Synthesis, spectral, electrochemical and magnetic properties of new phenoxo-bridged dicopper(II) complexes derived from unsymmetrical binucleating ligands

Amudha, P; Thirumavalavan, Munusamy; Kandaswamy, M.

doi:10.1016/s0277-5387(99)00014-5

Cited by 11 publications

(3 citation statements)

References 30 publications

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“…see Refs. [32][33][34][35][36][37][38][39], and it has also been proposed for both met and half-met hemocyanin (11,26,27,60). We note that exchange of the Cu 2 bridging ligand would affect the magnitude of antiferromagnetic coupling (i.e.…”

Section: Discussionsupporting

confidence: 52%

Structural Basis and Mechanism of the Inhibition of the Type-3 Copper Protein Tyrosinase from Streptomyces antibioticusby Halide Ions

Tepper¹,

Bubacco²,

Canters³

2002

Journal of Biological Chemistry

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The inhibition of the type-3 copper enzyme tyrosinase by halide ions was studied by kinetic and paramagnetic 1 H NMR methods. All halides are inhibitors in the conversion of L-3,4-dihydroxyphenylalanine (L-DOPA) with apparent inhibition constants that follow the order I ؊ < F ؊ < < Cl ؊ < Br ؊ at pH 6.80. The results show that the inhibition arises from the interaction of halide with both the oxidized (affinity F ؊ > Cl ؊ > Br ؊ > > I ؊ ) and reduced (affinity I ؊ > Br ؊ > Cl ؊ > > F ؊ ) enzyme. The paramagnetic 1 H NMR of the oxidized enzyme complexed with the halides is consistent with a direct interaction of halide with the type-3 site and shows that the (Cu-His 3 ) 2 coordination occurs in all halide-bound species. It is surmised that halides bridge both of the copper ions in the active site. Fluoride and chloride are shown to bind only to the low pH form of oxidized tyrosinase, explaining the strong pH dependence of the inhibition by these ions. We further show that p-toluic acid and the bidentate transition state analogue, Kojic acid, displace chloride from the oxidized active site, whereas the monodentate substrate analogue, p-nitrophenol, forms a ternary complex with the enzyme and the chloride ion. On the basis of the experimental results, a model is formulated for the inhibitor action and for the reaction of diphenols with the oxidized enzyme.One of the unresolved questions in the enzymology of the type-3 copper-containing tyrosinases (EC 1.14.18.1) is the detailed molecular mechanism of both inhibitor action and substrate conversion. This report focuses on the mechanism of their inhibition by halides. Tyrosinases are monooxygenating enzymes catalyzing the ortho-hydroxylation of monophenols and the subsequent oxidation of the diphenolic products to the corresponding quinones. The reactions take place under concomitant reduction of molecular oxygen to water. The formed quinones are reactive precursors in the synthesis of melanin pigments. In fruits, vegetables, and mushrooms, Ty 1 is a key enzyme in the browning that occurs upon bruising or long-term storage. In mammals, Ty is responsible for skin pigmentation. Defects in the enzyme may lead to some forms of oculocutaneous albinism or vitiligo (1). Furthermore, the enzyme has been linked to Parkinson's and other neurodegenerative diseases (2-6). Consequently, the enzyme poses considerable interest from medical, agricultural, and industrial points of view.The current knowledge of Ty at the biological, mechanistic, and structural levels has recently been reviewed (7-10). Ty harbors a dinuclear so-called type-3 copper center, the occurrence of which has also been established in hemocyanins, which act as oxygen carriers in arthropods and mollusks, and the catechol oxidases, which oxidize o-diphenols to the corresponding quinones. The two closely spaced copper ions in the type-3 active site are coordinated each by 3 histidine residues through the N⑀ nitrogen atoms (9). Although the known type-3 centers are found to be similar both in structure and in their a...

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Section: Discussionsupporting

confidence: 52%

Structural Basis and Mechanism of the Inhibition of the Type-3 Copper Protein Tyrosinase from Streptomyces antibioticusby Halide Ions

Tepper¹,

Bubacco²,

Canters³

2002

Journal of Biological Chemistry

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“…In our laboratory we are dealing with binucleating ligands and their metal complexes for more than one decade. So far we have synthesised series of binucleating ligands with phenolic and piperazinyl donor atoms [21][22][23][24][25][26][27][28][29]. The magnetic and ESR spectral behaviours of the complexes are interesting.…”

Section: Introductionmentioning

confidence: 99%

“…The magnetic and ESR spectral behaviours of the complexes are interesting. The dicopper(II) complexes of the ligand "a" [21,22] are strongly antiferromagnetic, the complexes of the ligand "b" are weakly antiferromagnetic [23,24], and the complexes of the ligand "c" are paramagnetic [25] as shown in Scheme 1. The present study deals with the synthesis of similar compounds like "c" in which the two 2-hydroxy-5-methyl-3-(4-methylpiperazinyl)substituted phenyl residues are separated by a -CH 2 -N-CH 2 -fragment instead of methylene group.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Characterisation of New Symmetrical Binucleating Ligands and Their Binuclear Copper(II) Complexes

Jothivenkatachalam

Mohan

2014

Journal of Inorganic Chemistry

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New symmetrical binucleating ligands N,N-bis[2-hydroxy-5-methyl-3-(4-methyl-piperazinomethyl)benzyl]-alkylamines L1and L2and their copper(II) complexes [Cu2L(X)2]·2H2O, where X = CH3COO−, C6H5COO−, Cl−, andClO4-, were prepared and characterised. All the complexes undergo quasi-reversible reduction at negative potential (E = −0.48 to −1.02 V). The acetate and benzoate complexes undergo a two-step single electron transfer at –0.48 to –0.60 V and −0.9 to −1.02 V. The chloro and perchlorate complexes undergo a single step two-electron transfer at −0.55 to −0.75 V. Variable temperature magnetic studies show the presence of weak exchange interaction for acetate (−2 J around 25 to 40 cm−1) and benzoate (−2 J around 45 to 55 cm−1) bridged complexes and no exchange interaction is found for chloro and perchlorate complexes. ESR spectra of chloro and perchlorate complexes are like mononuclear copper(II) complexes with hyperfine splitting (A= 165 ± 5,g∥= 2.17–2.23, andg⊥= 2.05–2.10). The ESR spectra of acetate and benzoate complexes are like binuclear copper(II) complexes with broad signal (g= 2.2).

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The challenge of cyclic and acyclic schiff bases and related derivatives

Vigato¹,

Tamburini²

2004

Coordination Chemistry Reviews

947

415

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Synthesis, spectral, electrochemical and magnetic properties of new phenoxo-bridged dicopper(II) complexes derived from unsymmetrical binucleating ligands

Cited by 11 publications

References 30 publications

Structural Basis and Mechanism of the Inhibition of the Type-3 Copper Protein Tyrosinase from Streptomyces antibioticusby Halide Ions

Structural Basis and Mechanism of the Inhibition of the Type-3 Copper Protein Tyrosinase from Streptomyces antibioticusby Halide Ions

Synthesis and Characterisation of New Symmetrical Binucleating Ligands and Their Binuclear Copper(II) Complexes

The challenge of cyclic and acyclic schiff bases and related derivatives

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