Momoyo Wada

Oriented thin films of conjugated polymers : polysilanes and polyphenylenes

Abstract In this paper, preparation of uniaxially oriented films of conjugated polymers, polysilanes and poly(p-phenylenes) (PPP) is investigated. Highly oriented thin films of poly(dimethylsilane) (PDMS) were prepared by the friction transfer method. The properties of PDMS films strongly depend on the preparation temperature. At a temperature higher than 210°C, uniform ultrathin films with extremely high orientation were obtained. It is considered that the friction transfer is related to the disorder (hexagonal) phase of PDMS. Other polysilanes, such as poly(diethylsilane) (PDES), poly(di-n-hexylsilane) (PDHS), poly(di-n-butylsilane) and poly(methylphenylsilane) also afforded oriented films by the same method. Oriented films of PPP were prepared by the friction transfer method. The thin films of the polymers were characterized mainly by ultraviolet absorption spectroscopy. The friction-transferred PDMS and PPP had abilities of orienting other materials. The films of polysilanes, such as PDHS, which were cast on the oriented PDMS from solution, were oriented along the PDMS chain direction. Oriented films of some oligophenylenes were obtained by vapor deposition or cast on the friction-transferred PPP. When the friction-transferred PPP film was immersed into the reaction mixture, a newly oriented PPP film were polymerized on the friction-transferred PPP films.

A high poly(ethylene glycol) density on graphene nanomaterials reduces the detachment of lipid-poly(ethylene glycol) and macrophage uptake

Amphiphilic lipid-poly(ethylene glycol) (LPEG) is widely used for the noncovalent functionalization of graphene nanomaterials (GNMs) to improve their dispersion in aqueous solutions for biomedical applications. However, not much is known about the detachment of LPEGs from GNMs and macrophage uptake of dispersed GNMs in relation to the alkyl chain coverage, the PEG coverage, and the linker group in LPEGs. In this study we examined these relationships using single walled carbon nanohorns (SWCNHs). The high coverage of PEG rather than that of alkyl chains was dominant in suppressing the detachment of LPEGs from SWCNHs in protein-containing physiological solution. Correspondingly, the quantity of LPEG-covered SWCNHs (LPEG-SWCNHs) taken up by macrophages decreased at a high PEG coverage. Our study also demonstrated an effect of the ionic group in LPEG on SWCNH uptake into macrophages. A phosphate anionic group in the LPEG induced lower alkyl chain coverage and easy detachment of the LPEG, however, the negative surface charge of LPEG-SWCNHs reduced the uptake of SWCNHs by macrophages.

Functionalized organic nanotubes as tubular nonviral gene transfer vector

Tubular nanomaterials are expected to represent a novel nonviral gene transfer vectors due to the unique morphology and potential biological functionalities. Here we rationally constructed functionalized organic nanotubes (ONTs) for gene delivery through the co-assembly of bipolar glycolipid, arginine-lipid and PEG-lipid. The arginine- and PEG-functionalized ONTs efficiently formed complexes with plasmid DNA without aggregation, and protect DNA from enzymatic degradation; while the arginine-functionalized ONTs aggregated with DNA as large bundles. Long ONTs exceeding 1μm in length was rarely taken up into the cells, while those with a length of 400-800nm could effectively deliver plasmid DNA into cells and induce high transgene expression of green fluorescense protein. This study demonstrated the usefulness of functionalized ONT in gene delivery, and the functionalized ONT represents a novel type of tubular nonviral gene transfer vector.

Cisplatin-encapsulated organic nanotubes by endo-complexation in the hollow cylinder.

A bipolar glycolipid self-assembles into organic nanotubes upon its chelation with an anticancer drug cis-dichlorodiamineplatinum(II) (CDDP). The facile synthesis of glycolipid, chelation-assisted formation of the nanotubes, and efficient loading and prolonged release of CDDP demonstrate a new approach to high-axial supramolecular drug nanocarriers.

Dicholesteryl icosanedioate as a glass-forming cholesteric liquid crystal: properties, additive effects and application in color recording

A cholesteric ester dimer – dicholesteryl icosanedioate – was examined for color imaging. Cholesterol was introduced as one of the dopants which performed an important role reducing phase transition temperatures. The other dopants, 4,4′-dialkoxyazobenzene and 4,4′-dialkoxybiphenyl promoted formation of smectic domains in cholesteric phases which resulted in the expansion of the reflective band shift over the whole visible region. In particular, the photo-responsive dopant 4,4′-dialkoxyazobenzene allowed us to realize reversible RGB color tuning of the cholesteric film by both photon and thermal modes. The trans–cis photoisomerization led to a cholesteric pitch change which resulted in reflective color change, and recorded optical images that have been stable for more than 8 months in a glassy solid film state.

