LUMINESCENCE OF L-TRYPTOPHAN IN THE DRY STATE AND IN AQUEOUS SOLUTION INDUCED BY X-RAYS AND U.V.-LIGHT AT 77°K

Abstract— The luminescence from tryptophan in the dry state and in aqueous glass. induced by u.v.-light and X-rays at 77°K, has been studied. The spectra of the luminescence from the dry material, which were identical for the two types of irradiation, were attributed to the same excited singlet level as that giving rise to the fluorescence from the aqueous sample. The strong phosphorescence exhibited by the latter. could not be detected for the dry material with either type of irradiation. This was attributed to a strong quenching of the radiative triplet level occurring upon crystallization of the substance. The yield of X-ray induced fluorescence of tryptophan in aqueous glass was found to be similar to that observed in the dry state. It was concluded that there is no extensive transfer of energy between the solvent and the solute molecules contributing to the fluorescence yield of tryptophan in aqueous glass.     

CARBOXYLATION OF FORMIC ACID IN AQUEOUS SOLUTIONS UNDER THE INFLUENCE OF U.V.-LIGHT

Abstract— Carboxylation of various organic substances by dissolved carbon dioxide or bicarbonate is achieved by the action of U.V. -Light of 184.9 and 253.1 mμ on water. The transformation of formic acid to oxalic acid was investigated in more detail as a function of u.v.-dose, pH-values and the formate concentration. For an irradiation period of 12 hr of 0.1 M formate, a yield of about 2 m mol.1^--¹ oxalic acid was obtained. A reaction mechanism for the photochemical carboxylation process is presented. The results are of some interest in respect of the synthesis of organic compounds under the primitive earth conditions.     

LUMINESCENCE AND PHOTOCHEMISTRY OF 4-THIOURIDINE IN AQUEOUS SOLUTION

Abstract— In bidistilled water, 4-thiouridine (4TU) exhibits a weak unusual luminescence, the quantum yield of which is 3 × 10^-4 at 25°C. The excitation spectrum corresponds well to the 4TU absorption spectrum. The emission lies at longer wavelengths (Λ_max 550 nm) than the 4TU phosphorescence observed at 77 K (Λ_max, 470–480 nm). From the emission signal obtained after an excitation flash of 3 ns half-width, an "apparent" rate constant for the radiative deactivation process, shorter than 5 × 10⁶ s, can be inferred. The 300 K emission is efficiently quenched by halides and by oxygen: quenching involves a long-lived intermediate (⋍ 200 ns).
Clearly the emissive state X is populated through the S₀-S₁ electronic transition π→π* of 4TU. The nature of X cannot be unambiguously determined: it cannot be an excimer but can be either the 4TU triplet state or another chemical state distinct from the 4TU excited singlet or triplet states.
An interesting finding is that the 300 K emission and the ability of 4TU to photoreact are related: they are quenched with the same efficiency by halide anions. This indicates that quenching occurs at the same long-lived intermediate species , which is either a precursor of the emitter or the emitter itself.     

水溶液中芘的荧光被核酸碱基猝灭的研究

众所周知,稠环芳烃是一类具有致癌性的物质.虽然对其致癌机理的认识尚未形成一致的看法,但一般都认为同稠环芳烃与DNA,蛋白质等生物活性物质的相互作用有关.因为致癌物后的致癌作用最终都是通过损伤细胞中的DNA而实现的.     

CHEMILUMINESCENCE INDUCED BY OXIDATION OF TRYPTOPHAN BY SINGLET OXYGEN AND BY HYPOCHLOROUS ACID. IMPLICATIONS IN THE LUMINESCENCE EMITTED IN PHAGOCYTOSIS

Abstract— The mechanism of the chemiluminescence emitted during phagocytosis of opsonized zymosan was investigated. The use of an artificial system generating singlet oxygen permitted the distinction between the respective roles of O₂ and HOCl in the light production via the reactions with opsonized zymosan, amino-acids and peptides. The reaction of free hypochlorous acid, produced by the myeloperoxidase H₂ O₂-Cl- system, with free tryptophan appears to be a likely path for the production of chemiluminescence. Implications for the mechanism of in vivo chemiluminescence during phagocytosis are considered.     

