Cysteine complex

The fast interaction of O2 with Fe(II)-cysteine complexes to give an oxygen adduct which rapidly undergoes one-electron breakdown to an Fe(III)-cysteine complex and -OJ has been examined by stopped-flow spectrophotometry at 570 nm . Subsequent decomposition of the Fe(IlI) complex to yield Fe(II) and the disulphide, cystine, was much slower. Both mono- and bis-complexes of Fe(Il) are involved and the reaction is first-order in both Fe(II) complex and O2 k (mono) = (5 +1) x 10 l.mole ksec" and k (bis) = (2 0.5) x lO l.mole . sec at 25 °C, corresponding to factors of 10 and 10 times faster than the analogous reactions with sulphosalicylic acid complexes of Fe(II), a feature attributed to Fe(ll)-S bonding in the cysteine complexes. ... 

Ammonio-2-carboxyethylthio)-5,7-dinitro-4,5-dihydrobenzofurazanide A-oxide (4,6-Dinitrobenzofurazan A-oxide.cysteine complex)... 

When thoroughly dry, the cysteine complex of 5,7-dinitrobenzofurazan N-oxide exploded on heating. 

Simmons-Willis, T. A., et al. Transport of a neurotoxicant by molecular mimicry the methylmercury-l-cysteine complex is a substrate for human L-type large neutral amino acid transporter (LAT) 1 and LAT2. Biochem. J. 2002, 367, 239-246. 

Oxygen radical anion 02( > is formed in an equilibrium reaction of the copper-cysteine-oxygen complex and a copper-cysteine complex ... 

The aquated iron(III) ion is an oxidant. Reaction with reducing ligands probably proceeds through complexing. Rapid scan spectrophotometry of the Fe(III)-cysteine system shows a transient blue Fe(lII)-cysteine complex and formation of Fe(II) and cystine. The reduction of Fe(lII) by hydroquinone, in concentrated solution has been probed by stopped-flow linked to x-ray absorption spectrometry. The changing charge on the iron is thereby assessed. In the reaction of Fe(III) with a number of reducing transition metal ions M in acid, the rate law... 

The synthesis and characterization of materials showing biological activity similar to that of GTF isolated from yeast is a logical objective. As already mentioned, Mertz found aqua and similar complexes of chromium to be more active than chelates with strong ligands. An exception to this was an unspecified cysteine complex,1193 prepared by C. L. Rollinson, which showed marked, but erratic, behaviour in GTF tests. Further investigation of this observation would be interesting, particularly as the crystal structure of a cysteine complex is now known.1185... 

In addition to its function in catalysis, zinc often plays an important structural role, e.g., in the zinc finger transcriptional regulators (Fig. 5-38).k Zinc ions bind to insulin and stabilize its hexameric structure (Fig. 7-18)/ Six Zn2+ ions are present in the hexagonal tail plate of the T-even bacteriophage (Box 7-C) and appear to be essential for invasion of bacteria.131 In carnivores, the tapetum, the reflecting layer behind the retina of the eye of many animals, contains crystals of the Zn2+-cysteine complex. 

Although such reactions have been known for a long time, it appears a somewhat neglected area of study. Most attention has been on cysteine and its oxidation to the disulfide which is catalyzed by metal ions, in particular CuI[ (see Section 20.2.2.2.2) and FeI,[.81 The likely intermediates in these reactions are metal-cysteine complexes which undergo internal electron transfer. As noted earlier (Section 20.2.2.2.2), penicillamine differs from cysteine in its reactivity and gives rise to mixed valence species. More recently Mn11 has also been found to catalyze the oxidations of Cys and Pen. 

For catalytic waves of hydrogen evolution in ammoniacal cobalt solutions, it has been observed (132) that ery/Aro-phenylcysteine gives a higher catalytic wave than the threo form (Fig. 28). These differences can be explained partly by differences in acid dissociation constants, and partly by variations in the stability constants of the cobalt-phenyl-cysteine complexes. 

Li and coworkers [193] reported a hybrid technique for rapid speciation analysis of Hg(I) and MeHg(II) by directly interfacing an NCE to atomic fluorescence spectrometry. Both mercury species were separated as their cysteine complexes within 64 seconds. The precision (RSD, n = 5) of migration time,... 

Model systems composed of Mo complexes and Fe-S clusters can give facile N2 reduction to NH3 under mild conditions. The Fe-S cluster is considered to act only as an electron transfer catalyst from reducing agents, such as BH4 and S2042, to the Mo complexes at which the reduction occurs [147-149]. Similarly the reduction of N2H4 to NH3 can be achieved by a catalyst of sodium molybdate, L-cysteine, and NaBH4 with a turnover number of 4.2 NH3 mol/(Mo-cysteine complex moljhr (148). 

FIGURE 7.3 51V NMR spectrum showing vanadate in the presence of cysteine at pH 8.4. Signals at high field derive from vanadate and its various oligomers. The low field signals are from S-coordinated cysteine complexes. 

Interest in potential anti-cancer activity has led to the preparation of a Pd-S-methyl-L-cysteine complex which analysed as [Pd3(SMCH)2Cl6].61 Its i.r. and visible spectra and conductivity are consistent with a chloro-bridged cation (19). On the other hand, the ethyl cysteinate complex of Pd, prepared according to equation... 

Figure 2. The cocatalytic effects of various charge carriers on acetylene reduction by the Mo(V)-cysteine complex (0.42 mmol) and NaBH4 (1.0 mmol), plotted against the reduction potentials (V vs. SHE) of the corresponding additives.

Figure 3. ESR spectra of Mo-cysteine complexes in borate buffer (pH 9.6) at 77 K (A), cysteine + MoCls (B), cysteine + K3MoCl6 or (A) + NaBH4...

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