taking phospholipase A₂ as an example, the relationship between association and enzymatic activity was investigated. A procedure for determination of the critical concentration of micelle formation (CCM) in surfactants was developed.     

A review of: “Instrumental HPTLC,by W. Bertsch,S. Hara,R. E. Kaiser,and A. Zlatkis,editors, H. Verlag,Heidelberg, West Germany, 1980, 390 pp., cloth bound.”

Abstract

To understand the retention mechanisms involved in reversed-phase micelle chromatography, two models were examined to study the temperature and micelle concentration contribution to the retention process. the first model described the temperature contribution, using the van's Hoff equation, for each of the three equilibria: micelle-to-extra-micelle-mobile-phase, extra-micellar-mobile-phase-to-stationary phase and micelle-to-stationary phase. the second model described the temperature contribution on k' irrespective of the various equilibria involved. It was found that the enthalpy of retention obtained with the second model decreased with increasing micelle concentration. This contradicted a primary assumption in the first model that the equilibrium constants were independent of micelle concentration. No relationship was found between the enthalpy of retention evaluated with either model and the polarity of the partitioned solute molecules. A correlation was found between the entropy of retention and the polarity of these molecules. Fluorescence studies indicated that the micelle solvated molecules were probably located in the core of the micelles which contained other mobile phase components such as 1-propanol and water.     

Dichroic Probe of the Equilibrium Constant of the Distribution of Bilirubin to Human and Bovine Serum Albumins

Abstract

We describe here a method to evaluate the equilibrium constant of the distribution of a ligand, bilirubin, to two different albumins (human and bovine serum albumins, HSA and BSA) and hence to determine the association constant of the ligand to an albumin (in this case HSA) with the knowledge of the association constant of the ligand to the other albumin (in this case BSA). The circular dichroic (CD) spectra of bilirubin (BR) induced by HSA and BSA are characteristically different. If in a pre-formed BSA-BR complex HSA is added, the negative bisignate CD spectrum of BSA-BR progressively changes sign characteristic to that of HSA-BR (positively bisignate). This change in dichroism has been used to calculate the equilibrium constant K of the process: BSA-BR + HSA = HSA-BR + BSA, the value of K comes to be 1.25. The individual association constant of BSA-BR has been determined fluorimetrically to be 2.7 × 10⁷ M-¹. Since, K of the above process must be the ratio of the individual association constants of HSA-BR and BSA-BR. the association constant of HSA-BR comes to be 3.37 × 107_M^?1      

An NMR Study of the Equilibration of d‐Glucaric Acid with Lactone Forms in Aqueous Acid Solutions

The aqueous solution equilibration of d‐glucaric acid with its lactone forms was studied by NMR with and without acid catalysis. The kinetics of the approach to equilibrium were simulated, and approximate equilibrium and rate constants were obtained.     

Bestimmung der Extraktionskonstanten der Tellur-Pyrasolindithiocarbaminate

Abstract

In this work the exchange reactions between the ion Te(IV) in the aqueous phase and the aryl substituted pyrasolindithiocarbaminates of zinc into chloroform have been investigated. The equilibrium (exchange) constants of these reactions have been determined experi mentally. The extraction constants and two-phase stability constants of Te(PDTC)₄ have been calculated.     

An NMR study of phenol self-association

This paper presents a study of the chemical shift of the phenol hydroxyl group as a function of concentration and temperature in cyclohexane, methylcyclohexane and carbon tetrachloride solutions. The chemical shift of monomeric phenol has been found. For these solutions monomertrimer equilibrium is observed within the entire temperature range and within a wide concentration range. At low phenol concentrations, from 1 to 3 mole-%, the monomer-dimer equilibrium is observed in cyclohexane, methylcyclohexane and carbon tetrachloride solutions. Chemical shift of the hydroxyl group of trimeric phenol is temperature-dependent. From the experimental data the association constants and thermodynamic functions of the systems under study have been determined. The association constants differ for the above systems at the same temperatures. Association entropy ΔS changes from one system to another, while ΔH is the same for all systems.     

Studies of Association Effects in Liquid Adsorption Chromatography with Ternary Mobile Phases

Abstract

In this paper a model of chromatographic process, which takes into account molecular association in the mobile phase is discussed. This model is applied to study the association effects in liquid adsorption chromatography with ternary mobile phases. Efects of nature of the eluent and structure of the chromatographed substance on the type of association is also investigated. Association effects in the chromatographic system containing ternary mobile phase can be evaluated by means of equations describing chromatographic process with the binary mobile phases.     

