Normal spectrophotometric and stopped-flow spectrofluorimetric sequential injection methods for the determination of alendronic acid, an anti-osteoporosis amino-bisphosphonate drug, in pharmaceuticals

A normal spectrophotometric and a stopped-flow (SF) spectrofluorimetric method have been developed and optimized for the determination of alendronic acid (ALD) in its pharmaceutical formulations. Both methods are automated using the sequential injection analysis (SIA) principle. The spectrophotometric assay is based on the reaction of the analyte with Cu(II) ions in acidic medium to form an UV-absorbing derivative (λ_max = 240 nm). The SF spectrofluorimetric method is based on the reaction of ALD with o-phthalaldehyde (OPA) in the presence of 2-mercaptoethanol at basic medium (λ_ex = 340 nm/λ_em = 455 nm). Linear calibration curves were obtained in the range 1.0-60.0 mg l⁻¹ ALD for the UV method, and in the range 0.13-10.0 mg l⁻¹ ALD for the SF spectrofluorimetric one. The sampling rates were 60 and 30 h⁻¹, respectively. The developed assays are critically compared and their advantages are discussed. Both methods were applied to the analysis of an ALD containing pharmaceutical formulation with satisfactory accuracy and precision.     

Bilayer-by-bilayer antiferroelectric ordering in freely suspended films of an achiral polymer-monomer liquid crystal mixture

Thin freely suspended films of a mixture of an achiral side-chain liquid crystal polymer and its monomer have been studied with depolarized reflected light microscopy. We observe that regions with an odd number of bilayers exhibit a net spontaneous polarization in the tilt plane of the molecules, while regions with an even number of bilayers have no net polarization. These odd-even effects are direct evidence that the tilted smectic bilayers are anticlinic at the polymer backbone and synclinic at bilayer interface and confirm that the phase is bilayer-by-bilayer antiferroelectric.     

Sequential injection affinity chromatography utilizing an albumin immobilized monolithic column to study drug-protein interactions

In this study, sequential injection affinity chromatography was used for drug-protein interactions studies. The analytical system used consisted of a sequential injection analysis (SIA) manifold directly connected with convective interaction media (CIM) monolithic epoxy disks modified by ligand-immobilization of protein. A non-steroidal, anti-inflammatory drug, naproxen (NAP) and bovine serum albumin (BSA) were selected as model drug and protein, respectively. The SIA system was used for sampling, introduction and propulsion of drug towards to the monolithic column. Association equilibrium constants, binding capacity at various temperatures and thermodynamic parameters (free energy DeltaG, enthalpy DeltaH) of the binding reaction of naproxen are calculated by using frontal analysis mathematics. The variation of incubation time and its effect in on-line binding mode was also studied. The results indicated that naproxen had an association equilibrium constant of 2.90 x 10(6)M(-1) at pH 7.4 and 39 degrees C for a single binding site. The associated change in enthalpy (DeltaH) was -27.36 kcal mol(-1) and the change in entropy (DeltaS) was -73 cal mol(-1)K(-1) for a single type of binding sites. The location of the binding region was examined by competitive binding experiments using a biphosphonate drug, alendronate (ALD), as a competitor agent. It was found that the two drugs occupy the same class of binding sites on BSA. All measurements were performed with fluorescence (lambda(ext)=230 nm, lambda(em)=350 nm) and spectrophotometric detection (lambda=280 nm).