Theoretical study of the separation mechanism of ionizable compounds in capillary electrochromatography

The migration mechanism of ionizable compounds in capillary electrochromatography (CEC) is more complicated than in high performance liquid chromatography (HPLC) due to the involvement of electrophoresis and the second chemical equilibrium. The separation mechanism of ionizable compounds in CEC has been studied theoretically. The electrochromatographic capacity factors of ions (k~*) in CEC and in the pressurized CEC are derived by phenomenologicai approach. The influence of pH, voltage, pressure on k~* is discussed. In addition, the k~* of weak acid and weak base are derived based on acid-base equilibrium and the influence of pH on k~* is studied theoretically.     

Enantiomer separation by CEC

Three chiral compounds were successfully separated in a short time with two enantiomer separation models on packed-capillary electrochromatography (CEC). (i) 75 μm I.D. capillaries were packed with 5 μm β-cyclodextrin (βCD) chiral stationary phase (CSP). Effects of voltage, pH and concentration of organic modifier on electroosmotic flow (EOF) and chiral separations were investigated systematically. Enantiomers of a neutral compound (benzoin) and a neutral drug (mephenytoin) were separated within a short time with high efficiency. Efficiency of 32 000 theoretical plates per meter and resolution (R8) of 1.42 were achieved for enantiomers of benzoin using a βCD packed column with 6.2crn packed length. Efficiency of 45 000 theoretical plates per meter andR8 of 3.40 were obtained for enantiomers of mephenytoin. Especially, the enantiomer separation of mephenytion was performed in just 3.4 min with R₈ of 2.60. (ii) 75 μm I.D. capillary was packed with octadecylsilica particles (ODs). Chiral separation of a basic drug, propranolol, was studied with chiral agent, via addition of the dimethyl-β-cyclodextrin (DM β-CD) directly into the mobile phase on this column. Baseline separation and efficiency of 81 000 theoretical plates per meter were achieved for propranolol. Project supported by the Natural Science Foundation of Liaoning Province, China, the National Natural Science Foundation of China (Grant No.29875030), and the Excellent Young Scientist Award from the National Natural Science Foundation of China. (Grant No.29725512).     

Preparation and Porous Property of C14-Monolithic Column for Capillary Electrochromatography

Capillary electrochromatography (CEC) has been performed with a series of C₁₄, methlyacrylamide based monolithic columns. These monoliths with different porosities were prepared by in-situ copolymerization in fused-silica capillaries. The porous properties of monoliths were further observed using scanning electron micrographs (SEM) and measured using a mercury porosimeter. The effect of various alcohols as porogens on porous structural properties and chromatographic behaviors were also investigated. The effects of organic additive, pH value and ionic strength in mobile phase on electroosmosis flow (EOF) and separation were further discussed. Meanwhile, the baseline separation of 6 neutral compounds can be well obtained. In addition, the monolithic column demonstrates the high column efficiency and satisfactory reproducibility.Acknowledgements We gratefully acknowledge the support of the National Natural Science Foundation of China.     

毛细管电色谱柱重复性考察及实验条件的选择

成功地研制了７５μｍ内径偶联式和７５,１００μｍ内径非偶联式毛细管电色谱柱。在自制电色谱柱上获得了小于２．１２％的保留时间ＲＳＤ值,考察了ｐＨ值、有机溶剂浓度对保留行为的影响,并用以指导实验条件的选择。比较了两种方式电色谱柱的峰形。     

Finite field study on nonlinear optical properties of substituted ketene N,S-acetals

Ｔｈｅｂｌｕｅｌｉｇｈｔｔｒａｎｓｐａｒｅｎｔｏｒｇａｎｉｃｆｒｅｑｕｅｎｃｙｄｏｕｂｌｉｎｇｍａｔｅｒｉａｌｓａｒｅｏｎｅｏｆｔｈｅｍｏｓｔｉｍｐｏｒｔａｎｔｆｉｅｌｄｉｎｔｈｅｄｅｖｅｌｏｐｍｅｎｔｏｆｎｅｗｗａｖｅｌｅｎｇｔｈｃｏｎｖｅｒｓｉｏｎｍａｔｅｒｉａｌｓ.Ｂｅｉｎｇｐｒａｃｔｉｃａｌｆｒｅｑｕｅｎｃｙｄｏｕｂｌｉｎｇｍａｔｅｒｉａｌｓ,ｔｈｅｙｍｕｓｔｈａｖｅｎｏｔｏｎｌｙｌａｒｇｅｍｏｌｅｃｕｌａｒｆｉｒｓｔｈｙｐｅｒｐｏｌａｒｉｚａｂｉｌｉｔｙβ,ｂｕｔａｌｓｏｇｏｏｄｔｒａｎ…     

