Program MINIQUAD75 Research Articles

Solvent Effect on Protonation Equilibria of L-Histidine and 1,10- Phenanthroline in 1-Propanol-Water Mixtures

Solute-solvent interactions of L-Histidine and 1,10- Phenanthroline have been studied in varying compositions (0-60% v/v) of 1-propanol-water mixtures using pH-metric technique. The ionic strength of 0.16 mol. L-1 is maintained at 303±0.1 K and protonation constants were calculated by using the computer program MINIQUAD75. The best suited chemical model of protonation equilibria was selected based on the statistical parameters. The solvent effect on log K values increased with the inverse of dielectric constants of 1-proponol-water mixtures and the trend was explained based on operation of electrostatic forces on protonation equilibria. This study also discusses the distribution of species and effect of influential parameters on the protonation constants.

Effect of triton-X100 on ternary complexes of cobalt (II), nickel(II),copper (II) & zinc(II) with aspartic and citric acids

A computer based investigation has been made pH-metrically on the chemical speciation of mixed ligand complexes in ternary systems consisting of cobalt (II) nickel(II), copper (II) and zinc (II) with aspartic and citric acids in triton- X 100 micellar media. The trend of the variation in the stability constants with changing dielectric constant as well as mole fraction of the medium is explained based on the electrostatic interactions of the side chains of the ligands, charge neutralization, chelate effect, stacking interactions and hydrogen bonding. The existence of different ternary species is established from modelling studies using the computer program MINIQUAD75. Distribution diagrams with pH at different compositions of surfactant and structures of plausible ternary complexes are presented.

Equilibrium studies of binary and mixed-ligand dimethyltin(IV) complexes involving homopiperazine and DNA constituents with reference to the antitumor activity

ABSTRACT The reaction of dimethyltin(IV) dichloride (DMT) with homopiperazine (HPIP) was studied. The equilibria of the complexes formed in solution were investigated. The complexes detected are of 1:1 stoichiometry in addition to the protonated and hydrolysed species. The complex formation constants were determined by the use of potentiometric technique and the non-linear computer program Miniquad-75. The dielectric constant effect of the reaction medium on the formation of the complexes was investigated. Formation constants of the complexes were determined at different temperatures and the thermodynamic parameters as ΔH° and ΔS° were estimated and discussed. The ternary complexes of dimethyltin(IV) with HPIP and DNA constituents are formed by a simultaneous mechanism. Their formation constants were determined. The speciation diagrams of the binary and mixed-ligand complexes were evaluated.

Mixed Ligand Complexes of Transition Metal Ions with Selective Bio-Ligands in Surfactant-Water Mixtures

Chemical speciation of ternary complexes of L-arginine and L-aspartic acid with essential transition metal ions was studied pH metrically. The following MLX, MLXH and ML2X ternary species are detected and reported in this paper. The existence of different ternary species is established from modeling studies using the computer program MINIQUAD75. The relative concentrations (M: L: X=1:2:2, 1:2:4, 1:4:2) and stabilities of the ternary species are compared with those of binary species. The extra stability associated with the ternary complexes is attributed to factors such as charge neutralization, chelate effect, stacking interactions and hydrogen bonding. Trend in variation of stability constants with the change in the mole fraction of the surfactant in various micellar media is explained on the basis of electrostatic and non-electrostatic forces. Distribution diagrams in relation to pH and plausible structures were presented.

EFFECT OF CATIONIC MICELLES OF CETYLTRIMETHYLAMMONIUM BROMIDE ON PROTONATION EQUILIBRIA OF SALICYLIC ACID DERIVATIVES

To gain more information about the effect of surfactant on salicylic acid derivatives, the stoichiometric protonation constants of 5-Sulphosalicylic acid and 5-Hydroxysalicylic acid in 0.0%-2.5% (w/v) cetyltrimethylammonium bromide (CTAB) - water mixtures were determined at an ionic strength of 0.16 mol dm-3 and at 303 K. A potentiometric method was used and the calculation of constants was carried out using the computer program MINIQUAD75. These protonation constants values have been found to shift in micellar media as compared to those in pure water. The differences in the values have been attributed to the solvent properties of the interfacial and bulk phases involving contribution from the micellar surface potential in the case of charged micelles. The trend of log values of step-wise protonation constants with mole fraction of the medium have been explained based on specific solute-solvent interactions. In this study Distributions of species, percentage of species composition, protonation equilibria and effect of influential parameters on the protonation were also discussed.

