Stability Constants for 1:1 Complexes Formed between2-hydroxypropyl-β-Cyclodextrin with an Average Substitution Degree of 4.4 and Benzene and Alkylbenzenes as Guests by Modified Static Head-Space Gas Chromatography Method

Modified static head-space gas chromatography method (M-SHSGC method) was used to determine the stability constants of benzene and alkylbenzenes with 2-hydroxypropyl-β-cyclodextrin inclusion complexes. The 1:1 stability constants were in agreement with those obtained by conventional SHSGC method. The M-SHSGC method precludes the necessity of the calibration curve by the use of Henry’s law constant of guest. Consequently, it is more advantageous than conventional SHSGC method because the time required to determine the stability constant is markedly reduced.     

Structure-Stability Study of Cyclodextrin Complexes with Selected Volatile Hydrocarbon Contaminants of Soils

The association constants for the inclusion compounds of various hydrocarbons (linear alkanes, cycloalkanes, aromatics) with different cyclodextrins (CDs) in aqueous solution have been determined using static headspace gas chromatography (SHSGC). The structure-stability relationship was examined.     

Structure-Stability Study of Cyclodextrin Complexes with Selected Volatile Hydrocarbon Contaminants of Soils

The association constants for the inclusion compounds of various hydrocarbons (linear alkanes, cycloalkanes, aromatics) with different cyclodextrins (CDs) in aqueous solution have been determined using static headspace gas chromatography (SHSGC). The structure-stability relationship was examined.     

A study of complexation thermodynamic of humic acid with cadmium (II) and zinc (II) by Schubert's ion-exchange method

The complexation of humic acid from Azraq Oasis with two heavy metal ions Cd(II) and Zn(II) was investigated at pH 4 and 5 under constant ionic strength of 0.1 and at different temperatures (25, 35, 45, 55 and 65 °C). This investigation was done by using Schubert's ion-exchange equilibrium method, and its modified version.The derived conditional stability constants (log β_n) for these two metal-humate complexes were determined; they formed 1:1 and 1:2 complexes. It was found that the conditional stability constants (log β_n) increased by increasing pH and temperatures for all metal-humate complexes. It was found that the conditional stability constant log β₁ for Cd-humate is bigger than Zn-humate at all the desired temperatures and at pH 4 and 5.The derived constants and their temperature dependences have been used to calculate the corresponding thermodynamic parameters ΔG, ΔH, and ΔS, the results indicate that the stability of these complexes derives from very favorable entropy.     

Calculation of indirect nuclear spin-spin coupling constants within the regular approximation for relativistic effects

A new method for calculating the indirect nuclear spin-spin coupling constant within the regular approximation to the exact relativistic Hamiltonian is presented. The method is completely analytic in the sense that it does not employ numeric integration for the evaluation of relativistic corrections to the molecular Hamiltonian. It can be applied at the level of conventional wave function theory or density functional theory. In the latter case, both pure and hybrid density functionals can be used for the calculation of the quasirelativistic spin-spin coupling constants. The new method is used in connection with the infinite-order regular approximation with modified metric (IORAmm) to calculate the spin-spin coupling constants for molecules containing heavy elements. The importance of including exact exchange into the density functional calculations is demonstrated.     

Calculation of stability constants for the chiral selector-enantiomer interactions from electrophoretic mobilities

Interactions of chiral selectors with enantiomers or with other chiral analytes, underlying their electrophoretic separations, are particular cases of interactions of dissolved species. The interaction model that describes these reversible, fast interactions is simple. Equations describing the model are also simple and applying equations for the calculation of respective equilibrium constants to experimental data is easy using computers. Obtaining the experimental mobility data, necessary for the calculation, is the critical step on the way to stability constants quantitating the strengths of interactions of chiral selectors with enantiomers and other analytes. These data are decisive for both the accuracy and precision of the calculated constants. The meaning and applicability of the particular constant depend on the type of the constant. The common method for the determination of stability constants from electrophoretic migration data is reasonable for low and medium stability constants. For stronger complexing, characterised by stability constants of the order of 10(4) l/mol, typical of affinity chiral selectors, the method becomes unreliable. For strong complexing giving constants of the order of 10(5) or higher of or higher the method is not applicable in its commonly used form.     

极谱配位吸附波测定配合物表观稳定常数的方法研究

对目前利用配位吸附波测定配合物表观稳定常数的常用方法进行了修正,提出了更具有普遍适用性的测定配合物表观稳定常数的理论公式,并对计算方法进行了探讨,获得了预期的满意的结果。     

A Method for the polarographic determination of the stability constants of mixed complexes

A new method for determining the stability constants of mixed complexes is proposed which is especially appropriate when only the mixed complex 1:1:1 is formed. In order to verify this method, the coordinate system Pb(II)-SCN^?-NO^?₃ has been studied polarographically in aqueous medium of a constant ionic strength of μ = 1.0 M. Using our knowledge of the stability constants of simple complexes and applying this method we obtain β₁₁ = 8 for the mixed complex.     

