从“验证模式”到“辩证模式”的转变——进一步增强高校本科生实验创新能力

为了进一步培养高校本科生实验创新能力,实验教学课程按部就班的"验证模式"亟待转变。如何改进和发展本科生实验课程教学模式已成为高校教师实验教学模式探索的一个重要方向。改变实验条件,辩证看待实验问题,更有利于学生观察、了解实验的本质和核心。这种兼看则明的"辨证模式"是一个很好的发展方向。我们将该种模式应用到硫酸亚铁铵的制备及其铁(Ⅲ)的限量分析实验中。通过控制合成条件可观察到三种不同颜色、光泽度、尺寸的晶体,这些实验结果的差异反过来激发了学生的兴趣和对实验条件与结果的深入讨论。实验课堂效果评价表明:这种教学模式有利于促进学生进行自主探究性学习,培养其辩证性的实验思维,进而增强学生的实践创新能力,提高学生的综合素质。同时,这种模式也可以适当地扩展到其他实验教学实践中。     

"In-house likeness": comparison of large compound collections using artificial neural networks

Binary classification models able to discriminate between data sets of compounds are useful tools in a range of applications from compound acquisition to library design. In this paper we investigate the ability of artificial neural networks to discriminate between compound collections from various sources aiming at developing an "in-house likeness" scoring scheme (i.e. in-house vs external compounds) for compound acquisition. Our analysis shows atom-type based Ghose-Crippen fingerprints in combination with artificial neural networks to be an efficient way to construct such filters. A simple measure of the chemical overlap between different compound collections can be derived using the output scores from the neural net models.     

Ionic Liquids-New "Solutions" for Transition Metal Catalysis

Ionic liquids are salts that are liquid at low temperature (<100 degrees C) which represent a new class of solvents with nonmolecular, ionic character. Even though the first representative has been known since 1914, ionic liquids have only been investigated as solvents for transition metal catalysis in the past ten years. Publications to date show that replacing an organic solvent by an ionic liquid can lead to remarkable improvements in well-known processes. Ionic liquids form biphasic systems with many organic product mixtures. This gives rise to the possibility of a multiphase reaction procedure with easy isolation and recovery of homogeneous catalysts. In addition, ionic liquids have practically no vapor pressure which facilitates product separation by distillation. There are also indications that switching from a normal organic solvent to an ionic liquid can lead to novel and unusual chemical reactivity. This opens up a wide field for future investigations into this new class of solvents in catalytic applications.     

An activated O --> N acyl transfer auxiliary: efficient amide-backbone substitution of hindered "difficult" peptides

Overcoming the phenomenon known as "difficult" synthetic sequences has been a major goal in solid-phase peptide synthesis for over 30 years. In this work the advantages of amide backbone-substitution in the solid-phase synthesis of "difficult" peptides are augmented by developing an activated N(alpha)()-acyl transfer auxiliary. Apart from disrupting troublesome intermolecular hydrogen-bonding networks, the primary function of the activated N(alpha)()-auxiliary was to facilitate clean and efficient acyl capture of large or beta-branched amino acids and improve acyl transfer yields to the secondary N(alpha)()-amine. We found o-hydroxyl-substituted nitrobenzyl (Hnb) groups were suitable N(alpha)()-auxiliaries for this purpose. The relative acyl transfer efficiency of the Hnb auxiliary was superior to the 2-hydroxy-4-methoxybenzyl (Hmb) auxiliary with protected amino acids of varying size. Significantly, this difference in efficiency was more pronounced between more sterically demanding amino acids. The Hnb auxiliary is readily incorporated at the N(alpha)()-amine during SPPS by reductive alkylation of its corresponding benzaldehyde derivative and conveniently removed by mild photolysis at 366 nm. The usefulness of the Hnb auxiliary for the improvement of coupling efficiencies in the chain-assembly of difficult peptides was demonstrated by the efficient Hnb-assisted Fmoc solid-phase synthesis of a known hindered difficult peptide sequence, STAT-91. This work suggests the Hnb auxiliary will significantly enhance our ability to synthesize difficult polypeptides and increases the applicability of amide-backbone substitution.     

"Contact voltage" in nanoparticle/molecule connections

This work presents conclusive evidence that connecting Pt and Co nanoparticles stabilized by an aluminum-organic shell with molecular spacers interacting with this shell can induce notable changes in the electronic structure of the metal. X-ray absorption spectroscopy measurements at the Al K-, the Pt L(III)-, and the Co K-edge provide consistent evidence for this effect. The changes induced by cross-linking with an acidic spacer are discussed in detail as an example to elucidate the mechanism of this effect. It turns out that a reconfiguration of the protection shell that occurs upon networking is responsible for the observed changes.     

