高压下聚苯胺的结构和电性能研究

 以金刚石压腔高压装置为工具，用Ⅱ型金刚石作压砧兼红外窗口，对本征态聚苯胺进行了高压（0~8.4 GPa）就位红外光谱测试。结果表明：在4.8~5.2 GPa压力区间，代表醌环振动的吸收峰相对代表苯环振动的吸收峰变小，表明聚苯胺在此压力区间结构上发生了显著变化，且这种变化是不可逆的。聚苯胺的高压（0~14.5 GPa）电阻测量结果表明：当压力小于7.5 GPa时，电阻随压力升高而显著降低，据此认为聚苯胺为电子性导电物质；在7.5 GPa处电阻出现极小值，然后又缓慢升高，至10 GPa后基本不变。推测聚苯胺电阻极小值是由结构变化引起的。至于红外光谱与电阻测量结果反映聚苯胺结构变化的压力值不一致，可能是由于测试条件不同所致。     

Efficient Demethylation of Methyl Esters with Anhydrous Trifluoroacetic Acid

Trifluoroacetic acid (TFA) is an effective reagent for the demethylation of methyl esters under anhydrous conditions, affording the parent acids and methyl trifluoroacetate.     

Formation of a crosslinked POSS network by an unusual hydrosilylation: Thermo‐oxidative stabilization of the α‐cristobalite phase in its amorphous regions

A semicrystalline inorganic–organic hybrid crosslinked network containing polyhedral oligomeric silsesquioxane (POSS) cores was constructed by the unusual hydrosilylation of the terminal vinyl groups of an internal acetylene‐containing silane linker by a POSS monomer. Products from the thermal treatments of this network in either argon or air at 250, 550, and 1000 °C, respectively, were characterized by Fourier transform infrared, Solid‐state ¹³C and ²⁹Si magic angle spinning NMR, X‐ray diffraction and XPS analyses. The highly symmetrically functionalized POSS silica clusters, in the fluorite silica phase, in the network were found to remain unchanged on thermal treatment possibly due to the shielding of the silica core by the functionalities and a cancellation of thermal stresses on the silica core. Stabilization of the metastable α‐cristobalite phase, which is typically formed on cooling by a β‐ to α‐transition of the β‐cristobalite phase formed above 1400 °C, was observed in the amorphous regions in the network sample treated only to 1000 °C in air. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Enantioselective Synthesis of Isoxazolines Enabled by Palladium-Catalyzed Carboetherification of Alkenyl Oximes

Reported here is a highly efficient Pd/Xiang-Phos catalyzed enantioselective carboetherification of alkenyl oximes with either aryl or alkenyl halides, delivering various chiral 3,5-disubstituted and 3,5,5-trisubstituted isoxazolines in good yields with up to 97 % ee. The sterically bulky and electron-rich (S,Rs)- NMe-X2 ligand is responsible for the excellent reactivities and enantioselectivities. The salient features of this transformation include mild reaction conditions, general substrate scope, good functional-group tolerance, good yields, high enantioselectivities, easy scale-up, and application in the late-stage modification of bioactive compounds. The obtained products can be readily transformed into useful chiral 1,3-aminoalcohols.     

Hybrid inorganic–organic poly(carborane‐siloxane‐arylacetylene) structural isomers with in‐chain aromatics: Synthesis and properties

Structural isomers of thermo‐oxidatively stable poly(carborane‐siloxane‐arylacetylene) (PCSAA), namely, m‐PCSAA and p‐PCSAA, were synthesized by the reaction of the dimagnesium salts of m‐diethynylbenzene or p‐diethynylbenzene with 1,7‐bis(chlorotetramethyldisiloxyl)‐m‐carborane. The developed polymers have exceptional thermo‐oxidative properties similar to their diacetylene counterpart poly(carborane‐siloxane‐acetylene), PCSA. Thermal treatment of either of the PCSAAs results in a fully crosslinked thermoset by 500 °C resulting from the cycloaddition reactions involving the acetylene and aryl functionalities and subsequent formation of bridging disilylmethylene entities as discerned from Fourier transform infrared, ¹³C and ²⁹Si solid‐state NMR, and XPS studies. X‐ray diffraction analysis revealed that the thermosets obtained from p‐PCSAA possess enhanced crystallinity when compared to that obtained from m‐PCSAA possibly due to more efficient packing interactions of the p‐diethynylbenzene groups during thermoset formation. The presence of the aryl groups in the backbone of the PCSAAs' chains appeared to have enhanced the storage and bulk moduli of their thermosets when compared to the thermoset of PCSA. Dielectric studies of m‐PCSAA and p‐PCSAA revealed segmental relaxation peaks, α, above their glass transition temperatures with p‐PCSAA exhibiting a broader peak with a slower relaxation rate than m‐PCSAA. © 2013 Wiley Periodicals, Inc.^? J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2638–2650     

