Masazo Niwa

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.

Kinetics of the photopolymerization of vinyl monomers by bis-[isopropylxanthogen] disulfide. Design of block copolymers

Abstract Bis(isopropylxanthogen) disulfide (BX) has been used as a photoinitiator with various vinyl monomers at 30°C. The kinetics of polymerization of styrene (St) and methyl methacrylate (MMA) at 30°C were studied for various concentrations of monomer and initiator. The observed deviations in polymerization rate from simple kinetic theory could be explained in terms of primary radical termination. The fraction of primary radical terminating chains was obtained as a function of various concentrations. The ratio of the rate constants for chain initiation and chain termination by a primary radical was determined to be 3.34 ± 107 for St and 2.60 ± 107 for MMA. The number-average degree of polymerization (DP n) of polymers obtained by photopolym-erization with BX was found to increase linearly with conversion. However, the DP n extrapolated to zero conversion was in good agreement with that calculated on the basis of the kinetic scheme. It was found that BX had interesting properties for the design of block...

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.

Block Polymerizations of Vinyl Monomers Initiated by Telechelicisopropyl Xanthate-Terminated Polymers as Macrophotoinitiator. Design Of Block Copolymers. 2

Abstract Both photopolymerization and thermal polymerization of a variety of vinyl monomers with bis(isopropylxanthogen) disulfide (BX) as initiator and as chain-transfer agent were carried out in benzene. The results of photopolymerizations to high conversion with BX support the polymerization mechanism given in a previous paper of this series. Telechelic isopropyl xanthate-terminated polymers (TXP) having a different backbone have been used as macroinitiator for the polymerization of vinyl monomers. The rate of polymerization of the functional polymers was found to be markedly dependent on the monomer species: block polymerization of methyl acrylate or methyl methacrylate proceeded rapidly compared to the chain-extension polymerization of styrene. However, in all cases the molecular weight of the polymers obtained was found to increase linearly with conversion, which is an interesting property for the design of block copolymers and which is similar in polymerization with BX. It is also found that the mo...

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.

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.

Specific binding of concanavalin A to glycolipid monolayers on gold electrodes

Formation of monolayers of disulfide-containing glycolipids by spontaneous adsorption onto gold electrodes and their specific binding properties to a lectin are described.

Interaction between polylysine monolayer and DNA at the air–water interface

The interaction of a polylysine amphiphile, which consists of a poly-L- or -D-lysine (1L or 1D) segment and two long alkyl chains at the C-terminus, with polynucleotides was studied with respect to the highly organized structure of polylysine assemblies on water. The results of surface pressure-area isotherm measurement showed that both of 1L and 1D formed stable monolayers on water in a neutral pH region. The secondary structure of polylysine segment for the surface monolayer was examined by means of circular dichroism and Fourier transform infrared spectroscopies. The helical structure was retained even at neutral pH, at which polylysine has been known to form a complete random coiled conformation in bulk solution. Protonated, positively charged and coiled 1L monolayer could interact electrostatically with guest polyanions including DNA in the subphase, and at the same time the conformation of the polylysine segment was converted from a random coil to an alpha-helix. Deprotonated, helical monolayers did not interact with single stranded polyadenylic acid, but with double stranded DNA. Double stranded DNA was found to interact more strongly with right-handed 1L monolayer than left-handed 1D monolayer. An obvious difference in the melting temperatures for these complexes was observed and discussed on the basis of difference in the interaction mode.