Preparation and evaluation of n-octadecylphosphonic acid-modified magnesia-zirconia stationary phases for reversed-phase liquid chromatography

Three n-octadecylphosphonic acid-modified magnesia-zirconia reversed stationary phases (C₁₈PZM) are prepared via the strong Lewis base interactions between organophosphonate and magnesia-zirconia composite. And two of them are end-capped by using trimethylchlorosilane as end-capping agent in different procedures. Stability studies at extreme high pH conditions (pH 9-12) show that both the non-endcapped and endcapped columns are quite stable at pH 12 mobile phase. The reversed-phase liquid chromatographic behavior of three C₁₈PZM stationary phases are comparatively investigated in detail using a variety of basic compounds as probes. The retention of basic compounds on the three phases is studied over a wide range of pHs. And the possible retention mechanisms of basic compounds on the three stationary phases are discussed. The results show that the basic solutes retain by a hydrophobic and cation-exchange interaction mixed mechanism on three stationary phases when they are operated in eluents at pH values near to the pK_a of the Brönsted conjugate acid form of the analyte, suggesting that inherent zirconol groups on ZM are not expected to interact with bases via cation-exchange interaction at lower pH. Nonetheless, the non-endcapped phase differs markedly from the edncapped ones in retention and selectivity of basic solutes using eluents at pH 4.1, implying a complex retention mechanism at this pH. The cation-exchange sites under such conditions are more likely due to the adsorbed Lewis base anionic buffer constituents (acetate) on accessible ZM surface sites than the chemisorbed phosphonate. Although the three phases exhibit very similar chromatographic behavior with eluents at pH 10.1, and show in general satisfactory separation of basic compounds and alkaloids studied, the performance for a specific analyte, however, differs largely from column to column.     

Relation between location of elements in periodic table and affinity for the malignant tumor (author's transl)

Affinity of many inorganic compounds for the malignant tumor was examined, using the rats which were subcutaneously transplanted with Yoshida sarcoma. And the relations between the uptake rate into the malignant tumor and in vitro binding power to the protein were investigated in these compounds. In these experiments, the bipositive ions and anions had not affinity for the tumor tissue with a few exceptions. On the other hand, Hg, Au and Bi, which have strong binding power to the protein, showed high uptake rate into the malignant tumor. As Hg++, Au+ and Bi+++ are soft acids according to classification of Lewis acids, it was thought that these elements would bind strongly to soft base (R-SH, R-S-) present in the tumor tissue. In many hard acids (according to classification of Lewis acids), the uptake rate into the tumor was shown as a function of ionic potentials (valency/ionic radii) of the metal ions. It is presumed that the chemical bond of these hard acids in the tumor tissue is ionic bond to hard base (R-COO-, R-PO3(2-), R-SO3-, R-NH2).     

Simple eluents for the formation of ascending pH gradients in chromatofocusing of bipolar compounds

The formation of ascending pH gradients was studied in carboxyl columns with the use of eluents of simple composition (one or two components). The obtained gradients are comparable in a wide pH range with the gradient formed with the use of the synthetic polyampholytic eluent Polybuffer-96. The smoothest nearly linear pH gradients are formed at the ionic strength 0.05–0.5 in one or both mobile phases: the starting solution and the eluent. Potentialities of the analytical use of simple eluents in chromatofocusing were demonstrated with the example of the separation of a model mixture of proteins and formate dehydrogenase isoforms.     

Influence of solute-solvent coordination on the orientational relaxation of ion assemblies in polar solvents

We have investigated the rotational dynamics of lithium thiocyanate (LiNCS) dissolved in various polar solvents with time and polarization resolved vibrational spectroscopy. LiNCS forms multiple distinct ionic structures in solution that can be distinguished with the CN stretch vibrational frequency of the different ionic assemblies. By varying the solvent and the LiNCS concentration, the number and type of ionic structures present in solution can be controlled. Control of the ionic structure provides control over the volume, shape, and dipole moment of the solute, critical parameters for hydrodynamic and dielectric continuum models of friction. The use of solutes with sizes comparable to or smaller than the solvent molecules also helps amplify the sensitivity of the measurement to the short-ranged solute-solvent interaction. The measured orientational relaxation dynamics show many clear and distinct deviations from simple hydrodynamic behavior. All ionic structures in all solvents exhibit multi-exponential relaxation dynamics that do not scale with the solute volume. For Lewis base solvents such as benzonitrile, dimethyl carbonate, and ethyl acetate, the observed dynamics strongly show the effect of solute-solvent complex formation. For the weak Lewis base solvent nitromethane, we see no evidence for solute-solvent complex formation, but still see strong deviation from the predictions of simple hydrodynamic theory.     

