1997年全国高中学生化学竞赛(初赛)试题与试题分析

今年的全国高中学生化学竞赛的初赛刚刚结束。我们认为这次竞赛的试题较好地体现了今年5月全国高中学生化学竞赛工作会议上再次肯定的试题的水平要求:原理水平大致与人民教育出版社的《化学读本》相当,基本上不涉及更高一级的,即大学化学的原理,但考虑到冬令营的优胜选手以及参加国际竞赛的选拔,需要补充一定量的静态立体化学的知识(包括立体异构),当然试题涉及的具体化学内容本身对中学生是陌生的,但用竞赛学生的已有知识以及适当增加的知识为基础是可以理解的。为进一步考察试题的难易,我们对试题作如下的分析。     

姜黄素衍生物与类似物的构效关系研究进展

根据目前对姜黄素衍生物与类似物的结构与药理作用的关系的研究现状,论述了姜黄素衍生物与类似物的结构与其抗氧化、抗炎和抗肿瘤的药理作用的关系,包括对姜黄素及其衍生物与类似物的结构修饰与其活性之间的关系的论述。大量的实验结果显示姜黄素衍生物与类似物的药理作用与其结构中所具有的官能团有着密切的关系,这为新药开发提供了一个很好的方向。     

泽林斯基学派底发展道路(二)

二、烃的互相转变泽林斯基及其学派在烃的互相转变方面的研究,也有不可比拟的巨大成就。石油工业在国民经济中是相当庞大的、最重要的工业部门之一,天然气和石油是烃的最重要的来源。全世界石油年产量达三亿吨以上(不包括苏联在内),它的产量仅次于煤炭工业。但是几乎所有产品都用来做内燃机的燃料、润滑油等,仅有少数的作为化学工业的原料,然而利用石油作化学工业原料的需要是与日俱增的。对于石油的产品用为内燃机燃料及润滑油的要求,在今后会变得更为严格,这就是说:在不同用途的产品中烃类的化学组成不是完全没有关系的,仅一定类型的烃类在现代的航空、汽车及拖拉机发     

在化学教学中对学生的科学—无神论教育

在对学生的科学-无神论的教育中,化学教师的任务取决于我们苏维埃学校的总任务。苏维埃的学校是“教育出能够彻底建成共产主义一代”的工具。共产主义与宗教是不相容的。共产主义者“不能够也不应该对表现在宗教信仰形式中的无知、愚昧、和黑暗势力熟视无睹。”“因为党是拥护科学的,而宗教偏见是反对科学的”。在培养极积的、自觉的共产主义建议者的事业中,对学生的科学-无神论教育是化学教师的一项极其重要的任务。在共产党和苏联政府的领导下,总的来讲我们的学校卓有成效地担起了自己的教育-教养的任务。她培养了掌握科学基础的、思想健全的、体魄     

定性分析教学中的一些问题

在当前的分析化学教学中,定性分析仍占有相当重要的地位。它的主要作用,是使学生在系统地学习元素周期律的基础上,进一步掌握常见离子的基本性质,为定量分析及今后的工作打下坚实的基础。但是,从最近几年来的实际教学情况来看,定性分析部分的教学工作一直存在一些问题。造成这种情况的原因是多方面的：如在编写教材过程中,对有些问题未能进一步进行研究;不同的参考书的提法不尽相同;硫代乙酰胺的引入带来了许多新的实验现象而目前得不到很好的解释;实验条件的改变导致许多离子的反应出现异常情况等。     

改进的微乳液聚合制备的聚甲基丙烯酸甲酯的力学和光学性能研究

研究了改进的微乳液聚合方法制备的聚甲基丙烯酸甲酯(PMMA)的力学和光学性能, 并与本体聚合制备的PMMA相比较. 研究结果表明, 由改进的微乳液聚合制备的PMMA具有较高的Tg和富间规度, 在较宽的温度范围内具有较高的力学模量. 此外, 它的拉伸强度、拉伸模量及断裂伸长率均比本体聚合制备的PMMA样品高. PMMA的折光率与制备方法关系不大, 但由改进的微乳液聚合制备的PMMA样品消光系数更小, 更加透明. 这说明由改进的微乳液聚合方法制备的PMMA具有更广泛的应用前景.     

