氨基甲酸酯功能化离子液体高效液相色谱固定相的制备与初步评价

合成一种了氨基酸衍生物：4,4′-二苯亚甲基桥联-二[2-(1-咪唑基)-3-苯基丙醇氨基甲酸酯](ImPh-Carb),并将其键合到硅胶上制备了一种新的氨基甲酸酯功能化的离子液体HPLC固定相（ImPh-Carb-Silica）。 利用1H NMR、13C NMR、MS和FTIR对ImPh-Carb进行了表征;通过FTIR和元素分析对ImPh-Carb-Silica固定相进行了表征,根据N含量计算得到ImPh-Carb-Silica的键合量为0.19 mmol/g。 以5种芳烃、5种酚类化合物和4种有机磷农药为分析物,分别在正相和反相色谱模式下对固定相的色谱分离性能进行了评价,同时考察了流动相的变化与溶质保留因子lg k之间的关系。 结果表明,该固定相与溶质分子间存在多重作用力,如疏水、氢键、π-π和偶极-诱导偶极作用等,使其能同时在正相和反相色谱模式下使用;在正相色谱条件下固定相对酚类化合物和有机磷农药表现出较好的分离选择性。     

Chromatographic characterization of a bonded liquid crystal stationary phase for HPLC

Summary A chromatographic and thermodynamic study of the compound [4-(allyloxy)benzoyl]-4-methoxyphenyl (ABMP) as a model of a chemically bonded liquid crystal stationary phase for HPLC was undertaken. A number of polycyclic aromatic hydrocarbons (PAHs) and two small solutes, carvone and pulegone, were studied under varying solvent and temperature conditions. Plots of log k vs. % organic in the mobile phase were not completely linear in all cases. The van't Hoff plots revealed at least one phase transition. The enthalpies of solute transfer from the mobile phase to the ABMP phase were determined for several PAHs. All tests indicate that ABMP possess liquid crystal properties when bonded to particulate silica.     

Retention characteristics of fluorinated bonded silica phase in reversed-phase liquid chromatography

Summary Fluorinated bonded silica has been evaluated as a packing material in reversed-phase liquid chromatography (RPLC) with polycyclic aromatic hydrocarbons, chlorinated benzenes and substituted benzenes as sample probes. The bonded material is useful as a reversed-phase stationary phase and for polar compounds it offers a specific selectivity not found with octadecylsilica (ODS) phases. The phase also retains non-planar compounds more than planar molecules. The results can be explained by conformational differences between ODS and the fluorinated bonded phase by MM2 calculation.     

Characterization of C18-bonded liquid chromatographic stationary phases by Raman spectroscopy: the effect of temperature

This study represents the first time that both the mobile phase composition and the temperature are simultaneously controlled to examine silica-bonded octadecylsilyl (C18) ligands spectroscopically at typical liquid chromatographic (LC) mobile phase flow-rates and back-pressures. Raman spectroscopy is used to characterize the behavior of the C18 bonded ligands equilibrated at temperatures from 45 to 2 degrees C in neat, single-component, mobile phase solvents including: water, acetonitrile, methanol, and chloroform. In addition, the effect of stationary phase ligand bonding density is examined by using two different monomeric reversed-phase liquid chromatographic (RPLC) stationary phases, a 2.34 and a 3.52 micromol m(-2) Microporasil C18 stationary phase, under identical conditions. The direct, on-column, spectroscopic analysis used in this study allows direct evaluation of the temperature-dependent behavior of the bonded C18 ligands. The temperature-dependent ordering of the stationary phase ligands is examined to determine if the ligands undergo a phase transition from a less-ordered "liquid-like" state at higher temperatures to a more-ordered "solid-like" state at lower temperatures. A discrete phase transition was not observed, but rather a continual ordering as temperature was lowered.     

