We demonstrate that solvates of fullerene C60 form very predictable structures with finely tunable properties through the choice of the second component or solvent. Cubic co-crystals of C60·12CCl2Br2 and C60·12CBr2(CH3)2 were grown at room temperature in saturated solutions of fcc C60 and the respective solvents (with C2v molecular symmetry) They are unstable in air and transform spontaneously into the hexagonal co-crystals C60·2CCl2Br2 or C60·2CBr2(CH3)2. Whereas, the cubic co-crystals have positive excess volumes (+2% and +5%, respectively), the stable hexagonal crystals, for which structures are given for the first time, possess negative excess volumes (-5% and -4.3%, respectively). The unit-cell volumes for both cubic and hexagonal co-crystals depend exclusively on the van-der-Waals volumes of the constituents and this correlation has been confirmed using previously published data.
Oliver, R.; Muñoz, A.; Ocampo, C.; Aleman, C.; Armelin, E.; Estrany, F. Chemical physics Vol. 328, num. 1-3, p. 299-306 DOI: 10.1016/j.chemphys.2006.07.013 Data de publicació: 2006-09 Article en revista
Aleman, C.; Oliver, R.; Brillas, E.; Casanovas Salas, Jordi; Estrany, F. Chemical physics Vol. 323, num. 2-3, p. 407-412 DOI: 10.1016/j.chemphys.2005.09.049 Data de publicació: 2006-04 Article en revista
A molecular dynamics study has been carried out to investigate the conformational, structural and dynamical properties of the surfactant molecules in the dodecyltrimethylammonium · poly(a,l-glutamate) self-assembled complex. Simulations were performed in chloroform solution using eight different temperatures. Results indicate that the strong electrostatic interactions between the carboxylate groups of the polyelectrolyte and the positively charged trimethylammonium moieties, which are retained even at high temperatures, are responsible of the molecular organization and the low mobility of the surfactant molecules.
The constrained molecular dynamics simulation method has been used to obtain the mean force and the mean force potential between two particles in solution. The method has been tested for a Lennard-Jones liquid and applied to the study of a Na+-Cl- ion-pair in aqueous solution. A flexible SPC model for water has been assumed. The results have been interpreted in the light of the solvent structure around the ions for separations corresponding to the maxima and minima of the mean force potential. In contrast to earlier studies using rigid water models, the solvent separated ion pair configurations are more stable than the contact ion pair configurations.