Redox function

NAD+ possesses some non-redox functions as well. The glycosidic linkage between nicotinamide and ribose is a high-energy bond. The energy provided by... 

Armentrout PB (2003) Threshold Collision-Induced Dissociations for the Determination of Accurate Gas-Phase Binding Energies and Reaction Barriers. 225 227-256 Astruc D, Blais J-C, Cloutet E, Djakovitch L, Rigaut S, Ruiz J, Sartor V, Valerio C (2000) The First Organometallic Dendrimers Design and Redox Functions. 210 229-259 Aug6 J, see Lubineau A (1999) 206 1-39... 

Blue copper proteins. A typical blue copper redox protein contains a single copper atom in a distorted tetrahedral environment. Copper performs the redox function of the protein by cycling between Cu and Cu. Usually the metal binds to two N atoms and two S atoms through a methionine, a cysteine, and two histidines. An example is plastocyanin, shown in Figure 20-29Z>. As their name implies, these molecules have a beautiful deep blue color that is attributed to photon-induced charge transfer from the sulfur atom of cysteine to the copper cation center. 

Similarly, acidic oxides without redox function, such as Si-Al, Si-P, and Ni-P oxides, are not effective as catalysts for this reaction. 

One-electron reduction or oxidation of organic compounds provides a useful method for the generation of anion radicals or cation radicals, respectively. These methods are used as key processes in radical reactions. Redox properties of transition metals can be utilized for the efficient one-electron reduction or oxidation (Scheme 1). In particular, the redox function of early transition metals including titanium, vanadium, and manganese has been of synthetic potential from this point of view [1-8]. The synthetic limitation exists in the use of a stoichiometric or excess amount of metallic reductants or oxidants to complete the reaction. Generally, the construction of a catalytic redox cycle for one-electron reduction is difficult to achieve. A catalytic system should be constructed to avoid the use of such amounts of expensive and/or toxic metallic reagents. 

So little is known about molybdenum enzymes other than milk xanthine oxidase that there is little to be said by way of general conclusions. In all cases where there is direct evidence (except possibly for xanthine dehydrogenase from Micrococcus lactilyticus) it seems that molybdenum in the enzymes does have a redox function in catalysis. For the xanthine oxidases and dehydrogenases and for aldehyde oxidase, the metal is concerned in interaction of the enzymes with reducing substrates. However, for nitrate reductase it is apparently in interaction with the oxidizing substrate that the metal is involved. In nitrogenase the role of molybdenum is still quite uncertain. 

An intriguing puzzle in NOS catalysis is the precise role of H4B. The traditional function of H4B is in aromatic amino acid metabolism where H4B directly participates in the hydroxylation reaction via a nonheme iron. However, the NOS pterin site has no similarity to the pterin site in the hydroxylases, nor does NOS have a nonheme iron to assist pterin in substrate hydroxylation as in the amino acid hydroxylases 111). NOS more closely resembles pterin-containing enz5unes that have a redox function 81). In particular, N3 and the 03 amino group form H-bonds with either GIu or Asp residues in a series of pterin enzymes 112-116) similar to NOS, except that NOS utilizes the heme propionate (Fig. 6). 

Heme coenzymes (8) with redox functions exist in the respiratory chain (see p. 140), in photosynthesis (see p. 128), and in monooxygenases and peroxidases (see p. 24). Heme-containing proteins with redox functions are also referred to as cytochromes. In cytochromes, in contrast to hemoglobin and myoglobin, the iron changes its valence (usually between +2 and +3). There are several classes of heme (a, b, and c), which have different types of substituent - Ri to - R 3. Hemoglobin, myoglobin, and the heme enzymes contain heme b. Two types of heme a are found in cytochrome c oxidase (see p. 132), while heme c mainly occurs in cytochrome c, where it is covalently bound with cysteine residues of the protein part via thioester bonds. 

The characterization of the semiquinone radical anion species of PQQ in aprotic solvents was undertaken to provide information about the electrochemistry of coenzyme PQQ and to give valuable insight into the redox function of this coenzyme in living systems <1998JA7271>. The trimethyl ester of PQQ and its 1-methylated derivative were examined in aprotic organic solvents by cyclic voltammetry, electron spin resonance (ESR), and thin-layer UV-Vis techniques. The polar solvent CH3CN was found to effectively solvate the radical anion species at the quinone moiety, where the spin is more localized, whereas the spin is delocalized into the whole molecule in the nonpolar solvent CH2CI2. 

While the variety of NPs used in catalytic and sensor applications is extensive, this chapter will primarily focus on metallic and semiconductor NPs. The term functional nanoparticle will refer to a nanoparticle that interacts with a complementary molecule and facilitate an electrochemical process, integrating supramolecular and redox function. The chapter will first concentrate on the role of exo-active surfaces and core-based materials within sensor applications. Exo-active surfaces will be evaluated based upon their types of molecular receptors, ability to incorporate multiple chemical functionalities, selectivity toward distinct analytes, versatility as nanoscale receptors, and ability to modify electrodes via nanocomposite assemblies. Core-based materials will focus on electrochemical labeling and tagging methods for biosensor applications, as well as biological processes that generate an electrochemical response at their core. Finally, this chapter will shift its focus toward the catalytic nature of NPs, discussing electrochemical reactions and enhancement in electron transfer. 

Various redox functionalities have been appended to NP cores via thiolated redox molecules, place exchange reactions, and postfunctionalization of a MPC through amide15 or ester-forming reactions.16 The redox moieties include ferrocene,17 biferrocene, phenol, nitrobenzene, and anthraquinone, which commonly are synthesized using a gold core composition. The observed voltammetry of these redox-active units tend to exhibit similar electrochemical potentials to their free... 

In isomer 1, where catalytic redox functions are retained, a facilitated inactivation reaction such as oxazole formation, which can take place even nonenzymatically in any cell, results in potential toxicity. 

In contrast to urease the nickel in other bacterial enzymes appears to have a redox function and to take up oxidation states Ni(I) and/or Ni(III). Fortunately these states have recently become better understood in inorganic systems (see the preceding review in this volume by... 

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