Metal-binding compounds

Both NH3 oxidizers and N02 oxidizers, but especially the former, are susceptible to inhibition by a wide range of compounds, and several different modes of action have been documented (Bedard and Knowles, 1989). The two most common modes of inhibition are (1) interference with the active site of the primary enzyme (i.e., NH3 monooxygenase in AOB N02 oxidoreductase in NOB) by compounds that share structural homology with NH3 or N02 and (2) metal binding compounds, which interfere with the action or availability of copper in the NH3-oxidizing enzymes. In both NH3- and N02 -oxidizers, the susceptibility to inhibitors by key enzymes forms the basis of some methods used to measure the rate of nitrification in the environment (see above). 

The metal-binding compound semi-xylenol orange is yellow at pH 5.9 but turns red ( niax = 490 nm) when it reacts with Pb ". A 2.025-mL sample of semi-xylenol orange was titrated with 7.515 X 10 " M Pb(N03)2, with the following results ... 

In general, it is considered desirable to reduce the initiation reaction as a means of controlling peroxidation. Apart from anti-oxidants (BHT 3,5-di-t-butyl-4-hydrotoluene is often used as a food additive), metal binding compounds and phenolic compounds may be inhibitory as well as the superoxide dismutase and glucose oxidase-catalase enzyme systems. 

Application of a New Tight-Binding Total Energy Method to 4-d Transition Metals and Compounds... 

A porphyrin compound with a 2,9-dimethyl- 1,10-phenanthroline functionality fused at the beta-pyrrole positions is a phthalocyanine analog, and formed a complex with zinc in the cavity and a further zinc binding to the phenanthroline group. The absorption and emission spectra of the compound with and without the external zinc demonstrated the strong effects of the second metal binding on the porphyrin 7r-system.840... 

The detection of metal-binding proteins, especially of Cd- and Hg-binding metallothioneins or of the merR protein, induced numerous studies of model compounds of Cd and Hg with more or less simple sulfur- and selenium-containing ligands. 

Note In this table all metal ions are in high-spin states and liganding atoms are small O, N donors. S-donors favour lower co-ordination numbers. Ligand-field theory, that is polarisation of and binding by the core electrons and orbitals of the metal ion compounds, can explain the above observations see inorganic chemistry textbooks in Further Reading . 

The discovery of BB-3497 was the result of screening a proprietary library for potential metalloenzyme inhibitors at the British Biotech Pharmaceutical Co. Ltd. [73]. This compound was originally prepared in a nonstereoselective manner and its stereochemistry was assigned on the basis of matrix metal-loprotease (MMP) inhibitory activity. The asymmetric synthesis of BB-3497 and the establishment of its stereochemistry by small-molecule X-ray crystallography was later reported by Pratt et al. [83]. Further structure-activity relationship studies of BB-3497 with respect to the modification of the P2 and P3 side chains [84] and metal binding group [85] were later reported by the scientists at British Biotech. These studies revealed that none of the... 

Compound (95a) bind metals more strongly when not centrally metalated. A titration of (95a) with Cd2+ revealed that the Mg center inhibited the ability of the macrocycle to show optical changes as a result of metal binding, it took an addition of more than 60 M of Cd2+ for any change in absorbance to be observed. This inhibition of optical changes may be due to either the increased symmetry of the centrally metalated pz or the central metal ion s electron-withdrawing effect. 

ESE envelope modulation studies of a number of Cu(II) compounds have been reviewed by Peisach1171. The aim of these investigations was to characterize the chemical environment of the metal binding site in Cu(II) proteins by comparison of the nuclear modulation pattern with those for Cu(II) complexes of known composition. 

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