Sulphur-containing complexes molybdenum

Add to the sample solution (containing 1 -25 g of Mo) 4 mL of 1 3 sulphuric acid, 3 drops of 85 per cent phosphoric(V) acid, and 0.5 g of citric acid. Dilute with water to 20 mL and add 2 mL of dithiol solution. Allow to stand at room temperature for 2 hours. Extract the molybdenum complex with 13 mL and 10 mL portions respectively of re-distilled butyl acetate, and make up to 25.0 mL with this solvent in a graduated flask filter through glass wool if not entirely clear. Determine the absorbance of the solution at 670 nm. Prepare a calibration curve as detailed in Section 6.14. 

At cellular level, the overall reduction process may be represented as (11.72), where the nitroge-nase system is an enzyme complex which includes phosphate energy carriers ATP and NADPH and three proteins. Two of these proteins are metalloenzymes, one of which contains iron, and the other both iron and molybdenum. The third protein, ferredoxin, contains iron and sulphur and acts as an electron provider through NADPH. 

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