Cationic liposomes are known to be useful tools for gene transfection. However, the relation between transfection efficiency and physicochemical properties of liposomes has not been well understood. Here, we synthesized eight cationic derivatives of cholesterol which contain a tertiary amino head group with a different spacer arm. Transfection of plasmid pSVZCAT DNA into cells was done by cationic liposomes made of a mixture of dioleoylphosphatidylethanolamine (DOPE) and each cationic cholesterol derivative. At the same time we measured zeta potential of cationic liposomes by laser Doppler spectroscopy. The present results indicated that zeta potentials of cationic liposomes were well related to transfection activity of pSV2CAT DNA. This suggested that zeta potential of cationic liposomes is one of important factors which control gene transfection.

The aim of the present study was to evaluate the bonding durability of resin-based luting cement to partially stabilized tetragonal zirconia (Y-TZP) achieved by combination treatment of tribochemical (TBC) treatment and two different phosphate acid ester monomers. Two phosphate acid ester monomers (EP: Epricord opaque primer, AZ: AZ primer) were applied to each surface modification followed by application of resin-based luting cement (Rely-X ARC). Bonding specimens were placed in deionized water at 37°C and stored for 24 h. The other groups were subjected to 30,000 cycles of a thermal stress for the durability test. Shear bond tests were done using a universal testing machine at 1 mm/min. Shear bond strengths of combination treatments using EP and AZ on TBC treatment after thermal stress showed no significant difference (p>0.05) compared with those of storage after 24 h. Combination treatment using phosphoric acid ester monomer could achieve a durable bond.

No abstract

The crystal structures of poly(di-n-butyl silane) and poly(di-n-pentyl silane) have been determined by comparing the experimental x-ray diffraction paltern with the theoretical pattern.The side-chain conformation i s mostly determined by the intramolecular steric hindrace as well 3s the van der Wmls interaction between the side chains. The Si backbone conformation of both crystals is a 3 helix. which 1s mainly determined by the intramolecular van der Waals interaction between the nearest-neighbour side chains. On the other hand. the Si backbone conformation of both crystals after a pressure treatment of 1500 MPa is all tmns. which is caused by the YM der Wads interaction between the side chains attached to the second-nearest-neighbour Si atoms.In all c~ses, one of the two CSi-C-C groups in Si(OHql3 or Si(C%Hu)2 is an essentially Irum conformation. whereas the other C-C-Si< gmup has a ci.r-like conformation, which is different from that generally accepted.

This paper describes the reasonable molecular configuration and inter-molecular packing of the poly(di-n-hexyl-silane) crystal. The crystal lattice is determined using a wide-angle X-ray diffraction method for the powdered specimen. The experimental diffraction pattern is compared with the theoretical one, in order to clarify the atom positions in the unit cell. The obtained unit cell contains the two polymer chains having an all-trans silicon backbone. The hexyl substituents are found to be asymmetrical conformations because of the steric hindrance. The orientation of the prepared thin film is also discussed on the basis of the obtained crystal structure.

This paper describes highly oriented films prepared by the evaporation of poly(dimethyl silane). The specimens are prepared at various evaporation speeds and substrate temperatures. The polymer is divided into species of about 2 nm length on the evaporation heater, and the species recrystallize on the substrate. The structure and orientation of the films are investigated using wide-angle X-ray diffraction and ultraviolet absorption methods. The substrates used are single-crystal silicon (100) for the X-ray diffraction measurement and fused silica for the ultraviolet absorption measurement. The polymer exhibits the same orientation on both substrates. It is found that most of the silicon chains are perpendicular to the substrate surface in the film prepared under the condition whose growth rate is lower than 20 nm min-1. On increasing the substrate temperature, the number of silicon chains whose orientation is normal to the substrate surface increases.

The packings of the poly(di-ethyl silane) and poly(di-n-propyl silane) crystals have been examined by comparing the experimental x-ray diffraction paltern with the theoretical panem. The silicon bxkbone conformation of both crystals is all trans, and the side-chain conformation is mostly determined by the intramolecular steric h i n h c e . The molecules are closely packed in both cases, and the intermolecular distance is well explained by considering the van der Waals ndii of the CH2 and C H 3 gxooups.

The lattice parameters and density of the polydimethylsilane crystal, and the stiffness constants of the film prepared by the evaporation of the source polydimethylsilane powder, have been estimated using the x-ray diffraction technique and the surface acoustic wave, respectively.In the former case, the experimental x-ray diffraction patterns are compared with the theoretid patterns. As a result. it is found that the crystallogaphic structure of the polydimethylsilane crystal is monoclinic, with the lattice parameters o = 0.745fO.M)l nm, b = 0.724i0.001 nm, c = 0.389 + 0.001 nm and y = 67.1 + 0:l". In the laner case, the stiffness constants are estimated from the velocity of the surface acoustic wave propagating along the evaporated fildpiezoelectric substrate suucture. The values obtained on the assumption that the film is isotropic are cL, = (5.9 & 0.9) x IO"' N Kz, c11 = (3.5 f 0.9) x IO"' N and c ~= ( 1 . 2 + 0 . 3 ) ~1 0 ' ~N m -~.