光催化乙醇水溶液脱氢的EPR研究

本文报道,在含有Pt/CdS的乙醇水溶液中分别加入不同俘获剂: POBN (α-(4-pyridyl N-oxide)-N-tert-butyl nitrone), MV²⁺(methylviologen), NB(nitrosobenzene)或 TCNQ(7,7,8,8-tetracyano-p-quinodimethane),在可见光(λ≥450nm)照射下,光催化产氢及其光催化脱氢机理的EPR(电子顺磁共振)研究。结果表明,在Pt/CdS-CH₃CH₂OH/H₂O体系中进行可见光反应3小时,其产氢量相当高(0.0136 mmol);在加入POBN的体系中,由于其俘获了CH₃HOH自由基而使产氢量降低了三分之二,这说明由CH₃HOH经H⁺产氢比水分解经H⁺产氢更容易。在加入TCNQ或NB的体系中,由于其俘获了电子(e^-)或自由基,因而都未检测到氢气;这说明在可见光照射下,Pt/CdS催化乙醇水溶液脱氢的机理是经由: H⁺+e^-→Ñ→1/2H₂.     

Zn在KOH水溶液中的阳极溶解和钝化机理

本文用旋转圆盘电极、稳态极化曲线、交流阻抗及恒电流充电曲线等方法研究了Zn在常温(30℃)和低温(-20℃)的KOH水溶液中阳极溶解和钝化过程的规律。从而提出其反应机理,并用最优化程序在TRS-80微型计算机上计算了反应机理中基元反应的速度和动力学参数的最佳值。由动力学参数计算的φ～i关系定量地符合从阳极溶解至钝化前整条极化曲线实验数据。旋转圆盘电极的转速效应、交流阻抗值以及恒电流充电电量值也都与提出的反应机理相符合。     

甲醇、乙醇、异丁醇对含水卵磷脂液晶结构影响的SAXS研究

本文报导采用小角X射线散射方法(SAXS)对甲醇、乙醇和异丁醇分别与含水卵磷脂所形成的液晶相结构的研究. 它们与水-卵磷脂形成的液品结构有较大区别. 在水-卵磷脂体系中, 随着含水量增加, 双分子层层间距增大. 但当醇类加入水-卵磷脂体系中, 随着醇类含量增加, 层间距变小, 随着醇类中碳链的增长, 支链的引入, 层间距变小趋势强化。     

THE PHOTOOXIDATION OF DIETHYLHYDROXYLAMINE BY ROSE BENGAL IN MICELLAR AND NONMICELLAR AQUEOUS SOLUTIONS

The photooxidation of N,N -diethylhydroxylamine (DEHA) by Rose Bengal (RB) has been investigated in micellar and nonmicellar aqueous solutions. We measured the quantum yield of oxygen consumption forming H₂O₂ and monitored two intermediates, the superoxide and diethylnitroxide radicals. When the pH was vaned, the quantum yield of oxidation remained constant for 6 < pH < 10.5, decreased in acidic pH, and increased considerably in NaOH solution; these changes could be attributed to the protonation and dissociation processes of the >N-OH moiety of DEHA. The formation of diethylnitroxide radical was enhanced by superoxide dismutase or strong alkaline solution. Around neutral pH, the oxidation proceeded mainly via electron transfer from DEHA to the RB triplet ( k _q = 10⁷ M ^-1 s^-1) with little ¹O₂ participation ( k_q < 10⁵ M ^-1 s^-1). However, when RB was incorporated into micelles in alkaline solution, the contribution of the singlet oxygen pathway increased at the expense of electron transfer, which was inhibited by the less polar micellar environment. Dark autoxidation of DEHA was accelerated by heavy metal impurities and increased very strongly in NaOH solution.     

PHOTOOXYGENATION OF METHYL LINOLEATE SENSITIZED BY PORPHYRINS AND DYES IN ACETONITRILE SOLUTION AND AQUEOUS EMULSION SYSTEMS

