Hydrogen sulfide molecular coordination

In a review of the thermodynamics of water, Franks and Reid (1973) showed that the optimum molecular size range for maximum solubility was similar to hydrate stability. Franks and Reid noted, this is not intended to imply that long-lived clathrate structures exist in solution—only that the stabilization of the water structure by the apolar solutes resembles the stabilization of water in a clathrate lattice. Glew (1962) noted that, within experimental error, the heat of solution for ten hydrate formers (including methane, ethane, propane, and hydrogen sulfide) was the same as the heat of hydrate formation from gas and ice, thereby suggesting the coordination of the aqueous solute with surrounding water molecules. 

Polarization infrared spectral data. X-ray analysis and normal coordinate treatment revealed the stable molecular conformation of poly(methylene disulfide) to be the GG G form [88] which was also confirmed from the results of semi-empirical CNDO/2SCF MO calculations [89]. Poly(ethylene disulfide) was also found to exist in a similar conformation as that of poly(methylene disulfide) [90]. Under vacuum at 50 °C, polysulfide polymers of methylene and ethylene with sulfur rank of two and four were exposed to UV radiation [91]. While poly(methylene disulfide) and poly(methylene tetrasulfide) yielded polymeric carbon monosulfide, hydrogen sulfide and carbon disulfide as the major degradation products, the ethylene counterparts produced the same compounds except carbon disulfide. The tetrasulfide polymers also formed volatile products which on condensation gave the original polymer. 

Iron Sulfur Compounds. Many molecular compounds (18—20) are known in which iron is tetrahedraHy coordinated by a combination of thiolate and sulfide donors. Of the 10 or more stmcturaHy characterized classes of Fe—S compounds, the four shown in Figure 1 are known to occur in proteins. The mononuclear iron site REPLACE occurs in the one-iron bacterial electron-transfer protein mbredoxin. The [2Fe—2S] (10) and [4Fe—4S] (12) cubane stmctures are found in the 2-, 4-, and 8-iron ferredoxins, which are also electron-transfer proteins. The [3Fe—4S] voided cubane stmcture (11) has been found in some ferredoxins and in the inactive form of aconitase, the enzyme which catalyzes the stereospecific hydration—rehydration of citrate to isocitrate in the Krebs cycle. In addition, enzymes are known that contain either other types of iron sulfur clusters or iron sulfur clusters that include other metals. Examples include nitrogenase, which reduces N2 to NH at a MoFe Sg homocitrate cluster carbon monoxide dehydrogenase, which assembles acetyl-coenzyme A (acetyl-CoA) at a FeNiS site and hydrogenases, which catalyze the reversible reduction of protons to hydrogen gas. 

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