REVERSIBLE PHOTODIMERIZATION OF ANTHRACENE AND TETRACENE

Abstract— Dianthracene is efficiently photodissociated, forming anthracene with a quantum yield of about 0.63. Like anthracene, tetracene undergoes a reversible photochemical reaction, the product of which appears to be di-tetracene. In dilute, deoxygenated solutions the of quantum yeild for the formation of di-tetracene is directly proportional to the concentration of the monomer ødim = 2.2 (). The quantum yield for the reverse reaction is approximately 0.74
When dilute deaerated solutions of anthracene are irradiated with the unfiltered radiation from a quartz-mercury arc, a degradation product is formed. Unlike the dimer, this product cannot be converted into anthracene either by heating it to 200C or by irradiating it in solution with light of 254 nm. This degradation product appears to be the compound or compounds which Birks et al. believed to be dianthracene. Irradiation of deaerated solutions of anthracene (or tetracene) with light of wavelenghts longer than 300 nm produces only the dimer, which has an absorption spectrum similar to that reported by Coulson et al.     

9-乙烯基蒽和对-N,N-二甲氨基苯乙烯激基络合物的生成和光二聚反应

测定了9-乙烯基蒽和对-N,N-二甲氨基苯乙烯体系在不同极性的溶剂中的荧光光谱和荧光量子产率。发现随着溶剂极性的增加,激基络合物的荧光发生红移,荧光量子产率降低。同时9-乙烯基蒽和对-N,N-二甲氨基苯乙烯之间的光二聚产物的相对产率也降低。并讨论了经过激基络合物中间体的光二聚反应机理。     

CALIXE[4] ARENE AS A TEMPLATE FOR CONTROLLING REGIOCHEMISTRY OF PHOTODIMERIZATION OF9-SUBSTITUTED ANTHRACENE

Photodimerization of anthracene and its derivatives has been extensively investigated^[1].In general,irradiation of 9-substituted anthracene in organic solvents results in the dimerization of the aromatic rings at 9,10-positions to yield head-to-tail (h-t) rather than head(h-h)photodimers^[2].     

TYROSINE-SENSITIZED PHOTODIMERIZATION OF THYMINE IN AQUEOUS SOLUTION

Abstract. Photodimerization of thymine in aqueous solution in the presence of tyrosine was studied with monochromatic UV irradiation. The total dimer formation was sensitized in the presence of tyrosine. The action spectrum of sensitized total dimer formation has a peak near 280 nm corresponding to the absorption maximum of tyrosine. Triplet quenchers reduced the sensitization substantially. It seems probable that tyrosine-sensitized photodimerization of thymine occurred via triplet-triplet energy transfer from tyrosine to thymine.     

KINETICS OF PHOTODIMERIZATION OF OROTIC ACID IN AQUEOUS MEDIUM

Abstract— Ultraviolet irradiation of orotic acid in aqueous medium leads to the formation of dimers with a cyclobutane ring between the 5,6 bonds of two monomers. These photodimers in turn undergo photodissociation, with the result that an equilibrium is established between photodimerization and photodissociation. The equilibrium point is independent of dose rate, but is appreciably dependent on the irradiation wavelength, pH of the medium (i.e. whether the monomer is in the neutral or anionic form), and initial monomer and oxygen concentrations; the effect of oxygen apparently being to deactivate excited monomers. The kinetics of photodimerization and photodissociation have been examined at different wavelengths and with varying oxygen concentrations at different initial monomer concentrations. The results have been compared with a theoretical model in which it is assumed that a dimer is formed between an excited monomer and second molecule in the ground state, and that oxygen can also react with, and deactivate, an excited monomer. The agreement between the proposed model and the experimental data is reasonably good, and has made possible an estimate of the lifetime of the excited state of orotic acid in aqueous medium, which is about 10^-6 sec.     

