Room temperature luminescence of a retinal complex of cyclodextrin

New potentiometric sensors based on selective recognition sites for determination of ephedrine in some pharmaceuticals and biological fluids

New cost-effective potentiometric membrane sensors with cylindrical configuration responsive to ephedrine are described. The sensors setup is, based on the use of triacetyl-β-cyclodextrin [(triacetyl-β-CD)] as a neutral ionophore embedded in a plasticized poly (vinyl chloride) (PVC) matrix (sensor I) and carboxylated poly(vinyl chloride) [(PVC-COOH)] as a simultaneous plastic matrix and ion exchanger (sensor II). Both sensors showed significant enhancement of response towards ephedrinium cation (EPD(+)) over a concentration range of 3.0 × 10(-5)-8.0 × 10(-3) mol L(-1) at pH 4-9 and 3-8 with low detection limits of 5.7 × 10(-6) and 6.2 × 10(-6) mol L(-1) for sensors (I) and (II), respectively. The sensors displayed near-Nernstian cationic slope of 57.0 and 55.6 mV decade(-1) for EPD(+) and the effects of lipophilic salts and various foreign common ions were examined. The sensors were also satisfactorily used as tubular detectors in a double channel flow injection system. The intrinsic characteristics of the detectors in a low dispersion manifold under hydrodynamic mode of operation were determined and compared with data obtained under batch mode of operation. Validation of the method revealed good performance characteristics including long life span, good selectivity for EPD(+) over a wide variety of other organic compounds, long term stability, high reproducibility, fast response, low detection limit, wide measurement range, acceptable accuracy and precision. Applications of the sensors to the determination of EPD(+) in pharmaceutical formulations and spiked biological fluid samples were carried out and compared with standard techniques. Notably, the sensors introduced offer several advantages over many of those previously described that are amenable to quality control/quality assurance assessment of the homogeneity, stability and purity of ephedrine drug tablets.

The design, synthesis and photochemical study of a biomimetic cyclodextrin model of photoactive yellow protein (PYP)

The design, synthesis and study of the photophysical and photochemical properties of the first biomimetic cyclodextrin (CD) model of photoactive yellow protein (PYP) are described. This model bears a deprotonated trans-p-coumaric acid chromophore, covalently linked via a cysteine moiety to a permethylated 6-monoamino β-CD. NMR and UV/Visible spectroscopy studies showed the formation of strong self-inclusion complexes in water at basic pH. Steady-state photolysis demonstrated that, unlike the free chromophore in solution, excitation of the model molecule leads to the formation of a photoproduct identified as the cis isomer by NMR spectroscopy. These observations provide evidence that the restricted CD cavity offers a promising framework for the design of biomimetic models of the PYP hydrophobic pocket.

Flow injection spectrofluorimetric study of the supramolecular interaction between beta-cyclodextrin and dequalinium chloride and its analytical application

The supramolecular interaction of dequalinium chloride (DQC) and beta-cyclodextrin has been studied by flow injection spectrofluorimetry. The results showed that beta-CD reacted with DQC to form a 1:1 host:guest complex with an apparent association constant of 4.99 x 10(2) L mol(-1). Based on the enhancement of the fluorescence intensity of DQC, a flow injection spectrofluorometric method for the determination of DQC in bulk aqueous solution in the presence of beta-CD was developed. The linear range was 0.0412-30.00 microg mL(-1). The detection limit was 12.3 ng mL(-1) with a sampling rate of 80 h(-1). There was no interference from the excipients normally used in tablets and serum compositions. The proposed method was successfully applied to the determination of DQC in tablets and serum.

Analytical applications of retinoid-cyclodextrin inclusion complexes. 1. Characterization of a retinal-beta-cyclodextrin complex

In studies in these laboratories on the supramolecular chemistry of the retinoids, it has been recently confirmed that inclusion of these substances within the cavity of cyclodextrins protects their excited states, thus improving their photochemical stability. In the present paper, the isolation is described of a crystalline stable complex between retinal and beta-cyclodextrin, which has been characterized by means of several techniques including atomic force microscopy (AFM). The complex shows distinct spectroscopic differences from both retinal and beta-cyclodextrin. Thus, it absorbs at lambda(max) = 380 nm in water whereas retinal is insoluble; it shows room-temperature luminescence, which retinal does not; finally, it give 1H-NMR and 13C-NMR spectra in d6-DMSO with clear differences in chemical shifts with respect to those of beta-cyclodextrin. Besides these studies in solution, the behaviour of the complex in the solid state has been compared with that of physical mixtures of retinal and beta-cyclodextrin. IR spectroscopy shows clear differences, particularly a shift in the retinal carbonyl absorption (1644-1672 cm-1). AFM studies reveal the existence of aggregates; X-ray diffractometry also supports the formation of a cyclodextrin-retinal complex.

Liquid chromatographic determination of beta-cyclodextrin derivatives based on fluorescence enhancement after inclusion complexation

A liquid chromatographic method using fluorescence detection for the determination of beta-cyclodextrin (beta CD) and its derivatives is presented. The chromatographic system is based on size-exclusion chromatography with the addition of the fluorophoric compound 1-naphthol to the mobile phase. Detection is based on fluorescence enhancement caused by the formation of inclusion complexes. By incorporating 10(-4) M 1-naphthol in the mobile phase, detection limits of 90, 27, 370 and 37 pmol were obtained for beta CD, hydroxypropyl-beta CD, trimethyl-beta CD and dimethyl-beta CD, respectively. The method was applied to the determination of dimethyl-beta CD in urine: the minimum detectable concentration was 0.2 microgram/ml after preconcentration of 10 ml of urine.