Biomedical subjects
Publications and source records attributed to Nobuo Kimizuka.
A lipophilic linear FeII 1,2,4-triazole complex containing azobenzene chromophores forms molecular wires in organic solvents; photoisomerization of azobenzene units induced morphological changes that lead to reversible, macroscopic gel-to-sol transition phenomena.
Gold nanoparticles (Au-NPs) are encased in aqueous nanospheres of alpha-helical poly(gamma-benzyl L-glutamate)s (PBLG, number average degree of polymerization: n = 32), with spatially controlled self-assembly structures of solid core-shell nanospheres or double-layered hollow nanocapsules.
Rational design of self-assembly of proteins, which plays pivotal roles in biology, is an important subject for biotechnology and also bottom-up nanotechnology. This paper has proposed a novel strategy for construction of artificial peptide-nanospheres by self-assembly. Mimicking formation of spherical viruses and clathrin, we designed a novel C3-symmetric peptide conjugate bearing three beta-sheet-forming peptides. These peptide conjugates formed antiparallel beta-structures and self-assembled into nanospheres with the size of about 20 nm in the acidic solution.
alpha-Helical peptide microcapsules were prepared by the emulsion-templated self-assembly of amphiphilic poly(gamma-benzyl L-glutamate)s (PBLG) 1. By mixing solutions of 1 in dichloromethane (in the form of a sodium salt) with water, oil-in-water emulsions were obtained. Spontaneous stripping of the dichloromethane phase caused a decrease in the diameter of the microdroplets and finally stable microcapsules formed. The microcapsules contain an inner aqueous phase as observed by confocal laser scanning microscopy (CLSM). Binding of hydrophobic pyrene molecules to the polypeptide shell was also demonstrated. The present polypeptide microcapsules are stable even after drying in air and they would serve as supramolecular vehicles for both hydrophobic and water-soluble molecules.
Supramolecular nanowires are specifically self-assembled from adenosine 5'-triphosphate (ATP) and dichloro-substituted thiacarbocyanine dyes. Spectral blue-shift and induced circular dichroism with exciton coupling are observed upon mixing the dye and ATP molecules in water. These observations indicate the formation of chiral 1/ATP supramolecular assemblies with excitation energy delocalized in the parallel-oriented (H-aggregated) chromophores. Interestingly, formation of H-aggregates is facilitated most in the presence of ATP and not by other nucleotides (ADP or AMP). In electron microscopy, aqueous 1/ATP mixture gives developed nanowires with a minimum width of ca. 10 nm and lengths of several micrometers. The ATP-directed nanowires exhibit reversible thermal self-assembly accompanied by supramolecular thermochromism. This is the first example of ATP-based supramolecular nanoassemblies, and the use of small biomolecules as building blocks for functional supermolecules provides a new perspective in the design of bio-nanomaterials.
A novel class of thermally responsive supramolecular assemblies is formed from the lipophilic cobalt(II) complexes of 4-alkylated 1,2,4-triazoles. When an ether linkage is introduced in the alkylchain moiety, a blue gel-like phase is formed in chloroform, even at very low concentration (ca. 0.01 wt %, at room temperature). The blue color is accompanied by a structured absorption around 580-730 nm, which is characteristic of cobalt (II) in the tetrahedral (T(d)) coordination. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) of the gel-like phase confirms the formation of networks of fibrous nanoassemblies with widths of 5-30 nm. The observed widths are larger than a molecular length of the triazole ligand (ca. 2.2 nm) and they are consisted of aggregates of T(d) coordination polymers. Very interestingly, the blue gel-like phase turned into a solution by cooling below 25 degrees C. A pale pink solution is obtained at 0 degrees C, indicating the formation of octahedral (O(h)) complexes. The observed thermochromic transition is totally reversible. The formation of gel-like networks by heating is contrary to the conventional organogels, which dissolve upon heating. Temperature dependence of the storage and loss moduli (G' and G") shows minima around at 27 degrees C, at which temperature they gave comparable values. On the other hand, G' exceeds G" both in the gel-like phase (temperature above 27 degrees C) and in the solution phase (temperature below 25 degrees C). These observations indicate that T(d) complexes are present as low-molecular weight species around at 25-27 degrees C. They are self-assembled to polymeric T(d) complexes by heating and form gel-like networks. Upon cooling the solution below 25 degrees C, T(d) complexes are converted to O(h) complexes and they also self-assemble into oligomeric or polymeric species at lower temperatures. The observed unique thermochromic transition (pink solution --> blue gel-like phase) is accompanied by an exothermic peak in differential scanning calorimetry (DSC), and is shown to be an enthalpy-driven process. The lipophilic modification of one-dimensional coordination systems provides unique solution properties and it would be widely applicable to the design of thermoresponsive, self-assembling molecular wires.
Hydrophobic vitamin B(12) was covalently immobilized onto a platinum electrode surface, and the immobilized complex exhibits Co(ii)/Co(i) redox couple and in situ the Co(i) species reacts with phenethyl bromide to form styrene under irradiation with visible light with a turnover number of over 6000 for 1 h.
