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901.
The electronic nature of substituents attached to the 4‐aryl moiety of 1,4‐dihydropyridines strongly affects the photophysical and photochemical behavior of these family of compounds. The presence of an electron donor substituent on the 4‐aryl moiety (or the absence of electron‐withdrawing ones) modifies the luminescence lifetimes (τ < 100 ps) and diminishes the photodecomposition quantum yields. For electron‐withdrawing substituents, the photodegradation quantum yield is affected by the media, changing more than two orders of magnitude as the polarity is increased. Studies in micellar media allow us to conclude that 4‐aryl‐1,4‐dihydropyridines are located near to the interface; however, the surface charge of micelles has no effect on the photodegradation rate constant or the photoproducts profile. The main conclusion of this work is that the photolability of 4‐aryl‐1,4‐dihydropyridines can be significantly reduced by the incorporation of antioxidant moieties.  相似文献   
902.
Template‐mediated synthesis is a powerful approach to build a variety of functional materials and complex supramolecular systems. However, the systematic study of how templates structurally evolve from basic building blocks, and then affect the templated self‐assembly, is critical to understanding and utilizing the underlying mechanism, to work towards designed assembly. Here we describe the templated self‐assembly of a series of gigantic Mo Blue (MB) clusters 1 – 4 using l ‐ornithine as a structure‐directing ligand. We show that by using l ‐ornithine as a structure director, we can form new template?host assemblies. Based on the structural relationship between encapsulated templates of {Mo8} ( 1 ), {Mo17} ( 2 ) and {Mo36} ( 4 ), a pathway of the structural evolution of templates is proposed. This provides insight into how gigantic Mo Blue cluster rings form and could lead to full control over the designed assembly of gigantic Mo‐blue rings.  相似文献   
903.
Biological materials generally require stabilization to retain activity or viability in a dry form. A number of industrial products, such as vaccines, probiotics and biopesticides have been produced as dry preparations. The same methods and materials used for stabilizing commercial microbial products may be applicable to preserving biothreat pathogens in a dry form. This is a likely step that may be encountered when looking at samples from terrorism attempts since only spores, such as those from Bacillus anthracis, are inherently stable when dried. The stabilizers for microbial preparations generally include one or more small carbohydrates. Different formulations have been reported for different industrial products and are often determined empirically. However sugar alcohols (mannitol and sorbitol) and disaccharides (lactose, sucrose and trehalose) are the common constituents of these formulations. We have developed an analytical method for sample preparation and detection of these simple carbohydrates using two complementary analytical tools, MALDI-MS and GC-MS. The native carbohydrates and other constituents of the formulation are detected by MALDI-MS as a screening tool. A longer and more detailed analysis is then used to specifically identify the carbohydrates by derivatization and GC-MS detection. Both techniques were tested against ten different types of stabilization recipes with Yersinia pestis cell mass cultured on different media types used as the biological component. A number of additional components were included in these formulations including proteins and peptides from serum or milk, polymers (e.g. poly vinyl pyrrolidone - PVP) and detergents (e.g. Tween). The combined method was characterized to determine several figures of merit. The accuracy of the method was 98% for MALDI-MS and 100% for GC-MS. The repeatability for detection of carbohydrates by MALDI-MS was determined to be 96%. The repeatability of compound identification by GC-MS was determined by monitoring variation in retention time, which is vital for identification of isomeric carbohydrates. The figures of merit illustrate an effective and accurate method for mono and disaccharide detection independent of formulation. This meets our primary goal for method development as small carbohydrates are among the most common stabilizers employed.  相似文献   
904.
We report a new sodium fast-ion conductor, Na3B5S9, that exhibits a high Na ion total conductivity of 0.80 mS cm−1 (sintered pellet; cold-pressed pellet=0.21 mS cm−1). The structure consists of corner-sharing B10S20 supertetrahedral clusters, which create a framework that supports 3D Na ion diffusion channels. The Na ions are well-distributed in the channels and form a disordered sublattice spanning five Na crystallographic sites. The combination of structural elucidation via single crystal X-ray diffraction and powder synchrotron X-ray diffraction at variable temperatures, solid-state nuclear magnetic resonance spectra and ab initio molecular dynamics simulations reveal high Na-ion mobility (predicted conductivity: 0.96 mS cm−1) and the nature of the 3D diffusion pathways. Notably, the Na ion sublattice orders at low temperatures, resulting in isolated Na polyhedra and thus much lower ionic conductivity. This highlights the importance of a disordered Na ion sublattice—and existence of well-connected Na ion migration pathways formed via face-sharing polyhedra—in dictating Na ion diffusion.  相似文献   
905.
