Kazushi Kinbara

High-water-content mouldable hydrogels by mixing clay and a dendritic molecular binder.

With the world’s focus on reducing our dependency on fossil-fuel energy, the scientific community can investigate new plastic materials that are much less dependent on petroleum than are conventional plastics. Given increasing environmental issues, the idea of replacing plastics with water-based gels, so-called hydrogels, seems reasonable. Here we report that water and clay (2–3 per cent by mass), when mixed with a very small proportion (<0.4 per cent by mass) of organic components, quickly form a transparent hydrogel. This material can be moulded into shape-persistent, free-standing objects owing to its exceptionally great mechanical strength, and rapidly and completely self-heals when damaged. Furthermore, it preserves biologically active proteins for catalysis. So far no other hydrogels, including conventional ones formed by mixing polymeric cations and anions or polysaccharides and borax, have been reported to possess all these features. Notably, this material is formed only by non-covalent forces resulting from the specific design of a telechelic dendritic macromolecule with multiple adhesive termini for binding to clay.

Mechanical twisting of a guest by a photoresponsive host

Molecular analogues of a variety of mechanical devices such as shuttles, brakes, unidirectional rotors and tweezers have been created. But these ‘molecular machines’ have not yet been used to mechanically manipulate a second molecule in a controlled and reversible manner. Here we show that light-induced scissor-like conformational changes of one molecule can give rise to mechanical twisting of a non-covalently bound guest molecule. To realize this coupling of molecular motions, we use a previously designed system: a ferrocene moiety with an azobenzene strap, each end of which is attached to one of the two cyclopentadienyl rings of the ferrocene unit, acts as a pivot so that photoisomerization of the strap rotates the ferrocene rings relative to each other and thereby also changes the relative position of two ‘pedal’ moieties attached to the ferrocene rings. We translate this effect into intermolecular coupling of motion by endowing the pedals with binding sites, which allow the host system to form a stable complex with a bidentate rotor molecule. Using circular dichroism spectroscopy, we show that the photoinduced conformational changes of the host are indeed transmitted and induce mechanical twisting of the rotor molecule. This design concept, which significantly extends the successful coupling of motion beyond the intramolecular level seen in synthetic allosteric receptors, might allow for the remote control of molecular events in larger interlocked molecular systems.

Chaperonin-mediated stabilization and ATP-triggered release of semiconductor nanoparticles

Various properties of semiconductor nanoparticles, including photoluminescence and catalytic activity, make these materials attractive for a range of applications. As nanoparticles readily coagulate and so lose their size-dependent properties, shape-persistent three-dimensional stabilizers that enfold nanoparticles have been exploited. However, such wrapping approaches also make the nanoparticles insensitive to external stimuli, and so may limit their application. The chaperonin proteins GroEL (from Escherichia coli) and T.th (‘T.th cpn’, from Thermus thermophilus HB8) encapsulate denatured proteins inside a cylindrical cavity; after refolding, the encapsulated proteins are released by the action of ATP inducing a conformational change of the cavity. Here we report that GroEL and T.th cpn can also enfold CdS semiconductor nanoparticles, giving them high thermal and chemical stability in aqueous media. Analogous to the biological function of the chaperonins, the nanoparticles can be readily released from the protein cavities by the action of ATP. We expect that integration of such biological mechanisms into materials science will open a door to conceptually new bioresponsive devices.

A Tubular Biocontainer: Metal Ion-Induced 1D Assembly of a Molecularly Engineered Chaperonin

GroEL(SP/MC), prepared by genetic and chemical modifications of group I chaperonin protein GroEL, site-specifically possesses approximately 28 photochromic (spiropyran [SP] and merocyanine [MC]) units in the entrance parts of its cavity. Addition of divalent metal ions such as Mg(2+) to a tris-HCl buffer solution of GroEL(SP/MC) results in one-dimensional (1D) assembly of GroEL(SP/MC), affording cylindrical hollow fibers with a very large aspect ratio; the longest fiber was approximately 2.5 microm long, corresponding to a 170-mer of GroEL(SP/MC) (MW approximately 1.4 x 10(8)). When such long fibers are mixed with EDTA, they are cut into short-chain oligomers and eventually into monomeric GroEL(SP/MC). Similar to GroEL, GroEL(SP/MC) possesses a large binding affinity toward denatured proteins. When GroEL(SP/MC) undergoes 1D assembly after incubation with a denatured protein, guest-containing cylindrical fibers result.

Molecular glues carrying multiple guanidinium ion pendants via an oligoether spacer: stabilization of microtubules against depolymerization.

