Potentiometric study of complexes formed between (s)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropanoic acid and some transition metal ions (original) (raw)
Related papers
Inorganic Chemistry, 2001
The stability constants of the 1:1 complexes formed between Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , or Cd 2+ ()M 2+ ) and 1-methyl-4-aminobenzimidazole (MABI) or 1,4-dimethylbenzimidazole (DMBI) were determined by potentiometric pH titrations in aqueous solution (25°C; I ) 0.5 M, NaNO 3 ). Some of the stability constants were also measured by UV spectrophotometry. The acidity constants of the species H 2 (MABI) 2+ and H(DMBI) + were determined by the same methods, some twice. Comparison of the stability constants of the M(MABI) 2+ and M(DMBI) 2+ complexes with those calculated from logK ML M versus pK HL H straight-line plots, which were established previously for sterically unhindered benzimidazole-type ligands ()L), reveals that the stabilities of the M(MABI) 2+ and M(DMBI) 2+ complexes are significantly reduced due to steric effects of the C4 substituents on metal ion binding at N3. This effect is more pronounced in the M(DMBI) 2+ complexes. Considering the steric equivalence of methyl and (noncoordinating) amino groups (as they occur in adenines), it is concluded that the same extent of steric inhibition by the (C6)NH 2 group is to be expected on metal ion binding at N7 with adenine derivatives. The basicity of the amino group in MABI is significantly higher than in its corresponding adenine derivative. Indeed, it is concluded that in the M(MABI) 2+ complexes chelate formation involving the amino group occurs to some extent. The formation degrees of these "closed" species are calculated; they vary for the complexes of Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , or Cd 2+ between about 50 and 90%. The stability of the M(MABI) 2+ and M(DMBI) 2+ complexes with the alkaline earth ions is very low but unaffected by the C4 substituent; this probably indicates that in these instances outersphere complexes (with a water molecule between N3 and the metal ion) are formed.
Bulletin of Electrochemistry
Proton–ligand dissociation constants of 4-p-[N-2-(pyrimidyl) sulphonamino-phenylazo]-3-methyl-2-pyrazolin-5-one (I) and the stability constants of its complexes with some metal ions were determined potentiometrically in 0.1 M KCl and 30% (v/v) ethanol–water mixture. The order of the st abi l ity was found t o be Mn 2+ < Co 2+ < Ni 2+ < Cu 2+ < La 3+ < Hf 3+ < UO 2 2+ < Zr 4+ . The effect of temperature on the di ssoci at ion of (I) and the st abi l ity of i t s complexes were st udi ed. The corresponding t hermodynami c funct i ons were derived and di scussed. The di ssoci at ion process i s non-spont aneous, endothermi c and ent ropi cal l y unfavourable. The format ion of t he met al compl exes was found to be spontaneous, exothermi c and ent ropical ly f avourable.
1992
The computer-based analysis of the pH titration data obtained in the M A B[M =Cu(I1)/Zn(I1); A = L-aspartic acid (aspt) and iminodiacetic acid (imda) and B= DL 2, 3-diaminopropionic acid (dapa), DL-2, 4-diaminobutyric acid (daba), and DL-Omithine (Om)] mixed ligand systemsshow the presence of mixed speciesof the types MABH2, MABH and/or MAB in addition to the various binary speciesdue to ligands A and B. The modes of binding ofligands in various speciesare discussedon the basis ofthe results obtained.
Chemical Speciation and Bioavailability, 2006
The stability constants of binary complexes of 2,4-dichlorophenoxyacetic acid (2,4-D), (4-chloro-2methylphenoxy)acetic acid (2,4-MCPA) and (4-chloro-2-methylphenoxy) propionic acid (2,4-MCPA) with Cu(II), Cd(II) and Zn(II) have bean calculated at 298 K and at ionic strength m ¼ 0:1 (NaNO 3 ). Potentiometric measurements display three hydroxide complexes: MH À 1 A, MH À 1 A 2 and MH À 2 A 2 . With regard to the successive complexes, no other system represents this type of complexes under our experimental conditions. The order of capacity of complexation compared to metal for the three ligands is Cu(II)4Zn(II)4Cd(II).
