Polymer crystallization dynamics,as reflected by differential scanning calorimetry. Part 2: Numerical simulations

With the aid of a model for the kinetics of polymer crystallization, as put forward in previous publications, the shape of DSC-curves and their position on the temperature scale were simulated for various conditions of heat transfer in the apparatus. It turns out that the outcome is very dependent on the assumptions made with respect to these heat transfer conditions. For the ideal condition — no temperature differences between sample, pan and furnace — an invariable shape is predicted for the DSC-curves. They only shift to lower temperatures with increasing cooling rates. For more realistic conditions, the curves not only shift but become broader and their maxima decrease. They show a more familiar appearance. These calculations are very involved, however, A simple balance equation is shown to yield equivalent results, if a dimensionless characteristic number like the Nusselt number remains considerably smaller than one. This number contains an effective heat transfer coefficient between sample and furnace which, surprisingly, should not be too high. Apparently, the heat capacity of the pan does not play an important role under these conditions. This is investigated in Appendix II. Appendix I describes the procedure of the numerical simulations.     

Poly(ethylene glycol) grafted onto Dowex resin: an efficient, recyclable, and mild polymer-supported phase transfer catalyst for the regioselective azidolysis of epoxides in water

In this study, an efficient method was designed to graft poly(ethylene glycol) effectively onto commercial Dowex resin. The catalytic efficiency of the copolymer obtained as a new solid-liquid phase transfer catalyst was studied. It was proved that this organocatalyst is an efficient heterogeneous catalyst for regioselective azidolysis of epoxide in water and gave azidohydrin in excellent yield under mild reaction conditions. The polymeric catalyst was easily recovered by simple filtration and showed no appreciable loss of activity when recycled several times.     

固载相转移催化剂催化合成1,4-二氢-2,6-二甲基-3,5-吡啶二甲酸二乙酯

采用三相相转移催化剂(四丁基溴化铵-聚苯乙烯树脂),以乙酰乙酸乙酯和六次甲基四胺为原料,合成了1,4-二氢-2,6-二甲基-3,5-吡啶二甲酸二乙酯,探讨了反应条件对产物收率的影响,并对产品结构进行了红外光谱及元素分析表征.     

Laser-initiated copolymerization of maleic anhydride with styrene,vinyltoluene, and t-butylstyrene

Laser-initiated polymerization of charge transfer monomer complexes has been investigated using an argon ion laser. The influence of solvents, monomer feed ratio, and irradiation time on the copolymer yield and composition was evaluated. The polymer yield was found to be directly proportional to the irradiation time and the molar concentration of maleic anhydride in the monomer feed. An enhanced rate of polymerization was obtained by substituting electron donating groups in the donor monomer. Polymerization, initiation, and propagation mechanisms, via charge transfer complexes, have been discussed. Comparison of laser-induced polymerization with UV-induced polymerization suggests that laser initiation is an energy-efficient process.     

Comparison of the separation of proteins of wide-ranging molecular weight via trilobal polypropylene capillary-channeled polymer fiber,commercial superficiously porous,and commercial size exclusion columns

Reversed phase and size-exclusion chromatography methods are commonly used for protein separations, although they are based on distinctly different principles. Reversed phase methods yield hydrophobicity-based (loosely-termed) separation of proteins on porous supports, but tend to be limited to proteins with modest molecular weights based on mass transfer limitations. Alternatively, size-exclusion provides complementary benefits in the separation of higher mass proteins based on entropic, not enthalpic, processes, but tend to yield limited peak capacities. In this study, microbore columns packed with a novel trilobal polypropylene capillary-channeled polymer fiber were used in a reversed phase modality for the separation of polypeptides and proteins of molecular weights ranging from 1.4 to 660 kDa. Chromatographic parameters including gradient times, flow rates, and trifluoroacetic acid concentrations in the mobile phase were optimized to maximize resolution and throughput. Following optimization, the performance of the trilobal fiber column was compared to two commercial-sourced columns, a superficially porous C4-derivatized silica and size exclusion, both of which are sold specifically for protein separations and operated according to the manufacturer-specified conditions. In comparison to the commercial columns, the fiber-based column yielded better separation performance across the entirety of the suite, at much lower cost and shorter separation times.     

