(3S,4S,5S,10S,13R,14R,17R)-4 alpha,14 alpha-Dimethyl-3 beta-tosyl-5 alpha-ergost-8-ene-7,11,24-trione at 100 K

The title compound, C36H50O6S, forms an extended sheet of four fused rings which exhibit different conformations, as already observed in previously reported triterpene structures. There are weak intra- and intermolecular C-(HO)-O-... inter-actions. A weak C-Hc pi interaction also occurs, involving the tosyl group

Experimental electron density and electrostatic potential analysis of zinc(aspirinate) 2 (H 2 O) 2 complex A 3d 10 metal bonding to a drug ligand

International audienceFor the protection against the side effects and the improvement of the pharmacological activity of nonsteroidal antiinflammatory drugs (NSAID's), one alternative way is to design a metal complex of these agents. In this context, we have investigated the electrostatic properties of the zinc-aspirinate dihydrate (Zn[C 9 H 7 O 4 ] 2 (H 2 O) 2 ) complex to characterize and to mimic the activity of this potent pharmaceutical compound. A high-resolution X-ray diffraction experiment at 100 K has been performed on the Zn[C 9 H 7 O 4 ] 2 (H 2 O) 2 complex which crystallizes in the C2/c space group displaying a tetrahedrally coordinated zinc atom. The Hansen-Coppens multipole model was used to derive the experimental electron density to study the chemical bonding and the metal-ligand charge transfer. The investigation of the electron density has revealed that only the Zn 4s orbital participates in the metal-ligand interaction whereas the metal 3d full valence shell remains unperturbated. The κ-model refinement yielded a zinc net charge of +1.3 e with a highly contracted 4s electronic shell. The most positive charge of the aspirinate ligand was found on the acetyl carbon (+0.8 e), in agreement with the previously observed nucleophilic attack on the aspirin drug in the inhibited cyclooxygenase (COX) enzyme channel. The electrostatic potential was calculated from the multipole populations and the net atomic charges derived from the X-ray diffraction data. This fundamental property was carefully analyzed through the 3D isopotential and molecular surface representations to highlight the active sites of the zinc-aspirinate complex

Experimental Electron Density Study of Tetrakis-mu-(acetylsalicylate)dicopper(II): a Polymeric Structure with Cu center dot center dot center dot Cu Short Contacts

International audienceThe electron density, its topological features, and the electrostatic potential of tetrakis-mu-(acetylsalicylate)dicopper(II), Cu[C9H7O4](2), have been derived from an accurate high-resolution diffraction experiment at 100 K. This complex exhibits a polymeric structure involving one acetyl oxygen atom as a bridge in the solid state. Only van der Waals interactions between the polymeric chains are observed. The copper cation is octahedrally coordinated with five oxygen atoms of the aspirinate ligands and one adjacent Cu with short Cu center dot center dot center dot Cu contact distances in the range of 2.6054(1) angstrom. The Cu-O bond lengths are equal to 1.96 angstrom except the apical one which is 2.2183(7) angstrom. The multipole refinements were carried out using the Hansen-Coppens model coded in the MOPRO computer program. Starling from the 3d(10)4s(1) copper electron configuration, the electron density analysis and Cu d-orbital populations reveal that the observed configuration is close to being [Ar]3d(9)4s(1). As expected from the ligand field theory, the most depopulated 3d-orbital is the d(x2-y2)(1.17 e) one with lobes pointing toward the carboxylic oxygen atoms. Conversely, the d(z2) is the most populated orbital for a z-axis directed along the Cu center dot center dot center dot Cu bond. The atomic charges were derived from a kappa-refinement and yielded a metal net charge of +1.20(3) e. Deficits of +0.72(6) and +0.59(7) e are obtained for the acetyl carbon atoms of the aspirinate ligands, those involved in the drug activity of aspirin. Comparisons are made to the results of our previous work on the zinc-aspirinate complex

