On physical meaning of van't Hoff equation and its applicability in chromatography.

The van't Hoff equation is a widely used tool to study adsorption thermodynamics in chromatography. Recent experimental data and some theoretical arguments questioned the accuracy of thermodynamic characteristics determined by using this equation. The present report addresses these concerns and shows that if certain requirements are satisfied, the van't Hoff analysis provide reliable results.

Chiral zwitterionic stationary phases based on Cinchona alkaloids and dipeptides: Application in chiral separation of dipeptides under reversed phase conditions.

Chromatographic behavior of novel chiral stationary phases with bonded selectors based on Cinchona alkaloids modified with dipeptides was studied using dipeptides as probe molecules. Buffer-free and salt containing hydro-organic solutions were used as the mobile phases. The selectors exhibit pseudoenantiomeric behavior with respect to the L/D or LL/DD enantiomers and do not behave so with respect to the LD/DL enantiomers.

Chiral zwitterionic stationary phases based on Cinchona alkaloids and dipeptides - design, synthesis and application in chiral separation.

Chiral resolution of polar organic compounds such as amino acids and peptides represents an important chromatographic task due to increasing significance of natural species, which play important signaling and regulatory roles in the living organisms. Despite the number of available chiral stationary phases, this task remains challenging, since not many of the commercially available systems are capable to resolve non-derivatized zwitterionic species. In this study, we present a target-oriented design of a new class of chiral selectors.

Retention mechanisms of rasagiline and its analogues on superficially porous particle vancomycin- and teicoplanin-based chiral stationary phases.

Retention and separation of enantiomers of amine derivatives of indane and tetralin (rasagiline and its analogues) on chiral stationary phases (CSPs) Chiral-T and Chiral-V with teicoplanin and vancomycin antibiotics grafted onto superficially porous silica particles under conditions of reversed-phase and polar organic chromatography were studied. The mobile phases (MP) were water-methanol and acetonitrile-methanol solvents modified with triethylamine-acetic acid buffer. The effects of molecular structure and physical properties of the analytes on enantioselective retention are discussed.

Elucidation of retention mechanism of dipeptides on a ristocetin A-based chiral stationary phase using a combination of chromatographic and molecular simulation techniques.

Two chiral stationary phases virtually reproducing the Nautilus-R column were modeled in silico to study the enantiorecognition mechanism of some selected dipeptides, taking into consideration the two different anchoring alternatives to the silica layer involving the two ristocetin A amino groups. A mobile phase composed of water-methanol (40:60, v/v) was included in the system. The analyses of the trajectories supported the experimental L(LL) View Article and Find Full Text PDF

Chiral separation of dipeptides on Cinchona-based zwitterionic chiral stationary phases under buffer-free reversed-phase conditions.

Chiral zwitterion ion exchangers represent efficient chiral stationary phases for stereoselective resolution of various analytes including chiral acids, bases, and zwitterions. In this contribution, we have focused on utilization of chiral zwitterionic sorbents, denoted as ZWIX (+A) and ZWIX (-A). These are analogical chiral systems to commercially available columns, Chiralpak ZWIX (+) and Chiralpak ZWIX (-), which are usually operated with buffered mobile phases.

Enantioselective adsorption dynamics of leucyl-leucine in a Chirobiotic R column.

The dynamics of adsorption of the Leu-Leu stereoisomers in a chromatographic column packed with the Chirobiotic R chiral stationary phase bearing grafted antibiotic ristocetin A was studied by means of measurement and analysis of van Deemter plots. Similar measurements were carried out with weakly retained Gly-Gly for the sake of comparison. The bulk diffusion coefficients of the investigated dipeptides were also determined.

Enantioselective retention mechanisms of dipeptides on antibiotic-based chiral stationary phases. II. Effect of the methanol content in the mobile phase.

Effect of mobile phase (water-methanol) composition on the enantioseparation of dipeptides on the chiral stationary phase Chirobiotic R was investigated using Ala-Ala, Leu-Leu, Gly-Leu, and Leu-Gly as case studies. The lipophilicity of dipeptides was found to be an essential factor in the dependence of their retention on the methanol percentage, the retention factor of lipophobic dipeptides increasing monotonously and that of lipophilic dipeptides changing according to an asymmetric U-shaped trajectory as methanol concentration increases. The behavior of enantioselectivity as a function of the methanol content also depends on the lipophilicity of dipeptide.

Enantioselective retention mechanisms of dipeptides on antibiotic-based chiral stationary phases: Leucyl-leucine, glycyl-leucine, and leucyl-glycine as case studies.

Chromatographic behaviors of dipeptides consisting of leucine and glycine were studied on two antibiotic-based chiral stationary phases (CSPs) with teicoplanin (Chirobiotic T) or ristocetin A (Chirobiotic R) as chiral selectors under reversed-phase conditions. The effect of mobile phase pH on the retention of stereoisomers of dipeptides was investigated and thermodynamic characteristic of adsorption were measured at different pH values. It was shown that the retention of dipeptides depends on the ionization of their molecules in the mobile phase, as different ionic forms have different affinity towards antibiotic selectors.

Unusual van Deemter plots of optical isomers on a chiral brush-type liquid chromatography column.

Unusual dynamic behavior of the enantiomers of 9-bromo-11b-(tert-butyl)-2,3,6,11b-tetrahydrooxazolo[3',2':1,5]pyrrolo[3,4-b]quinoline-5,11-dione (I) was observed on a Nautilus-R column packed with silica grafted with antibiotic ristocetin. It consisted in (i) antibatic behavior of the van Deemter plots of the enantiomers and (ii) high and strongly enantiomer dependent values of the A- and B-terms of the van Deemter equation. Although rare, such a pattern has been found earlier in chiral chromatography, with all reported cases limited to brush-type chiral stationary phases.