唑来膦酸合成方法的研究进展

综述了唑来膦酸(1)合成方法的研究进展。重点介绍了以咪唑为原料合成1的工艺条件,讨论了不同工艺条件的优缺点。结果显示,通过优选相转移催化剂和溶剂能高收率地合成1。参考文献30篇。     

Synthesis of sapphyrins, heterosapphyrins, and carbasapphyrins by a "4 + 1" approach

Sapphyrins are an important group of expanded porphyrins that show valuable anion binding characteristics. In this study, a "4 + 1" route to sapphyrin systems has been developed. Reaction of dialdehydes with a known tetrapyrrole intermediate 11b incorporating a bipyrrolic subunit afforded a wide range of sapphyrin-type products. The best conditions for these reactions involved carrying out the condensation of the dialdehydes with the tetrapyrrole in TFA-dichloromethane, followed by oxidation with dilute aqueous solutions of ferric chloride. A pyrrole dialdehyde reacted under these conditions to give sapphyrin in 50% yield, while furan and thiophene dialdehydes afforded the corresponding oxa- and thiasapphyrins in 66-90% yield. Pyrrole dialdehydes with fused phenanthrene or acenaphthylene rings also reacted with 11b to give the related phenanthro- and acenaphthosapphyrins in excellent yields. As was the case for acenaphthoporphyrins, the acenaphthosapphyrin gave longer wavelength absorptions than the corresponding phenanthrene fused structure, although the differences were not as marked as those seen in the porphyrin series. Reaction of 11b with 1,3-diformylindene gave a benzocarbasapphyrin in 38% yield, while a triformyl cyclopentadiene reacted with the tetrapyrrole to give a carbasapphyrin aldehyde in 7-12% yield. The free base carbasapphyrins were unstable but the monoprotonated hydrochloride salts could easily be isolated and characterized. Carbasapphyrins retain a strong diatropic ring current due to the presence of 22pi electron delocalization pathways. In the presence of trifluoroacetic acid, C-protonated dications are generated. Condensation of 1,3-azulenedicarbaldehyde with 11b gave an azulisapphyrin dihydrochloride salt in 35% yield, and this also showed a strong diatropic ring current. Addition of base gave the unstable free base form, while pyrrolidine formed an unstable adduct that showed an intense Soret band at 480 nm. These results demonstrate that many of the themes observed for modified porphyrins and carbaporphyrins also apply to the sapphyrin series, although in some cases reduced stability hampers these investigations.     

Effects of polarity and temperature on photoluminescence of a europium(III) chelate

The relative photoluminescence yield for (1,10-phenanthroline)europium(III) tris-thenoyltrinuoroacetonate (Eu(tta)₃Phen). an efficient enhancer of chemiluminescence, has been measured under the conditions (temperatures and solvents) specific for the oxidation of hydrocarbons. The yield is independent of viscosity and the presence of a heavy atom in the solvent, but the higher the polarity of the medium, the more the yield decreases as the temperature increases. The effect is interpreted as an acceleration of radiationless deactivation occurringvia the mechanism of electron transfer from a ligand to the excited Eu³⁺ ion.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1686–1690, July, 1996.     

Tuning Deazaflavins Towards Highly Potent Reducing Photocatalysts Guided by Mechanistic Understanding – Enhancement of the Key Step by the Internal Heavy Atom Effect

Deazaflavins are well suited for reductive chemistry acting via a consecutive photo-induced electron transfer, in which their triplet state and semiquinone – the latter is formed from the former after electron transfer from a sacrificial electron donor – are key intermediates. Guided by mechanistic investigations aiming to increase intersystem crossing by the internal heavy atom effect and optimising the concentration conditions to avoid unproductive excited singlet reactions, we synthesised 5-aryldeazaflavins with Br or Cl substituents on different structural positions via a three-component reaction. Bromination of the deazaisoalloxazine core leads to almost 100 % triplet yield but causes photo-instability and enhances unproductive side reactions. Bromine on the 5-phenyl group in ortho position does not affect the photostability, increases the triplet yield, and allows its efficient usage in the photocatalytic dehalogenation of bromo- and chloroarenes with electron-donating methoxy and alkyl groups even under aerobic conditions. Reductive powers comparable to lithium are achieved.     

