Coupling of protons

Trumpower, B. L., 1990. The protonmotive Q cycle—energy tran.sduction by coupling of proton tran.slocation to electron tran.sfer by the cytochrome bei corap[ x. Journal of Biological Chemistry 265 11409-11412. 

Ullmann, M., The coupling of protonation and reduction in proteins with multiple redox centers theory, computational method and application to cytochrome C3, J. Phys. Chem. B 2000,104, 6293-6301... 

Whereas in acetonitrile the rate limiting step is an opening of the solvent shell of a reactant, in benzonitrile the back reaction of (5) between the protonated acridine orange cation (BH ) and the 3-methyl-4-nitrophenolate ion (A ) to form the ion pair is diffusion controlled (although the overall reaction to the neutral molecules is an endothermic process). Because of its lower dielectric constant than acetonitrile, the electrostatic interactions between reactants in benzonitrile outweigh specific solvent effects. In other words, in benzonitrile a rate limiting coupling of proton transfer to the reorientation of solvent dipoles does not occur and the measured rates are very fast. The ion recombination (I) + (II) in benzonitrile has a diffusion controlled specific rate (theoretical) k = 9 -1 -1... 

The oxidation/reduction of redox cofactors in biological systems is often coupled to proton binding/release either at the cofactor itself or at local amino acid residues, which provides the basic mechanochem-ical part of a proton pump such as that foimd in cytochrome c oxidase (95). Despite a thermodynamic cycle that provides that coupling of protonation of amino acids to the reduction process will result in a 60 mV/pH decrease unit in the reduction potential per proton boimd between the pAa values in the Fe(III) and Fe(II) states, the essential pumping of protons in the respiratory complexes has yet to be localized within their three-dimensional structures. 

If the differences between the frequencies are substituted in the equation this gives a difference in frequency of Bl and B2 of 22 Hz, i.e. the germinal coupling (coupling of protons on the same carbon) of the two signals gives shifts of 7.5 Hz in one direction and 4.5 Hz in the other direction instead of the usual even splitting. 

Coupling of Proton-Transfer-Reaction Mass Spectrometry with Gas Chromatography-Mass Spectrometry... 

The answer to the first question relates to the coupling of proton energies generated by light or oxidation to ATP (adenosine triphosphate) synthesis... 

Another application of LC-NMR in natural products chemistry concerns biosynthetic studies employing feeding experiments with stable isotope-labelled compounds. H NMR spectra allow the determination of the amount of isotopic label incorporated into metabolites, e.g. by observing signals that arise from /-couplings of protons to 13C-labelled nuclei [41,42],... 

Suzuki, T., Ueno, H., Mitome, N., Suzuki, J., and Yoshida, M. (2002). F(0) of ATP synthase is a rotary proton channel Obligatory coupling of proton translocation with rotation of c-subunit ring./. Biol. Chem. 277, 13281-13285. 

The substrate water molecules are prepared in a stepwise fashion for 0-0 bond formation by binding to the M OjCa cluster and by (partial) deprotonation. The concerted oxidation of the activated substrate occurs then either in two 2e steps or in one concerted 4e reaction step, thus avoiding high-energy intermediates. It is the matrix (protein) and the Ca2+/CF ions that allow for the coupling of proton- and electron-transfer reactions to occur. These features are... 

An essential feature of reactions catalyzed by metal-sulfur oxidoreductases is the coupling of proton- and electron-transfer processes. In this context, an important question is how primary protonation of metal-sulfur sites influences the metal-sulfur cores, small molecules bound to them, and the subsequent transfer of electrons. In order to shed light upon this question, protonations, isoelectronic alkylations, and redox reactions of [M(L) (S )] complexes were investigated (M = Fe, Ru, Mo L = CO, NO S = Sj, US24 ). The CO and NO ligands served as infrared (IR) probe for the electron density at the metal centers. Resulting complexes were characterized as far as possible by X-ray crystallography. Scheme 23 shows examples of such complexes. 

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