Light-induced

The themial light induces transitions from a b and from b ain proportion to the iiumber of photons present. The iiumber of transitions per second induced by absorption is... 

Kothe G, Weber S, BittI R, Ohmes E, Thurnauer M and Norris J 1991 Transient EPR of light-induced radical pairs in plant photosystem I observation of quantum beats Chem. Rhys. Lett. 186 474-80... 

Department of Physical Chemistry and the Parkas Center for Light Induced Processes, Hebrew University of Jerusalem, Jerusalem, Israel... 

We thank Professor S. Shaik, Professor B. Dick, Professor L, S. Cederbaum, and Dr. W. Fuss for many enlightening discussions and suggestions, This research was supported by The Israel Science Foundation founded by The Israel Academy of Sciences and Humanities and partially by The VolkswagenStiftung. The Farkas Center for Light Induced Processes is supported by the Minerva Gesellschaft mbH,... 

From the colorless state it can be switched with light of short wavelength (A = 380 nm) via an electrocycHc ring opening and cis/trans rotation of one half of the molecule into a state with violet/purple color. The reverse reaction is effected by visible light (A = 580 nm). Since the system is metastable, one of the two reaction directions is matched by a rival thermal reaction, the thermoreversion. This progresses, however, in the case of benzospiropyran, at room temperature by a factor of 10 slower than the light-induced reaction. 

Water-soluble sdanols such as (1) were found to undergo successive oxidative demethylations with tropospheric ultraviolet irradiation in the presence of suitable chromophores, such as nitrogen oxides (516). The water-soluble methylated sdicones did not promote diatom (Nap cu/apelliculosd) growth but the demethylated photo products did. The sequence of sod-induced degradation of sdicones to water-soluble species such as (1), followed by light-induced conversion to sdicate, suggests a pathway, conceptually at least, for the mineralization of sdicones. 

Apart from the nuclear bromination observed (Section 2.15.13.1) in the attempted radical bromination of a side-chain methyl group leading to (396), which may or may not have involved radical intermediates, the only other reaction of interest in this section is a light-induced reduction of certain hydroxypyrido[3,4-f)]pyrazines or their 0x0 tautomers analogous to that well-known in the pteridine field (63JCS5156). Related one-electron reduction products of laser photolysis experiments with 1 -deazaflavins have been described (79MI21502). 

The light-induced rearrangement of 2-phenyl- to 3-phenyl-thiophene may occur by a similar mechanism an equilibrium between the bicyclic intermediate (26) and the cyclopro-penylthioaldehyde (27) has been suggested (Scheme 2). The formation of IV-substituted pyrroles on irradiation of either furans or thiophenes in the presence of a primary amine supports this suggestion (Scheme 3). Irradiation of 2-phenylselenophene yields, in addition to 3-phenylselenophene, the enyne PhC=C—CH=CH2 and selenium. Photolysis of 2-phenyltellurophene furnishes solely the enyne and tellurium (76JOM(108)183). 

FIGURE 22.21 The mechanism of photophosphorylation. Photosynthetic electron transport establishes a proton gradient that is tapped by the CFiCFo ATP synthase to drive ATP synthesis. Critical to this mechanism is the fact that the membrane-bound components of light-induced electron transport and ATP synthesis are asymmetrical with respect to the thylakoid membrane so that vectorial discharge and uptake of ensue, generating the proton-motive force. 

FIGURE 22.27 Light-induced pH changes in chloroplast compartments. Illumination of chloroplasts leads to proton pumping and pH changes in the chloroplast, such that the pH within the thylakoid space falls and the pH of the stroma rises. These pH changes modulate the activity of key Calvin cycle enzymes. 

As discussed in Section 22.7, illumination of chloroplasts leads to light-driven pumping of protons into the thylakoid lumen, which causes pH changes in both the stroma and the thylakoid lumen (Figure 22.27). The stromal pH rises, typically to pH 8. Because rubisco and rubisco activase are more active at pH 8, COg fixation is activated as stromal pH rises. Fructose-1,6-bisphosphatase, ribulose-5-phosphate kinase, and glyceraldehyde-3-phosphate dehydrogenase all have alkaline pH optima. Thus, their activities increase as a result of the light-induced pH increase in the stroma. 

Light-Induced Mg" Efflux from Thylakoid Vesicles... 

What is the for the light-generated primary oxidant of photosystem II if the light-induced oxidation of water (which leads to Og evolution) proceeds with a AG° of —25 kj/mol ... 

Model compounds in the study of repair of UV-light-induced DNA lesions 98EJ01245. 

The prototype of the antihistamines based on benzhydrol, diphenhydramine (3), is familiar to many today under the trade name Benadryl . Light-induced bromination of diphenylmethane affords benzhydryl bromide (2). This is then allowed to react with dimethylaminoethanol to give the desired ether. Although no mechanistic studies have been reported, it is not unlikely that I he bromine undergoes SNi solvolysis in the reaction medium the carbonitjm ion then simply picks up the alcohol. It might be noted in passing that the theophyline salt of 4 is familiar to many Iravelers as a motion sickness remedy under the trade name Oram amine . 

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