Photocrosslinking of functionalized rubber. II. Photoinitiated cationic polymerization of epoxidized liquid natural rubber

Low molecular weight epoxidized natural rubber has been crosslinked within seconds by UV irradiation in the presence of a triarylsulfonium salt. The photoinitiated cationic ring-opening polymerization was studied quantitatively by infrared spectroscopy and shown to proceed with surprisingly long kinetic chains in such solid medium. The high conversion (60%) needed for complete insolubilization, together with the presence of tetrahydrofuran structures, argue in favor of an intramolecular polymerization process involving neighboring epoxy groups. The photoinitiator concentration has a strong influence on the rate and extent of the reaction, as well as on the depth of cure profile. Because of an efficient dark process, close to 100% conversion was reached upon storage of the irradiated elastomer at ambient, with a concomitant increase of the gel fraction and the polymer hardness. The grafting of pendent acrylate groups onto the polymer chain leads to a three-fold decrease of the initial rate of polymerization of the epoxide. The photocuring of natural rubber bearing both epoxy and acrylate groups generates a dual polymer network which combines the properties of the two moieties. © 1995 John Wiley & Sons, Inc.     

内蒙古地区天然植物沙棘果中黄色素的提取工艺及性质研究

以内蒙古地区沙棘果实为原料，研究了提取黄色素的工艺条件，同时对该色素的性质进行了初步探讨。结果表明，以95％的乙醇溶液作浸提剂，提取的黄色素浓度最高，工艺流程简单易行，且无毒，无污染。对提取的黄色素进行的性质试验表明，沙棘黄色素对光、热具有较好的稳定性，适用于酸性或弱碱性的食品中，葡萄糖、氧化剂(H2O2)、还原剂(Na2SO3)等食品添加剂均无明显影响以上结果为这种优良天然色素的开发与应用提供了参考。     

Final elucidation of the absolute configuration of the signal metabolite hormaomycin

The complete absolute configuration of hormaomycin 1 a has been established by HPLC and HPLC/MS experiments with appropriately derivatized 4-propylprolines, (2S,4S)-6 and (2R,4R)-6, as well as 4-(Z)-propenylprolines, cis-5 and trans-5, and also feeding experiments with enantiomerically pure samples of the deuterium-labeled 3-(2'-nitrocyclopropyl)alanine, (2S)-3,3-[D2]15 and (2S)-2,2'-[D2]15, and 4-(Z)-propenylproline 2',4-[D2]-(2S,4R)-5. The latter five amino acids were prepared for the first time and allowed one to unequivocally assign the hitherto unknown absolute configurations of the last four stereocenters in hormaomycin 1 a. As a bonus, some new information about the biosynthesis of this molecule has also been gathered.     

A facile synthesis of (6S,1′S)-(+)-hernandulcin and (6S,1′R)-(+)-epihernandulcin

A facile total synthesis of (+)-hernandulcin (1) was accomplished from (−)-isopulegol in 6 steps with 15% overall yield. Epoxidation of (−)-isopulegol with m-chloroperbenzoic acid followed by opening of the epoxide 3a with prenyl Grignard afforded the tertiary alcohol 4a with correct C-6 and C-1′ stereochemistry as a major product. Oxidation of the secondary alcohol in compound 4a to the ketone 5a was accomplished in high yield by using TPAP and N-methylmorpholine N-oxide. Conversion of the ketone 5a to α,β-unsaturated ketone via organoselenium intermediate gave (+)-hernandulcin (1). This method was also successfully applied to the synthesis of (+)-epihernandulcin (2).     

