Convenient substitution of hydroxypyridines with trifluoroacetaldehyde ethyl hemiacetal

Designing Adsorption Centres for Biological Active Molecules on a Silica Surface

The chemical interaction between the surface of hydroxylated or aminated silicas and β-cyclodextrin, mono-tosyl-β-cyclodextrin and the bromine derivative of heptakis-[6- O-( p-tosyl-β-cyclodextrin)] has been investigated using IR spectroscopy, thermogravimetric analysis with programmed heating, pH titration, weight adsorption method, elemental analysis and quantitative chemical analysis of the surface compounds. The optimum conditions for chemical grafting of β-cyclodextrins onto the silica surface were established. The formation of supramolecular structures, viz. inclusion complexes between immobilized β-cyclodextrin and the hormone of pineal gland (melatonin), on the surface of highly dispersed silicas of 1:1 composition was demonstrated.

A modification of a conventional technique for the synthesis of hydrazones of racemic carbonyls: prevention of spontaneous chiral inversion

Conventionally hydrazones and other derivatives of carbonyls are synthesized under acidic conditions when spontaneous chiral inversion is a common problem if the carbonyl compound is chiral.

Enantiomeric Separation of 1-Phenyl-1-Propanol Using Calix[4]Arene-Capped β-Cyclodextrin-Bonded Silica Particles as Chiral Stationary Phase in Capillary Electrochromatography

A new type of calix [ arene-capped (3-(2-O-β-cyclodextrin)-2-hydroxypropoxy) propylsilyl-appended silica particles (C4CD-HPS) has been successfully used as chiral stationary phase (CSP) in capillary electrochromatography (CEC) for separation of enantiomers of 1-phenyl-1-propanol for the first time. C4CD-HPS contains a chiral selector with two recognition sites: calix [arene and β-cyclodextrin. Due to the cooperative functioning of the calix [arene and β-cyclodextrin, C4CD-HPS has exhibited excellent enantioselectivity for the enantiomers of 1-phenyl-1-propanol. After the multiple phenolic hydroxyl groups in the calix [arene moieties are ionized in the running buffer, the bonded stationary phase C4CD-HPS becomes negatively-charged to provide high electroosmotic flow (EOF) in CEC. Fast and high-resolution separation for enantiomers of 1-phenyl-1-propanol has been easily achieved on C4CD-HPS. This new type of chiral stationary phase has exhibited great potential for fast enantiomeric separations in CEC.

Microwave-Assisted Preparation of Trifluoroacetaldehyde (Fluoral): Isolation and Applications

A novel method for the preparation of trifluoroacetaldehyde (fluoral, TFAc, CF(3)CHO) from commercially available trifluoroacetaldehyde ethylhemiacetal (TFAE) by microwave irradiation is described. The isolation, characterization and reaction of fluoral with various nucleophiles were studied to verify the diverse applicability of this new method.

Fundamental and practical aspects of ultrahigh pressure liquid chromatography for fast separations

The ongoing development of HPLC has been focused on increasing the speed and efficiency of separations over the past decade. The advances in separation speed have been primarily related to the development of column technology and instrumentation. Relatively short columns packed with sub-2 microm particles provide high-speed separations while maintaining or increasing resolution. Ultrahigh pressure pump systems have been developed to overcome the high-pressure drop generated by such sub-2 microm packings. In this review, fundamental and practical aspects of ultrahigh pressure or ultrahigh performance liquid chromatography (U-HPLC) are discussed. Applications of fast U-HPLC separations are also presented.

Perphenylcarbamoylated β-cyclodextrin bonded-silica particles as chiral stationary phase for enantioseparation by pressure-assisted capillary electrochromatography

Perphenylcarbamoylated beta-cyclodextrin bonded-silica particles (5 microm) were packed into 75-mum fused-silica capillaries, and used for the enantiomer separation of neutral and basic solutes by pressure-assisted capillary electrochromatography. Triethylammonium acetate and phosphate buffer were employed as the BGEs. A cathodic EOF was observed with these two BGEs. Seven chiral analytes were successfully resolved into their enantiomers under optimized conditions, and five of them could be baseline-separated within 12 min due to their high electrophoretic mobility. Better results were achieved with phosphate buffer as the BGE. The effects of organic content and pH on the enantioseparation were also investigated.

Application of diaza-18-crown-6-capped beta-cyclodextrin bonded silica particles as chiral stationary phases for ultrahigh pressure capillary liquid chromatography

Two bonded chiral stationary phases (CSPs), 8-aminoquinoline-2-ylmethyl- and 8-aminoquinoline-7-ylmethyl-diaza-18-crown-6-capped [3-(2-O-beta-cyclodextrin)-2-hydroxypropoxy]propylsilyl silica particles (non-porous, 1.5 microm), have been prepared and evaluated using capillary liquid chromatography at high pressures (> or = 8000 p.s.i.). High column efficiency (up to 400 000 plates m(-1)) was achieved for chiral separations. These CSPs with two recognition sites, i.e. substituted-diaza-18-crown-6 and beta-cyclodextrin combined with high chromatographic efficiency provide good resolution of a variety of enantiomers and positional isomers in relatively short times under reversed-phase conditions. After inclusion of a Ni (II) ion from the mobile phase, the positively charged crown ether-capped beta-cyclodextrin facilitates specific static, dipolar, and host-guest complexation interactions with solutes.

Application of cyclam-capped beta-cyclodextrin-bonded silica particles as a chiral stationary phase in capillary electrochromatography for enantiomeric separations

Two novel types of substituted cyclam-capped beta-cyclodextrin (beta-CD)-bonded silica particles have been prepared and used as chiral stationary phases in capillary electrochromatography (CEC). The two stationary phases have a chiral selector with three recognition sites: beta-CD, cyclam, and the latter's sidearm. They exhibit excellent enantioselectivities in CEC for a wide range of compounds as a result of the cooperative functioning of the anchored beta-CD and cyclam. After inclusion of the metal ion (Ni2+) from the running buffer into the substituted cyclams and their sidearm ligands, the bonded stationary phases become positively charged and can provide extra electrostatic interactions with ionizable solutes and enhance the dipolar interactions with some polar neutral solutes. This enhances the host-guest interaction with some solutes and improves chiral recognition and enantioselectivity. These new types of stationary phases exhibit great potential for fast chiral separations in CEC.