Molecular modelling and NMR NOE experiments: Complementary tools for the investigation of complex ibuproxam-β-cyclodextrin topology

Effect of PVP K30 and/or L-arginine on stability constant of etoricoxib-HPbetaCD inclusion complex: preparation and characterization of etoricoxib-HPbetaCD binary system

The effect of polyvinyl pyrrolidone (PVP) K30 and/or L-arginine on etoricoxib-HPbetaCD complex was investigated. The phase solubility profiles were classified as A(L)-type, both in absence or presence of auxiliary substances used. The apparent stability constant (K(c)) of binary complex obtained at room temperature, 371.80 +/- 2.61 M(-1), was decreased with the addition of PVP and arginine indicating no benefit of addition of auxiliary substances to promote higher complexation efficiency. Therefore, solid etoricoxib-HPbetaCD binary systems were prepared and characterized by proton nuclear magnetic resonance spectroscopy (1HNMR), X-ray powder diffractometry, Fourier transformation-infrared spectroscopy, and dissolution studies. Among all binary systems, a lyophilized product showed superior performance in enhancing dissolution of etoricoxib.

Comparative study of ibuproxam complexation with amorphous beta-cyclodextrin derivatives in solution and in the solid state

The complexing, solubilizing and amorphizing abilities toward ibuproxam (a poorly water-soluble anti-inflammatory agent) of some randomly substituted amorphous beta-cyclodextrin derivatives (i.e. methyl- (MebetaCd), hydroxyethyl- (HEbetaCd), and hydroxypropyl- (HPbetaCd) beta-cyclodextrins) were investigated and compared with those of the parent beta-cyclodextrin. Equimolar drug-cyclodextrin solid systems were prepared by blending, cogrinding, coevaporation, and colyophilization. Drug-carrier interactions were studied in both the liquid and solid state by phase solubility analysis, supported by molecular modelling, differential scanning calorimetry, X-ray powder diffractometry, Fourier transform infrared spectroscopy and scanning electron microscopy. All the betaCd derivatives showed greater solubilizing efficacies toward ibuproxam than the parent one, due to their higher water solubility. On the contrary, a clear reduction of complexing ability was observed, indicative of some steric interferences to drug inclusion due to the presence of substituents, as confirmed by molecular modelling studies. However, this negative effect was not reflected in the dissolution behaviour (evaluated according to the dispersed amount method) of their solid binary systems, probably thanks to the greater amorphizing properties shown (DSC and X-ray analyses) by betaCd derivatives. In fact their dissolution efficiencies were not significantly different (MebetaCd) or only slightly lower (HEbetaCd and HPbetaCd) than those of the corresponding products with beta-cyclodextrin. Colyophilized products were in all cases the most effective, followed by coground and coevaporated systems, whose dissolution efficiencies were over four times higher than the corresponding physical mixtures and about 15 times higher than the pure drug.

Elucidation of solution state complexation in wet-granulated oven-dried ibuprofen and beta-cyclodextrin: FT-IR and 1H-NMR studies

The effect of oven-dried wet granulation on the complexation of beta-cyclodextrin with ibuprofen (IBU) in solution was investigated using Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H NMR), and molecular modeling. Granulation was carried out using 5 mL of three different granulating solvents; water, ethanol (95% v/v), and isopropanol and the granules were oven-dried at 60 degrees C for 2 h. The granules were compared to oven-dried physical mixture and conventionally prepared complex. Phase solubility study was performed to investigate the stability of the granulation-formed complexes in solution. FT-IR was used to examine the complexation in the granules while 1H NMR, and molecular modeling studies were carried out to determine the mechanism of complexation in the water-prepared granules. The solubility studies suggested a 1:1 complex between IBU and betaCD. It also showed that the stability of the complex in solution was in the following order with respect to the granulating solvents: ethanol > water > isopropanol. The FT-IR study revealed a shift in the carboxylic acid stretching band and decrease in the intensities of the C-H bending bands of the isopropyl group and the out-of-plane aromatic ring, of IBU, in granules compared to the oven-dried physical mixture. This indicated that granules might have some extent of solid state complexation that could further enhance dissolution and the IBU-betaCD solution state complexation. 1H NMR showed that water prepared oven-dried granules had a different 1H NMR spectrum compared to similarly made oven-dried physical mixture, indicative of complexation in the former. The 1H NMR and the molecular modeling studies together revealed that solution state complexation from the granules occurred by inclusion of the isopropyl group together with part of the aromatic ring of IBU into the betaCD cavity probably through its wider side. These results indicate that granulation process induced faster complexation in solution which enhances the solubility and the dissolution rate of poorly soluble drugs. The extent of complexation in the granules was dependent on the type of solvent used.

Interactions between lonidamine and beta- or hydroxypropyl-beta-cyclodextrin

The possibility of obtaining inclusion complexes between lonidamine and beta- or hydroxypropyl-beta-cyclodextrin have been evaluated by phase solubility diagram, differential scanning calorimetry (DSC), and x-ray diffractometry. The applied complexation methods were spray-drying, kneading, and solid dispersion. DSC and x-ray analyses of the powders revealed an external interaction between lonidamine and cyclodextrins. Dissolution profiles of the obtained powders were also studied to define the most appropriate preparation method and molar ratio to use in attempts to increase lonidamine water solubility.

Nuclear magnetic resonance investigations of the inclusion complexation of gliclazide with beta-cyclodextrin

The formation of the gliclazide-beta-cyclodextrin (GL-beta-CD) inclusion compound has been studied in the liquid state by phase solubility techniques and by 1H and 13C NMR spectroscopy. From the initial straight portion of the solubility curve (Bs type), the value of the apparent stability constant (Kc) was calculated as 1094 M(-1). The nuclear magnetic resonance studies confirm that GL yields a complex with beta-CD in aqueous medium, which is mainly due to the penetration of the azabicyclooctyl group of GL into the cavity of beta-CD. The study of the monodimensional nuclear Overhauser effect (NOE) of the H3 proton of CD has shown that the tolyl group also interacts with CD, but to a lesser extent than the azabicyclooctyl moiety. Finally, the application of the continous variation technique confirmed the 1:2 drug:CD stoichiometry of the complex.