Sterically Hindered Ferredoxin Complexes as a Model of High Potential Iron-Sulfur Proteins

Abstract

4Fe-4S ferredoxin model complexes, [NEt4]2[Fe4S4(Z-cys-Ile-Ala-OMe)4], [N(n-Bu)4]2[Fe4S4(2,4,6-trimethylbenezenethiolato)4], and [NMe4]2[Fe4S4(2,4,6-triisopropylbenzenethiolato)4] having highly sterically hindered ligands exhibit an electrochemically quasi-reversible redox couple of 2-/1- at +0.12 V, +0.02 V, and −0.03 V vs. SCE, respectively, but an irreversible redox couple of 3-/2-. The results suggest that [Fe4S4(SR)4]1− is stabilized with protection by hydrophobic bulkiness, but that [Fe4S4(SR)4]3− is destabilized by the bulkiness.

Condensation reactions of aqueous vanadate with the common nucleosides

“…It has a value of about 4 M"1, from Table I. The equilibrium constant for dimerization of this cyclic ester to form the -523 ppm product, V2l2, can then be obtained by dividing the value for formation of V2l2 from 2 T, and 2 l (about 5 X 107 M"3, from Table I) by the square of the value for formation of the cyclic Tl from T¡ and l (about 4 M"\ from Table I) to yield a value of 3 X 106 M"1 for the formation of V2l2 from two cyclic esters (see eqs 5,7,8).…”

Structure and Properties of [Fe4S4{2,6-bis(acylamino)benzenethiolato-S}4]2- and [Fe2S2{2,6-bis(acylamino)benzenethiolato-S}4]2-: Protection of the Fe−S Bond by Double NH···S Hydrogen Bonds

“…(NEt 4 ) 2 [Fe 4 S 4 (SPh) 4 ] 3 and (NEt 4 ) 2 [Fe 4 S 4 (S-2,4,6- i -Pr 3 C 6 H 2 ) 4 ] were prepared by the reported method. (NEt 4 ) 2 [Fe 2 S 2 (SC 6 H 5 ) 4 ] was prepared by the reported method. , 2,2‘-Dithiobis( N -phenyl-2,2-dimethylpropanamide), bis{2,6-bis(acetylamino)phenyl} disulfide, bis{2,6-bis((trifluoroacetyl)amino)phenyl} disulfide, and bis{2,6-bis(pivaloylamino)phenyl} disulfide were synthesized by literature methods …”

Catalytic applications of transition-metal complexes with sulfide ligands

“…Iron-sulfur cubane clusters [Fe4S4L4]2_ with bulky and hydrophobic terminal ligands such as L = triisopropylbenzenethiolate (A) or Z-Cys-Ile-Ala-OMe (B) (Z = benzyloxycarbonyl) have been found to undergo quasi-reversible one-electron oxidations in DMF (-0.03 V vs SCE for A and +0.12 V for B). 75 The relatively stable 2-/1-redox couple permitted the use of these clusters as catalysts in the oxidation of benzoin to benzil by 1,4-benzoquinone.76 (The average turnover number for B at 25 °C was 0.93/min for a total yield of 16800% /3 h.) Electron transfer from the 2cluster to benzoquinone was observed at room temperature in DMF. Benzoin was proposed to reduce the 1cluster to generate benzil and the original catalyst.…”