Comparison of the isolation of adducts of 2'-deoxycytidine and 2'-deoxyguanosine with phenylglycidyl ether by high-performance liquid chromatography on a reversed-phase column and a polystyrene-divinylbenzene column

2'-Deoxycitidine (dCyd) and 2'-deoxyguanosine (dGuo) were subjected to reaction with phenylglycidyl ether (PGE) in methanol in order to study the formation of the corresponding 2'-deoxynucleoside adducts. Separation methods were developed on analytical and semi-preparative scales using high-performance liquid chromatography with photodiode-array detection on a reversed-phase column and on a polystyrene-divinylbenzene column. The use of the latter column was prompted by decomposition of the preparatively isolated dGuo-PGE adducts on the reversed-phase column. The use of a polystyrene-divinylbenzene column solved this problem and also revealed the presence of one more peak in both the dCyd- and dGuo-PGE reaction mixtures. The adducts of dCyd and dGuo were isolated on preparative reversed-phase and polystyrene-divinylbenzene columns and characterized by UV, fast atom bombardment mass and 360 MHz 1H NMR spectrometry. The adducts of dCyd were the diastereomers of N-3-(2-hydroxy-3-phenoxypropyl)-2'-deoxycytidine and N4-(2-hydroxy-3-phenoxypropyl)-2'-deoxycytidine whereas those of dGuo were the two diastereomers of N-7-(2-hydroxy-3-phenoxypropyl)-2'-deoxyguanosine and a third peak which appeared to be mainly N2-(2-hydroxy-3-phenoxypropyl)-2'-deoxyguanosine.     

Surface-functionalized ionic liquid crystal-supported ionic liquid phase materials: ionic liquid crystals in mesopores

The influence of confinement on the ionic liquid crystal (ILC) [C(18)C(1)Im][OTf] is studied using differential scanning calorimetry (DSC), polarized optical microscopy (POM), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The ILC studied is supported on Si-based powders and glasses with pore sizes ranging from 11 to 50 nm. The temperature of the solid-to-liquid-crystalline phase transition seems mostly unaffected by the confinement, whereas the temperature of the liquid-crystalline-to-liquid phase transition is depressed for smaller pore sizes. A contact layer with a thickness in the order of 2 nm is identified. The contact layer exhibits a phase transition at a temperature 30 K lower than the solid-to-liquid-crystalline phase transition observed for the neat ILC. For applications within the "supported ionic liquid phase (SILP)" concept, the experiments show that in pores of diameter 50 nm a pore filling of α>0.4 is sufficient to reproduce the phase transitions of the neat ILC.     

Phase equilibria and modeling of ammonium ionic liquid, C2NTf2, solutions

Novel quaternary ammonium ionic liquid, ethyl(2-hydroxyethyl)dimethylammonium bis(trifluomethylsulfonyl)imide (C2NTf2), has been prepared from N,N-dimethylethanolamine as a substrate. The paper includes a specific basic characterization of the synthesized compound by NMR and the basic thermophysical properties: the melting point, enthalpy of fusion, enthalpy of solid-solid phase transition, glass transition determined by the differential scanning calorimetry (DSC), temperature of decomposition, and water content. The density of the new compound was measured. The solid-liquid or liquid-liquid phase equilibria of binary mixtures containing {C2NTf2+water or an alcohol (propan-1-ol, butan-1-ol, hexan-1-ol, octan-1-ol, decan-1-ol), aromatic hydrocarbons (benzene, toluene), aliphatic hydrocarbons (n-hexane, n-octane), dimethylsulfoxide (DMSO), or tetrahydrofuran (THF)} have been measured by a dynamic method in a wide range of temperatures from 230 to 430 K. These data were correlated by means of the nonrandom two-liquid (NRTL) equation utilizing temperature-dependent parameters derived from the solid-liquid or liquid-liquid equilibrium. From the solubility results, the negative value of the partition coefficient of ionic liquid in binary system octan-1-ol/water (log P) at 298.15 K has been calculated.     

Dye-sensitized TiO2 solar cells using imidazolium-type ionic liquid crystal systems as effective electrolytes