振动光谱法研究水溶液中十六烷基三甲基溴化铵的分子构象

研究长链分子在水溶液中的分子构型有助于更好地理解生物膜的结构及生物大分子链(如蛋白链)的结构,受到人们的高度重视。许多表面活性剂分子的结构和性质已用各种物理和化学方法广泛地研究过,但用振动光谱方法(尤其是红外光谱法)研究水溶液中表面活性剂分子构象的报道则很少。十六烷基三甲基溴化铵(CTMAB)是一种典型的阳离子型表面活性剂,我们曾讨论了温度对CTMAB分子链亚晶胞堆积形式的影响。本文在280～320K范围     

STUDY ON THE ADSORPTION OF PHENOL BY CHITOSAN FROM AQUEOUS SOLUTION

The effects of pH, initial concentration and temperature on the adsorption of phenol by chitosan were investigated in this paper. The isothermal data was applied to Langmuir linear and the Freundlich linear isotherm equation, and the thermodynamic parameters （AH, AG, AS） were calculated according to the values of binding Langmuir constant, KL. Results indicated that the adsorption between chitosan and phenol was significantly physical in nature, the negative ΔH constant at lower temperature confirmed that more phenol was adsorbed by chitosan at lower temperature. The kinetics of the sorption process of phenol on chitosan was investigated using the pseudo-first order and pseudo-second order kinetics, and results showed that the second order equation model provided the best correlation with the experimental results.     

ON THE NATURE OF SODIUM HYDROXYMETHANE SULFINATE IN AQUEOUS SOLUTION

Abstract

New data obtained on sodium hydroxymethane sulfinate in aqueous solution by voltammetry are presented, and discussed in relation to its chemistry. The most plausible explanation of the data would appear to be in terms of a tautomerism in solution, and such a thesis is compatible with the known behavior of this reducing agent.     

REDUCTION OF THE EXCITED SINGLET STATE OF CHLOROPHYLL AND PHEOPHYTIN AT THE ORGANIC CRYSTAL/AQUEOUS SOLUTION INTERFACE

Abstract— Reduction of the excited singlet state of chlorophyll a , chlorophyll b , and pheophytin a at the surface of perylene, anthracene, and chrysene single crystals has been measured as hole injection current. The dependence of the quantum yield on the standard free-energy difference of the reaction was in accordance with theoretical expectations without correcting for an interaction energy. The maximum quantum yield of only about 10⁻² holes per absorbed photon is ascribed to a very small effective lifetime of the excited singlet state due to concentration quenching of the excited singlet state in the adsorbed dye layer.     

EFFECTS OF SENSITIZED AND UNSENSITIZED LONGWAVE U.V.-IRRADIATION ON THE SOLUTION PROPERTIES OF DNA

Abstract— Two types of photoreactions occur in DNA irradiated in aqueous systems with longwave u.v.-light (Λ > 295 nm), namely, (a) thymine dimerization, and (b) single- and double-strand breakage of the sugar phosphate backbone; these two reactions are unrelated. The presence of acetophenone as a photosensitizer caused an increase in dimerization by a factor of 16, and an increase in single-strand breaks by a factor of 4. The number of thymine dimers per single-strand break is about 100 in the sensitized and 25 in the unsensitized reaction. The alteration of the radius of gyration of DNA molecules is that expected by the degradation observed. At the same time the change in hyperchromicity is very small. Therefore as far as can be detected by these methods of investigation the gross conformation of the DNA double helix is stable against thymine dimerization.     

用动态光散射跟踪钙-海藻酸水溶液凝胶化

海藻酸(alginate)是一种天然多糖,是直链键合的β-D-甘露糖醛酸(M)和α-L-古洛糖醛酸(G)的无规嵌段共聚物[1].在海藻酸水溶液中加入钙、铜、锌、铅等二价正离子,能够形成凝胶;其中钙-海藻酸凝胶在细胞输送、组织工程等领域受到人们的关注[2,3].影响海藻酸凝胶化的因素包括海藻酸的分子量和分子量分布、M/G值和序列分布、溶液浓度、正离子种类与浓度等[4,5].     

AN EPR STUDY ON THE TRIPLET STATE OF PURINE FREE BASE IN AQUEOUS GLASSES AT 77 K

Abstract— Since purine free base in aqueous solution exists in different ionic forms at different pHs and most of its photoreactions are likely to involve the triplet excited states of these different ionic forms, electron paramagnetic resonance studies (EPR) have been performed in order to determine intersystem crossing quantum yields and other characteristic parameters of the excited triplet state of these forms. Intersystem crossing yields decrease with a decrease in pH, being 0.62, 0.37 and 0.10 in 8 M NaOH, 8 M NaCIO₄ and 6M H₃P0₄ glasses, respectively. Differences in triplet decay lifetimes 3.4, 2.5 and 3.1 s, as well as in root mean-square zero-field splitting (ZFS) parameter, D_*, (0,1304, 0.1512 and 0.1353 cm_-1) are also observed for the anionic, neutral and cationic species of purine free base. The EPR signals of the triplet state of the neutral and anionic forms have been observed simultaneously in the pH range of7–10.     