Effect of anionic micelles of sodium dodecyl sulfate on protonation equilibria of salicylic acid derivatives

AbstractThe impact of sodium dodecyl sulfate (SDS) on the protonation equilibria of 5-sulfosalicylic acid and 5-Hydroxysalicylic acid has been studied in various concentrations (0.0−2.5% w/v) of sodium dodecyl sulfate solution maintaining an ionic strength of 0.16 mol dm−3 Nacl at 303 K. The protonation constants have been calculated with the computer program MINIQUAD75 and the best fit models are arrived at based on statistical grounds employing crystallographic R factor, χ2, skewness, and kurtosis. These protonation constants values have been found to shift in micellar media as compared to those in pure water. The differences in the values have been attributed to the solvent properties of the interfacial and bulk phases involving contribution from the micellar surface potential in the case of charged micelles. The trend of log values of stepwise protonation constants with mole fraction of the medium have been explained based on electrostatic and non-electrostatic forces operating on the protonation equi...

Speciation of binary complexes of Pb(II) and Cd(II) with L-asparagine in dimethyl sulfoxide - water mixtures

Chemical speciation of L-Asparagine complexes of Pb(II) and Cd(II) in presence of (0-50% v/v) dimethyl sulfoxide(DMSO)-water mixtures has been studied potentiometrically at 303.0 K and at an ionic strength of 0.16 mol L -1 . The models containing different number of species were refined by using the computer program MINIQUAD75. The number of species in the models is chosen based on exhaustive modeling. The predominant species formed are of the type ML 2 , ML 2 H, and ML 2 H 2. The best fit chemical models were chosen based on statistical parameters. The convenience of the models is ascertained by studying the effect of errors in concentrations of ingredients. The trend in variation of stability constants with change in the composition of medium is explained on the basis of predominant electrostatic and non-electrostatic forces. Chemical speciation was discussed based on the distribution diagrams. KEY WORDS : Chemical speciation, L-Asparagine, Dimethyl sulfoxide, Stability constants Bull. Chem. Soc. Ethiop. 2016 , 30(1), 71-78. DOI: http://dx.doi.org/10.4314/bcse.v30i1.6

Chemical Speciation of Binary Complexes of Pb(Ii), Cd(Ii) and Hg(Ii) with L-Methionine in Propylene Glycol -Water Mixture

Chemical speciation of Pb (II), Cd (II) and Hg (II) complexes of L-methionine in 0.0-60.0 % v/v propylene glycol-water mixtures has been studied pH metrically maintaining an ionic strength of 0.16 M at 303 K. The active forms of ligand are LH3 + , LH2 and LH. The predominant species detected are MLH, ML and ML2. Models containing different numbers of species were refined by using the computer program MINIQUAD75. The bestfit chemical models were arrived at based on statistical parameters. The trend in variation of complex stability constants with change in the dielectric constant of the medium is explained on the basis of electrostatic and non-electrostatic forces.

Evaluation of protonation constants of glycylglycine in acetonitrile– and ethylene glycol–water mixtures

Knowledge of the protonation constants of dipeptides is important and necessary for complete understanding of their physiochemical behavior. The effect of dielectric constant of medium on protonation equilibria has been studied by determining protonation constants of glycylglycine pH-metrically in various concentrations (0–60%v/v) of acetonitrile–water and ethylene glycol–water mixtures, at an ionic strength of 0.16 mol L−1 and at 303.0 ± 0.1 K. The protonation constants were calculated with the computer program MINIQUAD75 and selection of the best fit chemical models is based on the statistical parameters. Linear and non-linear variations of stepwise protonation constants with reciprocal of dielectric constant of the solvent mixtures have been attributed to the dominance of electrostatic and non-electrostatic forces, respectively. Distribution of species, protonation equilibria, and effect of influential parameters on the protonation constants have also been presented.