A novel ionic liquid crystal (ILC) system (C(12)MImI/I(2)) with a smectic A phase used as an electrolyte for a dye-sensitized solar cell (DSSC) showed the higher short-circuit current density (J(SC)) and the higher light-to-electricity conversion efficiency than the system using the non-liquid crystalline ionic liquid (C(11)MImI/I(2)), due to the higher conductivity of ILC. To investigate charge transport properties of the electrolytes in detail, the exchange reaction-based diffusion coefficients (D(ex)) were evaluated. The larger D(ex) value of ILC supported that the higher conductivity of ILC is attributed to the enhancement of the exchange reaction between iodide species. As a result of formation of the two-dimensional electron conductive pathways organized by the localized I(3)- and I- at S(A) layers, the concentration of polyiodide species exemplified by I(m)- (m = 5, 7, ...) was higher in C(12)MImI/I(2). However, as the increment of the concentration of polyiodide species is less than that of D(ex), the contribution of a two-dimensional structure of the conductive pathway through the increase of collision frequency between iodide species was proposed. Furthermore, a quasi-solid-state ionic liquid crystal DSSC was successfully fabricated by employing a low molecular gelator. Addition of the 5.0 g/L gelator to ILC improved light-to-electricity conversion efficiency through the increase of J(SC) due to the enhancement of the conductivity in C(12)MImI/I(2)-gel.     

Reducing residual silanol interactions in reversed-phase liquid chromatography. Thermal treatment of silica before derivatization

This study describes the thermal pretreatment of a silica gel between 150 and 800 degrees C before derivatization with dimethyloctadecylchlorosilane as a means of reducing residual silanol activity in HPLC bonded stationary phases. A time study was done from 12 to 48 h to find the optimum time needed for dehydroxylation. With increasing pretreatment temperatures, the number of reactive silanols is reduced from 8 micromol/m2 to essentially zero at 1000 degrees C (where sintering occurs). The effects of the thermal pretreatments were observed with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and solid state cross polarization magic angle spinning (CP-MAS) 29Si NMR. Following derivatization, residual silanol activity and pH stability were tested by packing columns with the derivatized silica and carrying out a series of reversed-phase liquid chromatography (RPLC) experiments. Residual silanol activity was greatly reduced when the silica was pretreated at 800 degrees C, leading to less peak tailing for basic solutes. In a strongly basic mobile phase (pH 11.5) the pretreated silica was surprisingly stable, although bond cleavage of C18 groups from the surface was observed.     

Cationic cyclodextrins chemically-bonded chiral stationary phases for high-performance liquid chromatography

Two covalently bonded cationic β-CD chiral stationary phases (CSPs) prepared by graft polymerization of 6^A-(3-vinylimidazolium)-6-deoxyperphenylcarbamate-β-cyclodextrin chloride or 6^A-(N,N-allylmethylammonium)-6-deoxyperphenylcarbamoyl-β-cyclodextrin chloride onto silica gel were successfully applied in high-performance liquid chromatography (HPLC). Their enantioseparation capability was examined with 12 racemic pharmaceuticals and 6 carboxylic acids. The results indicated that imidazolium-containing β-CD CSP afforded more favorable enantioseparations than that containing ammonium moiety under normal-phase HPLC. The cationic moiety on β-CD CSPs could form strong hydrogen bonding with analytes in normal-phase liquid chromatography (NPLC) to enhance the analytes’ retention and enantioseparations. In reversed-phase liquid chromatography (RPLC), the analytes exhibited their maximum retention when the pH of mobile phase was close to their pK_a value. Inclusion complexation with CD cavity and columbic/ionic interactions with cationic substituent on the CD rim would afford accentuated retention and enantioseparations of the analytes.     

Study on retention behavior of peropyrene-type polycyclic aromatic hydroccrbons with various bonded stationary phases in reversed-phase liquid chromatography

Summary The retention behavior of 15 peropyrene-type polycyclic aromatic hydrocarbons was investigated on various bonded stationary phases in reversed-phase liquid chromatography. On diphenyl and naphthylethyl bonded phases, high correlations were obtained between the molecular polarizability of solutes and their retention. However, very low or no correlations were found on various octadecyl bonded phases. These facts are discussed by using the electrostatic interaction concept between the solutes and the stationary phase. We conclude that these observations are due to two reasons: the difference in the degree of planarity of polycyclic aromatic hydrocarbons and the high ability of planarity recognition of octadecyl bonded phases.     