Acidic Phosphorus Esters,Synthesis and Structure-Reactivity Studies as Ligands

Abstract

Methods for the synthesis of five types of acidic phosphates, phosphonates as well as phosphinates have been described. The mechanism of extraction of various metals by these compounds is examined. A free energy relationship existed in plotting equilibrium constants against either pKa or ?σ values of the acidic organophosphorus compounds under investigation. Steric effects, which is closely related to the configuration of the coordination compounds play an important role in these extraction systems as expected. A trial on estimation of Es values in extraction reaction was proposed.     

Cationic Copolymerization with Depropagation. The Copolymerization of α-Methylstyrene and Styrene

ABSTRACT

To evaluate the existence of the depropagation reaction in the copolymerization of vinyl monomers, the cationic copolymerization of α-methylstyrene with styrene was studied. The copolymer composition exhibited an extensive dependency on the temperature of polymerization and the monomer concentration, this fact not being explained by the Mayo-Lewis equation. Treatment of the copolymerization in terms of the depropagation reaction led to an estimate of the monomer reactivity ratio and the equilibrium constant between the polymer and the monomer of α-methylstyrene. A comparison of the equilibrium constants thus obtained with those reported in the literature indicates that the magnitude of the equilibrium constants depends on the sequence length of α-methylstyrene units. By extrapolation to long sequence length, the equilibrium constants approach the values which are reported for high molecular weight poly(α-methylstyrene).     

Study of Binding of Benzyl-Thiouracil to Human Serum Albumin by Gel Filtration Chromatography

Abstract

The binding of benzyl-thiouracil to human serum albumin was studied at 37°C and pH 7.4 by Sephadex filtration chromatography based upon Hummel and Dreyer's method. As the benzyl-thiouracil (ligand) was adsorbed on to the gel matrix, the free ligand concentrations had to be corrected through the ligand distribution between the stationary and mobile phases.

A good agreement was found between binding parameters—calculated by this method and by the classical method (equilibrium dialysis). Binding is characterized by one binding site with a moderate association constant (K₁ = 5.7 × 10⁴ M^-1) and two binding sites with a low association constant (K₂ = 7.8 × 10³ M^-1).     

Kinetics and mechanism of interaction of Pt(II) complex with bio-active ligands and in vitro Pt(II)-sulfur adduct formation in aqueous medium: bio-activity and computational study

Kinetics of interaction between [Pt(pic)(H₂O)₂](ClO₄)₂, 2 (where pic = 2-aminomethylpyridine) with the selected ligands DL-methionine (DL-meth) and DL-penicillamine (DL-pen) have been studied spectrophotometrically in aqueous medium separately as a function of [2] as well as [ligand], pH and temperature at constant ionic strength. The association equilibrium constants (K_E) for the outer sphere complex formation have been evaluated together with the rate constants for the two subsequent steps. Activation parameters (enthalpy of activation ΔH^≠ and entropy of activation ΔS^≠) were calculated from the Eyring equation. An associative mechanism of substitution is proposed for both reactions on the basis of the kinetic observations, evaluated activation parameters, and spectroscopic data. Structural optimizations, HOMO-LUMO energy calculation, and Natural Bond Orbital (NBO) analysis of 2–4 were carried out with Density Functional Theory. Bonding mode of thiol and thio-ether is confirmed by spectroscopic analyses and NBO calculation. Cytotoxic properties of 2–4 were explored on A549 carcinoma cell lines; DNA-binding properties of the complexes were also investigated by gel electrophoresis.     

Random Error Analysis in the Determination of Equilibrium Constants of Very Stable Metal Complexes.

Abstract

The analysis of random errors is discussed for the equilibrium constants of very stable metal complexes, determined through competitive potentiometric methods. Prior to this analysis the calculation of standard deviations both for overall and stepwise equilibrium constants is considered. Clues are given as to how a system can be properly characterized. To illustrate the error analysis, the following systems were selected: Cu(II) and L-2,6-diaminohexanoic acid (L-lysine); Cu(II) and ethylene diaminotetraacetic acid (EDTA); and Cu(II), EDTA and 1,2-dihydroxybenzene (catechol).     

Equilibrium and kinetic studies on ligand substitution reactions of chloromethyl(aquo)cobaloxime with aromatic and aliphatic N-donor ligands

Equilibria and kinetics of the reactions of chloromethyl(aquo)cobaloxime with histamine, histidine, glycine and ethyl glycine ester were studied as a function of pH at 25°C, 10 M ionic strength (KCl) by spectrophotometric techniques. Comparison of equilibrium constants and rate constants tells that the order isK _Hisdn >K _Hiamn >K _Gly >K _EtGlyest. The rate of substitution of H₂O varies with the pKa of the incoming ligand and nucleophilic participation of the ligand in the transition state. The rate constants and equilibrium constants are correlated to the hardness and softness of the ligands and the Co(III) of cobaloxime.     

