Electronic and hydrogenation

Mitchell, P. (1961). Coupling of phosphorylation to electron and hydrogen transfer by a chemiosmotic type of mechanism. Nature 191, 144-148. 

C has 4 valence electrons, N has 5 valence electrons and hydrogen has 1 valence electron Total number of valence electrons = 4 + 5 + 1 = 10 valence electrons or 5 pairs of valence electrons. We place C between H and N, and use two electron pairs to hold the molecule together, one between C and N, as well as one between C and H. We complete the octet on N using three lone pairs. This uses all five electron... 

Isotope effects have been used to determine whether the hydride transfer from the enzyme cofactor nicotinamide-adenine dinucleotide (NADH) (reaction (43)) takes place as a hydride ion transfer in a single kinetic step or in a multistep reaction via an uncoupled electron and hydrogen transfer. 

The situation is different if electronic interaction between vicinal substituents is involved. Maciel and co-workers, for example, found large deviations from SCS additivity in 1,2-substituted ethanes if the substituents -I or -C CH are involved the deviations could be accounted for by the high polarizability of the two groups (311,312). Steric, electronic, and hydrogen-bridging effects are... 

The flavin adenine dinucleotide (FAD) and NADH deliver electrons and hydrogen directly to the respiratory cytochromes whilst acetyl-CoA enters the TCA cycle. 

There are three pathways for hydrons, electrons and hydrogen molecules leading into the enzyme to the catalytic site. 

This simplified approach is analogous to the more rigorous absolute rate treatment. The important conclusion is that the bimolecular rate constant is related to the magnitude of the barrier that must be surmounted to reach the transition state. Note that there is no activation barrier (/.e., that AG = 0) in cases where no chemical bond is broken prior to chemical reaction. One example is the combination of free radicals. (In other cases where electrons and hydrogen ions can undergo quantum mechanical tunneling, the width of the reaction barrier becomes more important than the height.)... 

Figure 9-6. Synthesis of tyrosine from phenylalanine. Hydroxylation of phenylalanine to tyrosine is one of several reactions in the body that require tetrahydrobiopterin as a cofactor to provide electrons and hydrogen as reducing equivalents.

The stoichiometry (equation 2) requires eight electrons transferred from vanadium(II) ions to dinitrogen atoms (six electrons) and hydrogen atoms (two electrons) and this kinetic equation (3) was interpreted as evidence for a polynuclear structure of the transition state during the reduction of dinitrogen. An alternative mechanism was suggested.145... 

Nishimoto S, Hatta H, Ueshima H, Kagiya T (1992) 1-(5 -Fluoro-6 -hydroxy-5, 6 -dihydrouracil-5 -yl)-5-fluorouracil,a novel N(1)-C(5) linked dimer that releases 5-fluorouracil by radiation activation under hypoxic conditions. J Med Chem 35 2711-2712 Norman ROC, Storey PM, West PR (1970) Electron spin resonance studies, part XXV. Reactions of the sulphate radical anion with organic compounds. J Chem Soc (B) 1087-1095 Novais HM, Steenken S (1986) ESR studies of electron and hydrogen adducts of thymine and uracil and their derivatives and of 4,6-dihydroxypyrimidines in aqueous solution. Comparison with data from solid state. The protonation at carbon of the electron adducts. J Am Chem Soc 108 1-6... 

Source includes data for other related compounds. Data for hydrated electrons and hydrogen atoms are available in (157). 

Rehm, D. and Weller, A. (1970) Kinetics of fluorescence quenching by electron and hydrogen-atom transfer. Israel Journal of Chemistry, 8 (2), 259-271. 

The conversion of substrate to product also requires immobilized water molecules within the active site and an appropriate charge environment to facilitate the transfer of electrons and hydrogens to pyruvate. After pyruvate is bound, its reduction to lactate involves addition of two electrons, one proton, and one hydride ion (H ). NADH provides the electrons and hydride ion the proton comes from the imidazole ring of His-193. The rate-determining step in the covalent chemistry taking place in the catalytic vacuole is that of hydride transfer, which occurs at a rate of approximately 750 s 1 at room temperature for bovine A4-LDH (Dunn et al., 1991). 

You can see that magnesium has lost two electrons and hydrogen has picked up one electron. Another way to see the process is to write an ionic equation, like you learned in the last section ... 

The involvement of both electrons and hydrogen ion in the high pH reaction explains the slope of the line. Because both reactions involve at least one solid species, the lines are solid, by convention. The diagram in Fig. 9a assumes that the concentration of all dissolved species except H+ and 02 is 10 6 M. Such simplified diagrams have pedagogical uses, but the dependence of the Nernst... 

New reactions have been described where earbanions function both as one electron and hydrogene atom donors [153],... 

Radiolysis has also been employed to generate the hydroxyl radical. However, because very energetic particles are used (x-rays, 7-rays, electron beams, etc.) aqueous solutions are used instead of hydrogen peroxide. Water molecules can be cleaved homolytically and heterolytically to produce three radical species hydroxyl radical, hydrated electron and hydrogen atom.30 A great many rate constants of hydroxyl radical with reductants, especially alcohols, have been measured using radiolysis combined with EPR or electronic spectroscopy.31... 

Figure 24 The mechanism of oxidation of heteroatom-containing compounds by P450 enzymes (a) The one-electron oxidation mechanism of heteroatom oxygenation (b) The one-electron and hydrogen atom abstraction mechanisms of heteroatom dealkylation...

In the electrochemical cell two separate reaction mechanisms can produce alane at the aluminum electrode, as shown in Figure 9.20. One possible mechanism is the oxidation of the alanate ion to produce alane, an electron, and hydrogen, as shown in Eq. (9.9) ... 

Reaction of hydrated electrons and hydrogen atom with nitrite to produce NOj", which undergoes hydrolysis to produce NO. ... 

This postulate assumes that steric, hydrophobic, electronic, and hydrogen bonding factors that affect partitioning in the biophase are handled by the octanol/water system. Given that the biological response (log I/O is proportional to logPbio then it follows that... 

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