Reversible molecular adsorption based on multiple-point interaction by shrinkable gels

A general approach is presented for creating polymer gels that can recognize and capture a target molecule by multiple-point interaction and that can reversibly change their affinity to the target by more than one order of magnitude. The polymers consist of majority monomers that make the gel reversibly swell and shrink and minority monomers that constitute multiple-point adsorption centers for the target molecule. Multiple-point interaction is experimentally proven by power laws found between the affinity and the concentration of the adsorbing monomers within the gels.     

Reversible optical transcription of supramolecular chirality into molecular chirality

In nature, key molecular processes such as communication, replication, and enzyme catalysis all rely on a delicate balance between molecular and supramolecular chirality. Here we report the design, synthesis, and operation of a reversible, photoresponsive, self-assembling molecular system in which molecular and supramolecular chirality communicate. It shows exceptional stereoselectivity upon aggregation of the molecules during gel formation with the solvent. This chirality is locked by photochemical switching, a process that is subsequently used to induce an inverted chiral supramolecular assembly as revealed by circular dichroism spectroscopy. The optical switching between different chiral aggregated states and the interplay of molecular and supramolecular chirality offer attractive new prospects for the development of molecular memory systems and smart functional materials.     

Detection of molecular oxygen on Mars

Molecular oxygen was detected in martian spectra near 7635 angstroms and its abundance measured both during and after the 1971 dust storm. Its column abundance in the clear martian atmosphere is about 10.4 +/- 1.0 centimeters amagat, giving a mixing ratio of molecular oxygen to carbon dioxide of 1.3 x 10-(3). The mixing ratio of molecular oxygen to carbon monoxide (1.4 +/- 0.3) is quite different from the value of 0.5 that would result from the photolysis of a pure carbon dioxide atmosphere, which indicates that there is or was a net source of oxygen relative to carbon (probably water) in the martian atmosphere.     

Reversible combination of carbon monoxide with a synthetic oxygen carrier complex

Chlorocarbonyl-bis(triphenylphosphine)iridium(I), in solution, reacts reversibly with carbon monoxide under normal conditions, one molecule per metal atom. Formation of a 1 : 1 metal complex-CO adduct is verified by CO absorption measurements and the infrared spectrum of the adduct measured in situ. The spectrum suggests that the metal-C-O bonding is of the type found in conventional metal carbonyl.     

Structural aspects of reversible molecular oxygen uptake

The system IrX(CO)[P(C(6)H(5))(3)](2) in benzene solution adds mo lecular oxygen reversibly if X is chlorine and irreversibly if X is iodine. The crystal structure of the complex IrIO(2)(CO)[P(C(6)H(5))(3)](2) * CH(2)Cl(2) is reported here and compared with a previous study of the structure of IrClO(2)(CO)[P(C(6)H(5))(3)](2). The O-O bond length is 1.47 +/- 0.02 angstroms in the irreversibly oxygenated iodo-compound and 1.30 +/- 0.03 angstroms in the reversibly oxygenated chloro compound.     

气相分子吸收光谱法测定海水中的化学需氧量

国标中采用传统的碱性高锰酸钾手工分析方法分析海水中的化学需氧量,耗时长、操作复杂、劳动强度大。针对以上缺点,本文采用气相分子吸收光谱法测定海水中的化学需氧量。结果表明:该方法线性相关系数为0.999 9,检出限为0.08 mg/L,相对标准偏差为2.8%～3.6%,相对误差为0.66%～3.51%;通过与国标手工方法比对,分析结果具有良好的一致性。该方法不但可以满足相关国家标准要求,还具有系统误差小、操作简单、分析快速准确的优点,大大提升了工作效率。     

A cytochrome C oxidase model catalyzes oxygen to water reduction under rate-limiting electron flux

We studied the selectivity of a functional model of cytochrome c oxidase's active site that mimics the coordination environment and relative locations of Fe(a3), Cu(B), and Tyr(244). To control electron flux, we covalently attached this model and analogs lacking copper and phenol onto self-assembled monolayer-coated gold electrodes. When the electron transfer rate was made rate limiting, both copper and phenol were required to enhance selective reduction of oxygen to water. This finding supports the hypothesis that, during steady-state turnover, the primary role of these redox centers is to rapidly provide all the electrons needed to reduce oxygen by four electrons, thus preventing the release of toxic partially reduced oxygen species.     

