Microwave-Assisted Preparation of a β-Cyclodextrin-Based Stationary Phase for Open Tubular Capillary Electrochromatography

Fluorescein isothiocyanate was used as a label to show that a 3-aminopropylmethyldimethoxysilane (KH 550)-modified capillary column was prepared by microwave irradiation. A bromoacetate-substituted β-cyclodextrin (Br-β-CD) was successfully bound to the KH 550-modified column as a chiral stationary phase for open tubular capillary electrochromatography. Compared with conventional synthesis, the microwave-assisted process significantly decreased the preparation time of the stationary phase from 16 h to 40 min. Baseline chiral separation of 1-phenyl-1,2-ethanediol was achieved using the Br-β-CD modified column.     

Rapid Preparation of Monolithic Columns for Capillary Electrochromatography Separation

Sol-gel technology can provide a versatile approach to the synthesis of organic polymers and organic-inorganic hybrid materials applied in HPLC, micro-HPLC and capillary electrochromatography (CEC)1. It can take place under extraordinarily mild thermal co…     

Carboxymethyl-β-Cyclodextrin for Chiral Separation of Basic Drugs by Capillary Elcctrophoresis

Theseparationofchiralcompoundsisofkeyimportanceindifferentareasofresearch,e,g.,pharmaceutical,biological.,environmentaletc.'Capillaryelectrophoresis(CE)isapowerfultechniqueforchiralreparation.ThegeneralmeritsofCEsuchasimpressivepeakefficiency,rapidityofanalysieismallvolumesandlowcostsarethemostimportantfactorsjcontributingtothesucclessfuldevelopmentofthistechnique"=.Currentlycyclodextrins(CDs)arethemostcommonlyusedchiralresolvingagentsinCE.Enantiomericseparationisbasedonthedifferenceinincl…     

Capillary Zone Electrophoretic Separation of Basic Proteins with Coated Columns Prepared by Sol-Gel Technology

l.1ntroductionItiswellknownthatthehighresolvingpowerofcaPillnyzoneelectrophoresistendstodecreaseserious1yin.theseparaionofproteinsduetotheadsorptionofproteinsontheinnerwallsoffusedsilicacaPillaries,whichleadtoconsiderablepeakbroadeningandpoorreproducibility[l].AtpresentseveralapproacheskavebeenemployedtoelhoinatethewalladsorptionofproteinsamongwhichcoatingthecaPillarysurfacewithaneutralweaklyhydrophilicpolyInercanalwaysgiveexcellent,esultS[2'3].Thispaperdescribesaone-stepmethodforthepreparai…     

Investigation of Mixed Chiral Selectors of Different Metal Ion-L-Alanine Complex and β-Cyclodextrin on the Chiral Separation of Dansyl Amino Acids with Capillary Electrophoresis

Chiral separation of dausyl amino acids by capillary electrophoresis using mixed selectors of Mn(ll)-L-alanine complex and β-cyclodextrin (β-CD) was studied. Resolution was considerably superior to that obtained by using either Mn (Ⅱ)-L-alanine complex or β-CD alone. The effects of separation parameters, such as pH value of buffer solution, capillary temperature, the concentration of Mn (Ⅱ)-L-alanine complex, the types of CD and ligand on the migration times and resolutions were investigated. Six different transition metal complexes,Cu(Ⅱ), Zn(Ⅱ), Co(Ⅱ), Ni(Ⅱ), Hg(Ⅱ) and Cd(Ⅱ)-L-alanine complexes have been employed and compared with Mn(Ⅱ)complex. Differences in retention and selectivity were found.The substitution of Cu(Ⅱ), Zn(Ⅱ), Co(Ⅱ) and Ni(Ⅱ) for Mn(Ⅱ) resulted in a better chiral resolution while Hg(Ⅱ) and Cd(Ⅱ) showed poorer resolution abilities. The chiral separation mechanism was also discussed briefly.     

Carboxymethyl-β-cyclodextrin for Chiral Separation of Amino Acids Derivatized with Fluorescene-5-isothiocyanate by Capillary Electrophoresis and Laser-induced Fluorescence Detection

A method using carboxymethyl-β-cyclodextrin (CM-β-CD) as selector for chiral separation of amino acids by capillary electrophoresis and laser-induced fluorescence detection was studied. Resolution was better than that obtained by β-CD or HP-β-CD.     