An interfacial sol-gel synthesis of inorganic hollow microspheres in room-temperature ionic liquids is newly developed. When metal alkoxides such as titanium tetrabutoxide, Ti(OBu)4, are dissolved in anhydrous toluene and injected into 1-buthyl-3-methylimidazolium hexafluorophosphate ([C4mim]PF6) under vigorous stirring, hollow titania microspheres are formed. The present technique is widely applicable to the reactive metal alkoxides such as Zr(OBu)4, Hf(OBu)4, Nb(OBu)4, and InSn3(OR)x, giving a general route to the metal oxide microspheres. When gold nanoparicles and carboxylate-containing dyes such as fluorescein isothiocyanate (FITC) are dissolved in the toluene microdroplets, they are stably immobilized in the microsphere shells. Calcination of the titania gel microspheres gives anatase TiO2 microspheres. The present method provides the first example of inorganic hollow microspheres formed in ionic liquids, and the ability to modify microspheres with metal nanoparticles or functional organic molecules would be widely applied to the design of smart organic/inorganic hybrid materials.
DNA three-way junctions formed from three 30-mer oligonucleotides that contain single-chained self-complementary sticky ends spontaneously self-assemble into 'nucleo-nanocages': the exo- and endo-nuclease digestion experiments indicate that defects such as the single and double strand end structures are absent on the spherical nano-assemblies, providing clear evidence for the closed nanocage structure.
The development of mesoscopic supramolecular architectures is an area of growing interest. The field has grown from early works on bilayer membranes, and the design of large (super- or giant-) amphiphiles, hybrid amphiphiles and supramolecular membranes have now been described. Impartment of amphiphilicity to a unit supermolecule allows their hierarchical self-assembly to the mesoscopic structures. A supramolecular combinatorial approach is useful in the development of functional self-assemblies. In addition, self-assembly in ionic liquids has been introduced as a promising area in materials chemistry.
A new colorimetric detection technique for glucose, based on electron transfer from glucose oxidase (GODred) to iron(III) acetylacetonate(acac)/phenanthroline(phen) mixed complexes, is developed. When GOD is added to an aqueous mixture that contains tris(acetylacetonato)iron(III) complex (FeIII-(acac)3), 1,10-phenanthroline (phen), and glucose, the color immediately changes from pale yellow to red. The red color originates from formation of tris(1,10-phenanthroline)iron(II) complex ([FeII(phen)3]2+). Differential pulse voltammetry indicates that cationic, mixed-ligand complexes of [Fe(acac)3-n-(phen)n]n+ are formed upon mixing the labile FeIII(acac)3 complex and phenanthroline. The cationic mixed-ligand complexes electrostatically bind to GOD (pI 4.2), and are easily reduced by electron transfer from GODred. This electron transfer is not affected by the presence of oxygen. The reduced complex [FeII(acac)3-n(phen)n](n-1)+ then undergoes rapid ligand exchange to FeII (phen)3. Formation of the colored FeII complex is repressed when the salt concentration in the mixture is increased, or when anionic bathophenanthroline disulfonate (BPS) is employed in place of phenanthroline. The use of labile metal complexes as electron acceptors would be widely applicable to the design of new biochromic detection systems.
A highly lipophilic polyion complex [Pt(en)(2)][PtCl(2)(en)(2)](1)(4) (en, 1,2-diaminoethane) is prepared from one-dimensional mixed valence Pt(II)/Pt(IV) complex and newly designed chiral amphiphile 1. The powdery sample showed purple color, which is a result of the mixed valence absorption of the linear chlorobridged complex (Pt(II)-Cl-Pt(IV)-Cl-)(n). When the lipid complex is dispersed in dichloromethane, purple-colored dispersion is obtained at 0 degrees C, whereas the color disappears after heating the solution to 21 degrees C. The observed thermochromism is reversible with respect to the temperature changes and is ascribed to the reversible dissociation and reassembly of the self-assembling inorganic wires. Casting of the 0 degrees C-purple dispersion on solid substrates affords honeycomb nanostructures in addition to the nanowires with the width of about 20 nm. The honeycomb patterns seem to be templated by the condensed water droplets that are formed and aligned on the rapidly evaporating dichloromethane solution. On the other hand, more regular honeycomb structures are exclusively obtained by casting the 21 degrees C-colorless solution. These observations indicate that the ordered honeycomb structures are obtainable on solid surfaces by the self-assembly of molecularly dispersed components [Pt(en)(2)](1)(2) and trans-[PtCl(2)(en)(2)](1)(2.) Very interestingly, formation of double-layered honeycomb nanostructure is observed by scanning electron microscopy. The unit hexagons and pillars of the honeycombs are made of nanowires that are hierarchically assembled from the lipid-packaged Pt(II)/Pt(IV) complexes. The surface self-organization of lipophilic inorganic complexes has a potential to fabricate novel nanoarchitectures with conjugated electronic structures.