a competitive spectrophotometric method has been used for the study of complexation between cu2+, zn2+ and cd2+ (m) and 18-crown-6(18c6, b) in methanol using 4-(2-thiazolylazo) resorcinol (tar, hl) as the colorimetric complexant. absorption spectra of the species in the m-tar-18 c6 system at a various concentrations of 18c6 showed no formation of ternary complex, mlb, and the stoichiometry of t...

the charge-transfer complexation reaction between iodine and dibenzo- 18-crown- 6 (db18c6) has been studied spectrophotometrically in chloroform solution at different temperatures. the resulting donor-acceptor complex was formulated as (db 18c6…i )i . the spectrophotometric results , as well as the conductivity measurements, indicated that the gradual release of tiiodide ion from its contact io...

Stepwise formation constants of folic acid, N[p[ [ (2-amino-4-hydroxy-6-pteridyl) methyl] ami­ no] benzyl] glutamic acid, with the carcinogenic metal ions, aluminium (III) , chromium (III) , beryl­ lium (II) , lead (II) and uranium (VI) have been determined at 30 °C, and at various ionic strengths, viz. 0.01 m, 0.05 M, 0.10 m, maintained by potassium nitrate solution. The formation of the chela...

Apotransferrin (apo Tf)  in 0.1 M N-(2hydroxyethyl)piperazine-N2-ethanesulfanic acid at 25 ˚C  and pH 7.4 has been titrated with acidic solution of Tb3+. The binding of Tb3+ at  the two specific metal-binding sites of transferrin was followed from the changes in the difference UV spectra at 245 nm. The molar absorptivity per binding site for Tb3+...

Dissolved organic matter (DOM) has been implicated as an important complexing agent for Hg that can affect its mobility and bioavailability in aquatic ecosystems. However, binding constants for natural Hg-DOM complexes are not well known. We employed a competitive ligand approach to estimate conditional stability constants for Hg complexes with DOM isolates collected from Florida Everglades sur...

The acid-base chemistry of a tetraprotic, ampholyte ACE inhibitor, lisinopril, was studied by different methods. Potentiometry in aqueous medium and a co-solvent technique in methanol-water mixtures as well as 1 H NMR-pH titration were applied for the highly precise measurement of protonation macroconstants. The log K values of lisinopril (at 25.0°C and 0.15 M ionic strength) were found: log K1...

The acid dissociation constants of long-chain esters of carnitine (5-hydroxy-~,trimethylammonium-butyrate) above the critical micelle concentration were determined potentiometrieally at several concentrations of added KC1. As the degree of protonation 5 increases the apparent pK values decrease owing to the increased positive charge on the micelle. The difference in pK between the neutral (zwit...

The use of H-point curve isolation (HPCIM) and H-point standard addition methods (HPSAM) for spectrophotometric studies of complex formation equilibria are proposed. One step complex formation, two successive stepwise and mononuclear complex formation systems, and competitive complexation systems are studied successfully by the proposed methods. HPCIM is used for extracting the spectrum of comp...

The complexation of alkali-metal cations with calix[4]arene tertiary amide derivative (L) was studied in N-methylformamide (NMF), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) by means of microcalorimetric and UV spectrophotometric titrations. The Gibbs energies, enthalpies, and entropies for transfer of reactants and products from N-methylformamide to other solvents were determine...