Chromatographic behaviour of cyclodextrin complexes of nucleotides, nucleosides and their bases

Spatial mismatch, non-additive binding energies and selectivity in supramolecular complexes

A geometric mismatch in supramolecular complexes often leads to deviations from the additivity of binding energies with the consequence of large changes in selectivity and binding mode.

Inclusion kinetics of a nucleotide into a cyclodextrin cavity by means of ultrasonic relaxation

To examine a dynamic interaction between nucleotide and cyclic oligosaccharide, ultrasonic absorption measurements were carried out in aqueous solution containing beta-cyclodextrin (beta-CD) and adenosine 5'-monophosphate (AMP) in the frequency range of 0.8-95 MHz. A relaxational absorption was observed in the solution, although it was not found in the individual solution of beta-CD or AMP. From the concentration dependences of AMP on the relaxation time and the maximum absorption per wavelength, the cause of the relaxation was attributed to a perturbation of a chemical equilibrium associated with a complex formation between beta-CD (host) and AMP (guest). The rate constants for the formation and breakup processes of the complex were determined. Also, a standard volume change of the reaction was obtained. From comparisons of the obtained rate and thermodynamic parameters with those for beta-CD and various guests, it has been concluded that the adenine moiety is included in the beta-CD cavity and that the hydrogen bonds may play a role in the complex formation.

Interaction between cyclodextrins and aflatoxins Q1, M1 and P1. Fluorescence and chromatographic studies

The fluorescence properties of the aflatoxins M1, Q1, P1 in solution and the effect of various cyclodextrins (alpha-, beta-, gamma-, hydroxypropyl-beta- and alpha-beta-heptakis-di-O-methyl-beta-) on their fluorescence emission were studied. Among the aflatoxins, a substantial enhancement of the fluorescence emission of aflatoxin Q1 in the presence of aqueous solutions of alpha-, beta-, hydroxypropyl-beta, and alpha-beta-heptakis-di-O-methyl-beta-cyclodextrin, was observed. On the contrary, gamma-cyclodextrin proved to be inefficient to enhance the fluorescence properties of this compound. No important fluorescence enhancement was found for aflatoxins P1 or M1 for any of the cyclodextrin derivatives tested. The complex formation constant (Kf) of these compounds with beta-cyclodextrin was chromatographically determined, and from the results obtained, we can conclude that Kf cannot be used alone to explain the fluorescence increase. Thermodynamic studies showed that delta-H and delta-S parameters, associated with the partition of aflatoxins in RP-HPLC, increased when beta-cyclodextrin was added to the eluent.

Effect of beta-cyclodextrin derivatives on the retention of steroidal drugs

The retention of eighteen steroid drugs was determined on a beta-cyclodextrin polymer (beta CDP)-coated silica column using methanol-water mixtures as eluents. The relative strength of inclusion formation between the drugs and hydroxypropyl-beta CD (HP beta CD) and dimethyl-beta CD was determined by charge transfer chromatography carried out on reversed-phase thin-layer chromatography plates. The retention characteristics of drugs were correlated with their physicochemical parameters and with their inclusion complex-forming capacity. Calculations indicated that the inclusion complex-forming capacity of the drugs has little impact on the retention that is due to the HP beta CD and water-insoluble beta CD polymers exposed to different retention characteristics. The hydrophilic molecular parameters of drugs significantly influenced their retention. This result suggests that the selectivity of the beta CDP-coated column may be different from that of the traditional reversed-phase columns.

Use of liquid chromatography for the determination of interactions between bioactive compounds

Molecular interactions can be easily determined both by thin-layer and high performance liquid chromatography. The theory and practice of the determination of molecular interactions and the various methods for the calculation of complex stability are presented. Examples of the application of liquid chromatographic methods for the measurements of molecular interactions are also discussed.

Use of principal component analysis for the evaluation of the retention behaviour of monoamine oxidase inhibitory drugs on beta-cyclodextrin column

The retention of 17 monoamine oxidase inhibitory drugs (proparlgylamine derivatives) were determined on a beta-cyclodextrin polymer (beta CDP)-coated silica column using ethanol-0.05 M K2HPO4 (6:4 v/v) as the eluent. The relative strength of interaction between the drugs and a water soluble beta-cyclodextrin polymer was determined by charge-transfer chromatography carried out on reversed-phase TLC layers. The relationship between capacity factors, physicochemical parameters and inclusion complex forming capacity of the monoamine oxidase inhibitory drugs were evaluated by stepwise regression analysis and by principal component analysis (PCA) followed by two-dimensional nonlinear mapping and varimax rotation. Calculations indicated that the retention of monoamine oxidase inhibitory drugs on beta CDP column is mainly governed by their steric and lipophylic parameters. Significant linear correlations were found between the corresponding coordinates of varimax rotation and two-dimensional nonlinear maps proving the suitability of both methods for the reduction of dimensionality of complicated data matrices.

Liquid chromatographic separation of zalcitabine and its stereoisomers

A liquid chromatographic method capable of separating and quantitating the stereoisomers of zalcitabine has been developed and validated. The separation was achieved with an Astec Cyclobond I--RSP column and a mobile phase of 0.25% triethylamine in water adjusted to a pH of 6.5 with glacial acetic acid. All enantiomers were found to exhibit a linear response in the range of 0.1-10% in the presence of 100% zalcitabine. Precision of analysis was found to be less than 1.5% at a level of 1% relative to zalcitabine. The limit of detection for two of the three enantiomeric impurities was determined to be 0.05% relative to zalcitabine. The detection limit for the third was found to be 0.1%. This method was successfully applied to the analysis of reference standards and several production scale batches. All of these materials were found to be stereochemically pure to a level of 99.8% or better.