Spontaneous Nematic Alignment of a Lipid Nanotube in Aqueous Solutions

The dispersibility and liquid crystal formation of a self-assembled lipid nanotube (LNT) was investigated in a variety of aqueous solutions. As the lipid component, we chose a bipolar lipid with glucose and tetraglycine headgroups, which self-assembled into an LNT with a small outer diameter of 16 to 17 nm and a high axial ratio of more than 310. The LNT gave a stable colloidal dispersion in its dilute solutions and showed spontaneous liquid crystal (LC) alignment at relatively low concentrations and in a pH region including neutral pH. The LNT samples with shorter length distributions were prepared by sonication, and the relationship between the LNT axial ratio and the minimum LC formation concentration was examined. The robustness of the LNT made the liquid crystal stable in mixed solvents of water/ethanol, water/acetone, and water/tetrahydrofuran (1:1 by volume) and at a temperature of up to 90 °C in water. The observed colloidal behavior of the LNT was compared to those of similar 1D nanostructures such as a phospholipid tubule.

Carbon Nanotubes Facilitate Oxidation of Cysteine Residues of Proteins

The adsorption of proteins onto nanoparticles such as carbon nanotubes (CNTs) governs the early stages of nanoparticle uptake into biological systems. Previous studies regarding these adsorption processes have primarily focused on the physical interactions between proteins and nanoparticles. In this study, using reduced lysozyme and intact human serum albumin in aqueous solutions, we demonstrated that CNTs interact chemically with proteins. The CNTs induce the oxidation of cysteine residues of the proteins, which is accounted for by charge transfer from the sulfhydryl groups of the cysteine residues to the CNTs. The redox reaction simultaneously suppresses the intermolecular association of proteins via disulfide bonds. These results suggest that CNTs can affect the folding and oxidation degree of proteins in biological systems such as blood and cytosol.

Preparation and properties of thin films of polysilane copolymers, poly(dimethylsilylene-co-methyl-n-propylsilylene)s

Abstract Oriented thin films and unoriented thin films of polysilane copolymers, poly(dimethylsilylene-co-methyl-n-propylsilylene)s, were prepared by friction transfer and solution cast method, and their properties were compared with each other. There were two solid states in the polysilane copolymers at room temperature. One is the stable phase, which absorbs the light around 300nm and emits the light at 360nm. Another is the metastable phase, which has the absorption band around 340nm and the fluorescence at 355nm.

Dynamic mechanical properties of extruded rods of poly(dimethylsilylene-co-methyl-n-propylsilylene)

Tractable polysilanes were prepared by the copolymerization of a methyl-n-propylsilylene (MP) unit into poly(dimethylsilylene), which neither dissolves in common solvents nor melts before decomposition. Although poly(dimethylsilylene-co-methyl-n-propylsilylene) has poor solubility in the composition range of the dimethylsilylene (DM) unit to the MP unit (DM/MP = 7/3 ∼ 9/1), the copolymers form the columnar mesophase at elevated temperatures. Highly oriented rods were prepared via the extrusion of the copolymers with a circular tube die in a temperature range in which the transition to the columnar mesophase began to occur (70°C when DM/MP = 7/3 and 8/2 and 120°C when DM/MP = 9/1). The extruded rods were characterized in detail by dynamic viscoelasticity and wide-angle X-ray diffraction (WAXD) to clarify the structure–mechanical-property relationship. The orientation functions of the extruded rods were determined by the azimuthal intensity distribution of the WAXD reflection. The orientation function and dynamic storage modulus increased with an increasing extrusion ratio. The dynamic storage modulus at −150°C was 8 ∼ 10 GPa at the highest extrusion ratio and correlated well with the crystal orientation function. The dynamic storage modulus at room temperature was lowered by the structural relaxations at −100 ∼ +30°C, which corresponded to the molecular motion of the rigid molecular chains of the copolymer and the local molecular motion of the MP unit.

Polysilane Photoluminescence Specific to Oriented Thin Films

Abstract Highly oriented ultrathin films of poly (dimethylsilylene) and poly (diethylsilylene) were prepared by friction-transfer technique. Photoluminescence spectra of the films were different from those of powder sample. The luminescence peak of thin film was observed at 10nm shorter wavelength than that of powder. The difference remained from −200° C to 250° C.