The ring-opening reactions of propylene oxide with chloroacetic acids

The association constants, k_d, of dichloroacetic acid (DCA) with ethers (tetrahydrofuran, tetrahydropyran, dibutyl ether, 1,4-dioxane) were measured in CCl₄ from 20°–40° using near IR spectra. A linear relationship between log₁₀K_D and log₁₀K_p was found, where K_p was the association constant of phenol with ethers. On the basis of their relationship the association constants of DCA with propylene oxide (PO) were estimated from those of phenol with PO. Furthermore, the ring-openings of PO with chloroacetic acids (trichloroacetic acid (TCA) or DCA) were studied kinetically in toluene. It was found that the PO-TCA reactions obeyed the second-order kinetics dependent on the first order both in the PO concn and in the TCA concn, and that the PO-DCA reactions obeyed the third-order kinetics on the first order in the PO concn and on the second order in the DCA concn. The elementary reaction rate constants were estimated on the basis of measured rate constants and estimated equilibrium constants and activation enthalpies were obtained from their temp dependence to be 13.5 $\text{kcal}\text{mol}$ in the PO-TCA reaction and 19.7 $\text{kcal}\text{mol}$ in the PO-DCA reaction. The mechanism was based on the activation enthalpy of elementary reaction and it was concluded that the main factor governing the reaction was the extent of activation of the protonated oxirane (the extent of polarization of the C-O bond in the oxirane ring).     

Determination of the Stability Constants of Inclusion Complexes of p-H-37-(2-carboxy-methyloxy)-calix-[6]-arene and p-sulphonato-37-(2-carboxy-methyloxy)-calix-[6]-arene with 15 Amino acids by RP-HPLC

Reversed-phase high performance liquid chromatography (Separon SGX CN, UV detection at 254~nm and water as mobile phase) was applied to thestudy of the host–guest complexation ofp-H-37-(2-carboxy-methyloxy)-calix-[6]-arene (1) and p-sulphonato-37-(2-carboxy-methyloxy)-calix-[6]-arene (2)with 15 amino acids in the mobile phase. It was established that the formation ofthe inclusion complexes results in changes in the retention times and capacity factorsof amino acids. Stability constants of the complexes were determined. The variations instability constant values may be explained in terms of the different interactions, whichmay occur between amino acids and 1 and 2.     

Kinetic Studies of the Addition of Formaldehyde to Carbamates

Abstract

The rate of formation and dissociation of alkyl N-methylol-carbamates in basic media were studied by electrochemical techniques. The effects of the presence of various N-substituents on these rate constants and equilibrium constants -were investigated. The reactions were carried out at 20. 4°C and pH 12. 45 in water and in a 66% water and 34% t-butanol (v/v) solvent. The rate constants were higher when water was used as the solvent.     

Bestimmung der Stabilitätskonstanten gemischter Hexahalogenokomplexe von Osmium(IV)

Determination of the Stability Constants of Mixed Hexahalogeno Complexes of Osmium(IV) The individual and total stability constants of the complex series [OsX_xY_6?x]^2?; X ≠ Y = Cl, Br, I; x = 0–6 are determined by radiometric measurements of the equilibrium concentrations of all compounds. The thermodynamical stability increases from the hexabromo- over the hexachloro- to the hexaiodo-complex. The total stability constants are in ratio of 1:5,2:1225. With the individual constants the equilibrium diagrams are calculated. The photometric determination of the cis/trans ratio in complexes with x = 2, 3, 4 gives the statistical distribution of the ligands in the octahedrons. The relationship between thermodynamical and kinetical data is discussed.     

Phase-equilibrium calculations for n-alkane + alkanol systems using continuous thermodynamics

A new association model based on continuous thermodynamics is introduced and applied to six systems of the type n-alkane (n-hexane, n-heptane, n-octane) + alkanol (methanol, ethanol). The alkanol is considered to be a mixture of chain associates with the composition described by a continuous distribution function. This distribution function is derived as an analytical expression from the mass action law applied to the association equilibrium. To consider the entropic contribution originating from the size differences of the molecules (associates) activity coefficients based on Flory–Huggins model are included in the mass action law. Unlike the molecular-mass distribution of a polymer the chain-length distribution of the associates depends on the temperature and on the mole fraction of the alkanol. The treatment of vapor–liquid equilibrium and liquid–liquid equilibrium is similar to that of an oil system or of a polymer solution using continuous thermodynamics. Different to other chemical models of association there is no additive split into a physical and a chemical contribution. The equilibrium constants of association were fitted to vapor-pressure data of methanol and ethanol. The model needs only one interaction parameter being independent of temperature and taking the same value for all systems studied. Considering the simplicity of the model, both the liquid–liquid equilibrium of the three methanol systems and the vapor–liquid equilibrium of all six systems are predicted with reasonable accuracy.