Mn助剂对CuFeZrO2低碳醇合成催化剂的修饰作用

利用程序升温还原和原位漫反射红外光谱技术研究了Mn修饰的CuFeZrO2催化剂的结构特性,并测试了催化剂的CO加氢合成低碳醇的反应性能.研究表明，适量添加锰助剂有利于提高催化剂的反应活性,提高产物中C2＋醇的含量,抑制甲烷的生成,但随锰含量的增加催化剂的活性和选择性呈现先增加后下降的趋势.程序升温还原的测试表明,锰助剂通过与铜的相互作用使铜的还原变得困难,影响铜在催化剂上的状态,随锰的加入量的增加这种作用得到加强.铜分散度的测定表明锰促进了铜的分散,利用探针分子CO在催化剂上吸附的漫反射红外光谱研究发现,锰助剂可以提高组分间的相互作用,影响铜的电子性质,从而增加了CO在铜上的吸附.     

伴有辅酶再生的生物催化过程

很多生物催化的氧化还原反应需要昂贵辅酶的参与,本文详细介绍了伴有辅酶再生的生物催化过程中,辅酶的使用、辅酶的酶反应再生、电化学再生及载体再生的特点,并对各种再生方法的优缺点进行了比较,同时介绍了辅酶的固定化及化学改性方法的研究进展.简单综述了伴有辅酶再生的基于细胞、游离酶和固定化酶的生物催化系统的研究和应用,并展望了辅酶的研究前景及辅酶再生研究的发展方向和亟待解决的问题.     

自然界中的原子核反应

宇宙中的实物根据宇宙各部分的温度和密度的不同而以各种形式存在着:有炽热的巨大的物体——恒星,有紧密的本身不发光的物体——行星,有尘雾状的和蒸气状的云彩,最后,还有充满在星球和银河之间的疏散的气体介质。实物的这一切形式是相互联系的。在宇宙的各部分之间存在着直接的联系——实物交换。譬如:宇宙线和陨石屑从宇宙空间不断地落到地球上来。在研究极光光谱时证明了,氢气不是从接近大地的大气层中进入大气的上层,而是以宇宙线的质子的形式侵入的。另一方面,地球也不断地在星际空间中损失气体(譬如,惰性气体)和极微小的尘粒。所以,无可争辩地,地     

我国古代人民制造陶器的化学工艺

我们伟大的祖国有极其悠久的文化史,这不是一句空洞的自豪的话,而是有许许多多的事实可以证明的。除了古代文献的纪载以外,我们在最近三十多年来,由於考古学家的努力,在地下发掘出很多文字所未曾记录的史前遗物,从这些遗物里,我们可以确切地认识到我们古代的文化,古代人民丰富的发明和创造。现在所已知的史前遗物可以说还仅仅是埋藏在地下的极小的一部分,将来继续不断的发掘可以有更大的收获,而已经得到的古物也尚有待於更深入的和广泛详细的研究。可是即就现有的资料和研究结果来说,已足以充分说明我国古代文化的悠久与可爱了。     

镉污染对蔬菜镉吸收和积累的影响

通过水培和土培试验研究了外源镉添加对3种蔬菜镉吸收和积累的影响。结果表明,随着外源镉添加质量浓度的提高,蔬菜可食用部位镉含量随着增加,蔬菜可食用部位镉含量与环境介质中外源镉添加质量浓度呈现出显著的线性相关。3种蔬菜中,芹菜对镉的吸收能力最强,其次为小白菜,而辣椒果实对镉的吸收能力最弱,仅为小白菜的25％。（以小白菜、芹菜、辣椒）中镉元素的最大允许量为限值,根据相关回归方程计算得到了溶液中镉的临界质量浓度值分别为0．06,0．086,0．11mg／L,而土壤中镉的临界质量分数分别为0．68、0．57、0．60mg／kg。     

