Electron Transfer to

The microsomal P450 monooxygenase complex is localized to the endoplasmic reticulum membrane. Like P450, CPR contains an N-terminal hydrophobic region that spans the lipid membrane and anchors it to the surface. In yeast. 

Transient monooxygenase complexes are formed on the membrane surface as a result of collisions between P450s and CPR as each diffuses laterally within the membrane of the endoplasmic reticulum. The role of the membrane in mediating these interactions is poorly imderstood. However, early work has shown that the phospholipid component of the membrane can affect intermolecular interactions of the monooxygenase complex and influence subsfrate binding and may therefore be important in maintaining efficient electron transfer from CPR to P450. 

Protein-protein interactions are essential to enable electron transfer from the reduced FMN of the flavoprotein to the substrate-bound ferric form of the P450. Since P450 is present in a 

While it is generally considered that charge-pair interactions are important in docking and 

Conformation in crystal appropriate for interflavin electron transfer 

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Williams R M, Koeberg M, Lawson J M, An Y-Z, Rubin Y, Paddon-Row M N and Verhoeven J W 1996 Photoinduced electron transfer to Cgg across extended 3- and 11 a-bond hydrocarbon bridges creation of a long-lived charge-separated state J. Org. Chem. 61 5055-62... 

Sodium naphthalene [25398-08-7J and other aromatic radical anions react with monomers such as styrene by reversible electron transfer to form the corresponding monomer radical anions. Although the equihbtium (eq. 10)... 

Subsequent studies (63,64) suggested that the nature of the chemical activation process was a one-electron oxidation of the fluorescer by (27) followed by decomposition of the dioxetanedione radical anion to a carbon dioxide radical anion. Back electron transfer to the radical cation of the fluorescer produced the excited state which emitted the luminescence characteristic of the fluorescent state of the emitter. The chemical activation mechanism was patterned after the CIEEL mechanism proposed for dioxetanones and dioxetanes discussed earher (65). Additional support for the CIEEL mechanism, was furnished by demonstration (66) that a linear correlation existed between the singlet excitation energy of the fluorescer and the chemiluminescence intensity which had been shown earher with dimethyl dioxetanone (67). 

Intense sodium D-line emission results from excited sodium atoms produced in a highly exothermic step (175). Many gas-phase reactions of the alkafl metals are chemiluminescent, in part because their low ioni2ation potentials favor electron transfer to produce intermediate charge-transfer complexes such as [Ck Na 2] (1 )- There appears to be an analogy with solution-phase electron-transfer chemiluminescence in such reactions. 

In the reaction of lead tetraacetate with 1,3- or 1,4-dihydtopetoxides (10) to produce cychc monoperoxides there are two electron transfers to the metal (eq. 14). 

Apparently the alkoxy radical, R O , abstracts a hydrogen from the substrate, H, and the resulting radical, R" , is oxidized by Cu " (one-electron transfer) to form a carbonium ion that reacts with the carboxylate ion, RCO - The overall process is a chain reaction in which copper ion cycles between + 1 and +2 oxidation states. Suitable substrates include olefins, alcohols, mercaptans, ethers, dienes, sulfides, amines, amides, and various active methylene compounds (44). This reaction can also be used with tert-huty peroxycarbamates to introduce carbamoyloxy groups to these substrates (243). 

The simplest electroplating baths consist of a solution of a soluble metal salt. Electrons ate suppHed to the conductive metal surface, where electron transfer to and reduction of the dissolved metal ions occur. Such simple electroplating baths ate rarely satisfactory, and additives ate requited to control conductivity, pH, crystal stmcture, throwing power, and other conditions. 

A type of molecular resonance scattering can also occur from the formation of short-lived negative ions due to electron capture by molecules on surfrices. While this is frequently observed for molecules in the gas phase, it is not so important for chemisorbed molecules on metal surfaces because of extremely rapid quenching (electron transfer to the substrate) of the negative ion. Observations have been made for this scattering mechanism in several chemisorbed systems and in phys-isorbed layers, with the effects usually observed as smaU deviations of the cross section for inelastic scattering from that predicted from dipole scattering theory. 