STUDIES ON THE UV PHOTODESTRUCTION OF PURINE FREE BASE IN AQUEOUS SOLUTIONS AT 77 and 298K

Abstract— The photodestruction of purine free base used as a model for the purine bases in DNA has been studied in order to better understand the effect of UV light on these molecules. Photodestruction yields have been determined in glassy aqueous solutions at 77 K and at room temperature at different pH's. The yield decreases in the order of 0.04, 0.01, 0.001 in 8 M NaOH, 8 M NaCIO₄ and 6 M H₃PO₄, respectively, while at room temperature the highest destruction yield is 0.005 for the unbuffered neutral solution. These yields have been determined by measuring the initial decrease in the purine absorption maximum as a function of irradiation time. During the illumination stable photoproducts, as well as reactive intermediates, such as trapped electrons, radical anions and cations, are formed and have been characterized from their absorption spectra. The addition of triplet quenchers and an electron scavenger resulted in a decrease in the yield, implying the participation of the purine triplet state and a radical anion in the reactions leading to the photodestruction of purine.     

单磺化酞菁镓在水、微乳液中的解聚反应动力学研究

本文研究了单磺化酞菁镓（ＳＰｃＧａ）在水、微乳液（ＴｒｉｔｏｎＸ－１００－壬烷－正戊醇－水）中的二聚现象和解聚反应动力学，测定了二聚平衡常数ＫＤ和解聚速率常数ｋ。结果表明：ＳＰｃＧａ的解聚反应速率与ＳＰｃＧａ的单体浓度ＣＭ和双体浓度ＣＤ的关系为：Ｖ＝ｋ１ＣＤ－ｋ２ＣＭ２     

黄原胶溶致液晶行为的研究

以小角激光光散射法、偏光显微镜法及旋转粘度计法研究了黄原胶水溶液在不同浓度和温度下的光学性质。结构区域及粘性行为。发现当溶液浓度达到3％(临界浓度值)时,呈现胆甾型液晶特征,液晶的形成对温度有显著的依赖性。     

三价铀的制备和稳定性研究

在盐酸和硫酸介质中,研究了汞阴极电解还原和液态Zn-Hg齐还原制备U(Ⅲ)的实验方法,比较了不同介质、酸度、铀浓度和电解时间对U(Ⅲ)还原率的影响,获得了用电解法定量还原制备U(Ⅲ)的最佳条件。经对U(Ⅲ)在空气和氮气中稳定性的测定,得出U(Ⅲ)在空气中的氧化速率呈一级反应。     

THE U.V. PHOTOLYSIS (Λ= 185nm) OF ETHYLENE GLYCOL IN AQUEOUS SOLUTION*

Abstract— –The u.v. photolysis (Λ= 185 nm) of 2 M aqueous solutions of ethylene glycol was studied at 22°C. Products (quantum yields) are hydrogen (0.20₄) formaldehyde (0.19₄), glycolaldehyde (0.08), methanol (0.07₄), glycerol (0.06), erythritol (0.03), acetaldehyde (0.02), 3,4-dihydroxybutanal (0.01) and succinaldehyde (0.001). With increasing temperature the yields of all products remain essentially unchanged except that of acetaldehyde (φ= 0.32 at 90°C) which is formed in a chain reaction. The photolysis of (CD₂OH)₂ yields 91% HD, indicating that the most important primary process is the homolytic splitting of the O-H bond. The resulting oxy radicals fragmentate largely into formaldehyde and CH₂OH radicals. Molecular fragmentation processes yielding hydrogen and glycolaldehyde, as well as formaldehyde and methanol, are discussed in the proposed decomposition scheme.     

PHOTODEGRADATION OF THE IMIDAZOLE RING INDUCED BY INDOLE DERIVATIVES IN OXYGEN-FREE AQUEOUS SOLUTIONS

Abstract— An imidazole ring photodegradation induced by indole derivatives in oxygen-free aqueous solutions (Λ_exc= 254 nm) was demonstrated and studied in various systems at low concentration (0.2 m M ). The degradation rate was maximal in the indole-imidazole system and decreased when a substituent was present on either or both rings. The degradation rate also depended on pH (maximal at pH ˜ 6) and on imidazole concentration. Results obtained under N₂O atmosphere, in the presence and absence of 1 M t -butanol, indicate that the imidazole degradation is promoted by hydrated electrons photogenerated by the indole chromophore. Kinetic analysis of the data confirms this mechanism.