Mossbauer analysis, sulfided iron

As-isolated wild-type LipA contained 6.9 0.5 mol of iron and 6.4 0.9 mol of sulfide per mol of protein, and possessed a UV—vis spectrum that resembled those previously reported. Mossbauer spectroscopy showed that the sample contained almost exclusively [4Fe-4S] clusters with at most 5% of the total iron in the form of [2Fe-2S] clusters, indicating that there were 1.7 0.2 [4Fe-4S] clusters per as-isolated wild-type LipA polypeptide. When the as-isolated protein was reconstituted in the presence of additional Fe and sulfide and then characterized, it was found to contain 13.8 0.6 mol of iron and 13.1 0.2 mol of sulfide per mol of polypeptide. However, Mossbauer analysis of the reconstituted protein showed it to contain significant amounts of adventitiously bound iron in addition to [4Fe-4S] clusters (67 6%), indicating that only... 

The weight change data indicated that the reaction of Fe with H2S results in a nonstoichiometric compound with the formula FeSi.i. Mossbauer spectroscopic analysis of the samples confirmed this. The compound represents a pyrrhotite, a nonstoichiometric iron sulfide, which is well known in the Fe-S system. Based on the above observations, the reactions in an absorber can be written as follows ... 

Well dispersed iron oxide on silica of a specific surface area of 50 m /g has proven to be a very suitable catalyst for the selective oxidarion of hydrogen sulfide to elemental sulfur. Under reaction conditions the iron oxide is transformed into ironCII sulfate as revealed by X ray diffraction, Mbssbauer spectroscopy, and wet chemical analysis. The presence of an iron(III) component as observed by ex situ Mossbauer spectroscopy can not be excluded. Although the transfomiation of iTon(]Il) oxide into iron(II) sulfate causes initial deactivation, the increase in selectivity (96%) results in high sulfur yields (up to 94%). 

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