Water as dual functional cocatalyst: A theoretical study on the mechanism of direct aldol reaction on water catalyzed by a leucine derivative

The role of water and stereoselectivity in the direct syn-aldol reaction involving 3-pentanone and 4-nitrobenzaldehyde catalyzed by amino acid derivatives on water has been investigated by density functional theory. Calculations indicate that the formation of intermediate enamine is the rate determining step via a three-step process with activation enthalpies of 50 kcal/mol in the gas phase and 21 kcal/mol in the presence of water. The subsequent nucleophilic addition of enamine to aldehyde is relatively easier with activation enthalpies below 10 kcal/mol both in the gas phase and in the presence of water. The diastereoselective formation of syn- and anti-aldol products results from the preferential formation of Z-enamine to E-enamine, kinetically and thermodynamically. The enantioselectivity of both syn- and anti-products is controlled by the steric repulsive interactions between the amino alcohol moiety of catalyst and the phenyl ring of aldehyde. Calculations show that water molecule can act as a proton shuttle in the proton-transport catalytic processes. The water-assisted proton-transfer is very efficient to reduce the activation barriers via protonation and deprotonation in the formation of C–N and C–C bonds, dehydration, and β-elimination processes by inhibiting the generation of zwitterionic transition states. The theoretical discoveries indicate that in the present proton-transport assistance, the amino alcohol moiety of the catalyst plays a critical role as hydrogen bond donor to anchor substrates with carbonyl group close to the amine or enamine moiety so that the water molecule can bridge the NH of amine and the oxygen of carbonyl by hydrogen bonding interaction around the reactive site to activate the reactants and promote the reaction effectively.     

Aluminium in Alzheimer’s disease: are we still at a crossroad?

Aluminium, an environmentally abundant non-redox trivalent cation has long been implicated in the pathogenesis of Alzheimers disease (AD). However, the definite mechanism of aluminium toxicity in AD is not known. Evidence suggests that trace metal homeostasis plays a crucial role in the normal functioning of the brain, and any disturbance in it can exacerbate events associated with AD. The present paper reviews the scientific literature linking aluminium with AD. The focus is on aluminium levels in brain, region-specific and subcellular distribution, its relation to neurofibrillary tangles, amyloid beta, and other metals. A detailed mechanism of the role of aluminium in oxidative stress and cell death is highlighted. The importance of complex speciation chemistry of aluminium in relation to biology has been emphasized. The debatable role of aluminium in AD and the cross-talk between aluminium and genetic susceptibility are also discussed. Finally, it is concluded based on extensive literature that the neurotoxic effects of aluminium are beyond any doubt, and aluminium as a factor in AD cannot be discarded. However, whether aluminium is a sole factor in AD and whether it is a factor in all AD cases still needs to be understood.Received 22 July 2004; received after revision 3 September 2004; accepted 16 September 2004     

岩土工程系统失效性的数值计算法

介绍了国际结构安全度联合委员会推荐的用于结构可靠性计算的改进型一次二阶矩法，将其推广到岩土工程系统，并给出算例。     

The antigenicity of sheep follicle-stimulating hormone

Résumé L'hormone folliculaire ovine (FSH) purifiée révèle la présence d'antigènes d'hormone lutéinare (LH) et de ceux du sérum ovin. L'antigène LH fait partie de ces derniers. L'absorption des antigènes d'antisérum de l'FSH avec le sérum ovin, élimine l'antigène qui accompagne ceux de l'hormone folliculaire ovine, de l'hormone lutéinaire et du sérum ovin. Ce fait suggère que le sérum ovin agit comme l'hormone lutéinaire. L'antisérum d'hormone lutéinaire est capable d'éliminer l'antigène d'hormone lutéinaire et les antigènes d'hormone folliculaire ovine. Cela signifie que l'un des andigènes du sérum ovin qui est présent aussi dans l'hormone folliculaire ovine, provient de l'hormone lutéinaire. Nos études en cours tendent à vérifier ce fait.     

