Redox properties characterization

It is very often necessary to characterize the redox properties of a given system with unknown activity coefficients in a state far from standard conditions. For this purpose, formal (solution with unit concentrations of all the species appearing in the Nernst equation its value depends on the overall composition of the solution. If the solution also contains additional species that do not appear in the Nernst equation (indifferent electrolyte, buffer components, etc.), their concentrations must be precisely specified in the formal potential data. The formal potential, denoted as E0, is best characterized by an expression in parentheses, giving both the half-cell reaction and the composition of the medium, for example E0,(Zn2+ + 2e = Zn, 10-3M H2S04). 

Catalyst redox properties, oxygen mobility and supported metal characterization... 

Transition metal oxides, rare earth oxides and various metal complexes deposited on their surface are typical phases of DeNO catalysts that lead to redox properties. For each of these phases, complementary tools exist for a proper characterization of the metal coordination number, oxidation state or nuclearity. Among all the techniques such as EPR [80], UV-vis [81] and IR, Raman, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and NMR, recently reviewed [82] for their application in the study of supported molecular metal complexes, Raman and IR spectroscopies are the only ones we will focus on. The major advantages offered by these spectroscopic techniques are that (1) they can detect XRD inactive amorphous surface metal oxide phases as well as crystalline nanophases and (2) they are able to collect information under various environmental conditions [83], We will describe their contributions to the study of both the support (oxide) and the deposited phase (metal complex). 

Using a deprotonated hydroxyiminoamide ligand, Kruger and co-workers33 structurally characterized a discrete copper(III) compound (6). The square-planar structure is retained even in solution. Absorption and redox properties of this complex were also investigated. 

Copper(l) analogues [(L)Cu(MeCN)][CF3S03] (747) [yellow, four-coordinate (two amine donors, one of the two pyridinyl groups and an MeCN] and [(L)Cu(MeCN)][BF4] (748) [red, five-coordinate (two tertiary amine, two pyridinyl and an MeCN] [L as that in copper(II) complex (241)] were structurally characterized and redox properties of these complexes were also investigated.224... 

Sardar, K., Playford, H.Y., Darton, R.J., Barney, E.R., Hannon, A.C., Tompsett, D., Fisher, J., Kashtiban, R.J., Sloan, J., Ramos, S., Cibin, G. and Walton, R.I. (2010) Nanocrystalline cerium-bismuth oxides synthesis, structural characterization, and redox properties. Chemistry of Materials, 22 6191-6201. 

In the NO-SCR by NH3, we note the highest reduction activity and selectivity on catalyst containing both vanadium and molybdenum than catalysts issued containing Mo or V, only. Furthermore, it should be underlined that a higher efficiency is obtained with ZSM-5 as host structure than samples issued from USY and MOR. Where a higher loss of porous volume were observed. On the basis of characterization data it has been suggested that the observed synergism in the SCR reaction is related to the existence of electronic interaction between the V and Mo species. In particular, it has been proposed that the presence of such electronic interactions modifies the catalysts redox properties, which have been claimed an essential property in the NO-SCR by NH3 reaction. 

The biogenic amines are the preferred substrates of MAO. The enzyme comes in two flavors, MAO-A and MAO-B, both of which, like FMO, rely on the redox properties of FAD for their oxidative machinery. The two isoforms share a sequence homology of approximately 70% (81) and are found in the outer mitochondrial membrane, but they differ in substrate selectivity and tissue distribution. In mammalian tissues MAO-A is located primarily in the placenta, gut, and liver, while MAO-B is predominant in the brain, liver, and platelets. MAO-A is selective for serotonin and norepinephrine and is selectively inhibited by the mechanism-based inhibitor clorgyline (82). MAO-B is selective for /1-phcncthylaminc and tryptamine, and it is selectively inhibited by the mechanism-based inhibitors, deprenyl and pargyline (82) (Fig. 4.32). Recently, both MAO-A (83) and MAO-B (84) were structurally characterized by x-ray crystallography. 

Cyclic voltammetric responses corresponding to the simple catalytic scheme in Figure 4.1 and to more complex schemes were discussed in detail in Section 2.2.6. The parameters that control the catalytic current have been identified and their effects quantified. Applications of homogeneous redox catalysis to the characterization of short-lived intermediates and the determination of their redox properties have been discussed in Sections 2.3 and 2.6.4. 

