Electron‐transfer Organic and Bioorganic Photochemistry

Pac, Chyongjin; Ishitani, Osamu

doi:10.1111/j.1751-1097.1988.tb02893.x

Cited by 39 publications

(7 citation statements)

References 233 publications

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“…18 The mechanism of the reaction can be intermolecular or intramolecular if the donor and the acceptor are in the same molecule. 19,20 Only a few studies have been carried out with drugs with clinical activity, but diclofenac undergoes dechlorination 21 and midazolam defluorination 22 under photolytic stress. Nitrogen atoms are known to be very good electron donors and since AL has four nitrogen atoms, an intramolecular electron transfer can be postulated to occur with any of them.…”

Section: Mechanism Of Formation Of Degradation Productsmentioning

confidence: 99%

Kinetic and mechanistic studies on the hydrolysis and photodegradation of diazepam and alprazolam

Cabrera

Waisbaum

Nudelman

2004

J of Physical Organic Chem

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The corresponding o-aminobenzophenones are usually reported as the main degradation products in the hydrolysis of 1,4-benzodiazepinones. Nevertheless, in previous studies of diazepam (DZ) in acidic aqueous medium we isolated and characterized seven unexpected degradation products. Kinetic measurements under several reaction conditions shed some light on the mechanisms of the complex reactions that are taking place, and photochemical studies give hints on the mechanisms of chlorination and annelation processes. Alprazolam (AL) seems to exhibit an unusually high stability against hydrolysis under several conditions; nevertheless, the structure is sensitive to photolytic cleavage. The photodegradation of AL was studied in aqueous and methanolic solutions. Characterization of the isolated products by 1 H and 13 C NMR and mass spectrometry revealed that electron transfer, oxidation and rearrangement reactions take place. The influence of several variables such as pH, solvent composition and light irradiation were examined and mechanisms for the formation of three photoproducts are proposed. A specific method for the determination of AL in the presence of photoproducts was developed, which allowed kinetic determinations of the photostability of AL. The photosensitivity observed in some patients treated with AL seems to be due to one of the characterized photoproducts.

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Section: Mechanism Of Formation Of Degradation Productsmentioning

confidence: 99%

Kinetic and mechanistic studies on the hydrolysis and photodegradation of diazepam and alprazolam

Cabrera

Waisbaum

Nudelman

2004

J of Physical Organic Chem

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“…Photosensitized splitting of pyrimidine dimers is amenable to study by use of simple systems (for a review, see Pac and Ishitani, 1988), including those in which a photosensitizer is covalently linked to a pyrimidine dimer . In such systems the photoinitiated electron transfer is rendered intramolecular, which is virtually the case in the enzyme-substrate complex composed of photolyase and DNA.…”

Section: Introductionmentioning

confidence: 99%

Solvent Dependence of Pyrimidine Dimer Splitting in a Covalently Linked Dimer‐indole System

Kim

Hartman

Rose

1990

Photochem & Photobiology

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Abstract— –Cyclobutadipyrimidines (pyrimidine dimers) undergo splitting that is photosensitized by indole derivatives. We have prepared a compound in which a two‐carbon linker connects a dimer to an indolyl group. Indolyl fluorescence quenching indicated that the two portions of the molecule interact in the excited state. Intramolecular photosensitization of dimer splitting was remarkably solvent dependent, ranging from φspl= 0.06 in water to a high value of φspl= 0.41 in the least polar solvent mixture examined, l,4‐dioxane‐isopentane(5: 95). A derivative with a 5‐methoxy substituent on the indolyl ring behaved similarly. These results have been interpreted in terms of electron transfer from the excited indolyl group to the dimer, which would produce a charge‐separated species. The dimer anion within such a species could split or undergo back electron transfer. The possibility that back electron transfer is in the Marcus inverted region can be used to rationalize the observed solvent dependence of splitting. In the inverted region, the high driving force of a charge recombination exceeds the reorganization energy of the solvent, which is less for solvents of low polarity than those of high polarity. If this theory is applicable to the hypothetical charge‐separated species, a slower back electron transfer, and consequently higher splitting efficiencies, would be expected in solvents of lower polarity. Photolyases may have evolved in which a low polarity active site retards back transfer of an electron and thereby contributes to the efficiency of the enzymatic dimer splitting.

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“…The high amount of colored compounds is a powerful tool to design material for processes driven by the visible light with good efficiency [6][7][8][9]. In solutions which contain sensitisers, charge separation, electron acceptors and donors or energy transfer within the very short excitation time of the sensitizers occur [6]. In solid devices of organic photovoltaic cells electrical energy can be obtained [10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

“…Photophysical properties of porphyrin dyes can be modified by attaching different substitutes to the tetrapyrrole ring. The high amount of colored compounds is a powerful tool to design material for processes driven by the visible light with good efficiency [6][7][8][9]. In solutions which contain sensitisers, charge separation, electron acceptors and donors or energy transfer within the very short excitation time of the sensitizers occur [6].…”

Section: Introductionmentioning

confidence: 99%

Photovoltage generation and fluorescence of charged tetraphenylporphyrins with dopa melanin

Hanyż

Wróbel²

2003

Cryst. Res. Technol.

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Positively charged tetra(4-N,N,N,N-trimethylanilinium) porphyrin (TAP) and negatively charged tetrakis(4-sulphonatophenyl) porphyrin (TPPS 4 ) and their mixtures with dopa melanin in polyvinyl alcohol have been investigated. On the basis of the absorption and fluorescence spectra it has been established the formation of TAP-dopa melanin complex which fluorescence is quenched whereas TPPS 4 fluorescence behaviour is only slightly changed in the presence of dopa melanin. Photovoltaic effects and photocurrent generation in a photoelectrochemical cell consisting of a layer dye solutions sandwiched between the semiconducting and gold electrodes have been investigated. The dependence of photovoltage signal on excitation wavelength (photovoltage action spectrum), kinetics of photocurrent rise and decay in the second time scale have been presented. Electric parameters of the photoelectrochemical cell (conductivity and capacitance) with porphyrin dyes, dopa melanin and their mixtures in the dark and upon illumination have been estimated. It was shown that all investigated dyes are able to generate photosignal but the values of photocurrent generated depend on the dye used in the experiment and the presence or absence of dopa melanin.

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Electron‐transfer Organic and Bioorganic Photochemistry

Cited by 39 publications

References 233 publications

Kinetic and mechanistic studies on the hydrolysis and photodegradation of diazepam and alprazolam

Kinetic and mechanistic studies on the hydrolysis and photodegradation of diazepam and alprazolam

Solvent Dependence of Pyrimidine Dimer Splitting in a Covalently Linked Dimer‐indole System

Photovoltage generation and fluorescence of charged tetraphenylporphyrins with dopa melanin

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