Journal of Chemical Sciences, 2002
Equilibrium and solution structural study of mixed-metal-mixed-ligand complexes of Cu(II), Ni(II) and Zn(II) with L-cysteine, L-threonine and imidazole are conducted in aqueous solution by potentiometry and spectrophotometry. Stability constants of the binary, ternary and quaternary complexes are determined at 25 ± 1°C and in I = 0⋅1 M NaClO 4. The results of these two methods are made selfconsistent, then rationalized assuming an equilibrium model including the species H 3 A, H 2 A, A, BH, B, M(OH), M(OH) 2 , M(A), MA(OH), M(B), M(A)(B), M 2 (A) 2 (B), M 2 (A) 2 (B-H), M 1 M 2 (A) 2 (B) and M 1 M 2 (A) 2 (B-H) (where the charges of the species have been ignored for the sake of simplicity) (A = L-cysteine, L-threonine, salicylglycine, salicylvaline and BH = imidazole). Evidence of the deprotonation of BH ligand is available at alkaline pH. N 1 H deprotonation of the bidentate coordinated imidazole ligand in the binuclear species at pH > 7⋅0 is evident from spectral measurements. Stability constants of binary M(A), M(B) and ternary M(A)(B) complexes follow the Irving-Williams order.
Inorganica Chimica Acta, 2002
Copper(II), nickel(II) and zinc(II) complexes of Phe-BIMA and His-BIMA were studied by potentiometric, UV Á/Vis and EPR spectroscopic methods. The nitrogen donor atoms of the bis(imidazol-2-yl)methyl residues were described as the primary metal binding sites in all systems studied. Deprotonation and coordination of the terminal amino and amide nitrogen atoms took place in the copper(II) complexes of both ligands and resulted in the formation of dinuclear complexes ([Cu 2 H (2 L 2 ] 2' ) containing [NH 2 , N ( , N(Im)] tridentate ligands and imidazole bridging. The presence of the histidyl side chain provides a great versatility in the complex formation reactions of His-BIMA. The existence of the species [Cu 2 L 2 ] 4' was detected in slightly acidic solution and its structure was described as a mixture of three isomeric forms. Deprotonation of the imidazole-N(1)H donor functions was detected under slightly alkaline conditions with pK values of 8.13 and 8.93. An excess of copper(II) ions shifted this reactions even into the slightly acidic pH range and resulted in the formation of a trinuclear complex ([Cu 3 H (4 L 2 ] 2' ). # (I. Só vágó). Inorganica Chimica Acta 339 (2002) 373 Á/382 www.elsevier.com/locate/ica 0020-1693/02/$ -see front matter # 2002 Published by Elsevier Science B.V. PII: S 0 0 2 0 -1 6 9 3 ( 0 2 ) 0 0 9 5 4 -4
Monatshefte f�r Chemie/Chemical Monthly, 2004
metal ions with some selected aliphatic and aromatic hydroxamic acids and some biologically important amino acids or nucleic acid components was investigated using the potentiometric technique at 25 C and I ¼ 0.10 mol dm À3 NaNO 3. The acid-base properties of the ligands were investigated and discussed. The acidity constants of the ligands were determined and used for determining the stability constants of the complexes formed in aqueous medium under the experimental conditions. The ternary complex formation was found to occur in a stepwise manner. The stability constants of these binary and ternary systems were calculated. The order of stability of the ternary complexes in terms of the nature of hydroxamic acid, amino acid, nucleic acid component and metal ions was investigated and discussed as well as the values of D log K and log X for the ternary systems. The concentration distribution of the various complex species in solution was evaluated. In addition, evaluation of the effect of temperature of the medium on the stability of the ternary system M III-benzohydroxamic acid-L-histidine or adenine (M III ¼ Fe III , Al III , and Cr III) has been studied. The thermodynamic parameters were calculated and discussed.