Hydrolysis light-induced

The photolysis of 2-methyl-5-nitro-l//-imidazoles 132 in a water-containing solvent80 gives oxime 133, which is in turn hydrolysed to 134 followed by a dehydrative cyclization to the 1,2,4-oxadiazole 135. Light-induced hydrolysis of 135 gives 136 (equation 68). 

Figure 11. Light-induced yellowing of filter paper sheets impregnated with fractions (F1-F3) of the extract obtained after acid hydrolysis of bleached CTMP (cf. Figure 10).

The activated membrane-bound ATPase is functionally coupled to proton movements. Thus, a transmembrane pH gradient (acid inside) of a magnitude similar to that observed during light-induced coupled electron flow is developed during ATP hydrolysis. ATP hydrolysis is stimulated, while the coupled proton transport is inhibited, by the addition of uncouplers, indicating that the rate of ATP hydrolysis is also partially limited by the electrochemical gradient which it creates. Nevertheless, attempts to measure H /ATP ratios in this system yielded numbers much below the expected ratio of 3. 

Barton [y] has shown that iV iodoamides of suitable structure e.g. 3) are converted into lactones (y) by irradiation followed by hydrolysis of the iminolactone intermediate (6) during working up. Of various mechanisms considered, the one most consistent with experimental evidence [y] involves light-induced homolysis of the weak N-I bond, hydrogen transfer from the <5 -carbon atom (Cp6)) to the -NH radical 4), combination of the C(i6> radical with an iodine atom, and... 

Figure 32.25. Visual Sigual Transductiou. The light-induced activation of rhodopsin leads to the hydrolysis of cGMP, which in turn leads to ion channel closing and the initiation of an action potential.

The A/Xh+ can be generated by light-induced or dark electron transport, as well as by hydrolysis of ATP, GTP or PPj [7,8], The rates of the ATP- and PP -driven reactions are about 70 and 56% of the light-driven reaction, respectively. The addition of both ATP and PPj stimulates the rate more than either alone, and gives a rate almost as high as light. The PP-driven reaction is inhibited by uncouplers of phosphorylation but not by electron-transport inhibitors or oligomycin. The stoicheiometries of ATP and PP hydrolyzed to NADP reduced are 1 and 10, respectively. 

Areas requiring special attention in the future include improved stabilization processes for existing polymers and the synthesis of new polymeric materials which are more resistant against environmental corrosion than those presently used. The implications of the stability of natural polymers for the prediction of service life of synthetic polymers,the general effects of hydrolysis, the light-induced hydrolytic degradation are relevant research topics. 

Wymer, N.J., Gerasimov, O.V., and Thompson, D.H. (1998) Cascade liposomal triggering light-induced Ca2+ release from diplasmenylcholine liposomes triggers PLA2-cata-lyzed hydrolysis and contents leakage from DPPC liposomes, Bioconjugate Chem., 9, 305-308. 

The hydrolysis of 146 (isopropyl carbene) is also catalyzed by light although the effect is smaller than for 144a or 144b and the phenomenon was not studied in detail. On the other hand, no light-induced rate accelerations were observed for the hydrolysis of the cyclic carbene complexes 8 and 141, " or of the ethyl carbene complex 145. " It is unclear at this point what structural factors power the photochemical reaction shown in Scheme 18. 

Many heterogeneous processes such as dissolution of minerals, formation of the solid phase (precipitation, nucleation, crystal growth, and biomineralization), redox processes at the solid-water interface (including light-induced reactions), and reductive and oxidative dissolutions are rate-controlled at the surface (and not by transport) (10). Because surfaces can adsorb oxidants and reductants and modify redox intensity, the solid-solution interface can catalyze many redox reactions. Surfaces can accelerate many organic reactions such as ester hydrolysis (11). 

Hydroxyl radicals (HO ) represent one of the most reactive species and may be generated in vitro by the Fe ion-induced decomposition of H O [59], by the light-induced scission of HjO or by H2O radiolysis [60]. Water hydrolysis is unequivocally the most specific method of HO radical generation and the radical yield can be easily altered by the applied energy dose [61]. 

Shimoyamada, M. Yoshimura, H. Tomida, K. Watanabe, K. Stabilities of bovine P-lactoglobulin/reti-nol or retinoic acid complexes against tryptic hydrolysis, heating and light-induced oxidation. Lebensm. Wiss. u. Technol. 1996, 29 (8), 763-766. 

Valerolactones.— The unstable dihydropyran anion (73) may be useful for the preparation of a-substituted valerolactones the intermediate dihydropyrans are converted into the latter by acid hydrolysis and Collins oxidation. A new route to the c/s-fused valerolactone portion of vemolepin has been developed which could have other applications. It has been briefly noted that benzene-seleninic anhydride can be used to dehydrogenate fused valerolactones to the a,j8-unsaturated derivatives the conditions, however, are somewhat drastic (120 °C, 42 h). Unsaturated valerolactones can also be obtained from vinyl-oxirans by a light-induced reaction with pentacarbonyliron followed by carbonyl-ation. ... 

Wilden, U., Duration and amplitude of the light-induced cGMP hydrolysis in vertebrate photoreceptors are regulated by multiple phosphorylation of rhodopsin and by arrestin binding. Biochemistry, 34,1446, 1995. 

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