The 3D quantitative structure-activity relationship for a series of hydroxymethylglutaryl-CoA (HMG-CoA) reductase inhibitors based on the pyrrolylethyl-tetrahydropyranone scaffold was examined using the Minimal Topological Difference (MTD) method and comparative molecular similarity index analysis (CoMSIA). The studied compounds were of the tetrahydro-4-hydroxy-6-[2-(1H)-pyrrol-1-yl]ethyl-2H-pyran-2-one type. In clinical practice, HMG-CoA reductase inhibitors are usually referred to by the generic name statins. The analysis performed using the MTD method showed that voluminous substituents produce a significant biological activity ( 2 R2CV=0.677>0.5; SEECV=0.319 ), while the CoMSIA method added useful information regarding the influence of the steric, electrostatic, hydrophobic, hydrogen bond donor, and acceptor properties on biological activity (R2CV=0.60; r2=0.98).

Electrostatic potential has been calculated for the different faces of the hydroxyapatite crystal, based on a mathematical model and using computational design software. Electrostatic potential values indicate the possibility to influence the crystalline habitus by modifying the composition of the crystallization environment. The goal of the present study is to assess the electrostatic potential at different distances from the crystal faces, and its role at the crystal-solution interface.

Free enthalpy for formation of the cobalthexamine cation in aqueous solution was calculated by an ab initio method at the 3-21G level, with a polarisable continuum method (BemCalc) for hydration free enthalpies. The calculated Delta G = -21.25 kcal/mol compares favourably with Delta G = -31.8 kcal/mol from the experimental stability constant.

The present paper describes the crystallization of magnesium trihydrate carbonate in particular conditions, the crystals are obtained by precipitation of Mg(HCO3)(2) Solutions in presence of alkyl-aryl-sulphonates as surface-active agents. The habitus is characterized by measurements Of crystal dimensions on microscope photography images and also, by indirect methods, such as the cake humidity. Generally, surface-active agents produce crystals with more balanced dimensions along their main crystallographic axes. The results are corroborated with electrostatic potential calculations along the main crystalline faces Of MgCO3-3H(2)O. The effect of surfactants can be explained by their adsorption on the crystal face with the highest electrostatic potential (the most rapid growing one), reducing thus the growth of the crystal along the perpendicular axis to that face. From a practical point of view, the change of the crystals habitus in presence of the surface-active agents is transposed in an advanced decrease of the cakes humidity.

Bond length and atomic charges are calculated for L,M and L2M2+ complexes, as well as dissociation energies in vacuum for the complexes, with semiempiric ZINDO1 and PM3 methods, and with ab initio method with 3-21G and 6-31G* basis sets. Here, L are CH3COO_-,CH3OSO3-, ethylenediol and 1,4-dioxane; M2+ are Ca2+ and Mg2+. Geometries for CH3COO- and 1,4-dioxane are in fair agreement with X-ray crystallographic data. Dissociation energies calculated by ab initio, are in the range of 200-500 kcal/mol, generally larger for Mg2+ then for Ca2+-complexes. (c) 2006 Wiley Periodicals, Inc.

Molecular modeling and MTD methods are useful tools to assess both qualitative (SAR) and quantitative (QSAR) chemical structure-biological activity relationships. The 1[( 2-hydroxiethoxi)-methyl]-6-(phenylthio) thymine congeners ( HEPT ligands) show in vitro anti-viral activity against the type-1 human immunodeficiency virus (HIV-1), which is the etiologic agent of AIDS. This work shows an extensive QSAR study performed upon a large series of 79 HEPT ligands using the MTD and HyperChem molecular modeling methods. The studied HEPT ligands are HIV reverse-transcriptase inhibitors. Their geometries were optimized and conformational analysis was carried out to build the hypermolecule, which allowed applying the MTD method. The hypermolecule was used for space mapping of the receptor's interaction site. The obtained results show that there are three 3D molecular zones important for the anti-HIV biological activity of the HEPT ligands under study.

Geometry, electronic structure and energetic calculations were performed with semiempiric and ab initio methods of the Hyperchem package for ML2 and M2+L2 complexes possibly implied in ionic bridges mediating glycan-glycan interactions (M: Ca2+ and Mg2+, L: acetate, methylsulphate, etandiol, 1,4-dioxane). Calculated dissociation energies, in vacuum, for ML2 complexes with anions as ligands are in the range of 400-600 kcal/mol and 150-300 kcal/mol for etheric and alcoholic O-atoms as ligands, by ab initio methods. Geometries for acetate ion and 1,4-dioxane, as calculated by ab initio methods, are in good agreement with available X-ray crystallographic data.