Of course, this simple picture constitutes only a crude approximation and should be valued only for showing that the completion of a metal layer around C o with 32 Ba-atoms is, indeed, plausible. More precise predictions would have to rely on ab initio calculations, including a possible change in bond lengths of Qo> such as an expansion of the double bonds of C o due to electron transfer to the antibonding LUMO (as was found in the case of QoLii2[I2,131T... 

FIGURE 18.19 The structures and redox states of the nicotinamide coenzymes. Hydride ion (H , a proton with two electrons) transfers to NAD to produce NADH. 

The proposed mechanism for the conversion of the furanone 118 to the spiro-cyclic lactones 119 and 120 involves electron transfer to the a -unsaturated methyl ester electrophore to generate an anion radical 118 which cyclizes on the /3-carbon of the furanone. The resulting radical anion 121 acquires a proton, giving rise to the neutral radical 122, which undergoes successive electron transfer and protonation to afford the lactones 119 and 120 (Scheme 38) (91T383). 

It has generally been concluded that the photoinitiation of polymerization by the transition metal carbonyls/ halide system may occur by three routes (1) electron transfer to an organic halide with rupture of C—Cl bond, (2) electron transfer to a strong-attracting monomer such as C2F4, probably with scission of-bond, and (3) halogen atom transfer from monomer molecule or solvent to a photoexcited metal carbonyl species. Of these, (1) is the most frequently encountered. 

The complex cyanides of transition metals, especially the iron group, are very stable in aqueous solution. Their high co-ordination numbers mean the metal core of the complex is effectively shielded, and the metal-cyanide bonds, which share electrons with unfilled inner orbitals of the metal, may have a much more covalent character. Single electron transfer to the ferri-cyanide ion as a whole is easy (reducing it to ferrocyanide, with no alteration of co-ordination), but further reduction does not occur. 

Electron transfer to vinylaziridines results in ring-opening reactions, yielding allyl amines. Treatment of 268 with SmI2/DMEA (N,N-dimethylethanolamine) provided allyl amine 269 as a 2 1 mixture of olefmic isomers in 88% yield (Scheme 2.66) [97]. 

Another example is indium(0)-induced electron transfer to aziridines 270 incorporating allyl iodide moieties (Scheme 2.66). Treatment with indium(O) in MeOH at reflux gave the corresponding chiral (E)-dienylamines 271 in excellent yields [98]. It should be noted that indium was found to be more effective for this transformation than other metals such as zinc, samarium, and yttrium. 

A different situation arises in the initiation reaction resulting from an electron transfer to a monomer. Such an initiation has been discussed recently42 43 and leads to a species containing one extra electron which behaves like a radical ion. It has been pointed out that the extra electron may be conveniently ascribed to the lowest unoccupied n orbital of the monomeric molecule (see Figure I), a... 

Electron transfer to a suitable monomer leads to the formation of an ion pair like M, NaL The negative monomer" ion may react again with sodium forming a Na—M—Na unit. The latter arises, therefore, as a product of two consecutive reactions, e.g.,... 

Whether the second step does take place depends on a number of factors. The electron affinity of the M ion must be sufficiently great, and this point can be appreciated by considering a few examples. Electron transfer to stilbene or tetraphenyl ethylene leads to the formation of negative ions which in turn rapidly ac-... 

Polymerization of some vinyl monomers initiated by those colored aromatic complexes was described by Scott38 over twenty years ago, and recently the mechanism of this reaction has been elucidated in our laboratory43 where we demonstrated that polymerization initiation is due to an electron transfer to monomer, namely A - -M A-f-M . This system is useful, therefore, in... 

Two pathways for the reaction of sulfate radical anion with monomers have been described (Scheme 3.81).252 These are (A) direct addition to the double bond or (B) electron transfer to generate a radical cation. The radical cation may also be formed by an addition-elimination sequence. It has been postulated that the radical cation can propagate by either cationic or a radical mechanism (both mechanisms may occur simultaneously). However, in aqueous media the cation is likely to hydrate rapidly to give a hydroxyelhyl chain end. 

Certain transition metal salts can be used as radical traps (Scheme 3.89, Scheme 3.90).486 These include various cupric (e.g. Cu(OAc)2, CuCl , Cu(SCN)i),l8 1<,8 J< 3 432 487 ferric (e.g. FeCli),316 488 and titanotis salts (eg. TiCL,).379 These traps react with radicals by ligand- or electron-transfer to give products which can be determined by conventional analytical techniques. 

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