"Alpha"-, "beta"- and "delta"-anhydrodigitoxigenin

The syntheses of 3β-hydroxy-5β-carda-14, 20:22-dienolide (= «β»-anhydro-), 3β-hydroxy-5β-carda-8:14, 20:22-dienolide (= «α»-anhydro-) and «δ»-anhydro-digitoxigenin (= probably 3β-hydroxy-5β, 14β-carda-8, 20:22-dienolide) by the best ways known to date, have been described. «δ»-Anhydro-digitoxigenin represents the thermodynamically most stable isomer. In this isomer the double bond in position 8 is unaffected by hydrogenation with Pt in acetic acid; with perbenzoic acid an epoxide results from which, on hydrogenation, the double bond can be regenerated in its original position. Analogous reactions are known to occur in the 8:14-epoxides.     

"Turn-on" fluorescent sensing with "reactive" probes

Chemical probes are valuable tools for the investigation of biochemical processes, diagnosis of disease markers, detection of hazardous compounds, and other purposes. Therefore, the development of chemical probes continues to grow through various approaches with different disciplines and design strategies. Fluorescent probes have received much attention because they are sensitive and easy-to-operate, in general. To realize desired selectivity toward a given analyte, the recognition site of a fluorescent probe is designed in such a way to maximize the binding interactions, usually through weak molecular forces such as hydrogen bonding, toward the analyte over other competing ones. In addition to such a supramolecular approach, the development of fluorescent probes that sense analytes through chemical reactions has witnessed its usefulness for achieving high selectivity, in many cases, superior to that obtainable by the supramolecular approach. Creative incorporations of the reactive groups to latent fluorophores have provided novel chemical probes for various analytes. In this feature article, we overview the recent progress in the development of turn-on fluorescent probes that are operating through chemical reactions triggered by target analytes. Various chemical reactions have been implemented in the development of many reactive probes with very high selectivity and sensitivity toward target analytes. A major emphasis has been focused on the type of chemical reactions utilized, with the hope that further explorations can be made with new chemical reactions to develop reactive probes useful for various applications.     

Making "wheels" and "cubes" from triangles

[Mn(IV)Mn(II)3] triangular units directed by the presence of tripodal alcohols self-assemble in the presence of azide and acetate ligands to form either a [Mn24] "wheel" or a [Mn32] "cube".     

化“材”为“筑”

Chemistry is a central, practical and creative discipline. The development of chemistry plays an important role in the progress of science and society, as well as the improvement of the quality of human life. This paper introduces the chemical knowledge of stone, concrete, glass and other inorganic nonmetallic building materials by the anthropomorphically story. Taking nanomaterials as an example, the prospect of building materials development in the future is put forward.     

The Immobiline family: from "vacuum" to "plenum" chemistry.

We list here a total of 17 acrylamido acids and bases as potential buffers and titrants for isoelectric focusing separations in immobilized pH gradients. The chemistry of these compounds is reviewed and general guidelines are given for their proper use. In particular, it is shown that the most delicate compounds are the basic species, since they can undergo several degradation pathways, including: (i) spontaneous hydrolysis to acrylic acid and a diamine; (ii) spontaneous autopolymerization to oligomers and n-mers; (iii) oxidation to N-oxides during the persulfate polymerization step. A hydrophobicity scale has been constructed, by partitioning the deprotonated species in water/1-octanol phases. A scale of resistance to alkaline hydrolysis for the basic acrylamido buffers is also given, followed by general consideration on the structure/stability relationship of these chemicals.     

A self-threaded "molecular 8"

A new type of [1]rotaxanes containing two aliphatic bridges between axle and wheel is obtained in 39% yield in a one-step synthesis starting from a [2]rotaxane which contained one sulfonamide group each in both the wheel and the axle. Temperature controlled chemoselective substitution reactions first at these sulfonamide nitrogens and then subsequently at the various other carboxamide nitrogens in the wheel and axle give rise to the formation of an isomeric mixture of three double-bridged [1]rotaxanes which could be separated by HPLC. Structure determination of the main product 3a was possible by NMR experiments supported by molecular modeling calculations. Using different reaction conditions, a double-substituted but not yet bridged [2]rotaxane 4 could be isolated as an intermediate giving further evidence for the assigned structure of 3a and the way of its formation. The shape of this double-bridged [1]rotaxane 3a reminds of a self-intertwining chiral "molecular 8", in which any possible racemization due to deslipping is hindered by the two stoppers originating from the former rotaxane axle. Hence, to the best of our knowledge this is the first example of a molecule in which both concepts, cycloenantiomerism and helical chirality, are realised in one structure. Enantiomer separation of the main product was possible by further HPLC using chiral stationary phases. The Cotton effects of the circular dichrograms are different to those of the already synthesized [1]rotaxanes bearing just one aliphatic bridge between axle and wheel.     

