Enantiomeric separation of α-phenylethylamine and its derivatives by series coupled open tubular columns

A series coupled fused-silica open tubular columns of a chiral and an achiral stationary phase were used to achieve the enantiomeric separation of a-phenylethylamine, o,m,p-methyl-and o,m,p-methoxy-a-phenylethylamine. A simplified equation describing the retention values of series coupled columns was derived, which relates the capacity factors of series coupled columns to the capacity factor of individual columns, their lengths, inlet and outlet pressure. Very good agreement was obtained both between calculated values by this equation and those by Krupcik's equation and between values measured experimentally and calculated theoretically. By means of this simplified equation a computer program was developed in locating the operating range of optimum amin, enantiomeric separation of all a-phenylethylamine and its derivatives were achieved in a single run.     

The correlation between molecular structure parameters of O-ethyl N-isopropyl phosphoro(thioureido)thioates and their retention data in RP-HPLC

A retention prediction system(RPS)of seven O-ethyl N-isopropyl phosphoro(thioureido)-thioates in reversed phase HPLC was investigated.The system is based on the solvent selectivitytriangle concept.Three molecular structure parameters(hydrophobicity Ⅱ,substituent length L,and substituent maximum width B_5)were used to describe the quantitative structure-retention relation-ships.With these quantitative relationships,the retention behaviours of other eight homologsfor different mobile phase composition were predicted.The predicted values were consistent with themeasured values within relative error of 10%,which means that it is possible to apply the reportedmethod to predict retention values for qualitative purposes for different mobile phase compositions.     

Synthesis and Chromatographic Properties of New β-Cyclodextrin Derivatives with α-Schiff Base Groups for HPLC

β-Cyclodextrin 1 was directly oxidized to the corresponding monoaldehyde 2 on their primary faces by cyclized 2-iodoxybenzoic acid(IBX) in DMSO, followed by the synthesis of β-cyclodextrin derivatives bearing Schiff-base group 3. A new chiral stationary phase(BCDS 6) was then prepared by immobilization of β-cyclodextrin derivative with α-Schiff base group onto the surface of sillica gel. A series of compounds with amino groups were readily separated using this CSE Methanol and acetonitrile were tested as the mobile phase while the influence of temperature and the addition of aqueous triethylammonium acetate buffer to the mobile phase was also innvestigated. Ferrocene ligand with Schiff-based groups have been separated satisfactorilly on BCDS column.     

Live retention database for identification of compounds in capillary gas chromatographic analysis --Principle and structure

A live retention database for compound identification in isothermal and any step temperature programmed capillary gas chromatography has been developed. The database utilizes the Kovats retention indices of compounds on a given stationary phase and the retention time of n-alkanes measured at isothermal conditions on the column to be used, together with the programming parameters. Identification is performed by search operation that compares the calculated results with the retention values of unknown peaks. Cross-reference of the search results of different operating conditions is performed automatically by the database in order to increase the reliability of the identification. The error of the database conversion is ≤± 0.5 index unit, or ≤± 1% on retention time. This paper describes the principle and the structure of the database in detail. The experimental results for different calsses of compounds tested at divers operating conditions will be presented in Part Ⅱ.     

Low Temperature Heat Capacities and Thermodynamic Properties of Zinc L-Threonate Zn（C4H7O5）2（s） by Adiabatic Calorimetry

Low-temperature heat capacities of the solid compound Zn（C4H7O5）2（s） were measured in a temperature range from 78 to 374 K, with an automated adiabatic calorimeter. A solid-to-solid phase transition occurred in the temperature range of 295？322 K. The peak temperature, the enthalpy, and entropy of the phase transition were determined to be （316.269±1.039） K, （11.194±0.335） kJ？mol-1, and （35.391±0.654） J？K-1？mol-1, respectively. The experimental values of the molar heat capacities in the temperature regions of 78？295 K and 322？374 K were fitted to two polynomial equations of heat capacities（Cp,m） with reduced temperatures（X） and [X = f（T）], with the help of the least squares method, respectively. The smoothed molar heat capacities and thermodynamic functions of the compound, relative to that of the standard reference temperature 293.15 K, were calculated on the basis of the fitted polynomials and tabulated with an interval of 5 K. In addition, the possible mechanism of thermal decomposition of the compound was inferred by the result of TG-DTG analysis.     

