闪光光解和脉冲辐解

<正> 长期以来,化学家渴望着能观测到化学反应中寿命仅微微秒(10~(-12)秒)的瞬息即逝的中间产物的分子构型。闪光光解的建立和发展,脉冲辐解技术的突破,已使这种愿望变成了现实。现在,在国外,这种测定技术正在对现代化学的微观、动态研究发挥着重大作用。瞬态产物测定原理光化学反应和辐射化学反应,很少由反应物直接形成最终产物,大都生成多种短寿命(10~(-6)～10~(-12)秒)的瞬态粒子(不稳定的中间产物),经过相当复杂的变化过程,才过渡到最终产物。因为各个中间步骤进行得很快,常规分析方法无济于事。人们后来也曾应用     

A Pulse Radiolysis Study of Interactions in Biological Molecules

Using pulse radiolysis techniques, the binding of penicillin and cephalosporin drugs to proteins (bovine serum albumin and lysozyme) has been studied using rate constants obtained for reactions with solvated electrons as a monitor of the binding. The results obtained are discussed in terms of three distinct types of binding.     

The Reduction of Ferricytochrome c Studied by Pulse Radiolysis

The formation of ferrocytochrome c upon pulse radiolysis of aqueous solutions of ferricytochrome c has been studied by following spectral shifts at 550 nm and 700 nm. The reaction between ferricytochrome c and hydrated electrons was studied by following the decay of hydrated electrons as well as the ferrocytochrome c formation. The two processes proceed with the same rate which indicate diffusion-controlled processes with a second order rate constant of 1.1 × 10¹¹ M^?1 sec^?1. The reaction between ferricytochrome c and H atoms was studied in a system containing H atoms only and found to be a second order reaction with a rate constant of 1.5 × 10¹⁰ M^?1 sec^?1. The formation of ferrocytochrome c by reaction between ferricytochrome c and OH radicals proceed by a first step with a second order rate constant of 1.4 × 10¹⁰ M^?1 sec^?1 during which OH radicals react with the protein part of ferricytochrome c forming an organic radical. Some of these radicals then undergo intramolecular reduction with a rate constant of 3.1 × 10³ sec^?1.     

Some Biochemical Processes Induced by Radiation as Studied by Pulse Radiolysis

The main types of biochemically important electron transfer substances can be made to undergo reactions under irradiation which in some ways mimic those which occur in nature. In the case of NAD⁺, pulse radiolysis shows that electrons add to the pyridine ring forming an NAD· radical with a characteristic absorption in the visible range which is capable of transferring its electron to oxygen. Using simpler pyridinyl compounds it has been found that, as well as the absorptions in the visible range, the radicals exhibit absorptions in the infrared range which correlate well with transitions which may be deduced from the known charge-transfer bands of the parent compound. The NAD· radical can be made by one-electron oxidation of NADH as well as by reduction of NAD⁺, and the reaction with oxygen enables NADH to be converted into NAD⁺ by an unambiguous free radical route. Cytochrome-c can be reduced either by hydrated electrons or CO₂^?. In solution buffered to neutral pH, the reduction gives rise immediately to normal reduced cytochrome-c, but in mildly alkaline solution, an unstable reduced form appears whose conformation changes over a fraction of a second to that of normal reduced cytochrome-c. As well as the hydrated electron and CO₂^?, the superoxide anion radical O₂^? has also been found to reduce cytochrome-c. This reaction is very slow (k ～ 10⁵ M^?1 sec^?1).     

Consecutive Radical Reactions and the Role of the Protein in the Pulse Radiolysis Of Enzymes

The reactions of H atoms, OH radicals and hydrated electrons acting as isolated reagents upon ribonuclease in dilute aqueous solution were studied by the technique of pulse radiolysis-kinetic spectroscopy. The experiments show that initial action of these reagents upon the protein molecule is followed by intramolecular transformations. Two consecutive intramolecular steps have been observed in the reaction of H atoms, with specific rates of approximately 10³ sec^?1 and 1 sec^?1. Some spectral features can be assigned to specific radical sites. For instance, electron adduct to disulfide is formed by the primary action of H atoms at pH 6.6, by the primary action of hydrated electrons at pH 7.6 and by intramolecular reaction of primary product formed by action of OH at pH 7.     

The Free-Radical Cleavage of the Disulfide Bond (Studied by Pulse Radiolysis)

Reaction of H atoms with glutathione leads rapidly to H + RSSR → RS · + RSH. The first observed product is RS, the spectrum of which is obtained. The spectrum of the RS?SR radical was obtained by direct attack of e^?_aq on glutathione. The rate constants of these processes were also measured. k_e?aq + RSSR = (2.7 ± 0.3) × 10⁹ M^?1 sec^?1 k_{H + RSSR} = (1.0 ± 0.2) × 10¹⁰ M^?1 sec^?1 When the OD of RS?SR is plotted vs pH a titration curve is obtained. This is due to the protonation of RS?SR with a rate constant of 2.6 × 10¹⁰ M^?1 sec^?1 which is probably followed by a cleavage to RS and RSH. In both cases the RSSHR radical cannot be detected. The spectrum attributed to the RSSHR radical is more likely to be that of RS.     