Sensitive Method for Enantioseparation of Rivastigmine with Highly Sulfated Cyclodextrin as Chiral Selector by Capillary Electrophoresis

A sensitive method for enantioseparation of a basic drug rivastigmine and determination of its optical impurityby capillary electrophoresis with highly sulfated β-cyclodextrin(HS-β-CD)as the chiral selector is described.Ingeneral,enantioseparation of basic chiral compounds is carried out in acidic condition(pH 2.5)to prevent analytesfrom adsorption on the capillary wall.However,in the case of rivastigmine,the detection sensitivity was too limitedto determine the optical impurity of S-rivastigmine lower than 1% when buffer pH was 2.5.It was found that thedetection sensitivity was improved 1.6 times just by raising the buffer pH value from 2.5 to 5.8.The poor columnefficiency due to the adsorption of the analytes on the capillary wall was resolved by using dynamical coating of thecapillary wall with the linear polyacrylamide solution.The experirnental parameters such as the concentration ofHS-β-CD,buffer pH and buffer ionic strength were optimized,respectively.The method was validated in terms ofrepeatability,linearity,limit of detection(LOD)and limit of quantitation(LOQ).Using the present method,the op-tical purity of nonracemic rivastigmine with the enantiomeric excess(ee)value of 99.14% was determined.     

Comparison of Carboxylic and Hydroxycarboxylic Acids as Complexing Agents for Transition Metal Separation with Nonaqueous Capillary Electrophoresis

Many papers have been published on the analysis of metal cations by capillary electrophoresis (CE), for example, lanthanide, transition metal, alkali, and alkaline earth metal ions. Separations of metal ions are based on the differences in their electrophoretic mobilities. Since most     

A Silica Monolithic Column with Chemically Bonded l-Pipecolic Acid as Chiral Stationary Phase for Enantiomeric Separation of Dansyl Amino Acids by CEC–MS

A silica monolithic column chemically modified with l-pipecolic acid as chiral stationary phase has been developed for chiral separation of dansyl amino acids by capillary electrochromatography–mass spectrometry (CEC–MS). The monolithic column was prepared by a sol–gel process and subsequent chemical modification by l-pipecolic acid as chiral selector with 3-glycidoxypropyltrimethoxysilane as spacer. Interestingly, it was found that the l-pipecolic acid-modified monolithic column can hold copper(II) ions tightly after loading Cu(II) ions during column preparation and conditioning and allows CEC separation to be conducted based on chiral ligand exchange with MS detection by a mobile phase without copper ions. It has been demonstrated that the chiral monolithic column operates well for enantioseparation of several dansyl amino acids by CEC–MS.

     

Highly enantioselective construction of CF3-bearing all-carbon quaternary stereocenters: Chiral spiro-fused bisoxazoline ligands with 1,1'-binaphthyl sidearm for asymmetric Michael-type Friedel-Crafts reaction

A novel class of chiral spiro-fused bisoxazoline ligands possessing a deep chiral pocket was prepared.The developed ligands have been employed in the nickel-catalyzed highly enantioselective Michael-type Friedel-Crafts reaction, affording the products bearing a trifluoromethylated all-carbon quaternary stereocenter with moderate to excellent yields（up to 99%） and good to excellent enantioselectivies（up to> 99.9% ee）. Moreover, a proposed model of chiral pocket revealed that the attack of indo...     

Separation of Yb as YbSO4 from the 176Yb target for production of 177Lu via the 176Yb(n, γ)177Yb→177Lu process

An effective and simple process for the separation of ¹⁷⁷Lu from neutron-irradiated Yb targets was developed. Irradiated Yb target was dissolved in H₂SO₄ solution and after reduction with sodium amalgam Yb was precipitated in the form of YbSO₄. From 50 mg of Yb irradiated target only 1 mg Yb remains in solution after precipitation and separation of YbSO₄. The overall recovery of ¹⁷⁷Lu is estimated at 73%. Further efficient chromatographic separation of carrier-free ¹⁷⁷Lu from 1 mg of Yb is relatively easy and is described in several papers.     

Chiral Counteranion Strategy for Asymmetric Oxidative C(sp3)?H/C(sp3)?H Coupling: Enantioselective α‐Allylation of Aldehydes with Terminal Alkenes

The first enantioselective α‐allylation of aldehydes with terminal alkenes has been realized by combining asymmetric counteranion catalysis and palladium‐catalyzed allylic C H activation. This method can tolerate a wide scope of α‐branched aromatic aldehydes and terminal alkenes, thus affording allylation products in high yields and with good to excellent levels of enantioselectivity. Importantly, the findings suggest a new strategy for the future creation of enantioselective C H/C H coupling reactions.