PHOTOSENSITIZED OXIDATION OF BIOMATERIALS and RELATED MODEL COMPOUNDS

Aluminium trisulfonatophthalocyanine (A1PCS), a dye being widely advocated for use in photodynamic therapy, produces singlet oxygen with a quantum yield of 0.34 in oxygenated water at pH 7. Triplet A1PCS abstracts an electron from a variety of amines and phenols, the rate of electron transfer depending upon the thermodynamic driving force, forming the A1PCS radical anion. This latter species reduces molecular oxygen to superoxide ions with high efficiency. The triplet state also abstracts an electron from biological components, including NADH, vitamin C, cysteine, methionine, tyrosine, tryptophan, uracil, and guanine, but not from DNA. These results suggest that photoinduced electron abstraction from appropriate biomaterials could compete with singlet oxygen production under in vivo conditions.     

橙花素的催化合成研究

将研制得的季鏻盐型高聚物相转移催化剂用于橙花素(即β-萘乙醚)的催化合成。研究结果表明,在β-萘酚∶溴乙烷为1∶1.3(摩尔比),通N2保护,反应温度为75℃,反应时间为5 h的条件下,可获得81.7%的收率。此法具有操作简便、反应温和、催化剂能重复使用、效果良好的优点。     

1,4-二乙氧基苯的相转移催化合成

采用大孔型交联聚苯乙烯为载体研制出新型季 钅盐型相转移催化剂Y98B ,并将其应用于 1 ,4-二乙氧基苯的催化合成反应 ,产品进行了红外光谱分析和熔点测定 ,探讨了催化剂用量、对苯二酚与溴乙烷物质的量比、反应温度和反应时间等动力学条件对产品收率的影响。确定了在反应温度为 70℃、对苯二酚∶溴乙烷 (摩尔比 )为 1∶3.5、反应时间为 4h、催化剂用量为 3.0g的条件下产品收率可达 84.3%     

Oxygen transfer from sulfoxides: oxidation of alkylarenes catalyzed by a polyoxomolybdate, [PMo12O40]3-

The polyoxomolydate of the Keggin structure, PMo12O403-, catalyzes, under anaerobic conditions, oxygen transfer from sulfoxides to alkylarenes such as xanthene and diphenylmethane to yield xanthen-9-one and benzophenone, respectively. With use of 17O and 18O labeled phenylmethylsulfoxide it was shown that the sulfoxide is complexed by the polyoxometalate and the oxygen is transferred from the sulfoxide to the alkylarene. There is a good correlation between the reaction rate and the heterolytic benzylic C-H bond energy indicating a hydride transfer reaction from the alkylarene to the polyoxometalate-sulfoxide complex. In the case of triphenylmethane the resulting carbocation reacts to yield 9-phenylfluorene as the major product. The reaction kinetics supports such a reaction pathway.     

Rapid,clean, and mild O-acetylation of alcohols and carbohydrates in an ionic liquid

Archetypal O-acetylation reactions of alcohols and carbohydrates proceed rapidly in high yield under mild conditions in a dicyanamide based ionic liquid, that is not only an effective solvent but also an active base catalyst.     