A comparison of temperature and mobile phase composition effects for bonded liquid crystal and polymeric stationary phases in HPLC

Summary Using two polycyclyic aromatic hydrocarbons as solutes, a comparison is made between a bonded liquid crystal stationary phase and a conventional polymeric C-18 phase. The bonded nematic liquid crystal phase was the silanized form of 4-[4-(allyloxy)benzoyl-oxy]biphenyl and the polymeric phase was Vydac 201TP. Both phases display shape and planarity selectivity as indicated by the results of the variable temperature and mobile phase composition studies. The slot theory of retention can be used to explain these results. However, the liquid crystal phase is more sensitive to molecular geometry, probably due to its more ordered structure on the surface. Variable temperature experiments which compare retention during both heating and cooling provides additional support for this conclusion. With the polymeric bonded C-18 phase, each solute had identical retention at the same temperature during both the heating and cooling cycles. On the bonded liquid crystal phase, measurable differences in retention were observed at identical temperatures depending on whether the column was heated or cooled. This effect is attributed to a degree of partially reversible disordering which occurs as the column temperature was increased. However, conditioning with the appropriate mobile phase can restore the original retention characteristics of the bonded liquid crystal phase.     

Preparation and characterization ofp-tert-butyl-calix[6]arene-bonded silica gel stationary phase for high-performance liquid chromatography

Summary For the first time calix[6]arene has been chemically combined with silica gel via a longer spacer to prepare calix[6]arene-bonded silica gel stationary phase for high-performance liquid chromatography (HPLC). The separation of positional isomers and polycyclic aromatic hydrocarbons on the calix[6]arene-bonded phase was achieved with methanol-water as mobile phase. Some nucleosides were also separated on the bonded phase. The reversed-phase chromatographic performance of the bonded phase was studied. The results showed that the calix[6]arene-bonded phase was highly hydrophobic. A possible separation mechanism has been proposed.     

Synthesis and properties of non-symmetric liquid crystal dimers containing a cholesteryl moiety

A series of non-symmetric liquid crystal dimers having cholesteryl and 4-trans-(4-n-alkylcyclohexyl)phenoxy groups were synthesized by condensation of cholesteryl ω-bromoalkanoates with appropriate 4-trans-(4-n-alkylcyclohexyl)phenols. The structures and thermal phase behaviour of the dimers were characterized using IR, ¹H NMR and mass spectroscopy, elemental analysis, differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction measurements. Their thermal phase behaviour is significantly different to that of other cholesterol-based liquid crystal dimers. All of these liquid crystal dimers exhibit low phase transition temperatures. The relationships between their properties and chemical structures of these new dimers are discussed.     

Pyrolysis of reversed-phase high-performance liquid chromatographic packing materials

Pyrolysis coupled with gas chromatography and or mass spectrometry, allows the identification of the bonded chain in reversed-phase high-performance liquid chromatographic stationary phases. It is possible to distinguish whether an octadecylated reversed-phase was prepared with a trifunctional(e.g., trichloro or monofunctional dimethyl, e.g., dimethyl-ethoxy) octadecylsilane from the relative heights of the heptadecene and octadecene peaks. The nature of the pyrolysis products was investigated. No carbon chains are formed with more carbon atoms than in the bonded chain. The peak area ratio of methane to that of the combined C₄ products allows one to deduce whether the reversed-phase was deactivated as not by reaction with a trimethylsilylating reagent (end-capping).     

The properties of phenyl cyclohexyl ferroelectric liquid crystals

To continue the search for novel series of ferroelectric liquid crystals, an additional two series of compounds, C S(+)-4-[(2-methylbutyl)phenyl]4'-trans-n-alkylcyclohexyl) benzoates and D S(+)-4-[(4-methylhexanoyl)phenyl]4'(4'-trans-n-alkylcyclohexyl) benzoates, where alkyl = C₅-C₆ are reported in this paper. Their mesomorphic properties have been characterized by optical textural observations and DSC. Some of these compounds show a C-S*_C-S_A-N*-I phase transition sequence. The effects of the alkyl chains on transition temperatures and optically active terminal groups on phase behaviour are discussed.     