Electron and electrostatic properties of three crystal forms of piracetam

International audienceThe electron densities in three crystal forms of piracetam (triclinic form II, monoclinic form III, and triclinic piracetam monohydrate) were derived from high resolution X-ray diffraction experiments carried out at 100 K. For comparison, quantum mechanics calculations were also performed for the three compounds. The experimental electron density was refined using the Hansen-Coppens multipole model. The electron deformation density and the electrostatic potential were carefully analyzed in the three forms of piracetam. The atomic charges obtained by the flux of the electric field were found in excellent agreement with those obtained by the conventional volume integration method. The charge values compare qualitatively well with those obtained by theoretical calculations. The total electrostatic force exerted on each atom of the molecule has been investigated by using the Maxwell stress tensor as well as the interatomic forces. The experimental electrostatic interaction energies between dimers in the three crystal forms of piracetam were also estimated. Monoclinic form III exhibits the strongest piracetam-piracetam dimer electrostatic interaction energy (-131.9 kJ/mol) compared to -116.0 and -103.3 kJ/mol found in triclinic form II and the monohydrate form, respectively. The experimental interaction electrostatic energy of the piracetam-water contact was estimated as -175.0 kJ/mol in the monohydrate form. © 2011 American Chemical Society

Molecular reactivity of busulfan through its experimental electrostatic properties in the solid state

International audiencePurpose. In the route of developing novel liquid phase formulations based on the encapsulation of busulfan into liposomes in nontoxic solvents, drug crystallization inevitably occurs. In order to better understand the reactivity of busulfan, the characterization of its molecular properties was therefore considered as a key point. Also, preliminary attempts to prevent crystallization using cyclodextrins were explored. Methods. An accurate single-crystal high-resolution X-ray diffraction experiment at 100 K has been carried out. The experimental electron density of busulfan was refined using a multipole model. Busulfan/ β-cyclodextrin coprecipitates were analyzed by powder X-ray diffraction and 1H-NMR spectroscopy. Results. The electrostatic properties of busulfan and the methylsulfonate fragment dipole moment (3.2 D) were determined. The polar moieties play a key role in the crystallization of busulfan, which presents a nucleophilic region surrounding the sulfonate part, whereas the carbon chain displays an electrophilic character. This highlights the subtle busulfan/β-cyclodextrin association. Conclusions. Busulfan electrostatic properties were used to quantify its chemical reactivity. This explains the difficulty to formulate busulfan into liposomes due to a strong polar character of the methylsulfonate terminal groups. The complexation with cyclodextrins deserves to be further investigated to allow the formulation of busulfan in nontoxic solvents

Theoretical approach, elaboration and physical characterization of ceramic materials, Modelisation of the electrostatic potential considering multipolar moments

We report here our magnetic study on amorphous Gd0.7Zr0.3 alloy. The magnetic saturation is difficult to obtain even for fields up to 50 kOe. This led us to the conclusion that ferromagnetic and antiferromagnetic clusters are present in this alloy. However, the presence of a well defined Tc indicate that the ferromagnetic clusters are dominant and the presence of the coherent anisotropy field can transform this type of magnetic ordering into a ferromagnetic domain structure. The thermomagnetization curve is found to obey the Bloch law; spin wave stiffness constant and the distance between nearest magnetic atoms were calculated from the experimental results.We report here our magnetic study on amorphous Gd0.7Zr0.3 alloy. The magnetic saturation is difficult to obtain even for fields up to 50 kOe. This led us to the conclusion that ferromagnetic and antiferromagnetic clusters are present in this alloy. However, the presence of a well defined Tc indicate that the ferromagnetic clusters are dominant and the presence of the coherent anisotropy field can transform this type of magnetic ordering into a ferromagnetic domain structure. The thermomagnetization curve is found to obey the Bloch law; spin wave stiffness constant and the distance between nearest magnetic atoms were calculated from the experimental results

Investigation of the cytosine–decavanadate interaction from an experimental charge density: a supramolecular arrangement of Na 3 V 10 O 28 (C 4 N 3 OH 5 ) 3 (C 4 N 3 OH 6 ) 3 ·10H 2 O in the solid state

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