Synthesis of spiro-cyclopropane derivatives containing multiple chiral centers

Tandem asymmetric double Michael addition/internal nucleophilic substitution of the novel chiral source, 5-(l-menthyloxy)-3-bromo-2(5H)-furanone with nucleophilic alcohol compounds has been investigated. The tandem asymmetric reaction can afford four new stereogenic centers with one reaction and give optically pure spiro-cyclopropane derivatives 5a--5d which are difficult to obtain by routine methods. The synthetic method for 5a--5d was studied in detail and the new compounds were identified on the basis of their analytical data and spectroscopic data, such as [α]~(20),IR,~1H NMR,~(13)C NMR, MS and elementary analysis. The absolute configuration of the sprio [5-l-menthyloxy-3-bromo butyrolactocyclopropane-3″, 3′(4′-methyloxy-5′-menthyloxybutyrolactone)] (5a) was established by X-ray crystallography. The work can provide important synthetic strategy in synthesis of some new optically active spiro-cyclopropane analogues and some biologically active molecules with complex structure.     

Properties of meso-tetrakis (4- n -alkanoyloxyphenyl) porphyrin liquid crystal Co and Ni complexes

Six series of meso-tetrakis (4-n-alkanoyloxyphenyl) porphyrin Co and Ni complexes (12 kinds) were reported. Nine of the compounds were found to exhibit liquid crystal properties and display a hexagonal columnar discotic columnar (Col_h) phase. Molecular structure of all synthesized compounds was confirmed by IR, UV, MS, ¹H NIVR, and elemental analysis. These liquid crystalline compounds have been studied by cyclic voltammetry, luminescence, and surface photovoltage spectroscopy. Supported by the National Natural Science Foundation of China (Grant No. 59783001), the Natural Science Foundation of Shandong Province (Grant No. Y2006B41), the Foundation of Shandong Provincial Education Department (Grant No. J06A53), the Natural Science Foundation of Shandong University of Technology (Grant No. 2004KJM15) and Doctor Foundation of Shandong University of Technology     

Preparation of polyacrylamide based monolith with immobilized pH gradient and its application for protein analysis

Monolithic materials were prepared in capillaries by in situ polymerization of acrylamide, glycidyl methacrylate and N,N′-memylenebisacrylamid in the presence of trinary porogens, including 1,4-butanediol, dodecanol and dimethyl sulphoxide. With Ampholine immobilized on the monolith by chemical bonding according to their pIs, the monolithic immobilized pH gradient (M-IPG) was prepared, and applied to the separation of four standard proteins. Compared with polyacrylate based M-IPG, the hydrophilicity of the new material was improved. It could not only avoid the adsorption of proteins, but also make the synthesized procedure simple, which showed great potential in the analysis of proteins.     

3D-QSAR and docking studies of estrogen compounds based on estrogen receptor β

Close attention has been paid to estrogen compounds because these chemicals may pose a serious threat to the health of humans and wildlife. Estrogen receptor (ER) exists as two subtypes, ERα and ERβ. The difference in amino acids sequence of the binding sites of ERα and ERβ might lead to a result that some synthetic estrogens and naturally occurring steroidal ligands have different relative affinities and binding modes for ERα and ERβ. In this investigation, comparative molecular similarity indices analysis...     

电色谱模式下四肽印迹整体柱分子识别机理的研究

本文采用原位聚合法制备了以四肽YPLG为模板的毛细管分子印迹整体柱,在毛细管电色谱模式下以模板分子和它的结构类似物YPGL为样品,对分子印迹聚合物的识别机理进行了研究。这两种四肽由于化学结构相似且等电点非常相近,普通的电色谱和毛细管电泳方法分离非常困难。但我们的实验表明,印迹整体柱对模板分子具有特异性识别能力,因此YPLG与YPGL之间的分离因子为1.73,分离度达3.72。实验中系统地研究了流动相中有机溶剂的含量、缓冲溶液的pH值、缓冲溶液的盐浓度以及柱温对四肽识别的影响。实验中我们观察到模板在印迹柱上具有非线性的Van’t Hoff行为,揭示可能存在多重保留机理。本研究结果表明,在毛细管电色谱模式下,分子印迹整体柱的分子识别主要决定于样品与印迹聚合物之间的氢键作用以及印迹孔穴的三维结构。     

Preparation of monolithic capillary columns for capillary electrochromatography by γ-ray irradiation

A novel approach is introduced and evaluated for the preparation of silica-based monoliths by a sol–gel technique where in situ polymerization was carried out by γ-ray irradiation within the capillary. The γ-radiation-initiated synthesis generated radicals directly on the monomer, thereby avoiding use of any initiator. The chromatographic behavior of the capillary monolithic columns was studied in the modes of CEC, p-CEC and low pressure-driven separation, all of which exhibited reversed-phase character. Various operational parameters, such as column temperature, separation voltage, acetonitrile content and buffer pH, were varied to assess their influence on column performance in the separation of a series of neutral compounds including thiourea, benzene, toluene, ethyl benzene, biphenyl and naphthalene. A scanning electron micrograph of a cross-section of the capillary column showed that the gel took the form of a spherical particle aggregate and adhered to the column inner wall. It provided a viable alternative to either thermally initiated or photo polymerization for the preparation of monolithic columns.     