乳化结晶法制精蒽新工艺的研究

研究了用乳化结晶法从粗蒽制精蒽的新工艺，考察了溶剂种类、乳化剂种类、乳化剂用量、水／粗蒽质量比、助剂加入量以及结晶终温等因素对精蒽质量的收率的影响，实验结果表明：以糖醛作溶剂，米唑啉物Ｓｐａｎ２０复合型乳化剂，经一次乳化结晶得得精蒽纯度大于９５％，符合国家一级精蒽标准，蒽收率大于８０％。     

PHOTODIMERIZATION OF THYMINE AND URACIL ON FILTER PAPER*

Abstract— Thymine and uracil dimerized by ultraviolet irradiation (principally at 253 7 mμ) on filter paper and on quartz fiber sheet show a fairly good yield. These irradiation products were identical with the photodimers prepared from frozen aqueous solution. Thymine and uracil dimer in an aqueous solution reverted to the original pyrimidines by the ultraviolet irradiation with quantum yields of 0.65 and 0.50 respectively. Uracil dimer was rather labile towards hot alkaline solution. In neutral and acidic media, both dimers were quite stable. Photodimers of cytosine and isocytosine were not obtained.     

PHOTOREACTIONS OF 5-BROMOURACIL IN THE PRESENCE OF CYSTEINE AND GLUTATHIONE

Abstract —Sulfhydryl compounds such as cysteine and glutathione enhance the photochemical reactivity of 5-bromouracil irradiated in aqueous solution with ultraviolet light (Λ > 240 nm). Production of uracil and addition of the sulfhydryl compound to the 5-bromouracil residue are the major photoreactions.     

ACTION SPECTRA FOR PHOTOREACTIONS I AND II OF PHOTOSYNTHESIS IN THE BLUE-GREEN ALGA ANACYSTIS NIDULANS

Abstract— Action spectra for photoreactions I and II of photosynthesis were obtained for Anacystis nidulans and three of its variants which had altered chlorophyll/phycocyanin ratios. The spectra are properly scaled to each other. They provide information on contributions of phycocyanin and chlorophyll to initial absorption and final distribution of excitation energy to reaction centers I and II. In normally pigmented cells the light harvesting pigments for photoreaction I include about 40% of the phycocyanin and 84% of the chlorophyll. Both in normal cells and in cells with altered pigmentation excitation energy from phycocyanin is delivered to photoreaction II via a small number of chlorophylls. In response to alterations in chlorophyll/phycocyanin ratio Action I spectra showed large variations whereas Action II spectra were essentially invariant. The result is taken to mean that alteration in chlorophyll components in Anacystis is attended by a special restriction: there are only small changes in amount of chlorophyll accessible to photoreaction II in the face of large changes in amount committed to photoreaction I.     

THE EFFECT OF 9-ETHYLADENINE ON THE PHOTODIMERIZATION OF 1-CYCLOHEXYLTHYMINE

Abstract— The photodimerization of 1-cyclohexylthymine (l-CT).and the effect of adding 9-ethyladenine (9-EA) on this reaction were studied in chloroform and/or acetonitrile solutions. The photodimerization of 1-CT is shown to occur through an excited triplet state. 9-EA works as an inhibitor against this reaction by quenching the excited singlet state of 1-CT. It is suggested that a singlet exciplex made up from the excited state 1-CT and the ground state 9-EA by hydrogen-bonding may play an important role in the quenching process.     

ON THE DISTRIBUTION OF EXCITATION ENERGY TO TWO PHOTOREACTIONS OF PHOTOSYNTHESIS

Abstract— From kinetic analysis of the Z-scheme we have derived expressions for fractions of open reaction centers and throughput quantum yield. The fraction of absorbed quanta available to photoreaction II has been treated by the wavelength dependent function, α. However, for purposes of analysis in terms of throughput electron flow it is necessary to introduce a related function, α', for actual processing of excitations by photoreaction II; α' differs from α if the individual quantum yields of the two photoreactions are not equal. 'Included in our findings are the following. As a close approximation quantum yield is maximum at α'= 0.5 and a symmetrical function of α' around the line α' =0.5. As previously noted, lowering of the apparent equilibrium constant between the photoreactions flattens dependence of quantum yield on α' near α' = 0.5 but also lowers the attainable quantum yield. For any given equilibrium constant the effective fractions of open reaction centers are equal at α' = 0.5 and mirror images of each other around the line α' = 0.5. Slow changes in quantum yield following changes in wavelength (the State 1-State 2 phenomenon) are explainable in terms of changes in α' which also have the effect of flattening dependence of quantum yield on wavelength. We have used these changes to estimate the neutral wavelength for α' = 0.5 as 681–682 nm in Chlorella .     

