硒缺乏的预防

防治硒缺乏可采用补硒方法。目前常用的补硒制剂主要包括有机物（硒蛋氨酸）和无机物（亚硒酸钠或硒酸钠）。硒主要在小肠吸收，人体对硒的吸收率很高，约为50％～100％。膳食来源的硒主要以硒蛋氨酸形式存在。硒蛋氨酸和硒酵母中生物结合形式的硒在直接消除氧自由基、抑制脂质过氧化方面，在激发免疫反应、促进免疫蛋白合成、刺激淋巴细胞增殖方面，在提高肝脏、肌肉中硒含量和提高肝GSH-Px活性方面，效果均明显好于无机硒化合物。与硒的无机盐相比，硒蛋氨酸不仅生物学活性高出许多，而且更容易被吸收，     

土壤环境中的硒对人和动物健康的影响

硒是人和动物必需的微量元素之一。土壤中的硒含量过多或过低，人和 动物都会出现地方性疾病。土壤中硒的含量与土壤母质、地形、气候条件和土壤条件性质等有关，调节土壤性质可以改善作物的含硒量。防治硒缺额症和硒中毒症，每天必需摄入适量的硒，以100－200μg为宜，但人体对硒的需要量也与食物成分有关。     

硒的土壤化学及其生物有效性

硒是重要的生命元素。高硒和低硒均会引起动物发生各种疾病，硒由土壤进入植物体，通过食物链控制着动物的硒营养状况，因此研究硒的土壤化学及其对生物的有效性对维护人类健康和牲畜生产是十分有意义的，本文拟就土壤中硒的含量、形态、有效性影响因素，硒的保健作用和调节措施等方面作一综述。     

富硒香菇规模化栽培实验及其富硒规律研究

为了了解规模化栽培后富硒香菇的产量（生物学效率）及富硒规律，本实验通过香菇栽培基质添加模式，采取规模化生产进行富硒香菇栽培试验，选取不同浓度硒营养强化剂对香菇品种“向阳二号”和“9608”进行添加，测定相对应的香菇生物学效率以及第一潮次和第二潮次的总硒及硒代氨基酸的含量。实验发现向阳二号香菇，在硒添加量较低（0-6mg/kg）时香菇的生物转化率基本不随硒添加量的增加而改变，当硒添加量继续增加（10-60mg/kg）时，香菇的生物转化率整体低于低添加量；9608香菇，随着硒添加量的增加（0～60mg/kg），香菇的生物转化率表现出微弱的增加趋势，但差异性不显著；而两种不同品种、潮次香菇的总硒及硒代氨基酸含量均随着硒添加量的增加而提高，但硒代氨基酸占总硒的比例变化趋势却有所不同，在66.7-85.4%范围内。此外，对于不同品种的香菇，其第一潮次总硒含量在硒的添加量在0～20 mg/kg的范围内呈现良好的规律性，总硒是基质（风干）中硒含量的约4-5倍。可见，按照该规模化栽培模式进行生产栽培，可以得到总硒含量稳定、硒代氨基酸占总硒比＞65%的富硒香菇产品，对富硒香菇产业的发展有一定的指导意义。     

硒对癌症的预防和临床问题的研究现状

从流行病学、实验室和临床等的研究均表明微量元素硒具有化学防癌的潜力，特别是近来富硒酵母应用于肺癌、肠癌、前列腺癌和肝癌等临床干预试验，表现出硒具有强大的保护作用。本文着重论述了硒化合物发展成为化学防癌药物的作用机制问题，这些机制表现在硒具有抗致癌的生物活性。还讨论了对硒的化学预防试验人群的选择，硒的干预试验，临床应用结果和安全范围的指标等问题。     

仿硒酶研究进展

硒是人体中必需的微量元素，它与各种疾病和人类健康息息相关。硒在生物体内以硒代半胱氨酸形式表现其生理活性和功能。为了探索硒在硒蛋白中结构和功能关系并可能发展成硒相关的适用药物，人们付出许多努力来发展硒蛋白模拟化学。由于硒酶—谷胱甘肽过氧化物酶（GPX）重要的抗氧化作用以及潜在的药用价值，国际上广泛开展了对它的人工模拟研究。本文对近年来硒酶模拟化学和生物学相关研究进展进行了综述。     

硝酸铜稳定消化—超声络合萃取测定硒

本文报道以硝酸铜作为稳定剂对含硒样品进行消化，用超声波加快硒和邻苯二胺的络合与萃取，利用紫外分光光度法测定硒。该方法使样品消化过程中的硒损失大为减少，使络合萃取时间变短，提高了硒测定的精密度和准确度。回收率达９８．３５％－１０２．１７％。     

