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.

SOME EQUILIBRIUM CONSTANTS OF TRANSITION METAL HALIDES

1960 ◽  
Vol 38 (10) ◽  
pp. 1827-1836 ◽  
Author(s):  
M. W. Lister ◽  
P. Rosenblum
Keyword(s):  
Ionic Strength ◽  
Transition Metal ◽  
Equilibrium Constant ◽  
Spectrophotometric Method ◽  
Equilibrium Constants ◽  
Cell Voltage ◽  
Metal Halides ◽  
Complex Ions ◽  
Anomalous Variation ◽  
A Cell

Measurements are reported on the formation of complex ions in solutions containing cupric and chloride or bromide ions, and solutions of nickel or cobalt with chloride. In each case the halide was present in very low amount. With copper a spectrophotometric method was used, and a cell voltage method with nickel and cobalt. The ionic strength was kept constant, but the temperature was varied. The data show difficulties of interpretation if it is assumed that only MX+ ions (M is the metal, X is the halogen) are formed, the difficulties arising from the anomalous variation of the equilibrium constant with temperature, and from the general drift of the calculated constants from the e.m.f. measurements. Various explanations are considered and it is shown that postulation of M2X+3 ions is at least a possible explanation.

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.

Schiff base equilibria. VI. n- and t-Butylimines of pyridine-2-aldehyde

1968 ◽  
Vol 21 (10) ◽  
pp. 2427 ◽  
Author(s):  
RW Green ◽  
MJ Rogerson
Keyword(s):  
Schiff Base ◽  
Schiff Bases ◽  
Formation Constant ◽  
Equilibrium Constants

Equilibrium constants at 25� have been measured for the formation of Schiff bases of pyridine-2-aldehyde with n-butylamine (1.45 x 108) and t-butylamine (93). The Schiff base of salicylaldehyde with t-butylamine has a formation constant 9.1 x 108 and pK 13.0.

Schiff base equilibria. IV. N-Methylimines of m- and p-hydroxybenzaldehydes

1966 ◽  
Vol 19 (2) ◽  
pp. 233 ◽  
Author(s):  
RW Green ◽  
RJ Sleet
Keyword(s):  
Schiff Base ◽  
Ionic Strength ◽  
Schiff Bases ◽  
Formation Constants ◽  
Dilute Solution

The formation of Schiff bases between methylamine and m- and p-hydroxybenzaldehydes has been studied by spectrophotometry. Because of overlapping equilibria and ionic strength effects, the formation constants, KF, of the neutral Schiff bases are determined with less precision than for the ortho compound. In dilute solution they are estimated by extrapolation to be 1.0 x 103 and 1.0 x 104, respectively. The formation constants, KA, of the anionic forms of the Schiff bases have been more precisely measured as 1.45 x 102 and 5.52, respectively. The equilibria are compared with those for salicylaldehyde.

Kinetics and mechanisms of oxidations by metal ions. Part VIII. Oxidation of n-propanol by aquomanganese(III) ions

1987 ◽  
Vol 65 (2) ◽  
pp. 277-281 ◽  
Author(s):  
Mahendra Mehta ◽  
Ratan R. Nagori ◽  
Raj N. Mehrotra
Keyword(s):  
Ionic Strength ◽  
Metal Ions ◽  
Equilibrium Constant ◽  
Thermodynamic Parameters ◽  
The Other ◽  
Constant Ionic Strength ◽  
Rate Law

The oxidation of n-propanol by aquomanganese(III) ions in perchlorate medium of constant ionic strength (4 mol dm−3, NaClO4) is described by the rate law [i] which is based on the consideration of the reactions [ii]–[ix].[Formula: see text]A further analysis of the rate law in terms of the results indicated that MnOH2+ (aq) is the major oxidant. The values of the equilibrium constant (β1) and rate determining constant (k1) are reported together with the associated thermodynamic parameters. The values of the other constants, k, Ka, and β, could not be determined though an assumption was made that β ≈ β1.

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.

SOME MEASUREMENTS ON THE IRON (111)–THIOCYANATE SYSTEM IN AQUEOUS SOLUTION

1955 ◽  
Vol 33 (10) ◽  
pp. 1572-1590 ◽  
Author(s):  
M. W. Lister ◽  
D. E. Rivington
Keyword(s):  
Aqueous Solution ◽  
Ionic Strength ◽  
Equilibrium Constant ◽  
Equilibrium Constants ◽  
Spectrophotometric Study ◽  
Concentrated Solutions ◽  
Extinction Coefficients ◽  
Ferric Thiocyanate ◽  
Different Temperatures

A spectrophotometric study of the ferric thiocyanate system is reported. The temperature and ionic strength of the solutions were carefully controlled, and suitable precautions were taken against fading. From the data, values of the equilibrium constant for the formation of FeSCN++ from simple ions, and of the extinction coefficients of FeSCN++ were obtained for different temperatures and ionic strengths, with results that differed somewhat from earlier values. The effect of varying acidity was also investigated. From more concentrated solutions, values for the equilibrium constants for the formation of Fe(SCN)2+ and Fe(SCN)3 were obtained; it was not necessary to postulate higher complexes.

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