氯化稀土催化ε-己内酯开环聚合

Ring-opening polymerization of ε-caprolactone catalyzed by rare earth chloride dissolved in N,N-dimethylformamide and adding a small amount of propylene oxide was studied.The optimum conditions for the ring-opening polymerization of CL are as follows.In the bulk polymerization: n(DMF)/n(LaCl₃)=10,n(PO)/n(LaCl₃)=20,aging temperature: 30 ℃,aging time: 1 h,c(CL)=7.91×10^-3 mol/L,c(LaCl₃)=1.58×10^-5 mol/L,the polymerization carried out at 30 ℃ for 1 h,yield=83.3%,M_ν=1.93×10⁴.In the solution polymerization: n(DMF)/n(LaCl₃)=10,n(PO)/n(LaCl₃)=20,aging temperature: 30 ℃,aging time: 1 h,toluene as the solvent,c(CL)=4.22×10^-3 mol/L,c(LaCl₃)=8.43×10^-6 mol/L,the polymerization was carried out at 30 ℃ for 2 h,yield=62.9%,M_ν=1.21×10⁴.     

DMF竞争性抑制大豆脂氧酶好氧催化及其松弛底物抑制的综合作用

在大豆脂氧酶催化亚油酸的氧化反应中加入溶剂二甲基甲酰胺DMF(lgP为-1.01)可将底物亚油酸浓度提升到232 mmol/L而不产生底物抑制作用, 并使平衡产率从38.93%提高到66.09%. 在有底物存在时, 质量分数为5%的DMF基本不影响酶活; 此时体系具有最大的Kss与Ki值, 表明5%DMF对底物抑制作用的松弛效应最强, 而对酶的抑制作用最小.     

Kinetic Investigation of the Electrochemical Oxidation of Bis(benzene)chromium(0) in Diethyl ketone/N,N-Dimethylformamide

The cyclic voltametric technique utilizing a platinum working electrode was applied for the investigation of the electrochemical oxidation of bis(benzene)chromium(0), (C₆H₆)₂Cr to bis(benzene)chromium(I), (C₆H₆)₂Cr⁺ in diethyl ketone (DEK), N,N-dimethylformamide (DMF), and DEK/DMF binary mixtures containing n-tetrabutylammonium hexafluorophosphate (TBAPF₆) as the supporting electrolyte at T=298.15 K. The half-wave potentials (E _1/2) of the (C₆H₆)₂Cr^+/0 redox couple in DEK, DMF and DEK/DMF binary mixtures, were determined. The variation of E _1/2 with the solvent composition was found to be almost linear. The E _1/2 results were analyzed in terms of the electron-donating power of the solvent medium. The diffusion coefficients, D, were calculated using the Randles-Sevcik equation. The kinetics of the electrode reaction were investigated through the determination of the heterogeneous electron-transfer rate constants, k _s, according to the electrochemical rate equation proposed by Nicholson. Furthermore, the activation Gibbs energies for the electron-transfer process (ΔG ^≠) were also calculated. The results indicate that the redox couple (C₆H₆)₂Cr^+/0 exhibits an electrochemically reversible and diffusion-controlled process in all the investigated solvent media.     

盐-N,N-二甲基甲酰胺/乙醇双溶剂体系的荧光光谱分析

利用荧光光谱和量子化学计算方法研究了LiCl和MgCl2对N,N-二甲基甲酰胺(DMF)/乙醇双溶剂体系的微观结构变化的影响。通过对DMF的N—C O键以及盐与DMF和乙醇相互作用的研究发现,离子溶剂化作用导致溶剂体系结构变化,生成多种具有荧光属性的团簇,且随浓度的变化而变化。结合具有荧光属性的团簇分子跃迁能和可能的配位构型的优化以及热力学性质计算得到,共轭体系越大的团簇分子受盐的影响越小且其跃迁能越小的规律。比较Li+和Mg2+形成配位构型离子簇的稳定性和荧光强度,说明了离子极化对溶剂化的影响。     

Determination of electroosmotic flow mobility with a pressure-mediated dual-ion technique for capillary electrophoresis with conductivity detection using organic solvents

A method is described for the indirect determination of the mobility of the electroosmotic flow (EOF), which can be carried out within a few minutes even for very low mobilities. It is independent of the direction of the EOF. It is based on the comparison of the measured mobilities of two oppositely charged reference ions (tetraphenylphosphonium and tetraphenylborate) with given mobilities in different organic solvents (methanol, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, propylene carbonate) at ionic strengths between 5 and 50 mM. The method is based on the sequential movement of the reference ions in a three-step process: first by a laminar flow to a certain position in the separation capillary, followed by electromigration due to application of voltage, and pressurised migration towards the detector. In this way the total mobilities of the reference ions can be determined from their residence times, and the difference to their known actual mobilities gives the mobility of the EOF. The method avoids misinterpretations caused by system- and eigen-peaks, which often bias the results especially when a conductivity detector is used. The method is suitable for all solvents, and is an advantage especially for organic and mixed aqueous–organic background electrolytes with high UV absorbance.     

膜溶解富集吸光光度法测定微量铜

以5-Br-PADAP为显色剂,用硝化纤维素膜为富集分离膜测定微量铜,然后用N,N-二甲基甲酰胺(DMF)溶解滤膜和捕集物[Cu(Ⅱ)-5-Br-PADAP],Cu(Ⅱ)-5-Br-PADAP在DMF溶液中最大吸收波长为560nm,表观摩尔吸光系数9.58×10~4.铜量在0.1～5.0μg/5ml范围内符合比耳定律,方法灵敏度高.操作简便、快速,应用于食品、水样中铜的测定结果满意.     

Crystallization-driven self-assembly of isotactic polystyrene in N,N-dimethylformamide

Herein we demonstrate crystallization-driven self-assembly of isotactic polystyrene(i PS) with high isotacticity and narrow molecular weight distribution and crystallization-induced switching of the morphology of i PS aggregates in N, N-dimethylformamide(DMF). The formation and morphology switching of the self-assembled aggregates of i PS are investigated by means of dynamic light scattering(DLS), scanning electron microscopy(SEM), differential scanning calorimetry(DSC) and wide angle X-ray diffraction(WXRD). The results reveal that cooling DMF solution of i PS promotes i PS chains to self-assemble into spherical aggregates with a gelled core cross-linked by microcrystals, which is surrounded by solvent-swollen corona. Furthermore, crystallization induces the deformation of i PS aggregates from spherical to plate-like or nest-like.     

Lithium Chloride–Assisted Selective Hydrolysis of Methyl Esters Under Microwave Irradiation

A rapid and mild method for the selective hydrolysis of methyl ester in lithium chloride–N,N-dimethylformamide (LiCl–DMF) system under microwave irradiation has been developed. The effects of substituent, metal salt, and solvent on the reactivity and selectivity of the hydrolysis reaction have been investigated. Microwave irradiation significantly improves the reaction yield within a short time in an LiCl–DMF system. Moreover, the chiral α-carbon of methyl esters retained its configuration during the reaction. Finally, the catalytic mechanism of hydrolysis by LiCl salt has also been proposed.