scholarly journals Acid-base equilibria of the Zn(II) and Fe(III) complexes with condensation products of 2-acetylpyridine and the dihydrazide of oxalic and malonic acid

2009 ◽  
Vol 74 (3) ◽  
pp. 269-277 ◽  
Author(s):  
Branka Drazic ◽  
Gordana Popovic ◽  
Ratomir Jelic ◽  
Dusan Sladic ◽  
Dragana Mitic ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Cytotoxic Activity ◽  
Malonic Acid ◽  
Equilibrium Constants ◽  
Aqueous Media ◽  
Constant Ionic Strength ◽  
Acid Base ◽  
Condensation Products

Acid-base equilibria of Zn(II) and Fe(III) complexes with N',N'2-bis- [(1E)-1-(2-pyridyl)ethylidene]ethanedihydrazide (ligand L1) and N',N'2-bis[(1E)- -1-(2-pyridyl)ethylidene]propanedihydrazide (ligand L2), i.e., [Fe(L1)Cl2(H2O)], [Fe(L2)Cl(H2O)]2+, [Zn(L1)(H2O)3]+ and [Zn(L2)(H2O)2]2+, which expressed cytotoxic activity, were investigated in aqueous media. The equilibrium constants were determined potentiometrically at 25?C at a constant ionic strength of 0.10 mol/dm3 (Na2SO4). The results showed that at pH < 8 both the Fe(III) complexes studied here have three, while [Zn(L1)(H2O)3]+ and [Zn(L2)(H2O)2]2+ have one and two titratable protons, respectively. Based on the obtained values for the equilibrium constants, protonation schemes of the examined complexes are proposed.

scholarly journals Fluorimetric studies on the dimerization equilibrium of protoporphyrin IX and its haemato derivative

1983 ◽  
Vol 209 (2) ◽  
pp. 547-552 ◽  
Author(s):  
R Margalit ◽  
N Shaklai ◽  
S Cohen
Keyword(s):  
Ionic Strength ◽  
Fluorescence Quenching ◽  
Fluorescence Intensity ◽  
Salt Concentration ◽  
Equilibrium Constants ◽  
Protoporphyrin Ix ◽  
Constant Ionic Strength ◽  
Aggregation Process ◽  
Buffer Concentration ◽  
Common Anion

The aggregations of protoporphyrin IX and haematoporphyrin IX in aqueous solutions were studied by fluorimetric techniques. Porphyrin concentrations were limited to 0.001-0.1 microM and 0.01-1 microM for protoporphyrin and haematoporphyrin respectively, where dimerization is the dominant aggregation process. The dimerization equilibrium constants (at 25 degrees C, neutral pH, 50 mM-Tris/HCl buffer) were determined to be 3×10(7) M and 4×10(5) M for the proto and the haemato derivatives respectively. The fluorescence intensity of a given protoporphyrin solution (within the range indicated above) was markedly decreased by salts in the system, over the salt concentration range 0.1-7 mM at constant ionic strength, in the sequence CaCl2 greater than MgCl2 greater than KCl greater than NaCl. The direction of this effect, fluorescence quenching, suggests that these salts promote an increase in aggregation. The differences in the magnitudes of the effect, among different salt species sharing a common anion, at constant ionic strength, imply that the effect is cation-specific. In contrast, the fluorescence intensity of a given solution of haematoporphyrin (within the range indicated above) was unaffected by these salts, under similar concentrations, nor was it sensitive to the total buffer concentration, or to the type of buffer in the system.

Acid−Base Equilibrium Constants for Glycine in NaClO4, KCl, and KBr at 298 K. Dependence on Ionic Strength

1998 ◽  
Vol 43 (5) ◽  
pp. 876-879 ◽  
Author(s):  
P. Alonso ◽  
J. L. Barriada ◽  
P. Rodríguez ◽  
I. Brandariz ◽  
M. E. Sastre de Vicente
Keyword(s):  
Ionic Strength ◽  
Equilibrium Constants ◽  
Acid Base ◽  
Base Equilibrium ◽  
Acid Base Equilibrium ◽  
Dependence On Ionic Strength

scholarly journals Acid-base equilibria of 2,4-diiodo-6-methylphenylcarbamoylmethyl iminodiacetic acid and its labeling with technetium-99m

2006 ◽  
Vol 71 (1) ◽  
pp. 55-65 ◽  
Author(s):  
Jasmina Brboric ◽  
Mirjana Jovanovic ◽  
Gordana Popovic ◽  
Vera Kapetanovic ◽  
Sote Vladimirov
Keyword(s):  
Ionic Strength ◽  
Radiochemical Purity ◽  
Equilibrium Constants ◽  
Iminodiacetic Acid ◽  
Carboxylic Group ◽  
Acid Base ◽  
Acidity Constants ◽  
Technetium 99M ◽  
Ph Range ◽  
Influence Of Ph