Trypsin Inhibitor Assay: Expressing,Calculating, and Standardizing Inhibitor Activity in Absolute Amounts of Trypsin Inhibited or Trypsin Inhibitors

For expressing trypsin inhibitor activity (TIA), trypsin units inhibited (TUI), trypsin inhibited, and trypsin inhibitors have been used. Although the last two units are preferred, their calculations in current practices require refinement. With the proposed AOCS method Ba 12a-2020, four experiments were conducted, using four trypsin preparations having specific activity of 11,625, 12,602, 13,728, and 14,926 Nα-benzoyl-L-arginine ethyl ester (BAEE) units/mg protein, respectively. Experiment 1 determined the relationship between absorbance at 410 nm (A410) and trypsin concentration. Experiment 2 involved assaying raw and heated soybeans, expressing TIA as TUI/mg sample and μg trypsin inhibited/mg sample, and determining conversion factors between the two units. Experiment 3 resembled Experiment 2 except for using purified soybean Kunitz inhibitor (KTI) and Bowman-Birk inhibitor (BBI). Conversion factors determined correlated highly with trypsin-specific activity (R² = 0.9789). After standardizing against a reference trypsin having 15,000 BAEE units/mg protein, a standardized conversion factor of 0.03 A410 (1.5 TUI) = 1 μg trypsin inhibited was determined. It remained consistent regardless of trypsin specific activity, with or without inhibitors, and type of inhibitor samples. By using purified inhibitors (Experiment 3), conversion values between TUI and μg trypsin inhibitor and between μg trypsin inhibited and μg trypsin inhibitor could also be calculated, enabling expression of TIA in amounts of pure KTI, BBI or their equivalents. Furthermore, when the AOCS method was modified with half substrate concentration, half trypsin concentration or half both (Experiment 4), TIA values in TUI could change with modifications but values in mg trypsin inhibited (standardized) or trypsin inhibitor remained consistent.     

Radiolysis of Ribonuclease in Controlled Environments

The separate contributions of the primary aqueous radicals to the changes in activity, molecular configuration and amino acid composition of RNase, produced by γ-irradiation of dilute solutions, have been identified. The most effective radical for inactivation is the H atom. Additional molecular products are formed on irradiation of the enzyme. Amino acid analyses of the irradiation products show significant damage only to the aromatic and sulfur-containing residues.     

固定化胰蛋白酶制备条件的优化及其在纯化抑肽酶中的应用

目的优化固定化胰蛋白酶的制备条件,并探讨固定化胰蛋白酶在纯化抑肽酶中的应用。方法以介孔分子筛SBA-15作为载体,戊二醛作为交联剂,对胰蛋白酶进行固定化,并对固定化条件进行优化。将优化条件制备的固定化胰蛋白酶作为亲和吸附剂,对抑肽酶进行分离纯化。结果固定化胰蛋白酶制备的最适条件为:戊二醛浓度0.8%,加酶量3.0mg,反应温度35℃,反应时间3h。以此条件制备的固定化胰蛋白酶活力可达15.6U/mg。以此酶作为亲和吸附剂纯化抑肽酶,纯化倍数可达420倍以上,活性回收率超过80%。结论优化了固定化胰蛋白酶的制备条件,以此酶作为亲和吸附剂用于抑肽酶的分离纯化,效果较好。     

Hydrogen Production in the Radiolysis of Dodecane and Hexane

The yields of molecular hydrogen, H₂, have been measured in the radiolysis of dodecane and hexane following radiolysis by γ-rays and a variety of heavy ions. Measured yields with γ-rays are found to be slightly higher than literature values and decrease by about 25% on aeration of the sample. Increasing the linear energy transfer (LET) from γ-rays to radiolysis with protons results in a decrease of H₂ yields by about 15% due to the increased importance of second-order H atom combination reactions. A further increase in LET results in a slight increase in H₂ yields.     

Radiolysis and Hydrolysis of Magnetically Assisted Chemical Separation Particles

Abstract

The magnetically assisted chemical separation process is designed to separate transuranic (TRU) elements from high-level waste or TRU waste. Magnetic micro-particles (1–25 μm) were coated with octyl (phenyl)-N,N-diisobutylcarbamoyl-methylphosphine oxide dissolved in tributyl phosphate and tested for removing TRU elements from acidic nitrate solutions. The particles were contacted with nitric acid solutions or simulated Hanford Plutonium Finishing Plant waste solution, irradiated with a high intensity ⁶⁰Co γ-ray source, and evaluated for their effectiveness in removing TRU elements from 2 M HNO₃ solutions. The resistance of the coatings and magnetic cores to radiolytic damage and hydrolytic degradation was investigated by irradiating samples of particles suspended in a variety of solutions with doses of up to 5 Mrad. Transmission electron microscopy, magnetic susceptibility measurements, and physical observations of the particles and suspension solutions were used to assess physical changes to the particles. Processes that affect the surface of the particles were found to dramatically alter the binding sites for TRU in solution. Hydrolysis played a larger role than radiolysis in the degradation of the extraction capacity of the particles.     

