Biocatalytic synthesis of polymers. III. Formation of a high molecular weight polyester through limitation of hydrolysis by enzyme-bound water and through equilibrium control

Enzyme-catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures and has been studied for several years. A significant limitation on the polyesters prepared to date has been the low molecular weights achieved. The present studies have established that, in the polycondensation of bis(2,2,2-trifluoroethyl) glutarate with 1,4-butanediol using porcine pancreatic lipase as the catalyst, this limitation arises from at least two sources: hydrolysis of activated ester end groups by water introduced along with the enzyme and the polymerization's reaching equilibrium despite using the poorly nucleophilic 2,2,2-trifluoroethanol as the leaving group. Evidence is also developed that the presence of trifluoroethanol accelerates the release of the enzyme-bound water which hydrolyzes the activated ester end groups. The hydrolysis could be avoided by choosing a relatively high-boiling solvent, such as bis(2-ethoxyethyl) ether, then removing the trifluoroethanol by placing the reaction mixture under vacuum periodically or by drying the enzyme rigorously. The vacuum method also removed the limitation on molecular weight resulting from the reaction's reaching equilibrium. A further improvement in the molecular weight to nearly 40,000 daltons, well within the range that is technically interesting, was achieved by using 1,2-dimethoxybenzene or 1,3-dimethoxybenzene as the polymerization solvent. © 1995 John Wiley & Sons, Inc.     

Substituenteneffekte auf die C–C-Bindungsstärke, 8. Standardbildungsenthalpien und Spannungsenthalpien von 1,1,2,2-Tetraethylethylenglykol-dimethylether und D,L-1,2-Dimethyl-1,2-diphenylethylenglykol-dimethylether

Effects of Substituents on the Strength of C - C Bonds, 8¹. - Heats of Formation and Strain of 1,1,2,2-Tetraethylethylene Glycol Dimethyl Ether and D,L .-1,2-Dimethyl-l,2-diphenylethylene Glycol Dimethyl Ether The heats of combustion of the title compounds 1 and 2 were measured calorimetrically with the result (kcal mol ^-1, s. d. in parentheses) ΔH°_c = − 1880.1 (± 0.6) and − 2373.3 (± 1.4). The heat of vaporisation of 1 ΔH^v = 14.3 (± 0.3) and the heat of sublimation of 2 ΔH^sub = 27.2 (± 0.5) were derived from their temperature dependance of the vapor pressure. The latter were determined between 30 and 80°C using a flow method. The resulting standard heats of formation ΔH°_t(g) = −122.4 (± 0.7) and −43.8 (±1.5) for 1 and 2 correspond to a strain enthalpy (_s) of 15.9 and 8.0 kcal mol^-1, respectively. The steric strain of the dimethoxyethanes 1 and 2 is about one fourth lower than the strain of the corresponding dimethylethanes 3 and 4 bearing the same substituents. Thus, a methoxy group causes less steric stress than a methyl group.     

Sugar-water interaction from diffusion measurements

The diffusion coefficients of deoxyribose and ribose in water were measured at 25°C. The Stokes-Einstein relation for mono-, di-, and tri-saccharides are discussed. The diffusion coefficient at infinite dilution D_o for deoxyribose was the largest among these sugars. It appears that the deoxyribose breaks local water structure but the ribose hardly affects the structure. D_o correlates well with the mean number of e-OH groups in the sugar molecule. It is suggested that the mean number of e-OH groups is a good parameter to describe the properties of sugar hydration.     

Interactions between terminally substituted amino acids in an aqueous and a non-aqueous environment. Enthalpic interaction coefficients in water and in N,N-dimethylformamide at 25°C

Enthalpies of dilution of the N-acetyl amides of glycine, L-alanine, L-valine, L-leucine, and L-phenylalanine, dissolved in N,N-dimethylformamide (DMF) as a solvent have been measured at 25°C. The results obtained have been analyzed to give the enthalpic interaction (or virial) coefficients of the solutes and these are compared with information previously obtained in aqueous systems. There are marked differences in the interaction properties in the two solvents and, while the additivity approach of Savage and Wood is applicable to the solutes in water it is not suitable for representing the interactions in DMF. A correlation is presented between the enthalpic second virial coefficients in DMF and the propensity of side-chains to be in proximity in globular proteins.     

ω-氟砜基氟烷基格氏试剂的制备及其反应

合成氟烷基酮的通用方法是将全氟烷基金属试剂与羰基类化合物反应。但对于ω位带有官能团的全氟烷基金属试剂的研究,唯一的例子是:     

N,N′-双吡咯的合成及其邻位基团效应

2,2-联吡咯是某些天然存在的活性吡咯化合物中关键组成,关于手性联吡咯的研究己有详细的综述报道。近年发现,某些含N-取代氨基的空间阻碍吡咯有明显的生理活性和可贵的药理性质。N,N′-联吡咯中N-N键,很容易发生均裂反应而生成游离基,后     

Zur Synthese von fungizid wirksamen Isocamphanderivaten: Synthesen in der Isocamphanreihe, 34. Mitt.

Summary Some esters of isocamphenilanic acid (4) have been prepared and tested for their fungicidal and insecticidal activity. Esters of various acids with isocamphanyl ethylalcohol (5) have also been synthesized and included in the fungicidal/acaricidal/insecticidal screening programme. All esters bear a geminal dimethyl group at C-3 of the bicyclus which is important because of its shielding effect.

     

Regioselective synthesis of 5-trifluoromethyl-1,2,3-triazole nucleoside analogues via TBS-directed 1,3-dipolar cycloaddition reaction

Herein described was a straightforward method for the highly regioselective synthesis of 5-trifluoromethyl-1,2,3-triazole nucleoside analogues, which featured the utilization of tert-butyldimethylsilyl (TBDMS) group as the directing group in the 1,3-dipolar cycloaddition reactions. 4-tert-Butyldimethylsilyl-5-trifluoromethyl-1,2,3-triazole nucleoside analogues were generated as the only cycloaddition products in moderate yields (15-79%) via the treatment of glycosyl azides with 3,3,3-trifluoro-1-tert-butyldimethylsilylpropyne 1 in toluene at 85 °C. Removal of TBS groups in these triazole cycloadducts with tetrabutylammonium fluoride (TBAF) smoothly afforded the various 5-trifluoromethyl-1,5-disubstituted 1,2,3-triazole nucleoside analogues in good yields (40-88%).     

取代基对依布硒啉电子结构及光谱性质影响的理论研究

采用密度泛函理论B3LYP方法在6-311++G**水平对依布硒啉及其6个衍生物进行结构优化,并分析了取代基对分子几何构型、电荷分布、前线轨道能级分布的影响.在相同计算水平上采用含时密度泛函理论方法进行了电子光谱研究,讨论了取代基对电子光谱的影响.计算结果表明,标题化合物分子为非平面结构,苯并异硒唑酮环与苯环之间存在一...