MECHANISM OF PHOTOSENSITIZATION BY PHEOPHORBIDE a STUDIED BY PHOTOHEMOLYSIS OF ERYTHROCYTES AND ELECTRON spIN RESONANCE SPECTROSCOPY

Abstract Phcophorbide a (PPa), a causal substance of food intoxication, when excited by exposure to light wavelengths of over 600 nm, caused the photohemolysis of goat erythrocytes in proportion to the incubation time of the cells. The addition of N-₃, an effective scavenger of ¹O₂, to the medium markedly inhibited the hemolysis of erythrocytes in a concentration-dependent manner, whereas the addition of superoxide dismutase (SOD) and catalase, inhibitors of O^-₂ and H₂O₂ generation, respectively, to the medium had little effect on it.
Methods for converting ¹O₂ to a nitroxide radical by 2,2,6,6-tetramethyl-4-piperidone (TMPD) and for trapping O^-₂ and OH by 5,5-dimethyl-l-pyrroline-A'-oxide (DMPO) were employed to observe directly these activated oxygens by electron spin resonance (ESR). The methods provided evidence that only ¹O₂, was produced by PPa, which was excited by light wavelengths of over 600 nm. Both the addition of N₃ to the solution and the removal of oxygen from the solution inhibited the generation of ¹O₂.
These results led us to conclude that ¹O₂ was mainly responsible for the hemolysis of erythrocytes by photoexcited PPa.     

PHYTOCHROME INTERMEDIATES IN VIVO–II. CHARACTERISATION OF INTERMEDIATES BY DIFFERENCE SPECTROPHOTOMETRY

Abstract— In epicotyl tissue of Pisum , irradiation of P_r at – 196°C forms a stable product P₆₉₈, whereas P_fr forms a stable product P₆₅₀. On warming P₆₉₈, dark transformation to P_r predominates. On warming P₆₅₀ to – 70°C an intermediate P₆₉₀ is formed which bleaches on further warming to –10°C. When tissue is cooled to –196°C during actinic irradiation, difference spectra for subsequent warming to –10°C indicate that P_r, P_fr and an intermediate P₇₁₀ are formed from weakly absorbing intermediates. Complete photoconversion of P_r to P_fr is not possible at temperatures below –5°C. As the temperature is reduced, the amount of P_fr produced from P_r decreases, while P₇₁₀ increases. P₇₁₀ can be photoconverted at –20°C and above, ultimately forming P_r, but in contrast to P_fr it is not photoconvertible at –196°C.     

HYDROGEN PEROXIDE INDUCED RESISTANCE TO BROAD-SPECTRUM NEAR-ULTRAVIOLET LIGHT(300–400 nm) INACTIVATION IN Escherichia coli

Abstract— Strains of Escherichia coli carrying the four possible combinations of the alleles nur, nur⁺, uvrAb, and uvrA ⁺ were either untreated or pretreated with a sublethal dose of H₂0₂ prior to inactivation with NUV radiation. Pretreated cells exhibited a greater resistance to NUV than did untreated cells. Pretreatment with H₂O₂ did not induce resistance to FUV radiation. The induction of resistance to NUV inactivation by H₂O₂ pretreatment apparently leads to protection against the damage caused by NUV radiation. Although pretreatment of cells with H₂0₂ leads to resistance of such cells to inactivation by H₂O₂ and NUV, survival of H₂O₂ treated bacteriophage PI cml clr100 is not enhanced when assayed on H₂O₂ pretreated E. coli host cells.     

