Cation-pi interactions with a model for the side chain of tryptophan: structures and absolute binding energies of alkali metal cation-indole complexes

Threshold collision-induced dissociation techniques are employed to determine bond dissociation energies (BDEs) of mono- and bis-complexes of alkali metal cations, Li+, Na+, K+, Rb+, and Cs+, with indole, C8H7N. The primary and lowest energy dissociation pathway in all cases is endothermic loss of an intact indole ligand. Sequential loss of a second indole ligand is observed at elevated energies for the bis-complexes. Density functional theory calculations at the B3LYP/6-31G level of theory are used to determine the structures, vibrational frequencies, and rotational constants of these complexes. Theoretical BDEs are determined from single point energy calculations at the MP2(full)/6-311+G(2d,2p) level using the B3LYP/6-31G* geometries. The agreement between theory and experiment is very good for all complexes except Li+ (C8H7N), where theory underestimates the strength of the binding. The trends in the BDEs of these alkali metal cation-indole complexes are compared with the analogous benzene and naphthalene complexes to examine the influence of the extended pi network and heteroatom on the strength of the cation-pi interaction. The Na+ and K+ binding affinities of benzene, phenol, and indole are also compared to those of the aromatic amino acids, phenylalanine, tyrosine, and tryptophan to elucidate the factors that contribute to the binding in complexes to the aromatic amino acids. The nature of the binding and trends in the BDEs of cation-pi complexes between alkali metal cations and benzene, phenol, and indole are examined to help understand nature's preference for engaging tryptophan over phenylalanine and tyrosine in cation-pi interactions in biological systems.     

Construction of recombinant Bacillus subtilis for production of polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyalkanoates synthesized by numerous bacteria as intracellular carbon and energy storage compounds and accumulated as granules in the cytoplasm of cells. In this work, we constructed two recombinant plasmids, pBE2C1, and pBE2C1AB, containing one or two PHA synthse, genes, respectively. The two plasmids were inserted into Bacillus subtilis DB104 to generate modified strains, B. subtilis/pBE2C1 and B. subtilis/pBE2C1AB. The two recombinants strains were subjected to fermentation and showed PHA accumulation, the first reported example of mcl-PHA production in B. subtilis. Gas Chromatography analysis identified the compound produced by B. subtilis/pBE2C1 to be a hydroxydecanoate-co-hydroxydodecanoate (HD-co-HDD) polymer whereas that produced by B. subtilis/pBE2C1AB was a hydroxybutyrate-co-hydroxyde-canoate-co-hydroxydodecanoate (HB-HD-HDD) polymer.     

A new veratramine alkaloid from the bulbs of Fritillaria hupehensis

A new highly conjugated alkaloid of veratramine type, 225,25S,5α-veratramine-7(8),12(14)-diene-3β,13β,23β-triol-6-one (1), was isolated from the bulbs of Fritillaria hupehensis Hsiao et K.C. Hsia. Its structure was determined on the basis of spectroscopic evidences.     

速差动力学分析及其应用进展

速差动力学分析是不经分离同时或连续测定混合物中性质密切相关的多组份的重要方法。本文综述了该法在１９８９－１９９２年间国内外新进展，尤着重其在有机，生物混合物中多组份分析的应用及新的计算方法，化学计量学的引入。引用最新文献６７篇。     

无烟煤结构的高分辨电镜研究

镜质组不仅是煤结构变化最具规律性，也是影响煤质的主要微成分。用点分辨率为２．１Ａ的高分辨电镜对几种不同煤化程度的无烟煤大分子结构进行了研究。结果表明：电镜图像直接表征了无烟煤分子的非均匀性孔隙结构。京西煤分子方向化程度强，主要以芳层平行堆或有序化前结构为主；晋城煤方向化程度弱，主要以粒状嵌晶结构为主。高分辨电镜技术是研究煤分子结构和煤化作用实质的有效方法。     