A versatile synthetic approach to peptidyl privileged structures using a "safety-catch" linker

Peptidyl privileged structures have been widely used by many groups to discover biologically active molecules. In this context, privileged substructures are used as "hydrophobic anchors", to which peptide functionality is appended to gain specificity. Utilization of this concept has led to the discovery of many different active compounds at a wide range of biological receptors. A synthetic approach to these compounds has been developed on a "safety-catch" linker that allows rapid preparation of large libraries of these molecules. Importantly, amide bond formation/cleavage through treatment with amines is the final step; it is a linker strategy that allows significant diversification to be easily incorporated, and it only requires the inclusion of an amide bond. In addition, chemistry has been developed that permits the urea moiety to be inserted at the N-terminus of the peptide, allowing the same set of amines (either privileged substructures or amino acid analogues) to be used at both the N- and C-termini of the molecule. To show the robustness of this approach, a small library of peptidyl privileged structures were synthesized, illustrating that large combinatorial libraries can be synthesized using these technologies.     

“课前六备、课中六讲、课后六辅”在线课程混合式教学模式研究与实践——以基于“雨课堂+钉钉直播”的中等无机化学课程为例

Taking the online teaching of "inorganic chemistry" course at Dezhou University as an example, the "six steps before class, six steps in class, six steps after class" online course teaching model based on "Rain Class + Dingding Live" and an online "short class" were constructed. The main content and implementation methods of teaching design, teaching process, teaching effect, teaching reflection, teaching evaluation in online course teaching were discussed. It has been proved in practice that this model can effectively improve students' learning interest and enhance teaching effects.     

中国的百岁老人研究Ⅳ.2009,上海成为中国长寿之乡

分析了上海的自然地理、社会经济和人口结构特征,探讨了上海百岁老人的发展规律。结果表明,上海已具备形成长寿之乡的主客观条件,如能保持目前的态势,到2009年底,上海百岁老人数将超过1000人,百岁老人占总人口比例亦将达到百万分之70的中国长寿之乡标准,有望成为人口规模最大,社会经济最发达的中国长寿之乡。     

Hybridization-based unquenching of DNA hairpins on au surfaces: prototypical "molecular beacon" biosensors

There is a keen interest in developing techniques for rapid genetic analysis that do not require labeling of an analyte. Here we demonstrate that fluorophore-tagged DNA hairpins attached to gold films can function as immobilized "molecular beacons". Two DNA hairpins incorporating portions of the Staphlococcus aureus FemA and mecR methicillin-resistance genes were attached to a gold substrate. Upon exposure to the complement, a approximately 26-fold increase in fluorescence intensity was measured corresponding to a 96 +/- 5% quenching efficiency. Studies with nonspecific DNA indicate that DNA hairpins immobilized on a gold surface retain their ability to bind complementary DNA sequences selectively.     

二氧化碳共聚物的合成,性质和应用

二氧化碳是开发中的重要的碳资源,它的一个有效利用方式是和环氧化物等单体共聚生成脂肪族聚碳酸酯。该反应现已能够较顺利地实现。反应中加入第三单体、扩链剂、调节剂,可以使共聚物具有不同的化学结构,以及能随意控制分子量和官能度。在了解反应系统的相平衡特性和共聚动力学以后,可以聚合过程的计算机模拟。使用交联,共混复合或网络互穿等手段,能够使产物具有各种不同的性能。二氧化碳共聚物已在许多方面获得重要的应用,是     

Preparation of highly exfoliated epoxy/clay nanocomposites by "slurry compounding": process and mechanisms

Epoxy/clay nanocomposites with a high degree of exfoliation were achieved using a so-called "slurry-compounding" process with which the dispersed state of clay in water can be successfully transferred to an epoxy matrix. In this process sodium montmorillonite was first exfoliated and suspended in water. This suspension was further treated with acetone to form a clay-acetone slurry followed by chemical modification using silane. The modified slurry was then mixed extensively with epoxy to form epoxy/nanoclay composites. It has been shown that the morphologies of clay before and after curing are quite similar and the exfoliation process is termed "slurry compounding". Furthermore, the amount of organic modifier used is only 5 wt % of clay, in contrast to conventional organoclays which normally contain at least 25-45 wt % of organic surfactant. The resulting epoxy/nanoclay composites exhibit a high degree of clay exfoliation and a better thermal mechanical property.     

