Characterization of the Sublimation and Vapor Pressure of 2-(2-Nitrovinyl) Furan (G-0) Using Thermogravimetric Analysis: Effects of Complexation with Cyclodextrins.

In the present work, the sublimation of crystalline solid 2-(2-nitrovinyl) furan (G-0) in the temperature range of 35 to 60 °C (below the melting point of the drug) was studied using thermogravimetric analysis (TGA). The sublimated product was characterized using Fourier-transformed-infrared spectroscopy (FT-IR) and thin layer chromatography (TLC). The sublimation rate at each temperature was obtained using the slope of the linear regression model and followed apparent zero-order kinetics. The sublimation enthalpy from 35 to 60 °C was obtained from the Eyring equation. The Gückel method was used to estimate the sublimation rate and vapor pressure at 25 °C. Physical mixtures, kneaded and freeze-dried complexes were prepared with 2-hydroxypropyl-ß-cyclodextrin (HP-ß-CD) and sulfobutyl ether-ß-cyclodextrin (SBE-ß-CD) and analyzed using isothermal TGA at 50 °C. The complexation contributed to reducing the sublimation process. The best results were achieved using freeze-dried complexes with both cyclodextrins.

Characterization and molecular modeling of the inclusion complexes of 2-(2-nitrovinyl) furan (G-0) with cyclodextrines.

The objective of this study was to prepare and characterize complexes of 2-(2-nitrovinyl) furan (G-0) with 2-hydroxypropyl-ß-cyclodextrin (HP-ß-CD) and sulfobutyl ether-ß-cyclodextrin (SBE-ß-CD). The solid inclusion complexes were prepared using kneading and freeze-drying methods. Phase solubility profiles were used to obtain the apparent stability constants and the complexation efficiency. They were classified as A(L) type for both systems: the apparent stability constants K(1:1) of the complexes were 48.7 and 79.2 M(-1) for HP-ß-CD and SBE-ß-CD respectively. The solid inclusion complexes were evaluated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD) and nuclear magnetic resonance spectroscopy (NMR). Especially the use of the two-dimensional ROESY spectrum was useful to confirm the presence of an inclusion complex. The spatial configuration of the drug inside the cyclodextrin cavity was investigated using molecular modeling studies. The latter results were in agreement with the experimental data. Inclusion complexes of G-0 with HP-ß-CD contributed to improve the chemical stability of the drug in the presence of other commonly used pharmaceutical excipients.

Polysaccharides as excipients for colon-specific coatings. Permeability and swelling properties of casted films.

Oligosaccharides such as inulin (In) and polysaccharides such as galactomannans, combined with polymethacrylates on isolated films for film coatings, were obtained from aqueous-based solvents and investigated as potential vehicles for colonic drug delivery. These compositions, which are susceptible to fermentation by colonic microflora, constitute promising excipients for the development of new colon-specific therapeutic systems. The characteristics of several compositions have been demonstrated in permeability and swelling studies on isolated films composed of a polymethacrylate associated with In or galactomannans of mesquite seed gum (MSG). Results reported prove a dependency of the properties of mixed films on the polymethacrylate-polysaccharide concentration ratio and on the composition of the dissolution media. An increase in permeability through the mixed films was observed in a simulated colonic environment for the following compositions: Eudragit RS30D-MSG 70:30 w/w; Eudragit RS30D-In 90:10 w/w; Eudragit RS30D-In 76:24 w/w.