Proton activity induced reactions

This method is based on the polarimetric measurement of the optical activity induced by the KIE in a reaction mixture containing an isotopic quasiracemate, i.e. an approximately 50/50 mixture of the (+)-H and (-)-D substrate or vice versa, as one of the reactants. Variants of the method were independently reported by Bergson et al. (1977), Nadvi and Robinson (1978) and Tencer and Stein (1978). Later the method was successfully applied, particularly by Matsson and co-workers (Matsson, 1985 Hussenius etal., 1989 Hussenius and Matsson, 1990) to determine both primary and secondary KIEs in proton transfer reactions, and by Sinnott and co-workers (Bennet et al., 1985 Ashwell et al., 1992 Zhang et al., 1994) to determine both primary and secondary as well as heavy-atom KIEs for reactions of carbohydrate derivatives. 

Direct formation of protons by anodic oxidation of dihydrogen, H2, on activated Pt anodes allows the formation of well-defined quantities of acid [4, 5]. However, this method of proton generation has not been used in typical EGA-induced reactions. 

Some of the accessible reactions are directly important in the nucleosynthetic processes while other experiments can only serve as tests of the theoretical approaches (Kiss et al. 2008). The reactions can either be studied in online beam experiments detecting directly emitted y-rays or particles. Another important type of experiment is that of activation (see, e.g., Gyiirky et al. 2006, and references therein). A material sample is activated by neutron, proton, or a beams at the energy of interest and the long-term radiation is counted over an extended period of time. Alternatively, the amount of the nuclei produced by the activation can be measured by the very sensitive accelerator mass spectrometry (AMS), which has become an important tool also for astrophysical measurements. It is especially well suited to study neutron-induced reactions producing different isotopes of the same element. 

Important contributions towards a detailed state specific understanding of H-D exchange reactions in collisions of with H or H2 in all possible deuterated variants have been made in the last years in several laboratories. The activities, which all use low temperature 22-pole traps in combination with the method of laser induced reactions, have been summarized in Ref. 3. The feasibility of analyzing cold H3 via laser excitation, followed by proton transfer to Ar, has been first demonstrated in a compact trapping machine which has been mainly developed as an ion source. Meanwhile high power CW diode lasers are applied to excite ions and isotopic variants in specific states via overtone transitions. Also the first spectra with a free electron laser have been reported. ... 

Contaminant adsorption (competitive in mixtures with preferential adsorption of the largest-affinity contaminant), contaminant decomposi-tion/electrochemical reaction intermediates production, O reduction reaction pathway modification (atop Oj adsorption favored rather than bridged Oj, electric double layer structure change induced by cation insertion in iono-mer, Pt oxide modification including kinetics, changes in proton activity) or contaminant deposition reduces the catalyst area, increases the reduction reaction overpotential, decreases faradaic efficiency, and increases product selectivity (increased HjO contaminant production) Pt particle dissolirtion acceleration by adsorbed S on Pt from SOj or other soirrces decreasing iono-mer ionic conductivity... 

Finally, Mukaiyama-Mannich-type reactions can also be induced and mediated by proton activation of the imine component, which thereby obtains a sufficient degree of reactivity to be attacked by highly nucleophilic silicon enolates. Thus, Wenzel and Jacobsen have shown that the specific protection by N-aryl substituents with a pendant ortho-hydioxy or ortho-methoxy chelating group is not required, if the acetate-derived sHyl ketene acetals 362 are reacted with simply BOC-protected aryl and hetaryl imines 361. Thus, P-amino esters 364 are obtained in excellent enantiomeric excess, if the reaction is catalyzed by the chiral urea derivative 363 that is assumedto act by activation through hydrogen bonding (Scheme 5.95) [181]. 

Electron transfer by cytochrome-c oxidase is associated with a proton-translocation activity which is believed to reside within polypeptide chain III. Therefore, as electrons are transferred by oxidation-reduction reactions in Complexes I, III and IV, migration of protons is induced, events of major significance (Section 13.6). 

That is, the activated complex contains one Cr(V) atom and one Fe(II) atom. Espenson has shown, from a consideration of the induced oxidation of iodide ion, that the reaction between Cr(VI) and Fe(Il) requires one added proton. Consequently, the [H ] -dependence of the rate can be viewed as the addition of two protons in a pre-equilibrium followed by the addition of a further proton in the slow step, viz. 

The above observations strongly indicate that O-protonation is an important step in this particular reaction for the reduction of coordinated CO. Recent studies in our laboratory provide other examples of proton induced reduction in metal cluster systems, and an example of proton induced CO reduction has recently been reported by Atwood (44). It thus appears that protons as well as Lewis acids are effective in the bifunctional activation of coordinated CO. 

When the protonated amine-arm does not participate in the reaction (TS1-I ), the reaction is very endothermic. However, the activation barrier decreases to 2.6 kcal/mol and the endothermicity of the reaction becomes very small (only 0.2 kcal/mol), if the protonated amine-arm participates in the reaction (TS1-II). In this transition state the O-H distance is 1.709A, typical of a hydrogen bond. The origin of the acceleration was explained in terms of the enhancement of polarization of CO2 induced by the protonated amine arm, which increases the positive charge in the carbon atom. This polarization favors the electrostatic interaction between hydride and C02, and since this polarization increases the contribution of the C p orbital in the it orbital of C02, it favors also the charge-transfer from the H ligand to the 71 orbital of C02. In other paths starting with direct interaction between C02 and Ru the effect of the protonated amine was much smaller. 

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