Effect of promoter Ce on silver-molybdenum-phosphate catalysts for selective oxidation of propane to acrolein

A series of Me_nAg_0.3Mo_0.5P_0.3O_y (Me=Cu, Zn, Mn, W, Ce, Pr, Nd) and Ag_0.3Mo_0.5P_0.3O_x catalysts were prepared. The addition of Ce to Ag_0.3Mo_0.5P_0.3O_x catalysts improved the catalytic performance in selective oxidation of propane to acrolein, and Ce_0.1Ag_0.3Mo_0.5P_0.3O_x catalysts showed the highest acrolein selectivity (28.7%) and yield (4.4%). The physicochemical properties of Ag_0.3Mo_0.5P_0.3O_x and Ce_nAg_0.3Mo_0.5P_0.3O_x (n=0.1–0.5) catalysts have been comparatively characterized by BET, XRD, H₂-TPR, XPS, EPR and C₃H₈(C₃H₆)-TPD. Significant differences in physicochemical properties between Ag_0.3Mo_0.5P_0.3O_x and Ce doped Ag_0.3Mo_0.5P_0.3O_x catalysts have been observed, which is due to the formation of the redox cycle (Ce³⁺+Mo⁶⁺Ce⁴⁺+Mo⁵⁺) in the Ce_nAg_0.3Mo_0.5P_0.3O_y catalyst. Such effect modified the reducibility, the concentration of Mo⁵⁺, the activation of propane and the transformation of possible intermediate propene to acroelin, which in return greatly influenced the catalytic performance of Ce doped Ag_0.3Mo_0.5P_0.3O_x catalysts in selective oxidation of propane to acroelin. The proper addition of Ce to Ag_0.3Mo_0.5P_0.3O_x catalyst improved the acrolein selectivity and yield.     

Dnd点群的几点释疑

Point group in crystallography is one of the important subjects in structural chemistry.Some topics are very difficult to understand.To name a few, why does point group of D_2d belong to tetragonal? Why are D_4d and D_6d not included in 32 kinds of crystallographic point groups? The two questions are easy to answer if we understand the following topic:for the D_nd point group, when n is odd, it contains an I_n symmetry axis; when n is even, it contains an I_2n symmetry axis.In this work, graphic method and matrix method are adopted to clarify why the D_nd point group includes an S_2n axis, and thus give explanations that D_2d belongs to tetragonal as well as D_4d and D_6d are not included in 32 kinds of crystallographic point groups.     

MXene-碳黑/硫复合材料在锂硫电池一体式电极的研究

锂硫电池的实际能量密度不高和多硫化物（LiPSs）的穿梭效应等问题严重影响了该电池的实际应用。本文通过将二维的Ti₃C₂T_x Mxene纳米片与碳黑/硫（CB/S）材料进行混合,制备了Ti₃C₂T_x-CB/S正极材料并将其涂覆在商业隔膜（PP）上,最终获得了Ti₃C₂T_x-CB/S-PP一体式电极并用于锂硫电池。利用Ti₃C₂T_x纳米片对CB/S进行修饰,不仅能提高活性物质硫的导电性,还能对扩散的LiPSs进行物理阻挡和化学吸附。而一体式电极的设计有利于提高电池的能量密度。恒流充放电测试结果表明,Ti₃C₂T_x-CB/S-PP电极在0.1 C电流下的初始放电容量为1028.8 mAh·g^-1,高于不含Ti₃C₂T_x的CB/S-PP电极的896.8 mAh·g^-1。Ti₃C₂T_x-CB/S-PP电极还展示出了比基于传统铝箔集流体的Ti₃C₂T_x-CB/S-Al电极更好的循环稳定性,前者在0.5 C下400圈长循环测试中的每圈衰减率为0.072%,而后者则为更高的0.10%。本文利用Ti₃C₂T_x-CB/S构建一体式电极的策略为实现高性能和高能量密度的锂硫电池提供了新的研究方向。     

沉淀基离子选择电极对干扰离子的动力学响应研究

用活度阶梯法研究了AgI,AgBr,CuS,PbS和CdS电极对干扰离子的动力学响应.溶液中含一定浓度主要离子时上述电极对某些干扰离子响应非单一突跃型瞬时信号;溶液中不含主要离子时,除了AgBr电极响应Cl^-外,其它都响应单一瞬时信号.离子交换产物的溶解度越小,离子的水合焓差越小,瞬时信号峰高度越大.离子水合焓差对瞬时信号峰高度的影响说明,试液高速喷向电极表面时由于扩散层厚度很薄,电极对干扰离子响应瞬时信号的峰电位不决定于离子扩散速度,而决定于离子交换速度.除CuS电极外,根据其它电极非单一突跃型瞬时信号所测定的平衡电位选择性系数K_xy^e与相应化合物溶度积比值是一致的.     

