NMR studies on synthesized diosgenyl saponin analogs

The identification of six synthesized diosgenyl saponin analogs with up to five sugars was accomplished by NMR studies. A combination of homo- and heteronuclear two-dimensional NMR techniques was utilized to achieve the complete H-1 and C-13 NMR assignments. Copyright (C) 2000 John Wiley & Sons, Ltd.

A high-resolution solid-state NMR study on nano-structured HZSM-5 zeolite

Variations in the structure and acidity properties of HZSM-5 zeolites with reduction in crystal sizes down to nanoscale (less than 100 nm) have been investigated by XRD, TEM and solid-state NMR with a system capable of in situ sample pretreatment. As evidenced by a combination of Al-27 MAS NMR, Si-29 MAS, CP/MAS NMR and H-1 MAS NMR techniques, the downsize of the zeolite crystal leads to an obvious line broadening of the Al-27, Si-29 MAS NMR spectrum, an increasing of the silanol concentration on the external surface, and a pronounced alteration of the acidity distribution between the external and internal surfaces of the zeolite. In a HZSM-5 zeolite with an average size at about 70 nm, the nonacidic hydroxyl groups (silanols) are about 14% with respect to the total amount of Si, while only 4% of such hydroxyl groups exist in the same kind of zeolite at 1000 nm crystal size. The result of H-1 MAS NMR obtained using Fluorinert(R) FC-43 (perfluorotributyl amine) as a probe molecule demonstrates that most of the silanols are located on the external surface of the zeolite. Moreover, the concentration of Bronsted acid sites on the external surface of the nano-structured zeolite appears to be distinctly higher than that of the microsized zeolite.

New rotenoids from roots of Mirabilis jalapa

Four new rotenoids named mirabijalone A-D-1) (1-4), together with 9-O-methyl-4-hydroxyboeravinone B (5), boeravinone C (6) and F (7), and 1,2,3,4-tetrahydro-1-methylisoquinoline-7,8-diol (8), were isolated from the roots of Mirabilis jalapa. The structures of these compounds were determined on the basis of their HR-EI-MS, IR, UV, H-1- and C-13-NMR (DEPT). and 2D NMR (HMQC, HMBC, NOESY) data. Among them, 1,2,3,4-tetrahydro-1-methylisoquinoline-7,8-diol (8) showed a 48% inhibition against HIV-1 reverse transcriptase at 210 mug/ml.

有机化合物结构解析专家系统研究从二维连接表生成分子结构图

有机化合物结构解析专家系统的研究一直是计算机化学领域的前沿课题．在ESESOC系统已有的基础上，进行了从二维连接表生成分子结构图的研究，程序可从化合物的二维连接表出发，生成化合物的分子结构图．从二维连接表生成的分子结构图必须满足以下要求：美观而且符合化学家的习惯，生成的效率要高，一个美观的分子结构式必须做到以下几点：环能容易被人识别；一般情况下键一长应该一致；链上的原子之间无重叠，也不拥挤；完整的结构应有正确的取向，如烷烃的最长链保持水平，且相似的结构应该有相同的取向．从二维连接表生成的分子结构图是一个非常复杂的过程，涉及到图论，几何学，化学，以及计算机多方面的知识．所以尽管有很多方法可以用来生成分子结构图，但是还没有一种非常完美的办法．本工作在这些已有方法中选取了一种方法，同时结合其他方法对之进行了改进，并在计算机上编程实现了这种方法，最终得到一个能从分子的二维连接表生成美观的分子结构图的程序．Internet为科学研究提供了巨大的便利．本工作利用XML技术，实现了网上分子结构数据中分子结构的动态显示；利用ASP技术实现了网上C-13-NMR谱图数据库相似检索．

“PP-PE”聚合合金结构与性能的关系及PP/HDPE共混体系增容改性的新途径

试图澄清“PP-PE”结构与性能的关系，并以此为指导寻求增容改性PP/HDPE体系的新途径是本工作的主要内容。在本工作中，考虑到分子量、EPC组分和共混均匀性因素之后发现，“PP-PE”与相同条件下合成的均聚物样品构成的共混物之间在应力-应变行为、抗冲击性能和动态力学行为上并没有明显差别。在结合文献中有关现象详尽讨论了关于活性链寿命报导值和“（PP-PE）_(200)"的C~(13)NMR谱支持嵌段结构观点的可靠性之后，得到的结论是，现有实验现象不中以证明“PP-PE”具有嵌段结构，尽管四十年来这一观点已被普遍接受。通过TEM观察到，“PP-PE”与PP/HMWPE共混物结晶结构相同，“PP-PE”中的PE部分明显具有HMWPE的片晶特征，应力-应变和SEM实验的结果显示，“PP-PE”与HMWPE具有完全相同的增容PP/HDPE的作用。结合有关共混物结构和性能的实验结果，发现“PP-PE”主要是一个共混物，其中的HMWPE和EPC组分是决定其性能行为的主要因素。尽管在理论和实验上都已确认，分子量的增大不利于共混物组分间的相容，但通过应力-应变实验和形态结构的观察发现，虽然均聚物HMWPE的加入使PP/HDPE体系中PE组分平均分子量增大，但是体系中分散相尺寸却随HMWPE含量的增加大幅度减小，力学性能全面提高。HMWPE这种同接枝和嵌段共聚相似的增容作用既不能用“相似相容”，也不能用所谓“特殊相互作用”来阐明。为此，在本工作中提出了一个新的增容机制——“缠结作用”。应力-应变实验表明，PP/HMWPE体系的力学性能明显优于PP/HDPE体系。前者强度和断裂伸长率都高于后者，其差别尤以断裂伸长率为甚，而模量相差不大。SEM形态结构的观察发现，虽然PP/HDPE体系中的分散相尺寸随其量的增加而增大，并且界面清晰，但PP/HMWPE中的缠结作用使得组分间界面模糊，甚至消失。这种较强的组分间相互作用使得材料由脆性断裂转变为韧性断裂。PP/HMWPE的性能特点进一步证实了非理想换气条件下制备的“PP-PE”结构与性能的关系。