Reconstructing NMR spectra of "invisible" excited protein states using HSQC and HMQC experiments

Carr-Purcell-Meiboom-Gill (CPMG) relaxation measurements employing trains of 180 degrees pulses with variable pulse spacing provide valuable information about systems undergoing millisecond-time-scale chemical exchange. Fits of the CPMG relaxation dispersion profiles yield rates of interconversion, relative populations, and absolute values of chemical shift differences between the exchanging states, |Deltaomega|. It is shown that the sign of Deltaomega that is lacking from CPMG dispersion experiments can be obtained from a comparison of chemical shifts in the indirect dimensions in either a pair of HSQC (heteronuclear single quantum coherence) spectra recorded at different magnetic fields or HSQC and HMQC (heteronuclear multiple quantum coherence) spectra obtained at a single field. The methodology is illustrated with an application to a cavity mutant of T4 lysozyme in which a leucine at position 99 has been replaced by an alanine, giving rise to exchange between ground state and excited state conformations with a rate on the order of 1450 s(-1) at 25 degrees C.     

"Imaging" combustion chemistry via multiplexed synchrotron-photoionization mass spectrometry

The combination of multiplexed mass spectrometry with photoionization by tunable-synchrotron radiation has proved to be a powerful tool to investigate elementary reaction kinetics and the chemistry of low-pressure flames. In both of these applications, multiple-mass detection and the ease of tunability of synchrotron radiation make it possible to acquire full sets of data as a function of mass, photon energy, and of the physical dimension of the system, e.g. distance from the burner or time after reaction initiation. The data are in essence an indirect image of the chemistry. The data can be quantitatively correlated and integrated along any of several dimensions to compare to traditional measurements such as time or distance profiles of individual chemical species, but it can also be directly interpreted in image form. This perspective offers an overview of flame chemistry and chemical kinetics measurements that combine tunable photoionization with multiple-mass detection, emphasizing the overall insight that can be gained from multidimensional data on these systems. The low-pressure flame apparatus is capable of providing isomer-resolved mass spectra of stable and radical species as a function of position in the flame. The overall chemical structure of the flames can be readily seen from images of the evolving mass spectrum as distance from the burner increases, with isomer-specific information given in images of the photoionization efficiency. Several flames are compared in this manner, with a focus on identification of global differences in fuel-decomposition and soot-formation pathways. Differences in the chemistry of flames of isomeric fuels can be discerned. The application of multiplexed synchrotron photoionization to elementary reaction kinetics permits identification of time-resolved isomeric composition in reacting systems. The power of this technique is illustrated by the separation of direct and dissociative ionization signals in the reaction of C(2)H(5) with O(2); by the resolution of isomeric products in reactions of the ethynyl (C(2)H) radical; and by preliminary observation of branching to methyl + propargyl products in the self-reaction of vinyl radicals. Finally, prospects for future research using multiplexed photoionization mass spectrometry are explored.     

"Simulating synthesis": ceria nanosphere self-assembly into nanorods and framework architectures