Heterocyclic benzoxazole-based liquid crystals

The synthesis, characterization, and mesomorphic properties of a new type of heteronuclear compounds 1a-c and a Pd complex 1d derived from benzoxazole as the core group are reported. These compounds were prepared by the ring closure reaction of 4-alkoxybenzoic acid 4-[(4-alkoxy-2-hydroxyphenylimino)methyl]phenyl esters 6 in the presence of lead(IV) acetate. All the compounds were characterized by ¹H and ¹³C NMR spectroscopies and elemental analysis. The phase behaviour of these mesogenic compounds was characterized and studied by differential scanning calorimetry and polarizing optical microscopy. All the compounds 1a exhibited nematic (N) and/or smectic C (SmC) phases, as expected for rod-like molecules; however, the compounds 1b and 1c exhibited crystal phases. For those compounds 1a having shorter carbon chains (n = 1, 3, 4) nematic phases were observed, whereas for compounds having longer carbon chains (n = 6, 7, 8, 10, 12, 14) smectic C behaviour was also observed at lower temperatures. The greater aspect ratio (l/d) of compounds 1a compared with 1b and 1c was found to be required for the observation of liquid crystallinity. The fluorescent properties of these compounds were also examined. All λ_max peaks of the absorption and photoluminescence spectra of compounds 1a-1c occurred at c. 316-322 nm and 371-382 nm, respectively. The quantum yields of some compounds were relatively low, and also slightly solvent-dependent.     

Synthesis and mesomorphic properties of chiral liquid crystals derived from (S)-lactic acid with 3-pentanol

The chiral swallow-tailed liquid crystals, 1-ethylpropyl (R)-2-[4-(4'-alkoxybiphenylcarbonyloxy)-phenoxy]propionates, EPmPBPP (m = 8-12), were prepared by using chiral (S)-lactic acid with 3-pentanol as starting materials. Mesophases and their corresponding transition temperatures were determined by polarizing microscopic textures and DSC. The results showed that all the chiral materials exhibited enantiotropic BP, N*, TGBA*, SmA*, and SmC* phases. Spontaneous polarization, dielectric constant and electro-optical response for the materials in the ferroelectric SmC* phase were investigated. It was noted that the electro-optical response of transmittance versus applied voltage obtained from the ferroelectric phase of material EPmPBPP (m = 10) displayed V-shaped switching, while that of other materials displayed the typical characteristics of ferroelectric hysteresis switching or U-shaped switching.     

Optimization of the dopant for the trace determination of polycyclic aromatic hydrocarbons by liquid chromatography/dopant-assisted atmospheric-pressure photoionization/mass spectrometry

The composition of the dopant for the analysis of polycyclic aromatic hydrocarbons (PAHs) by liquid chromatography/dopant-assisted atmospheric-pressure photoionization/mass spectrometry under reversed-phase conditions was optimized to enhance the ionization efficiency for PAHs. The most suitable dopant was a toluene/anisole mixture (99.5:0.5, v/v) and it could improve limit of detections (LODs) to 0.79-168 ng mL(-1) (signal-to-noise (S/N)=3) for 16 common PAHs. The LODs are 3.8-40 times lower than those obtained with toluene alone and are comparable to those obtained using gas chromatography/mass spectrometry.     

Structural and magnetic studies of two-dimensional solvent-free manganeseII complexes prepared via ligand exchange reaction under solvothermal conditions

Systematic investigation of the ligand exchange reactions between manganese(II) acetate and benzoic acid under solvothermal conditions led to the isolation of crystalline complexes {Mn5(OC(O)CH3)6(OC(O)C6H5)4}(infinity) ( 1) and {Mn5(OC(O)CH3)4(OC(O)C6H5)6}}(infinity) ( 2) in high (i.e., >90%) yields. The complexes are characterized structurally as 2-D honeycomb-like sheets comprised of edge-shared Mn 12 loops with some noteworthy differences as follows. First, buckling of the 2-D sheet in 1 is not observed for 2, presumably as a consequence of additional intersheet phenyl groups in the latter. Second, complex 1 is comprised of only six-coordinate MnII, while 2 has both pseudo-octahedral and distorted trigonal bipyramidal coordinate metal ions. Third, while complex 2 exhibits pi-stacking interactions with intersheet phenyl-phenyl contacts of 3.285 and 3.369 A, 1 exhibits no such bonding. Antiferromagnetic exchange is observed with Weiss constants (theta) of -28 and -56 K and Neel temperatures of 2.2 and 8.2 K for complexes 1 and 2, respectively. The paramagnetic transition at higher temperatures for complex 2 may be attributed to pi-pi exchange through phenyl groups in adjacent layers. Preliminary gas sorption studies (76 K) indidate preferential adsorption of H2 versus N2 for complex 1 only.