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1.
R. F. Bayfield E. R. Cole 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):19-23
Abstract A study has been made of photocatalyzed interchange reactions of aromatic sulfenamides. The significance of the results in relation to the relative ease of S[sbnd]N and S[sbnd]S bond fission is discussed, together with possible mechanisms of interchange. Relevance to industrial processes is noted. 相似文献
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本文按合成产物的结构类型,综述分子内 Diels-Alder 反应在有机合成方面的新进展。 相似文献
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芳杂环的亲电取代活性及定位效应是许多理论研究的对象。研究的重点多是同系物间的活性比较及分子内的取代定位效应。其规律往往用反应活性部位的电荷数量及分布来解释。量子化学计算结果,一般也符合物理有机的这一传统解释。因此,电荷数量及分布决定分子的取代活性及定位仍是有机化学中普遍接受的观点[1]。不少量子化学活性指标也用于亲电取代活性及定位效应的解释,但一般只局限于同系物的比较,不同母核的芳杂环的亲电取代活性比较则较少为人们所注意。 相似文献
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A number of electron donors, acceptors and diads containing xanthene dyes were sythesized. When the dyes were excited, the rate constants and the efficiencies of the intermolecular and intramolecular photo-induced electron transfer reactions were determined and calculated. It is found that the photo-induced electron transfer reactions occurred between xanthene dyes and many, including very weak donors or acceptors. The rate constants of intermolecular reactions were controlled by diffusion, and influenced by the reactant concentrations. The laser flash experiments showed that for low reactant concentrations, this kind of reactions took place mainly via the triplet excited state of the dyes. If different electric charges exist with dyes and donors/acceptors, there will be static quenching of the dyes' fluorescence. The intramolecular electron transfer reactions are independent of the solution concentrations, and they may directly proceed via the singlet excited state of the dyes effectively. 相似文献
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Haruo Ohmura Shinichi Motoki 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2):19-28
Abstract The reactions of aryl 1-naphthyl thiones and aryl 2-naphthyl thiones with maleic anhydride, norbornene, and norbornadiene gave the 1,4-cycloadducts containing 3,4-dihydro-2 H-thiopyran rings. 7H-Benz[de]anthracene-7-thione also reacted with norbornene and norbornadiene to give similar 1,4-cycloadducts. In the reaction of aryl phenyl thiones with norbornene, initially formed cycloadducts rearranged to aromatized compounds. In these reactions, the aromatic thiones reacted with the olefins as a heterodiene system. 相似文献
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采用荧光分光光度法,实验测定了聚苯乙烯磺酸钠在无盐和有盐的水溶液中,单体和激态缔合体的荧光发射光谱.结果表明:激态缔合体单体发射强度比I_E/I_M随外加盐种类、浓度和价态而变化.在相同盐浓度下,各体系的I_E/I_M次序为:KCl>NaCl>LiCl和CaCl_2>MgCl_2。 也研究了NaCl水溶液中聚电解质分子的荧光猝灭.结果表明:随外加盐浓度逐渐增大,聚电解质分子由类棒状向无规线团状转化,该状态有利于激态缔合体的形成. 相似文献
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Lin-xi Zhang Ting-ting Sun Xiang-hong Wang Department of Physics Wenzhou University Wenzhou China Department of Physics Zhejiang University Hangzhou China 《高分子科学》2007,(2):197-201
In this paper, we estimate the rate of contact formation between two residues in the interior of the proteins using the Szabo, Schulten, and Schulten formula with the probability distribution P(r) based on 375 proteins from PDB (Protein Data Bank). The probability distribution for residue pair in proteins is different from the Gaussian distribution, especially for short distance between two residues in proteins. The rate of contact formation in the interior of protein is discussed as a function of distance n (=|j-i|) between two residues, and it decreases monotonically with n and follows the scaling relationship of k∞n-γwithγ= 1.43 for the contact radius a= 0.40 nm andγ= 1.05 for a = 0.50 nm. The diffusion coefficient for the relative diffusion of two residues in the interior of proteins is estimated as D = 6.4×10-6 cm2/s, which is close to the result that is found for monomer diffusion. 相似文献
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Wataru Ando Toshiaki Nagashima 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2)
Abstract Dye sensitized photooxidation of sulfides proceeds by way of singlet oxygen to give sulfoxides and sulfones, and the evidence for several intermediates has been reported. We now report that photooxidation of aromatic sulfides gives the product of an unusual type; and the reaction may proceed by either superoxide or hydroperoxysulfurane. 9-Ethylthiofluorene was photooxidized in dichloromethane or acetone with methylene blue as sensitizer. Three main products were isolated and identified as fluorenone (15%), 9-fluorenyl ethyl sulfoxide (19%) and 1-hydroxyl-9-fluorenone (23%). 相似文献
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Abstract— The quenching of intramolecular exciplex fluorescence in 2,6-bis(methylamino)naphtha]ene, (II), 2,6-bis(/V-methyl, methylamino)naphthalene, (III) and 2,6-bis(N-dimethy], methylamino)naphthalene, (IV) by water was investigated. Exciplex fluorescence intensity decreased continuously with increase in water concentration; while monomer fluorescence intensity remained constant up to 25% of water, followed by a rapid increase in intensity.