Preparation of polypropylene/poly(styrene-co-(butyl methacrylate)) nanoblends by diffusion and subsequent copolymerization of monomers in isotactic polypropylene pellets

The diffusion and subsequent copolymerization of styrene(St)/butyl methacrylate(BMA) mixed monomers in i PP pellets to prepare copolymer nanoblends were investigated. The diffusion step was carried out at 90 ℃ for 2 h in water, and the copolymerization was initiated by the addition of BPO with the aid of a small amount of St. The diametrical distributions of both St and BMA units and their ratio St/BMA were investigated by micro FTIR. Both St and BMA can diffuse into the centres of i PP pellets. The diametrical distribution of St/BMA ratio is constant in all the copolymer blends. The copolymer composition depends on the comonomer feed ratio. The molecular weights of the copolymers were measured by GPC after extraction with tetrahydrofuran. The phase morphology of the copolymer blends was investigated by FESEM, showing the average particle sizes of less than 100 nm. DSC measurements show that the diffusion and subsequent copolymerization of St/BMA monomers only occur in the amorphous regions of i PP pellets.     

OXIDATIVE COUPLING OF METHANE OVER Sr-Pb-O AND Sr-Pb-O/γ-Al_2O_3 CATALYSTS

Two series of Sr-Pb-O and Sr-Pb-O/γ-Al_2O_3 catalysts of differentcomposition were investigated for the oxidative coupling of methane.Theeffects of reaction conditions on the catalytic behavior have been studied.Catalyst characterization was carried out by XRD,TPR,TPD and XPS tech-niques.It was found that a strong interaction took place between Sr-Pb-Oand γ-Al_2O_3 so that Sr_3Al_(32)O_(51)phase and a small amount of PbAl_2O_4 formedin the bulk and the surface was mainly enriched with Pb.A 30 wt% Sr-Pb-O/γ-Al_2O_3 catalyst gave a 30.4% methane conversion and a 50% C_2 selec-tivity at 750℃ and with a feed gas composition of CH_4:O_2=2.5:1.Theenrichment of Pb on the surface may be responsible for the higher catalyticactivity and selectivity.     

Iodide analysis by ion chromatography on a new stationary phase of polystyrene-divinylbenzene agglomerated with polymerized-epichlorohydrin-dimethylamine

A new stationary phase for iodide ion analysis has been developed. The cationic polymerepichlorohydrin-dimethylamine(PEPI-DMA) was served as modifier in synthesizing polyelectrolyte sorbents and the macroporous polystyrene-divinylbenzene(PS-DVB) resin was used as support. The positively charged polymer(PEPI-DMA) was electrostatically bonded to a negatively charged particle(PS-DVB sulfonated). The new stationary phase was characterized by scanning electron microscopy(SEM), Fourier transform infrared(FTIR), elemental analysis, chemical adsorption and desorption measurements. The chromatographic evaluation of the new stationary phase was performed using various anions with a conductivity detector. The new stationary phase was also applied to the determination of iodide directly with a DC amperometric detector using a platinum working electrode and an Ag/Ag Cl reference electrode. The chromatographic conditions were optimized and the eluent solution contained 5 mmol/L HNO3 and 15 mmol/L Na NO3 at a flow rate of 1.0 m L/min and column temperature of 30 8C. The applied voltage of the DC amperometric detector was 0.9 V. Under the optimum conditions, the linear range of the method was 0.2–50 mg/L for iodide ion with a correlation coefficient of 0.9990. The detection limit was 0.05 mg/L(calculated at S/N = 3) and the relative standard deviations(RSD, n = 6) were all less than 1% for retention time, peak area and peak height. This method was also utilized for the determination of iodide ions in samples of povidone iodine solution and kelp samples with satisfactory results.     

New,selectively substituted cyclodextrins as stationary phases for the analysis of chiral constituents of essential oils

New β- and γ-cyclodextrin derivatives, selectively substituted with n-pentyl and methyl groups, e.g. heptakis(2,6-di-O-methyl-3-O-pentyl)-β-cyclodextrin, octakis(2-O-methyl-3,6-di-O-pentyl)-γ-cyclodextrin, and octakis(2,6-di-O-methyl-3-O-pentyl)-γ-cyclodextrin, have been prepared from specifically protected intermediates. The new cyclodextrin derivatives exhibit unique enantioselectivity towards important chiral constituents of essential oils. The enantiomers of lavandulol, α-bisabolol, nerolidol, and other terpenoid alcohols could be resolved and their presence in different essential oils could be proved. Methyl jasmonate and epi-methyl jasmonate could, in addition, be detected in jasmine concrete by two-dimensional gas chromatography. The enantiomers of the macrocyclic ketone muscone have been separated for the first time.     

