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Usnic acid is a secondary metabolitefound in several species oflichens, organisms resulting from the symbiosis between fungi andalgae. This compound has been extensively studied because of its pharmacologicalproperties. Despite its potential medicinal importance, it exhibitsa high degree of toxicity. The confinement of the usnic acid withinliposomes has been investigated as a possibility to reduce its toxicity.In this work, we characterize the interaction of usnic acid in itsneutral and anionic states (usniate) with DPPC and DOPC by means ofmolecular dynamics simulations. A lamellar to nonlamellar transitionis observed for both membranes upon contact with usniate within 100ns time scale. The transition suggests the formation of a liposome-likestructure encapsulating the metabolyte. Furthermore, such processoccurs at a significantly shorter time frame for DOPC. [ABSTRACT FROM AUTHOR]

Theoretical studies involving minimization of model 3-propanoylaminopicolinic acids (10d-trans, 10d-cis), methyl ester (10a), and corresponding -N-oxide derivatives (10b, 10c-trans, 10c-cis) using AM1 gave conformations contrary to both sound chemical intuition and experimental data. RHF ab initio calculations using the 6-31G and 6-31G basis sets on the other hand corroborated spectroscopic data. 3-Amidopicolinic acid derivatives (7a-9a, 7b-9b, 7c-9c, 9d) were prepared and studied by NMR and IR spectroscopy. The results show that a strong intramolecular hydrogen bond between amide-H and the 2-carboxyl substituent results in a planar molecular conformation. This is particularly profound in the 3-acylaminopicolinic acid N-oxides (c-series). When the 2-substituent is a methyl ester on the other hand, repulsion between N-oxide and ester functions induces twisting of the carbomethoxy group out of the plane of the aromatic ring. The type of method used in molecular modeling can have profound impact on the final theoretical result in the case of the above-mentioned class of compounds. Our results indicate, that it is advisable to employ ab initio methods for modeling these types of compounds, and further, that the choice of basis set used for such calculations should depend on the type of information required. Thus, for most purposes pertaining to molecular conformation the 6-31G basis set provides sufficiently sound data in relatively short CPU time. For data related to electronic properties such as involvement of the N-oxide function or spectroscopic information such as IR frequencies or (1)H or (15)N NMR chemical shifts, the use of polarization functions as contained in the 6-31G basis set seems to be a must.