Chiral separation and modeling of quinolones on teicoplanin macrocyclic glycopeptide antibiotics CSP.

New chiral high-performance liquid chromatography (HPLC) method for the enantiomeric resolution of quinolones is developed and described. The column used was Chirobiotic T (150 × 4.6 mm, 5.

Van't Hoff analysis in chiral chromatography.

The present review discusses the theory and application of van't Hoff analysis in chiral chromatography, with main focus on liquid chromatography. The topics considered include the physical meaning of van't Hoff equation's parameters, interpretation of thermodynamic data in terms of retention and enantioseparation mechanisms, abnormal behavior of van't Hoff plots, and best practices to avoid biased results.

Chiral separation of quinolones by liquid chromatography and capillary electrophoresis.

The quinolones are derivatives of oxoquinolines and mostly known for their antibacterial and antiviral activities. Many quinolones are chiral compounds having asymmetric centers and important due to their enantioselective biological activities. In order to study the biological activities of quinolone enantiomers, to control the manufacturing of homochiral drugs and to prepare necessary quantities of pure enantiomers for preclinical or clinical trials, respective chiral separation methods are urgently needed.

Chiral HPLC Separation and Modeling of Four Stereomers of DL-Leucine-DL-Tryptophan Dipeptide on Amylose Chiral Column.

Chiral high-performance liquid chromatography (HPLC) separation and modeling of four stereomers of DL-leucine-tryptophan DL-dipeptide on AmyCoat-RP column are described. The mobile phase applied was ammonium acetate (10 mM)-methanol-acetonitrile (50:5:45, v/v). The flow rate of the mobile phases was 0.

Advances in Nanocarriers for Anticancer Drugs Delivery.

Cancer is the most dangerous disease to haunt the mankind in the world today. Generally, the overall cancer mortality rates are similar in both the sexes. The reasons for most of these deaths are inefficacy and failure of the current methods of treatments or the unavailability of treatment options.

Validated chiral high performance liquid chromatography separation method and simulation studies of dipeptides on amylose chiral column.

Chiral resolution of dl-alanine-dl-tyrosine and dl-leucine-dl-phenylalanine dipeptides was achieved on AmyCoat-RP column. The mobile phase used for dl-alanine-dl-tyrosine was acetonitrile-ammonium acetate (10mM, pH 6.0) [50:50, v/v].

Adsorption of aqueous organic mixtures on a chiral stationary phase with bound antibiotic eremomycin.

The adsorption of two typical hydro-organic mobile phases, with methanol and acetonitrile as the organic component, on an antibiotic based chiral stationary phase (CSP) Nautilus-E was studied by the minor perturbation method. In both cases, the excess adsorption of water was positive over a wide range of concentrations from 0 to ∼75 or 90 mol% for MeOH or MeCN containing mobile phases, respectively. Such hydrophilic properties of the CSP were attributed to multiple polar functional groups of the chiral ligand and to the residual silanol groups of the silica support.

Advances in chiral separations of small peptides by capillary electrophoresis and chromatography.

Many chemical and biological processes are controlled by the stereochemistry of small polypeptides (di-, tri-, tetra-, penta-, hexapeptides, etc). The biological importance of peptide stereoisomers is of great value. Therefore, the chiral resolution of peptides is an important issue in biological and medicinal sciences and drug industries.

Isolation and analysis of bioactive compounds in Capsicum peppers.

An overview of the state of the art in the extraction, isolation, and analytical determination of bioactive compounds in peppers of the genus Capsicum is presented. The review is structured by classes of phytochemicals. Both major and minor constituents of peppers are considered.

Effect of competing binding modes on retention in chromatography and capillary electrophoresis. A theoretical consideration.

A mathematical formalism has been developed to describe equilibrium in a system involving a single selector and a selectand molecule capable of binding to this selector by different modes. The generalization of this model to a multiselector system has also been considered. Applications of the developed equations in chromatography and CE are discussed.

Adsorption models in chiral chromatography.

The review delivers the analysis of the literature data on adsorption equilibrium in chiral systems. Chiral adsorbents usually comprise several groups of nonselective and enantioselective active sites. Each group may be heterogeneous in itself.

Chromatographic retention and thermodynamics of adsorption of dipeptides on a chiral crown ether stationary phase.

The enantioselective adsorption of several dipeptides on the crown ether-based stationary phase ChiroSil RCA(+) was studied by means of the linear chromatography method. The retention of analytes was measured with acidified water-methanol mobile phases with varied concentration of methanol (from 60 to 90%, v/v) at different temperatures. Thermodynamic characteristics of adsorption were determined and analyzed applying extrathermodynamic relationships.

Transgenic potato overproducing L-ascorbic acid resisted an increase in methylglyoxal under salinity stress via maintaining higher reduced glutathione level and glyoxalase enzyme activity.

Salt-tolerance was studied in transgenic potato. It was conferred by overexpression of ascorbate pathway enzyme (D-galacturonic acid reductase, GalUR). As genetic engineering of the GalUR gene in potato enhances its ascorbic acid content (L-AsA), and subsequently plants suffered minimal oxidative stress-induced damage, we now report on the comprehensive aptness of this engineering approach for enhanced salt tolerance in transgenic potato (Solanum tuberosum L.

A study of mass transfer kinetics of alanyl-alanine on a chiral crown ether stationary phase.

The mass transfer kinetics of alanyl-alanine enantiomers in a column packed with a chiral stationary phase (CSP) ChiroSil RCA(+) was studied by means of the moment method. Methanol-water solutions acidified with sulphuric acid were used as the mobile phase. It was shown that the spreading of peaks in the column was strongly affected by abnormal eddy diffusion.