微波消解试样氢化物发生-原子荧光光谱法测定黄花菜中硒

硒是目前研究非常活跃的一种人体必需微量元素。由于硒是重金属的天然解毒剂和有希望的抗癌元素，因此在人体中起着非常重要的生理作用。缺硒可导致克山病和大骨节病的发生，而硒过量也可导致硒中毒，引起脱发、脱甲等病症，故硒量的摄人直接影响人的身体健康。作为传统土特产品的黄花菜营养价值高，深受消费者特别是孕妇、婴幼儿等的喜爱，由于黄花菜对土壤中的硒具有一定的富集作用，因此测定黄花菜中硒的含量具有重要的实际意义。     

硒与肿瘤关系研究的进展

概述了近20年来，硒与肿瘤关系的研究进展．包括：环境中的硒水平与肿瘤，肿瘤患者硒水平及其临床意义，硒的抗癌机理和在防治肿瘤上的应用。     

硒与癌症

硒是人体必需微量元素。流行病学调查表明。土壤硒含量，谷物硒含量。食物硒摄入量及人体血硒水平与多种癌症发病率（死亡率）呈负相关，动物实验证实，适量硒具有抑癌抗癌作用，硒抗癌机理研究及人体干预试验进一步说明硒与癌症关系密切。     

Quasi-steady-state laws in enzyme kinetics

To understand how enzymes work is essential for understanding life processes. And, in enzyme kinetics, a fundamental assumption is the so-called Quasi-Steady-State Assumption, which has the history of more than 80 years and has been proven very fruitful in analyzing the equations of enzyme kinetics. Many experimental results and numerical results have shown the validity of the assumption. So, an important problem is if it is always true. If it is always true, then it should be a law, not only an assumption. In this paper, we prove mathematically rigorously that it is indeed always true. Hence, it is a law, and we name it the Quasi-Steady-State Law. Actually, more precisely, we have two Quasi-Steady-State Laws. In one of them quasi-steady state means that the concentration of the enzyme-substrate complex remains approximately constant, and in the other it means that the change rate of the concentration of enzyme-substrate complex is extremely tiny.     

Baseline changes in an isothermal titration microcalorimeter

Summary Isothermal titration microcalorimeters are submerged in an ambience at constant temperature and, this is the reason why there should not be variations in the baseline; but the experimental measures show that, in some cases, it is produced a jump in the baseline after the liquid injection. In this paper, it is studied the origin of this variation of the baseline in order to avoid it, if it is possible, or correct it and thus, to determine with the minimum error the amounts of energy or power developed in the energetic process that is being studied. The experimental results that are shown support the hypothesis that states that the cause of the baseline jump in an isothermal microcalorimeter is the variation of the thermal coupling between the content of the mixture cell and the axis of the stirrer, which is coupled, at the same time, with an area with a temperature slightly lower (in this case) than the thermostat temperature. This jump is independent from the dissipation and it always has the same sign. The magnitude of the baseline jump is variable and it mainly depends on the volume that the liquid content in a cell reaches and the placement of the stirrer within the cell, that can be changed in the handling process.     

Binding: A unifying notion or a pseudoconcept?

Communication between chemists and physicists working in different domains of physical chemistry may sound like a dream, but actually it must be established in order that the whole field may develop in a more efficient way. Binding is a unifying concept whose discussion may make it possible for specialists of different extractions to profit from each other's work. When different specialists speak of binding, they have some intuitive picture in mind. Does it correspond to a unique well-defined concept, or is it just a cover for ignorance? A tentative definition is proposed as a starting point for discussion, but it is also emphasized that only from an open-minded and thorough analysis of the various interpretations it should be possible to make real progress. An example showing very clearly the relationship between the various topics is that of biopolymers, whose understanding depends on the specification of the role of a variety of binding effects, from chemisorption to charge transfer to (one-dimensional) metallic binding.     

Note on the correction of negative measured values if the measurand is nonnegative

Often, the concentration of a substance or the activity of radionuclides in a sample is measured indirectly as the difference between signal and noise, i.e. the difference between the measured value obtained at the sample and that obtained at a sample not containing the substance or the radionuclides (blank sample). The difference can be negative, especially if the concentration or the activity is low. Since a negative measurement result for a nonnegative measurand does not make sense, measured values must be corrected to nonnegative measurement results. Weise et al. and Korun/Maver Modec use a Bayesian approach in order to obtain a nonnegative estimate of the nonnegative measurand. Their estimate is the mean of the posterior distribution. Korun and Zorko modify this estimate slightly and obtain a less biased estimate. In this paper, it is proposed to use the mode of the posterior distribution instead of the mean. The resulting estimate is equal to the measured value if it is nonnegative and 0 if it is negative. This estimate has three advantages: it is extremely easy to calculate, it is less biased than the posterior mean proposed in the other papers, and it does not use the known standard deviation, i.e. it can also be used if the standard deviation is unknown.     