PREPARATION AND PHOTOPHYSICAL STUDIES OF PORPHYRIN-C60 DYADS

Abstract Porphyrin-C₆₀ dyads in which the two chromophores are linked by a bicyclic bridge have been synthesized using the Diels-Alder reaction. The porphyin singlet lifetimes of both the zinc (Pz_n-C₆₀) and free base (P-C₆₀) dyads, determined by time-resolved fluorescence measurements, are ≦17 ps in toluene. This substantial quenching is due to singlet-singlet energy transfer to C₆₀ The lifetime of Pzn-¹C₆₀ is -5 ps in toluene, whereas the singlet lifetime of an appropriate C₆₀ model compound is 1.2 ns. This quenching is attributed to electron transfer to yield P_zn^bull;+-C₆₀^bull;-. In toluene, P-¹C₆₀ is unquenched; the lack of electron transfer is due to unfavorable thermodynamics. In this solvent, a transient state with an absorption maximum at 700 ran and a lifetime of-10 μs was detected using transient absorption methods. This state was quenched by oxygen, and is assigned to the C₆₀ triplet. In the more polar benzonitrile, P-¹C₆₀ underoes photoinduced electron transfer to give P^•+-C₆₀^bull;-. The electron transfer rate constant is −2 × 10¹¹ s⁻¹.     

CoAl2O4包覆LiNi1/3Co1/3Mn1/3O2的电化学性能

通过共沉淀法制得类球形锂离子电池正极材料LiNi_1/3Co_1/3Mn_1/3O₂,并用非水相共沉法对其进行CoAl₂O₄包覆得到LNCMO(x). 采用X射线衍射（XRD）、扫描电子显微术（SEM）和透射电子显微术（TEM）测试材料的结构和观察材料形貌. 结果表明,CoAl₂O₄在材料表面形成8 nm均匀包覆层,未改变主体材料的结构. 电化学性能测试表明,1%（by mass）CoAl₂O₄包覆量的LiNi1/3Co1/3Mn1/3O2材料（LNCMO(1)）高充电电压（3.0 ~ 4.6 V,150 mA·g^-1）100周期循环放电容量保持率为93.7%（无包覆LNCMO(0)保持率为74.4%）;55 °C高温100周期循环容量保持率为77%（无包覆LNCMO(0)保持率17%）. XRD和电感耦合等离子体原子发射光谱（ICP-AES）测试表明,CoAl₂O₄包覆的LNCMO(x)材料可有效地减缓材料中Mn离子在电解液的溶解,提高材料结构稳定性和热稳定性.     

Microwave assisted hydrothermal synthesis of tin niobates nanosheets with high cycle stability as lithium-ion battery anodes

SnNb₂O₆ and Sn₂Nb₂O₇ nanosheets were synthetized via microwave assisted hydrothermal method, and innovatively employed as anode materials for lithium-ion battery. Compared with Sn₂Nb₂O₇ and the previously reported pure Sn-based anode materials, the SnNb₂O₆ electrode exhibited outstanding cycling performance.     

