Jingang Yu

Rapid Reaction‐Diffusion Model for the Enantioseparation of Phenylalanine across Hollow Fiber Supported Liquid Membrane

Abstract This paper deals with the rapid reaction‐diffusion model of the transport and enantioseparation factor of (d/l)‐phenylalanine across hollow fiber supported liquid membranes. Mass transfer resistance of the boundary layer in the tube side and the boundary layer in the shell‐side, diffusion in the membrane phase, and interfacial chemical reactions at the liquid membrane interfaces are taken into account in the model equations. The experimental results show that the proposed model can simulate the concentration of the (d/l)‐phenylalanine and the separation factor of the enantioselective process satisfactorily. It is simply a mathematical model which can be easily used to predict the concentration of the enantiomers and the separation factor of the enantioseparation process.

Chromatographic Separation of Naproxen Enantiomers using Hydroxypropyl‐β‐Cyclodextrin as Chiral Mobile Phase Additive

Abstract Chromatographic separation of naproxen has been studied using hydroxypropyl‐β‐cyclodextrin as chiral mobile phase additive. The effects of mobile‐phase composition were researched in detail. The appropriate composition of mobile phase was 85:15 (v/v) aqueous with 0.5% TEA at pH 3.5/ ethanol containing 25 mM HP‐β‐CD, and the column temperature was set of 25°C. Graphs of 1/k versus [HP‐β‐CD] gave good linear relationships, indicating the stoichiometry ratio of naproxen with HP‐β‐CD of 1:1. Apparent thermodynamic parameters were also calculated from the plots of lnα versus 1/T, it was found that the enantioseparation was enthalpy driven and the inclusion process was exothermic.

Cross-Linking of Multi-Walled Carbon Nanotubes with Polyethylene Glycol

In this paper a new approach to cross-link two individual multi-walled carbon nanotubes (MWCNTs) by a nucleophilic substitution of brominated MWCNTs using polyethylene glycol anion was introduced. The functionalized MWCNTs were characterized using thermogravimetric analysis (TGA), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. It is found that polyethylene glycol act as cross-linking agents to interconnect or cross-link the MWCNTs within and among the bundles, as demonstrated by TEM analysis, and few defects will be induced to the nanotube sidewalls. After cross-linking of PEG, the functionalized MWCNTs are still insoluble in any solvent; however, the morphologies of the cross-linked MWCNTs were largely intact, undoubtedly which will provide a useful way to construct nanoscale devices with MWCNTs in the future.

Enantioseparation of racemic alpha-cyclohexyl-mandelic acid across hollow fiber supported liquid membrane

This paper deals with the enantioseparation of racemic a-cyclohexyl-mandelic acid containing copper(II) N-dodecyl-(L)-hydroxyproline (CuN2) as a chiral carrier using hollow fiber supported liquid membrane. A mathematical model of transport and enantioseparation of chiral compounds was deduced, the observed partition coefficient between the feed phase and the membrane phase, the stripping phase and the membrane phase, mass transfer resistance of boundary layer in strip phase inside the hollow fibers, boundary layer in feed phase and the diffusion in the membrane phase are taken into account in the model equations. Using the experimental results, several parameters of the proposed model have been achieved by nonlinear fitting method. It is a simply mathematical model which can be easily used to predict the concentration of the enantiomers and the separation factor of the enantioseparation process, and it can also be used to design and scale up the enantioseparation process.

Improvement of electrochemical performance of LiMn2O4 composite cathode by ox-MWCNT addition for Li-ion battery

Oxidized multi-walled carbon nanotubes (ox-MWCNT) were used as conducting addition to prepare a novel network composite cathode for lithium ion battery. The morphology was analyzed by scanning electron microscope, LiMn2O4 active particles were connected by ox-MWCNT with the formation of three-dimensional networking wiring. Electron transport and electrochemical activity were improved effectively. Galvanostatic charge-discharge tests of LiMn2O4/ox-MWCNT cathode showed that the initial discharge capacities are 119.4, 110.6, 105.5 and 91.4 mAh g-1 at the rate of 0.1, 0.5, 1 and 2 C, respectively, which were much higher than LiMn2O4/acetylene black (AB) at the same content. The electrochemical AC impedance spectroscopy showed that the charge transfer resistance (Rct) of the composite electrode reduced obviously contrasting to 34.32xa0Ω for LiMn2O4/ox-MWCNT and 53.2 Ω for LiMn2O4/AB. Overall, it is found that a conductive network to facilitate electron transfer and good connection of the active-material particle to the network were playing an important role to rate capability and cycle efficiency.

Preparation and electrochemical properties of homogeneous carbon-coated LiFe0.9Mn0.1PO4 as cathode material for lithium-ion batteries

Homogeneous carbon-coated LiFe0.9Mn0.1PO4 cathode material was synthesized by one-step solid-state reaction using glucose as carbon source. Powder X-ray diffractometry (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic measurements were employed to characterize the samples. Mn-doping and carbon co-modification did not affect the olivine structure of LiFePO4, but improved its kinetics in terms of capacity delivery, polarization and rate capability. When compared with the undoped LiFePO4/C, the LiFe0.9Mn0.1PO4/C sample presented good size distribution - around 100-200 nm - and better electrochemical performance. At current rates of 0.1, 1.0, 3.0 and 10.0 C (C = 170 mA g-1), the LiFe0.9Mn0.1PO4/C electrode delivered discharge capacities of 154.1, 138.8, 120.0 and 94.0 mA h g-1, respectively. Results obtained by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) indicated that the polarization and charge transfer resistance of the sample were greatly decreased by Mn-doping.

Crystal structure of N-(3-hydroxyphenyl)-5-chlorosalicylideneimine, C13H10ClNO2

C13H10ClNO2, monoclinic, P21/n (no. 14), a = 10.149(7) Å, b = 5.925(4) Å, c = 18.27(1) Å, ) = 90.84(1)°, V = 1098.5 Å, Z = 4, Rgt(F) = 0.046, wRref(F) = 0.164, T = 293 K. Source of material To the solution of m-hydroxyaniline (1.09 g, 10 mmol) dissolved in 50 ml ethanol, was added 5-cholosalicylaldehyde (1.57 g, 10 mmol), and the mixture was refluxed for 0.5 h. Then the solution was evaporated slowly at room temperature to obtain orange red prismatic crystals suitable for X-ray structure determination. Experimental details The H atoms were positioned geometrically with d(C—H) = 0.93 0.98 Å and refined as riding with Uiso(H) = 1.2 Ueq(carrier) or 1.5 Ueq(methyl). Discussion Proton tautomerization plays an important role in many fields of chemistry and biochemistry. Schiff bases of salicylaldehyde with amines (anils) comprise a chemical system undergoing hydrogen-atom tautomerism between enol and keto forms and show the phenomena of solid state photochromism and thermochromism [1-3]. In the title compound, the bond length of C4—O1 (1.302(2) Å) is shorter than that of O2—C12 (1.354(2) Å) indicating hydrogenatom tautomerism between O1–H1O–N1. Supposedly, there should be intramolecular proton transfer from the hydroxyl O atom to the imine N atom in the solid state of the compound [4]. The dihedral angle between the plane (N1–C7–C5–C4– O1–H1O) and the plane (C1–C2–C3–C4–C5–C6) is 2.7°, which shows the hydrogen bonded ring is almost coplanar with the adjacent ring. Z. Kristallogr. NCS 226 (2011) 275-276 / DOI 10.1524/ncrs.2011.0123 275