Electronic energy transfer involving carotenoid pigments in chlorosomes of two green bacteria: Chlorobium tepidum and Cholroflexus aurantiacus

Electronic energy transfer processes in chlorosomes isolated from the green sulphur bacterium Chlorobium tepidum and from the green filamentous bacterium Chloroflexus aurantiacus have been investigated. Steady-state fluorescence excitation spectra and time-resolved triplet-minus-singlet (TmS) spectra, recorded at ambient temperature and under non-reducing or reducing conditions, are reported. The carotenoid (Car) pigments in both species transfer their singlet excitation to bacteriochlorophyll c (BChlc) with an efficiency which is high (between 0.5 and 0.8) but smaller than unity; BChlc and bacteriochlorophyll a (BChla) transfer their triplet excitation to the Car's with nearly 100% efficiency. The lifetime of the Car triplet states is approximately 3 micros, appreciably shorter than that of the Car triplets in the light-harvesting complex II (LHCII) in green plants and in other antenna systems. In both types of chlorosomes the yield of BChlc triplets (as judged from the yield of the Car triplets) remains insensitive to the redox conditions. In notable contrast the yield of BChlc singlet emission falls, upon a change from reducing to non-reducing conditions, by factors of 4 and 35 in Cfx. aurantiacus and Cb. tepidum, respectively. It is possible to account for these observations if one postulates that the bulk of the BChlc triplets originate either from a large BChlc pool which is essentially non-fluorescent and non-responsive to changes in the redox conditions, or as a result of a process which quenches BChlc singlet excitation and becomes more efficient under non-reducing conditions. In chlorosomes from Cfx. aurantiacus whose Car content is lowered, by hexane extraction, to 10% of the original value, nearly one-third of the photogenerated BChlc triplets still end up on the residual Car pigments, which is taken as evidence of BChlc-to-BChlc migration of triplet excitation; the BChlc triplets which escape rapid static quenching contribute a depletion signal at the long-wavelength edge of the Qy absorption band, indicating the existence of at least two pools of BChlc.     

微波辅助合成菲并咪唑衍生物及微波非热效应

以1,10-邻菲啰啉5,6-二酮及苯甲醛(或取代苯甲醛)为原料, 在微波辐射条件下制备了一系列菲并咪唑类衍生物, 考察了温度、 时间以及投料比对微波辅助合成菲并咪唑类衍生物的影响, 并进一步探讨了微波非热效应的影响. 设计正交实验优化了反应条件; 使用SiC管作为反应容器屏蔽微波对反应的影响; 通过元素分析、 核磁共振波谱、 质谱及红外光谱等对化合物进行了表征. 结果表明, 微波辅助反应的最佳反应条件为: 1,10-邻菲啰啉-5,6-二酮与苯甲醛(或取代苯甲醛)的投料比为1: 1.5, 反应温度为100℃, 反应时间为20 min; 并且发现SiC管中反应的产率明显低于石英管反应容器. 与传统制备方法相比, 微波辅助合成方法可在更短时间内快速方便地制得菲并咪唑类衍生物; 反应温度、 反应时间以及投料比对微波辅助合成反应有明显影响; 微波非热效应有助于提高反应产率.     

Effects of Temperature and Catalyst to Oil Weight Ratio on the Catalytic Conversion of Heavy Oil to Propylene Using ZSM-5 and USY Catalysts

It is useful for practical operation to study the rules of production of propylene by the catalytic conversion of heavy oil in FCC (fluid catalytic cracking). The effects of temperature and C/O ratio (catalyst to oil weight ratio) on the distribution of the product and the yield of propylene were investigated on a micro reactor unit with two model catalysts, namely ZSM-5/Al2O3 and USY/Al2O3, and Fushun vacuum gas oil (VGO) was used as the feedstock. The conversion of heavy oil over ZSM-5 catalyst can be comparable to that of USY catalyst at high temperature and high C/O ratio. The rate of conversion of heavy oil using the ZSM-5 equilibrium catalyst is lower compared with the USY equilibrium catalyst under the general FCC conditions and this can be attributed to the poor steam ability of the ZSM-5 equilibrium catalyst. The difference in pore topologies of USY and ZSM-5 is the reason why the principal products for the above two catalysts is different, namely gasoline and liquid petroleum gas (LPG), repspectively. So the LPG selectivity, especially the propylene selectivity, may decline if USY is added into the FCC catalyst for maximizing the production of propylene. Increasing the C/O ratio is the most economical method for the increase of LPG yield than the increase of the temperature of the two model catalysts, because the loss of light oil is less in the former case. There is an inverse correlation between HTC (hydrogen transfer coefficient) and the yield of propylene, and restricting the hydrogen transfer reaction is the more important measure in increasing the yield of propylene of the ZSM-5 catalyst. The ethylene yield of ZSM-5/Al2O3 is higher, but the gaseous side products with low value are not enhanced when ZSM-5 catalyst is used. Moreover, for LPG and the end products, dry gas and coke, their ranges of reaction conditions to which their yields are dependent are different, and that of end products is more severe than that of LPG. So it is clear that maximizing LPG and propylene and restricting dry gas and coke can be both achieved via increasing the severity of reaction conditions among the range of reaction conditions which LPG yield is sensitive to.     

