Search

In bio-systems, nano-composites with complex micro-structures are formed by self-assembly only using low energy at room temperature. If these mechanisms of biological tissue are identified, we can possibly propose a new process to fabricate composites by mimicking tissue formation in vivo. As a bio-material, we paid attention to bio-tissue reinforced with collagen fibrils. Collagen fibrils are of baculiform; Thus the self-assembly process through liquid crystalline transition has been proposed by a French group [1]. In the present study, factors controlling liquid crystalline transition, e.g. concentration and pH, are discussed using collagen solution. When liquid crystalline phase is produced, aligned molecules exhibits optical anisotropy. This anisotropy was observed with a polarized optical microscopy (POM). By observations with POM, development of cholesteric phase in collagen solution was clarified.

In bio-systems, nano-composites with complex micro-structures are formed by self-assembly only using low energy at room temperature. If these mechanisms of biological tissue are identified, we can possibly propose a new process to fabricate composites by mimicking tissue formation in vivo. As a bio-material, we paid attention to bio-tissue reinforced with collagen fibrils. Collagen fibrils are of baculiform; Thus the self-assembly process through liquid crystalline transition has been proposed by a French group [1]. In the present study, factors controlling liquid crystalline transition, e.g. concentration and pH, are discussed using collagen solution. When liquid crystalline phase is produced, aligned molecules exhibits optical anisotropy. This anisotropy was observed with a polarized optical microscopy (POM). By observations with POM, development of cholesteric phase in collagen solution was clarified.

Using a redox titration method in the pulse radiolysis of N2O-saturated phosphate buffer solution, the redox properties of the intermediate radicals derived from OH radical reactions of 5-substituted uracils 1c−h (R = F, Cl, Br, NO2, NH2, OH) have been characterized. While the primary intermediates were oxidizing C(5) radicals 2c−h and reducing C(6) radicals 3c−h of the respective OH adducts, a common allyl-type radical of “redox ambivalence” with limiting mesomeric forms of reducing carbon-centered 5-oxo-5,6-dihydrouracil-6-yl radical (4) and oxidizing oxygen-centered uracil-5-oxyl radical (5) was secondarily formed via elimination of 5-substituents from 3c−h. The rate of 5-substituent elimination decreased with varying structures of the 5-substituents in the order halo > amino, nitro > hydroxy groups. The common radical 4/5 showed weaker reducing/oxidizing abilities than the typical pyrimidine C(6) and C(5) radicals. The product study demonstrated that the one-electron reduction of 5-oxyl radical 5 by N,N,N‘,N‘-tetramethyl-p-phenylenediamine ((2.0 ± 0.1) × 10⁸ dm³ mol^-1 s^-1) increased the yield of isobarbituric acid (1h), while the one-electron oxidation of 5-oxo C(6) radical 4 by tetranitromethane increased the yield of isodialuric acid (6).

Radiation-induced and photosensitized reductive splitting of stereoisomeric C5−C5‘-linked dihydrothymine dimers (1a,b[meso], meso compound of (5R,5‘S)- and (5S,5‘R)-bi-5,6-dihydrothymines; 1a,b[rac], racemic compound of (5R,5‘R)- and (5S,5‘S)-bi-5,6-dihydrothymines) in aqueous solution were studied to compare with the one-electron oxidative splitting mechanism and the photorepair reaction of cyclobutane pyrimidine photodimers. Reacting with radiation-chemically and photochemically generated hydrated electrons or with photoexcited reduced form of flavin adenine dinucleotide (*FADH^-), the C5−C5‘-linked dihydrothymine dimers 1a,b produced the corresponding 5,6-dihydrothymine derivatives (3a,b) along with the thymine monomers (2a,b) in minor yields. Both the product and laser flash photolysis studies indicated that one-electron adducts of the C5−C5‘-linked dimers 1a,b undergo C5−C5‘-bond cleavage to generate the 5,6-dihydrothymin-5-yl radicals (5a,b) and the 5,6-dihydrothymine C5-anions (6a,b) resulting in the formation of 3a,b by facile protonation at C5. In the reduction by *FADH^-, splitting of the 5,6-dihydro-1-methylthymine dimer 1a[meso] into the monomer 2a was more efficient than that of the racemic isomer 1a[rac]. Conformational analysis by NMR of 1a[meso] and 1a[rac] in solution suggested that 1a[meso] may favor a “closed-shell” conformation and undergo one-electron reduction to form 5a and 6a, whereas 1a[rac] may be in a “opened-shell” conformation and undergo successive two-electron reduction by *FADH^- to produce 2 equiv of 6a as a precursor of 3a.