Absorption spectra showed that specific interaction occurred between water and ground state amine molecules at high concentrations (25% by volume) of water. These observations were interpreted in terms of a static quenching involving the interaction of water with the ground-state amine and a dynamic quenching involving the interactions of water with the exciplex. Our observations explain the greater efficiency of exciplex-fluorescence quenching by protic polar solvents. 相似文献
Absorption spectra showed that specific interaction occurred between water and ground state amine molecules at high concentrations (25% by volume) of water. These observations were interpreted in terms of a static quenching involving the interaction of water with the ground-state amine and a dynamic quenching involving the interactions of water with the exciplex. Our observations explain the greater efficiency of exciplex-fluorescence quenching by protic polar solvents. 相似文献
11.
PHOTOINHIBITION OF CHLOROPLAST REACTIONS 总被引:2,自引:0,他引:2
Abstract— An attemlpt was made to localize the site of photoinhibition of photosynthesis by measuring the decay of various chloroplast reactions after exposure to very strong light. A11 substrate reductions coupled to oxygen evolution as well as photophosphorylation mediated by PMS, proved equally sensitive to photoinhibition. Reactions involving only the long wave photosystem, such as TPN reduction with ascorbate as electron donor and photooxidation of cytochromec by detergent-treated chloroplasts were sensitive to a lower degree.
Photoinhibition irreversibly annihilated the 'variable' fraction of fluorescence emission —it decreased the steady state yield 2-3 fold and abolished the slow rise of the emission at the onset of illurnination.
It is concluded that the primary site of light inactivation is in, or close to, the trapping centers of the oxygen evolving step of photosynthesis. Pre-illumination leaves these traps in a state capable of draining light from sensitizing pigments but unable to perform useful photochemistry. 相似文献
Photoinhibition irreversibly annihilated the 'variable' fraction of fluorescence emission —it decreased the steady state yield 2-3 fold and abolished the slow rise of the emission at the onset of illurnination.
It is concluded that the primary site of light inactivation is in, or close to, the trapping centers of the oxygen evolving step of photosynthesis. Pre-illumination leaves these traps in a state capable of draining light from sensitizing pigments but unable to perform useful photochemistry. 相似文献
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R. Carruthers R. M. Laird E. Sayers 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2)
Abstract Substituent effects have been investigated for both nucleophili -ic and reduction reactions of arylsulphonyl fluorides in aqueous media. The significance of the results will be discussed in relation to the reactions of arylsulphonyl chlorides. 相似文献
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Abstract— The rapid bimolecular reaction SO + O3 = SO2 +O2 + 106 kcal/mole
yields electronically excited SO2 in the 3 B 1 and 1 B2 states with some vibrational excitation, as well as SO2 in its electronic ground state. It is shown that k1 = 1.5 x 1012 exp (-2100/ RT ) cm2 mole-1 s-1 and that the formation of electronically excited SO2 involves higher activation energies. 相似文献
yields electronically excited SO
14.
