Almost seventy years ago, chemist Dorothy Jordan noted that "gels are easier to recognize than to define"."] We will attempt a definition nonetheless : Gels are semi-rigid colloidal systems rich in liquid. Protoplasm ranks as the most widespread example of this peculiar state of matter. A gel is formed by a molecular network, often fibrous in nature, that entrains the dispersing medium within its capillary spaces. Most organic gelators are polymeric (for example, gelatin, ['] poIy(acry1ic acid) ,I3] and hyaluronic acidr4]), but small molecules (for example. cholesteryl 4-(2-anthryloxy)b~tanoate, [~~ 5-hexadecyl-2,4,6-triaminopyrimidine,l6] N-octylglucona~nide,~'~ and arborolsr8]) can induce gelation as well.We have long been interested in a little-known but remarkable gelator. dibenzoyl-L-cystine (DBC).19] Although most gels require 1 -1 0 O i O gelator, DBC in water rigidifies at concentrationsas low as 2 mM (0.1 YO). While attempting to learn how such miniscule quantities of DBC manage to self-assemble into a macroscopic network, we performed an X-ray analysis of a gel "fiber". Structural data at the atomic level is virtually unavailable for gel networks, and it is only through good fortune that these data became accessible. But before giving the details, let us summarize the properties of acylcystines in water.DBC forms a firm, translucent gel in a thermally reversible process at a concentration of 4 mM in ethanol (5%)/water. Ethanol was used because the DBC tends to crystallize from pure water. There is, clearly. a delicate balance between gelation and crystallization. The gelating properties are destroyed when the S-S linkage is replaced by CH,CH, or CH=CH groups."'] This implies that the CH,-S-S-CH, dihedral angle["] of about 90 'C plays a key role in the formation of the molecular network. Gels d o not form from esterified DBC or at basic p H values, which suggests the presence of either a favorable -COOH/-COOH attraction or a deleterious -COY /-CO; repulsion. Addition of NaCl (0.1 M) softens the gels, whereas more than 10 YO dioxane induces crystallization.Diacetyl-L-cystine fails to gelate in ethanol ( 5 %)/water. Di-noctanoyl-L-cystine (4 mM) forms only a soft and cloudy gel. The superior quality of the DBC gel leads us to suspect that aromatic K -~T stacking stabilizes the creation of fibers. This conclusion is appealing. because intermolecular hydrogen bonding between DBC molecules in water would seem too unfavorable to serve as the sole adhesive force. Assembly of DBC molecules appears to be a cooperative event much like the micellization of surfactants. This was affirmed by a primitive yet informative experiment in which 2.0 x 2.0 cm2 squares of Parafilm were placed on the surface of aged DBC gels. Known weights were then positioned carefully at the center of a film until the film submerged. A plot of "supportable weight" vs. DBC concentration (not shown) gave a sharp break at 1.6 KIM, a value that might be qualitatively regarded as the "critical gelation concentration".Spin-lattice relaxation stud...

Qualitative and quantitative analyses of hydrophilic and lipophilic antioxidants, such as polyphenols, by simple electrochemical measurements were conducted in a bicontinuous microemulsion (BME), in which water and oil phases coexisted bicontinuously on a microscopic scale. Hydrophilic and lipophilic antioxidants were individually monitored in the same BME solution using a hydrophilic indium tin oxide (ITO) electrode and a lipophilic fluorinated nanocarbon film electrode (F-ECR), respectively. The combination of well-balanced BME and extremely biased electrodes, such as ITO and F-ECR, in terms of hydrophilic-lipophilic balance allowed us to achieve individual monitoring of hydrophilic and lipophilic antioxidants in the same BME solution without extraction. Furthermore, the antioxidant activities of functional liquid foods, such as coffee and olive oil, were also evaluated by means of electrochemical measurements in BME solutions containing analytes in concentrations of several percent. The technique we propose provides a very simple, rapid, easily serviceable, and highly reproducible analysis and can be extended to a wide range of analytes and media.

Janus nanosheets were prepared from K4Nb6O17·3H2O by modifying surfaces of their two distinct interlayers in a regioselective and sequential manner and subsequent exfoliation. The surface properties of nanosheets were investigated by phase atomic force microscopy imaging and two types of surfaces were discriminated, indicating that Janus nanosheets were successfully prepared.

A new class of unique soft gels was produced by gelations of bicontinuous microemulsions (BME). Three alternative composite gel systems, namely BME organogel, hydrogel and an organo/hydro hybrid gel, prepared by hydrogelation and/or organogelation of BME solutions were proposed. These gels were self-supported, and aqueous and oil microphases bicontinuously coexisted and were immobilized in the gels. Even in "one side only" gelation products such as the BME organogel and the BME hydrogel, alternate solvent phases without gelator were also macroscopically immobilized. Microscopic structures of the gels were confirmed by CLSM and SEM observation. The BME organogels or hydrogels and BME hybrid gels showed continuous porous structures and double network structures, respectively. Mesostructures of the gels significantly depended on gelation conditions. It was found that the hierarchical structure of the BME gels was regulated by competition among three synergetic rate factors: immobilization of the BME structure by gelation, mesoscopic phase separation by gelation, and the time-dependent transformation of a solution/ solution structure toward a thermodynamic structure in an equilibrium state.

A “middle phase” microemulsion, which bicontinuously composed of saline and toluene microphases, with sodium dodecylsulfate (SDS) and n-butanol was electrochemically characterized. When electrochemistry was performed in the “middle phase” microemulsion, reversible redox peaks of the Fe(CN)6 ion in the micro water phase and the ferrocene in the micro toluene phase could be observed simultaneously, although the electrolyte was present only in the water phase.