蜂蜜中氯霉素残留量测定的不确定度评估

按照SN/T1864-2007《进出口动物源食品中氯霉素残留量的检测方法第2部分:液相色谱串联质谱法》对蜂蜜中氯霉素残留量进行分析。通过建立数学模型,对测量结果的各不确定度来源,如标准使用液、内标、回归方程、方法重复性等引入的不确定度分量及其灵敏系数进行分析和量化。当蜂蜜中氯霉素残留量为0.108μg/kg时,扩展不确定度为0.012μg/kg(k=2)。     

核磁共振INDOR法研究若干单糖分子的构型和构象

本文用核磁共振谱的INDOR,研究若干单糖在DMSO溶液中的构型和构象。在单糖分子中,除少数质子如差向异构氢(C₁—H)外,大多数质子处于相似的化学环境中,相邻者又彼此偶合,在常规核磁共振谱上产生的信号重迭交错,形成峰包,无法一一辨认以确定归属。从木糖、阿拉伯糖、甘露糖、鼠李糖等单糖在DMSO中的1NDOR谱,可间接测得C₂～C₄上质子的各组谱线,进而获得每一质子的化学位移及偶合常数。用Karplus方程定出相邻碳上质子的两面角及C—H键取向,因而确证这些分子在DMSO中的立体结构。     

THE PHOTOLYSIS OF TRYPTOPHAN IN THE PRESENCE OF OXYGEN

Abstract— Quantum yields for the destruction of tryptophan by a single 500 J flash in aqueous solution have been determined over the pH range 1–13 in both air-equilibrated and nitrogen-saturated conditions. When these quantum yields are compared with the quantum yields for radical formation and photoejection of electrons, it is found that there is good agreement only for the nitrogen-saturated case. In air-equilibrated solutions of tryptophan, there is a large disparity between the measured degradation quantum yields and those for photoejection of electrons and radical formation. Oxygen, therefore, is playing a major role in the photochemical decomposition and it is proposed that the major reaction which occurs, under normal atmospheric conditions, is the reaction of the lowest triplet excited state of tryptophan with oxygen.
Preliminary photolysis-product distributions against pH are discussed, and indicate that a total of nine major products are formed in the presence of oxygen.     

THE ROLE OF HYDRATION IN THE PHOTOTRANSFORMATION OF PHYTOCHROME

Abstract— Changes in the visible absorption spectrum and in phototransformation of phytochrome have been found to be associated with dehydration and rehydration. These spectral properties explain the previously reported rapid appearance of phytochrome in imbibing seeds. No evidence was found for the orientation of the phytochrome chromophore in gelatin films or in preparations subjected to a shearing force.     

丙烯聚合络合催化剂形成过程的研究

以倍半物为还原剂还原TiCl_4,经异戊醚络合处理,然后在TiCl_4己烷溶液中35℃条件下热处理,制得对丙烯聚合具有高活性和高定向度的络合催化剂。研究了制备过程中各步反应产物的组成和结构特征,并讨论了TiCl_3低温晶型转变机理。     

合金中痕量元素标准物质研制进展

通过对国内外高温合金、铝合金痕量元素标准物质的比较,评述了我国合金中痕量元素标准物质在种类、量值水平及不确定度等方面的进展。     

STEPS IN THE POPULATION OF THE EMITTER IN THE BACTERIAL LUCIFERASE REACTION

Abstract— The reaction of luciferase-bound flavin hydroperoxide with both I-¹H and 1–²H decanal has been examined at 2°C in both low (0.01 M ) and high (0.35 M ) phosphate buffer, pH 7, where the kinetics and deuterium isotope effects are quite different. Upon reaction in both buffers there are rapid (<2 ms) increases in absorption at both 380 and W nm, followed by decay over the subsequent seconds and minutes. The changes at 380 nm exhibit a primary isotope effect and are rapid compared to bioluminescence, indicating that the scission of the aldehyde C — H bond occurs prior to the step responsible for populating the electronically excited state. However, the final absorbance change at 600 nm decays in parallel to bioluminescence under the several different conditions studied, suggesting the involvement of a long-wavelength absorbing flavin species in the production of, the excited state. Evidence is also presented indicating that under certain conditions there may be two (sequential) steps, each of which exhibits a primary isotope effect involving the same H atom.     