柱上衍生反相色谱法测定金属配合物的稳定常数

提出一种计算金属配合物稳定常数的新方法。应用住上衍生反相高效液相色谱法,以二乙基二硫代氨基甲酸钠为配体,测定金属配合物的保留时间,用以推导金属配合物的稳定常数。     

Spectrophotometric studies on 5,7-dibromo-8-aminoquinoline chelates of some bivalent transition metals

The acid dissociation constant of 5,7-dibromo-8-amino-quinoline and the stability constant of 1:1 chelates of some bivalent transition metals were determined spectrophotometrically in 50% v v dioxan-water medium at an ionic strength of 0.50 at 25.0 +/- 0.1 degrees and compared with those of 8-aminoquinoline. The dissociation constant was found to be 7.54 x 10(-2) and the stability constants (log K(1)) were 2.3 (copper), 1.8 (nickel), 1.8 (zinc), 2.2 (cobalt) and 1.6 (cadmium), respectively. The dissociation constants are greater and the stability constants smaller than the corresponding values for 8-aminoquinoline and 8-quinolinol.     

Physico-chemical studies on the chelation behaviour of acenaphthenequinone monothiosemicarbazone (AQTS) with some bivalent metal ions

Summary The stability constants of the chelates formed from acenaphthenequinone monothiosemicarbazone and magnesium(II), manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) or cadmium(II) have been determined pH-metrically in 75% v/v aqueous dioxan at various ionic strengths of NaClO₄ and at different temperatures. The method of Bjerrum and Calvin^{(1, 2)} as modified by Irving and Rossotti⁽³⁾, has been used to determine the ñ and pL values. The stability constants were calculated on an IBM 360 FORTRAN-IV computer patterned after that of Sullivanet al. ⁽⁴⁾ to give _n values using a weighted least squares method. The S_min, values were also calculated. The thermodynamic stability constant has been determined by extrapolating the log K₁ vs plot at zero ionic strength. The other thermodynamic functions have been calculated from the stability constants obtained for different temperatures at constant ionic strength. The bivalent metal stability sequence of AQTS chelates is in agreement with reported metal orders for other chelating reagents. The order of free energies and enthalpies of chelate formation for AQTS are: Mn²⁺2+2+2+>Zn²⁺.     

介质对配合物稳定性的影响I.Cu(SCN)^+-NaNO3-C2H5OH-H2O体系

本文用分光光度法测定了25℃时配阳离子Cu(SCN)^+在乙醇-水介质中的稳定常数.乙醇在混合溶剂中的重量百分数为0,5,10,15,20和25.用NaNO3调节溶液离子强度I=0.2--2.0mol.dm^-^3.实验的pH=1.5--1.6.本文提出了基于Pitzer方程式的曲线拟合法,确定混合溶剂中配合物的热力学稳定常数.讨论了该常数和一级介质效应与溶液组成和介电常数的关系.     

Investigation of drug-cyclodextrin complexes by a phase-distribution method: some theoretical and practical considerations

The purpose of the study was to evaluate an octanol-water phase distribution method for investigation of drug/cyclodextrin (D/CD) complexes and to compare stability constant values obtained by this method to values obtained by the phase solubility method. A general equation for determination of 1 : 1 D/CD complex stability constant (K1 : 1) from the slope of a phase-distribution diagram (a diagram of the reciprocal of the apparent partition coefficient vs. the total CD concentration) was derived. The equation accounted for the possible inclusion of the organic solvent in the CD cavity and the gradual saturation of the CD binding with increasing concentration of the guest compound. This method was used to determine K1 : 1 for 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD) complexes of hydrocortisone, prednisolone, diazepam, beta-estradiol and diethylstilbestrol. These values were comparable to K1 : 1 values determined by the phase-solubility method. The phase-distribution method could also be applied to determine stability constants for the neutral and ionic forms of the weakly acidic drugs, naproxen and triclosan and the weakly basic drug lidocaine. The phase-distribution method is a very versatile and fast method and has the advantage, compared to the phase-solubility method, that it only requires very small drug samples. Thus, this method would be suitable for screening of new drug candidates.     

Conditional Stability Constant Determination of Metal Aquatic Fulvic Acid Complexes

Abstract

An ion-exchange chromatography/atomic absorbance spectroscopy method for the determination of the conditional stability constants for metal complexes of an aquatic fulvic acid is described. Employing the Scatchard model, conditional stability constants were determined for metal(II) fulvic acid complexes of cadmium, copper, nickel and zinc at pH 7. The effect of pH on the stability constant of the copper-fulvic acid complex is also described.     

