Spectrophotometric determination of acidity constants of salicylaldoxime in aqueous solution at 25 degrees C and ionic strength of 0.5 M controlled with NaCl

The equilibrium constants of salicylaldoxime in water at 25 degrees C, 0.5 M of ionic strength with NaCl and concentration of 1x10(-4) M were determined spectrophotometrically. The spectral data were processed using SQUAD program. The salicylaldoxime in acid medium has the value of pKa1=1.224+/-0.027. In alkaline medium the salicylaldoxime has the values of pKa2=8.551+/-0.024 and pKa3=11.728+/-0.016.     

Speciation of the new ligand di-isopropyliminodiacetoamide with Cu(II) using computational processing and graphical methods

The importance assigned to chelating agents in diverse areas has impelled studies concerning their development as related to metal ions representing a biological concern. The synthesis of di-isopropyliminodiacetoamide (D) is presented in this work. The acidity constant obtained for D was pKa = 5.79 +/- 0.04 with the aid of program SUPERQUAD. The equilibrium constants for D with Cu(II) were obtained with the aid of program SQUAD for CuD2+ and CuD2(2)+ species giving log beta1 = 4.795 +/- 0.002 and log beta2 = 8.374 +/- 0.004, respectively.     

Multiwavelength Spectrophotometric Determination of Dissociation Constants of Mercaptopyrimidines

Abstract

The dissociation constants of some 2- and 6-mercaptopyrimidine derivatives with amino or hydroxy substituents are reported. The constants have been determined at 25° C in 0.1 M KCl aqueous solution. The multiwavelength spectrophotometric data obtained have been 3mlyzed by means of the SQUAD program (Stability Quotients from Absorbance Data).     

High-speed computers as a supplement to graphical methods--V. HALTAFALL, a general program for calculating the composition of equilibrium mixtures

A computer program, HALTAFALL, is described which calculates the equilibrium concentrations of the species in mixtures of any number of components, which can form any number of complexes and solid phases, provided concentrations (or partial pressures) can be used in the equilibrium calculations. Of course, the equilibrium constants must be known and enough data be given about the gross composition. Some applications are indicated. The flexible input rules make it applicable to a variety of problems. From the input information, the program itself devises an efficient plan for solving the simultaneous equations. The program also provides an efficient means of finding out which of many possible solid phases can actually appear in a certain equilibrium mixture.     

Multiparametric curve fitting-IX Simultaneous regression estimation of stoichiometry and stability constants of complexes

A chemical model (i.e., the number of complexes, their stoichiometry and stability constants with molar absorptivities) in solution equilibria may be established by (i) the trial-and-error method in which stability constants are estimated for an assumed set of complexes in the mixture and a fitness test is used to resolve a choice of plausible models to find the true one; (ii) the simultaneous estimation of the stoichiometry and stability constants for species divided into "certain" species for which the parameters beta(pqr), (p, q, r) are known and held constant, and "uncertain" species with unknown parameters which are determined by regression analysis. The interdependence of stability constants and particular sets of stoichiometric indices requires that the computational strategy should be chosen carefully for each particular case. The benefits and limitations of both approaches are compared by means of examples of potentiometric titration data analysis by the POLET(84) program and of spectrophotometric data analysis by the SQUAD(84) program. A strategy for efficient computation is suggested.     

In Process Citation

The basic computer program MICMAC has been developed to fit equilibrium constants to various types of experimental data with a microcomputer. The program uses the very efficient Gauss-Newton-Marquardt algorithm for non-linear least-squares multiparametric refinement. Highly interactive, convenient to use and of modular design, it allows for a rigorous weighting scheme, and it takes account of possible systematic errors. This program is useful for solving problems with several sets of experimental data. Some examples dealing with polarography, pH-metric titration and (13)C-NMR are given, illustrating the versatility of MICMAC. Comparison is made with some recently published programs.     

Spectrophotometric study of the complex formation of 3-(2-hydroxyphenyl)-2-mercaptopropenoic acid with Ni(II) and Zn(II)

The dissociation and complex formation equilibria between Ni(II) and Zn(II) with 3-(2-hydroxyphenyl)-2-mercaptopropenoic acid, at 25 degrees in aqueous 0.1 and 1.0M sodium perchlorate solutions, containing about 1% ethanol, have been studied spectrophotometrically. The data were connected directly from the spectrophotometer to an IBM-PC via a serial interface, using the DUMOD program (written in BASIC), described in the paper. The obtained spectra were treated by the factor analysis program NIPALS in order to determine the number of absorbing species and the experimental error. Dissociation constants of ligand (H(3)L), and formation constants for the complexes Ni(HL), Ni(HL)(2), Zn(HL) and Zn(HL)(2) at 0.1 and 1.0M ionic strengths, refined by the SQUAD program, are reported.     

Sulfoxide as a ligand in iron(II) porphyrinates: S- or O-bound?

