Water Aggregate in a Reversed Micelle and Hydrated Cluster in a Molecular Beam

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A small water aggregate located near a biopolymer is known to work as an important reaction medium. We have investigated the properties of such a water aggregate based on the following two model: Water pool in a reversed micellar solution from H_2O/isooctane/ AOT(Aerosol OT) and hydrated clusters formed in a supersonic molecular beam. In this work we mainly investigated solubilization of a series of pyrenyl compounds with different polarity, sodium pyrenesulfonate (PSA^-Na^+) and sodium 8-acetoxypyrene-1,3,6-trisulfonate (APTSNa), in the reversed micelle. The location and distribution of the probe molecules in the reversed micelle was determined by analyzing time profiles as well as absorption and fluorescence spectra of laser-induced transient species. The transient absorption spectra and their time profiles strongly depend on the size of water pool. Those dependences can be explained in terms of location and distribution of PSA^- or APTS in the reversed micelle. In conclusion, (1) PSA^- molecules are located both in the water pool and in the hydrophbic part of the surfactant. Its distribution in the water pool decreases with decrease of the size of water pool and most of PSA^- are located in the hydrophobic part in the smallest reversed micelle. On the other hand, more polar molecule, APTS, is predominantly distributed in the water pool. (2) A sufficiently large size of water pool to solubilize these pyrenyl compounds in the water pool. (3) Solubilities of these molecules in a sufficiently large water pool are less than those in bulk water. Only a small number of water pools contain more than two PSA^- or APTS moleculs. These properties for solubilization of pyrenyl compounds in the water pool are in contrast to a hydrated cluster formed in a supersonic beam. It suggests that the layer surrounding water pool or bound water strongly affects solubilization of a solute molecule in the water pool.