Redox activity determination

If cellular redox state, determined by the glutathione status of the heart, plays a role in the modulation of ion transporter activity in cardiac tissue, it is important to identify possible mechanisms by which these effects are mediated. Protein S-,thiolation is a process that was originally used to describe the formation of adducts of proteins with low molecular thiols such as glutathione (Miller etal., 1990). In view of the significant alterations of cardiac glutathione status (GSH and GSSG) and ion-transporter activity during oxidant stress, the process of S-thiolation may be responsible for modifications of protein structure and function. 

The equilibrium constant K for (por)Fe(OH2) (por)Fe, which determines the molar fraction of the 5-coordinate redox-active Fe catalyst. This constant was estimated from analysis of the catalytic turnover frequencies in the presence of varying concentrations of an inhibitor, CN, which competes with both O2 and H2O for the 5-coordinate Fe porphyrin. 

The X-ray structure of zinc naphthalocyanate has been determined with Zn—N bond lengths of 1.983(4) A.829 Pentanuclear complexes with a zinc phthalocyanine core and four ruthenium subunits linked via a terpyridyl ligand demonstrate interaction between the photoactive and the redox active components of the molecule. The absorbance and fluorescence spectra showed considerable variation with the ruthenium subunits in place.830 Tetra-t-butylphthalocyaninato zinc coordinated by nitroxide radicals form excited-state phthalocyanine complexes and have been studied by time-resolved electron paramagnetic resonance.831... 

The determination of catalyst composition and the kinetics of epoxide opening constitute the experimental basis for any mechanistic discussion and catalyst design. For this purpose, Zn-reduced THF solutions of the prepar-atively important 21 [44-46], 22 [47], 23, and 24 were analyzed by cyclic voltammetry, a technique uniquely suited to the investigation of redox active... 

Compounds [54] and [55] have been shown to complex group 1 and 2 metal cations and also ammonium and alkylammonium cations by nmr and UV/Vis spectroscopies and also by a number of solid-state X-ray crystallographically determined structures. The quinone moieties in these molecules constitute not only the coordination site but also the redox-active centre. The complexation... 

A more detailed discussion on this topic will be considered in Chapter 4, Section 1.3. Structurally, to a first approximation, a criterium to determine the electronic interaction between redox active sites is to evaluate the distance between the sites the greater the distance between redox centres, the smaller their interaction. 

The investigation on the use of molecules suitable for modifying the electrode surface so as to favour electron transfers with proteins (so-called promoters, which are non-redox active molecules and therefore unable to act as redox mediators) has determined that they must be bifunctional molecules X—V /—Y, in which X is a group able to... 

More recent approaches to the effects of the ligands on the redox activity of metal complexes are based upon the assumption that the electrode potential of a redox change involving a metal complex is determined by the additivity of the electronic contribution of all the ligands linked to the metal centre, or to the overall balance between the c-donor and the 7r-acceptor capability of each ligand.3 In particular two ligand electrochemical parameters have gained popularity ... 

In protein-protein reactions, the donor-acceptor distance is determined by the structure of the reacting proteins, and the way(s) in which they bind and interact. For example, it is generally believed that cytochrome c binds to its reaction partners at or near the exposed heme edge, in order to minimize the reactant distance and thereby maximize the rate. The redox active centers of most proteins are sufficiently buried that the large protein imposed distances provide low intrinsic reactivity for the proteins with respect to exogenous... 

Very recently evidence was provided that Hmd contains a low-molecular-mass, thermolabile cofactor that is tightly bound to the enzyme but could be released upon enzyme denaturation in urea or guanidinium chloride (Buurman et al. 2000). No indications were found that the cofactor contains a redox-active transition metal. Further studies are needed to determine the structure of the cofactor and its putative role in the catalytic mechanism. 

Table 1 lists some of the binding constants and rate constants measured for the reaction of CO2 with redox-active molecules. Various techniques have been used to measure these constants including cyclic voltammetry, pulsed radiolysis, and bulk electrolysis followed by UV-visible spectral measurements. The binding constants span an enormous range from less than 1 to 10 M [13-17]. Co(I) and Ni(I) macrocyclic complexes have been studied in some detail [13-16]. For the cobalt complexes, the CO2 binding constants K) and second-order rate constants for CO2 binding (kf) are largely determined by the Co(II/I) reduction potentials... 

---