A simple preparation of stationary phase of alkylamide reversed-phase liquid chromatograph for the separation of basic substances

A simple preparation process of alkylamide phase for reversed-phase HPLC (RP-HPLC) is described. The process includes aminopropyltrimethoxysilane firstly reacted with octanoyl chloride, then the intermediate was coupled onto porous silica. The resultant bonded silica has a reproducible ligand surface concentration and homogenous bonded ligand distribution on the porous silica. Characterization of prepared packing was carried out with elemental analysis, solid-state C-13 NMR and Fourier transform infrared (FT-IR). Chromatographic evaluations were carried out by using a mixture of organic compounds including acidic, basic and neutral analytes under methanol/water as binary mobile phase. The results showed that the stationary phase have excellent chromatographic properties and can be efficiently used for the separation of basic compounds.

Structure of an unexpected trimer from the reaction of ageratochromene II with aluminum chloride

A new trimer from the reaction of ageratochromene [1] (6,7-dimethoxy-2,2-dimethyl-1-benzopyran) with anhydrous aluminum chloride was shown to be 3,4-dihydro-6,7-dimethoxy-2,2-dimethyl-3-(6',7'-dimethoxy-2',2'-di-methyl-2H-1-benzopyran-4'-yl)-4-(3" 4"-dihydro-6", 7"-dimethoxy-2",2"-dimethyl-2H-1-benzopyran-3"-yl)-2H-1-benzopyran. Its structure was confirmed by NMR (H-1, C-13, DEPT-135. COSY, HMBC, HSQC, TOCSY and NOESY), IR, mass spectra and elemental analysis. Copyright (C) 2002 John Wiley Sons, Ltd.

Effect of acetylation on the properties of corn starch

Acetylated corn starches with different degrees of substitution (DS 0.85, DS 1.78, DS 2.89) were synthesized by the reaction of corn starch with acetic anhydride in the presence of acetic acid under varying reaction temperatures. The product was characterized by FTIR spectroscopy, H-1 NMR, X-ray diffraction and contact angle measurement. Acid-base titration and H-1 NMR methods were employed to determine the degree of substitution of product. FTIR spectroscopic analysis showed that the characteristic absorption intensities of esterified starch increased with increase in the degree of substitution, and the characterized peak of hydroxyl group almost disappeared in the spectrum of DS 2.89 acetylated starch. The detailed chemical microstructure of native starch and acetylated starch was confirmed by H-1 NMR, C-13 NMR and C-13-(1) H-1 COSY spectra.

Solution-processable highly efficient yellow- and red-emitting phosphorescent organic light emitting devices from a small molecule bipolar host and iridium complexes

A bipolar transport compound, 2,5-bis(4-(9-(2-ethylhexyl)-9H-carbazol-3-yl) phenyl)-1,3,4-oxadiazole (CzOXD), incorporating both electron-and hole-transport functionalities, was synthesized and fully characterized by H-1 NMR, C-13 NMR, elemental analysis and mass spectrometry. Its thermal, electrochemical, electronic absorption and photoluminescent properties were studied

Spontaneous volume transition of polyampholyte nanocomposite hydrogels based on pure electrostatic interaction

A circular system is employed in this paper to investigate the swelling behaviors of polyampholyte hydrogels; this circular system can effectively eliminate the disturbance of various factors and keep the surrounding environment constant. It is found that there exists a spontaneous volume transition to the collapsed state of polyampholyte hydrogels, which is attributed to the overshooting effect, and the transition can occur repeatedly under certain conditions. C-13 NMR is employed to investigate the swelling behavior of polyampholyte hydrogels.

Styrene polymerization catalyzed by metal porphyrin complex/MAO for in situ synthesizing polystyrene containing air stable pi cation radicals

A novel catalyst system based on nickel(II) tetraphenylporphyrin (Ni(II)TPP) and methylaluminoxane for styrene polymerization was developed. This catalyst system has a high thermal stability and show fairly good activity. The obtained polystyrene (PS) was isotactic-rich atactic polymer by C-13 NMR analysis, and its molecular weight distribution was rather narrow (M-w/M-n approximate to 1.6, by GPC analysis). ESR revealed that Ni(II)TPP pi cation radicals were formed in the polymerization and could remain in the resulting PS stably. The mechanism of the polymerization was discussed and a special coordination mechanism was proposed. The PS product containing Ni(II)TPP pi cation radicals can be used as a potential functional material.