摘要 :
Reaction of 1,3-bis(2′-Ar-imino)isoindolines (HL~n, n = 1-7, Ar = benzimidazolyl, N-methylbenzimidazolyl, thiazolyl, pyridyl, 3-methylpyridyl, 4-methylpyridyl, and benzthiazolyl, respectively) with Cu(OCH_3)_2 yields mononuclear ...
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Reaction of 1,3-bis(2′-Ar-imino)isoindolines (HL~n, n = 1-7, Ar = benzimidazolyl, N-methylbenzimidazolyl, thiazolyl, pyridyl, 3-methylpyridyl, 4-methylpyridyl, and benzthiazolyl, respectively) with Cu(OCH_3)_2 yields mononuclear hexacoordinate complexes with Cu(L~n)_2 composition. With cupric perchlorate square-pyramidal [Cu~(II)(HL~n)(NCCH_3)(OClO _3)]ClO_4 complexes (n = 1, 3, 4) were isolated as perchlorate salts, whereas with chloride Cu~(II)(HL~n)Cl _2 (n = 1, 4), or square-planar Cu~(II)Cl_2(HL n) (n = 2, 3, 7) complexes are formed. The X-ray crystal structures of Cu(L~3)_2, Cu(L~5)_2, [Cu ~(II)(HL~4)(NCCH_3)(OClO_3)]ClO _4, Cu~(II)Cl(L_2) and Cu~(II)Cl(L ~7) are presented along with electrochemical and spectral (UV-Vis, FT-IR and X-band EPR) characterization for each compound. When combined with base, the isoindoline ligands in the [Cu~(II)(HL~n)(NCCH _3)(OClO_3)]ClO_4 complexes undergo deprotonation in solution that is reversible and induces UV-Vis spectral changes. Equilibrium constants for the dissociation are calculated. X-band EPR measurements in frozen solution show that the geometry of the complexes is similar to the corresponding X-ray crystallographic structures. The superoxide scavenging activity of the compounds determined from the McCord-Fridovich experiment show dependence on structural features and reduction potentials.
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摘要 :
Six dichloroiron(III) complexes of 1,3-bis(2′-arylimino)isoindoline (BAIH) with various N-donor aryl groups have been characterized by spectroscopy (infrared, UV-vis), electrochemistry (cyclic voltammetry), microanalysis, and in ...
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Six dichloroiron(III) complexes of 1,3-bis(2′-arylimino)isoindoline (BAIH) with various N-donor aryl groups have been characterized by spectroscopy (infrared, UV-vis), electrochemistry (cyclic voltammetry), microanalysis, and in two cases X-ray crystallography. The structurally characterized Fe ~(III)Cl_2(L~n) complexes (n = 3, L~3 = 1,3-bis(2′-thiazolylimino)isoindoline and n = 5, L~5 = 1,3-bis(4-methyl-2′-piridylimino)isoindoline) are five-coordinate, trigonal bipyramidal with the isoindoline ligands occupying the two axial and one equatorial positions meridionally. These compounds served as precursors for catechol dioxygenase models that were formed in solution upon addition of 3,5-di-tert-butylcatechol (H_2DBC) and excess triethylamine. These adducts react with dioxygen in N,N-dimethylformamide, and the analysis of the products by chromatography and mass spectrometry showed high intradiol over extradiol selectivity (the intradiol/extradiol product ratios varied between 46.5 and 6.5). Kinetic measurements were performed by following the change in the intensity of the catecholate to iron ligand-to-metal charge transfer (LMCT) band, the energy of which is influenced by the isoindolinate-ligand (827-960 nm). In combination with electrochemical investigations the kinetic studies revealed an inverse trend between reaction rates and oxidation potentials associated with the coordinated DBC~(2-). On the basis of these results, a substrate activation mechanism is suggested for this system in which the geometry of the peroxide-bridged intermediate may be of key importance in regioselectivity.
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Mononuclear complexes of N-methylpropanoate-N,N-bis-(2-pyridylmethyl)amine (MPBMPA) and N-propanoate-N,N-bis-(2-pyridylmethyl)amine (HPBMPA) with first row transition metals from Mn to Cu were synthesized and characterized by spec...