We predict, from computer modeling and simulation in partnership with experiment, a general strategy for synthesizing spherical oxide nanocrystals via crystallization from melt. In particular we "simulate synthesis" to generate full atomistic models of undoped and Ti-doped CeO2 nanoparticles, nanorods, and nanoporous framework architectures. Our simulations demonstrate, in quantitative agreement with experiment [Science 2006, 312, 1504], that Ti (dopant) ions change the shape of CeO2 nanocrystals from polyhedral to spherical. We rationalize this morphological change by elucidating, at the atomistic level, the mechanism underpinning its synthesis. In particular, CeO2 nanocrystals can be synthesized via crystallization from melt: as a molten (undoped) CeO2 nanoparticle is cooled, nucleating seeds spontaneously evolve at the surface and express energetically stable [111] facets to minimize the energy. As crystallization proceeds, the [111] facets grow, thus facilitating a polyhedral shape. Conversely, when doped with Ti, a (predominantly) TiO2 shell encapsulates the inner CeO2 core. This shell inhibits the evolution of nucleating seeds at the surface thus rendering it amorphous during cooling. Accordingly, crystallization is forced to proceed via the evolution of a nucleating seed in the bulk CeO2 region of the nanoparticle, and as this seed grows, it remains surrounded by amorphous ions, which "wrap" around the core so that the energies for high-index facets are drastically reduced; these amorphous ions adopt a spherical shape to minimize the surface energy. Crystallization emanates radially from the nucleating seed, and because it is encapsulated by an amorphous shell, the crystallization front is not compelled to express energetically favorable surfaces. Accordingly, after the nanoparticle has crystallized it retains this spherical shape. A typical animation showing the crystallization (with atomistic detail) is available as Supporting Information. From this data we predict that spherical oxide nanocrystals can be synthesized via crystallization from melt in general by suppressing nucleating seed evolution at the surface thus forcing the nucleating seed to spontaneously evolve in the bulk. Nanospheres can, similar to zeolitic classifications, constitute Secondary Building Units (SBUs) and can aggregate to form nanorods and nanoporous framework architectures. Here we have attempted to simulate this process to generate models for CeO2 and Ti-doped CeO2 nanorods and framework architectures. In particular, we predict that Ti doping will "smooth" the surfaces: hexagonal prism shaped CeO2 nanorods with [111] and [100] surfaces become cylindrical, and framework architectures change from facetted pores and channels with well-defined [111] and [100] surfaces to "smooth" pores and channels (expressing both concave and convex curvatures). Such structures are difficult to characterize using, for example, Miller indices; rather we suggest that these new structural materials may be better described using minimal surfaces.     

CeO_2@NiCo_2O_4 nanowire arrays on carbon textiles as high performance cathode for Li-O_2 batteries

The successful development of Li-O_2 battery technology depends on developing a stable and efficient cathode. As an important step toward this goal, for the first time, we report the development of CeO_2 nanoparticles modified NiCo_2O_4 nanowire arrays(NWAs) grown on the carbon textiles as a new carbon-free and binder-free cathode system. In this study, the Li-O_2 battery with the CeO_2@NiCo_2O_4 NWAs has exhibited much reduced overpotentials, a high discharge capacity, an improved cycling stability,outperforming the Li-O_2 battery with NiCo_2O_4 NWAs. These improvements can be attributed to both the tailored morphology of discharge product and improved oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) activity after CeO_2 NPs deposition. To a considerable extent, this idea of cathode construction including structure design and composition optimization can provide guidance for further researches in developing more powerful cathode for Li-O_2 battery.     

On the nature of organic catalysis "on water"

A molecular origin of the striking rate increase observed in a reaction on water is studied theoretically. A key aspect of the on-water rate phenomenon is the chemistry between water and reactants that occurs at an oil-water phase boundary. In particular, the structure of water at the oil-water interface of an oil emulsion, in which approximately one in every four interfacial water molecules has a free ("dangling") OH group that protrudes into the organic phase, plays a key role in catalyzing reactions via the formation of hydrogen bonds. Catalysis is expected when these OH's form stronger hydrogen bonds with the transition state than with the reactants. In experiments more than a 5 orders of magnitude enhancement in rate constant was found in a chosen reaction. The structural arrangement at the "oil-water" interface is in contrast to the structure of water molecules around a small hydrophobic solute in homogeneous solution, where the water molecules are tangentially oriented. The latter implies that a breaking of an existing hydrogen-bond network in homogeneous solution is needed in order to permit a catalytic effect of hydrogen bonds, but not for the on-water reaction. Thereby, the reaction in homogeneous aqueous solution is intrinsically slower than the surface reaction, as observed experimentally. The proposed mechanism of rate acceleration is discussed in light of other on-water reactions that showed smaller accelerations in rates. To interpret the results in different media, a method is given for comparing the rate constants of different rate processes, homogeneous, neat and on-water, all of which have different units, by introducing models that reduce them to the same units. The observed deuterium kinetic isotope effect is discussed briefly, and some experiments are suggested that can test the present interpretation and increase our understanding of the on-water catalysis.     

Deformation of a "rigid" molecule in self-assembled nanostructures

A simple spirobifluorene molecule with pseudotetrahedral structure was investigated for its supposed conformational resilience upon adsorption. Through deposition at room temperature of this molecule on a Cu(111) surface and subsequent observation at 5 K with an ultrahigh vacuum scanning tunneling microscope, this "rigidity" upon physisorption is confirmed. However, an unexpected chemisorbed state was also found with the molecules arranged in trimers. The unique coexistence of physisorbed and chemisorbed states on the same substrate is thus demonstrated at the early stage of self-assembly.