Pd/Co3O4纳米颗粒负载于Al2O3纳米片高效催化甲烷燃烧

We report an efficient catalyst composed of ternary components prepared by inlaying Pd/Co₃O₄ nanoparticles in alkaline Al₂O₃ nanosheets for catalytic oxidation of methane. Pd/Co₃O₄ inlaid in alkaline Al₂O₃ exhibited a higher ability to break the C-H bond of methane than Pd/Co₃O₄ supported on SiO₂, ZrO₂, CeO₂, and acidic or neutral Al₂O₃. Our results show more oxygen vacancies and higher amounts of surface adsorbed oxygen on the surface of Pd/Co₃O₄/alkaline Al₂O₃ than on other catalysts, which is responsible for methane activation and conversion. Further, the Pd/Co₃O₄/alkaline Al₂O₃ catalyst can almost restore to its initial value in the absence of water when 5% (volume fraction) vapor water was cut off, although a decrease in activity occurred when water vapor was introduced to the reaction system. Even under a condition similar to the exhaust of a lean-burn natural gas engine, the catalytic performance of the Pd/Co₃O₄/alkaline Al₂O₃ catalyst is excellent, that is, methane could be completely converted when the sample temperature in the reaction atmosphere was ramped to 400℃.     

EFFECT OF SODIUM AZIDE ON PHOTODYNAMIC INDUCTION OF GENETIC CHANGES IN YEAST

Abstract— In view of the increasing attention to ¹O₂ (¹Δ_g) participation in the photodynamic action, different types of genetic changes in Saccharomyces cerevisiae by acridine orange sensitization were compared with respect to the response to N₃^-, a well known quencher of ¹O₂. The induction of mitotic crossing over with respect to ade 2 locus and mitotic gene conversion at trp 5 locus were suppressed by the addition of N₃^- suggesting the involvement of ¹O₂ as a major intermediate. However, the induction of reverse mutation at ilv 1 was only slightly suppressed. These results may indicate that there are two types of photodynamic DNA damage; one is produced via ¹O₂ and the other via non-¹O₂ reaction pathway which lead to mitotic gene conversion and mitotic crossing over, and to mutation, respectively.     

Relationship between the molybdenum phases and the conversion of n-butane over Mo/HZSM-5

The conversion of n-C₄H₁₀ was undertaken on MoO₃/HZSM-5 catalyst at 773–973 K and the phases of molybdenum species were detected by XRD. The XRD results show that bulk MoO₃ on HZSM-5 can be readily reduced by n-C₄H₁₀ to MoO₂ at 773 K and MoO₂ can be gradually carburized to molybdenum carbide above 813 K. The molybdenum carbide formed from the carburization of MoO₂ with n-C₄H₁₀ below 893 K is -MoC_1−x with fcc-structure, while hcp-molybdenum carbide formed above 933 K. During the evolution of MoO₃ to MoO₂ (>773 K) or the carburization of MoO₂ to molybdenum carbide (>813 K), deep oxidation, cracking and coke deposition are serious, in particular at higher reaction temperatures, these lead to the poor selectivity to aromatics. Aromatization of n-C₄H₁₀ can proceed catalytically on both Mo₂C/HZSM-5 and MoO₂/HZSM-5, the distribution of the products for the two catalysts is similar below 813 K, but the activity for Mo₂C/HZSM-5 is much higher than that for MoO₂/HZSM-5.     

EVIDENCE AGAINST THE PRODUCTION OF SUPEROXIDE BY PHOTOIRRADIATION OF HEMATOPORPHYRIN DERIVATIVE

Abstract Experiments were performed to ascertain whether superoxide anion (O₂⁻) was produced by the photodynamic activation of hematoporphyrin derivative (HPD). Three different systems were utilized to detect formation of O₂⁻, oxidation of epinephrine to adrenochrome, reduction of cytochrome c and reduction of nitro blue tetrazolium (NBT). The effects on these detectors under identical conditions for HPD + h ν were compared to those obtained with two O₂⁻ generating systems, riboflavin + by and xanthine-xanthine oxidase, and to a singlet oxygen generating system, photoradiation of methylene blue. The results indicated that HPD + hv differed from the two O₂⁻ generating systems in failing to reduce cytochrome c or NET, and that HPD + h ν was similar to the behavior of methylene blue + h ν . In addition, HPD + h ν but not the O₂⁻ generating systems could inhibit mitochondrial cytochrome c oxidase activity. We conclude that the photodynamic activation of HPD does not produce O₂⁻ as a major oxygen radical and that the effects of HPD + h ν on mitochondrial cytochrome c oxidase are not caused by O₂⁻.     

