单重态氧化学 V: 二烷基取代酚光敏氧化反应的研究

本文研究了2,6-二甲基酚、2,4-二甲基酚及3,4-二甲基酚的光敏氧化反应, 应用竹红菌甲素作敏化剂匹配高压钠灯首次提供了二烷基取代酚同单重态氧发生化学反应的例证, 并测定了它们对单重态氧的反应速度常数, 其反应活性顺序为:BHT>2,4-DMP>3,4-DMP>DBP>2,6-DMP.二烷基取代酚同单重态氧可能通过1,4-环加成反应的机理, 再经重排生成最终产物.     

单重态氧化物 IV: 6-取代-1,4-环辛二烯的光敏氧化反应

6-取代-1,4-环辛二烯与单重态氧立体有选择地氧化成顺式5,8-和反式5,6-二取代-1,3-环辛二烯的含氧衍生物. 依据产物的分子结构推知, 6-取代-1,4-环辛二烯发生“ene"反应时的优势构象不同于环辛烷, 而是具有角张力的扭曲构象(1), 这为研究环烯的分子构象提供了一种实验方法.用Monroe法测定了6-取代-1,4-环辛二烯对单重态氧反应的β值. 其反应活性顺序为:3>1>4>1, 5-环辛二烯>2>5. 表明推电子取代基增加了同单重态氧反应的能力, 而吸电子取代基则降低了同单重态氧的反应能力, 但是不论取代基性质如何, 都不能改变“ene"反应的本质.     

Spreading and recoil of a surfactant-containing water drop on glass-supported alcohol films

In this paper we report the experimental observation of spreading and recoil of surfactant-containing water drops on various alcohol films supported on glass slides. The time evolution of spreading and recoil behavior was recorded by placing a web camera above the drop. We observed that the drop spread the fastest on CH3OH, followed by C2H5OH, and the slowest on i-PrOH. On the other hand, the recoil behavior was just the opposite. The drop recoiled the slowest on CH3OH and fastest on i-PrOH, while it recoiled in an intermediate time on C2H5OH. In addition, concentration of surfactant in the drop played a prominent role in the spreading and recoil time of the drop, with higher surfactant concentration making the drop spread and recoil faster. The time evolution of spreading velocity of the drop on different alcohol films at various surfactant concentrations occurred with a Gaussian distribution and the peak velocity was reached earliest on CH3OH followed by C2H5OH, while on i-PrOH it took the longest time. The recoil behavior was similar. The variation of velocity as a function of radius exhibited oscillatory behavior, indicating the existence of an interfacial phenomenon. We also report the observation that spreading of the drop occurred without observable fingering instability. Further, we observed by Fourier transform infrared (FTIR) spectroscopic measurements that the drop had mixed with the alcohol films as it spread. Miscibility of the alcohol in the film with the drop, alcohol evaporation cooling-induced temperature gradient, and Marangoni effect probably play important roles in the spreading and recoil behavior of the drop.     

单重态氧化学VII. 迷迭香中主要抗氧化成分对单重态氧的猝灭作用

本文研究了迷迭香酚和鼠尾草酚对单重态氧的猝灭作用。实验证明迷迭香酚和鼠尾草酚在甲醇中猝灭单重态氧的总速率常数K~A分别为2.51×10^7和7.19×10^6mol^1.dm^-3.s^-1, 其中化学猝灭的速率常数k~r分别为1.27×10^7和9.82×10^5mol.dm^-3.s^-1, 相应的半猝灭浓度β值为4.6×10^-3和1.6×10^-2mol.dm^-3。这是一类有实用价值的高效抗氧化剂。     

