Sulphur Complexes

The authors believe that the results are more readily explainable on the basis of a two-point absorption involving the vanadium-carbon-sulphur complex, the formation of which may be effected with little distortion of the tetrahedral valence angles. 

As with some other enzymes involved in the generation of ATP in the mitochondria (e.g. oxoglutarate dehydrogenase), aconitase possesses an iron-sulphur complex in its... 

Fig. 9. A proposed structural configuration for the polynuclear iron-sulphur complex in clostridial ferredoxin.

You will recall that thionyl chloride usually reacts via an SNi mechanism. In this case, the intermediate is attacked by the displaced chloride ion at the 3-position, i.e. in an SN2 manner, before the sulphur complex has had a chance to fragment in order to allow internal attack by the second chloride ion. 

An EPR signal centred at about g=1.94 is observed from the reduced iron-sulphur complex (27) and poseed a considerable problem in its interpretation until the suggestion came that one was dealing with a coupled pair having Si = f, S2 = 2 and a large positive J (22, 24). From Eqs. (8) and (15) it follows that the g values and hyperfine constants for the coupled system are given by... 

The behaviour of these samples measured by IGC shows a reduction of the adsorption capacity for both linear and cyclic hydrocarbons (Table 5). Moreover, Vs for the hydrocarbon 2,2 DMB on the oxidized carbons is quite close to the gas hold up time, similar to that on the original samples, and the separation ratio for the couple benzene/cyclohexane is similar in both cases. These results show that the oxygen surface complexes fixed on the surface produce constrictions at the entrance of the pores, but do not result in the production of carbon materials with improved molecular sieve properties. One reason for this could be that the size of the oxygen complexes is not large enough. Therefore, if the size of the chemical complexes is increased the molecular sieve character for the couple benzene/cyclohexane would be expected to be developed. For this purpose, the S900 carbon was treated to introduce sulphur complexes on the surface [30]. Also a commercial acti-... 

Figure 5.2 Energy surface associated with two variable torsional angles in one of the side chains of an iron sulphur complex (structure taken from Kanatzidis et ah, 1984). The resulting energy map, a function of the two variable side chain angles highlighted, a and b, is shown on the right-hand side of the figure, as both a contour map and a three-dimensional histogram. A variety of maxima and minima are readily apparent in the...

While most of the tetrapyrrole pigments in the RC (FeS) type function as light harvesting, six central tetrapyrroles and three iron-sulphur complexes appear to constitute the photochemical heart of the reaction center. 

The electrochemistry of mononuclear metal - sulphur complexes and metallo-sulphur clusters which interact with dinitrogen (or other substrates and inhibitors of the enzyme) or which bear groups such as hydrazide, nitride, or amide are consequently of some relevance to biological nitrogen fixation. 

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