78318-86-2Relevant academic research and scientific papers
Definition of Reaction Sequences Resulting in Self-Assembly of 2- Cluster from Simple Reactants
Hagen, Karl S.,Reynolds, John G.,Holm, R. H.
, p. 4054 - 4063 (1981)
Several reaction systems which result in the assembly of the biologically relevant 2- cluster (1) from simple reactants have been examined by spectrophotometry and 1H NMR spectroscopy in order to define reaction sequences and identify intermediates.Systems I and II were based on the reactant mole ratios PhS-/FeCl3/S = 3.5/1/1 and >=5/1/1, respectively, and were conducted in acetonitrile and methanol solutions.In system I the first identifiable intermediate is the adamantane-like species 2- (4), which reacts with sulfur in an all-or-nothing process in both solvents to afford 1.No other intermediates were identified in this system.In system II the first recognizable species formed is tetrahedral 2- (2).Reaction of 2 with sulfur in acetonitrile yields binuclear 2- (3), but in methanol 3, which also results from 2 and sulfur, spontaneously forms 1 in a slow reaction.Thus system II provides the first demonstrated instance of elaboration of a tetranuclear cluster through mononuclear and binuclear intermediates.In methanol the overall reactions affording 1 from initial reactants are quantitative when assayed spectrophotometrically.Salts of intermadiates 2, 3, and 4 have been independently synthesized, and the reactions 4 + S -> 1 and 2 + S -> 3 have been executed in good yield on a preparative scale.Reaction system III, having the reactant mole ratio PhS-/FeCl3/S2- = 1.5/1/1, affords 1 in 82percent spectrophotometric yield but proceeds too rapidly for detection of intermediateds by the methods employed.The results are used to interpret reaction sequences in previously reported preparative methods for 2- clusters.Certain limitations of the investigation are noted.
Assembly of [FenSn(SPh)4]2- (n = 2, 4) and their iron-thiolate precursors in aqueous media
Stevens, William C.,Kurtz Jr., Donald M.
, p. 3444 - 3449 (2008/10/08)
Tetraalkylammonium salts of [FenSn(SPh)4]2- (n = 2, 4), which are synthetic analogues of [2Fe-2S] and [4Fe-4S] sites in proteins, can be prepared in >80% yields from 4/1/1 PhSH/FeCl3/S in a medium consisting of 90/5/5 vol % (pH ～8) aqueous buffer/CH3CN/Triton X-100. For this system the sole assembly pathway appears to be [Fe(SPh)4]2- → [Fe2S2(SPh)4]2- → [Fe4S4(SPh)4]2-, which suggests an analogous assembly pathway for [4Fe-4S] sites in ferredoxins. At lower PhSH/Fe mole ratios or at lower pH the [Fe4(SPh)10]2- → [Fe4S4(SPh)4]2- pathway appears to occur, but to a lesser extent in aqueous Triton than in organic solvents. High yields of the precursors [Fe(SPh)4]2- and [Fe4(SPh)10]2- are also achieved in the aqueous-based detergent medium. Evidence from 1H and 19F NMR indicates that the equilibrium [Fe4(SPh)10]2- + 6PhS- ? 4[Fe(SPh)4]2- is established prior to addition of S. The two most prominent unique features in the 90/5/5 medium are (i) the ability of detergent aggregates in the presence of relatively hydrophobic R4N+ to shield [Fe2S2(SPh)4]2- from water, thereby inhibiting the rate of conversion to [Fe4S4(SPh)4]2-, and (ii) the facility with which the [Fe4(SPh)10]2- ? [Fe(SPh)4]2- equilibrium can be shifted. Unique feature i leads to the ability to achieve essentially quantitative production of either [Fe2S2(SPh)4]2- or [Fe4S4(SPh)4]2- from the same 4/1/1 PhSH/FeCl3/S reagent ratio. Unique feature ii leads to the production of substantial proportions of [Fe2S2(SPh)4]2- upon reaction of [Fe4(SPh)10]2- with S, due to a shift of the above equilibrium to the right. Unique feature ii also leads to larger proportions of [Fe4S4(SPh)4]2- at pHs below 6 (below the pKa of PhSH), apparently due to a shift of the above equilibrium to the left. These two unique features suggest means by which ferredoxins could exert both kinetic and thermodynamic control over assembly of [2Fe-2S] and [4Fe-4S] sites.