Photooxygenation reaction of an unsaturated fatty acid ester, methyl linoleate (methyl 9- cis. 12- cis -octadecadienoate, ML-H), sensitized by porphyrins and several types of dyes has been studied in aqueous emulsion and acetonitrile solution under air at 40°C. The oxygen (O₂) uptake proceeded slowly in the absence of sensitizers upon irradiation of an aqueous emulsion and an acetonitrile solution of ML-H (20 m M ) at ℷ_ex > 290 nm (11.4 and 6.1 μmol h^-1, respectively). The rate of O₂ uptake was enhanced by a catalytic amount (0.1 m M ) of porphyrins and dyes; hematoporphyrin (HP), zinc tetrakis(N-methyl-4-pyridiniumyi)porphyrin (ZnTMPyP), methylene blue (MB), rose bengal (RB), acridine orange (AO), and acriflavine (AF). In both systems, the sensitized photooxidation of ML-H by O₂ proceeded equimolarly to produce isomeric mixture of C9 and C13 hydroperoxides having the trans,cis and trans,trans conjugated diene configurations, independent of the types of the sensitizers used. The yield ratio of trans,trans/ trans,cis products in the MB-sensitized photooxygenation in acetonitrile and aqueous emulsion were almost equal (0.32 and 0.35. respectively). The sensitizing activity of the sensitizers, as measured by the quantum yield of O₂ uptake, increased in the order: MB (≃ 0) < ZnTMPyP < RB < HP < AF < AO in the aqueous emulsion and AO < AF < HP < RB = MB in the acetonitrile solution. The order in homogeneous acetonitrile solution was interpreted by the sensitizing ability of the dyes to produce singlet oxygen, while that in heterogeneous aqueous emulsion was correlated to the lipophilicity of dyes as well as the singlet-oxygen-producing ability.     

ADSORPTION PROPERTIES OF THE STEARIC ACID-OCTADECANE PARTICLES IN AQUEOUS SOLUTIONS

The adsorption properties and surface charge creation for the stearic acid and octadecane/aqueous electrolyte solutions are considered. The hairy structure of surface charge for these systems was confirmed on the basis of potentiometric titration, ion adsorption and electrophoretic measurement data. For the system with stearic acid the reaction of ionization and complexation of carboxyl groups of stearic acid molecules from subsurface layer are responsible for the creation of surface charge and adsorption properties. The surface charge at octadecane particle is probably the results in adsorption and orientation of water molecules at the interface.     

ON THE PHOTOIONIZATION ENERGY THRESHOLD OF TRYPTOPHAN IN AQUEOUS SOLUTIONS

Abstract— To investigate the existence and energy position of a photoionization threshold. tryptophan (Trp) has been photoionized in desecrated neutral aqueous or alcoholic solution under monochromatic light of variable frequency, in presence of N₂O to scavenge the photoelectron.
Present findings and some literature data converge to show the existence of a threshold for the one photon ionization process. This threshold is located at 4.5 ± 0.1 eV and 4.85 ± 0.1 cV for Trp in aqueous and ethanol solutions. respectively, which corresponds to a lowering with respect to the gas phase ionization potential of 3.4 and 3.0 eV.
The photoionization quantum yields for Trp is found about 4 times greater at 250 nm than at Λ_cx= 265 nm, where φe^-_4M=0.080±0.025. In such spectral range. at most one photoelectron out of 4–5 escaping geminate recombination would lead to Trp photodegradation in acrated solutions.
These results also point out that the neutral radical Trp. which has been previously observed for Λ_cx > 275 nm, i.e. below the ionization threshold energy—would not necessarily derive from Trp ⁺ deprotonation or cation-electron dissociative recombination. Similarly, the opening of the indole ring with formylkynurenine (FK) formation which is observed under aerobic conditions and Λ_cx >, 280 nm would not imply an electron attachment on O₂ but reactions such as Trp +³O₂ or Trp*+³O₂ or else
     

A WATER-SOLUBLE RUBRENE DERIVATIVE: SYNTHESIS, PROPERTIES AND TRAPPING OF 1O2 IN AQUEOUS SOLUTION

Abstract A rubrene derivative has been synthesized as a new trap for singlet oxygen in aqueous solution. Photooxygenation and evolution of the endoperoxide under various conditions have been investigated. This trap may be used either as a colorimetric test or as a specific one by isolation of the endoperoxide.     

INTERSYSTEM CROSSING AND DIMERIZATION IN AQUEOUS SOLUTIONS OF URACIL AND OROTIC ACID

Un analisis cinético de la fotoquímica en el u.v. de uracilo y ácido orótico muestra que el hidrato se forma a partir del estado singulete, mientras que el dímero lo hace a partir del estado triplete. El rendimiento cuantico de la formación del hidrato es independiente de la longitud de onda de irradiación, mientras que el rendimiento cuántico de la formación de triplete aumenta a longitudes de onda menores. Se presenta además una explicación para el aumento de “intersystem crossing” a altos niveles de excitación basada en la presen-cia de tautomeros.     