The acid-base equilibria of a novel hepatobiliary imaging agent, 2,4-diiodo-6-methylphenylcarbamoylmethyl iminodiacetic acid (DIIODIDA) were studied. The potentiometrically determined acidity constants of the second carboxylic group, amino and amide groups were pK2 = 2.52 ? 0.02; pK3 = 5.86 ? 0.06 and pK4 = 10.9 ? 0.1. The determinations were performed at 25 ?C and an ionic strength of 0.1 mol/dm3 (NaCl). The acidity constants (pK1 = 1.3 ? 0.4) corresponding to the first carboxylic group was determined indirectly, on the basis of equilibrium constants obtained in a heterogeneous system, at 25 ?C and an ionic strength 1 mol/dm3 (HCl, NaCl). DIIODIDA was labeled with technetium-99m, and the influence of pH on the yield of labeling was investigated. It was found that labeling within the pH range from 5.5 to 6.5 provided a radiopharmaceutical of high radiochemical purity (>98 %).

scholarly journals Protolytic equilibria in homogeneous and heterogeneous systems of ketoconazole and its direct spectrophotometric determination in tablets

2005 ◽  
Vol 70 (1) ◽  
pp. 67-78 ◽  
Author(s):  
Mirjana Vojic ◽  
Gordana Popovic ◽  
Dusan Sladic ◽  
Lidija Pfendt
Keyword(s):  
Ionic Strength ◽  
Spectrophotometric Determination ◽  
Spectrophotometric Method ◽  
Equilibrium Constants ◽  
Heterogeneous Systems ◽  
Water Systems ◽  
Acidity Constant ◽  
Acid Base ◽  
Protolytic Equilibria

The acid-base equilibria of a diprotic, slightly hydrosoluble base ketoconazole were studied in homogeneous and heterogeneous water systems. The determinations were performed at 25?C at a constant ionic strength of M(NaCl). The acidity constant Ka1 was determined by potentiometric (pKa1 3.20) and spectrophotometric (pKa1 3.26) methods. A pKa2 constant of 6.10 was obtained based on the equilibrium constants pKs0 4.84 and pKs1 -1.26, determined in a heterogeneous ketoconazole system. The obtained values of the constants served to calculate the solubility and the distribution of the equilibrium forms of ketoconazole as a function of pH. On the basis of the distribution of the equilibrium forms of ketoconazole, a spectrophotometric method for the determination of its content in commercial tablets was developed. The determinations were performed at 225 nm in 0.1 M HCl. The method is simple and rapid and enables the direct spectrophotometric determination of the content of ketoconazole without previous isolation.

Equilibrium constants of pyridoxal 5'-phosphate Schiff bases - A polarographic study

1983 ◽  
Vol 48 (7) ◽  
pp. 1950-1955 ◽  
Author(s):  
Juan Llor ◽  
Javier Bonal ◽  
Manuel Cortijo
Keyword(s):  
Schiff Base ◽  
Ionic Strength ◽  
Equilibrium Constant ◽  
Schiff Bases ◽  
Ph Dependence ◽  
Equilibrium Constants ◽  
Constant Ionic Strength ◽  
Polarographic Study ◽  
Ionic Forms

The equilibrium constant for the formation of the Schiff base between pyridoxal 5'-phosphate and n-hexylamine has been evaluated from polarographic measurements. The pH dependence of the equilibrium constant has been investigated at constant ionic strength. The values thus obtained for the equilibrium constant compare well with those computed from the pK of the several ionic forms of pyridoxal 5'-phosphate, its Schiff base and the amine present in the solution.

scholarly journals Acid-base behaviour of sanguinarine and dihydrosanguinarine

2009 ◽  
Vol 7 (4) ◽  
pp. 876-883 ◽  
Author(s):  
Helena Absolínová ◽  
Luděk Jančář ◽  
Irena Jančářová ◽  
Jaroslav Vičar ◽  
Vlastimil Kubáň
Keyword(s):  
Optical Properties ◽  
Acetic Acid ◽  
Ionic Strength ◽  
Equilibrium Constants ◽  
Ionic Species ◽  
Transport Proteins ◽  
Priority Effect ◽  
Acid Base ◽  
Strength Of Interaction ◽  
Transition Reaction

AbstractAcid-base and optical properties of sanguinarine and dihydrosanguinarine were studied in the presence of HCl, HNO3, H2SO4, H3PO4, CAPSO and acetic acid (HAc) of different concentrations and their mixtures. The equilibrium constants pKR+ of the transition reaction between an iminium cation Q+ of sanguinarine and its uncharged QOH (pseudo-base, 6-hydroxy-dihydroderivative) form were calculated. A numerical interpretation of the A-pH curves by a SQUAD-G computer program was used. Remarkable shifts of formation parts of absorbance-pH (A-pH) curves to alkaline medium were observed. The shifts depend on the type and concentration of inert electrolyte (the most remarkable for HNO3 and HCl). The corresponding pKR+ values ranged from 7.21 to 8.16 in the same manner (ΔpKR+ = 0.81 and 0.73 for HNO3 and HCl, respectively). The priority effect of ionic species and ionic strength was confirmed in the presence of NaCl and KCl. The strength of interaction of SA with bioactive compounds (i.e. receptors, transport proteins, nucleic acids etc.) may be affected because of the observed influence of both cations and anions of the inert electrolytes.

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