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The first molecule that assembles by ultrasound is described. An association-inert dinuclear Pd complex, anti-1a, which is stabilized by intramolecular pi-stacking interactions, gelatinizes a variety of organic solvents instantly upon brief presonication for a few seconds. This is the first quick, positive, and reversible method for the remote switching of stable sol-gel phases. Uniquely, the rate can be precisely controlled over the range between "no gelation" and "instant gelation" simply by tuning the sonication time.

Primary alcohols undergo oxidative condensation upon treatment with RuH2(PPh3)4 catalyst to give esters and molecular hydrogen. Similarly, 1,4-and 1,5-diols can be converted into the corresponding 7-and -lactones, respectively. The lactonization is greatly enhanced by accepting hydrogen with an appropriate hydrogen acceptor such as acetone. Primary alcohols are oxidized chemoselectively in the presence of secondary alcohols to give

Instant and precise control of phosphorescent emission can be performed by ultrasound-induced gelation of organic liquids with chiral, clothespin-shaped trans-bis(salicylaldiminato)Pt(II) complexes, anti-1. Nonemissive solutions of racemic, short-linked anti-1a (n = 5) and optically pure, long-linked anti-1c (n = 7) in organic liquids are transformed immediately into stable phosphorescent gels upon brief irradiation of low-power ultrasound. Emission from the gels can be controlled by sonication time, linker length, and optical activity of the complexes. Several experimental results indicated that structure-dependent homo- and heterochiral aggregations and ultrasound-control of the aggregate morphology are key factors for emission enhancement.

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Stimuli-responsive supramolecular assembly has been studied extensively as a forward-looking technology for the precise control of the physical properties and functions of aggregates. [1][2][3] Recently, it was found that a blast of ultrasound can act as a trigger for the instant gelation of stable organic fluids when a small amount of a clothespin-shaped dinuclear palladium complex is used as a type of switchable gelator. [4,5] The ultrasound waves were thought to cleave the intramolecular p-stacking interactions of the complexes, inducing rapid and spontaneous aggregation through interpenetrating stacking interactions. Now this self-lock/interlock switching has been carried out with hydrogen-bonded aggregates, using the newly designed metalated dipeptide 1 a (Fmoc = 9-fluorenylmethyloxycarbonyl). This work is expected to provide a new methodology for the creation of stimuli-responsive H-bonded supramolecular assemblies, [1b-f, 2b-d] especially those containing peptide nanoarchitectures. [1c-f, 2c, 6] This paper describes the sound-induced gelation of palladium-bound peptides, and the precise control of their switchable aggregation by the tuning of sound factors.Brief ultrasound irradiation (0.45 W cm À2 , 40.0 kHz, 60 s) of a homogeneous 1.50 10 À2 m solution of dipeptide 1 a (n = 2, X = Cl) in EtOAc turned the stable pale-yellow solution into a stable opaque gel (Figure 1). Gelation was observed exclusively when ultrasound was used as an external stimulus, and spontaneous aggregation or formation of pregels did not occur without sonication. When nonsonicated samples were cooled or left to stand for a long time, ordinary precipitation of a small amount of amorphous solids or crystals resulted. Gels formed by sonication were stable but were readily converted to the original stable solutions upon heating and subsequent cooling to room temperature. This switchable solgel transition occurred exclusively when esters or chlorobenzene were used as solvents, while other solvents such as benzene, toluene, acetone, and acetonitrile did not provide gels regardless of concentration and sonication conditions. The chloro ligand and the short methylene spacer have proven to be indispensable for this switchable gelation. Typically, the dipeptidyl NCS complex 1 b and the Cl complex with longer spacer 1 c did not cause the gelation of any organic solvents. Also, solutions of amino acid 2, tripeptide 3, and tetrapeptide 4 in various organic solvents were stable under similar sonication conditions. Kinetic studies on the gelation of a 7.00 10 À3 m solution of 1 a in [D 8 ]EtOAc at 25 8C after sonication (0.45 W cm À2 , 43.5 kHz) were carried out by means of 1 H NMR (500 MHz) analysis, in which mobile, unaggregated 1 a in sol and gel states could be observed as distinct detectable species similar to conventional gelators. [7] The time dependence of the concentration of 1 a during the entire gelation process indicated that gelation began immediately after sonication, and proceeded until 1 a was almost completely consumed ( Figure...

Highly chemoselective Baeyer–Villiger oxidations can be performed in the presence of other reactive functionalities such as alcohols, olefins, and sulfides, which would undergo electrophilic oxidation under conventional conditions (see scheme). [DMRFlEt]+[ClO4]− (depicted blue) is a new class of flavin compound that catalyzes aerobic Baeyer–Villiger oxidations in the presence of Zn dust as the electron source.