Adsorption and selectivity characteristics of several human serum proteins with immobilised hard Lewis metal ion-chelate adsorbents

In this investigation, human serum has been used as an example of a crude protein mixture to define the protein binding characteristics and selectivity of several immobilised hard Lewis metal ion affinity chromatographic (IMAC) adsorbents. Specifically, the binding properties of immobilised O-phosphoserine (im-OPS) and 8-hydroxyquinoline (im-8-HQ), with immobilised iminodiacetic acid as a control system, have been investigated in combination with the hard Lewis metal ions, Al3+, Ca2+, Fe3+, Yb3+, and the borderline metal ion, Cu2+, over the pH range pH 5.5 to pH 8.0 with buffers of 0.5 M ionic strength. The same IMAC adsorbents were also investigated for their protein binding capabilities with buffers of an ionic strength of 0.06 M at pH 5.5 and pH 8.0. The binding behaviour of four "marker" proteins, namely transferrin, alpha2-macroglobulin, gammaglobulin and human serum albumin have furthermore been employed to monitor the differences in protein selectivity exhibited by these IMAC systems. The experimental findings confirm that these hard Lewis metal ion IMAC adsorbents function in a "mixed" binding mode with both coordination and electrostatic characteristics evident, depending on the ionic strength and pH of the equilibration or elution buffers. Based on a screening protocol, several members of the im-Mn+-8-HQ and im-Mn+-OPS adsorbent series have been identified with high selectivity for transferrin and alpha2-macroglobulin. These hard Lewis metal ion IMAC adsorbents thus provide attractive alternatives for selective fractionation of human serum proteins.     

一种不含胶凝剂的凝胶电解质在准固态染料敏化太阳能电池中的应用

报道了一种不含胶凝剂的凝胶电解质的制备及在准固态染料敏化太阳能电池中的应用.这种新型凝胶电解质仅含有机溶剂和碘盐,即3-甲氧基丙腈、苯胺、三碘化铝和碘.上述混合物通过路易斯酸性三碘化铝离子导体和路易斯碱性苯胺有机溶剂间的路易斯酸-碱相互作用形成凝胶,无需额外添加传统凝胶电解质的关键组分—胶凝剂.形成的三碘化铝-苯胺复合物在凝胶电解质中能同时发挥离子导体和胶凝剂的作用.红外光谱图中苯胺的氨基和苯环特征峰的变化证实了三碘化铝-苯胺复合物的形成.含这种新型凝胶电解质的准固态染料敏化太阳能电池光电性能和稳定性与含三碘化铝-3-甲氧基丙腈液体电解质的染料敏化太阳能电池相比有很大提高.     

Computational investigation of reactive to nonreactive capture of carbon dioxide by oxygen-containing Lewis bases

Recent work has shown that room temperature ionic liquid systems reactively absorb CO(2) and offer distinct advantages over current CO(2) capture technologies. Here we computationally evaluated CO(2) interaction energies with a series of oxygen-containing Lewis base anions (including cyclohexanolate and phenolate and their respective derivatives). Our results show that the interaction energy can be tuned across a range from reactive to nonreactive (or physical) interactions. We evaluated different levels of theory as well as possible corrections to the interaction energy, and we explained our calculated trends on the basis of properties of the individual anions. We found that the interaction energy between CO(2) and the Lewis bases examined here correlates most strongly with the atomic charge on the oxygen atom. This insight provides a useful handle to tune the anion-CO(2) interaction energy for future experimental and computational studies of novel CO(2) capture systems.     

离子液体的酸性测定及其催化的异丁烷／丁烯烷基化反应

 初次采用吡啶红外光谱探针法测定了离子液体的酸性．该方法能鉴别离子液体的Br¨onsted／Lewis酸类型，并可以粗略指示离子液体的Lewis酸强度．将［bmim］Cl／AlCl3类离子液体用于催化异丁烷与丁烯的烷基化反应，考察了酸强度、反应温度、压力和时间对产物分布的影响，并在最优操作条件下与传统的H2SO4催化剂进行了比较．结果表明，离子液体对烷基化反应的催化活性和选择性与H2SO4可比，而且它更容易与产物分离，不经任何处理可循环利用10次．     

Lewis base catalyzed addition of trimethylsilyl cyanide to aldehydes

A variety of achiral Lewis bases were found to catalyze the addition of TMSCN to the aldehydes. Among them, phosphines and amines were the most efficient catalysts. In addition, several chiral amines and phosphines were examined in a catalytic, asymmetric addition of TMSCN to benzaldehyde albeit with low enantioselectivity. A mechanistic study revealed that the reaction was first order in aldehyde, first order in Lewis base, and zeroth order in TMSCN, suggesting the complex formation of TMSCN and Lewis base formation of complex i. However, there are at least two possible scenarios for this catalytic process, and in view of the low selectivities observed, it is not clear which mechanism is operative.     