Fabrication of "roll-off" and "sticky" superhydrophobic cellulose surfaces via plasma processing

Most of the artificial superhydrophobic surfaces that have been fabricated to date are not biodegradable, renewable, or mechanically flexible and are often expensive, which limits their potential applications. In contrast, cellulose, a biodegradable, renewable, flexible, inexpensive, biopolymer which is abundantly present in nature, satisfies all the above requirements, but it is not superhydrophobic. Superhydrophobicity on cellulose paper was obtained by domain-selective etching of amorphous portions of the cellulose in an oxygen plasma and subsequently coating the etched surface with a thin fluorocarbon film deposited via plasma-enhanced chemical vapor deposition using pentafluoroethane as a precursor. Variation of plasma treatment yielded two types of superhydrophobicity : "roll-off" (contact angle (CA), 166.7 degrees +/- 0.9 degrees ; CA hysteresis, 3.4 degrees +/- 0.1 degrees ) and "sticky" (CA, 144.8 degrees +/- 5.7 degrees ; CA hysteresis, 79.1 degrees +/- 15.8 degrees ) near superhydrophobicity. The nanometer scale roughness obtained by delineating the internal roughness of each fiber and the micrometer scale roughness which is inherent to a cellulose paper surface are robust when compared to roughened structures created by traditional polymer grafting, nanoparticle deposition, or other artificial means.     

Comparison of new microemulsion prepared "Pt-in-Ceria" catalyst with conventional "Pt-on-Ceria" catalyst for water-gas shift reaction

New "Pt-in-CeO(2)" catalyst prepared by microemulsion method is shown to give higher activity for a water-gas shift reaction but with no formation of CH(4), the side product from hydrogenation of carbon oxides using a hydrogen-rich reformate as compared to conventional "Pt-on-CeO(2)" catalysts. Detailed characterization by DRIFT analysis and temperature programmed reduction presented in this work clearly suggest the ceria coverage on Pt inhibits the metal from forming a strong CO adsorption.     

Hydrogen evolution from organic "hydrides"

Benzimidazolines (dihydrobenzimidazoles) are shown for the first time to eliminate hydrogen (H2) by catalyzed reaction with protic compounds.     

尼古丁的“口供”

This is a piece of confession made by Nicotine where its molecular structure and some physiological functions are introduced. The toxicity of Nicotine on human body has been revealed, based on an authentic suicide case. Combined with medical knowledge, the process of Nicotine intoxication, the mechanism of smoking addition and Nicotine's negative effect on human body, have been presented. Ultimately non-smoking advice is suggested for the sake of human health.     

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。     

Surfactant-free "emulsions" generated by freeze-thaw

The stability ofsurfactantless dispersions of surface chemically pure alkanes was studied in the presence and absence of dissolved gas. It was found that simply freezing and thawing a sample of oil and water results in a dispersion. A mechanism based on fingering of the insoluble oil into the aqueous phase, due to local surface tension gradients, followed by separation and nucleation into droplets, is proposed to account for this observation.     

How to find "missing" genes

Assigning function to "new" proteins is frequently the rate-determining step for deciphering metabolic pathways and regulatory networks. Osterman and Begley break down this barrier by demonstrating that comparative analyses of microbial genomes is a powerful strategy for identifying pathway components.     

"Volatilizable" supports for high-throughput organic synthesis

The concepts and use of "volatilizable" solid supports are presented. Such supports, which are completely removed by volatilization following decomposition, improve the efficiency of the solid-phase synthesis of both individual and mixtures of low-molecular weight acyclic and heterocyclic compounds as well as peptides, peptidomimetics, and protected peptide fragments. The "volatilizable" silica-based solid supports and linkers used to illustrate this concept were found to be completely removed by their decomposition and ultimate "volatilization" during the final cleavage step of synthetic process to yield solely the desired synthetic product(s) in the final reaction vessel.     