With R-(+) ethyl (or methyl) S-methyl methylphosphonothioate and (+)-pinacolyl alkoxide competitive and highly stereoselective displacements of O-alkyl and S-methyl occur, both reactions being with inversion of configuration. With the enantiomeric S-(-) ethyl (and methyl) S-methyl methylphosphonothioates and (+)-pinacolyl alkoxide the reactions, although still competitive, are no longer stereoselective. In contrast similar reactions with the sodium salt of (-)-menthol, (which might be considered to be the mirror image of (+)-pinacolyl alkoxide) occur highly stereoselectively with the S-(-) but not with R-(+) enantiomers. The displacement of O-alkyl from alkyl S-methyl methyl-phosphonothioates by ethoxide, pinacolyl alkoxide and menthyl alkoxide is not observed when methoxide is the nucleophile; in this case only displacement of S-alkyl group occurs.  相似文献   
906.
The serendipitous formation of 2,5-dimethoxy- 1,4-benzoquinone is reported from the reaction of 1,4-benzoquinone with methanol, DABCO, and paraformaldehyde. This monomer, and its di-n-butoxy analog, are also available from 2,5-dihydroxy-1,4-benzoquinone. These materials are capable of novel polycondensation reactions with diamines such as 1,6-hex-anediamine. Use of m-crexsol as polymerization solvent gave a dark, insoluble product while various amide solvents lead to orange or pink polymers that had average degrees of polymerization from 5 up to >30. These polymers, Plus model compounds obtained from 1-aminopropane and N,N'- dimethyl-1,6-hexanediamine, were characterized by FTIR, solution, and solid-state NMR.  相似文献   
907.
Previous work using infrared spectroscopy has shown potential for rapid discrimination between bacteria in either their sporulated or vegetative states, as well as between bacteria and other common interferents. For species within one physiological state, however, distinction is far more challenging, and requires chemometrics. In the current study, we have narrowed the field of study by eliminating the confounding issues of vegetative cells as well as growth media and focused on using IR spectra to distinguish only between different species all in the sporulated state. Using principal component analysis (PCA) and a classification method based upon similarity measurements, we demonstrate a successful identification rate to the species level of 85% for Bacillus spores grown and sporulated in a glucose broth medium.  相似文献   
908.
909.
The reaction of N‐methyl‐2,2′‐diphenolamine 1 and 2,2′‐diphenolamine 2 with some diorganotin(IV) oxides [R1/2SnO: R1 = Me, n‐Bu, t‐Bu and Ph] led to the syntheses of diorgano[N‐methyl‐2,2′‐diphenolato‐O,O′,N]tin (IV) 3–6 and diorgano[2,2′‐diphenolato‐O,O′,N]tin (IV) 7–9 . All compounds (except 7 ) studied in this work were characterized by 1H, 13C, 119Sn NMR, infrared, and mass spectroscopy. Their 119Sn NMR data show that the tin atom is tetracoordinated in CDCl3 but penta and hexacoordinated in DMSO‐d6. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 133–139, 1999  相似文献   
910.
The reactions of methyl glyoxylate hemiacetal 1 with 2-(methylamino)ethanol 2 , (1R,2S)-(–)-ephedrine 3 and (1S,2S)-(+)-pseudoephedrine 4 provide the (2S)-2-hydroxy-1,4-oxazin-3-ones 2a , 3a , 4a in good yield. They were characterized by 1H, 13C, NMR, and infrared and mass spectroscopy. The structures of 2a and 3a were established by X-ray diffraction. The configuration of C2 (S) is demonstrated by 1H NMR data and confirmed for compounds 2a and 3a by single-crystal X-ray diffraction studies. © John Wiley & Sons, Inc.  相似文献   
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