Dendron G1(Gu(+))(9)R and linear peptide oligomer Asn(TEG-Gu(+))(9), decorated with multiple guanidinium (Gu(+)) ions as sticky pendants via an oligo(oxyethylene) spacer, adhere to BSA and protein assemblies such as microtubules in aqueous buffers. Using fluorescently labeled G1(Gu(+))(9)R with pyrenyl and rhodamine focal cores, the adhesion process can be visualized by FRET or confocal laser scanning microscopy. The adhesion to microtubules leads to their stabilization against depolymerization into alpha/beta-tubulin heterodimer components, where the effects of G1(Gu(+))(9)R and Asn(TEG-Gu(+))(9) are comparable to that of paclitaxel, known as an anticancer drug. Since G1(Gu(+))(9)R and Asn(TEG-Gu(+))(9) are superior to lower-generation G0(Gu(+))(3)OMe and arginine nonamer, respectively, the multivalency of the interaction and a conformational flexibility of the oligoether spacers play a crucial role in the efficient adhesion to proteins.

Design of resolving reagents: p-substituted mandelic acids as resolving reagents for 1-arylalkylamines

Abstract The resolution of 1-arylalkylamines 2–10 by mandelic acid 1 was studied. It was found that a substituent, which elongated the molecular length of the amines, diminished the resolution efficiency. On the basis of these results, (S)-p-methylmandelic acid (S)- 11 and (R)-p-methoxymandelic acid (R)- 12 were selected as new resolving reagents for the 1-arylalkylamines; these acids were found to have a higher resolving ability than (R)- 1 .

A Structured Monodisperse PEG for the Effective Suppression of Protein Aggregation

Part of the solution: A PEG with a discrete triangular structure exhibits hydrophilicity/hydrophobicity switching upon increasing temperatures, and suppresses the thermal aggregation of lysozyme to retain nearly 80 % of the enzymatic activity. CD and NMR spectroscopic studies revealed that, with the structured PEG, the higher-order structures of lysozyme persist at high temperature, and the native conformation is recovered after cooling.

Effect of a Substituent on an Aromatic Group in Diastereomeric Resolution

Abstract The diastereomeric resolution of p-substituted 1-arylethylamines by enantiopure (S)-3′,4′-methylenedioxymandelic acid ((S)-2) was carried out in order to know how an electron-donating or -withdrawing group on the aromatic group of the racemic amines would affect the efficiency of resolution. As a result, it was found that 1-arylethylamines having an electron-withdrawing substituent could be efficiently resolved by (S)-2, while the amines having an electron-donating group could not. The crystal structures of the less- and more-soluble salts, and the molecular orbital calculations of the ammonium cations indicated that the p-substituted electron-withdrawing group enhanced the positive charge on the meta-hydrogen of the aromatic group of the ammonium cations, which is favorable for the formation of a CH⋯π interaction in crystal.

Controlling volume shrinkage in soft lithography through heat-induced cross-linking of patterned nanofibers.

When poly(isopropylidene diallylmalonate) rich in threo-disyndiotactic sequences (st(rich)-2) was utilized as a cross-linkable ink for microcontact printing, the resultant submicrometer-scale patterns featuring 700 and 300 nm wide stripes were successfully insolubilized while maintaining their high dimensional integrity by heat-induced cross-linking with elimination of CO(2) and acetone. In sharp contrast, although the thermal properties and reactivities of a polymer rich in threo-diisotactic sequences (it(rich)-2) and a polymer having low stereoregularity (2(low)) are little different from those of st(rich)-2, the patterns printed with these reference polymers collapsed considerably upon heating as a result of a volume shrinkage effect. The striking difference between st(rich)-2 and the other two polymers most likely arises from the nanofiber-forming character of st(rich)-2, where the printed stripes are porous and much less affected by the volume shrinkage of individual nanofibers.

Thermally driven polymorphic transition prompting a naked-eye-detectable bending and straightening motion of single crystals.

The amplification of molecular motions so that they can be detected by the naked eye (10(7) -fold amplification from the ångström to the millimeter scale) is a challenging issue in the development of mechanical molecular devices. In this context, the perfectly ordered molecular alignment of the crystalline phase has advantages, as demonstrated by the macroscale mechanical motions of single crystals upon the photochemical transformation of molecules. In the course of our studies on thermoresponsive amphiphiles containing tetra(ethylene glycol) (TEG) moieties, we serendipitously found that thermal conformational changes of TEG units trigger a single-crystal-to-single-crystal polymorphic phase transition. The single crystal of the amphiphile undergoes bending and straightening motion during both heating and cooling processes at the phase-transition temperatures. Thus, the thermally triggered conformational change of PEG units may have the advantage of inducing mechanical motion in bulk materials.