Electron donor a

The triply connected phosphoms compounds have a lone electron pair that dominates much of the chemistry for these compounds. Triply connected compounds typically exhibit pyramidal symmetry arising fromp hybridization. A considerable amount of sp character may be present as well. Bond angles range near 100° vs 90° theoretical. Tricoordinate compounds typically act as electron donors, forming metal coordination compounds and addition compounds such as H P BF [41593-56-0]. 

The O or S atoms in P=0 and P=S groups may act as electron donors although these groups form relatively weak complexes with electron acceptor compounds such as nonpolarizable, more electropositive (ie, hard) acids, including protons (14). Use is made of this property in the recovery of uranium from wet-process phosphoric acid by extractants such as trioctylphosphine oxide [78-50-2] and di(2-ethylhexyl) hydrogen phosphate [298-07-7]. 

A review of the role of thiols as electron donors in photoinduced electron-transfer reactions has been compiled (49). 

The alkaline and rare-earth metals, and positive actinide ions, generally have greater affinity for —0 groups as electron donors. Many transition metals complex preferentially with enoHc —0 and some nitrogen functions. PolarizabiUty of the donor atoms correlates with stabiUty of complexes of the heavier transition metals and the more noble metal ions. 

Esters such as ben2oates and phthalates are also used in the preparation of high activity catalysts for olefin polymeri2ation. They appear to function as electron donors in the catalyst complex, and play a significant role in catalyst performance (115). 

Experimentally, the rates of Diels-Alder reactions between electron-rich dienes and electron-poor dienophiles generally increase with increased alkyl substitution on the diene. This is because alkyl groups act as electron donors and lead to buildup of electron density on the diene. An exception to this is the reaction of Z,Z-hexa-2,4-diene with tetracyanoethylene (TCNE), which is actually slower than the corresponding addition involving E-penta-1,3-diene. 

The investigation by Becker et al. (1977 b) also included work on the effect of pyrene added as electron donor. Pyrene has an absorption maximum at 335 nm (e = 55000 M-1cm-1, in petroleum). Much more hydro-de-diazoniation takes place in the presence of pyrene with irradiation at 365 nm, and even more on irradiation with light of wavelength <313 nm. Photoexcited pyrene has a half-life of 300 ns and is able to transfer an electron to the diazonium ion. This electron transfer is diffusion-controlled (k= (2-3) X 1010 m 1s 1, Becker et al., 1977a). The radical pairs formed (ArN2 S +) can be detected by 13C- and 15N-CIDNP experiments (Becker et al., 1983, and papers cited there). 

The ability to ionically polymerize apparently correlates in many cases with the capacity of the substituents to act as electron acceptors (anionic polymerizability) or as electron donors (cationic polymerizability) on the rt-bond of the vinyl group. These relationships should be visible in carefully chosen quantum chemical parameters. 

In one compound iron carbonyl moieties serve as electron donors to the B of a simple aminoborane, whereas the N atoms have donor functions to Fe ... 

From a detailed analysis of the stability regions in the alloy series MR Rh3Bi y and Er(Rh, yM,)3B y the formation of the perovskite structure was discussed in terms of a stabilizing charge transfer (B as electron donor) and a corresponding characteristic VEC, 31 < VEC < 34. 

The ability of compounds with double bonds to act both as electron donors and as electron acceptors in charge transfer complex formation is well known (81,82). Hammond (83) has studied the correlations of association constants and of the energy of the charge transfer absorption of 2-substituted-l,4-benzoquinones complexed with hexamethylbenzene with the Hammett equation. Charton (84) has studied the correlation with eq. (2) of association constants of 1-substituted propenes with Ag. ... 

It has always been assumed that these simple proteins act as electron-transfer proteins. This is also a fair conclusion if we take in account that different proteins were isolated in which the Fe(RS)4 center is in association with other non-heme, non-iron-sulfur centers. In these proteins the Fe(RS)4 center may serve as electron donor/ac-ceptor to the catalytic site, as in other iron-sulfur proteins where [2Fe-2S], [3Fe-4S], and [4Fe-4S] clusters are proposed to be involved in the intramolecular electron transfer pathway (see the following examples). 

Catalase Uses Hydrogen Peroxide as Electron Donor Electron Acceptor... 

All characterized BVMOs contain a flavin cofactor that is crucial for catalysis while NADH or NADPH is needed as electron donor. An interesting observation is the fact that most reported BVMOs are soluble proteins. This is in contrast to many other monooxygenase systems that often are found to be membrane-bound or membrane-associated. In 1997, Willetts concluded from careful inspection of... 

Although they have not been obtained in pure culture, chemolithotrophic anaerobic bacteria (anammox) that oxidize ammonia using nitrite as electron donor and CO2 as a source of carbon have been described. In addition, they can oxidize propionate to CO2 (Giiven et al. 2005) by a pathway that has not yet been resolved. 

Under anaerobic conditions with H2 as electron donor—when growth did not take place—S. putre-faciens rednced Tc(Vll) to Tc(IV) that was associated with the cell or with Tc(lV) complexes in the presence of carbonate (Wildnng et al. 2000). 

Humic acid and the corresponding fulvic acid are complex polymers whose structures are incompletely resolved. It is accepted that the structure of humic acid contains oxygenated structures, including quinones that can function as electron acceptors, while reduced humic acid may carry out reductions. These have been observed both in the presence of bacteria that provide the electron mediator and in the absence of bacteria in abiotic reactions, for example, reductive dehalogenation of hexachloroethane and tetrachloromethane by anthrahydroquininone-2,6-disulfonate (Curtis and Reinhard 1994). Reductions using sulfide as electron donor have been noted in Chapter 1. Some experimental aspects are worth noting ... 

Bacteria have been isolated using reduced anthraquinone-2,6-disulfonate (HjAQDS) as electron donor and nitrate as electron acceptor (Coates et al. 2002). The organisms belonged to the a-, p-, y-, and 5-subdivision of the Proteobacteria, and were able to couple the oxidation of H AQDS to the reduction of nitrate with acetate as the carbon source. In addition, a number of C2 and C3 substrates could be used including propionate, butyrate, fumarate, lactate, citrate, and pyruvate. 

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