土壤中镉及镉的赋存形态研究进展

综述了土壤中镉及镉的赋存形态研究进展,包括:土壤环境中镉及其污染来源,土壤中镉的赋存形态,镉赋存状态同镉生物活性的关系,土壤性状对镉赋存形态的影响,土壤中镉的测定方法等。     

发镉测定的临床意义

综述了，发镉测定的临床意义，内容包括：(1)母亲镉暴露对婴儿镉负荷的影响；(2)发镉与认知功能的关系；(3)发镉对精神发育不全的诊断检验。     

Effect of stabilizers in the thermal treatment of PVC—XI.: Effect of the reaction products on the stability of PVC mixtures stabilized by barium and cadmium stearates

The effects of cadmium and barium chlorides and stearic acid on the thermal stability of PVC mixtures stabilized by barium and cadmium stearates respectively and by their equimolar combination have been studied under static conditions of thermal treatment at 180° in air. The stabilizing effect of cadmium stearate drops in the presence of stearic acid owing to the formation of higher co-ordination cadmium compounds, only formed in the simultaneous presence of cadmium chloride, stearic acid and hydrogen chloride. The synergism is thought to be associated with the possibility of formation of a complex compound of barium stearate with cadmium chloride or stearic acid.     

Effects of three dithiocarbamates on tissue distribution and excretion of cadmium in mice

N-Benzyl-D-glucamine dithiocarbamate (BGD), N-p-hydroxymethylbenzyl-D-glucamine dithiocarbamate (HBGD), and N-p-carboxybenzyl-D-glucamine dithiocarbamate (CBGD) were compared for their relative efficacies in the distribution and excretion of cadmium in mice exposed to cadmium. Mice were injected intraperitoneally with 109CdCl2 (1 mg of Cd/kg and 2 microCi of 109Cd/one animal). Three days later, they were injected with chelating agents (400 mumol/kg) every other day for 2 weeks. After injections of BGD and HBGD, cadmium was excreted mainly in the feces through the bile, and the fecal excretion of cadmium by HBGD was significantly higher than that by BGD or CBGD. These chelating agents increased the urinary excretion of cadmium to a small extent. The hepatic cadmium content was decreased only after HBGD injection. Also, the injection of HBGD caused a much greater decrease in renal cadmium content than did BGD or CBGD. These chelating agents did not result in the redistribution of cadmium to the brain, testes, or heart. The growth of mice was only slightly retarded by injections of these chelating agents. The results of this study indicate that the injection of HBGD to mice pretreated with cadmium can remove cadmium from the body, mainly through fecal excretion, without redistribution of cadmium to other tissues such as the brain, testes, and heart, more effectively than BGD or CBGD.     

Determination of cadmium in uranium by ion exchange and square-wave polarography

Traces of cadmium in uranium and its compounds can be determined by ion-exchange separation and square-wave polarography. With a small column of anion-exchange resin, cadmium can be separated from uranium and recovered quantitatively from hydrochloric acid solution, Separations of cadmium from uranium are not perfect but are sufficient for the determination of traces of cadmium by square-wave polarography. The lower limit of the method is 0.01 p.p.m. of cadmium.     

改性竹炭脱除贝类酶解液中的重金属镉

以蚶子贝肉酶解液为材料,利用聚天冬氨酸(PAsp)改性的竹炭吸附脱除酶解液中的重金属镉。考察了pH、脱除时间、竹炭投加量和温度对酶解液中镉脱除率的影响,并在单因素试验基础上通过响应面法确定了镉的最佳脱除条件。当pH为5.0、反应时间为25min、竹炭投加量(10m L酶解液)为0.26g,重金属镉的脱除率可达96.59%。研究表明,PAsp改性竹炭能显著提高吸附重金属的效率和能力,可用于脱除蚶子贝肉酶解液中的镉。     