THE PHOTOSENSITIZED FORMATION AND REACTION OF SINGLET OXYGEN, O2*(1Δ), IN AQUEOUS MICELLAR SYSTEMS

Abstract— Oxygenated aqueous solutions of methylene blue containing dispersions of sodium dodecyl sulphate micelles with solubilised diphenyl isobenzofuran were irradiated with red light and the rate of loss of furan was followed over several min. The results are consistent with a mechanism in which singlet oxygen is produced by energy transfer from methylene blue triplet in the aqueous phase, and then diffuses to and penetrates the interior of the micelles where it reacts with the furan. The competition between this process and the natural decay of the excited oxygen has been examined and a β-value of 9.7 times 10^-5 M determined which is comparable to that for the same reaction in homogeneous solvents. A model of the system is proposed and its kinetic features discussed.     

X-RAY DIFFRACTION DETERMINATION OF THE STRUCTURE OF THE ION NEAREST ENVIRONMENT IN AQUEOUS SOLUTIONS OF MAGNESIUM CHLORIDE AND NITRATE

Journal of Structural Chemistry - Quantitative characteristics of the nearest environment of ions in aqueous solutions of magnesium chloride and nitrate are determined by single crystal X-ray...     

THE PHOTOCHEMISTRY OF 5-METHYLCYTOSINE AND 5-METHYL-2''-DEOXYCYTIDINE IN AQUEOUS SOLUTION

The nucleobase 5-methylcytosine (I) is a minor component of eukaryotic DNA thought to be important in regulation of gene expression. The photochemical reactions of this nucleobase and its 2'-deoxyribonucleoside, 5-methyl-2'-deoxycytidine (II), in water have been studied. These reactions lead, respectively, to 3-amino-2-methylacrylamidine (Ib) and 3-(2-erythro-D-pentopyranos-1-yl)amino-2-methylacrylamidine (IIb) as the main photoproducts. The structure of the photoproducts was established by spectroscopic methods (1H and 13C NMR, UV spectroscopy, electron impact and liquid secondary ion mass spectrometry); in the case of Ib, confirmatory evidence was obtained by chemical methods (photolysis of 5-methyl[2-13C]cytosine, hydrolysis of N-carbomethoxy-3-amino-2-methylacrylamidine and reaction of Ib with 1,1'-carbonyldiimidazole to give I). The quantum yield for formation of Ib was determined to be 1.8 x 10(-3) at pH 7.5 while the quantum yield for formation of IIb has a lower value of 0.2 x 10(-3) at pH 7.5. These quantum yields depend strongly on pH and reach maximum values of 2.0 x 10(-3) at pH 7.0 (Ib) and 0.6 x 10(-3) at pH 5.0 (IIb). The mechanism of formation of Ib (or IIb) is proposed to involve nucleophilic attack of water on the C-2 position of photoexcited I (or II), followed by ring opening and decarboxylation of an intermediate carbamic acid.     

水及有机溶剂中离子溶剂化焓的理论计算

离子溶剂化热力学的理论研究是一项令人感兴趣的工作.在Born理论的基础上人们先后提出了多种较详细的计算离子溶剂化热力学量的模型或公式,并对离子在不同溶剂中的溶剂化自由能进行了理论计算.本文从离子-溶剂间的相互作用力出发,分别考虑了离子溶剂化过程中造腔作用、静电吸引、静电排斥及非静电相互作用对离子溶剂化焓的贡献,得到了一个具有一定意义的、计算离子溶剂化焓的理论公式。     

INTERMEDIATES IN THE PHOTOLYSIS OF INDOLE: ROOM TEMPERATURE AQUEOUS SOLUTIONS AND LOW TEMPERATURE GLASSES

Abstract— Flash photolysis of indole aqueous solutions produces four transients with absorption maxima, in their order of appearance in time, at 720, 370, 380 and 520 nm. These correlate with low temperature photolysis observations. The results are interpreted in terms of electron-radical cation generation and subsequent production of the indolyl radical.     

THE PHOTO-OXIDATION OF N, N-DIETHYLHYDROXYLAMINE BY ROSE BENGAL IN ACETONITRILE AND WATER

The Rose Bengal photosensitized oxidation of N,N-diethylhydroxylamine has been investigated in water and acetonitrile using the techniques of oxygen uptake, singlet oxygen phosphorescence and electron spin resonance. In both solvents H₂O₂ is the major oxidation product and diethylnitroxide is an intermediate. In water, superoxide dismutase decreases oxygen uptake suggesting involvement of superoxide anions in the oxidation process. Results indicate that in water the photo-oxidation proceeds mainly by a Type I(electron transfer) mechanism, while in acetonitrile a Type II(energy transfer) mechanism has been confirmed (Encinas et al., 1987, J. Chem. Soc. Perkin Trans. II,1125–1127).     