Protonation equilibria of glycylglycine and histamine in aqueous solution of an anionic surfactant

The protonation constants of glycylglycine and histamine are studied in sodium lauryl sulfate–water mixtures (0.5–2.5% w/v) at 303.0 ± 0.1 K at an ionic strength of 0.16 M using a pH-metric technique. The protonation constants are calculated with the computer program MINIQUAD75 and the best fit chemical model is based on the statistical parameters. The effect of solvent on protonation constants is discussed based on electrostatic and non-electrostatic forces operating on the protonation equilibria. Distribution of species, protonation equilibria and effect of influential parameters on the protonation constants are also presented.

Protonation equilibria of L-phenylalanine and maleic acid in cationic micellar media

Solute-solvent interactions of L-phenylalanine and maleic acid have been studied in various concentrations (0.5-2.5% w/v) of cetyltrimethylammonium bromide solution maintaining an ionic strength of 0.16 mol dm-3 at 303 K. The protonation constants have been calculated using the computer program MINIQUAD75 and the best fit models are arrived at based on statistical grounds employing crystallographic R factor, x2, skewness and kurtosis. These protonation constants values have been found to shift in micellar media as compared to those in pure water. The differences in the values have been attributed to the solvent properties of the interfacial and bulk phases involving contribution from the micellar surface potential in the case of charged micelles. The trend of log values of step-wise protonation constants with mole fraction of the medium have been explained based on electrostatic and non-electrostatic forces operating on the protonation equilibria. Distributions of species, protonation equilibria and effect of influential parameters on the protonation constants have also been presented.

Formation of binary complexes of Pb(II), Cd(II) and Hg(II) with maleic acid in CTAB-water mixtures

Complexation of toxic metal ions with maleic acid in (0.0–2.5% w/v) cetyltrimethylammonium bromide (CTAB)–water mixtures has been studied pH-metrically at ambient conditions and an ionic strength of 0.16 mol L-1. The existence of different binary species was established from modelling studies using the computer program MINIQUAD75. The best-fit chemical models were selected based on statistical parameters such as the crystallographic R factor and sum of the squares of residuals in mass-balance equations. The models for binary complex systems contain the chemical species ML2, ML2H and ML3 for Pb(II), Cd(II) and Hg(II) in CTAB–water mixtures. The trend in the variation of stability constants with change in the mole fraction of the medium was explained based on electrostatic and non-electrostatic forces. Distribution of the species with pH at different compositions of CTAB–water mixtures was also presented.

Influence of dielectric constant on protonation equilibria of maleic acid and L-asparagine in acetonitrile water-mixtures

The protonation constants of maleic acid and L-asparagine have been studied pH-metrically in various concentrations (0–50% v/v) of acetonitrile–water mixtures maintaining an ionic strength of 0.16 mol L-1 at 300C. The protonation constants have been calculated using the computer program MINIQUAD75 and are selected based on statistical parameters. Linear variation of step-wise protonation constants (log K) with the reciprocal of the dielectric constant of the solvent mixture has been attributed to the dominance of the electrostatic forces.

Chemical speciation of binary complexes of L-valine with Co(II), Ni(II) and Cu(II) in propylene glycol-water mixtures

Chemical speciation of Co(II), Ni(II) and Cu(II) complexes of L-valine in 0.0-60.0% v/v propylene glycol-water mixtures at an ionic strength of 0.16 mol L-1 and 303.0 K was studied pH-metrically. Models containing different number of species were refined by using the computer program MINIQUAD75. The number of species in the models was chosen based on exhaustive modelling. The best-fit chemical models were arrived at based on statistical parameters. The formation and distribution of different species with varying pH were represented in the form of distribution diagrams. Influence of the solvent on the speciation was discussed based on the dielectric constant of the medium.

Speciation studies of Co(II), Ni(II) and Cu(II) complexes of L-valine in acetonitrile–water mixtures

Chemical speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-valine in 0.0-60.0% v/v acetonitrile-water mixtures was studied pH-metrically at an ionic strength of 0.16 mol L-1 at 303.0 K. The existence of different binary complexes was established from the modelling studies, using the computer program MINIQUAD75. The appropriateness of the model was ascertained by studying the effect of errors in concentrations of the reagents. The trend in variation of stability constants with change in the permittivity of the medium is explained on the basis of electrostatic and non-electrostatic forces. The species distribution diagrams and the plausible equilibria for the formation of the species are also presented.