抽吸过程中尼古丁在烟丝和滤咀中分布的研究

吸烟有害健康。尤以香烟中尼古丁对人体健康的危害 ,已众所周知。美国卫生局和各种癌症研究机构一再就吸烟的危害对人们作出警告 ,但人们所吸的烟还是比以往任何时候都要多 ,完全消灭吸烟在相当长时期内难以实现。因此 ,研究吸烟过程中尼古丁在香烟中的分布情况 ,寻找较为安全、适宜的吸烟区间 ,减少吸烟过程中尼古丁对人体健康的危害 ,成为本文关心的问题。为了降低烟草中有害物质对人体的危害 ,目前在国内外 ,一般均在香烟上加一过滤咀 ,以吸滤烟草中部分尼古丁及其它物质。因而 ,为了提高滤咀对其尼古丁的吸滤率 ,在滤咀中添加油酸酰胺、…     

聚硅烷高分子对烯类单体的光敏聚合作用

<正> 可溶性聚硅烷高分子(polysilane polymer)是80年代初期才发展起来的一种功能高分子,有关文献对于聚硅烷高分子的紫外光解及光刻作用有较详细的报道,然而有关它的光敏引发聚合作用则鲜有报道。我们研究了聚硅烷高分子对苯乙烯的光敏引发聚合作用及其特点,这对于开发一类新的高分子光敏剂有重要的意义。     

ON THE ROLE OF TYROSINE IN THE PHOTOCYCLE OF BACTERIORHODOPSIN

Abstract -The rate of formation of the M intermediate ( k _M) in the photocycles of bacteriorhodopsin (bR₅₇₀) and of nitrated bacteriorhodopsin (bR₅₃₂ⁿ), is measured over the range between pH 6.5 and 11.5. In the case of bR₅₇₀, k _M is markedly pH dependent, exhibiting a titration-like curve with pK ∽ 10.3. The pH dependency is completely eliminated by nitration. On the basis of previous work by Lemke and Oesterhelt (1981), the effect is attributed to the specific modification of the Tyr 26 residue. The data are rationalized by a mechanism in which deprotonation of Tyr 26 at the stage of the L intermediate constitutes a prerequisite for deprotonation of the retinal-lysine SchifT base. Both reactions are intimately associated with the photo-induced proton pump mechanism.     

THE ROLE OF SURFACE FORCES IN FOULING OF STAINLESS STEEL IN THE DAIRY INDUSTRY

The major cause of fouling of processing equipment in the Dairy Industry used for the pasteurization of milk and whey resides in particle formation in the bulk of the dairy fluid. As a result of processing at elevated temperatures, the heat sensitive whey proteins aggregate and calcium phosphate becomes insoluble and precipitates. Hence, the process of fouling can be understood as a subsequent deposition of these particles onto the heating surface.

On the basis of model calculations it is demonstrated that at neutral pH both the calcium phosphate particles, and to a limited extent also the whey proteins, are attracted by stainless steel. This is the result of the monopolar character of steel, which leads in an aqueous environment to an attractive Lewis acid/base interaction term with both components. In combination with the Lifshitz-van der Waals contribution both contributions to the overall interaction are sufficiently large to overcome the electrostatic repulsion at the given pH.

This result points to the specific role of stainless steel in the process of fouling and has far reaching consequences for the way the process of fouling can be controlled as the behaviour of the contaminants, e.g. their heat sensitivity, can not be altered.     