PHOTOPHYSICAL AND PHOTOCHEMICAL PROPERTIES OF TRITON X-165 IN AQUEOUS AND METHANOLIC SOLUTIONS

Abstract Laser flash photolysis of the nonionic surfactant Triton X-165 was carried out at 248 nm in methanolic and aqueous solutions at different pHs. Cation radical, triplet, phenoxy radical and solvated electron were observed as the transient absorbing species. Various characteristics of these transient species and their decay constants are reported. Photoionization was found to be a major process and it was monophotonic. The results obtained are compared with the photolysis of a small molecule p -methoxytoluene (PMT). Fluorescence and phosphorescence properties of the surfactants Triton X-100, Triton X-165 and PMT are also studied. A suitable reaction scheme is proposed to account for the observed results.     

ELIMINATION OF THE EFFECT OF CONTAMINATING CO2 IN THE 18O-LABELING OF THE CO2 PRODUCED IN BIOLUMINESCENT REACTIONS

Abstract— Although the mechanism of bioluminescent reactions in various species, such as fireflies, ostracod crustaceans ( Cypridina ), sea pansies ( Renilla ), and the deep-sea shrimp Oplophorus , are thought to involve dioxetanone intermediates, studies reported in the past from different laboratories have included widely different experimental results, most likely due to various factors including the effects of contaminating CO₂. With the improved technique employed in the present study, bioluminescent reactions of the firefly and Cypridina in ¹⁸O₂ gas resulted in an incorporation of over 75% of ¹⁸O into one oxygen of the product CO₂. with a reproducibility within a few per cent. When ¹³CO₂. instead of the product CO₂ of the bioluminescent reaction, was studied in an H₂¹⁸O medium, the exchange of one oxygen of ¹³CO₂ with H₂O was 64%. and the effect of contaminant CO₂ amounted to 1418% of the total CO₂. These results suggest that every molecule of CO₂ formed in the bioluminescent reactions of the firefly and Cypridina had intially contained 1 oxygen atom derived from O₂.     

ASSOCIATION OF KETOROLAC TROMETHAMINE IN AQUEOUS SOLUTIONS AND ITS RELATIONSHIP TO SOLUBILIZATION

Some physico-chemical properties of aqueous racemic Ketorolac Tromethamine (KT) solutions were measured as a function of concentration (0-1.0 M). These included surface tension, osmolality, partition coefficients and electrical conductivity at different temperatures (10, IS, 20, 25, 30, 40 and 50° C). These measurements indicate that KT undergoes nonmicelar self-association in water. Comparison of thesolubilitiesof spironolactone and diazepam in aqueous KT with the corresponding solubilities in known aqueous hydrotropic agents (sodium benzoate and salicylate) nonmicellar chlorpheniramine maleate (BP grade of  99 % purity) and miceilar chlorpromazine hydrochloride (BP grade of  99 % purity) indicates KT to undergo nonmicellar association, with a capacity for solubilization intermediate between hydrotropic agents and miceilar solubilizers. The solubilities of normal alkanols (C₄-C₁₀ ) were also measured against aqueous KT concentration. Compared with their solubilities in miceilar surfactants (sodium dodecylsulfate and chlorpromazine hydrochloride) aqueous KT appears to be a less efficient solubilizer. Molecular mechanical modeling of intermolecular interactions between KT species in water indicate that trimeric species have lower energies compared with those of the same number of monomeric (or monomeric plus dimeric) entities.     

脂肪酸钠盐对于苯甲酸在水中溶度的影响

在25°脂肪酸钠盐对正戊酸在水中溶度的影响是不规则的盐溶和盐析作用,其原因是排代出的新酸分布于正戊酸相和盐溶液相间^[1]。黄子卿等^[2]曾在25°研究脂肪酸盐(甲酸钠至戊酸钠)对正己酸在水中溶度的影响,除甲酸钠外,盐溶随盐的碳原子数目的增加而下降。Philip等^[3]曾在25°测定苯甲酸在甲酸钠和乙酸钠水溶液中的溶度。在本文中,作者测定在25°苯甲酸在五种脂肪酸钠(甲酸钠至戊酸钠)水溶液中的溶度。