Ionic strength dependence of formation constants. Alkali metal complexes of ethylenediaminetetraacetate nitrilotriacetate, diphosphate, and tripolyphosphate in aqueous solution (original) (raw)
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Chemistry ofProteins which are the most complex substances known to man is one of the great challenges in modern science. In the present work peptides of amino acid were used to study metal-ligand stability constants. Various chelates of metal ions like Al(III), Cr(III), Fe(III), Pt(IV) etc. with various chalcones and amino acids were studied for their stability determination. In the present work complexes of transition metal ions like Cu(II) and Ni(II)with peptide; DL-Alanyl-DL-Alanine were prepared and progress of their formation and metal-ligand stability constants at 0.1M ionic strength were studied potentiometrically. It was found that for Cu(II) the colourlesssolution changed to blue at about pH 5.0 and for Ni(II) at pH 5.25 the colourless solution changed to orange. The stability was studied from Ƞ (ligand number) values and logK values. It is concluded from results that complex of Cu(II) with DL-Alanyl-DL-Alanine is more stable than that for Ni(II).
Thermochimica Acta, 1985
The stability constants, K,, of the complexes formed by 4-amino-2.6-dioxo-3-methyl-5nitroso-1,2,3.6-tetrahydro-pyrimidine (LH), 4-amino-1.3-dimethyl-2.6-dioxo-5-nitroso-1,2,3,6-tetrahydro-pyrimidine (RH) and 4-amino-1,6-dihydro-l-methyl-2-methoxy-5-nitroso-6-oxo-pyrimidine (JH) with Ag(I). Zn(l1). Cd(I1) and Hg(II) ions. in aqueous media at different ionic strengths and 25°C. have been calculated by Bjerrum's method.
Talanta, 1983
The dependence of L-glutamine protonation and its complexation with dioxovanadium(V) on ionic strength ( I ) is reported in sodium perchlorate solution as a background salt. The measurements have been performed at 25 ± 0.1 ° C and various ionic strengths in the range 0.1 to 1.0 mol/l, using a combination of potentiometric and spectrophotometric techniques. The overall analysis of the present and the previous data dealing with the determination of stability constants at different ionic strengths allowed us to obtain a general equation, by which a formation constant determined at a fixed ionic strength can be calculated, with a good approximation, at another ionic strength, if 0.1 ≤ I ≤ 1.0 mol/l (NaClO 4 ).
The Stability of Some Metal Complexes in Mixed Solvents
Canadian Journal of Chemistry, 1974
Acidity constants and stability constants of certain metal complexes (nickel(II), zinc(II), and manganese(II)) with ethylenediamine and glycine were determined at 25 °C and in 0.1 M ionic strength in mixed aqueous solutions of methanol (MeOH), dioxane (DOX), acetonitrile (MeCN), and dimethylformamide (DMF). In general, the stability constants of the metal complexes and the first protonation constant of glycine increase with increasing composition of the co-solvent in the order[Formula: see text]The protonation constants of ethylenediamine pass through a minimum at some particular solvent composition, while the second protonation constant of glycine exhibits behavior characteristic of the particular solvent employed.These results are discussed in terms of medium and solvent effects and properties of the solvent that might affect these, but find more satisfactory explanation in terms of solvent displacement during the association reactions. The observations can be accounted for in ter...
American Journal of Chemical Engineering
Background. Metal complexes of biologically active ligands had considerable interests. L-cysteinate residue, L-Cys, is a biologically abundant and important versatile binding site of proteins. Diphenylamine, DPA, is an important aromatic amine containing two phenyl groups. Complexation equilibria of the divalent metal ions, Ca 2+ and Zn 2+ with the bio-relevant α-amino acid, L-cysteine and the nitrogen-containing diphenylamine ligand were investigated by means of the potentiometric technique at 25.0 ± 0.1°C and constant ionic strength of 0.200 ± 0.001 mol•dm-3 NaNO 3. Objective. The stability constants and standard free energy changes of the α-amino acid, L-cysteine and diphenylamine complex species were determined at 0.200 ± 0.001 mol•dm-3 ionic strength. Methods. The formation of the different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes were inferred from the potentiometric titrations. Results. The concentration distribution of L-cysteine species formed in solution was evaluated. The dissociation constants of the α-amino acid and diphenylamine were determined at different ionic strength. The stability constants of these binary and ternary systems were calculated. The values of ∆ log 10 K, percent relative stabilization, %R.S. and log 10 X for the ternary systems were evaluated and discussed. Concussion. The ternary complex formation occurred in a stepwise manner with L-cysteine acting as the primary ligand. The obtained values of ∆ G 0 indicated that Complex formation reactions are spontaneous. Also, for all systems studied, the ternary complexes formed are more thermodynamically stable than the binary complexes.