In order to study the bonding of sulfoxides to iron(II) porphyrinates, an equilibrium study of Fe(TPP) with tetramethylenesulfoxide (TMSO) has been performed. UV-vis spectra at different concentrations of TMSO have shown distinct character belonging to three species: four-coordinate Fe(II)(TPP), five-coordinate [Fe(II)(TPP)(TMSO)], and six-coordinate [Fe(II)(TPP)(TMSO)2]. The isosbestic points for the low TMSO concentrations suggest that the equilibrium constant K1 is much larger than K2. Analysis of spectral data by the nonlinear least-squares program SQUAD gives K1 = 267 and K2 approximately 1. Even though the five-coordinate species is the dominant species under the synthetic conditions, only the six-coordinate species was crystallized and characterized by an X-ray diffraction study. [Fe(TPP)(TMSO)2] (C52H44Fe-N4O2S2): monoclinic, P2(1)/c, a = 11.2580(3) A, b = 15.9262(5) A, c = 12.3930(4) A, beta = 116.246(1) degrees , V = 1992.95(10) A3, Z = 2. X-ray crystallography demonstrates the complex is a low-spin bis-TMSO ligated species. The average Fe-Np distance is 1.999(4) A. The most important feature is that TMSO is coordinated to iron(II) by the sulfur donors, not oxygen. The Fe-S distance is 2.2220(3) A.     

Spectrophotometric Study of Mithramycin Complexes with Cu(II), Fe(III) and Tb(III)

Abstract

The coordination of the anticancer drug mithramycin to Tb(III), Fe(III) and Cu(II) was studied in aqueous solution using absorption measurements. The stability constants were calculated from equilibrium competition experiments by means of the SQUAD program. For both first ions, the competitor was oxalic acid and for the latter the competitor was the Cu(II) ions. Cu(II) at pH 7.5, Fe(III) at pH 3.5 and Tb(III) at pH 5.5 formed respectively 1:2, 1:3 and 1:4 metal-to-ligand species.     

Computer evaluation of water sorption on ion exchangers

Water sorption on an ion exchanger can be described by formation of several hydrates. The general least squares program WSLET based on the "pit-mapping" approach has been written for evaluating such equilibria. It is written in FORTRAN 77 for use on personal computers. Besides finding the best values for the equilibrium constants of the various hydrates the program also searches for best values of the stoichiometric indices by using the so-called ESI-method. The program is provided with least-squares procedures and blocks for statistical analysis of the residuals as well as for data simulation. It has been tested with data on the strong base resin Dowex 1 as well as on simulated data. In the present paper an illustrative example is given together with data simulation. It is found that in most cases WSLET helps to find a better fit than earlier models quite efficiently, showing the advantage of the ESI method in combination with least-squares methods.     

POLAG-a general computer program to calculate stability constants from polarographic data

A general computer program, POLAG, that will calculate stability constants from polarographic data, has been written. The program requires no pretreatment of the experimental data. Any equilibrium model, consisting of species having the general formula M(m)H(j)(OH)(k)L(n)L'(p) may be fitted to the data. The performance and versatility of POLAG has been demonstrated by reprocessing polarographic data previously published by four different research groups.     

Spectrophotometric study of the complex formation of 3-(1-naphthyl)-2-mercaptopropenoic acid with nickel(II), palladium(II) and hydrogen ions

The equilibria between 3-(1-naphthyl)-2-mercaptopropenoic acid (H(2)NMP) and nickel, palladium and hydrogen ions at 25 degrees in aqueous 0.1 M NaClO(4) solution containing 1-2% ethanol have been studied spectrophotometrically. Protonation constants for the ligand and formation constants for the complexes Ni(NMP), Ni(NMP)(2-)(2), Pd(NMP) and Pd(NMP)(2-)(2), refined by the SQUAD program, are reported.     

Speciation of strontium in human and bovine milk

The speciation of strontium in human and bovine milk has been computed using a chemical equilibrium model and the ECCLES program. The calculations show     

UV/vis, 1H, and 13C NMR spectroscopic studies to determine mangiferin pKa values

The acid constants of mangiferin (a natural xanthonoid) in aqueous solution were determined through an UV/vis spectroscopic study employing the SQUAD program as a computational tool. A NMR study complements the pK(a) values assignment and evidences a H-bridge presence on 1-C. The chemical model used was consistent with the experimental data obtained. The pK(a) values determined with this procedure were as follows: H(4)(MGF)=H(3)(MGF)(-)+H(+), pKa1 (6-H)=6.52+/-0.06; H(3)(MGF)(-)=H(2)(MGF)(2-)+H(+), pKa2 (3-H)=7.97+/-0.06; H(2)(MGF)(2-)=H(MGF)(3-)+H(+), pKa3 (7-H)=9.44+/-0.04; H(MGF)(3-)=(MGF)(4-)+H(+), pKa4 (1-H)=12.10+/-0.01; where it has been considered mangiferin C(19)H(18)O(11) as H(4)(MGF). Mangiferin UV/vis spectral behavior, stability study in aqueous solution as well as NMR spectroscopy studies: one-dimensional (1)H,(13)C, 2D correlated (1)H/(13)C performed by (g)-HSQC and (g)-HMBC methods; are also presented. pK(a) values determination of H(4)(MGF) in aqueous solution is a necessary contribution to subsequent pharmacokinetic study, and a step towards the understanding of its biological effects.     

