Radical reductions of Cu(II)–penicillamine complexes: Evidence for a Cu(II)– disulphide anion intermediate (original) (raw)
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Canadian Journal of Chemistry, 1989
The Cu(I)•L2 complex with cysteine ligands at total Cu(I) concentrations of 10–30 μM was shown to be oxidised by cysteinyl radicals (RS•) with a diffusion-controlled rate constant k11a = 1.8 × 109 M−1 s−1. The corresponding reaction with the cysteine disulphide anion (RS•—SR−) proceeded at a slower rate, k11b = 2.7 × 108 M−1s−1. At higher Cu(I) concentrations, a slow and a fast component of absorption growth was observed. The slow component rate was independent of Cu(I) concentration, but it became more intense as the Cu(I) concentration rose. The yields and kinetic data were shown to be consistent with the presence of an equilibrium between the Cu(I)•L2 species and a second Cu(I) complex, Cu(I)2•L3, with an equilibrium constant of K1 = 162.[Formula: see text]This finding is consistent with the earlier work of Bagiyan etal. The rate constant of the oxidation of Cu(I)2•L3 by the cysteinyl radical was k12 = 1.0 × 109 M−1 s−1. Similar results were obtained with penicillamine, except th...
Theor Exp Chem, 1986
The optical and ESR spectra have been examined for complexes of Cu(1) with various radicals, which contain various numbers of CI ions in the central-atom coordination sphere. The spin-Hamiltonian parameters have been determined for all these radical complexes,and the observed ESR spectra have been compared with those calculated with allowance for second-order effects. The observed values for the isotropic and anisotropic components of the HFI constant from the central ion have been used to estimate the contributions from the 4s and 3d2z orbitals of the copper ion to the unpaired-electron MO. Quantum-chemical calculations have been performed by the lNDO.method on the electronic structures and geometries of complexes formed by CHmOH with Cu(1) for various CI contents in the coordination sphere. The radical is coordinated by the ~ orbital on the carbon atom, and the stabilities of the radical complexes decrease as the number of CI ions in the coordination sphere increases. A geometry close to planar is proposed for the CuCI43-fragment in a complex containing four C1 ions.
2003
Copper(lI) complexes of a series of tetradentate tripodal and lin ear li gand s co nta ining two substi tu ted pheno lates appended to N,N-dimethylethylenediamine a nd N,N'-dime thy lethyle nediamine moieties viz. N,N-dimethy l-N'.N'-bi s(2hydrox y-4-nitro be nzyl)ethy lenediamine [H 2 (L I)], N ,N-di methyl-N',N'-bis(2-hyd roxy-3 ,5-dime thylbe nzy l)ethy le ned iami ne [H 2 (L2)], N,N-dime th yl-N',N'-bi s(2-hydrox y-3 ,5-di-te rt-butylbe nzy I)ethyle nedi a mine [H2(L3)], N,N'-dimelhy l-N.N'-bis(2hydrox y-4-n itrobenzy I)eth y lenediami ne [H 2 (L4)l , N ,N'-di melhy 1-N ,N'-bi s(2-hyd rox y-3,5-di me thy Ibe nzy I)eth y lened iami ne [H 2 (L5)] a nd N,N'-dimelhyl-N,N'-bis(2-hydrox y-3,5-d i-tert-butylbenzyI)ethylenediallline [H 2 (L6)] have bee n isolated a nd characte ri zed by e lectro ni c abso rpti o n and EPR spectroscopy and cyclic a nd differential pulse vo ltamme try. Of th e~e compl exes, [C u(L1)h.2H 2 0 I , [Cu(L1)(py)] la and [Cu(L4)(H 2 0)].H 2 0 4 have been struc tura ll y cha racterized by X-r;] y crys tall og raph y. The coordination structure of 1 is dimeric with a tri gonal bipyramidal d isto rted square based pyra midal geo me try (TBOSBP) aro und each Cu(II). In complex la a lso a trigonal bipyramidal di sto rt ed sq uare based pym mid;]1 geometry (TB OSBP) aro und Cu(lI) is present. The Cu 20 2 basal plane is comprised two phe nolates a nd a terti;]ry amin e nitrogen of H 2 (L1) a nd an exogenous pyridine nitrogen and the dimethyl substi tuted amine nitrogen of H 2 (L1) is ax iall y coo rdin a ted. In 4, the re are two different copper(lI) complex molecules in the same un it cell with tri gonal bipy ramida l di storted sq uare based pyra mid al geo metry (TBOSBP) around Cu(II). The me thy l gro up s o f th e e th y lenedi ami ne fraill e are cis to each other in o ne mo lec ule (A) a nd a re trans to each o the r in the o the r molecule (B). The bond lengt hs ;] nd bond ang les in th e two molecules are different. The li gand field and EPR spec tra of