Potentiometric and Thermodynamic Studies of Binary and Ternary Transition Metal(II) Complexes of Imidazole-4-acetic Acid and Some Bio-relevant Ligands

Al-Jahdali, Mutlaq; El‐Sherif, Ahmed A.; Shoukry, Mohamed M.; Mohamed, Seham E.

doi:10.1007/s10953-013-0015-9

Cited by 37 publications

(13 citation statements)

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“…The positive Dlog 10 b values (log 10 b 1110 -log 10 b stat ) indicate that the Cu(Bipy)L complexes are more stable than both Cu(Bipy) 2 and Cu(L) 2 complexes. Similar results (Dlog 10 b = 0.04 -2.73) are found in literature for the interaction of copper(II) with imidazole acetic and some bioactive ligands [52].…”

Section: Disproportionation Constant (Log 10 X)supporting

confidence: 90%

Thermodynamics, Chemical Speciation and Complex Formation Equilibria Studies of Binary and Mixed Ligand Complexes of Cu(II) with 2,2′-Bipyridyl and Some Aromatic Diamines

2015

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The formation of mixed ligand complexes of Cu(II) with 2,2 0 -bipyridyl (Bipy) in the presence of some selected aromatic diamines (L) (L = 3,4-diamino benzoic acid (DABA), 2-hydazinopyridine (hzpy) or 4-chloro-o-phenylenediamine has been studied by pH-metric titrations. Potentiometric measurements show that ternary complexes are formed in a simultaneous manner. The pH-titrations of the reaction mixtures are shown to yield 1:1:1 ternary complex formation. The equilibrium and formation constants of the resulting ternary complexes have been calculated at I = 0.1 molÁdm -3 of NaNO 3 . The order of stability in terms of the secondary ligands has been found to be DABA [ hzpy [ CAPA. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameters Dlog 10 K, Dlog 10 b and log 10 X. The concentration distributions of various species formed in solution were also evaluated as a function of pH. In addition, the effect of temperature on both the ionization process of the ligands and complex formations for Cu-Bipy-L ternary systems was studied. The thermodynamic parameters were calculated from the temperature dependence of the equilibrium constants and are discussed. The structure of the Cu(II) complexes have been geometrically optimized using the parameterized PM3 semiempirical method.

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Section: Disproportionation Constant (Log 10 X)supporting

confidence: 90%

Thermodynamics, Chemical Speciation and Complex Formation Equilibria Studies of Binary and Mixed Ligand Complexes of Cu(II) with 2,2′-Bipyridyl and Some Aromatic Diamines

2015

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“…Moreover, there are different methods allowing the stability of heteroligand complexes to be compared with those of the corresponding binary systems. One such method is calculation of the stabilization constant (Δlog 10 β ) [ 11 , 20 ] (Eq. 3 ) on the grounds of the difference between the experimental stability constant for the mixed-ligand complex (log 10 β 1110 ) and the constant based on statistical data (log 10 β stat ): where: …”

Section: Resultsmentioning

confidence: 99%

“…For the complexes containing protonated ligand forms (lysine and histidine), Δlog 10 K is calculated as shown in the Eq. ( 8 ) [ 11 ]: …”

Section: Resultsmentioning

confidence: 99%

“…The stability constants of mixed-ligand cobalt(II) complexes, with amino acids as primary ligands and imidazole as secondary ligand, under oxygen-free conditions have so far been determined potentiometrically for glycine, DL -α-alanine and DL -valine [ 7 ], but the stability constants resulting from combined potentiometric and spectrophotometric titrations have been determined only for L-α-alanine (a monoaminocarboxylic acid) [ 8 ]. It should be emphasized that coordinating interactions in the cobalt(II)–amino acid–imidazole systems have been also investigated in solid state: with acetyl- DL -phenylglycine [ 9 ], N -acetyl, N -benzoyl and N -tosyl derivatives of amino acids [ 10 ] as well as in solution: with imidazole-4-acetic acid [ 11 ], bis(imidazolyl) derivatives of amino acids [ 12 ], 1,2-disubstituted derivative of L -histidine [ 13 ] and biomimetic models of coenzyme B 12 [ 14 ].…”

