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21.
Charles E. Carraher Jr. George F. Peterson John E. Sheats Ted Kirsch 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):1009-1022
The synthesis of oligomeric tin poly(cobalticinium esters) is presented as a function of the particular reaction variables stirring rate, pH and amount of added base, mole ratio of reactants, concentration of reactants, and volume of organic phase. Factors which decrease the solubility of the stannane apparently act to increase the yield of polyester. The thermal characterization of I was carried out via DSC and TGA. The products generally exhibit endotherms below 150 to 200[ddot]C which may be related to Tg. Above 200[ddot]C, degradation occurs in air by an oxidative mode. 相似文献
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Given the steady increase in cores per CPU, it is only a matter of time before supercomputers will have a million or more cores. In this article, we investigate the opportunities and challenges that will arise when trying to utilize this vast computing power to solve a single integer linear optimization problem. We also raise the question of whether best practices in sequential solution of ILPs will be effective in massively parallel environments. 相似文献
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Many antibiotics of the anthracycline family1 possess structures for which 3-methoxyphthalic anhydride (1) would be a suitable synthon2 in a total synthesis. A classic synthesis of (1) has employed 3-nitrophthalic acid3 but, in our hands, proceeded in low overall yield. Recent syntheses have utilized the Diels Alder reaction of dimethyl acetylenedicarboxylate (2) with 1-methoxy-1,3-cyclohexadiene,4 1,4-diacetoxybutadiene,5 2-acetoxyfuran,6 2-methoxyfuran7 or furan8 to obtain 3-hydroxyphthalic acid or a derivative. We now wish to report a convenient Diels-Alder synthesis of (1) from 3-methoxy-2-pyrone (3). 相似文献
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Abstract In 1981, Mallams and coworkers reported1 the discovery of - D-kijanose 1, a branched-chain nitro sugar, isolated from the antitumor antibiotic kijanimicin by acid hydrolysis. The structure of this unusual carbohydrate was established 1,2 as 2,3,4,6-tetadeo xy-4 - (methoxy carbony1 amino 1-3-c-methyl - 3 -nitro - D-xylo-hexopyranose by spectroscopic and crystallographic analysis, and comparison with D-rubranitrose 2, a carbohydrate found in the antibiotic rubradirin .3Two other nitro sugars, L-evernitrose 3 and - L-decilonitrose 45, have been discoveredas components of antibiotics. 相似文献
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Dr. Rubén D. Costa Dr. Juan Aragó Prof. Dr. Enrique Ortí Dr. Ted M. Pappenfus Prof. Dr. Kent R. Mann Dr. Katarzyna Matczyszyn Prof. Dr. Marek Samoc Dr. José L. Zafra Prof. Dr. Juan T. López Navarrete Prof. Dr. Juan Casado 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(4):1476-1488
The linear and non‐linear optical properties of a family of dumbbell‐shaped dinuclear complexes, in which an oligothiophene chain with various numbers of rings (1, 3, and 6) acts as a bridge between two homoleptic tris(2,2′‐bipyridine)ruthenium(II) complexes, have been fully investigated by using a range of spectroscopic techniques (absorption and luminescence, transient absorption, Raman, and non‐linear absorption), together with density functional theory calculations. Our results shed light on the impact of the synergistic collaboration between the electronic structures of the two chemical moieties on the optical properties of these materials. Experiments on the linear optical properties of these compounds indicated that the length of the oligothiophene bridge was critical for luminescent behavior. Indeed, no emission was detected for compounds with long oligothiophene bridges (compounds 3 and 4 , with 3 and 6 thiophene rings, respectively), owing to the presence of the 3π? π* state of the conjugated bridge below the 3MLCT‐emitting states of the end‐capping RuII complexes. In contrast, the compound with the shortest bridge ( 2 , one thiophene ring) shows excellent photophysical features. Non‐linear optical experiments showed that the investigated compounds were strong non‐linear absorbers in wide energy ranges. Indeed, their non‐linear absorption was augmented upon increasing the length of the oligothiophene bridge. In particular, the compound with the longest oligothiophene bridge not only showed strong two‐photon absorption (TPA) but also noteworthy three‐photon‐absorption behavior, with a cross‐section value of 4×10?78 cm6 s2 at 1450 nm. This characteristic was complemented by the strong excited‐state absorption (ESA) that was observed for compounds 3 and 4 . As a matter of fact, the overlap between the non‐linear absorption and ESA establishes compounds 3 and 4 as good candidates for optical‐power‐limiting applications. 相似文献
30.
Nam T. Nguyen Edward Greenhalgh Mohd J. Kamaruddin Jaouad El harfi Kim Carmichael Georgios Dimitrakis Samuel W. Kingman John P. Robinson Derek J. Irvine 《Tetrahedron》2014
This paper reports the first detailed study focussed upon identifying the influence that microwave heating (MWH) has upon the mechanic steps involved in the tin catalysed ring-opening of lactones such as ?-caprolactone (CL). Direct comparison of conventional (CH) and microwave (MWH) heated kinetic studies showed that a key factor in the reduction of the polymerisation cycle time with MWH was the elimination of the induction period associated with in situ catalyst manufacture and initiation. NMR studies demonstrated that the most significant mechanistic change contributing to the observed induction time reduction/elimination was faster initiation (i.e., reaction of the initiatior/catalyst complex with the first monomer unit). Consequently, analysis of the dielectric properties of the reaction components predicted that this MWH induced change was related to the selective volumetric heating of both the catalyst and the monomer. Furthermore, this indication of the greater significance of the initiation step in defining the length of the induction period suggests that this is the rate determining step of the process, whether conducted by CH or MWH. Increasing the catalyst concentration was demonstrated to produce significant reductions in reaction heat-up time and to induce a significant (up to 30 °C) overshoot in reaction mixture bulk temperature in with MWH only. Thus supporting the conclusion that selective heating of the organometallic species in the system contributes directly to differences in the reaction conditions and which need to be taken into account when drawing comparisons with CH systems. Consequently, both effects were concluded to be thermally generated from selective volumetric heating. 相似文献