Doxycycline as a new chiral selector in capillary electrophoresis.

Doxycycline (DOX) is one of the tetracycline class of antibiotics and has not been examined for its enantioseparation abilities previously. The purpose of the present work was to evaluate DOX as a chiral selector (CS) using capillary electrophoresis (CE) in nonaqueous mode. Systematic experiments were performed to investigate the effects of concentration of CS, compositions of organic solvents and background electrolytes, applied voltage on chiral separation of a set of acidic chiral compounds.

Carbamoylated azithromycin incorporated zirconia hybrid monolith for enantioseparation of acidic chiral drugs using non-aqueous capillary electrochromatography.

Carbamoylated derivatives of two antibiotics, namely, clindamycin phosphate (CLIP) and erythromycin (ERY) were successfully employed as co-precursors, in combination of zirconium tetrabutoxide as a precursor, to prepare chiral organic-zirconia hybrid monoliths (i.e., CLIP-ZHMs and ERY-ZHMs, respectively) via a single-step in-situ sol-gel approach in our previous works.

Application of rifampicin as a chiral selector for enantioresolution of basic drugs using capillary electrophoresis.

Rifampicin, a member of rifamycin sub-class of antibiotics which belongs to the naphthalenic ansamycin class of antibiotics, has a characteristic ansa structure, i.e., a ring structure or chromophore spanned by an aliphatic chain.

Enantioseparation of basic chiral drugs on a carbamoylated erythromycin-zirconia hybrid monolith using capillary electrochromatography.

An organic-inorganic hybrid monolithic column was prepared within the confines of a capillary via a single-step in situ sol-gel approach using zirconium tetrabutoxide as a precursor to compose the inorganic backbone and 3-triethoxysilylpropyl carbamoylated derivative of erythromycin (TEOSPC-ERY) as a co-precursor to introduce the organic chiral selector moiety in the zirconia backbone. The resulting carbamoylated ERY-zirconia hybrid monolith (ERY-ZHM) showed homogeneous morphology with well-defined through pores and was tightly connected with the inner wall of the capillary. The column was employed for capillary electrochromatographic enantioseparation of six basic chiral drugs in mobile phases (MPs) consisting of acetonitrile (ACN) and triethylammonium acetate (TEAA) buffer.

Enantiomer separation of acidic chiral compounds on a quinine-silica/zirconia hybrid monolith by capillary electrochromatography.

A weak anion-exchanger chiral selector, quinine-incorporated silica/zirconia hybrid monolithic (QUI-S/ZHM) capillary column was prepared by sol-gel technology. The performance of the QUI-S/ZHM column was investigated for enantioresolution of a set of acidic chiral drugs and dinitrobenzoyl (DNB)-amino acids by capillary electrochromatography in aqueous organic mobile phases composed of acetonitrile (ACN) and triethylammonium acetate (TEAA) buffer. Effects of several parameters including the ACN content, concentration and pH of the mobile phase on the chiral separation were examined.

Enantioseparation of basic chiral compounds on a clindamycin phosphate-silica/zirconia hybrid monolith by capillary electrochromatography.

An organic-inorganic silica/zirconia hybrid monolithic capillary column was prepared by sol-gel process in a fused-silica capillary by using triethoxysilylpropylcarbamate (TEOSPC) derivative of clindamycin phosphate (CLIP) as a chiral selector. A sol solution consisting of 6 × 10(-3)M of polyethylene glycol, 1 M of water, 2M of acetic acid and 0.04/0.

Enantiomer separations of basic chiral compounds by capillary electrochromatography on a phosphated β-cyclodextrin-modified zirconia monolith.

Phosphated β-cyclodextrin (PCD)-coated zirconia monolith was used as the chiral stationary phase in capillary electrochromatography (CEC) for separation of four basic chiral compounds including metoprolol (MET), sertraline (SER), citalopram (CIT) and atenolol (ATE). Migration, chiral selectivity and resolution data were measured in reversed-phase mobile phases of varying pH, buffer and organic modifier compositions. Optimum mobile phase conditions for CEC separation of the compounds studied were found to be a 15-mM aqueous buffer of pH 5.

