Browsing by Author "Arnst, Theodore Carl"

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    Progress towards a model compound for the active site of sulfite reductase. Part I. Synthesis of tetrathiol porphyrin ligands. Part II. Reaction of a tetrathiol porphyrin with the iron-sulfur cubane cluster
    (1993) Arnst, Theodore Carl
    Part I. Novel mercaptoethoxy and mercaptoxylyleneoxy derivatives of meso-tetraphenylporphyrin, H$\sb2$TPP, and meso-tetranaphthalporphyrin, H$\sb2$TNP, with the potential for coordinating an iron-sulfur cubane cluster, have been synthesized and characterized. The thiol function is guarded during synthesis by an acetate protecting group, which is removed quantitatively by an acid-catalyzed hydrolysis reaction in the final workup step. The four "thiol-arms" on these light-sensitive porphyrins allows for the presence of atropisomers which have been observed and, in the case of the tetranaphthalporphyrin derivative, separated. The atropisomers of the acetylmercaptoxylyleneoxy derivatized tetraphenylporphyrin, H$\sb2$TAMXPP, interconvert at a rapid rate and are only observable by $\sp1$H NMR spectroscopy at $-$70$\sp\circ$C. The free-base porphyrins, in the thiol-protected form, are easily metallated by literature procedures and the zinc(II) and iron(III) chloro derivatives of these new porphyrin compounds have been synthesized and characterized. Part II. The thiol functionality of the mercaptoxylyleneoxy derivative of tetraphenylporphyrin, H$\sb2$TAMXPP, readily exchanges for ethanethiol when H$\sb2$TAMXPP is reacted with (Fe$\sb4$S$\sb4$(SEt)$\sb4\rbrack\sp{2-}.$ The dioxygen and light sensitive product, (cation)$\sb2$ (Fe$\sb4$S$\sb4$(H$\sb2$TMXPP)) has been isolated and characterized. Mossbauer and $\sp1$H NMR spectroscopy provide evidence for the successful synthesis of the desired porphyrin/iron-sulfur cluster compound. As such, this compound is the first example for the synthesis and isolation of a 1:1 porphyrin/iron-sulfur cluster compound and provides as a first generation model compound for the siroheme/iron-sulfur cluster structural unit found at the active site of sulfite reductase.