A built-in route leading to a self-inclusion complex of 6A,6B-(bis-O-p-allyloxyphenyl)hexakis(2,3-di-O-methyl)-α-cyclodextrin

Hexakis(2,3-di-O-methyl)-α-cyclodextrin was treated with 2,4-dimethoxybenzene-1,5-disulfonyl chloride to give 6^A,6^B-di-O-sulfonated product 5 in only a 3.0% yield. When treated with sodium p-allyloxyphenoxide, 5 gave 6^A,6^B-(bis-O-p-allyloxyphenyl)hexakis(2,3-di-O-methyl)-α-cyclodextrin (6) in a 57% yield. A careful ¹H nmr analysis of 6 shows that one of the allyloxphenyl groups is in the α-cyclodextrin cavity. This is the first intramolecular complex formed from a modified α-cyclodextrin. Molecular modeling was used to explain the experimental facts. A novel built-in route leading to a self-inclusion α-cyclodextrin complex is proposed for this reaction.     

Separation of Cyclodextrins Using Cyclodextrin Bonded Phases

Abstract

Two different cyclodextrin bonded phases (α and β) were used for the separation of α-, β-and γ-cyclodextrins. The β-cyclodextrin phase was found to be, in general, more effective at resolving the cyclodextrins than the α-cyclodextrin bonded phase. Acetonitrile/water mixtures were used as mobile phases. The effect of mobile phase composition on retention and resolution is examined. The elution order was found to be size dependent. The results are discussed in terms of the overall retention mechanism.     

Enantiomeric composition of the chiral constituents in essential oils. Part 1: Monoterpene hydrocarbons

Using a dual column gas chromatograph equipped with two capillary columns coated with heptakis(6-O-methyl-2,3-di-O-pentyl)-β-cyclodextrin (6-me-2,3-pe-β-CD) and octakis(6-O-methyl-2,3-di-O-pentyl)-γ-cyclodextrin (6-me-2,3-pe-γ-CD), respectively, all important olefinic monoterpene hydrocarbons occurring in essential oils, including α-thujene, α- and β-pinene, camphene, sabinene, α- and β-phellandrene, Δ-3-carene and limonene can be resolved into enantiomers. With the chromatographic system described the characteristic enantiomeric composition of these monoterpene hydrocarbons in essential oils can be determined.     

Dependence of the relative retention of compounds on the average pressure of helium as a carrier gas in capillary GLC

The dependence of retention factork _i , relative retention time α _i , and retention indexI _i of organic compounds on the average pressure (p _av) of the carrier gas (helium) was studied experimentally using a long narrow-bore capillary column with the SE-30 nonpolar phase at 120°C. The linear dependencesk _i =f(p _av), α _i =φ(p _av), andI _i =φ(p _av) obtained previously were found to be in good agreement with experimental data. Invariant relative retention valuesk _0,i , α _0,i , andI _0,i , which do not depend on the helium pressure, were determined for some organic compounds of various chemical classes. The dependence of the relative retention on the carrier gas pressure needs to be taken into account in precision measurements and in experiments with narrow-bore capillary columns. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 314–316, February, 1998.     

Determination of the maximum monolayer dispersion and dispersed state for WO3 on γ-Al2O3

The maximum monolayer dispersion (the threshold) for WO₃ on γ-Al₂O₃ calcined at 500°, 550°, 600°, and 640°C has been determined quantitatively by XRD (amount of crystalline phase) and XPS (intensity ratios I_w4f/I_Al2). The results show that if the amount of WO₃ loaded is lower than the maximum monolayer dispersion, WO₃ will react with γ-Al₂O₃ to form surface compound due to mutual ionic interaction, and will be dispersed on γ-Al₂O₃ surface as monolayer then. In case the amount is higher than this value, the residual crystalline WO₃ will remain. The maximum monolayer dispersion (threshold) is 0.21 g and 0.20 g WO₃/100 m² γ-Al₃O₃ by XRD and XPS respectively. It agrees with the value (0.189 g WO₃/100 m² or 4.90 × 10^?18 W atoms/m²) calculated from the model on assumption that the WO₃ is dispersed as a closed-packed monolayer on γ-Al₂O₃ surface. Inasmuch as WO₃/γ-Al₂O₃ system is stable up to higher temperature, e.g. 700°C, than MoO₃/γ-Al₂O₃ system, WO₃ seems unfavorable to form new bulk compound with γ-Al₂O₃ at that temperature. However, Al₂(MoO₄)₃ forms perceptibly in MoO₃/γ-Al₂O₃ system at 500°C. Besides, the size of residual crystalline WO₃ in WO₃/γ-Al₂O₃ is much smaller than that of MoO₃ in MoO₃/γ-Al₂O₃. It might be the reason that WO₃/γ-Al₂O₃ catalyst is superior to MoO₃/γ-Al₂O₃ in hydrodesulfurization (HDS) or hydrodenitrogenation (HDN) in some cases.     