Chemical speciation of L-proline complexes of Ca(II), Zn(II) and Mn(II) in acetonitrile-water mixtures

Chemical speciation of binary complexes of Ca(II), Zn(II) and Mn(II) with L-proline is investigated pH-metrically in acetonitrile-water mixtures. The stability constants are calculated using the computer program MINIQUAD75. The best-fit chemical models are selected based on statistical parameters and residual analysis. The models for the binary species contained ML+, MLH2+and ML2H+ for Ca(II), Zn(II) and Mn(II). The trend in variation of stability constants with change in the dielectric constant of the medium is explained on the basis of structure forming nature of acetonitrile. Distribution of the species with pH at different variations (0.0-60.0% v/v) in acetonitrile-water mixtures is also presented.

Effect of non ionic micelles on the chemical speciation of binary complexes of Pb(II), Cd(II) and Hg(II) with L-phenylalanine

Complexes of Pb(II), Cd(II) and Hg(II) with L-phenylalanine in the presence of non-ionic surfactants, at an ionic strength of 0.16 mol dm-3 and temperature 303 K are investigated pH-metrically. The existence of different binary complex species is established from modelling studies using the computer program MINIQUAD75. The increased stability of the complexes with increasing micellar content is explained by electrostatic forces. The influence of the micelles on the chemical speciation is discussed based on the mole fraction of the medium. Distribution diagrams of various species of the complexes in relation to pH are presented.

Chemical speciation of 2,3-dihydroxybenzoic acid complexes with some biologically essential metal ions in 1, 2-propanediol–water mixtures

Chemical speciation of Co(II), Ni(II), Cu(II) and Zn(II) complexes of 2,3-dihydroxybenzoic acid in 0.0-60.0% v/v 1, 2-propanediol-water mixtures maintaining an ionic strength of 0.16 mol dm-3 at 303±0.1 K has been studied pH metrically. The predominant complexes formed are ML, ML2 and ML2H2 for Co(II), Ni(II) and Zn(II) and ML, ML2, ML2H and ML2H2 for Cu(II). Models containing different numbers of species were refined by using the computer program MINIQUAD75. Selection of the best fit chemical models was based on statistical parameters and residual analysis. The trend in variation of complex stability constants with dielectric constant of the medium is explained on the basis of electrostatic and non-electrostatic forces. Distributions of species, formation equilibria and effect of influential parameters on the stability constants have been presented. The possible structures of the various species are elucidated on the basis of the analysis of the pH-metric data.

Effect of Dielectric Constant on Protonation Equilibria of l-Aspartic Acid and Ethylenediamine in 1,2-Propanediol–water Mixtures

Solute–solvent interactions of l-aspartic acid and ethylenediamine have been studied in various concentrations (0–60 % v/v) of 1,2-propanediol–water mixtures maintaining an ionic strength of 0.16 mol l−1 at 303 ± 0.1 K using pH-metric method. The protonation constants have been calculated with the computer program MINIQUAD75. Selection of the best fit chemical model of the protonation equilibria is based on SD in protonation constants and residual analysis using crystallographic R-factor and sum of squares of residuals in all mass balanced equations. Linear variation of protonation constants with inverse of dielectric constants of the solvent mixture has been attributed to the dominance of the electrostatic forces. Distribution of species, protonation equilibria and effect of influential parameters on the protonation constants has also been presented.

Chemical speciation of L-glutamine complexes with Co(II), Ni(II) and Cu(II) in cationic micellar medium

The impact of cationic micelles on the protonation equilibria of L-glutamine and chemical speciation of its complexes with Co(II), Ni(II) and Cu(II) have been studied by monitoring hydrogen ion concentration pH metrically at 303 K and at an ionic strength of 0.16 M. The protonation constants and binary stability constants have been calculated with the computer program MINIQUAD75. The best fit chemical models are selected based on standard deviations in the model parameters and residual analysis using crystallographic R-factor and sum of squares of residuals in all mass-balance equations. The trend in the variation of stability constants of the complexes with mole fraction of the surfactant is attributed to the compartmentalization of complexation equilibria. Distribution of species and effect of influential parameters on chemical speciation have also been presented. KEY WORDS: Chemical speciation, complex equilibria, L-glutamine, cationic micelles Bull. Chem. Soc. Ethiop. 2012, 26(3), 383-394.DOI: http://dx.doi.org/10.4314/bcse.v26i3.7