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Mononuclear complexes of N-methylpropanoate-N,N-bis-(2-pyridylmethyl)amine (MPBMPA) and N-propanoate-N,N-bis-(2-pyridylmethyl)amine (HPBMPA) with first row transition metals from Mn to Cu were synthesized and characterized by spectroscopy (infrared, UV-visible), electrochemistry (cyclic voltammetry), microanalysis and in four cases X-ray crystallography. Structure of the complexes revealed high flexibility of these ligands that can adopt facial (Fe) and meridional (Cu) geometry. Activity in the degradation of reactive oxygen species (superoxide radical anion: superoxide dismutase (SOD)-like activity and hydrogen peroxide: catalase-like activity) was tested throughout the complex series in aqueous solutions. In connection with the catalytic dismutation of H_2O_2, bleaching tests with morin were also conducted in water. Comparison of the two ligands helped in elucidating the possible role of the carboxylate moiety in the different catalytic reactions. Although no general trends could be revealed between reactivity and constitution of the first coordination sphere, plausible explanations for differences are discussed individually for SOD like, catalase-like and bleaching activity.
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摘要 :
Recently, a series of Fe(II) complexes have been published by our group with 3 N-donor 1,3-bis(2′-Ar-imino)isoindoline ligands containing various Ar-groups (pyridyl, 4-methylpyridyl, thiazolyl, benzimidazolyl and N-methylbenzimid...
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Recently, a series of Fe(II) complexes have been published by our group with 3 N-donor 1,3-bis(2′-Ar-imino)isoindoline ligands containing various Ar-groups (pyridyl, 4-methylpyridyl, thiazolyl, benzimidazolyl and N-methylbenzimidazolyl). The superoxide scavenging activity of the compounds showed correlation with the Fe(III)/Fe(II) redox potentials. Analogous, electroneutral chelate complexes with Mn(II) and Ni(II) in 2:1 ligand:metal composition are reported here. Each Mn(II) complex exhibits one reversible redox wave that is assigned as the Mn(III)/Mn(II) redox transition. The E _(1/2) spans a 180 mV range from -98 (Ar = 3-methylpyridyl) to 82 mV (Ar = thiazolyl) vs. the Fc~+/Fc depending on the Ar-sidearm. The SOD-like (SOD=superoxide dismutase)activity of all complexes was determined according to the McCord-Fridovich method. The Mn(II) isoindolinates have IC _(50) values - determined with 50 μM cytochrome c Fe(III) - that range from (3.22 ± 0.39) × 10~(-6) (Ar = benzimidazolyl) to (10.80 ± 0.54) × 10~(-6) M (Ar = N-methylbenzimidazolyl). In contrast with the Fe(II) complexes, the IC_(50) concentrations show no significant dependence on the E_(1/2) values in this narrow potential range emphasizing that the redox potential is not the governing factor in the Mn(II)-containing scavengers. The analogous Ni(II) compounds show no redox transitions in the thermodynamically relevant potential range (-0.40 to 0.65 V vs. SCE) and accordingly, their superoxide scavenging activity (if any) is below the detection level.
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The mononuclear complex, Fe ~(III)(O-bs)(salen) (salenH _2 = 1,6-bis(2-hydroxyphenyl)-2,5-diaza-hexa-1,5-diene; O-bsH = O-benzoylsalicylic acid) was synthesized as synthetic enzyme-depside complex, and characterized by spectroscop...
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The mononuclear complex, Fe ~(III)(O-bs)(salen) (salenH _2 = 1,6-bis(2-hydroxyphenyl)-2,5-diaza-hexa-1,5-diene; O-bsH = O-benzoylsalicylic acid) was synthesized as synthetic enzyme-depside complex, and characterized by spectroscopic methods and X-ray crystal analysis. The dioxygenation of flavonol (flaH) and 3-hydroxy-4-quinolone (quinH _2) derivatives in the presence of catalytic amounts of Fe ~(III)(O-bs)(salen) results in the oxidative cleavage of the heterocyclic ring to give the corresponding O-benzoylsalicylic and anthranilic acid derivatives with concomitant release of carbon monoxide. These reactions can be regarded as biomimetic functional models with relevance to the iron-containing flavonol and the cofactor-independent 3-hydroxy-4(1H)-quinolone 2,4-dioxygenases.
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