Copper histidine complexes

L-ascorbic acid Amperometric Enzyme-less biosensor using poly-L-histidine-copper complex as an alternative biocatalyst Hasebe et al. (1998)... 

High-spin/low-spin transitions bipyridyl metal complexes, 90 iron complexes, 94 polypyridyl metal complexes, 91 Histamine metal complexes, 82 Histidine copper complexes naturally occurring, 965 metal complexes, 746 naturally occurring, 966 reactivity, 756 stereoselectivity, 754 Schiff bases... 

The presence of residual unbound transition-metal ions on a dyed substrate is a potential health hazard. Various eco standards quote maximum permissible residual metal levels. These values are a measure of the amount of free metal ions extracted by a perspiration solution [53]. Histidine (5.67) is an essential amino acid that is naturally present as a component of perspiration. It is recognised to play a part in the desorption of metal-complex dyes in perspiration fastness problems and in the fading of such chromogens by the combined effects of perspiration and sunlight. The absorption of histidine by cellophane film from aqueous solution was measured as a function of time of immersion at various pH values. On addition of histidine to an aqueous solution of a copper-complex azo reactive dye, copper-histidine coordination bonds were formed and the stability constants of the species present were determined [54]. Variations of absorption spectra with pH that accompanied coordination of histidine with copper-complex azo dyes in solution were attributable to replacement of the dihydroxyazo dye molecule by the histidine ligand [55]. 

On immersion of cellophane films dyed with four copper-complex azo reactive dyes in aqueous histidine, the absorption spectra of the dyeings changed as a result of abstraction of... 

Figure 3.13 Dynamic salicylamide-copper complexation identifies a histidine-snbstitnted salicylamide that selectively binds an RNA hairpin based on the Gronp 1 intron of P. carinii over the analogous DNA hairpin.

L-histidine, L-glutamine, and L-histidine anhydride27 and by copper complexes of organic bases such as o-phenanthroline and a,a -dipyridyl has also been reported these complexes were more active than Cu++ ions alone.28... 

Substantial rate accelerations are observed in these systems for base hydrolysis. Thus for the ethylenediamine complex (18) rate increases of 4x 104 for GlyOEt to 1.4 x 107 for ethyl picolinate are observed.85 These rate accelerations are consistent with the formation of carbonyl-bonded species (18). The effects with methyl L-cysteinate and methyl L-histidinate are much less marked as such ligands can give mixed ligand complexes which do not involve alkoxycarbonyl donors. Thus in the case of methyl L-histidinate the complex (20) is formed. For these latter two esters only relatively small rate accelerations of 20-100 occur. For the chelate ester complexes, the ratios of kcm/kH2o fail within the range 3.8 x 109 to 3.2 x 1011. Such values for the relative nucleophilicity of water and hydroxide ion are comparable with those previously noted for copper(II) complexes.82... 

The structure and enzyme kinetics of bovine erythrocyte superoxide dismutase are reviewed. The protein has a novel imidazolate-bridged copper(II)-zinc(II) catalytic center in each of two identical subunits. Since a C /Cu1 redox couple is responsible for the dismutase activity of the enzyme, the role of zinc is of interest. Both 220-MHz NMR measurements of the exchangeable histidine protons and chemical modifications using diethylpyrocarbonate demonstrate that zinc alone can fold the protein chain in the region of the active site into a conformation resembling that of the native enzyme. Other possible roles for zinc are discussed. Synthetic, magnetic, and structural studies of soluble, imidazolate-bridged copper complexes of relevance to the 4 Cu(II) form of the enzyme have been made. 

The reduction of oxygen by copper(I) is faster than that of the iron(II) complexes 5x 104M 1 s-1 for CuI(phen)2 [52] and 4xl04M 1 s 1 for Cu1 (histidine [76]. It is this relatively fast autoxidation that limits the usefulness of copper complexes as mimics of superoxide dismutase under conditions of high superoxide concentrations [77]. Copper(II) catalyses the dismutation of superoxide at near diffusion-controlled rates kcat = 8 x 109 M 1 s-1 [78,79],... 

Initially, copper(II) coordinates to the octapeptide angiotensin II (Asp Arg Val Tyr Ile-His-Pro-Phe) at the imidazole nitrogen. At neutral pH the main copper complex is CuL, which is a 3N complex (Figme 2). The copper(II) is bonded via the imidazole nitrogen of the histidine residue, and two deprotonated peptide nitrogens. As the pH is raised above 8.0, the coordination site changes to the N-terminus... 

Figure 3 Binuclear copper complexes in octopus hemocyanin (a) and sweet potato catechol oxidase (b) showing the thioether linkage between a cysteine residue and a directly coordinating histidine imidazole. Heteroatoms (N,0,S) are indicated by a shaded quadrant. [ortep-III views based on PDB ID 1JS8 and IBTl]...

Chen, T.S., Liu, C.Y. Histidine-functionalized silica and its copper complex as stationary phases for capillary electrochromatography. Electrophoresis 22,2606—2015 (2001)... 

Two different copper complexes were found on the zeolite, a mono histidine complex (A) and a bis-histidine complex (B). The influence of the initial copper concentration in the ion exchange solution on the A to B ratio was studied. A high A/B ratio was found at low copper concentrations and vice versa. For high copper concentrations the ratio leveled off at a value of A/B = 1.5. Full exchange was only achieved at low concentrations up to 1.0 Cu/UC. At higher copper concentrations the copper was no longer totally exchanged on the zeolite and the A/B ratio became independent of the external copper concentration. 

A number of new copper complexes have also been found to have antiinflammatory activity. Copper(II)(j8-oxo-2-thiophenepropionitrile) is effective in treating rat polyarthritis [175]. The copper complex of glycyl-L-histidyl-L-lysine, Cu(II)(GHL), is claimed to have anti-inflammatory activity and increase the rate of wound healing [176, 177] consistent with earlier reports of increased gastric wound healing rates associated with Cu(II)(aspirinate)4 and Cu(II)(tryptophanate)2 treatment [178]. Copper(II)(L-histidinate)2, Cu(II)-... 

The observation that copper supplementation modulates the formation of arachidonic acid by regulating A -desaturase activity, which converts diho-mo-y-linolenic acid to arachidonic acid, has led to the suggestion that combinations of linoleic, y-linolenic or dibromo-y-linolenic acid with assimilable copper complexes might be useful in the treatment of inflammatory disorders, cardiovascular and thrombotic disorders, menstrual cycle disorders, diabetes, endometriosis, nutritional deficiencies and malignancies [255]. Modulation of stearoyl CoA A -desaturase activity by Cu(II)(tyrosinate)2, Cu(II)(lysinate)2, and Cu(II)(histidinate)2 [599] may also have a bearing on these uses of copper complexes. 

These observations are also consistent with copper complex modulation of A terminal desaturase activity [702]. A purified chicken liver microsomal preparation of stearoyl-CoA A -desaturase was inhibited with Cu(IIXtyrosi-nate)j, Cu(II)(lysinate)2 and Cu(II)(histidinate)2. These chelates lowered the steady-state level of ferrocytochrome only 20% and only partially inhibited the NADH-ferricyanide reductase activity, indicating that the terminal desaturation step was being inhibited. Since oxygen is known to be involved in this desaturation and that there is an initial reduction of the desaturase iron, it is plausible that these chelates are decreasing desaturase activity by acting as superoxide scavengers [702]. 

Copper complexes of amines such as histidine,42 ethylenediamine and 2,2 -bipyridine have been studied as models for the behavior of copper enzymes which catalyze the decomposition of H202 to 02 and H20 peroxo species are believed to be intermediates.428... 

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