Multiparametric curve fitting-XII Resolution capability of two programs for analysing multicomponent spectra, squad(84) and psequad(83)

The resolving power of multicomponent spectra analysis and the computation reliability of the stability constants and molar absorptivities determined for nine variously protonated anions of three sulphonephthaleins and an impurity, by analysis of data for a mixture by programs SQUAD(84) and PSEQUAD(83), has been examined by use of synthetic and experimentally measured spectra containing severely overlapping spectral bands. The model mixture of Bromocresol Green, Phenol Red, Thymol Blue and azoxine as impurity, with five yellow, three blue and one red species in the pH range from 2 to 10, was used to examine the influence of precision of spectral data and of use of the spectra of the individual components, on the precision and accuracy of the estimated parameters when the chemical model is known. An efficient computation strategy has been found and both programs were shown to lead to the same values and reliability of the parametric estimates. Of the various diagnostics considered, the goodness-of-fit achieved is used as the criterion of whether the parameters found adequately represent the data.     

NABTIT-a computer program for non-aqueous acid-base titration

A program NABTIT written in BASIC has been developed for the treatment of data (ml/mV) obtained from potentiometric acid-base titrations in non-aqueous solvents. No preliminary information on equilibrium constants is required for the input. The treatment of the data is based on known equations and uses least-squares procedures. The essence of the method is to determine the equivalence volume (V(e)) accurately, and to use the data acquired by adding titrant after V(e) for the pH*-calibration of the non-aqueous potentiometric cell. As a by-product or the calculations, the pK* value of the substance titrated is also obtained, and in some cases the autoprotolysis constant of the medium (pK*(s)). Good agreement between experiment and theory was found in the treatment of data obtained for water and methanol-water mixtures.     

Equilibrium and kinetic studies of the Fe(III) complex formation with glycinehydroxamic acid

Spectrophotometric methods were utilized for stability constant determinations of the Fe(III) interaction with glycinehydroxamic acid (GX) at I = 0.15 M NACl and T = 25°C. Program SQUAD II was used to assess the absorbance data in the wavelength range 300–520 nm. Four constants were determined for 1:1:1, 1:1:0, 2:1:1 or 3:1:3 and 2:1:0 complex species in the pH range 1.0–7.5. The kinetics of the interactions of Fe(III) with GX were also studied in the pH range 1.0–3.0 by the stopped flow method. The observed rate constant at a given pH was k_obs = _A + BT_GX. The parameters A and B are functions of pH in the range 1.7–3.0 and only A is a function of pH in the range 1.0–1.7. The mechanism of complex formation was discussed in the light of the experimental results and the equilibrium study. It has been concluded that FeOH²⁺ is the reactive species in the complex formation of FeGXH³⁺ species while Fe(OH)₂⁺ is the reactive species in the complex formation of FeGX²⁺ species.     

A computer program for the optimal ion chromatographic determination of anions in waters

Summary A general form of computer program which can assist in method development for any natural water has been developed. Necessary input data, sequence of main operations, necessary mathematical relationships and the output data are specified. The development of the structure of the computer program was based on experiences with real samples.     

Application of SQUAD to the refinement of formal potentials from coulometric steady-state and spectrophotometric measurements

The application of SQUAD to the refinement of formal potentials from potentiometric or coulometric steady-state and spectrophotometric measurements was tested. The formal potential thus obtained for the Fe(CN) (3-)(6)Fe(CN) (4-)(6) couple in 0.5 M H(2)SO(4) agreed with published data. This method was found to be satisfactory for the determination of typical standard potentials and it is suggested that it may be advantageous when dealing with multi-component systems.     

Application of personal microcomputers in the analytical laboratory--I: Potentiometric analysis

A novel general-purpose interface-controller unit has been designed and applied in potentiometric analysis. The unit is operated by a personal microcomputer programmed in BASIC. The interface-controller permits direct reading of specific ion-electrodes and can activate, under program control, laboratory instruments such as motor-driven burettes. The interface-controller is expendable to 16 analogue input channels, 16 binary (logic) input lines and 16 control relays but requires only one microcomputer I/O port (a total of 9 I/O lines) to handle all operations. Analogue to digital conversion is realized by counting, with the microcomputer, the output frequency of an analogue-to-frequency converter. This inexpensive method is effective in rejecting interfering signals such as power-line interference. The system has been applied in potentiometric titration analysis for determining the apparent dissociation constants of carbonic acid in sea-water and Dead Sea brines, and for ammonia determination with a gas-sensing electrode.