Cobalt(II) complexes reversibly uptaking nitric oxide in aqueous solution

Jeżowska‐Trzebiatowska, B.; Gerega, K.; Vogt, A.

doi:10.1016/s0020-1693(00)94998-3

Cited by 12 publications

(8 citation statements)

References 10 publications

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“…The procedure for preparation of the polymeric, pseudo-tetrahedral, semi-conductive Co(II) complex with imidazole–[Co(imid) 2 ] n , as well as analytical and IR spectroscopic identification, have already been reported in [ 3 , 4 , 8 ]. The purity of amino acids used in this investigation: L-α-asparagine (Sigma Aldrich), L-α-aspartic acid (Fluka), L-α-lysine (Sigma Aldrich) and L-α-histidine (Fluka) was determined potentiometrically.…”

Section: Methodsmentioning

confidence: 99%

“…The structure is regarded as analogous to the binary amino acid complexes of Co(II) and other divalent metals, where the amino acid chelate rings are known to be in an equatorial trans -position [ 2 ]. The axial sites are occupied by imidazole (coordinated by N3) and a water molecule [ 3 ]. Due to the “trans-effect” of imidazole, these complexes are capable of the multiple cyclic uptake and release of molecular oxygen and therefore, are capable of imitating natural O 2 carriers.…”

Section: Introductionmentioning

confidence: 99%

“…Existing literature data suggests that heteroligand complexes in the cobalt(II)–amino acid–imidazole systems are formed within the range pH 6–10 [ 1 , 3 , 5 ]. This indicates the deciding donor properties of the amino groups: they dissociate in basic medium.…”

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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Section: Methodsmentioning

confidence: 99%

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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“…In contrast to classical methods of preparing such compounds by mixing separate solutions of Co(II) salts, appropriate amino acids and imidazole [16–18], an original method has been applied, in which cobalt(II) and imidazole were introduced in the form of a polymeric, pseudo-tetrahedral, semi-conductive complex [Co(imid) 2 ] n . This results in the formation of definite, unique structures with an imidazole molecule in an axial position opposite the O 2 molecule [19–26]. …”

Section: Introductionmentioning

confidence: 99%

“…accurate calculations of the Co(II), amac and Himid concentrations at equilibrium, by using the formation constants reported in our work for analogous oxygen-free systems [37]. These calculations may allow the equilibrium concentrations of all equilibrium forms present in solution to be determined, and for the equilibrium constants to be evaluated without using any simplified approximations, which for instance take into account only the “active” complex and the oxygen adduct within the mass balance system [19, 38]. Moreover, the advantage of the experimental methods used in the present work, i.e.…”

Section: Introductionmentioning

confidence: 99%

Reversible uptake of molecular oxygen by heteroligand Co(II)–l-α-amino acid–imidazole systems: equilibrium models at full mass balance

Pająk

Woźniczka

Vogt

et al. 2017

Chemistry Central Journal

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BackgroundThe paper examines Co(II)–amino acid–imidazole systems (where amino acid = l-α-amino acid: alanine, asparagine, histidine) which, when in aqueous solutions, activate and reversibly take up dioxygen, while maintaining the structural scheme of the heme group (imidazole as axial ligand and O2 uptake at the sixth, trans position) thus imitating natural respiratory pigments such as myoglobin and hemoglobin. The oxygenated reaction shows higher reversibility than for Co(II)–amac systems with analogous amino acids without imidazole. Unlike previous investigations of the heteroligand Co(II)–amino acid–imidazole systems, the present study accurately calculates all equilibrium forms present in solution and determines the equilibrium constants without using any simplified approximations. The equilibrium concentrations of Co(II), amino acid, imidazole and the formed complex species were calculated using constant data obtained for analogous systems under oxygen-free conditions. Pehametric and volumetric (oxygenation) studies allowed the stoichiometry of O2 uptake reaction and coordination mode of the central ion in the forming oxygen adduct to be determined. The values of dioxygen uptake equilibrium constants were evaluated by applying the full mass balance equations.ResultsInvestigations of oxygenation of the Co(II)–amino acid–imidazole systems indicated that dioxygen uptake proceeds along with a rise in pH to 9–10. The percentage of reversibility noted after acidification of the solution to the initial pH ranged within ca 30–60% for alanine, 40–70% for asparagine and 50–90% for histidine, with a rising tendency along with the increasing share of amino acid in the Co(II): amino acid: imidazole ratio. Calculations of the share of the free Co(II) ion as well as of the particular complex species existing in solution beside the oxygen adduct (regarding dioxygen bound both reversibly and irreversibly) indicated quite significant values for the systems with alanine and asparagine—in those cases the of oxygenation reaction is right shifted to a relatively lower extent. The experimental results indicate that the “active” complex, able to take up dioxygen, is a heteroligand CoL2L′complex, where L = amac (an amino acid with a non-protonated amine group) while L′ = Himid, with the N1 nitrogen protonated within the entire pH range under study. Moreover, the corresponding log value at various initial total Co(II), amino acid and imidazole concentrations was found to be constant within the limits of error, which confirms those results. The highest log value, 14.9, occurs for the histidine system; in comparison, asparagine is 7.8 and alanine is 9.7. This high value is most likely due to the participation of the additional effective N3 donor of the imidazole side group of histidine.ConclusionsThe Co(II)–amac–Himid systems formed by using a [Co(imid)2]n polymer as starting material demonstrate that the reversible uptake of molecular oxygen occurs by forming dimeric μ-peroxy adducts. The essential impact on the electron structur...

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ChemInform Abstract: COBALT(II) COMPLEXES REVERSIBLY UPTAKING NITRIC OXIDE IN AQUEOUS SOLUTION

Jeżowska‐Trzebiatowska¹,

Gerega²,

Vogt³

1979

Chemischer Informationsdienst

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Cobalt(II) complexes reversibly uptaking nitric oxide in aqueous solution

Cited by 12 publications

References 10 publications

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

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

Reversible uptake of molecular oxygen by heteroligand Co(II)–l-α-amino acid–imidazole systems: equilibrium models at full mass balance

ChemInform Abstract: COBALT(II) COMPLEXES REVERSIBLY UPTAKING NITRIC OXIDE IN AQUEOUS SOLUTION

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