PHOTOREACTIONS OF THE CHROMOPHORE CATIONS OF DENATURED SPECIES OF C-PHYCOCYANIN AND ALLOPHYCOCYANIN

Abstract— C-phycocyanin dissolved in buffer containing 75% ethylene glycol (vol/vol) shows photorevers-ible reactions which are ascribed to the interconversion by light of two species: PC_r, PC_g. After denaturation with formic acid, the chromophore cation of PC_g, can be irreversibly photoconverted to that of PC_r A conversion of the chromophore of denatured PC_g, to that of denatured PC_r also occurs after adjustment of the pH to about 8. Under the same conditions the chromophore of allophycocyanin shows similar reactions. Moreover, the reactions of the chromophores of the denatured species of these phycobiliproteins are similar to the reactions of the chromophore of the denatured species P_fr of photochrome.     

热退火气氛对溶液法制备的Sb2S3薄膜组成、结构及光伏性能的影响

采用化学浴(CBD)法在TiO₂薄膜表面制备结晶性Sb₂S₃膜层, 获得了TiO₂/Sb₂S₃平板异质结, 并结合聚[2,6-{4,4-双-(2-乙基己基)-4H-环戊并[2,1-b;3,4-b']-二噻吩}-交替-4,7-(2,1,3-苯并噻二唑)](PCPDTBT)空穴传输层和MoO₃电极界面修饰层, 制备了FTO/TiO₂/Sb₂S₃/PCPDTBT/MoO₃/Au平板结构太阳能电池, 研究了CBD方法中热退火气氛对Sb₂S₃薄膜的组成、 结构及光伏性能的影响. 结果表明, 在N₂气氛下退火时, 所得的Sb₂S₃膜层不致密且含有Sb₂O₃杂相, 电池效率仅为0.90%; 而在N₂-S气氛下退火时, 硫会与杂相Sb₂O₃发生反应生成Sb₂S₃, 进而得到纯净、 致密、 平整的结晶Sb₂S₃膜层. 在平板结构太阳能电池中, 光生空穴对电池光电流的产生有明显的贡献; 随着Sb₂O₃杂相的消除, Sb₂S₃薄膜中载流子的复合减少且传输速率增大, 使太阳能电池器件中电子与空穴的收集效率和短路电流显著提高, 电池效率提高了1.34倍, 达到2.04%.     

Ultraviolet Radiation Effects on a Microscopic Green Alga and the Protective Effects of Natural Dissolved Organic Matter

Abstract— The population and photosynthetic responses of a microscopic green alga ( Selenastrum capricornutum ) to realistic levels of UV radiation (UVA and UVB) were assessed in natural lake waters of different dissolved organic carbon (DOC) concentration. Specific growth rates and photosynthetic competence (as reflected by F_v/F_m [measure of maximal quantum efficiency of photosystem II] and t_1/2 [estimate of electrons transported to the plastoquinone pool] measured by in vivo variable chlorophyll a fluorescence) were compared between two exposure levels of UVR and two concentrations of DOC (2.5 mg C L⁻¹ 7.7 mg C L⁻¹). Exposure periods of 6–9 days (five to nine generations) were used. Exposure to UVA primarily affected the efficiency of photosystem II, as evidenced by significant decreases of F_v/F_m but not growth rates or t_1/2 Exposure to UVB, in the presence of UVA, did not cause significant additional decreases of F_v/F_m but did diminish growth rates. In the low DOC water, t_1/2 was also diminished, suggesting different proximate sites of action from those for UVA. The high DOC water decreased the effective exposure to both UVA and UVB and diminished the negative impact of UV radiation on the cells, but the apparent protection was not explicable solely by the shading action of the DOC. Control values for F_v/F_m, growth rates and t_1/2 were all lower in the high DOC water, suggesting a negative side effect to the apparent protective action of the DOC against UVB.     