Reversible Aggregation of alpha-Gliadin to Fibrils

Acetic-acid (0.01 molar) extracts of wheat flour contain fibrils of alpha-gliadin which are about 80 angstroms thick and up to several thousand angstroms long. These fibrils dissociate to globular protein subunits at very low ionic strength and low pH. The fibrils can be reformed by increasing the pH to 5.1 and the ionic strength to about 0.005.     

分子模拟法研究聚多巴胺与色氨酸的分子印迹手性识别机理

【目的】考察聚多巴胺(PDA)与L-色氨酸(L-Trp)、D-色氨酸(D-Trp)分子间的相互作用差异,以揭示分子印迹手性识别的机理。【方法】采用计算机分子模拟法研究以手性色氨酸为模板,聚多巴胺为功能单体的分子印迹预组装体系。首先通过构象搜索,获得聚多巴胺四聚体可能的稳定结构;然后采用分子对接研究手性色氨酸分子与多巴胺的作用形式;最后通过量子化学方法,从电子结构层面上分析L-Trp、D-Trp分子与聚多巴胺结合力差异产生的原因。【结果】Trp与PDA的结合力以氢键作用为主,L-Trp与PDA的氢键作用强于D-Trp;L-Trp与PDA的复合物(L-Trp-PDA)的前线轨道能级差比D-Trp-PDA的大,且前者的结合更紧密,弱相互作用更强。【结论】分子模拟方法使用相对简便,计算速度快,适用于研究分子印迹手性识别机理。     

外源过氧化氢处理对采后荔枝褐变及活性氧代谢的影响

【目的】研究外源过氧化氢（H2O2）处理对采后荔枝褐变及活性氧代谢的影响,为荔枝采后保鲜提供途径,以期提高果实的贮藏品质。【方法】以清水处理为对照（CK）,采用不同浓度（1、5和10mmol/L）的外源H2O2浸泡荔枝3min,在4℃下冷藏放置,每隔3d取样一次,进行失重率、褐变指数、丙二醛（MDA）含量、细胞膜透性、...     

High rates of oxygen reduction over a vapor phase-polymerized PEDOT electrode

The air electrode, which reduces oxygen (O2), is a critical component in energy generation and storage applications such as fuel cells and metal/air batteries. The highest current densities are achieved with platinum (Pt), but in addition to its cost and scarcity, Pt particles in composite electrodes tend to be inactivated by contact with carbon monoxide (CO) or by agglomeration. We describe an air electrode based on a porous material coated with poly(3,4-ethylenedioxythiophene) (PEDOT), which acts as an O2 reduction catalyst. Continuous operation for 1500 hours was demonstrated without material degradation or deterioration in performance. O2 conversion rates were comparable with those of Pt-catalyzed electrodes of the same geometry, and the electrode was not sensitive to CO. Operation was demonstrated as an air electrode and as a dissolved O2 electrode in aqueous solution.     

Electrolytic univalent reduction of oxygen in aqueous solution demonstrated with superoxide dismutase

The superoxide anion, generated electrolytically at a platinum electrode in buffered aqueous solution, was detected by its ability to cause the oxidation of epinephrine to adrenochrome. The rate of electrolytic oxidation of epinephrine varied with the applied potential in a manner reminiscent of an oxygen reduction half wave. This oxidation of epinephrine was dependent upon the presence of oxygen and was completely inhibitable by superoxide dismutase. It may be concluded that superoxide radicals, generated at the electrode, diffuse into the solution to an extent which allows reaction with small molecules such as epinephrine or with enzymes such as superoxide dismutase.     

Reversible unfolding of single RNA molecules by mechanical force

Here we use mechanical force to induce the unfolding and refolding of single RNA molecules: a simple RNA hairpin, a molecule containing a three-helix junction, and the P5abc domain of the Tetrahymena thermophila ribozyme. All three molecules (P5abc only in the absence of Mg2+) can be mechanically unfolded at equilibrium, and when kept at constant force within a critical force range, are bi-stable and hop between folded and unfolded states. We determine the force-dependent equilibrium constants for folding/unfolding these single RNA molecules and the positions of their transition states along the reaction coordinate.     