CAST/CNMR: highly accurate C NMR chemical shift prediction system considering stereochemistry

Accurate, practical prediction of ¹³C NMR chemical shifts has been achieved with a new system, CAST/CNMR, taking account of stereochemistry. The CAST/CNMR system has solved the critical problem of the accurate distinction of differences and similarities in stereochemical structures around a specific carbon, which has not yet been achieved by any other database-oriented system for prediction of ¹³C NMR chemical shifts. CAST/CNMR uses a three-dimensional structural database together with a ¹³C NMR spectral database. Absolute/relative configurational and conformational structural information are described by the CAST (CAnonical-representation of STereochemistry) coding method. This paper provides an overview of the CAST/CNMR system, and describes its application to two natural products as examples.     

Air-Segmented Continuous-Flow Analysis for Molybdenum in Various Geochemical Samples

 An air-segmented continuous-flow method has been developed for the determination of molybdenum at ultra trace levels using the catalytic effect of molybdate during the oxidation of L-ascorbic acid by hydrogen peroxide. Incorporation of an on-line ion exchange column improved the tolerance limit for various ions. The detection limits with and without the column were 64 pmol L⁻¹ and 17 pmol L⁻¹, and the reproducibilities at 10 nmol L⁻¹ were 2.1% and 0.2%, respectively. The proposed method was applied to the determination of molybdenum in seawater and lake water as well as in rock and sediment samples. This method has the highest sensitivity among the available literature to our knowledge, and is also convenient for routine analysis of molybdenum in various natural samples. Author for correspondence. E-mail: masahito.sugiyama@ sojin0206.mbox.media.kyoto-u.ac.jp Received October 23, 2002; accepted January 28, 2003 Published online May 19, 2003     

The unrestricted natural orbital-restricted active space method: methodology and implementation

The full configuration interaction method in the space of fractionally occupied unrestricted natural orbitals (UNO-CAS method) is extended to excited states as well as to strongly correlated and reactive systems with large active spaces. This is accomplished by␣using restricted active space (RAS) wave functions introduced by Olsen et al. [(1988) J Chem Phys 89: 2185] and using the UNOs without the expensive orbital optimization step. In RAS, the space of active orbitals is subdivided into three groups: a group with essentially doubly occupied orbitals (RAS1), the usual CAS space (RAS2), and a space with weakly occupied active orbitals (RAS3). We select these spaces on the basis of the occupation numbers of the UNOs. All possible electron distributions are allowed in the usual CAS space, but the number of vacancies is limited in RAS1 and the number of electrons is limited in RAS3. We discuss an efficient algorithm for generating a RAS wave function. This is based on the Handy-Knowles determinantal expansion with an addressing scheme adopted for the restricted expansion. Results for both ground and excited states of azulene and free base porphyrin are presented. Received: 16 July 1998 / Accepted: 7 August 1998 / Published online: 19 October 1998     

MgO、Al_2O_3、SiO_2催化剂上湿天然气中乙烷氧化脱氢的研究(英文)

研究了ＭｇＯ、Ａｌ２Ｏ３、ＳｉＯ２催化剂对湿天然气中乙烷氧化脱氢反应的影响，发现ＭｇＯ对乙烷脱氢有较好的活性，７００Ｃ时，Ｃ２Ｈ４选择性达４１．８５％，收率达１８．７５％。考察了催化剂酸碱性对反应的影响，适当碱性的催化剂有利于反应的进行，催化剂活性顺序与碱性大小顺序相一致为ＭｇＯ＞Ａｌ２Ｏ３＞ＳｉＯ２。催化剂活性顺序与其晶格氧流动性有顺应关系。     

Stereoselective allyl amine synthesis through enantioselective addition of diethylzinc and [1,3]-chirality transfer: synthesis of lentiginosine and polyoxamic acid derivative

A new synthetic method for the preparation of allyl amines has been developed. The key steps of this method are enantioselective addition of diethylzinc and [1,3]-chirality transfer through the [3.3] sigmatropic rearrangement of allyl cyanates. Stereocontrolled syntheses of lentiginosine (1) and polyoxamic acid derivative 2 from a common intermediate 7 derived from D-tartaric acid (8), have been accomplished.