Cell surface acid-base properties of Escherichia coli and Bacillus brevis and variation as a function of growth phase, nitrogen source and C:N ratio

Potentiometric titration has been conducted to systematically examine the acid–base properties of the cell surfaces of Escherichia coli K-12 and Bacillus brevis as a function of growth phase, nitrogen source (ammonium or nitrate), and carbon to nitrogen (C:N) ratio of the growth substrate. The two bacterial species revealed four distinct proton binding sites, with pK_a values in the range of 3.08–4.05 (pK₁), 4.62–5.57 (pK₂), 6.47–7.30 (pK₃), and 9.68–10.89 (pK₄) corresponding to phosphoric/carboxylic, carboxylic, phosphoric, and hydroxyl/amine groups, respectively. Two general observations in the data are that for B. brevis the first site concentration (N₁), corresponding to phosphoric/carboxylic groups (pK₁), varied as a function of nitrogen source, while for E. coli the fourth site concentration (N₄), corresponding to hydroxyl/amine groups (pK₄), varied as a function of C:N ratio. Correspondingly, it was found that N₁ was the highest of the four site concentrations for B. brevis and N₄ was the highest for E. coli. The concentrations of the remaining sites showed little variation. Finally, comparison between the titration data and a number of cell surface compositional studies in the literature indicates one distinct difference between the two bacteria is that pK₄ of the Gram-negative E. coli can be attributed to hydroxyl groups while that of the Gram-positive B. brevis can be attributed to amine groups.     

REACTIVITY OF ACRIDINE DYE TRIPLET STATES IN ELECTRON TRANSFER REACTIONS

Abstract—Rate constants, k _q , for the reaction of cationic and neutral acridine orange and 10-methylacridine orange triplet states (³AOH ⁺, ³AO, ³MAO⁺) with a series of electron donors have been measured. Two different protolytic forms of the semireduced dye radical are produced by acridine orange triplet quenching at various pH^M values in methanolic solution.
It is found that k ₄ decreases with increasing oxidation potential of the reducing agent for all triplet states in a manner which is expected for electron transfer reactions. The different reactivities of the cationic and neutral triplet forms can, therefore, be attributed to the difference in reduction potentials of these species. The difference in reduction potentials is related to the p K ^M values of triplet state, p K _T^M , and semireduced dye radical, p K ^M_S , by thermodynamic consideration. p K _T^M (³AOH⁺/³AO) is determined to be 11.2. From thisp K _S^M (AOH./AO;) is estimated to be 17–18. This is in striking contrast to the protolytic equilibrium of the semireduced dye radicals found to be pK^F= 4.1. We conclude that the last value represents the second protonation equilibrium (AOH⁺₂./AOH). This conclusion is confirmed by spectroscopic data.     

THE REACTION OF METHYLENE WITH HYDROGEN

Abstract— An investigation has been made of the reaction between methylene, formed by the photolysis of ketene, and hydrogen. Ethane, ethylene and methane are the major hydrocarbon products, and it has been shown that the formation of these products may be adequately described by the sequence of processes
CH₂CO + hv → CH₂+ CO (1)
CH₂+ H₂→ CH₃+H (2)
2CH₃→ C₂H₆ (3)
CH₃+ H₂+ CH₄+ H (4)
CH₂+ CH₂CO → C₂H₄+ CO (7)
In particular, the relative rates of ethane and methane formation are consistent with the known rate constants for reactions (3) and (4), and it is not therefore necessary to postulate the participation of an 'insertion' process
CH₂+ H₂→ CH₄ (6) to account for the formation of methane.
Decrease of the energy possessed by the methylene, either by increase of the wavelength of ketene photolysis, or by increase of gas pressure, is shown to result in an increase in the reactivity of the methylene towards ketene relative to its reactivity towards hydrogen (i.e. the ratio k₂/k₂ increases).