We prepared novel transition-metal (Ti, Ta, V) oxide fibers with chiral, helical, and nanotubular structures. The nanostructured metal oxide materials were provided by the sol-gel polymerization of metal alkoxides using chiral self-assemblies of organogelators as structure-directing agents. The chiral structures of the metal oxide fibers can be created by the formation of chiral self-assemblies constructed by organogelators and the transcription of the organogel superstructure into metal oxides.

Cyclo(l-beta-3,7-dimethyloctylasparaginyl-L-phenylalanyl) (1) and cyclo(L-beta-2-ethylhexylasparaginyl-L-phenylalanyl) (2), prepared from L-asparaginyl-L-phenylalanine methyl ester, have been found to be specialist gelators for ionic liquids. They can gel a wide variety of ionic liquids, including imizazolium, pyridinium, pyrazolidinium, piperidinium, morpholinium, and ammonium salts. The mean minimum gel concentrations (MGCs) necessary to make gels at 25 degrees C were determined for ionic liquids. The gel strength increased at a rate nearly proportional to the concentration of added gelator. The strength of the transparent gel of 1-butylpyridinium tetrafluoroborate ([C(4)py]BF(4)), prepared at a concentration of 60 g L(-1) (gelator 1/[C(4)py]BF(4)), was ca. 1500 g cm(-2). FT-IR spectroscopy indicated that a driving force for gelation was intermolecular hydrogen bonding between amides and that the phase transition from gel to liquid upon heating was brought about by the collapse of hydrogen bonding. The gels formed from ionic liquids were very thermally stable; no melting occurs up to 140 degrees C when the gels were prepared at a concentration of 70 g L(-1) (gelator/ionic liquid). The ionic conductivities of the gels were nearly the same as those of pure ionic liquids. The gelator had electrochemical stability and a wide electrochemical window. When the gels were prepared from ionic liquids containing propylene carbonate, the ionic conductivities of the resulting gels increased to levels rather higher than those of pure ionic liquids. The gelators also gelled ionic liquids containing supporting electrolytes.

Low-molecular-weight gelators form supramolecular gels in organic fluids, aqueous solutions and both organic and aqueous solutions through supramolecular interactions such as hydrogen-bonding, van der Waals, hydrophobic, pi-stacking, coordination, donor-acceptor and charge-transfer interactions. Molecules having chirality, especially, L-amino acids, are often used as a platform of low-molecular-weight gelators. This tutorial review highlights recent and current advances in low-molecular-weight gelators based on L-lysine. L-lysine based gelators are prepared through easy synthetic procedures, and some classes of gelators are synthesized by the introduction of various functional groups. In this review, the synthesis of organogelators, hydrogelators and amphiphilic gelators and their gelation properties are discussed.

The kinetics of electron transfer and oxygen evolution at citrate-stabilized IrO x ‚nH 2 O colloids were studied by time-resolved UV-visible spectrosopy and by steady-state photolysis of [Ru(bpy) 3 ] 2+ (bpy ) 2,2′-bipyridyl) and persulfate in a hexafluorosilicate/bicarbonate buffer. Time-resolved studies of the reaction of [Ru(bpy) 3 ] 3+ with these colloids show an initial fast electron transfer, corresponding to oxidation of Ir(III) to Ir(IV). Further oxidation of surface Ir atoms occurs concomitantly with oxygen evolution with a second-order rate constant of 1.3 × 10 6 M -1 s -1 . Both the time-resolved reduction of [Ru(bpy) 3 ] 3+ by IrO x ‚nH 2 O and the photocatalytic oxygen evolution under non-light-limited photolysis conditions have a H/D kinetic isotope effect (KIE) of 1.0. This contrasts with significantly higher KIE values for oxygen evolution from molecular cis,cis-[(bpy) 2 Ru-(OH 2 )] 2 O] 4+ and [(terpy)(H 2 O)Mn III (O) 2 (OH 2 )terpy)] 3+ water oxidation catalysts. This is consistent with the conclusion that, under the conditions of most photocatalytic experiments (∼10 -4 M [Ru(bpy) 3 ] 2+ concentration), electron transfer from the colloid to the oxidized sensitizer rather than formation of a surface-bound hydroperoxy species is the rate-determining step in photocatalytic oxygen evolution.

Experimental SectionMaterials. N ε -Lauroyl-L-lysine was supplied from the Ajinomoto Co., Inc. Methyl 2,6-diisocyanatohexanoate was supplied from the Kyowa Hakko Kogyo Co., Ltd. The other chemicals were of the highest commercially grade available and used without further purification.All solvents used in the syntheses were purified, dried, or freshly distilled as required. The N ε -Lauroyl-L-lysine ethyl ester (C 2 AmiNH 2 ) was prepared according to the literature. 1