Penicillin G as a novel chiral selector in capillary electrophoresis.

The penicillin sub-class of β-lactam antibiotics has not been examined for its enantiodiscriminating abilities in capillary electrophoresis (CE) until date. The present work was therefore designed to evaluate penicillin G potassium salt (PenG) as an ion-pair chiral selector (CS) using CE for its several attributes, namely, high solubility in water and lower alcohols, structure allowing multiple interactions with analytes and cost-effectiveness. Systematic experiments were performed to investigate the effect of composition of background electrolyte, applied voltage and capillary temperature on chiral separation.

Application of antibiotics as chiral selectors for capillary electrophoretic enantioseparation of pharmaceuticals: a review.

Recent years have witnessed several new trends in chiral separation, for example, the enantiorecognition ability of several new antibiotics has been explored using capillary electrophoresis (CE) prior to HPLC; antibiotics have been employed as chiral selectors (CSs) in a nonaqueous CE (NACE) mode; and several new detection techniques (namely, capacitively coupled contactless conductivity detection) have been used in combination with CE for quantification of enantiomers. On account of these emerging trends, this article aims to review the application of various classes of antibiotics for CE enantioseparation of pharmaceuticals. A detailed account of the basic factors affecting enantioseparation, certain limitations of antibiotics as CSs and strategies to mitigate them, and advantages of NACE while using antibiotics as CSs has also been presented.

Enantioseparation of chiral acids and bases on a clindamycin phosphate-modified zirconia monolith by capillary electrochromatography.

Porous zirconia monolith modified with clindamycin phosphate (CLIP-ZM) was used as chiral stationary phase (CSP) to separate a set of six acidic and basic chiral compounds in capillary electrochromatography (CEC). Resolutions and chiral selectivity factors of the chiral compounds were measured in ACN/MeOH mobile phases of varying compositions of MeOH and ammonium acetate as the electrolyte. In contrast to the CE separations where only chiral separations of acidic compounds were achieved enantiomers of both acidic and basic compounds were separated with acidic compounds better resolved than basic ones by CEC on the CLIP-ZM CSP.

Chiral separation of basic compounds on a cellulose 3,5-dimethylphenylcarbamate-coated zirconia monolithin basic eluents by capillary electrochromatography.

Porous zirconia monolith (ZM) modified with cellulose 3,5-dimethylphenylcarbamate (CDMPC) was used as chiral stationary phase to separate basic chiral compounds in capillary electrochromatography. The electroosmotic flow behavior of bare and CDMPC-modified zirconia monolithic (CDMPC-ZM) column was studied in ACN/phosphate buffer eluents of pH ranging from 2 to 12. The CDMPC-ZM column was evaluated by investigating the influences of pH, the type and composition of organic modifier of the eluent on enantioseparation.

Fast separations of chiral β-blockers on a cellulose tris(3,5-dimethylphenylcarbamate)-coated zirconia monolithic column by capillary electrochromatography.

Cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) is an excellent chiral selector for enantioseparation of a wide variety of chiral compounds. The monolithic chiral columns are becoming popular in liquid chromatography and capillary electrochromatography. In this work, we present the fast separation of chiral β-blockers on a CDMPC-modified zirconia monolithic column by capillary electrochromatography (CEC).

Azithromycin as a new chiral selector in capillary electrophoresis.

In capillary electrophoresis (CE), separation of enantiomers of a chiral compound can be achieved through the chiral interactions and/or complex formation between the chiral selector and the enantiomeric analytes on leaving their diastereomeric forms with different stability constants and hence different mobilities. A great number of chiral selectors have been employed in CE and among them macrocyclic antibiotics exhibited excellent enantioselective properties towards a wide number of racemic compounds. The use of azithromycin (AZM) as a chiral selector has not been reported previously.