all the co mpl exes are consiste nt w ith a squarebased geometry even in soluti o n. An intense band observed in the range 390-465 nm may originate fro m Cu(l l) ~ (p henolate)O-(axial) and/or equato ri al(phe nolat e)O-~ Cu(lI) CT tra nsiti o ns. The gil values lie in the m nge 2.23-2.29 indi catin g th e presence of CuN 2 0 2 o r CuNO) chromop hores. All the compl exes show an irreversible CUll/CUi redox proce~s at increased negative EII2 values. whi ch are consisten t with the prese nce of two coordin ated phe no late gro ups. The ox idation wave(s) occ urrin g in th e ra nge 0.06-0.89 V (vs Ag/Ag+) demonstrate(s) the formation of ph e noxyl radica l-copper(l\) species. The influe nce o f th e phe no late substituents o n the PhO-~ Cu(lI) LMCT tmn sitio n and th e C u(IJ)-p he no late/C u(I1)phenoxyl radi cal redox potentials are di sc ussed. The stabi lity of the radicals is e nh anced with the inc rease in do no r abi lit y of the substitue nts. The re leva nce of the notabl e structural a nd spectral features of the co mpl exes containing two redox active phenolates bound to coppe r(I1) in a squ are pyra mida l environment, to th ose of ga lac tose and g lyoxal ox idases are hi g hli g hted.
Molecules, 2018
X-and Q-band electron paramagnetic resonance (EPR) spectroscopy was used to characterize polycrystalline Cu(II) complexes that contained sodium 5-sulfonate salicylaldehyde thiosemicarbazones possessing a hydrogen, methyl, ethyl, or phenyl substituent at the terminal nitrogen. The ability of thiosemicarbazone proligands to generate superoxide radical anions and hydroxyl radicals upon their exposure to UVA irradiation in aerated aqueous solutions was evidenced by the EPR spin trapping technique. The UVA irradiation of proligands in neutral or alkaline solutions and dimethylsulfoxide (DMSO) caused a significant decrease in the absorption bands of aldimine and phenolic chromophores. Mixing of proligand solutions with the equimolar amount of copper(II) ions resulted in the formation of 1:1 Cu(II)-to-ligand complex, with the EPR and UV-Vis spectra fully compatible with those obtained for the dissolved Cu(II) thiosemicarbazone complexes. The formation of the complexes fully inhibited the photoinduced generation of reactive oxygen species, and only subtle changes were found in the electronic absorption spectra of the complexes in aqueous and DMSO solutions upon UVA steady-state irradiation. The dark redox activity of copper(II) complexes and proligand/Cu(II) aqueous solutions towards hydrogen peroxide which resulted in the generation of hydroxyl radicals, was confirmed by spin trapping experiments.
Structural and Spectroscopic Characterization of Two New Cu(II)-Dipeptide Complexes
Zeitschrift für Naturforschung B, 2000
Copper(II)-Dipeptide Complexes, Electronic Spectra, SOD Activity Two new Cu(II) complexes of stoichiometry [Cu(L-dipept)], containing as ligands the dipep tides L-alanine-L-valine and L-alanine-L-phenylalanine were prepared. They were character ized by single crystal X-ray diffractometry, and infrared and electronic spectroscopy. Both crystallize in the orthorhombic space group P2i2i2i with Z = 4. The Cu(II) ion has essentially the same elongated pyramidal coordination, being equatorially cis coordinated by a N2O2 ar rangement of ligand atoms and axially by a carbonyl oxygen atom. The compounds show rather similar polymeric structures that differ from each other basically in the dihedral angle between adjacent N2O2 planes. The infrared and electronic spectra are briefly discussed on the basis of the structural characteristics of the complexes. Superoxide dismutase-like activity was tested for both compounds.
European Journal of Inorganic Chemistry, 2015
The reactions of copper(I) iodide with N 1-substituted 2benzoylpyridine thiosemicarbazones [(C 6 H 5)(C 5 H 4 N)C 2 =N 3-N 2 H-C(=S)-N 1 HR (R = Me, HL Me ; Et, HL Et ; Ph, HL Ph)] in acetonitrile/dichloromethane mixtures have formed the complexes [Cu 2 II I 2 (μ 4-N,N,S-L Me) 2 ] (1), [Cu II I(κ 3-N,N,S-L Et)] (4), and [Cu II I(κ 3-N,N,S-L Ph)] (7) through proton-coupled electron transfer (PCET), and these complexes have rare Cu II-I bonds. The above thio ligands with copper(I) bromide and copper(I) chloride also formed similar Cu II-Br and Cu II-Cl bonds in complexes of stoichiometry [Cu II X