Synthesis, characterization, and biological evaluation of new oxime-phosphazenes

Hexachlorocylotriphosphazene (1) was reacted with 4-hydroxy-3-methoxybenzaldehyde to give hexakis[(4-formyl-2-methoxy)phenoxy]cyclotriphosphazene (2). Hexakis[(4-(hydroxyimino)2-methoxy)phenoxy]cyclotriphosphazene (3) was synthesized by reaction of 2 with hydroxlamine hydrochloride in pyridine. Compound 3 was reacted with benzyl chloride, acetyl chloride, allyl bromide, benzoyl chloride, propanoyl chloride, 4-methoxybenzoyl chloride, 2-chlorobenzoyl chloride, chloroacetyl chloride, methyl iodide, and thiophene-2-carbonyl chloride. From these reactions, full or partially substituted compounds were obtained, usually in high yields. Pure or defined products could not be obtained from reaction of 3 with methacryloyl chloride and O-acetylsalicyloyl chloride. The structures of the compounds were determined by elemental analysis, and IR, ¹H, ¹³C, and ³¹P NMR spectroscopy. The synthesized compounds were screened for in-vitro antimicrobial activity against two Gram-positive bacteria (Staphylococcus aureus and Enterococcus faecalis), two gram-negative bacteria (Escherichia coli and Klebsiella pneumonia), and fungal strains (Aspergillus niger, and Candida albicans) by the agar well diffusion method. Few compounds had significant activity against both Gram-positive and Gram-negative bacteria. None of the compounds had antifungal activity except compounds 7 and 9, which had moderate activity.     

Characterisation of Taxlllaids A–G; Natural Products from Xenorhabdus indica

Six new lipodepsipeptides and an additional linear derivative named taxlllaids A–G ( 1 – 7 ) have been identified in the entomopathogenic bacterium Xenorhabdus indica. The structures of the main compounds have been solved by detailed NMR spectroscopic analysis and the structures of minor derivatives were elucidated by a combination of labelling experiments and detailed MS experiments. The absolute configuration of the taxlllaids was deduced by using the advanced Marfey method and analysis of the biosynthesis gene cluster showing the presence of epimerisation domains, which was subsequently proved to be correct by solid‐phase peptide synthesis of all taxlllaids. The exchange of a single amino acid in the adenylation domain was shown to be responsible for substrate promiscuity of the third A domain, resulting in the incorporation of leucine, phenylalanine or tyrosine. Bioactivity testing revealed the taxlllaids to be weakly active against Plasmodium falciparum and against a number of eukaryotic cell lines.     

The Effect of Enantiomer Elution Order on the Determination of Minor Enantiomeric Impurity in Ketoprofen and Enantiomeric Purity Evaluation of Commercially Available Dexketoprofen Formulations

In a recent study, opposite enantiomer elution order was observed for ketoprofen enantiomers on two amylose-phenylcarbamate-based chiral columns with the same chemical composition of the chiral selector but in one case with coated while in the other with an immobilized chiral selector. In the present study, the influence of this uncommon effect on method validation parameters for the determination of minor enantiomeric impurity in dexketoprofen was studied. The validated methods with two alternative elution orders for enantiomers were applied for the evaluation of enantiomeric impurity in six marketed dexketoprofen formulations from various vendors. In most of these formulations except one the content of enantiomeric impurity exceeded 0.1% (w/w).