Molecular modeling of the structure and dynamics of the interlayer species of ZnAlCl layered double hydroxide.

Molecular dynamics simulations of the ZnAl layered double hydroxide containing interlayer chloride anions have been performed in the NpT and Np(zz)T statistical ensembles for metal Zn/Al ratios of 2 and 3. We have monitored the interlayer spacing as a function of the number of intercalated water molecules for each statistical ensemble. We have studied how these profiles are affected by the method of calculation of the charges of the hydroxide layer atoms. Diffusion coefficients of the interlayer water molecules have been calculated for different Zn/Al ratios. The calculation of the chemical potential of the interlayer water molecules has been carried out for three amounts of interlayer water molecules. The calculation showed a qualitative agreement with the bulk water chemical potential within a range of interlayer water molecule contents.

Computational and experimental investigations of supramolecular assemblies of p-sulfonatocalix[4]arene organized by weak forces.

We report the study of the supramolecular assemblies formed by the incorporation of quaternary ammonium cations such as Me4N+ or Et4N+ into host-guest assemblies with p-sulfonatocalix[4]arene in the presence of a lanthanide(III) cation in water. We use microcalorimetry to characterize the formation of these supramolecular assemblies. We obtain a molecular description of these assemblies by performing molecular dynamics simulations over a very large period of time. The structures of these supramolecular complexes have been determined and discussed through specific interaction energy contributions. By combining MD simulations and 1NMR spectroscopy, we highlight a specific behavior of the supramolecular assembly with the Me4N+.

MD simulations of the binding of alcohols and diols by a calixarene in water: connections between microscopic and macroscopic properties.

We report results of molecular dynamics (MD) simulations of the complexes of p-sulfonatocalix[4]arene with linear alcohols from ethanol to heptanol in water at 25 degrees C. We show that these complexes are of the inclusion type and are governed by van der Waals interactions between the calixarene cavity and the inserted alkyl chain of the alcohol. We establish a correlation between the experimental Delta(r)H degrees values and the number of atoms inserted into the calixarene cavity. We also focus on the desolvation of the host and guest to establish the importance, at the enthalpic level, of the formation of hydrogen bond bridges between the calixarene and the alcohol molecule. The fact that methanol is not complexed by p-sulfonatocalix[4]arene is explained by calculating the cost of the desolvation of the guest upon complexation. We complete this study by modeling the complexes formed with 1,4-butanediol and 1,5-pentanediol. To explain the difference between the thermodynamic properties for the binding of 1,4-butanediol and butanol, we examine the insertion rate and the solvation of each hydroxy group. We show a specific behavior of one of the two hydroxy groups at the structural and energetic levels.

[Multiple lentigines syndrome. Apropos of 2 cases. Critical study of the leopard syndrome]. / Le syndrome des lentigines multiples. A propos de deux observations. Etude critique du syndrome leopard.

With regard to 2 cases of a same family associating: multiple lentigos, osseous signs and impairment of E.C.G., the authors recall the differents visceral manifestations which can be associated to lentigos and the relative frequency of every one of them. The authors report 38 indisputable observations of the literature that associated the 2 criterions: multiple lentigos symmetrical in their distribution and histological confirmation of sun spots. The authors perfer the term: multiple lentigos syndrome to the LEOPARD syndrome. The last term (LEOPARD), in spite of his attractive character contains a part of possible associated signs (osseous signs, primordial in our observations, are not present in that syndrome). But another way, contrary to, not any observation, up to now, allowed all the symptomes present in the acrostic LEOPARD. Through it should appear difficult to define actually the scope of the multiple lentigos syndrome, the knowledge of that entity offers a real interest for the dermopath: the discovery of a symmetrical lentiginosis, extensive or not, must lead to the exploration, as well as possible, of organs susceptible to be out of order: heart, nervous system and hearing, skeleton and facial malformations, genital-organs, and also to a family inquiry.