Enantioseparation on cellulose dimethylphenylcarbamate-modified zirconia monolithic columns by reversed-phase capillary electrochromatography.

This work reports the preparation of monolithic zirconia chiral columns for separation of enantiomeric compounds by capillary electrochromatography (CEC). Using sol-gel technology, a porous monolith having interconnected globular-like structure with through-pores is synthesized in the capillary column as a first step in the synthesis of monolithic zirconia chiral capillary columns. In the second step, the surface of the monolith is modified by coating with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) as the chiral stationary phase to obtain a chiral column (CDMPCZM).

Enantioseparation of alpha-amino acids on an 18-crown-6-tetracarboxylic acid-bonded silica by capillary electrochromatography.

(-)-(18-Crown-6)-2,3,11,12-tetracarboxylic acid-bonded silica was used as the chiral stationary phase in capillary electrochromatography (CEC) for enantioseparation of some alpha-amino acids. Separation data in CEC were measured in mobile phases of varying pH, and composition of methanol and buffer, and compared with those in capillary liquid chromatography (CLC). In CEC better enantioseparation was generally obtained in the eluent of lower pH, higher buffer concentration and intermediate MeOH content, usually at the expense of analysis time.

Cellulose dimethylphenylcarbamate-immobilized zirconia for chiral separation in reversed-phase CEC.

Cellulose dimethylphenylcarbamate (CDMPC)-immobilized zirconia (CDMPCZ) was used as a chiral stationary phase for enantioseparation of a set of nine racemic compounds in reversed-phase CEC. Influences of the type and composition of organic modifier and the applied voltage on enantioseparation were examined. Separation data on CDMPCZ were also compared with those on CDMPC-immobilized silica (CDMPCS).

Chiral separation of amides of amino acid on a (S)-N-(3,5-dinitrobenzoyl)leucine-N-phenyl-N-propylamide-bonded silica using nonaqueous capillary electrochromatography.

(S)-N-(3,5-dinitrobenzoyl)leucine-N-phenyl-N-propylamine-bonded silica was used as a chiral stationary phase for separation of a set of racemic pi-acidic and pi-basic alpha-amino acid amides in electrolyteless ACN-water eluents by CEC in the RP and polar organic (PO) modes. The effect of the amount of water in the ACN-water eluent on chiral separation was examined. As water is added to ACN, retention was shortened but resolution and selectivity deteriorated severely.

Enantioseparation of amino acid amides on an (S)-N-(3,5-dinitrobenzoyl)leucine-N-phenyl-N-propylamide-bonded silica in normal phase CEC.

(S)-N-(3,5-Dinitrobenzoyl)leucine-N-phenyl-N-propylamide-bonded silica was used as a chiral stationary phase for separation of enantiomers of some racemic pi-acidic and pi-basic amino acid amides in normal phase capillary LC (CLC) and CEC. For generation of EOF in CEC, different amounts of water were added to n-hexane-isopropanol (IPA) eluents. Influences of added water and composition of polar modifier on retention, enantioselectivity and resolution were studied.

Cellulose dimethylphenylcarbamate-bonded carbon-clad zirconia for chiral separation in high performance liquid chromatography.

Porous zirconia particles are very robust material and have received considerable attention as a stationary phase support for HPLC. We prepared cellulose dimethylphenylcarbamate-bonded carbon-clad zirconia (CDMPCCZ) as a chiral stationary phase (CSP) for separation of enantiomers of a set of 14 racemic compounds in normal phase (NP) and reversed-phase (RP) liquid chromatography. Retention and enantioselectivity on CDMPCCZ were compared to those on CDMPC-coated zirconia (CDMPCZ) to see how the change in immobilization method of the chiral selector affects the retention and chiral selectivity.

