Reiko Oda

Gemini Surfactants as New, Low Molecular Weight Gelators of Organic Solvents and Water**

As many as 1200 solvent molecules can be entrapped by one molecule of the cationic dimeric surfactants 1 to form a gel in CHCl3 . These new gelators contain chiral counterions and form gels with both organic solvents and water upon their assembly into helical aggregates, which have similar structures in both media.

Individualized Silica Nanohelices and Nanotubes : Tuning Inorganic Nanostructures Using Lipidic Self-Assemblies

Diverse chiral nanometric ribbons and tubules formed by self-assembly of organic amphiphilic molecules could be transcribed to inorganic nanostructures using a novel sol-gel transcription protocol with tetraethoxysilane (TEOS) in the absence of catalyst or cosolvent. By controlling parameters such as temperature or the concentration of the different reactants, we could finely tune the morphology of the inorganic nanostructures formed from organic templates. This fine-tuning has also been achieved upon controlling the kinetics of both organic assembly formation and inorganic polycondensation. The results presented herein show that the dynamic and versatile nature of the organic gels considerably enhances the tunability of inorganic materials with rich polymorphisms.

Molecular Structure of Self-Assembled Chiral Nanoribbons and Nanotubules Revealed in the Hydrated State

A detailed molecular organization of racemic 16-2-16 tartrate self-assembled multi-bilayer ribbons in the hydrated state is proposed where 16-2-16 amphiphiles, tartrate ions, and water molecules are all accurately positioned by comparing experimental X-ray powder diffraction and diffraction patterns derived from modeling studies. X-ray diffuse scattering studies show that molecular organization is not fundamentally altered when comparing the flat ribbons of the racemate to chirally twisted or helical ribbons of the pure tartrate enantiomer. Essential features of the three-dimensional molecular organizations of these structures include interdigitation of alkyl chains within each bilayer and well-defined networks of ionic and hydrogen bonds between cations, anions, and water molecules between bilayers. The detailed study of diffraction patterns also indicated that the gemini headgroups are oriented parallel to the long edge of the ribbons. The structure thus possesses a high cohesion and good crystallinity, and for the first time, we could relate the packing of the chiral molecules to the expression of the chirality at a mesoscopic scale. The organization of the ribbons at the molecular level sheds light on a number of their macroscopic features. Among these are the reason why enantiomerically pure 16-2-16 tartrate forms ribbons that consist of exactly two bilayers, and a plausible mechanism by which a chirally twisted or helical shape may emerge from the packing of chiral tartrate ions. Importantly, the distinction between commonly observed helical and twisted morphologies could be related to a subtle symmetry breaking. These results demonstrate that accurately solving the molecular structure of self-assembled soft materials--a process rarely achieved--is within reach, that it is a valid approach to correlate molecular parameters to macroscopic properties, and thus that it offers opportunities to modulate properties through molecular design.

Counteranion Effect on Micellization of Cationic Gemini Surfactants 14-2-14: Hofmeister and Other Counterions

The effect of counterions was investigated and analyzed to probe the principal ionic effects influencing the micellization behavior of dimeric cationic surfactant ethanediylbis(dimethyltetradecylammonium), referred to as gemini 14-2-14. The 30 counterions were classified to four different families depending on their nature: (1) small and inorganic counterions which are typically taken from the Hofmeister series were studied to focus on the effect of ion type; (2) n-alkyl carboxylate counterions were studied to focus on the effect of the hydrophobicity of counterions; (3) aromatic carboxylate counterions were included to focus on the effect of the position of substitutions; and (4) other counterions were included in order to shed light on other parameters. By investigating the critical micelle concentration (CMC), ionization degree of micelle (alpha), free energy of micellization (DeltaG(M)), and aggregation numbers N of the gemini surfactant with these different types of anions, we demonstrated the effect of different ion properties independently. This approach allowed us to describe the effect of counterions on the micellization behavior of the gemini surfactant in terms of complex interplay between hydrophobicity of anions and other ion properties such as counterion hydration, interfacial packing of ions, and ionic morphology. Indeed, our results clearly demonstrate that a counterion effect on micellization properties cannot be described as a result of one single parameter of ions, as is too often assumed, but rather the balancing effects cooperatively affect the propensity of counterions to form ion pairs with surfactant headgroups and the entropy gain upon micellization. These results provide new insight in understanding the effect of ions on the delicate balance of forces controlling aggregate morphology and solution properties of charged amphiphilic molecules.

