Thermal analysis of chiral drug mixtures: the DSC behavior of mixtures of ephedrine HCl and pseudoephedrine HCl enantiomers

A method for peak shape analysis and deconvolution of overlapping endotherms in differential scanning calorimetry (DSC) data has been previously reported. In this study the method is applied to binary mixtures of, (i) (1S,2S)-(+)- and (1R,2R)-(-)-ψ-ephedrine HCl, and (ii) (1S,2S)-(+)-ψ-ephedrine HCl and its diastereomer, (1S,2R)-(+)-ephedrine HCl. Phase diagrams based on enthalpies of fusion at the melting point (ΔH ) as a function of mol% composition are linear. However, the phase diagrams based on melting temperature as a function of mol% composition are non-linear and show deviations from the theoretical Prigogine-Defay and Schröder-van Laar equations. Estimates of eutectic compositions are more definitive from the diagrams based on ΔH values. The phase diagram for the ψ-ephedrine HCl enantiomers demonstrates racemic compound formation with eutectic points for the compound and the pure enantiomers at 28.1 ± 2.5 mol% and 71.9 ± 2.5 mol%. The ΔH phase diagram for mixtures of (1S,2R)-(+)-ephedrine HCl and (1S,2S)-(+)-ψ-ephedrine HCl suggested the formation of a weak complex with a composition close to 60 mol% of the (1S,2S)-(+)-isomer

Corrosion inhibition efficiency of some hydrophobically modified chitosan surfactants in relation to their surface active properties

This work deals with surface activity and corrosion inhibition efficiency of the natural polymer chitosan and its hydrophobically modified derivatives (eight polymeric compounds). Chitosan was found to be inactive at interfaces but the hydrophobic modification using different aliphatic and aromatic substituents renders the products surface active polymers. From the obtained data it was found that the surface active properties increased by increasing the hydrophobic character of these polymers. Chitosan and its based surfactants were investigated as corrosion inhibitors for carbon steel in 1 M HCl solution using the potentiodynamic polarization method. The resulted corrosion inhibition efficiency situated between 67.56% and 93.23% at 250 ppm and 25 °C. The inhibition efficiency was discussed on the light of surface active properties and the chemical structure of the used derivatives. The quantum chemical calculations were performed for some chitosan derivatives. The charge density distribution, highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and dipole moment were considered

Polymerization of monolayers of 3-substituted pyrroles

Derivatives of 3-substituted pyrroles were spread at the air-water interface. Stable films could be obtained for pyrroles with side chains containing more than 10 carbons. 3-Hexadecanoylpyrrole could not be polymerized as a monolayer whereas the alkyl derivatives could be polymerized successfully without having additional monomer in the subphase. The monolayers could be transferred onto hydrophobic substrates with transfer ratios close to unity. The polymers formed were soluble in chloroform and tetrahydrofuran. Molecular-weight averages obtained by gel permeation chromatography ranged from 3500 to 6000 when polymerized on ammonium peroxydisulfate and 5000 to 15000 when polymerized on ferric chloride subphase solutions. 1H NMR indicates that the polymerization is highly regular, leading to a constitutionally ordered 2,5-poly(3-alkylpyrrole)