Frustrated Lewis Pairs: Metal‐free Hydrogen Activation and More

Sterically encumbered Lewis acid and Lewis base combinations do not undergo the ubiquitous neutralization reaction to form “classical” Lewis acid/Lewis base adducts. Rather, both the unquenched Lewis acidity and basicity of such sterically “frustrated Lewis pairs (FLPs)” is available to carry out unusual reactions. Typical examples of frustrated Lewis pairs are inter‐ or intramolecular combinations of bulky phosphines or amines with strongly electrophilic RB(C₆F₅)₂ components. Many examples of such frustrated Lewis pairs are able to cleave dihydrogen heterolytically. The resulting H⁺/H^? pairs (stabilized for example, in the form of the respective phosphonium cation/hydridoborate anion salts) serve as active metal‐free catalysts for the hydrogenation of, for example, bulky imines, enamines, or enol ethers. Frustrated Lewis pairs also react with alkenes, aldehydes, and a variety of other small molecules, including carbon dioxide, in cooperative three‐component reactions, offering new strategies for synthetic chemistry.     

Lewis base ionic liquids

Ionic liquids which are (weak) Lewis bases have a number of interesting and useful properties different to those of traditional ionic liquids, including volatility and the possibility of being distillable in some cases, a base catalysis effect in others and enhancement of the acidity of dissolved acids.     

Mixed-mode reversed-phase and ion-exchange separations of cationic analytes on polybutadiene-coated zirconia

The retention and selectivity of the chromatographic separation of basic (cationic) analytes on a polybutadiene-coated zirconia (PBD-ZrO2) stationary phase have been studied in greater detail than in previous studies. These separations are strongly influenced by the chemistry of the accessible surface of zirconia. In the presence of buffers which contain hard Lewis bases (e.g., phosphate, fluoride, carboxylic acids) zirconia's surface becomes negatively charged due to adsorption of the buffer anion at the hard Lewis acid sites. Consequently, under most conditions (e.g., neutral pH), cationic analytes undergo both hydrophobic and cation-exchange interactions. This mixed-mode retention process generally leads to greater retention factors for cations relative to those on silica-based reversed phases despite the lower surface areas of the zirconia phase, but, more importantly, adsorption of hard Lewis bases can be used to control the chromatographic selectivity for cationic analytes on these zirconia-based stationary phases. In contrast to our prior work, here we show that when mixed-mode retention takes place, both retention and selectivity are easily adjusted by changing the type of hard Lewis base buffer anion, the type of buffer counter-ion (e.g., sodium, potassium, ammonium), the pH, and the ionic strength of the eluent as well as the type and amount of organic modifier.     

Retention of alkali,alkaline earth and transition metals on an itaconic acid cation-exchange column. Eluent pH,ionic strength and temperature effects upon selectivity

The unusual selectivity of a methylene succinic (itaconic) acid modified polymeric column was investigated for the separation of alkali, alkaline earth, transition and heavy metals employing non-chelating inorganic eluents. The retention of selected metal ions on the column was investigated with simple HNO3 eluents and eluents prepared from KNO3 and KCl salts of varying pH (adjusted using HNO3). From these studies both the effect of eluent ionic strength and pH upon retention was evaluated for the itaconic acid stationary phase. The results obtained showed that despite slow exchange kinetics causing poor efficiencies, acceptable baseline separations of selected alkaline earth and transitions could be obtained under optimum conditions (the baseline separation of Mg(II), Ca(II), Mn(II), Cd(II), Zn(II) and Co(II) was possible using a 15 mM KNO3-5 mM KCl eluent at pH 3.50 in under 25 min). The use of an simple ionic strength step gradient was shown that facilitated the addition of Pb(II) to the above group of metal ions. An investigation into the effect of temperature upon peak efficiency and retention showed increased column temperature could be used to improve the resolution of closely eluting metal ions such as Ca(II) and Sr(II) and Ca(II) and Mn(II).     

New membrane-based electrolytic suppressor device for suppressed conductivity detection in ion chromatography

This paper discusses the newest advancement in chemical suppression preceding conductivity detection. The new suppressor uses electrolysis of deionized water to generate the required acid or base for the suppression neutralization reaction and utilizes the electrical field to enhance, through electrodialysis, the suppressor's capacity for neutralization. The suppressor is able to accommodate eluents as high as 150 mM NaOH, without the need for a separate regenerant solution, by recycling the conductivity detector cell waste to the regenerant and electrolysing the water in the waste stream to the required acid or base. The device is able to use deionized water as regenerant and neutralize the eluent stream to deionized water without the expected increase in resistance by employing ion exchange material in intimate contact with the electrodes and the membranes. The current is carried with low resistance through the ion-exchange material via ion transport from one ion-exchange site to another.     