Enantioselective recognition by a highly ordered porphyrin-assembly on a chiral molecular gel

Enantioselective recognition of amino acids was achieved by using a highly ordered chiral assembly of achiral porphyrin on a chiral molecular gel. Exceptionally high enantioselectivity was observed for histidine derivatives by monitoring the CD patterns and fluorescence quenching, K(SV) (l): 26.3 × 10(3) M(-1); K(SV)(D)-enantiomer: 7.03 × 10(3) M(-1).

Gemini surfactants, the effect of hydrophobic chain length and dissymmetry

The synthesis of a new series of dimeric surfactants is reported; chain length and dissymmetry are shown to be critical factors for the richness of phases observed in water.

Influence of nanohelical shape and periodicity on stem cell fate.

Microenvironments such as protein composition, physical features, geometry, and elasticity play important roles in stem cell lineage specification. The components of the extracellular matrix are known to subsequently assemble into fibrillar networks in vivo with defined periodicity. However, the effect of the most critical parameter, which involves the periodicity of these fibrillar networks, on the stem cell fate is not yet investigated. Here, we show the effect of synthetic fibrillar networks patterned with nanometric periodicities, using bottom-up approaches, on the response of stem cells. We have used helical organic nanoribbons based on self-assemblies of Gemini-type amphiphiles to access chiral silica nanoribbons with two different shapes and periodicities (twisted ribbons and helical ribbons) from the same native self-assembled organic nanostructure. We demonstrate the covalent grafting of these silica nanoribbons onto activated glass substrates and the influence of this programmed isotropically oriented matrix to direct the commitment of human mesenchymal stem cells (hMSCs) into osteoblast lineage in vitro, free of osteogenic-inducing media. The specific periodicity of 63 nm (±5 nm) with helical ribbon shape induces specific cell adhesion through the fibrillar focal adhesion formation and leads to stem cell commitment into osteoblast lineage. In contrast, the matrix of periodicity 100 nm (±15 nm) with twisted ribbon shape does not lead to osteoblast commitment. The inhibition of non-muscle myosin II with blebbistatin is sufficient to block this osteoblast commitment on helical nanoribbon matrix, demonstrating that stem cells interpret the nanohelical shape and periodicity environment physically. These results indicate that hMSCs could interpret nanohelical shape and periodicity in the same way they sense microenvironment elasticity. This provides a promising tool to promote hMSC osteogenic capacity, which can be exploited in a 3D scaffold for bone tissue engineering.

Zwillingstenside als neue niedermolekulare Gelbildner in organischen Lösungsmitteln und Wasser

1200 Molekule des Losungsmittels konnen von einem Molekul des kationischen, dimeren Tensids 1 bei der Gelbildung in CHCl3 immobilisiert werden. Diese neuen Geliermittel enthalten chirale Gegenionen und bilden sowohl in organischen Losungsmitteln als auch in Wasser Gele, indem sie sich zu helicalen Aggregaten zusammenlagern, die in beiden Medien ahnliche Strukturen aufweisen.

Induction of Strong and Tunable Circularly Polarized Luminescence of Nonchiral, Nonmetal, Low-Molecular-Weight Fluorophores Using Chiral Nanotemplates

A new strategy is described for generating strong circularly polarized luminescence with highly tunable emission bands through chiral induction in nonchiral, totally organic, low-molecular-weight fluorescent dyes by chiral nanotemplate systems. Our approach allows the first systematic investigation to clarify the correlation between the circular dichroism and circularly polarized luminescence intensities. As a result, a dilute solution system with the highest circularly polarized luminescence intensity achieved to date and a dissymmetry factor of over 0.1 was identified.

Viscoelastic solutions formed by worm-like micelles of amine oxide surfactant

Formation and properties of viscoelastic wormlike aqueous micellar solutions of the zwitterionic surfactant p-dodecyloxybenzyldimethylamine oxide (pDoAO) were studied. Semi-dilute aqueous solutions of pDoAO show a sharp increase in viscosity, which exceeds 160 cST for concentrations >50 mM, leading to viscoelastic solutions. Viscoelasticity relates to the surfactant charge type. In fact this viscoelastic system reverses to fluid when acid is added (pH<2), which changes the system to cationic. Under acidic conditions the system resembles solutions of the similar cationic surfactant p-dodecyloxybenzyltrimethylammonium bromide, (pDoTABr) in terms of viscosity. Properties of aqueous solutions of pDoAO were investigated by dynamic light scattering (DLS), rheology and small angle neutron scattering (SANS). Data support the idea that small micelles grow in length (wormlike or threadlike micelles) as surfactant concentration increases and viscoelastic solutions form as micelles become entangled. The micellar diameter as calculated by different techniques is about 5 nm.