The very fact that chemical catalysis involves the formation of an adduct opens up possibilities of selectivity, particularly stereoselectivity, that are absent in redox catalysis. Several examples of homogeneous chemical catalysis are described in the following section, illustrating the improvements that can be achieved when passing from redox to chemical catalysis. It remains true that redox catalysis has several useful applications that have already been discussed, such as kinetic characterization of fast follow-up reactions (Section 2.3) and determination of the redox properties of transient radicals (Section 2.6.4). 

Franco, R., Moura, I., LeGall, J., Peck, H. D. Jr, Huynh, B. H. and Moura, J. J. (1993) Characterization of D. desulfuricans (ATCC 27774) [NiFe] hydrogenase EPR and redox properties of the native and the dihydrogen reacted states. Biocbim. Biopbys. Acta, 1144, 302-8. 

The characterization, redox properties, and pulse radiolysis study of manganese(III) complexes of type [MnLCy (where L = cyclam, meso-, and rac-5,7,7,12,14,14-hexamethylcyclam (tet a and tet b, respectively)) have been reported." An X-ray crystal structure of the meso-5,l,l, 2, A, A-hexamethyl-l,4,8,ll-tetraazacyclotetradecane complex shows that the coordination geometry of the tet a complex is close to octahedral with the macrocycle coordinated equatorially and the chlorides occupying irons axial sites. 

NMR and UV-visible techniques have been used in the characterization of intermediates in the [Fe (edta)]" -promoted decomposition of hydrogen peroxide7 Fe complexes of edta, nta, and dtpa react with FISOs by an inner-sphere one-electron transfer mechanism with transient production of S04, in contrast to Cu, which reacts by an outer-sphere mechanism to give S04 and hydroxy radicalsFe -edta redox properties are relevant to Fe /Cu /H202 systems. ... 

The preparation and characterization of K3[0s(CN)5(NH3)] 2H20 have been described. This complex is a useful starting material for the synthesis of other [Os (CN)5L] species (e.g., L = py, pyz) and [0s(CN)5(H20)] can be obtained by the controlled aquation of [Os(Cf 5(NH3)f The kinetics of these ligand displacements have been investigated and mechanisms for the processes have been discussed. The UV-vis spectrum of each complex in the series [Os"(CN)5L] in which L is py, pyz, Mepz, or derivatives thereof, exhibits an intense, asymmetric MLCT absorption, split by spin-orbit coupling, and the effects of the electronic properties of L on the spectra have been examined. Redox properties of the complexes and the kinetics of the dissociation of pyz from [Os(CN)s(pyz)] have also been reported. ... 

An almost complete description of both OH radical-mediated and one-electron oxidation reactions of the thymine moiety (3) of DNA and related model compounds is now possible on the basis of detailed studies of the final oxidation products and their radical precursors. Relevant information on the structure and redox properties of transient pyrimidine radicals is available from pulse radiolysis measurements that in most cases have involved the use of the redox titration technique. It may be noted that most of the rate constants implicating the formation and the fate of the latter radicals have been also assessed. This has been completed by the isolation and characterization of the main thymine and thymidine hydroperoxides that arise from the fate of the pyrimidine radicals in aerated aqueous solutions. Information is also available on the formation of thymine hydroperoxides as the result of initial addition of radiation-induced reductive species including H" atom and solvated electron. 

The covalent chemistry of fullerenes has developed very rapidly in the past decade in an effort to modify fuUerene properties for a number of applications such as photovoltaic cells, infrared detectors, optical limiting devices, chemical gas sensors, three-dimensional electroactive polymers, and molecular wires [8, 25, 26, 80-82]. Systematic studies of the redox properties of Cgo derivatives have played a crucial role in the characterization of their unique electronic properties, which lie at the center of these potential applications. Furthermore, electrochemical techniques have been used to synthesize and separate new fullerene derivatives and their isomers as well as to prepare fullerene containing thin films and polymers. In this section, to facilitate discussion of their redox properties, Cgo derivatives have been classified in three groups on the basis of the type of attachment of the addend to the fullerene. In group one, the addends are attached via single bonds to the Cgo surface as shown in Fig. 6(a) and are referred to as singly bonded functionalized derivatives. The group includes... 

This chapter consists of a description of the ions formed in aqueous solutions by the transition elements - the d-block elements - and a discussion of the variations of their redox properties across the Periodic Table from Group 3 to Group 12. There is particular emphasis on the first transition series from scandium to zinc in the fourth period, with summaries of the solution chemistry of the second (Y to Cd) and third (Lu to Hg) series. The d-block ions in solution are those restricted solely to aqua complexes of cations, e.g. [Fe(H20)f,]" +, and the various oxocalions and oxoanions formed, e.g. V02+ and MnCXj". Oxidation states that are not well characterized are omitted or referred to as such. 

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