EXCITED STATES IN PHOTODIMERIZATION OF AQUEOUS TYROSINE AT ROOM TEMPERATURE

Abstract— The photoionization of tyrosine in aqueous solution in the liquid state was studied at room temperature by analyzing the kinetics of formation of bityrosine upon irradiation of tyrosine, and the external heavy-atom effect on the formation of bityrosine. The relative number of bityrosine molecules was determined by measuring the fluorescence intensity at 400 nm. A kinetic model for the formation of bityrosine was formulated on the assumption that the rate constants were first-order for production of radicals and for recombination with ejected electrons. The applicability of this model to the present case was confirmed by the experimental data. On the basis of the model, we found that the electronic process of photoionization of tyrosine at room temperature is different in acidic and alkaline media. In acidic media a tyrosine molecule absorbs one light quantum and photoionizes through a singlet excited state, while in alkaline media a tyrosinate ion photoionizes after absorption of two light quanta. The intermediate product that absorbs the second photon is in a triplet excited state.     

SIMULTANEOUS MEASUREMENT OF ACTION SPECTRA FOR PHOTOREACTIONS I AND II OF PHOTOSYNTHESIS

Abstract— We have devised a method of obtaining simultaneous action spectra for photoreactions I and II by analysis of direct and indirect effects involved in enhancement. The method requires previous determination of the neutral wavelength which gives maximum quantum yield by virtue of equal fractions of open reaction centers ( p and q ) for each photoreaction. A sufficient intensity of the neutral wavelength is used as a constant background. Upon addition of a weak modulated measuring light of intensity I_m and wavelength λ _m two amperometric signals are obtained for rate of oxygen evolution. A modulated signal (AC¯) isolates the direct effect of I_m and gives action of photoreaction II as AC/ I_m . An increment in total rate (ΔDC) also includes an indirect effect of I_m in perturbing reaction center conditions ( p and q ). From analysis of interaction of the two photoreactions, action for photoreaction I can be estimated as (2 ΔDC-AC)/ I_m . The method is applicable to whole cells, properly scales the two action spectra to each other, and removes contribution of the State 1-State 2 phenomena. Action spectra were obtained for Chlorella.     

BINDING OF ANTHRACENE TO CELLULAR MACROMOLECULES IN THE PRESENCE OF LIGHT

Ultraviolet radiation (δ > 295 nm) induced covalent binding of anthracene to DNA which increased with time and was not affected by oxygen. Irradiation in the presence of anthracene induced nicking of Col E, circular DNA and decreased the thermal denaturation temperature of calf thymus DNA. These effects were oxygen dependent, and were decreased by GMP. Irradiation of anthracene and human serum albumin resulted in covalent binding of the hydrocarbon to the protein accompanied by crosslinking of the protein. Protein crosslinking decreased under anaerobic conditions. Irradiation of anthracene bound to liposomes induced lipid peroxidation which was not affected by superoxide dismutase or catalase.     

硝酸氧化蒽制备蒽醌

蒽醌是用途广泛的化工原料和中间体,主要用于生产还原染料、分散染料、活性染料和酸性染料等。此外,用蒽醌制造变性剂,可以保护植物种子,蒽醌还可用于制造双氧水。近几年来,蒽醌在纸浆制造方面的需求也在迅速扩大。目前,蒽醌的制造方法基本上可分为两种类型。一类是...     

PHOTOCHEMISTRY OF BIOLOGICAL MOLECULES – II. PHOTOLYSIS OF DIPEPTIDES IN THE SOLID STATE

Abstract— Photolysis with light of 2537 Å of a series of aliphatic dipeptides in the solid state has been shown to lead to bond rupture and free radical formation. The structures of the radicals have been determined by ESR techniques and in general, the free electron has been shown to reside on the carbon atom attached to the nitrogen atom of the peptide bond. Dipeptides containing phenylalanine residues show ESR spectra typical of the free amino-acid in the terminal position.