GMA熔融接枝EPDM的研究

以甲基丙烯酸缩水甘油酯（ＧＭＡ）为接枝单体，过氧化二异丙苯（ＤＣＰ）为引发剂，对三元乙丙胶（ＥＰＤＭ）进行了熔融接枝，在烃链上引入极性基团，以改善ＥＰＤＭ与极性聚合物的相容性。用差示扫描量热计（ＤＳＣ）研究了ＧＭＡ的聚合温度，用富里叶红外（ＦＴ－ＩＲ）、凝胶渗透色谱（ＧＰＣ）对接枝产物进行了表征。实验结果表明，产物的接枝率和凝胶量可以通过反应条件（温度、时间、反应物组成及加料方式）来控制。     

甲基化的β-环糊精与十六烷基三甲基溴化胺的相互作用

环糊精与表面活性剂的相互作用已有许多研究,但多局限于β－环糊精（β－CD）,而修饰的β－环糊精与表面活性剂的相互作用研究较少[1－3]．分子内扭转电荷转移（TICT）激发态对介质极性高度敏感性,已成功地用于探针环糊精与表面活性剂的相互作用[4]．研究表明,β－CD能够诱     

Liquefaction of corn stover and preparation of polyester from the liquefied polyol

This research investigated a novel process to prepare polyester from corn stover through liquefaction and crosslinking processes. First, corn stover was liquefied in organic solvents (90 wt% ethylene glycol and 10 wt% ethylene carbonate) with catalysts at moderate temperature under atmospheric pressure. The effect of liquefaction temperature, biomass content, and type of catalyst, such H₂SO₄, HCl, H₃PO₄, and ZnCl₂, was evaluated. Higher liquefaction yield was achieved in 2 wt% sulfuric acid, 1/4 (w/w) stover to liquefying reagent ratio; 160°C temperature, in 2h. The liquefied corn stover was rich in polyols, which can be directly used as feedstock for making polymers without further separation or purification. Second, polyester was made from the liquefied corn stover by crosslinking with multifunctional carboxylic acids and/or cyclic acid anhydrides. The tensile strength of polyester is about 5 MPa and the elongation is around 35%. The polyester is stable in cold water and organic solvents and readily biodegradable as indicated by 82% weight loss when buried in damp soil for 10 mo. The results indicate that this novel polyester could be used for the biodegradable garden mulch film production.     

Structure and electrical properties of Pb(Zr<Subscript>0.25</Subscript>Ti<Subscript>0.75</Subscript>)O<Subscript>3</Subscript> thin films on LaNiO<Subscript>3</Subscript>—Coated thermally oxidized Si substrates

Pb(Zr_0.25Ti_0.75)O₃ (PZT25) thin films were prepared on LaNiO₃-coated thermally oxidized silicon substrates by chemical solution deposition method, where LaNiO₃ electrodes were also prepared by a chemical solution deposition technique. The dielectric constant and dielectric loss of the PZT25 thin films were 570 and 0.057, respectively. The remanent polarization and coercive field were 20.11 μC/cm² and 60.7 kV/cm, respectively. The PZT25 thin films on LaNiO₃-coated thermally oxidized silicon substrates showed improved fatigue characteristics compared with their counterparts on plantium-coated silicon substrates.     

高效液相色谱用标样——多缩乙二醇二甲基丙烯酸酯的研制

本工作对多缩乙二醇二甲基丙烯酸酯标样的制备条件进行了研究。结果表明,应用经典柱色谱及制各级高效液相色谱两步分离,能方便地从合成反应所得粗试样制取纯样品,但是合成反应所用阻聚剂(包括贮存时所用阻聚剂)需要选择易分离的化合物,例如对苯二酚。结果还表明,对于已经过经典色谱柱预分离的二缩三乙二醇二甲基丙烯酸酯试样,硅胶/含0.25%(体积比)甲醇的二氯甲烷二元溶剂,是制备级HPLC比较理想的分离体系,可高效率地制备标样。