Sulfides biologically relevant

The chief use of molybdenum is in steels. The oxides and sulfides have some applications as catalysts. Molybdenum is the only element in the second and third transition series which appears to have a major role as a trace metal in enzymes. Several aspects of molybdenum chemistry have been widely studied in order to gain a better understanding of the biological relevance. Molybdenum is one of the few elements which currently has its own series of international conferences.1... 

This section will mainly focus on two biologically relevant sulfur-centered radical species, thiyl radicals (RS ) and sulfide radical cations (R2S +). 

Our preliminary survey of Fe-NR cluster chemistry reveals strong parallels between imide and sulfide ligation on high-spin iron. The dinuclear, trinuclear, and tetranuclear geometries found in imidoiron clusters all have structural counterparts in fundamental biologically-relevant Fe-S cluster motifs (Figure... 

Some similarities with the Murchison meteorite can be noticed. The Murchison mineral structure is dominated with a phyllosilicate (serpentine) matrix which contains minerals such as olivine, pyroxenes, calcium carbonates, iron oxides (magnetite), iron-nickel sulfides and sulfates [23-25]. It has been altered by water, by heat, by pressure shock waves, by short-lived radionuclides [26,27]. The transformation of olivine and pyroxene chondrules seems to grow with the extent of mineral hydrolysis and the formation of water-soluble organic compounds is described at temperatures below -125 C [28,29]. Aside from any terrestrial contamination, all the classes of organic molecules considered of biological relevance are identified [30-32 and Ref therein] and also non-terrestrial amino acids and enantiomeric excesses [33-35]. 

A comparatively large selection of thioureas can be formed from the reaction of amines with isothiocyanates, hence they are attractive starting materials for formation of guanidines. A common solution-phase approach to this reaction involves abstraction of the sulfur via a thiophillic metal salt, like mercuric chloride.10 For solid-phase syntheses, however, formation of insoluble heavy-metal sulfides can have undesirable effects on resin properties and on biological assays that may be performed on the product. A more relevant strategy, with respect to this chapter, is S-alkylation of thioureas and then reaction of the methyl carbamimidothioates formed (e.g., 5, Scheme 6) with amines. This type of process has been used extensively in solution-phase syntheses.1 Ul4 Two examples are shown in Scheme 6 11 the second is an intramolecular variant, which involves concomitant detrity-lation.15... 

Among some kinds of reactions which are slow on a relevant time scale and in particular environments are certain metal-ion oxidations, oxidation of sulfides, sulfate reduction, various metal ion polymerizations (e.g., vanadium, aluminum), aging of hydroxide and oxide precipitates, precipitation of metal-ion silicates and carbonates (e.g., dolomites), conversions among aluminosilicates (e.g., feldspar-kaolinite), and solution or precipitation of quartz (9). Some of these reactions can be accelerated greatly by biological catalysis (e.g., sulfate reduction, metal ion oxidations) (7). 

Where might this be important As discussed above, biological activity can result in the simultaneous precipitation of mixtures of nanoscale sulfide minerals under certain conditions. Each mineral will exhibit a particular particle size distribution, dependent on the solution composition, bacterial activity, rate of crystal growth, and the nature of electrochemical interactions between the particles. These electrochemical reactions could lead to oxidation of one type of nanophase sulfide mineral of a certain size, and reduction of another type of nanophase sulfide particle or other species in the solution. In this way, a tremendous number of mineral-solution-mineral galvanic cells could develop, with potentially significant impact on dissolution kinetics, growth kinetics, and the mixture of phases observed. In addition to environmental relevance, these processes may shape the mineralogy of low-temperature ore deposits. 

The main nickel compounds are oxides, sulfides, and salts. Nickel compounds are sometimes classed as soluble or insoluble in water such classification can be useful in technical applications but may not be relevant to determining their biological activity. Water-soluble nickel compounds include nickel chloride and nickel sulfate, whereas nickel monosulfide and nickel carbonate are classed as insoluble [1]. 

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