Rhodium-mediated stereoselective polymerization of "carbenes"

Unprecedented rhodium-catalyzed stereoselective polymerization of "carbenes" from ethyl diazoacetate (EDA) to give high molecular mass poly(ethyl 2-ylidene-acetate) is described. The mononuclear, neutral [(N,O-ligand)M(I)(cod)] (M = Rh, Ir) catalytic precursors for this reaction are characterized by (among others) single-crystal X-ray diffraction. These species mediate formation of a new type of polymers from EDA: carbon-chain polymers functionalized with a polar substituent at each carbon of the polymer backbone. The polymers are obtained as white powders with surprisingly sharp NMR resonances. Solution and solid state NMR data for these new polymers reveal a highly stereoregular polymer, with a high degree of crystallinity. The polymer is likely syndiotactic. Material properties are very different from those of atactic poly(diethyl fumarate) polymer obtained by radical polymerization of diethyl fumarate. Other diazoacetates are also polymerized. Further studies are underway to reveal possible applications of these new materials.     

Synthesis of "solid solution" and "core-shell" type cobalt--platinum magnetic nanoparticles via transmetalation reactions

In this article, we report the synthesis of "solid solution" and "core-shell" types of well-defined Co--Pt nanoalloys smaller than 10 nm. The formation of these alloys is driven by redox transmetalation reactions between the reagents without the need for any additional reductants. Also the reaction proceeds selectively as long as the redox potential between the two metals is favorable. The reaction between Co(2)(CO)(8) and Pt(hfac)(2) (hfac = hexafluoroacetylacetonate) results in the formation of "solid solution" type alloys such as CoPt(3) nanoparticles. On the other hand, the reaction of Co nanoparticles with Pt(hfac)(2) in solution results in "Co(core)Pt(shell)" type nanoalloys. Nanoparticles synthesized by both reactions are moderately monodispersed (sigma < 10%) without any further size selection processes. The composition of the alloys can also be tuned by adjusting the ratio of reactants. The magnetic and structural properties of the obtained nanoparticles and reaction byproducts are characterized by TEM, SQUID, UV/vis, IR, EDAX, and XRD.     

Nonlinear electrokinetics and "superfast" electrophoresis

Nonlinear and nonequilibrium electrophoresis of spherical particles of radius a is shown to be possible when the solid surface allows field or current penetration. At low particle Peclet numbers, transient capacitative charging occurs until the surface polarization completely screens the external field. For a DC applied field [see text], the resulting electrokinetic velocity reaches Dukhin's maximum value of [formula: see text], where [see text] and mu are the liquid permittivity and viscosity. At high Peclet numbers, electroosmotic convection of the electroneutral bulk stops the transient charging before complete field-line exclusion. For an ion-selective and conducting spherical granule, the polarization is then determined by the steady-state Ohmic current driven by the penetrated external field. The high-Peclet electrokinetic velocity is lower, diffusivity-dependent and scales as [see text].     

Wettability increase by "corona" ionization

Experiments showing an increase in the wettability of a hydrophobic surface when using corona air ionization are shown. Photoluminiscence observations support the predictions of charge accumulation at the triple line and confirm previous experiments. In all of the experiments, the contact angle was in the saturation regime at a value smaller than that predicted by the condition of a zero value for the solid-liquid surface tension. The PDMS did not show any deterioration due to the corona exposure under the experimental conditions used. The contact angle is shown to increase with humidity.     

Spontaneous formation of an "antidrop"

We have observed, with great surprise, the spontaneous formation of a quite unusual drop. Because of its similarity to the antibubble [(a) Hughes, W.; Hughes, A. R. Nature 1932, 129 (3245), 59. (b) Skogen, N. Am. J. Phys. 1956, 24, 239. (c) Strong, C. L. Sci. Am. 1974, 230 (4), 116.], we describe our find as an "antidrop", a thin spherical shell of an aqueous salt solution, surrounded by an inner and outer organic liquid phase. Two of these antidrops, about 8 mm in diameter, are shown in the present paper resting on a bed of smaller conventional drops. Drops of this size do not normally appear so spherical, however the antidrop is a mere shell, and hence its geometry is dominated by the interfacial tension. We found these drops to be remarkably stable, given it was possible to reversibly deform the drops and even slice through a drop with a glass rod to produce two antidrops. Ultimately, after some finite time period, the antidrops simply disintegrated into clouds of tiny droplets of the aqueous salt solution because of the drainage and concomitant rupturing of the liquid comprising their thin spherical shells.