Histidine complexes

III)—L- histidine complex a multi-instmmental approach. Journal of Environmental Monitoring, 2, 355. 

The FePcY-PDMS supramolecular catalyst resembles the architecture of natural enzymes. In this system the PDMS membrane takes over the role of the phospholipid double layer likewise, the zeolite imitates the protein and the FePc complex the Fe-protoporphyrin. Zeolite-encaged Cu-histidine complexes were also studied as mimics of natural Cu-enzyme complexes.173... 

Thus, the mechanism of MT antioxidant activity might be connected with the possible antioxidant effect of zinc. Zinc is a nontransition metal and therefore, its participation in redox processes is not really expected. The simplest mechanism of zinc antioxidant activity is the competition with transition metal ions capable of initiating free radical-mediated processes. For example, it has recently been shown [342] that zinc inhibited copper- and iron-initiated liposomal peroxidation but had no effect on peroxidative processes initiated by free radicals and peroxynitrite. These findings contradict the earlier results obtained by Coassin et al. [343] who found no inhibitory effects of zinc on microsomal lipid peroxidation in contrast to the inhibitory effects of manganese and cobalt. Yeomans et al. [344] showed that the zinc-histidine complex is able to inhibit copper-induced LDL oxidation, but the antioxidant effect of this complex obviously depended on histidine and not zinc because zinc sulfate was ineffective. We proposed another mode of possible antioxidant effect of zinc [345], It has been found that Zn and Mg aspartates inhibited oxygen radical production by xanthine oxidase, NADPH oxidase, and human blood leukocytes. The antioxidant effect of these salts supposedly was a consequence of the acceleration of spontaneous superoxide dismutation due to increasing medium acidity. 

The lower activity of most chelate complexes than that of the aquo complex of Cu was attributed to small amounts of free Cu liberated by the labile complexes The dismutase activity reported for the [Cu(I)gCu(II)g(D-penicillamine)jjCl] complex was suppressed by EDTA or by a Chelex 100 treatment Free Cu cations can, however, not explain the very high second-order rate constant of 6x 10 M " s measured at pH 7.0 with the [Cu findomethacin) ] complex by the decay of OJ at 250 nm. With the Cu-histidine complexes, moreover, it was concluded from the influence of pH on the pseudo-first order rate constant of the dismutation of HOj/Oj that [CuHiSjH] was the active species with a second-order rate constant of 3x 10 M" s between pH 2 and 7. It was not possible kinetically to distinguish between the classical and the alternative mechanism, with respectively Cu(I) or a Cu(II)—Oj" complex as intermediate... 

Van Willigen and co-workers reported an ENDOR study of frozen solutions containing V02+ and histidine (20), camosine (21) and imidazole (19) (cf. Section 33.5.3.2).383 The complex formed between V02+ and an excess of histidine in aqueous solutions of pH 7 showed no axial H20 lines. Coordination involved the N-3 nitrogen atom of the im ring of histidine, giving a structure in which the cation is shielded from water. According to the ENDOR spectra,383 the geometry of the V02+-im moiety in the [VO(im)4]2+ and V02+ carnosine complexes is similar but a distinct structure appears to exist for the V02+ histidine complex. 

Monzani E, Linati L, Casella L et al (1998) Synthesis, characterization and stereoselective catalytic oxidations of chelated deuterohaemin-glycyl-L-histidine complexes. Inorg Chim Acta 273 339-345... 

First we selected, as QC, the CO-heme-histidine complex shown in Figure 8-1 with a schematic view of the Mb. 

Comparing the most conserved parts, the active site, reveals two different types of type 3 copper proteins, an arthropod hemocyanin-like one and a molluscan hemocyanin-hke one. While the Cn-B site is highly conserved in both types, the Cu-A site differs. In the case of molluscan hemocyanins, one helix is too short for stabihzing the important histidine complexing Cu-A so that it has to be tied down by an unusual His ys bond as shown in Figure 2 (d-f). 

The " Sn Mossbauer spectra of triethyltin compounds bound to high-affinity, protein sites indicate that the quadrupole splitting, AEq, is less than 2.3 mm sec (479, 491), which would be consistent with tetrahedral, RsSnX, tin-atom geometry, or a 5-coordinate, cis-RaSnX chelated structure. However, the trialkyItin-histidine complex, having a planar, RsSn unit, suggested earlier by Rose and Lock (485,... 

In other tests of the ligand exchange/CD detection assay procedure, it was demonstrated that 51 of a total of 53 di- and tripeptides could be uniquely identified by the character of the changes in the CD spectra for the mixed Cu(II)-peptide-D-histidine complexes. A series of 19 neuropeptides was the focus of another... 

A variety of N20-ligands are thought to bind titanium in a tridentate fashion in a number of complexes including pyridyl hydrazone derivatives762 and the histidine complex... 

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