Comparative Measurements of Calcium Stability Constants of Some Dicarboxylic Acids by Titrimetry with pH Glass and Calcium Ion-Selective Electrodes (original) (raw)
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Ion-pair formation between Ca 2+ and α-isosaccharinate, Ca 2+ + ISA − → ← CaISA + , was studied by two independent methods: an ion-exchange and a potentiometric method (Ca-selective electrode). The two methods gave similar values for the complexation constant, log K o CaISA + at I = 0, (22 ± 1) • C. The ion-exchange method gave a value of log K o CaISA + = (1.8 ± 0.1) and the potentiometric method resulted in logK o CaISA + = (1.78 ± 0.04). These values are in good agreement with the estimated value, log K o CaISA + = 1.7, based on the formation of a Ca-gluconate ion pair.
Talanta, 2000
Stability constants (K ijk) of complexes Na i K j H k L + i + j + k − 2 (0B i +j + k5 2) formed by dicarboxylic (oxalic, malonic, succinic, glutaric, adipic and methylmalonic, dimethylmalonic, ethylmalonic) acids in solutions of mixed salts (NaNO 3 , KNO 3) of ionic strength I= 1.64 mol l − 1 are presented. The unbiased values for K ijk , (K ijk) % e = 0 , were obtained from the linear relationships log K ijk = a+b(% e) stated on the basis of the results of repeated titrations made in titrand+ titrant systems of high ionic strength, % e is the relative error of determination of the weak acid (H 2 L) concentration. These data were then applied to indicate the catenation or the isomerisation effects on the K ijk values.
The dissociation constants of carminic acid (7-D-glucopyronosyl-3,5,6,8-tetrahydroxy-1-methyl-9,10-dioxo-anthracene-2-carboxylic acid) (CA), together with the stability constants of its Cu(II), Zn(II), Ni(II), Co(II) and Hg(II) complexes, were studied potentiometrically in aqueous medium at 25.0 (1)°C, and at the ionic background of 0.1 mol·dm −3 of NaCl, and determined with the SUPERQUAD computer program. It has been observed that carminic acid has five dissociation constants, and for H 5 L their values are 3.39 , 5.78 (7), 8.35 , 10.27 (7), and 11.51 (7). This ligand behaves as a bi-dentate ligand, and the carboxyl and the ortho hydroxy groups of the ligand coordinate to the metal ions. Various metal complexes were produced in solution under the experimental conditions, for each metal ion used, including hydrolyzed species. The species distribution curves of the complexes formed in the solution were calculated and reviewed. The stability of the complexes was found to follow the order: Cu(II) > Zn(II) > Ni(II) > Co(II) > Hg(II).
On the dissociation constants of BAPTA-type calcium buffers
Cell Calcium, 1989
We have determined or redetermined the calcium dissociation constants of seven BAPTA-type buffers with KD's in the range from 0.4 microM to about 20 mM in 300 mM KCl. These include four newly synthesized ones: 5-nitro BAPTA; 5,5'-dinitro BAPTA; 5-methyl-5'-nitro BAPTA; and 5-methyl-5'-formyl BAPTA. Moreover, we tabulate dissociation constants or KD's for BAPTA and eleven BAPTA-type buffers, compare most of them with an empirical curve based upon so-called Hammett values, and predict KD's for several still unsynthesized but potentially valuable buffers.
Beni-Suef University Journal of Basic and Applied Sciences, 2015
Formation of binary and ternary complexes of the divalent transition metal ions, Cu 2þ , Ni 2þ , Co 2þ and Zn 2þ with gallic acid and the biologically important aliphatic dicarboxylic acids (adipic, succinic, malic, malonic, maleic, tartaric and oxalic acids) were investigated by means of the potentiometric technique at 25 C and I ¼ 0.10 mol dm À3 NaNO 3. The acidbase properties of the ligands were investigated and discussed. The acidity constants of gallic acid and aliphatic dicarboxylic acids were determined and used for determining the stability constants of the binary and ternary complexes formed in the aqueous medium under the above experimental conditions. The formation of the different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes are inferred from the corresponding potentiometric pH-metric titration curves. The ternary complex formation was found to occur in a stepwise manner. The stability constants of these binary and ternary systems were calculated. The values of D log K, percentage of relative stabilization (%R.S.) and log X were evaluated and discussed. The concentration distribution of the various complex species formed in solution was evaluated and discussed. The mode of chelation of ternary complexes formed was ascertained by conductivity measurements.
Journal of Chemical & Engineering Data, 1995
A maceutical scientist wants to know the dissociation constant' for a particular drug. He might want to know whether his drug is in the ionic or nonionic form, if it will be sufficiently soluble in the gastrointestinal fluid, or how the gastric fluid might affect the rate of dissolution of the drug. He might wish to predict the stability or explain the kinetics of degradation for a dissociable drug in various buffer solutions. He might want to hypothesize a mechanism of action, predict the extent of binding, or examine complex formation. In all of these cases and in many others the pharmaceutical scientist needs to know the dissociation constant in order to solve his problem. His first reaction will be to "look i t up" and if he is lucky he will find critically evaluated values in either "Dissociation Constants of Organic Acids in Aqueous Solutions" (1) or the companion volume for organic bases (2). However, in most cases he will be working with a drug for which the dissociation constant is not readily available, and unfortunately when dealing with drugs in biological systems a t 37' the reliable data available Received from the College of Pharmacy, Washington State University, Pullman, WA 99163 and the. *School of Pharmacy, University pf California, SHn Franusco, CA 94122
Talanta, 2003
This work reports the results of studies into the solubility and thermal decomposition of various sparingly soluble complexes of calcium with two isomeric benzene tricarboxylates, and with benzene penta-and hexa-carboxylates. The dependence of their solubility on ionic strength and, for the calcium benzene hexacarboxylate, the dependence of solubility on Na ' concentration in solution were studied. Comparison between structure and solubility of the calcium insoluble compounds here and previously studied, is also reported. In order to perform solubility calculations, we determined also the formation constants of trimellitic and trimesic anions with H ' , Na ' and Ca 2' potentiometrically (H ' -ISE), since these are not reported in literature. All solid compounds were characterised by TG-FTIR measurements, and comparable behaviours in thermal decomposition as a function of ligand structure were found. #
Analytica Chimica Acta, 1993
Two sets of oxa-amide and oxa-ester tripodal ligands have been prepared and evaluated as ionophores in PVC membrane electrodes for the analysis of Li+, Na+, K+, Ca*' and Mg *+ ions. The effects of the nature of the plasticiser bis(butylpentyl)adipate (BBPA) vs. o-nitrophenyl octyl ether (oNPOE), the structure of the ionophore, the pH and the ionic strength of the analyte solution on the electrode response were studied. The oxa-amides gave a superior performance (slope, limits of detection) than the oxa-esters particularly at higher ionic strengths, although super-Nernstian responses were observed with the more charge-dense ions in the presence of chloride and/or with the less polar plasticiser BBPA. Intracellular measurements of sodium concentration could be effected with a sensor based on bis (N,N',N"-tributy1~,4',4"-propy1dintris(3-oxabutanamide) and oNPOE for which -log KNyE = 2.64 and -log KNyM = 3.0, while bis(N,N',N"-tributyl)-2,2',2"-phenylmethylidintris(3-oxabutanamide) and oNPOE functioned as an effective calcium sensor with high selectivity over magnesium (-log KCa,Mg = 4.8).