氟树脂辐射降解产物研究

氯树脂F2314在真空、空气、氮气三种气氛中经γ射线辐照后发生了降解反应,产生的气体及其水溶液经GC-MS、离子选择性电极分析,发现生成的HF、HCl的量随剂量的增大而增大.真空和氮气气氛中有H2产生,H2的量随剂量的变化不明显,空气气氛中未检测出H2.空气气氛中产生的CO2的量随剂量的增大而增大,真空和氮气气氛中未检出CO2.辐照后的样品经IR分析发现有-CF=CH-、-CF=CF-基团,空气气氛中还产生了=C=O基团.     

尿胰蛋白酶抑制剂(UTI)分离纯化研究

尿胰蛋白酶抑制剂(UTI))是具有抑制胰蛋白酶作用的一类物质,可以调控生物体内多种生理反应,具有许多临床应用功能。目前,关于UTI来源、结构、功能以及它与疾病的关系都有较深入的研究,但有关其分离纯化的文献报道相对较少。文章就近年来对UTI的分离纯化研究进展予以综述。     

Hydrogen Isotope Effects in the Radiolysis of Water

The tritium fractionation between water and radicals formed in the radiolysis of dilute solutions of monomerous methyl methacrylate in H₂O-HTO and D₂O-DTO mixutres was studied. A parallel determination of the tritium content in molecular hydrogen was performed. Also, the isotopic composition of the initial molecular hydrogen was measured in the concentration range 10 to 90 Mol% D₂O of H₂O-HDO-D₂O mixtures. Hydrogen atoms, hydroxyl radicals and molecular hydrogen produced in the radiolysis of these solvents were found to be depleted in heavier hydrogen isotopes. The isotope effects on the composition of hydrogen atoms are discussed in terms of the rate isotope effects in proton transfer. The isotope effects on the composition of hydroxyl radicals are close to those on molecular hydrogen and their extent suggests ionic dissociation of water as a rate-determining step in the process of formation of both products.     

胰蛋白酶降解琥珀明胶的研究

对以胰蛋白酶为催化剂,琥珀明胶为底物的酶解反应体系进行了考察。结果表明,胰蛋白酶不仅可以切断琥珀明胶主链上的肽键,对琥珀酸分子上羧基和侧链氨基所形成的酰胺键也具有反应活性,导致降解产物的酰化度下降。研究了胰蛋白酶降解琥珀明胶的反应中,底物质量浓度、反应时间、温度、pH值和酶用量等条件对该反应的影响规律。找出了胰蛋白酶催化水解琥珀明胶的最适反应条件为:反应温度T=40℃,底物质量浓度约为100g L,体系pH=8 5,酶和底物质量比≥0 005。     

Trypsin Induced Degradation of Amyloid Fibrils

Proteolytic enzymes are known to be involved in the formation and degradation of various monomeric proteins, but the effect of proteases on the ordered protein aggregates, amyloid fibrils, which are considered to be extremely stable, remains poorly understood. In this work we study resistance to proteolytic degradation of lysozyme amyloid fibrils with two different types of morphology and beta-2-microglobulun amyloids. We showed that the proteolytic enzyme of the pancreas, trypsin, induced degradation of amyloid fibrils, and the mechanism of this process was qualitatively the same for all investigated amyloids. At the same time, we found a dependence of efficiency and rate of fibril degradation on the structure of the amyloid-forming protein as well as on the morphology and clustering of amyloid fibrils. It was assumed that the discovered relationship between fibrils structure and the efficiency of their degradation by trypsin can become the basis of a new express method for the analysis of amyloids polymorphism. Unexpectedly lower resistance of both types of lysozyme amyloids to trypsin exposure compared to the native monomeric protein (which is not susceptible to hydrolysis) was attributed to the higher availability of cleavage sites in studied fibrils. Another intriguing result of the work is that the cytotoxicity of amyloids treated with trypsin was not only failing to decline, but even increasing in the case of beta-2-microglobulin fibrils.     

γ Radiolysis of cellulose acetate

The major degradative process in γ-irradiated cellulose acetate is chain scission. For the dry powder the G_s value (number of scissions per 100 eV of energy absorbed) was found to be 7.1. The water-swollen material was found to degrade at the higher rate of G_s = 9.45. Additions of ethanol and methanol to the water brought about reductions in G_s, whereas dissolved nitrous oxide produced an increase in G_s. The useful life of cellulose acetate reverse osmosis membranes exposed to γ radiation was estimated by observations of the water permeation rate during irradiation. Membrane breakdown occurred at 15 Mrad in pure water, but the dose to breakdown was extended to 83 Mrad in the presence of 4% methanol.