Runaway growth of planetary embryos facilitated by massive bodies in a protoplanetary disk

About 30% of detected extrasolar planets exist in multiple-star systems. The standard model of planet formation cannot easily accommodate such systems and has difficulty explaining the odd orbital characteristics of most extrasolar giant planets. We demonstrate that the formation of terrestrial-size planets may be insulated from these problems, enabling much of the framework of the standard model to be salvaged for use in complex systems. A type of runaway growth is identified that allows planetary embryos to form by a combination of nebular gas drag and perturbations from massive companions-be they giant planets, brown dwarfs, or other stars.     

Singlet molecular oxygen from superoxide anion and sensitized fluorescence of organic molecules

The superoxide anion, O(2)-, evolves singlet molecular oxygen in dimethylsulfoxide solution. Pronounced water quenching of superoxide-sensitized luminescence is indicative of the preferential generation of the (1)sigma(g)+ state. Recent identification of O(2)- in the xanthine oxidase system suggests that the generation of singlet oxygen may also occur in enzymatic systems.     

Reversible Section of the Brain by a Wall of Cold

A fork made up of hollow tubing may be chronically implanted in the cat's brain. When cooling fluid is pumped through this fork a reversible plane lesion is formed. This technique permits analysis of functional parts of the nervous system in unanesthetized animals.     

Rapid total destruction of chlorophenols by activated hydrogen peroxide

A practical, inexpensive, green chemical process for degrading environmental pollutants is greatly needed, especially for persistent chlorinated pollutants. Here we describe the activation of hydrogen peroxide by tetraamidomacrocylic ligand (TAML) iron catalysts, to destroy the priority pollutants pentachlorophenol (PCP) and 2,4,6-trichlorophenol (TCP). In water, in minutes, under ambient conditions of temperature and pressure, PCP and TCP are completely destroyed at catalyst:substrate ratios of 1:715 and 1:2000, respectively. The fate of about 90% of the carbon and about 99% of the chlorine has been determined in each case. Neither dioxins nor any other toxic compounds are detectable products, and the catalysts themselves show low toxicity.     

Reversible inhibition of mammary gland growth by transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) can stimulate or inhibit growth of cells in vitro, as well as induce the transformed phenotype. Although widely distributed in animal tissue, the effects of TGF-beta in vivo are largely unknown, and a physiological role for the peptide hormone has not been demonstrated. The effect of TGF-beta on developing epithelial tissue in situ was studied by using slow-release plastic pellets containing TGF-beta to treat developing mouse mammary gland. Powerful inhibition of mammary growth and morphogenesis was observed. This growth-inhibited mammary tissue was histologically normal, and the inhibitory effect was fully reversible. Under the conditions of these experiments, TGF-beta displayed many of the characteristics expected of a physiologically active growth-regulatory molecule.     

Evolution of cell recognition by viruses

Evolution of receptor specificity by viruses has several implications for viral pathogenesis, host range, virus-mediated gene targeting, and viral adaptation after organ transplantation and xenotransplantation, as well as for the emergence of viral diseases. Recent evidence suggests that minimal changes in viral genomes may trigger a shift in receptor usage for virus entry, even into the same cell type. A capacity to exploit alternative entry pathways may reflect the ancient evolutionary origins of viruses and a possible role as agents of horizontal gene transfers among cells.     

Reversible inhibition of beef heart cytochrome c oxidase by polyionic macromolecules

The basic proteins protamine (sulfate), histone, lysozyme, and ribonuclease were found to be potent inhibitors of mammalian heart muscle cytochromec oxidase. Their inhibitions were completely reversed in the presence of a strongly anionic polyglucose sulfate. With fresh rat heart muscle homogenates, Keili and Hartree type of beef heart muscle particulates, and deoxycholate-solubilized oxidase preparations, the reversible nature of the phenomenon was demonstrated with manometric and spectrophotometric assays for cytochrome c oxidase.