Structural features and hydrogen-bond properties of galanthamine and codeine: an experimental and theoretical study

Structural features of galanthamine and codeine, two allosteric potentiating ligands of nicotinic acetylcholine receptors (nAChRs), have been investigated through experimental studies in solution by FTIR and NMR spectroscopy and by quantum chemical calculations in the isolated state. The infrared spectra accumulated in solvents of various polarities show that the intramolecular OH···O hydrogen bond in galanthamine is stronger than the corresponding interaction in codeine. Molecular electrostatic potential calculations allow rationalisation of the experimental trends. NOE measurements on the two ligands in the same solvent range show significant differences. In apolar solvents, the NMR spectroscopic data indicate the occurrence of CH···O hydrogen-bond interactions, whereas in the more polar solvents, a trans orientation of the methoxy group with respect to the furanyl oxygen atom is favoured. A natural bond orbital (NBO) analysis provides evidence that these stabilising interactions originate in the hyperconjugation between the lone pairs of the furanyl oxygen atoms, n(O), and the methoxy antibonding σ*(C-H) orbitals within the two molecules. Despite the strong structural similarities between the two allosteric modulators, FTIR equilibrium constants measurements of hydrogen-bond complexation combined with quantum chemistry calculations point out the significant increase of hydrogen-bond accepting strength of galanthamine relative to codeine. This increase is mainly assignable to the stronger hydrogen-bond basicity of the hydroxyl group, and to a lesser extent to the higher hydrogen-bond accepting strength of the amino nitrogen of galanthamine in comparison with the corresponding groups of codeine. An analysis of the interactions that occur between the two ligands and acetylcholine esterase (AChE) suggests significant differences with Trp84, a key component of the AChE catalytic active site. In contrast, both ligands appear to interact similarly with acetylcholine binding protein (AChBP).     

HPLC determination of majdine in Vinca herbacea

A reliable HPLC method coupled with DAD detection was developed and validated for determination of majdine in Vinca herbacea. The chromatographic separation was carried out on a Symmetry C18 column (250 mm x 4.6 mm, 5 microm, Waters) with an isocratic solvent system of 25 mM potassium phosphate buffer (pH = 3.0)-acetonitrile. UV detection was performed at 225 nm. Good linear behavior over the investigated concentration range was observed with the value of r2 > 0.9978. The method was reproducible with intra- and inter-day variations of less than 4.38%. The proposed method was linear, accurate, precise and specific. The validated method was successfully applied to quantify majdine in various parts of V. herbacea, which was collected during the flowering months of April and May. The results indicated that the developed HPLC method could be used for the quality control of V. herbacea and for the standardization of its extracts in majdine.     

Thermophysical properties of polypropylene/aluminum composites

This article is dedicated to the study of the thermal parameters of composite materials. A nonlinear least‐squares criterion is used on experimental transfer functions to identify the thermal conductivity and the diffusivity of aluminum‐polymer composite materials. The density measurements were achieved to deduce the specific heat and thereafter they were compared to values given by differential scanning calorimetry measurement. The thermal parameters of the composite material polypropylene/aluminum were investigated for the two different types of aluminum filler sizes. The experimental data were compared with several theoretical thermal conductivity prediction models. It was found that both the Agari and Bruggeman models provide a good estimation for thermal conductivity. The experimental values of both thermal conductivity and diffusivity have shown a better heat transport for the composite filled with large particles. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 722–732, 2004     

Synthesis of substituted amido-isogranulatimide analogues as potential checkpoint1 kinase inhibitors

Two new regioisomeric series of substituted amido-isogranulatimide analogues were prepared in three steps from 2-imidazol-1-yl-1H-indol-5-ylamine. The experimental conditions of the last photocyclization step were determinant to obtain one or the other series.     

Aspects of the capillary GC analysis of all-trans- and 13-cis-acitretin

The capillary gas chromatographic (CGC) analysis of the der-matological drug trans-acitretin (Neotigason^R) and its cis metabolite is described. Separation of the methyl ester derivatives can be achieved on a 90% biscyanopropylsiloxane phase. The importance of using cold on-column injection and short, thin film capillary columns is discussed. For patients treated with the prodrug of acitretin, etretinate (Tigason^R), i.e. the ethyl ester of Neotigason, three compounds have to be separated. Selectivity tuning is required for successful CGC separation. An alternative can be found in the selectivity of ion monitoring mass spectroscopy. Analysis of plasma samples involves liquid-liquid extraction, a derivatization step, and HPLC purification.     

Hamiltonian pancyclic graphs

The class of 3-connected bipartite cubic graphs is shown to contain a non-Hamiltonian graph with only 78 vertices and to have a shortness exponent less than one.