Reduction potentials thiolate complexes

A 10-step kinetic model has been developed (Santolini et al., 2001). Crystal structures of xyNOS show that a Tyr-409 indol nitrogen atom forms a strong hydrogen bond with the heme thiolate (Crane et al., 1988 Raman et al.1998 Fishmann et al., 1999). The Try-409 mutation suggests that the heme potential controls the NOS reactions (Adak et al. 2001). Suppression of this hydrogen bond through the mutation lowers the reduction potential of the heme, inhibits heme reduction and accelerates oxidation of the Fe(II) heme-NO complex. The Arg binding increases the reduction potential of the NOS heme. 

As shown in Table III, the high-spin complex 1 and the low-spin nitrosyl complex 3 display charge transfer bands at 631 nm (15,800 cm ) and 650 nm (15,400 cm ), respectively. This is a difference of only 400 cm even though Ae spin-states are different and the reduction potentials differ by -300 mV. The similarities result from nearly identical potential differences between thiolate oxidation and metal reduction, 1.24 and 1.19 V, respectively. Conversely, the... 

Although thiolate-surface complexes form at electrodes [58] and electrode potential measurements under reversible conditions are not usually possible, a great deal of useful information has been obtained by various electrochemical methods [35,36]. However, thermochemical properties of sulfur-centered radicals in aqueous solution have generally been obtained from studies of redox equilibria, such as those by BonifSeic and Asmus [52] and Surdhar and Armstrong [59], by methods described in Wardman [60]. In this section it will be convenient to consider sulhdes, disulfides, and sufhydryl compounds in that order. Afso alkyl and aryl compounds will be treated separately. Reduction potentials will be identified by placing the reactants and products of the half cell reaction in parenthesis [60], for example, (RS, H /RSH) is the reduction potential for ... 

Other electrochemically characterized organometallic V(IV) complexes are rare. The thiolate bridged [Cp(CO)2V(/o,-SR)2V(CO)2Cp] (R = Me, Ft, Ph) have reversible reduction processes that range from —1.89 to —2.01 V versus Cp2Fe/THF in addition to two other irreversible reduction processes at more negative potentials. For R = Me, an oxidation at —0.20 V versus Cp2Fe/THF is reported. Reductive bulk electrolysis results in the decomposition of [Cp CO)2V(fi-SMe)2V(CO)2Cp] by loss of SMe [62]. 

With the exception of B = OH-, which relates in fact to an acid-base reaction, the other nucleophiles are potential reductants. After forming the reversible adducts [Eq. (5)], redox reactions are usually operative, leading to the reduction of nitrosyl and oxidation of the nucleophile in Eq. (6). Nevertheless, we will consider first the reaction with B = OH- for the sake of simplicity, and also because it allows for some generalizations to be made on the factors that influence the electrophilic reactivities of different nitrosyl complexes (51). We continue with new results for some N-binding nucleophiles (62,67), which throw light on the mecanisms of N20/N2 production and release from the iron centers. A description of the state of the art studies on the reactions with thiolate reactants as nucleophiles will be presented later. 

---