Solvation plays an essential role in controlling the mechanism and dynamics of chemical reactions in solution. The present study reveals that changes in the local solute-solvent interaction have a great impact on the timescale of solvent rearrangement dynamics. Time-resolved IR spectroscopy has been applied to a hydration rearrangement reaction in the monohydrated 5-hydroxyindole-water cluster induced by photoionization of the solute molecule. The water molecule changes the stable hydration site from the indolic NH site to the substituent OH site, both of which provide a strongly attractive potential for hydration. The rearrangement time constant amounts to 8 ± 2 ns, and is further slowed down by a factor of more than five at lower excess energy. These rearrangement times are slower by about three orders of magnitude than those reported for related systems where the water molecule is repelled from a repulsive part of the interaction potential toward an attractive well. The excess energy dependence of the time constant is well reproduced by RRKM theory. Differences in the reaction mechanism are discussed on the basis of energy relaxation dynamics.

In connection with our studies on hydantoin derivatives, a conventional regioselective chemical transformation of 5-methylene hydantoins 4a-c to 5-aminomethyl-substituted hydantoins 5-10 or to 5-amino-5-methyl-disubstituted hydantoins 11-14 is described. Synthesis of bivalent twin-drug type hydantoin derivatives 19-24 and the binding property of a bivalent symmetrical hydantoin derivative 24b to sulfated glycosaminoglycans are also described.

Peculiar low-temperature electronic properties induced by the filling change from a half-filled band realized in -͑BEDT-TTF͒ 4 Hg 2.89 Br 8 and -͑BEDT-TTF͒ 4 Hg 2.78 Cl 8 , which belong to the well-known -type family of organic conductors, were studied by thermodynamic measurements. We observed unusual behaviors both in the lattice and the electronic heat capacities. The former is associated with the dimensional crossover in the acoustic phonons, which is attributable to the peculiarity of mercury chains in the anion layers. The electronic heat capacity represented by the ␥ term at low temperatures is enhanced up to 52-55 mJ K −2 mol −1 ͓for the formula ͑BEDT-TTF͒ 2 Hg 1.5−1/2␦ X 4 ͔ due to anomalous growth of the antiferromagnetic spin fluctuations in these salts.

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