Derivatization for electrospray ionization-mass spectrometry. 4. Alkenes and alkynes

A survey of derivatization strategies and prospective derivatization reactions for conversion of simple alkenes and alkynes to 'electrospray-active' species is presented. General synthetic strategies are discussed and illustrative examples of prospective derivatives prepared from model compounds are presented along with their electrospray ionization (ES) mass spectra. The identified derivatives of these neutral, nonpolar analytes are either ionic or are ionizable in solution through Bronsted acid/base chemistry, by Lewis acid/base chemistry, or by chemical or electrochemical electron-transfer chemistry. Once ionized, the derivatives are expected to be amenable to detection by electrospray ionization-mass spectrometry. Derivatives are identified for positive and negative ion analysis of both alkenes and alkynes. Copyright 2000 John Wiley & Sons, Ltd.     

Chromatography in silico, quantitative analysis of retention of aromatic acid derivatives

A quantitative analysis of the retention of aromatic acid derivatives in reversed-phase liquid chromatography (RPLC) is conducted using a molecular mechanics calculation in the CAChe program. The molecular interaction energy value is calculated by subtracting the energy value of the complex from the sum of energy values of a model phase and an analyte. Several model phases are constructed, and the feasibility of applying the method to a variety of compounds is examined based on improving the contact surface area and the capability of computer software and hardware. Interaction energy values are calculated for both molecular and ionic forms. The predicted retention factors of partially ionized acids obtained using a combination of dissociation constants correlated well with the values measured by RPLC with pH-controlled eluents.     

Study on the NaNp/Al2O3-SiO2 system

Sodium naphthenide (NaNp) deposited on aluminosilicate gels yields systems that exhibit signals in EPR spectra, the multiplicity, g values, and intensities of which depend on the gel composition. The symmetrical singlets (I) of a g(1) value of 2.00 were assigned to the complexed naphthalene anion radicals on the centers occurring on the surfaces of the alumina and silica phases of the gels studied. Those radicals complexed on surface Lewis acid sites are of hard acid/hard base type according to Pearson theory, and are bonded to the sites by ionic forces. The asymmetrical singlets (II) described by the value g(2)=1.95 were assigned to naphthalene anion radicals, which are complexed by the centers of the aluminosilicate phase of the gels studied. Those radicals, complexed on surface Lewis acid sites of this phase, are of soft acid/soft base type and are bonded to the sites by covalent bonds. The highest intensity of the singlet (I) was recorded for the system containing alumina gel. The highest intensity of the singlet (II) was recorded for the system containing Al(2)O(3) in 30 wt%. The structures of Lewis acid sites on aluminosilicate phases are postulated to be different from those on alumina or silica phases.     

Suppression of deleterious effects of free silanols in liquid chromatography by imidazolium tetrafluoroborate ionic liquids

Silica-based stationary phases are commonly used in liquid chromatography, but their surface acidity causes known problems, especially when separating basic compounds. Deleterious effects of free silanols are not fully removed by standard prevention procedures consisting in adding alkylamines or other amino quenchers to the eluents. We found that ionic liquids of the imidazolium tetrafluoroborate class, added to mobile phases at concentrations of 0.5-1.5% (v/v), blocked silanols and provided excellent thin-layer chromatographic separations of strongly basic drugs which were otherwise not eluted, even with neat acetonitrile as the mobile phase. The silanol suppressing potency of imidazolium tetrafluoroborates was demonstrated to markedly exceed that of the standard mobile phase additives, like triethylamine, dimethyloctylamine and ammonia. The proposed new mobile phase additives were also demonstrated to provide reliable lipophilicity parameters of base drug analytes as determined by gradient mode of high-performance liquid chromatography. By applying the readily available and environmentally friendly imidazolium tetrafluoroborate ionic liquids, simple and efficient means of improvement of liquid chromatographic analysis of organic bases were elaborated.     

离子液体中Lewis酸催化葡萄糖和果糖脱水制备5-羟甲基呋喃甲醛

在离子液体中采用不同的Lewis酸催化葡萄糖和果糖脱水制备5-羟甲基呋喃甲醛(5-HMF).结果表明,CrCln和SnCln均可高效催化葡萄糖转化为5-HMF.另外,Lewis酸的酸性越强,其催化果糖转化为5-HMF的产率越高.镧系金属氯化物在反应中表现出较好的催化活性和产物选择性.同时还研究了离子液体结构对催化反应的...     

Friedländer反应中催化体系的研究进展

综述了近几年来国内外Friedländer反应中催化体系的研究进展, 其中涉及质子酸碱/Lewis酸碱催化、有机金属催化以及离子液体催化等, 并讨论了部分反应机理.