Kesheng Feng Farah Mahdavi-Anary Richard E. Partch Yuzhuo Li 《Photochemistry and photobiology》1995,62(5):813-817
Abstract— Photochemical reactions of 6-azidocoumarin and 7-azido-4-methylcoumarin in the presence of secondary amines have been investigated for their potential applications in photoaffinity labeling. It was found that the singlet nitrene generated from 6-azidocoumarin isomerized to a dehydroazepine intermediate that reacted with an amine to yield two isomeric adducts. Photolysis of 7-azido-4-meth-ylcoumarin, in contrast, gave a triplet nitrene that abstracted hydrogen atoms from secondary amine molecules to form 7-amino-4-methylcoumarin as the major product. The difference in the intersystem crossing rate between the two compounds originates from the azido position relative to the carbonyl group. Because of its ability to form a covalent linkage with a nucleophile, 6-azidocoumarin is deemed to have a greater potential as a photoaffinity label than 7-azido-4-methylcoumarin. 相似文献
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Abstract The photosynthetic electron transport inhibitor dibromothymoquinone was found to mediate the photoreduction of horse heart cytochrome c in aqueous solution. This process appears to involve the reduction of dibromothymoquinone to the corresponding hydroquinone followed by direct electron transfer to cytochrome c. A subsequent'autoxidation'of the reduced cytochrome c takes place which requires the presence of both oxygen and quinone. Irradiation of ethanolic stock solutions of dibromothymoquinone generates a hydroquinone species which is (1) capable of reducing cytochrome c directly in aqueous solution in the dark and (2) chemically distinct from the parent compound. This photore-duced species is stabilized in ethanolic solution but undergoes autoxidation ( t 1/2 = 24 s) when placed in an aqueous medium. Because dibromothymoquinone is used in photosynthetic studies, some care must be taken to avoid complications which might arise from the above reactions; suitable precautions are discussed. 相似文献
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This paper reports the reactions of benzothiazolone with phosphites,tris-(dialkylamino)-phosphines and bis-(dialkylamino)-phen-ylphosphines.Benzothiazolone could not react with various phosphites,but it gave N-phosphorylated products when reacted with phosphorus amides.The restricted rotation about P桸 bond at room temperature was observed and discussed. 相似文献
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2-戊酮、芳香醛与芳香胺的Mannich反应邹君华,易林(西南师范大学化学系,重庆630715)关键词Mannich反应,芳香醛,芳香胺,2-戊酮80年代以前,一般认为芳香胺与甲醛及含有α-氢的酮不能发生Mannich反应 ̄[1,2,3],相应的Ma... 相似文献
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Abstract— The photochemical reactions of benzophenone and acetophenone with purine and pyrimidine derivatives in aqueous solutions have been investigated by flash photolysis and steady-state experiments. Upon excitation of these two ketones in aqueous solutions, two transient species are observed: molecules in their triplet state and ketyl radicals. The triplet state lifetimes are 65 μsec for benzophenone and 125 μsec for acetophenone. The ketyl radicals disappear by a second order reaction, controlled by diffusion. In the presence of pyrimidine derivatives, the triplet state is quenched and the ketyl radical concentration is decreased without any change in its kinetics of disappearance. Ketone molecules in their triplet state react with purine derivatives leading to an increase in the yield of ketyl radicals due to H-atom abstraction from the purines. Steady-state experiments show that benzophenone and acetophenone irradiated in aqueous solution at wavelengths longer than 290 nm undergo photochemical reactions. The rate of these photochemical reactions is increased in the presence of pyrimidine derivatives and even more in the presence of purine derivatives. Following energy transfer from the triplet state of benzophenone to diketopyrimidines, cyclobutane dimers are formed. The energy transfer rate decreases in the order orotic acid > thymine > uracil. Benzophenone molecules in their triplet state can also react chemically with pyrimidine derivatives to give addition photoproducts. All these results are discussed with respect to photosensitized reactions in nucleic acids involving ketones as sensitizers. 相似文献
19.
The reaction mechanism of the intramolecular cycloaddition ofN-3-butenyl nitrone has been investigated theoretically by using AM1 MOmethod and transition state theory.There are two parallel reactionsleading to two different regioisomers.The ratio of the rate constantsof these two reactions was calculated to be 124.1(at 383.75 K).Theobtained results can be used to explain the high regiospecificity ofthe reaction product. 相似文献