Nobuyuki Higashi

Dendrimers with Attached Helical Peptides

The attachment of peptides to the surface of spherical dendrimers via graft polymerization is described here (see Figure). It is shown that the resulting peptide dendrimers display greatly enhanced helicity compared to non-dendrimer-based analogues. This effect is attributed to aggregation of peptide segments on the dendrimer surface.

Synthesis of polysilane–acrylamide copolymers by photopolymerization and their application to polysilane–silica hybrid thin films

Abstract Various polysilane–acrylamide block copolymers have been prepared from photopolymerization of acrylamide-type monomers using poly(methylphenylsilane) (PMPS) as a macro-photo-radical initiator. The acrylamide block in the copolymers improved the hydrophilic property of PMPS. These PMPS–acrylamide block copolymers have been applied to formation of PMPS–silica hybrid thin films via sol–gel reaction. Homogeneous and transparent PMPS–silica hybrid thin films were obtained from a few PMPS–acrylamide block copolymers. It was found for these hybrid thin films based on hydrogen bonding formation between amide group and silanol group. The surface properties of hybrid thin films were evaluated by water contact angle measurement, scanning electron microscope (SEM), and atomic force microscope (AFM) images.

Enantioselective Binding and Stable Encapsulation of α-Amino Acids in a Helical Poly(L-glutamic acid)-Shelled Dendrimer in Aqueous Solutions

A novel water‐soluble peptide‐shelled dendrimer containing a poly(L‐glutamic acid) segment grafted on the third‐generation poly(amido amine) dendrimer was successfully synthesized, and its secondary structural properties and interaction with α‐amino acids (Trp, Phe, and Tyr) were revealed by spectroscopic measurements. In the lower pH region, this peptide–dendrimer adopted an α‐helix conformation with almost 100 % helicity resulting from the three‐dimensional aggregation of the segment. Interactions with α‐amino acids proceeded with positive cooperativity on the basis of a Hill plot, and as a result, D isomers preferentially bound to the α‐helical segments relative to L isomers. The bound α‐amino acids were not released into the water phase but were transferred into the inner core of the dendrimer where they remained stable, even when a conformational change of the helix segment was caused by pH variation.

Novel peptide-shelled dendrimer with dramatically changeable thermo-responsive character.

The preparation of a novel peptide/dendrimer hybrid is reported in which an elastin-like oligopeptide is successfully assembled onto a poly(amidoamine) dendrimer surface (G4-ELP), and its unique thermo-responsive behavior is discussed. As a result, the G4-ELP is found to exhibit LCST behavior in the pH range 3-10 including physiological temperature range under neutral-pH conditions. Moreover, cooperative interplay between the folding state of the ELP shell and the ionization state of the dendrimer core enables the G4-ELP to control its LCST widely by pH variation. This achievement provides a new insight for the design of dual-responsive materials with a potential in biological applications.

Steric forces between brush layers of poly(l-glutamic acid) and their dependence on secondary structures as determined by FT-IR spectroscopy

Abstract Interactions between apposed poly( l -glutamic acid) monolayers in water were investigated by direct surface forces measurement. The average degree of polymerization was 21. The monolayers of anchored poly( l -glutamic acid) were prepared on mica surfaces by the Langmuir-Blodgett deposition of monolayers of an amphiphile containing the polypeptide as the hydrophilic head group. Various secondary structures of poly( l -glutamic acid) were formed in this monolayer at the air-water interface, through intra- and intermolecular hydrogen bonding, depending on the surface pressure and the pH value of the aqueous subphase, and transferred onto mica surfaces. Formation of the secondary structures was characterized by Fourier transform-infrared (FT-IR) spectroscopy prior to the forces measurement. Surface force profiles consisted of a long-range electrostatic and a short-range steric repulsion. Secondary structures of poly( l -glutamic acid), identified by FT-IR with respect to their composition and orientation, were found to determine the short-range steric repulsion. The obtained elastic compressibility moduli of the polypeptide monolayers were 5.6 ± 2.2 MPa for the β2-structure rich layer, and 0.2 ± 0.1 MPa for the layer of ionized extended chains.

Preparation and self-assembly behavior of β-sheet peptide-inserted amphiphilic block copolymer as a useful polymeric surfactant.

A hybridization of structurally regulated biopolymers and conventional synthetic polymers offers promising opportunities to design novel polymeric nanomaterials. In this study, we newly prepared an amphiphilic triblock copolymer with β-sheet forming peptide as a central block, polystyrene-block-tetra(leucine)-block-poly(ethylene glycol) (PS-L4-PEG), by combining the solid phase peptide synthesis with the atom transfer radical polymerization (ATRP). On the basis of several morphological and structural analyses using atomic force microscopy, transmission electron microscopy, FTIR spectroscopy, and contact angle measurement, the PS-L4-PEG was found to form PEG-shell spherical and/or elliptical vesicles with a diameter of 30-100 nm in aqueous medium. By contrast, the PS-L4-PEG self-assembled into PS-shell spherical aggregates in toluene, which is good solvent for both PEG and PS. In both cases, the central peptide formed a β-sheet network in the nanoassemblies. Furthermore, the PS-L4-PEG was found to stabilize a water-in-oil emulsion remarkably in comparison with the PS-PEG diblock copolymer, demonstrating the potential of this peptide-polymer hybrid as a useful polymeric surfactant.

Self-Assembled Peptide Nanofibers

Molecular self-assembly is a powerful approach being explored for novel supramolecular nanostructures and bio-inspired nanomaterials. In this article, we focus on recent research concerning the self-assembly of de novo designed artificial peptides and peptidomimetics into nanofiber structures, specifically towards developing a new class of soft-materials. These nanofiber architectures have potential use not only in biomedical applications, such as 3D-matrix scaffolds for tissue engineering and biomineralization, but also in nanotechnology such as nano-templates and dimension-regulated functional nano-objects.

Spontaneous formation of single- and double-layered polypeptide assemblies based upon a helix-macrodipole interaction

A novel gold-adsorbable poly(γ-benzyl-L-glutamate) has been prepared, and its adsorption processes onto gold substrates from CHCl 3 solutions have been examined by means of a quartz crystal microbalance technique. The aggregation state of the resultant polypeptide assemblies was found to be controllable on the basis of the helix-helix macrodipole interaction.

Immobilization and cleavage of DNA at cationic, self-assembledmonolayers containing C60 on gold

A cationic, self-assembled monolayer on gold substrate can immobilize DNA without impairing its native structure; the site-specific photocleavage of the DNA is achieved by incorporation of [60]fullerene into the monolayer.

Enzymatically triggered self-assembly of poly(ethylene glycol)-attached oligopeptides into well-organized nanofibers

A unique and programmable peptide self-assembling system has been fabricated by using poly(ethylene glycol)-attached amphiphilic oligopeptide, which shows rapid self-assembly into well-organized beta-sheet nanofibers in response to an enzymatic reaction.