Radiation-induced and photosensitized one-electron oxidation of stereoisomeric C5−C5‘-linked dihydrothymine dimers (1a,b[meso], meso compound of (5R,5‘S)-bi-5,6-dihydrothymine; 1a,b[rac], racemic compound of (5R,5‘R)- and (5S,5‘S)-bi-5,6-dihydrothymines), which are the major products yielded by radiolytic reduction of 1-methylthymine (2a) and 1,3-dimethylthymine (2b) in aqueous solution, was studied to compare with the photoreactivating repair mechanism of cyclobutane pyrimidine photodimers. Reacting with sulfate radical anion (SO4^•-), azide radical (N3^•), or photoexcited anthraquinone-2-sulfonate (AQS) as oxidants, the C5−C5‘-linked dihydrothymine dimers 1a,b split to regenerate the corresponding thymine monomers 2a,b along with 5,6-dihydrothymines (3a,b) in a pH dependent manner. The transient absorption spectra of 5,6-dihydrothymin-5-yl radicals (6a,b) were observed in the nanosecond laser flash photolysis of 1a,b in phosphate buffer under conditions of SO4^•- generation. Both the product study and the laser flash photolysis study indicated an oxidative splitting mechanism by which one-electron oxidation of the C5−C5‘-linked dimers 1a,b produces the radical cation intermediates (4a,b), which undergo facile fragmentation into 5,6-dihydrothymin-5-yl radicals 6a,b and C5-cations (5a,b), followed by deprotonation at C6 of 5a,b to regenerate the monomers 2a,b.

A hybridoma cell line producing the monoclonal antibody against erythropoietin receptor (EpoR) was established using the soluble ectodomain of mouse erythropoietin receptor (sEpoR) as an antigen. The monoclonal antibody termed 1G3 bound to the denatured sEpoR. Epitope mapping with peptide library revealed that 1G3 recognized the amino terminal region including the hexapeptide (positions 6 to 11; LeuProAspProLysPhe). The amino acid sequence in this hexapeptide was identical in mice, rats, and humans, and therefore 1G3 bound to EpoR from all of these sources. Using 1G3, we evaluated sEpoR by a sandwich enzyme-linked immunoassay, and EpoR in the solubilized membrane preparation was detected by Western blotting. The cells expressing EpoR were identified with immunochemical staining. We confirmed the presence of EpoR in a neuronal cell line and PC12 cells, and EpoR was expressed in primary cultured hippocampal neurons.

A combined analytical/experimental study has been undertaken to in vestigate the effective thermal conductivity of hybrid composite materials. The analysis utilizes the equivalent inclusion approach for steady state heat conduction (Hatta and Taya, 1986), through which the interaction between the various reinforcing phases at finite con centrations is approximated by the Mori-Tanaka (1973) mean field approach. The multiple reinforcing phases of the composite are modeled as ellipsoidal in shape and thus can simulate a wide range of microstructural geometry ranging from thin platelet to con tinuous fiber reinforcement. The case when one phase of the composite is penny-shaped microcracks is studied in detail. Multiphase composites consisting of a Kerimid matrix and Al2O3short fibers and Si3N4whiskers were fabricated and after a careful study of their microstructure, their thermal conductivities were measured. Analytical predictions are shown to be in good agreement with experimental results obtained for the Al2O3/Si3N4/ Kerimid short fiber composites.

To reinforce the interlaminar of laminated composites, a novel method was proposed by the authors [1]. In this method, whiskers were added in the matrix resin to reinforce the interlaminar, and the orientation of the whiskers were magnetically con trolled to improve the reinforcement efficiency. In this paper, mode I (cleavage) inter laminar fracture toughness was shown to be remarkably improved as a result of the addi tion of oriented whiskers to the direction of the plate thickness. Whereas, mode II (inplane shear) interlaminar fracture toughness and interlaminar shear strength (ILSS) were not raised. Parameters of interlaminar reinforcement such as volume fraction of whiskers and whisker dimension were also discussed for exploring the optimum condition.

Tanaka, T., Y. Ohira, M. Danda, H. Hatta, and I. Nishi.Improved fatigue resistance not associated with maximum oxygen consumption in creatine-depleted rats. J. Appl. Physiol.82 (6): 1911–1917, 1997.—Effects of feeding of either creatine or its analog β-guanidinopropionic acid (β-GPA) on endurance work capacity and oxygen consumption were studied in rats. Resting high-energy phosphate contents in hindlimb muscles were lower in the β-GPA group and higher in the creatine group than in controls. The glycogen contents in resting hindlimb muscles of rats fed β-GPA were significantly higher than those in controls. The endurance run and swimming times to exhaustion were significantly greater (32–70%) in the β-GPA group than in the control and creatine groups. However, there were no beneficial effects on the maximum oxygen consumption (V˙o2 max) and oxygen transport capacity of blood by the feeding of β-GPA. None of these parameters were significantly influenced by creatine supply. Both maximum exercise time andV˙o2 maxin the β-GPA group were not changed by normalization of glycogen levels. The activities of mitochondrial enzymes in skeletal muscles were higher in the β-GPA group than in the controls. Thus endurance capacity is improved if the respiratory capacity of muscles is increased, even when the contents of high-energy phosphates in muscles are lower. Increased endurance capacity was not directly associated with the elevated levels of muscle glycogen, oxygen transport capacity of blood, orV˙o2 max.