Intermolecular interactions on multiwalled carbon nanotubes in reversed-phase liquid chromatography.

Retention on multiwalled carbon nanotubes (MWCNTs) in RPLC has been correlated with solute descriptors of dispersion, polarizability, dipolarity, hydrogen bond donor acidity, and hydrogen bond acceptor basicity through the use of the linear solvation energy relationship. Intermolecular interactions influencing solute retention on MWCNTs were compared with those on a graphitic carbon-deposited zirconia and a common RPLC stationary phase, octylsilane-bonded silica.

Separation of racemic 2,4-dinitrophenyl amino acids on 9-O-(phenyloxycarbonyl)quinine-bonded carbon-clad zirconia in reversed-phase liquid chromatography.

Zirconia is known to be one of the best materials for the chromatographic support due to its excellent chemical, thermal, and mechanical stability. In this work, we report preparation and use of 9-O-(phenyloxycarbonyl)quinine-bonded carbon-clad zirconia (QNCZ) as a chiral stationary phase (CSP) for separation of N-(2,4-dinitrophenyl) (DNP)-amino acids (AAs) enantiomers in reversed-phase liquid chromatography. Retention and enantioselectivity of the QNCZ CSP were compared with those of quinine 3-triethoxysilylpropylcarbamate-coated zirconia (QNZ) and quinine 3-triethoxysilylpropylcarbamate-bonded silica (QNS).

Separation of racemic 2,4-dinitrophenyl amino acids on zirconia-immobilized quinine carbamate in reversed-phase liquid chromatography.

Zirconia is known to be one of the best chromatographic support materials due to its excellent chemical, thermal, and mechanical stability. A quinine carbamate-coated zirconia was prepared as a chiral stationary phase for separation of enantiomers of DNP-amino acids in reversed-phase liquid chromatography. Retention and enantioselectivity of this phase were compared to those for quinine carbamate bonded onto silica.

Enantioseparation of tiropramide by HPLC.

Tiropramide is an antispasmodic drug that has a chiral center. Resolution of tiropramide enantiomers on various kinds of chiral stationary phases was performed by HPLC. A good resolution on a leucine-derived chiral stationary phase was found.

Enantioseparation of racemic N-acylarylalkylamines on various amino alcohol derived tau-acidic chiral stationary phases.

Five tau-acidic chiral stationary phases (CSPs), CSP 4, CSP 5, CSP 6, CSP 7 and CSP 8, were prepared by connecting the N-(3,5-dimethylbenzoyl) derivative of (R)-alaninol, (S)-leucinol, (1S,2R)-ephedrine and (S)-tert-leucinol and the O-(3,5-dinitrobenzoyl) derivative of (R)-phenylglycinol to silica gel through a carbamate or urea linkage. The CSPs were applied to the resolution of various racemic N-acyl-1-naphthylaminoalkanes by chiral HPLC, and the chromatographic resolution results were compared with those of previously reported CSPs (CSP 2, CSP 3), which are derived from N-(3,5-dinitrobenzoyl)-(1S,2R)-norephedrine and N-(3,5-dinitrobenzoyl-(R)-phenylglycinol. Based on a comparison of the resolution results for each CSP, the role of each functional group on the five chiral selectors is explained.

Dipolarity, hydrogen-bond basicity and hydrogen-bond acidity of aqueous poly(ethylene glycol) solutions.

Poly(ethylene glycol) (PEG) in water is known to alter the structure and/or state of water to give a different polarity from that of pure water. We determined using the solvatochromic comparison method the dipolarity/polarizability (pi*), hydrogen bond (HB) accepting basicity (beta) and HB donating acidity (alpha) of aqueous solutions of PEGs of variegated molecular weights at different concentrations in order to understand the influence of the polymer on these properties of water. It was observed that PEG decreases alpha for water while it does not change pi* and beta appreciably in the range of the molecular weight and compositions studied.