Singlet oxygen in the environmental sciences

This review of the part played by the singlet states of molecular oxygen in the environment deals with atmospheric aspects. There are five bound excited states of molecular oxygen that correlate with two ground state, ³P, oxygen atoms. Of these, three are singlets, although the other two states (triplets) are closely associated with singlet oxygen processes, especially in the mesosphere. A weakly bound quintet state has been invoked, as well, in explaining some aspects of the physical chemistry of the singlet species. Of the three singlet states, the a¹Δ_g is the most familiar. It has a low excitation energy, a long radiative lifetime, and is rather resistant to collisional deactivation in the gas phase. As a consequence, its chemistry has been susceptible to detailed study in the laboratory. These investigations, coupled with estimates of production rates, suggest that O₂(a¹Δ_g) is probably not important in initiating much chemical change in the lower atmosphere, at least in the gas phase; excited molecules dissolved in water droplets may promote chemical change under special circumstances. In the stratosphere and mesosphere, each of the bound excited states gives rise to characteristic emission features of the airglow, both by day and by night. The observational data, obtained from the ground, and from balloons, high-flying aircraft, rockets and satellites is surveyed as a background to examining the chemical and photochemical mechanisms by which the different states become excited. These mechanisms clearly differ by day and by night, and they also depend on the altitude from which the emission comes. The most intense feature of the oxygen dayglow, the Infrared Atmospheric Band, comes from O₂(a¹Δ_g) that is produced in the photolysis of ozone. Because dayglow measurements are sometimes used to derive ozone concentrations and altitude profiles in the atmosphere, the efficiency of production of the species in the photolysis of ozone is examined critically, and some unexpected laboratory findings are reported. The b¹Σ⁺ _g state of oxygen is excited during the day largely by resonance scattering, although some is also populated by energy transfer from O(¹D) to O₂. At night, recombination of O(³P) atoms is the most likely source of excitation of all the states of oxygen. Laboratory experiments that bear on these processes are reviewed, and theoretical estimates of the partitioning of recombination events between the different states are presented. Direct recombination into the a¹Δ_g and b¹Σ⁺ _g states is unlikely to be efficient enough to produce the observed concentrations of these species, and some indirect process is thus implicated. Laser excitation experiments show that quenching of the three higher excited (ungerade) states of oxygen by O₂ and, especially, N₂, can generate O₂(b¹Σ⁺ _g) with high efficiency; similar experiments demonstrate explicitly that the quenching of O₂(b¹Σ⁺ _g) by the atmospheric gases yields O₂(a¹Δ_g). A consistent excitation scheme for the nightglow emissions is presented; this scheme also pays attention to the “auroral green” line produced by the ¹S state of atomic oxygen, the intensities of which in the atmospheres of Earth and Venus provide some clues about the excitation of the molecular states. Finally, the laboratory studies are shown to indicate that the formation of excited molecular oxygen from vibrationally rich hydroxyl (OH) radicals is unlikely to be of major importance in the atmosphere.     

Singlet oxygen reaction—II: Alkylthiosubstituted ethylene

The reaction of singlet oxygen with tetrakis(ethylthio)ethylene has been shown to afford diethylthiooxalate and diethyl disulfide. The expected diethylthiocarbonate was also obtained as a minor product. A similar reaction with bis(ethylthio)ethylene gave ethylthioglyoxalate together with diethyl disulfide. Formation of diethylthioacetaldehyde was also observed, and is suggested to proceed via the intermediary 1,2-dioxetane or perepoxide followed by preferential migration of the ethyltilio group. On the other hand, phenylthioethylene is oxidized with singlet oxygen to give a thiol ester together with disulfide. This suggests that the formation of disulfide probably occurs via a radical pathway. The photooxygenation of disulfide in alcohol was also studied.     

The three-dimensional structure of water confined in nanoporous vycor glass

Neutron diffraction data, in conjunction with isotopic substitution of deuterium (D) for hydrogen (H), have been analyzed to determine the three-dimensional structure of water confined in vycor, an archetypal hydrophilic porous silica glass containing channels or pores of approximately 40 A diameter. The data have been incorporated into a Monte Carlo computer simulation of the confined water system, and the site-site potentials have been iteratively refined in order to produce a model ensemble which is consistent with both the neutron diffraction data and two possible geometries of the vycor pores (cylindrical and spherical). This approach has allowed us to investigate in detail the contributions to the experimentally accessible partial pair correlation functions, and ascertain whether particular features arise from interactions of the water molecules with the substrate surface, or from purely geometrical confinement effects. We observe a significant decrease in the first shell water oxygen-oxygen co-ordination number, and a decrease in the number of hydrogen bonds per water molecule from approximately 3.6 in bulk water to approximately 2.2 in confinement. In addition, we observe a significant shift inward of the second peak in the water oxygen-water oxygen coordination shell. Overall, we therefore find that the structure of the water in vycor is strongly perturbed relative to the bulk.     

