Deuterium exchange reactions detection

Alumina was the first substance for which a large, positive effect of irradiation upon catalytic activity was reported (11, 84). The hydrogen-deuterium exchange reaction was chosen for the catalyzed reaction because it could be followed at a relatively low temperature, —78°, where, it was hoped, electrons or holes would remain trapped long enough for any effects of their presence to be detected. It was indeed found that as little as 5 x 10 ev/gm of y-rays at —78° increased the rate of the exchange about 10-fold, and that the enhanced activity was removed rapidly by annealing at room temperature. 

A transient intermediate (10) has also been detected during the chlorination of [Co(acac)al by IV-chlorosuccinimide, using a relatively new technique of stopped-flow pulse Fourier-transform n.m.r. This technique should be very useful for investigating the rates of moderately rapid hydrogen-deuterium exchange reactions and for establishing the site of deprotonation in base catalysis. 

Since spillover phenomena have been most directly sensed through the use of IR in OH-OD exchange [10] (in addition, in the case of reactions of solids, to phase modification), we used this technique to correlate with the catalytic results. One of the expected results of the action of Hjp is the enhancement of the number of Bronsted sites. FTIR analysis of adsorbed pyridine was then used to determine the relative amounts of the various kinds of acidic sites present. Isotopic exchange (OH-OD) experiments, followed by FTIR measurements, were used to obtain direct evidence of the spillover phenomena. This technique has already been successfully used for this purpose in other systems like Pt mixed or supported on silica, alumina or zeolites [10]. Conner et al. [11] and Roland et al. [12], employed FTIR to follow the deuterium spillover in systems where the source and the acceptor of Hjp were physically distinct phases, separated by a distance of several millimeters. In both cases, a gradient of deuterium concentration as a function of the distance to the source was observed and the zone where deuterium was detected extended with time. If spillover phenomena had not been involved, a gradientless exchange should have been observed. 

That products of intermediate oxidation level can be detected in the photocatalytic reactions of hydrocarbons and fossil fuels is also consistent with a surface bound radical intermediate . Photocatalytic isotope exchange between cyclopentane and deuterium on bifunctional platinum/titanium dioxide catalysts indicates the importance of weakly adsorbed pentane at oxide sites. The platinum serves to attract free electrons, decreasing the efficiency of electron-hole recombination, and to regenerate the surface oxide after exchange. Much better control of the exchange is afforded with photoelectrochemical than thermal catalysis > ) As before, hydrocarbon oxidations can also be conducted at the gas-solid interface... 

The protons of backbone >NH groups of small peptides dissolved in water are labile and exchange with those of the solvent. The exchange is readily detectable by NMR methods by studying a peptide containing the normal isotope dissolved in deuterium oxide (D20 or 2H20), or vice versa 41,4S The reaction is acid-and base-catalyzed, following the rate law... 

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