Maltase activity in human semen

Résumé Nous avons étudié l'activité de la maltase dans la semence humaine en utilisant la technique de la chromatographie sur papier. L'activité de la maltase est exprimée en mg de glucose liberé du substrat de maltose. L'activité de la maltase est spécialement associée avec le plasma séminal. Elle est maximale au pH 5.0. Nous avons aussi étudié les activités de la maltase dans des plasma séminaux des êtres humains, des bufs, des coqs et des lapins. Nous avons trouvé que l'activité de la maltase est la plus haute chez l'homme. En comparaison avec les autres substrats de sucre, l'activité du plasma séminal se montre plus haute dans la maltose.     

The effect of electrical stimulation of olfactory tract on the nucleus preopticus in the catfishHeteropneustes fossilis (Bloch)

Résumé Chez leHeteropneustes fossilis normal le périkaryon des neurons du noyau préoptique montrent une grande accumulation de substance neurosécrétaire AF-positive. Stimulation électrique du nerf olfacteur pendant une minute menait à une dégranulation incomplète, tandis qu'un traitement de dux minutes produisait un épuisement presque complet de la substance neurosécrétoire. Les neurons de la portion magnocellulaire du noyau préoptique paraissent répondre plus rapidement que ceux de la portion parvocellulaire.     

Remote intelligent identification system of structural damage

The focus of this paper is to build the damage identify system, which performs “system identification“ to detcct the positions and extents of structural damages. The identification of structural damage can be characterized as a nonlinear process which linear prediction models such as linear regression are not suitable. However. neural network techniques may provide an effective tool for system identification. The method of damage identification using the radial basis function neural network (P, BFNN) is presented in this paper. Using this method, a simple reinforced concrete structure has been tested both in the absence and presence of noise. The resuits show that the RBFNN identification technology can he used with related success for the solution of dynamic damage identification problems, even in the presence of a noisy identify data. Furthermore, a remote identification system based on that is set up with Java Technologies.     

Angiotensin-converting enzyme 2 protects from severe acute lung failure

Acute respiratory distress syndrome (ARDS), the most severe form of acute lung injury, is a devastating clinical syndrome with a high mortality rate (30-60%) (refs 1-3). Predisposing factors for ARDS are diverse and include sepsis, aspiration, pneumonias and infections with the severe acute respiratory syndrome (SARS) coronavirus. At present, there are no effective drugs for improving the clinical outcome of ARDS. Angiotensin-converting enzyme (ACE) and ACE2 are homologues with different key functions in the renin-angiotensin system. ACE cleaves angiotensin I to generate angiotensin II, whereas ACE2 inactivates angiotensin II and is a negative regulator of the system. ACE2 has also recently been identified as a potential SARS virus receptor and is expressed in lungs. Here we report that ACE2 and the angiotensin II type 2 receptor (AT2) protect mice from severe acute lung injury induced by acid aspiration or sepsis. However, other components of the renin-angiotensin system, including ACE, angiotensin II and the angiotensin II type 1a receptor (AT1a), promote disease pathogenesis, induce lung oedemas and impair lung function. We show that mice deficient for Ace show markedly improved disease, and also that recombinant ACE2 can protect mice from severe acute lung injury. Our data identify a critical function for ACE2 in acute lung injury, pointing to a possible therapy for a syndrome affecting millions of people worldwide every year.     

浅议工科院校经管类学生的能力培养

针对工科院校经管类专业学生能力培养方面较为薄弱的状况，论述了通过重视基础理论、加强工程背景、强调能力培养、开展技能培训等措施来改善学生能力培养与质量的必要性。     

Nanotube electronics: large-scale assembly of carbon nanotubes

Nanoscale electronic devices made from carbon nanotubes, such as transistors and sensors, are much smaller and more versatile than those that rely on conventional microelectronic chips, but their development for mass production has been thwarted by difficulties in aligning and integrating the millions of nanotubes required. Inspired by biomolecular self-assembly processes, we have created chemically functionalized patterns on a surface, to which pre-grown nanotubes in solution can align themselves in huge numbers. This method allows wafer-scale fabrication of millions of carbon-nanotube circuits with single-nanotube precision, and may enable nanotube-based devices, such as computer chips and high-density sensor arrays, to be produced industrially.