Induced proton transfer

Photo-induced proton transfer Aerosol-OT. The efficiency of proton transfer depends on HzO. Pyranine used as a fluorescent probe. Bardez et al., 1984... 

Sometimes, FI mass spectra show signals due to reactions of the analyte with the emitter surface or between molecules adsorbed to that surface. In case of acetone for example, it was demonstrated that [M+H]" quasimolecular ions are produced mainly by a field-induced proton-transfer reaction in the physically adsorbed layer. [59] The mechanism of this field-induced reaction depends on the existence of tautomeric structures of the neutral molecule. Besides the [M+H] quasimolecular ions, [M-H] radicals are formed ... 

Example D-Glucose may be evaporated into the ion source without complete decomposition as demonstrated by its FI spectrum (Fig. 8.13). FD yields a spectrum with a very low degree of fragmentation that is most probably caused by the need for slight heating of the emitter. The occurrence of ions, m/z 180, and [Mh-H]" ions, m/z 181, in the FD spectrum suggests that ion formation occurs via field ionization and field-induced proton transfer, respectively. However, thermal... 

J. Ho and E. Po, Biochem. Educ. 24, 179-180 (1996). Light-induced proton transfer through chloroplast membrane. 

Thermally or photochemically induced proton transfers represent bistable switching processes and are of interest for information storage. A lateral transfer of information on the surface of biological membranes is thought to occur by fast proton conduction through protonic networks [8.234]. 

To determine these data, the unstable tautomers were mostly generated by flash photolysis in order to measure their relaxation kinetics in aqueous solution at various pH. Some prototype precursors for the photochemical generation of unstable tautomers are shown in Scheme 4. In a few cases they are formed directly by irradiation of the stable form either by intramolecular photoenolization such as in 2-alkylacetophenones,30 2-nitrobenzyl derivatives28,31 such as 2-(2, 4 -dinitrobenzyl)pyridine,32 or by light-induced proton transfer to solvent water, as in the case of 9-anthrone.33... 

In some rigid planar systems snch as 34 photochemically induced proton transfer occurs in benzene as solvent, but this is followed by cyclization resulting in the formation of the acridine 35 . The cychzation is a common oxidative process in c -stilbenoid systems. The proton transfer is an essential feature in the cyclization, since it was demonstrated that the reaction fails with the methoxylated analogue. With the bis hydroxy compound 34, X = = OH, a second cyclization affords 36 albeit in lower yield (14%). 

Type II hydrogen abstraction by the keto group from the adjacent aryl methyl group to give the biradical (60) from which both products (61) and (62) are formed. The reaction is solvent dependent. In cyclohexane solvent only the cyclobutanols (61) are formed, but in methanol a mixture of (61) and the new diketone (62) are obtained in a ratio which is dependent upon steric factors. The photochemically induced proton transfer in 3-methyl-6-hydroxy-m-phthalic acid has been reported. ... 

Figure 13.10 Arrhenius plot for photo-induced proton transfer from DCN2to alcohols. Dashed line represents 25 °C.

Induced proton transfer in an adduct of squaric acid and bipyridine... 

Fig. 10b), where an ultrafast intramolecular excited-state charge-induced proton transfer occurs in tens of femtoseconds after the vertical excitation of the ground state. The proton transfer alters the energy landscape and IC to the ground-state surface takes place with no cis-trans isomerisation, unlike other chromophores, where the intramolecular proton transfer is not possible. 

Physical nature of the solvent induced proton transfer... 

Preliminary results presented in the Table 7 indicate that the changes of potential energy barrier inducing proton transfer upon HNOz..NH H20)z dehydration are dominated by the first order electrostatic term ( 71-78% of overall energy change ) and in particular by its multipolar contribution... 

An experimental approach based on induced proton-transfer may be more profitable. This could be effected either by irradiation techniques, since proton-transfer is facilitated in the excited state or perhaps through the study of the effects of intercalated mutagens and carcinogens (such as acridine dyes or anthracene derivatives) into the double helical structure. It may be that the enhanced environmental mobility conferred on the otherwise rigid helical structure is one factor facilitating proton-transfer within the intact DNA, and this may help to explain the carcinogenic action of certain types of molecules. 

Recently, Leszczynski and coworkers (Bao et al. 2006 Gu et al. 2006) used theB3LYP/DZP-H-t method to study the 5/ -O5 and Cy -Oy bond cleavage in pyrimidine nucleotides anion radical in their adiabatic states. This work supported the mechanism suggested by Simons and coworkers (Barrios et al. 2002). An alternative mechanism using the concept of electron-induced proton transfer mechanism was proposed by Dabkowska et al. (2005) considering a cytosine nucleotide as a model of DNA for creating SSBs in DNA. In this model. 

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