Separation of rhubarb anthraquinones by capillary electrochromatography

Summary A rapid, simple method for packing capillary electrochromatography (CEC) columns with HPLC stationary phases is described. The basis of the method is the use of a vacuum to suck a slurry of stationary phase into the fused-silica tubing, a procedure which takes approximately ten seconds only, then compression of the stationary phase by means of an HPLC pump. These packed CEC columns have been investigated for the separation of five anthraquinones from rhubarb. Separation of the anthraquinones inRheum palmatum L. under optimized conditions is presented.     

Nanosilver resonance scattering spectral method for determination of hydroxyl radical and its application

Silver nanoparticles were prepared under a microwave high-pressure condition using citric acid sodium as a reducer while the excess citrate was removed under high speed centrifugation. There is a resonance scattering (RS) peak at 470 nm for silver nanoparticles. In a pH 4.0 HAc-NaAc buffer solution, hydroxyl radicals from the Fenton reaction can oxidize silver nanoparticles to Ag , resulting in the RS intensity decreasing. The decreased RS intensity at 470 nm (△I 470 nm) is linear with respect to the concentration of H2O2 (C) in the range of 0.27-7.56 μmol/L with a detection limit of 0.23 μmol/L. Its regression equation is △I 470 nm = 24.3 C 13.8 with a correlation coefficient of 0.9959. This method was applied to screening the antioxidants with satisfactory results.     

Description of adsorption equilibrium of PAHs on hypercrosslinked polymeric adsorbent using Polanyi potential theory

In this research,static adsorption of three polycyclic aromatic hydrocarbons(PAHs),naphthalene,acenaphthene,and fluorene,from aqueous solutions onto hypercrosslinked polymeric adsorbent within the temperature range of 288-308 K is investigated.Several isotherm equations are correlated with the equilibrium data,and the experimental data is found to fit the Polanyi-Dubinin-Manes model best within the entire range of concentrations,providing evidence that pore-filling is the dominating sorption mechanism for PAHs.The study shows that the molecular size of adsorbates has distinct in-fluence on adsorption capacity of hypercrosslinked polymeric adsorbent for the PAHs;the larger the adsorbate molecular size,the lower the adsorption equilibrium capacity.Based on the Polanyi-Dubinin-Manes model,the molecular size of adsorbates was introduced to adjust the adsorbate molar volume.Plots of qv vs.(σε /Vs) are collapsed to a single correlation curve for different adsorbates on hypercrosslinked polymeric resin.     

Anab initio MO study on the direct and migratory reaction mechanism for the formation of HF in H + CIF system

Anab initio MO method has been used to calculate the potential energy surface for the formation of HF when H reacts with C1F. The various transition states possibly related to forming HF were optimized. An IRC calculation starting from the collinear F-centered transition state was performed and energies of a series of points with bending configurations were also calculated to determine the direct reaction path leading to HF product. Another IRC calculation starting from the H-centered transition state was run to determine the migratory path to forming HF. By doing so, the Polanyi’s assumption that it would involve the direct and a migratory mechanisms for the formation of HF when H reacts with CIF has been verified theoretically. Project supported by the National Natural Science Foundation of China.     

Characterization of catechol 1,2-dioxygenase from cell extracts of <Emphasis Type="Italic">Sphingomonas xenophaga</Emphasis> QYY

Sphingomonas xenophaga QYY, capable of growing significantly on more than ten kinds of aromatic compounds as sole carbon source, was used to study characterization of catechol 1,2-dioxygenase (C12O) in cell extracts. Characterization of the crude C12O showed that the maximum activity was obtained at 40–70°C and pH 7.8–8.8. Metal ions had different influences on the activity of crude C12O. It was suggested that strain QYY possessed an inducible and ferric-dependent C12O. Kinetic studies showed that the value of V _max and K _m was 0.25 μmol catechol/L/mg protein/min and 52.85 μmol/L, respectively. In addition, the partial purification of C12O was achieved by a HiTrap Q Sepharose column chromatography. Supported by the National Natural Science Foundation of China (Grant No. 50608011) and the 39th Postdoctoral Funds of China (Grant No. 20060390983)     

Retention prediction and hydrophobicity estimation of weak acidic compounds by reversed-phase liquid chromatography using acetic and perchloric acids as ion suppressors