Temperature-controlled changeable oxygenation selectivity by singlet oxygen with a polymeric photosensitizer

A polymeric photosensitizer, poly(NIPAM-co-RB), consisting of N-isopropylacrylamide and rose bengal units, demonstrates a temperature-controlled changeable oxygenation selectivity by singlet oxygen in water.     

Positronium chemistry in porous materials

Porous materials have fascinated positron and positronium chemists for over decades. In the early 1970s it was already known that ortho-positronium (o-Ps) exhibits characteristic long lifetimes in silica gels, porous glass and zeolites. Since then, our understanding of Ps formation, diffusion and annihilation has been drastically deepened. Ps is now well recognized as a powerful porosimetric and chemical probe to study the average pore size, pore size distribution, pore connectivity and surface properties of various porous materials including thin films. In this paper, developments of Ps chemistry in porous materials undertaken in the past some 40 yr are surveyed and problems to be addressed in future are briefly discussed.     

Singlet oxygen luminescence as a probe of the stilbene triplet surface

The quenching of stilbene triplet by oxygen in benzene produces singlet oxygen, O₂(¹Δ_g), with an efficiency of 18±5%. This value, together with the corresponding rate constant, shows that the O₂(¹Δ_g) produced cannot be the consequence of exclusive oxygen quenching of a low concentration of planar trans-triplet in rapid equilibrium with the perpendicular form.     

Singlet oxygen formation in monomeric and aggregated porphyrin c

The absorption and fluorescence spectra of monomeric and aggregated species present in aqueous solutions of porphyrin c have been resolved by steady-state and time-resolved spectroscopy. The dependence of the singlet oxygen formation yield (phi delta) on excitation wavelength has also been determined. In the Q-band spectral region, the aggregate absorption and emission spectra are shifted to longer wavelengths with respect to the monomer spectrum with phi delta (monomer) = 0.59 and phi delta (aggregate) = 0.33. The relevance of these findings to the optimization of irradiation conditions in tumour phototherapy using porphyrin c are discussed.     

Singlet oxygen in the heterogeneous catalytic oxidation of benzene

The partial oxidation of benzene on vanadium and molybdenum oxides and the participation of singlet oxygen in this reaction were studied. A correlation between the activity of the catalysts in the partial oxidation of benzene and their ability to generate singlet oxygen was observed. The character of the initiation of oxidative benzene transformations under the action of molecular singlet oxygen was analyzed.     

Singlet molecular oxygen quenching ability of carotenoids in a reverse-micelle membrane mimetic system

The influence of the medium heterogeneity upon the bimolecular rate constants for the physical quenching, kq, and chemical quenching, kr, of singlet molecular oxygen O2(1deltag) by seven natural and three synthetic carotenoids (CAR) with different substituent patterns was studied in a reverse micelle system of sodium bis(2-ethylhexyl)sulfosuccinate, hexane and water. Because O2(1deltag) was generated inside the water pools of the reverse micelles by photosensitization of the water-soluble dye rose bengal and the CAR are mainly located in the external hexane pseudophase, the quenching process was interpreted using a pseudophase model for the partition of 02(1deltag) between the water pools and the organic pseudophases. The kq values were mainly dependent on the extent of the double-bond conjugation of the CAR, as demonstrated by a good empirical relationship between log(k(q)) and the energy E(S) of the longest wavelength transition pi-->pi* of the CAR. In contrast, the kr values were almost independent of the extent of the double-bond-conjugated system and about four orders of magnitude lower than kq. However, in all cases, CAR photobleaching was observed with the formation of various oxidation products, depending on the photosensitization time. Chromatographic and spectroscopic product analysis for the reaction products of beta-carotene with O2(1deltag) indicated the formation of the beta-carotene-5,8-endoperoxide as the primary oxidation product.     