The separation of enantiomers on modified cyclodextrin columns: Measurements and molecular modeling

The enantiomers of 2-chloropropionic acid methyl ester, cis-pinane, 2-bromoethylbenzene, 2-bromobutane, 2-hydroxybutane trifluoroacetyl ester, and styrene oxide have been resolved on an octakis-(3-O-butyryl-2,6-di-O-pentyl)-γ-cyclo-dextrin capillary column, and the separation of the styrene oxide enantiomers has also been studied on columns coated with octakis-(3-O-trifluoroacetyl-2,6-di-O-pentyl)-cyclodextrin, octakis-(2,3,6-tri-O-pentyl)-γ-cyclodextrin, heptakis-(3-O-trifluoroacetyl-2,6-di-O-pentyl)-β -cyclodextrin, and heptakis-(2,3,6-tri-O-methyl)-β-cyclodextrin. Thermodynamic parameters (ΔG, ΔH, and ΔS) were determined from variable temperature measurements. The inclusion complexes containing styrene oxide were also studied by molecular modeling techniques. It has been found that a combined molecular mechanics–molecular dynamics approach may be a valuable tool for rationalizing the qualitative trends observed in the experimental separation factors. For the inclusion complexes considered here it is shown that the orientation of the guest relative to the cyclodextrin host is determined by the size and polarity of the cyclodextrin.     

Calculating the standard values of the heat capacity of alkaline metal ions and iodide ions in a mixed N-methylpyrrolidone-water solvent at 298.15 K

A system of ionic components of [`(C)]<sub>p,i</sub><sup>0</sup>\bar C_{p,i}^0 is proposed for the standard partial molar heat capacities [`(C)]_p2⁰\bar C_{p2}^0 of electrolytes in a mixed N-methylpyrrolidone (MP)-water solvent. The [`(C)]<sub>p,i</sub><sup>0</sup>\bar C_{p,i}^0 values are calculated for Li<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>, Rb<sup>+</sup>, Cs<sup>+</sup>, and I<sup>−</sup> ions in a mixed MP-water solvent at 298.15 K. The individual components of [`(C)]_p,i⁰\bar C_{p,i}^0 values and their dependence on the solvent composition and ion size are considered.     

Gas chromatographic enantiomer separation of agrochemicals using modified cyclodextrins

The enantiomers of phenoxypropionic acid type herbicides have been resolved by capillary gas chromatography employing modified cyclodextrins as chiral stationary phases. Excellent separations were obtained with columns containing a 1:1 mixture of per-O-pentylated and per-O-methylated γ-cyclodextrin. The enantiomers of the methyl esters of mecoprop and dichlorprop were also resolved on octakis(3-O-butyryl-2,6-di-O-pentyl)-γ-cyclodextrin. On this phase the order of elution of the enantiomers was temperature-dependent, the elution order being reversed as the temperature passed through the isoenantioselective temperature. This is the first time such behavior has been observed with cyclodextrin derivatives. The enantiomers of the polychlorinated polycyclic pesticides cis- and trans-chlordane, oxychlordane, heptachlor, heptachlorepoxide, and three chiral organophosphorus pesticides could be resolved using selectively derivatized cyclodextrin derivatives.     

Small-angle X-ray scattering from binary liquid-crystalline mixtures of polar and non-polar compounds

The phase diagrams of several binary mixtures consisting of cyanobiphenyls and different terminally non-polar mesogenic compounds exhibit induced smectic A phases. The smectic A layer spacing, d, of these induced phases have been investigated by small-angle X-ray scattering as a function of the molar fraction x_i . Large deviations of the layer spacings from the additivity rule d _mix = σ x_id_i , have been observed in all mixed systems. Assuming a dimerization of the terminally polar compounds, the degree of association β(x) was calculated as a function of composition for different dimerization constants. The theoretical relations d _mix(x) obtained from the calculated β(x) values do not fit the experimental curves for d(x). This fact can be interpreted by the formation of weak complexes between the polar and the terminally non-polar molecules of the binary mixtures. This kind of complexing seems to be responsible for the formation of induced smectic phases of the S_Ad-type and might disturb the monomer-dimer equilibrium 2M _p D _p of the polar compounds.