Section: Introductionmentioning

confidence: 99%

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Equilibria in cobalt(II)–amino acid–imidazole system under oxygen-free conditions: effect of side groups on mixed-ligand systems with selected L-α-amino acids

Woźniczka

Vogt

Kufelnicki

2016

Chemistry Central Journal

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BackgroundHeteroligand Co(II) complexes involving imidazole and selected bio-relevant L-α-amino acids of four different groups (aspartic acid, lysine, histidine and asparagine) were formed by using a polymeric, pseudo-tetrahedral, semi-conductive Co(II) complex with imidazole–[Co(imid)2]n as starting material. The coordination mode in the heteroligand complexes was unified to one imidazole in the axial position and one or two amino acid moieties in the appropriate remaining positions. The corresponding equilibrium models in aqueous solutions were fully correlated with the mass and charge balance equations, without any of the simplified assumptions used in earlier studies. Precise knowledge of equilibria under oxygen-free conditions would enable evaluation of the reversible oxygen uptake in the same Co(II)–amino acid–imidazole systems, which are known models of artificial blood-substituting agents.ResultsHeteroligand complexes were formed as a result of proton exchange between the two imidazole molecules found in the [Co(imid)2]n polymer and two functional groups of the amino acid. Potentiometric titrations were confirmed by UV/Vis titrations of the respective combinations of amino acids and Co-imidazole. Formation of MLL′ and ML2L′ species was confirmed for asparagine and aspartic acid. For the two remaining amino acids, the accepted equilibrium models had to include species protonated at the side-chain amine group (as in the case of lysine: MLL′H, ML2L′H2, ML2L′H) or at the imidazole N1 (as in the case of histidine: MLL′H and two isomeric forms of ML2L′). Moreover, the Δlog10 β, log10 βstat, Δlog10 K, and log10 X parameters were used to compare the stability of the heteroligand complexes with their respective binary species. The large differences between the constant for the mixed-ligand complex and the constant based on statistical data Δlog10β indicate that the heteroligand species are more stable than the binary ones. The parameter Δlog10K, which describes the influence of the bonded primary ligand in the binary complex CoII(Himid) towards an incoming secondary ligand (L) forming a heteroligand complex, was negative for all the Amac ligands (except for histidine, which shows stacking interactions). This indicates that the mixed-ligand systems are less stable than the binary complexes with one molecule of imidazole or one molecule of amino acid, in contrast to Δlog10 β, which deals with binary complexes CoII(Himid)2 and CoII(AmacH−1)2 containing two ligand molecules. The high positive values of the log10X disproportionation parameter were in good agreement with the results of the Δlog10β calculations mentioned above.ConclusionThe mixed-ligand MLL′-type complexes are formed at pH values above 4–6 (depending on the amino acid used), however, the so-called “active” ML2L′-type complexes, present in the equilibrium mixture and known to be capable of reversible dioxygen uptake, attain maximum share at a pH around nine. For all the amino acids involved, the greater the excess of amino acid, the lower the pH where the...

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“…[345][346][347][348][349][350][351][352] The results of these studies may contribute to the better understanding of the transport processes of various metal containing drugs. The area of these applications is very wide and only the most interesting and important examples will be summarized here.…”

Section: Applications Of Peptide Complexesmentioning

confidence: 99%

Metal complexes of amino acids and peptides

Farkas¹,

Sóvágó²

2014

Amino Acids, Peptides and Proteins

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Potentiometric and Thermodynamic Studies of Binary and Ternary Transition Metal(II) Complexes of Imidazole-4-acetic Acid and Some Bio-relevant Ligands

Cited by 37 publications

References 33 publications

Thermodynamics, Chemical Speciation and Complex Formation Equilibria Studies of Binary and Mixed Ligand Complexes of Cu(II) with 2,2′-Bipyridyl and Some Aromatic Diamines

Thermodynamics, Chemical Speciation and Complex Formation Equilibria Studies of Binary and Mixed Ligand Complexes of Cu(II) with 2,2′-Bipyridyl and Some Aromatic Diamines

Equilibria in cobalt(II)–amino acid–imidazole system under oxygen-free conditions: effect of side groups on mixed-ligand systems with selected L-α-amino acids

Metal complexes of amino acids and peptides

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