单重态氧化学 VI: 胶束中竹红菌甲素诱导的二苯基异苯并呋喃光敏氧化反应动力学

本文研究了增溶于胶束内部的HA诱导的DPBF光敏氧化动力学。测定了DPBF在不同胶束中光敏氧化总速率常数, 分别为5.12×10^9(SDS), 2.31×10^9(Triton X-100)和6.21×10^9L/mol.s(TDPB)。实验证明胶束可有效猝灭单重态氧却不猝灭HA的激发三重态, 从而导致DPBF光敏氧化双分子反应可按假一级动力学规律处理, 可求出表观速率常数为1.52×10^-^3s^-^1(SDS)或1.54×10^-^3s^-^1(Triton X-100), 相应的半寿命为7.5min, 这些结果为HA在水溶液中的光动态行为的研究提供了依据。     

Singlet oxygen toxicity is cell line-dependent: a study of lipid peroxidation in nine leukemia cell lines

Singlet oxygen (1O2) can be quenched by water, lipids, proteins, nucleic acids and other small molecules. Polyunsaturated fatty acids (PUFA) of cells principally quench 1O2 by chemical mechanisms, producing lipid hydroperoxides, while proteins physically and chemically quench 1O2. Because cell lines can have different PUFA and protein levels, we hypothesized that 1O2 toxicity will vary between cell lines. We used Photofrin as a source of 1O2. Exposure of nine different leukemia cell lines (CEM, HEL, HL-60, K-562, KG-1, L1210, Molt-4, THP-1 and U-937) to Photofrin and light results in changes in membrane permeability (trypan blue) that vary with cell line. The greater the lipid content of the cell line, the less susceptible they are to membrane damage. When the cell media was supplemented with docosahexaenoic acid (DHA, 22:6), the overall unsaturation of cellular lipids increased. Photofrin and light resulted in increased radical formation in these supplemented cells compared to controls; however, there was no difference in membrane permeability between DHA-supplemented and control cells. Lipid-derived radical formation (electron paramagnetic resonance spin trapping) was cell line dependent; but no correlation between lipid content of cells and radical formation was found. However, we found that the greater the protein content of cells the more they were protected against membrane damage induced by Photofrin photosensitization. This suggests that cellular proteins are a key target for 1O2-mediated toxicity. A remarkable observation is that cell size correlates inversely with ability of cells to cope with a given flux of 1O2.     

Singlet oxygen addition to homoallylic substrates in solution and microemulsion: novel secondary reactions

The photooxygenation of three homoallylic substrates, the γ,δ-unsaturated ketone 1a, nitrile 2a, and the γ,δ-unsaturated ester 3a was investigated in homogeneous solution and in microemulsion (for 1a). Two secondary reaction pathways were detected for the allylic hydroperoxides of type b and c, respectively. The cyclization reactions of 1b and 2b to the 1,2-dioxanes 1d and 2d followed well-known reaction patterns, whereas the base-catalyzed epoxide (1e-3e) formation from the tertiary allylic hydroperoxides 1c-3c is a unprecedented reaction type.     

Singlet oxygen generation in PUVA therapy studied using electronic structure calculations

The ability of furocoumarins to participate in the PUVA (Psoralen + UV-A) therapy against skin disorders and some types of cancer, is analyzed on quantum chemical grounds. The efficiency of the process relies on its capability to populate its lowest triplet excited state, and then either form adducts with thymine which interfere DNA replication or transfer its energy, generating singlet molecular oxygen damaging the cell membrane in photoactivated tissues. By determining the spin–orbit couplings, shown to be the key property, in the intersystem crossing yielding the triplet state of the furocoumarin, the electronic couplings in the triplet–triplet energy transfer process producing the singlet oxygen, and the reaction rates and lifetimes, the efficiency in the phototherapeutic action of the furocoumarin family is predicted as: khellin < 5-methoxypsoralen (5-MOP) < 8-methoxypsoralen (8-MOP) < psoralen < 4,5′,8-trimethylpsoralen (TMP) < 3-carbethoxypsoralen (3-CPS), the latter being the most efficient photosensitizer and singlet oxygen generator.