Solvation of Coumarin480 within nano-confining environments: structure and dynamics

ELOLA, MARÍA DOLORES; RODRIGUEZ, JAVIER

JOURNAL OF CHEMICAL PHYSICS

AMER INST PHYSICS

Lugar: New York; Año: 2014 vol. 140 p. 34702 - 34712

0021-9606

Equilibrium and dynamical characteristics pertaining to the solvation of the fluorescent probe Coumarin480 within different confining environments are investigated using Molecular Dynamics simulations.Three kinds  of confining systems are examined: (i)the  cetyltrimethylammonium bromide (CTAB)/isooctane/1-hexanol/water;cationic inverse micelle (IM); (ii)a CTAB/water direct micelle (DM) and (iii)a silica-surfactant nanocomposite, comprising a cylindrical silicapore (SP) containing small amounts of water and CTAB species adsorbed at the pore walls. The solvation structures  in the threeenvironments differ at a qualitative level: an exchange betweenbulk- and interface-like solvation states was found in the IM, whereas in the DM, the solvation states of the probe are characterized by its embedding at the interface, trapped among the surfactant heads and tails. Within the SP structure, the coumarin exhibits alternationsbetween internal and interfacial solvation states that occur on a 20ns time scale and operate via  90º rotations of its molecular plane.The solvation responses of the environment following a verticalexcitation of the probe are also investigated. Solvation times resultedbetween 2 and 1000~times longer than those found in bulk water,with a fast-to-slow trend IM-->DM-->SP, which can be interpreted in terms of the solvation structures that prevail in each case.