Ultrafast dynamics of epicocconone, a second generation fluorescent protein stain

Femtosecond upconversion experiment has been carried out for epicocconone and its butylamine adduct in acetonitrile and tert-butanol. An ultrafast component is found to dominate the decay of fluorescence of epicocconone in acetonitrile solution. Upon reacting with butylamine, a model for the epicocconone-protein adduct, this ultrafast component remains almost unaffected but an additional rise time occurs, indicating the formation of a highly emissive species from the locally excited state. This phenomenon is central to the extraordinary applications of epicocconone in biotechnology. The magnitude of the rise time of the butylamine adduct is similar to that of the longer component of the decay of epicocconone in acetonitrile, suggesting that the dynamics of epicocconone and its butylamine adduct are similar. The ultrafast component is slowed upon increasing the viscosity of the solvent. This results in a marked increase in quantum yield and suggests that it corresponds to rapid bond isomerization, leading to a nonradiative decay. Surprisingly, in water/sucrose mixtures, the ultrafast component remains unaffected but there is still an increase in quantum yield, suggesting that there are at least two nonradiative pathways, one involving bond isomerization and another involving proton transfer. The correct interpretation of these data will allow the design of second generation protein stains based on the epicocconone scaffold with increased quantum yields and photostability.     

Synthesis of 4-hydroxymethylbenzophenone by phase transfer catalytic method

An important organic intermediate 4-hydroxymethylbenzophenone was synthesized by halogenation and hydrolyzation with phase transfer catalytic method using 4-methylbenzophenone as raw material and the technological conditions of reactions were investigated as well. Experimental results show that N-bromosuccinimide (NBS) is a good reagent to give 4-bromomethylbenzophenone undergoing a radical reaction with 4-methylbenzophenone with the yield of about 70.7%; 4-bromomethylbenzophenone can be hydrolyzed under basic conditions in the presence of phase transfer catalyst triethylbenzylammonium chloride for 5 h to give 4-hydroxymethylbenzophenone with yield of 84.4%. After the crude product is recrystallized from tetrahydrofuran (THF), the final product is obtained with purity above 99%. The structure of the titled compound is determined by infrared spectrum(IR), proton nuclear magnetic resonance (HNMR), and mass spectrum (MS) and elemental analysis (EA). __________ Translated from Journal of central south university, 2005, 36(4) (in Chinese)     

Synthesis of the aziridinomitosene skeleton by intramolecular Michael addition: alpha-lithioaziridines and nonaromatic substrates

The bicyclic pyrrole ketone 16 has been prepared by using an oxaza-Claisen rearrangement, followed by nitrogen deprotection. Coupling with the stannylaziridine mesylate 15a or nosylate 15b affords 17. Conversion to 40 provides a substrate for generation of an alpha-lithioaziridine 41 by tin lithium exchange. An intramolecular Michael addition pathway for 41 has been demonstrated by the isolation of 46 in 20% yield under conditions where the intermediate enolate 43 is trapped by selenenylation, but competing proton transfer gives 42. The synthetic potential of the process is limited by stability problems at the stage of the enolate 43 or the protonated product 44.