Determination of mineral balances in sheep offered feed with added cadmium and zinc

The optimum conditions for microwave digestion of herbage and faeces to determine mineral concentrations were obtained by varying sample mass, reagent and heating programme, and it was confirmed that the resulting element concentrations were the same as for certified reference material. The effects of feeding cadmium to sheep at a level that is typical of polluted regions (1 mg/kg) for ten days were investigated, as well as the possible amelioration of cadmium effects by adding 30 mg/kg Zn to the diet. Cadmium in the feed increased the cadmium balance and produced several mineral disturbances, in particular a reduction in sodium balance which is typical of renal tubular disorders. Including zinc in the diet as well as cadmium reduced the cadmium balance to a level similar to that of sheep that did not receive cadmium or zinc, which suggests that the zinc status is critical in determining whether cadmium in feed increases the cadmium balance in sheep.     

Rapid coprecipitation-separation and flame atomic absorption spectrometric determination of lead and cadmium in water with cobalt (II) and ammonium pyrrolidine dithiocarbamate

A coprecipitation technique which does not require complete collection of the precipitate was proposed for the determination of trace lead and cadmium in water with flame atomic absorption spectrometry (FAAS) after preconcentration of lead and cadmium by using cobalt (II) and ammonium pyrrolidine dithiocarbamate (Co-APDC) as coprecipitant and known amount of cobalt as an internal standard. Since lead, cadmium and cobalt were well distributed in the homogeneous precipitate, the concentration ratio of lead to cobalt, and cadmium to cobalt remained unchanged in any part of the precipitate. The amount of lead and cadmium in the original sample solution can be calculated respectively from the ratio of the absorbance values of lead and cadmium to cobalt in the final sample solution that is measured by FAAS and the known amount of the lead and cadmium in the standard series solutions. The optimum pH range for quantitative coprecipitation of lead and cadmium is from 3.0 to 4.5. The 16 diverse ions tested gave no significant interferences in the lead and cadmium determination. Under optimised conditions, lead ranging from 0 to 40?µg and cadmium ranging from 0 to 8?µg were quantitatively coprecipitated with Co-APDC from 100?mL sample solution (pH?～?3.5). This coprecipitation technique coupled with FAAS was applied to the determination of lead and cadmium in water samples with satisfactory results (recoveries in the range of 94.0–108%, relative standard deviations <6.0%).     

Dynamics of mononuclear cadmium beta-lactamase revealed by the combination of NMR and PAC spectroscopy

The two metal sites in cadmium substituted beta-lactamase from Bacillus cereus 569/H/9 have been studied by NMR spectroscopy ((1)H, (15)N, and (113)Cd) and PAC spectroscopy ((111m)Cd). Distinct NMR signals from the backbone amides are identified for the apoenzyme and the mononuclear and binuclear cadmium enzymes. For the binuclear cadmium enzyme, two (113)Cd NMR signals (142 and 262 ppm) and two (111m)Cd PAC nuclear quadrupole interactions are observed. Two nuclear quadrupole interactions are also observed, with approximately equal occupancy, in the PAC spectra at cadmium/enzyme ratios < 1; these are different from those derived for the binuclear cadmium enzyme, demonstrating interaction between the two metal ion binding sites. In contrast to the observation from PAC spectroscopy, only one (113)Cd NMR signal (176 ppm) is observed at cadmium/enzyme ratios < 1. The titration of the metal site imidazole (N)H proton signals as a function of cadmium ion-to-enzyme ratio shows that signals characteristic for the binuclear cadmium enzyme appear when the cadmium ion-to-enzyme ratio is between 1 and 2, whereas no signals are observed at stoichiometries less than 1. The simplest explanation consistent with all data is that, at cadmium/enzyme ratios < 1, the single Cd(II) is undergoing exchange between the two metal sites on the enzyme. This exchange must be fast on the (113)Cd NMR time scale and slow on the (111m)Cd PAC time scale and must thus occur in a time regime between 0.1 and 10 micros.