THE KINETICS OF THE DECOMPOSITION OF CYCLOHEXYL HYDROPEROXIDE IN THE PRESENCE OF VANADYL DIBENZOYLMETHANE

The kinetics of the decomposition of cyclohexyl hydroperoxide(CHHP) in benzene catalyzed by vanadyl dibenzoylmethane[V0(DBM).,] has been studied.It was found that the products of decomposition of CHHP were cyclohexanol and cyclohexanone,which are produced in about equimolar amount,and the product cyclohexanol obviously inhibited the decomposition of CHHP.The kinetics data can be satisfactorily described by the following equation (with [CHHP]0>>[VO(DBM)2]0)R0=kK[CHHP]0[VO(DBM)2]0/(1+k[CHHP]0)This is the kinetic evidence for the formation of a catalyst-hydro-peroxide intermediate.In the equation K is the stability constant of the catalyst-hydroperoxide intermediate complex;k is the rate constant for the decomposition of the complex.The rate constant K at 500℃ may be expressed as follows:k=1.9×108exp(-53.7×103/RT)S-1 with the activation energy Ea=53.7kJ mol-1     

THE ROLE OF HEMOGLOBIN IN THE PHOTOTAXIS OF THE NEMATODE Mermis nigrescens

Abstract A dense zone of crystalline hemoglobin in the head has been presumed to be involved in the photosensitivity of Mermis. With the aim of identifying its role, we have studied the wavelength dependence of the phototaxis. Measuring phototaxic efficiency at constant photon fluence rate (intensity), we find that the spectral response curve is approximately fiat from 350–540 nm and falls to an insignificant level by 580 nm. This is unlike the absorptance (fraction absorbed) spectrum of the hemoglobin pigmentation. Also, fluence-rate/response curves at 420 and 500 nm occur at the same fluence rates even though these wavelengths correspond to a maximum and a minimum of hemoglobin absorption. These results prove that the hemoglobin cannot be functioning as the visual pigment in phototaxis but, for reasons discussed, they neither confirm nor rule out a role as a shadowing pigment. The results are consistent with a shadowing role in the presence of contrast enhancement by the nervous system.
A steep fluence-rate dependence suggests that contrast enhancement does occur in Mermis phototaxis. The 420 or 500 nm fluence rate for half-maximal response is 6 times 10 photons s^-1 cm^-2 (about equivalent in effectiveness to pre-dawn twilight). The wide range of sensitivity, 350–560 nm, has interesting implications as to the nature of the visual pigment.
†NATO reaearch collaborator a n leave from the Department of Biophysics. Laboratorium voor Algemene Natuurkunde, Rijksuniversiteit Groningen, Westersin-gel 34. 9718 CM Groningen, The Netherlands.     

THE ROLE OF SINGLET OXYGEN IN THE PHOTOOXIDATION OF POLYMERS

Abstract— This paper is a critical review of the singlet oxygen oxidation of polymers in solid state and in solution, referring in particular to polydienes, polystyrene and polyvinyl chloride). The singlet oxygenation of polydienes resulted in formation of allylic hydroperoxide groups with shifted double bonds, according to the "ene"-type process. The singlet oxygenation of polystyrene and polyvinyl chloride) occurs only when the new double bonds are formed in these polymers. During dye-photosensitized singlet oxygenation of polydienes in methanol-benzene solution, a very rapid decrease in the molecular weight was observed. For the chain-scission which occurs, not only singlet oxygen but several intermediates such as radicals, bi-radicals and cation-radicals which are formed during light fading of dyes are responsible. At the end of this paper a short review appears which has been focused on the quenching behavior of stabilizers, particularly interactions with singlet oxygen.     

氧对四氟乙烯悬浮聚合的影响

合氟单体的聚合极易受杂质的影响,氧气是影响聚合反应的物质,因此,研究氧对合氟单体聚合的影响是颇有意义的。 氧对自由基引发聚合的影响早已引起人们的注意,并且对于一些常用的单体作了比较仔細的研究。当有氧存在时,乙烯系单体的聚合反应有一个阻化期,在阻化期内氧与     

水中微量磷的磷钼蓝光度法测定 --还原剂的研究

研究和配制了一种作为水中微量磷(磷钼蓝)光度法测定的还原剂,其稳定性、灵敏度、准确性均较好,适用干多种水样中微量磷的测定。     

工作用玻璃液体温度计温度修正值的测量不确定度分析

依据JJF1059－1999，利用二等水银湿度计标准装置，分析了工作用玻璃液体温度计温度修正值的测量不确定度。当温度测量点为20℃时，工作用玻璃液体温度计温度修正值的扩展不确定度为0.054℃，当温度测量点为95℃时，工作用玻璃液体温度计温度修正值的扩展不确定度为0.055℃。