Synthesis of Low Dielectric Constant Polyetherimide Films

As the demand for downsizing in microelectronics is increasing, devices require material with lower dielectric constant accordingly. The dielectric constants for most polyimide (PI), including polyetherimide (PEI), films are ∼3.5. In this study, we modified the PEI by incorporating various monomers (fluorinated dianhydride 6FDA and phenylene ether diamines) to reduce the dielectric constant. The dielectric constants of synthesized PEIs decreased with increasing amounts of 6FDA content and phenylene ether units. The T_g decreased gradually with PEI containing longer phenylene ether units, but increased with the content of 6FDA. The thermal decomposition temperatures at 10% weight loss were ∼550 °C, indicating that these PEIs have high thermal stability. Both the tensile strength and the modulus decreased with the PEI containing longer phenylene ether units. The PEI synthesized with 40% 6FDA dianhydride and 1,4-bis(4-aminophenoxy)benzene (pBAB) diamine has the lowest dielectric constant of 2.78 at 1 MHz.     

Determination of the stability constants of uranyl complex with 8-hydroxyquinolinium sulfate

8-Hydroxyquinoline (8-HOQ) is known as an important chelating agent for several metal ions. This compound is practically insoluble in water. For this reason, in this study its water soluble sulfate salt has been used for complexing uranyl ions and the stability constants of the complex have been determined. The Irving-Rosotti method computing the Calvin-Bjerrum pH-titration data, was applied. Finally, the stability constants of the complex formed between (8-HOQN-H)₂SO₄ and uranyl ions were found to be lgK₁=8.25 and lgK₂=4.15, the overall stability constant being {ie55-1}.     

Determination of Stability Constants for Alkanol/α-Cyclodextrin Inclusion Complexes using the Surface Tension Method

The stability constants for the inclusion of alkanols with-cyclodextrin (-CD) in aqueous solutionhave been determined using the surface tension method. Dataanalyses assuming 1 : 1 stoichiometry were appliedto estimate the stability constants of thesecomplexes. The stability constants obtained using this methodwere in reasonable agreement with the corresponding values inthe literature. Chemically modified -CDs could not beused in this method because those CDs themselves have surfaceactivity. In addition, the relation between the stability constantsand the carbon number of alkanols is discussed.     

Application of Ion-Exclusion Chromatography to the Study of Equilibria of Anionic Complexes

Abstract

An ion-exclusion chromatographic method for the determination of a stability constant of an anionic metal complex has been devised. The stability constants (1og β₁) of magnesium diphosphate and magnesium triphosphate complexes at 1=0.1 and 15°C were evaluated to be 5.06 and 5.89 in sodium chloride solution.     

Study of coordination equilibria in systems of coexisting mononuclear and polynuclear complexes by an isosbestic point-spectrophotometric method

This paper reports a method for determining the stability constants of complexes in a system of coexisting mononuclear and polynuclear complexes based on analysis of dual isosbestic points. First it is necessary to determine the dissociation degrees of either of the two complexes concerned in two directions, and then their stability constants. With this method, the conditional constant can be evaluated by appropriate treatment and selection of the proper equations for solutions. For demonstration purposes the scandium/Xylenol Orange system was used to test the model and satisfactory results were obtained.     

Bubble particle heterocoagulation under turbulent conditions

An analytical model that enables the calculation of the flotation rate constant of particles as a function of particle size with, as input parameters, measurable particle, bubble, and hydrodynamic quantities has been derived. This model includes the frequency of collisions between particles and bubbles as well as their efficiencies of collision, attachment, and stability. The generalized Sutherland equation collision model and the modified Dobby-Finch attachment model developed previously for potential flow conditions were used to calculate the efficiencies of particle-bubble collision and attachment, respectively. The bubble-particle stability efficiency model includes the various forces acting between the bubble and the attached particle, and we demonstrate that it depends mainly on the relative magnitude of particle contact angle and turbulent dissipation energy. The flotation rate constants calculated with these models produced the characteristic shape of the flotation rate constant versus particle size curve, with a maximum appearing at intermediate particle size. The low flotation rate constants of fine and coarse particles result from their low efficiency of collision and low efficiencies of attachment and stability with gas bubbles, respectively. The flotation rate constants calculated with these models were compared with the experimental flotation rate constants of methylated quartz particles with diameters between 8 and 80 micro m interacting with gas bubbles under turbulent conditions in a Rushton flotation cell. Agreement between theory and experiment is satisfactory.