Proton transfer photo-induced

S0 -> Sx -> Tx transition Tt is a base of pyridine strength (pK 5), while S0 and Sj are practically non-basic (pK 0),1S9). Moreover, the site of protonation is Nl/2a for S0 andSi,butN5 forTj (Fig. 4). Hence, Hemmerich and Schmidt proposed87) that a regiospecific rearrangement of hydrogen bridges between flavin and an apoprotein environment may occur in a photo-excited flavoprotein, which would induce a unidirectional 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... 

Most fluorescent PET molecular sensors, including pH indicators of this type, consist of a fluorophore linked to an amine moiety via a methylene spacer. Photo-induced electron transfer (see Chapter 4, Section 4.3), which takes place from amino groups to aromatic hydrocarbons, causes fluorescence quenching of the latter. When the amino group is protonated (or strongly interacts with a cation), electron transfer is hindered and a very large enhancement of fluorescence is observed. 

A novel synthesis of 5,6-dihydro-4//-1,2-oxazines (20) is presented via the photo-induced cyclization of y. d-unsaturated oximes (21) see Scheme 4. Irradiation of (21) in the presence of 9,10-dicyanoanthraccnc (DCA) led to the heterocycle (20) only. The proposed mechanism proceeds via the radical cation (22), generated by single-electron transfer (SET) from the oxime (21) to the excited sensitizer (DCA. Cyclization of (22) affords the oxazine (20) after proton transfer to the DCA radical anion (DCA ) and H abstraction.61... 

The photo-induced electron transfer of l,4-bis(methylene)cyclohexane in acetonitrile-methanol solution with 1,4-dicyanobenzene (DCB) affords two products, both consistent with nucleophilic attack on the radical cation followed by reduction and protonation or by combination with DCB ).63 In the absence of a nucleophile, the product mixture is highly complex, as is the case under electro-oxidative conditions. Under UV irradiation, /nmv-stilbene undergoes dimerization and oxygenation (to benzaldehyde) by a single-electron mechanism in the presence of a sensitizer such as 2,4,6-triphenylpyrilium tetrafluoroborate (TPT).64 This reaction was found to yield a similar product mixture with the sulfur analogue of TPT and their relative merits as well as electrochemical and photophysical properties are discussed. 

The selective two-electron reduction of C60 to C60H2 has been achieved by photo-induced electron transfer in benzonitrile-TFA solution with 10-methyl-9,10-dihydroa-cridine (AcrHy.65 The proposed mechanism begins with electron transfer from AcrIU to C60 to afford the radical ion pair (C60 AcrHj ). The strongly acidic AcrHj species protonates Q,(l to afford the C6qH radical which is rapidly converted into the dihydrofiillerene (C60H2) by electron transfer from AcrH in the presence of TFA. The... 

Since coiled chains of proteins are known to uncurl because of ionic repulsions when ionization occurs, Reid (1957) suggested that excited state dissociation acts as a trigger in rapid biological processes. The 7-azaindole dimer, which undergoes photo-induced double proton transfer (see Section 4), has similarities to the adenine-thymine and guanine-cytosine base pairs of DNA. Its excited state proton transfers have been proposed as possible mechanisms of mutagenesis (Ingram and El-Bayoumi, 1974). 

While the slow protonation of the hydride species leads to H2 evolution, the ligation of acetylene to the Co(II)-protoporphyrin results in intramolecular hydride transfer and the hydrogenation of acetylene to ethylene. The oxidized dye is reduced by EDTA and thus the photobiocatalyst functions as a cyclic photoen2yme. Photo-induced hydrogenation of acetylenedicarboxylic acid proceeds stereoselectively and yields the thermodynamically less stable cis product, maleic acid. 

Compound 639 also promotes the photo induced reduction of ketones whereas 2-(2 -hydroxyphenyl)-l,3-dimethyl-benzimidazoline 640 promotes benzpinacol formation (Scheme 153) <2005JOC9632>. Photoinduced single electron transfer (SET) followed by regiospecific proton transfer (PT) led to the formation of either benzhydrol or benzpinacol, depending on the 2-aryl substituent. 

According to Mitchell s chemiosmotic theory, photophosphorylation is driven by energy derived from electron transfer coupled to proton translocation. The results of postillumination discussed in the previous section further supports the notion that a proton gradient is the driving force for phosphorylation. It is therefore possible in principle that a similar proton gradient produced by artificial means might also be able to drive phosphorylation in a chloroplast membrane, entirely in the dark, i. e., without the aid of photo-induced electron transport. Such a scheme was indeed realized by the so-called acid-bath ATP-forma-tion demonstrated by Jagendorf and Uribe " in 1966. 

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

The orientation and conformation of protein at the surface of electrodes represent key factors, as they influence the interfacial electron speed. A direct reversible fast electron transfer was observed for RC of Rhodobacter sphaeroides reconstituted in polycation sandwiched monolayer film. This layer-by-layer technique allows a such ordered orientation of RC that favours the electron transfer in film. Furthermore, RC in the film features a photo-induced redox-peak fluctuation, suggesting an intact and functional state redox peaks were also found dependent on pH, Implying a proton-coupled electron transfer. 

Gunnlaugsson and co-workers have studied several receptors containing a thiourea group attached to an anthracene moiety [33]. These compounds were designed to behave as fluorescent PET (photo-induced electron transfer) sensors for the detection of anionic species. Proton NMR titration experiments, conducted in DMSO-de, confirmed that the anions bind to the... 

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