Water and biomolecules: an introduction

As an introduction to the eighth session ‘Water and Biosystems’ of the XVth ‘Horizon in Hydrogen Bond Research’, water molecules are presented with the stress on some elusive points which justify the existence of a session devoted to this topics. Thus, despite its familiar character, H₂O is a molecule which remains still poorly known, especially when it is part of large orderless systems such as liquid water or macromolecules. It is then difficult to observe it. It has consequently for long been ignored despite the fundamental role it may play, in biosystems for instance. The central importance it has in the reactivity of aqueous sytems is evocated, with a particular emphasis on the difference between proton transfers, which are encountered in the chemistry of acid/base in water, and H atoms transfers in cyclic hydrogen bonded structures by tautomerism. Arguments are given which suggest that this latter mechanism is the basic mechanism in bioreactivity and that it is the presence of water molecules that makes it efficient. In the final part the different lectures delivered during this session are presented in the line of this viewpoint.     

Wavepacket Splitting and Two‐Pathway Deactivation in the Photoexcited Visual Pigment Isorhodopsin

Isorhodopsin is the visual pigment analogue of rhodopsin. It shares the same opsin environment but it embeds 9‐cis retinal instead of 11‐cis. Its photoisomerization is three times slower and less effective. The mechanistic rationale behind this observation is revealed by combining high‐level quantum‐mechanical/molecular‐mechanical simulations with ultrafast optical spectroscopy with sub‐20 fs time resolution and spectral coverage extended to the near‐infrared. Whereas in rhodopsin the photoexcited wavepacket has ballistic motion through a single conical intersection seam region between the ground and excited states, in isorhodopsin it branches into two competitive deactivation pathways involving distinct conical intersection funnels. One is rapidly accessed but unreactive. The other is slower, as it features extended steric interactions with the environment, but it is productive as it follows forward bicycle pedal motion.     

The convergence properties of direct energy minimisation with respect to linear coefficients in the MC-LCAO-MO-SCF approach

It is shown that in the LCAO-MO-MC-SCF problem, if the molecular orbital orthonormality constraints are introduced in the manner suggested by Kari and Sutcliffe or indeed by any similar method then the Hessian of the problem with respect to the linear coefficients is singular. The nature of this singularity is analysed and it is shown that in general it is possible to remove it in a level-shifting-like scheme, but that only in certain special cases is this procedure likely to be quickly convergent.     

Physical–chemical analyses of irradiated papayas (Carica papaya L.)

Papaya is cultivated in Espírito Santo State/Brazil and as it stands up to irradiation, it is important to validate this technology, since it is already being applied in some countries. Penetration energy, ratio (relation between soluble solids and titrable acidity) and skin color were evaluated to verify the influence of four different doses of irradiation (0.0, 0.5, 0.75 and 1.00 kGy) on papayas, during 21 days. As a result for the skin color and the penetration energy, it was found that in the first days after irradiation, these variables increased with increase in radiation dose; however, after a time lapse, the tendency inverted and the irradiated fruits had a slower ripening process. For the ratio, a very important variable that it is responsible for the fruit taste, no difference was found between irradiated and the control fruit. Color and texture measurements are dependent on the storage temperature.     

Chemistry and the worm: Caenorhabditis elegans as a platform for integrating chemical and biological research

This Review discusses the potential usefulness of the worm Caenorhabditis elegans as a model organism for chemists interested in studying living systems. C. elegans, a 1 mm long roundworm, is a popular model organism in almost all areas of modern biology. The worm has several features that make it attractive for biology: it is small (<1000 cells), transparent, and genetically tractable. Despite its simplicity, the worm exhibits complex phenotypes associated with multicellularity: the worm has differentiated cells and organs, it ages and has a well-defined lifespan, and it is capable of learning and remembering. This Review argues that the balance between simplicity and complexity in the worm will make it a useful tool in determining the relationship between molecular-scale phenomena and organism-level phenomena, such as aging, behavior, cognition, and disease. Following an introduction to worm biology, the Review provides examples of current research with C. elegans that is chemically relevant. It also describes tools-biological, chemical, and physical-that are available to researchers studying the worm.