Simple acids are usually applied to suppress the ionization of weakly ionizable acidic analytes in reversed-phase liquid chromatography. The purpose of this study is to investigate the retention behavior of various weak acidic compounds (monoprotic, diprotic, triprotic, and tetraprotic acids) using acetic or perchloric acid as ion suppressor in a binary hydroorganic mobile phase. The apparent n-octanol–water partition coefficient (K _ow ″) was proposed to calibrate the n-octanol–water partition coefficient (K _ow) of weak acidic compound. LogK _ow ″ was found to have a better linear correlation with logk _w, the logarithm of the retention factor obtained by extrapolating to neat aqueous fraction of the mobile phase, for all weakly ionizable acidic compounds. This straightforward relationship offers a potential medium for direct measurement of K _ow data of weak acidic analytes and can be used to predict retention behavior of these compounds in the ion suppression reversed-phase liquid chromatographic mode.     

Resonance scattering spectral detection of ultratrace IgG using immunonanogold-HAuCl<Subscript>4</Subscript>-NH<Subscript>2</Subscript>OH catalytic reaction

Nanogold particles of 10 nm were used to label goat anti-human IgG (GIgG) to obtain nanogold-labeled GIgG (AuGIgG). In a citrate-HCI buffer solution of pH 2.27, AuGIgG showed a strong catalytic effect on the reaction between HAuCl₄ and NH₂OH to form big gold particles that exhibited a resonance scattering (RS) peak at 796 nm. Under the chosen conditions, AuGIgG combined with IgG to form immunocomplex AuGIgG-IgG that can be removed by centrifuging at 16000 r/min. AuGIgG in the centrifuging solution also showed catalytic effect on the reaction. On those grounds, an immunonanogold catalytic RS assay for IgG was designed. With addition of IgG, the amount of AuGIgG in the centrifuging solution decreased; the RS intensity at 796 nm (I _{796 nm}) decreased linearly. The decreased intensity ΔI _{796 nm} was linear with respect to the IgG concentration in the range of 0.08–16.0 ng · mL⁻¹ with a detection limit of 0.02 ng · mL⁻¹. This assay was applied to analysis of IgG in sera with satisfactory sensitivity, selectivity and rapidity. Supported by the National Natural Science Foundation of China (Grant No. 20667001), Natural Science Foundation of Guangxi Province (Grant No. 0728213), and the Foundation of New Century Ten-Hundred-Thousand Talents of Guangxi Province     

Fluorescent sensing of anions based on excited state intramolecular proton transfer in <Emphasis Type="Italic">N</Emphasis>-(3-hydroxy-2-naphthamido)-<Emphasis Type="Italic">N</Emphasis>′-phenylthiourea

A neutral N-amidothiourea-based excited state intramolecular proton transfer (ESIPT) anion receptor bearing an o-hydroxynaphthamide fluorophore and a thiourea binding site, N-(3-hydroxy-2-naphthamide)-N′-phenylthiourea (1a), was designed and synthesized. Fluorescence and absorption response of 1a toward anions were assessed in acetonitrile. IR and NMR experiments indicated that the “OH⋯O=C” intramolecular hydrogen bond (IHB) in 1a was weak so that it only exhibited the short-wavelength normal emission other than ESIPT fluorescence. Due to the high anion binding affinity of the N-amidothiourea binding site and the formation of a hydrogen binding network in the 1a-anion complex, 1a underwent structural change upon anion binding that strengthens the “OH⋯O=C” IHB, leading to the ESIPT and the observation of the long-wavelength ESIPT emission whereas the normal fluorescence is quenched. On the basis of NMR and fluorescence titrations and control experiments with model compounds, a sensing mechanism of the anion-binding-induced ESIPT was proposed. Supported by the National Natural Science Foundation of China (Grant Nos. 20425518, 20675069 & 20835005) and the National Fund for Fostering Talents of Basic Science (Grant No. J0630429)     

An accurate three-dimensional potential energy surface for the He-Na<Subscript>2</Subscript> complex

An accurate three-dimensional potential energy surface (PES) for the He-Na₂ van der Waals complex was calculated at the coupled cluster singles-and-doubles with noniterative inclusion of connected triple (CCSD(T)) level of theory. A mixed basis set, aug-cc-pVQZ for the He atom and cc-pCVQZ for the sodium atom, and an additional (3s3p2d1f) set of midbond functions were used. The computed interaction energies in 819 configurations were fitted to a 96-parameter analytic potential model by least squares fitting. The PES has two shallow wells corresponding to the T-shaped structure and the linear configuration, which are located at 12.5a ₀ and 14 a ₀ with depths of 1.769 and 1.684 cm⁻¹, respectively. The who potential energy surface exhibits weak anisotropy. Based on the fitted PES, state-to-state differential cross sections were calculated. Supported by the Natural Science Foundation of Anhui Educational Committee (Grant No. 2006kj072A) and the Natural Science Foundation of Anhui Province (Grant No. 070416236)