Liquid crystalline side-chain polysiloxanes containing mesogenic groups attached by esterification

Summary Liquid crystalline side-chain polysiloxanes were prepared without metal complex catalyst. Mesogenic groups such as cholesteryl, 4-cyano-4-biphenyl and 4-methoxy-4-biphenyl group were introduced into polysiloxane by esterification and from DSC measurements they were compatible with other liquid crystalline polysiloxanes reported previously.     

Sintering Kinetics at Constant Rates of Heating: Effect of Al2O3 on the Initial Sintering Stage of Fine Zirconia Powder

The sinterabilities of fine zirconia powders including 5 mass% Y₂O₃ were investigated, with emphasis on the effect of Al₂O₃ at the initial sintering stage. The shrinkage of powder compact was measured under constant rates of heating (CRH). The powder compact including a small amount of Al₂O₃ increased the densification rate with elevating temperature. The activation energies at the initial stage of sintering were determined by analyzing the densification curves. The activation energy of powder compact including Al₂O₃ was lower than that of a powder compact without Al₂O₃. The diffusion mechanisms at the initial sintering stage were determined using the new analytical equation applied for CRH techniques. This analysis exhibited that Al₂O₃ included in a powder compact changed the diffusion mechanism from grain boundary to volume diffusions (VD). Therefore, it is concluded that the effect of Al₂O₃ enhanced the densification rate because of decrease in the activation energy of VD at the initial sintering stage.     

Digital watermarking by a holographic technique

A holographic technique is applied for digital watermarking by a computer. A digital-watermark image to be hidden is phase modulated in a random fashion, and its Fourier-transformed hologram is superposed on a content image. The watermark is reconstructed by means of a holographic-reconstruction technique from the bit-map image that hides it. In the study the processes of constructing and reconstructing a digital hologram are described on the basis of the theory of Fourier optics. The conditions for superposing the hologram onto the content images are investigated in detail. The validity of the present method is verified by changing the weighting of the hologram relative to that of the content image. The effect of image size is also discussed with respect to reconstruction of the watermark, and it is shown that watermark information in a form of a diffuse-type Fourier-transform hologram cannot be removed by cutting it out of the host image.     

Synthesis and Thermal Characterization of Novel Poly(tetramethylsilanthrylenesiloxane) and Poly(tetramethylsilphenanthrylenesiloxane) Derivatives

Summary Novel poly(tetramethylsilarylenesiloxane) derivatives, i.e. poly(tetramethyl-2,6-silanthrylenesiloxane) (P1), poly(tetramethyl-9,10-silanthrylenesiloxane) (P2), and poly(tetramethyl-1,8-silphenanthrylenesiloxane) (P3), were synthesized by polycondensation of novel disilanol monomers, i.e. 2,6-bis(dimethylhydroxysilyl)-anthracene (M1), 9,10-bis(dimethylhydroxysilyl)anthracene (M2), and 1,8-bis(dimethylhydroxysilyl)phenanthrene (M3), respectively. P1 and P3 were soluble in common organic solvents, such as benzene, toluene, chloroform, dichloromethane, tetrahydrofuran, etc. whereas P2 was almost insoluble in common organic solvents. It was revealed that P1 and P3 were amorphous and that P2 exhibited the crystallinity, as deduced from differential scanning calorimetry (DSC) and X-ray diffraction measurements. The glass transition temperatures (T_g’s) of P1 (118 °C) and P3 (100 °C) were much higher than that of poly(tetramethyl-1,4-silphenylenesiloxane). The temperature at 5% weight loss (T_d5) of P3 was 500 °C, which was higher than those of P1 and P2, and comparable to that of poly(tetramethyl-1,4-silphenylenesiloxane). It would be speculated that the thermostability of the series of poly(tetramethyl-silarylenesiloxane) derivatives is dependent on the stability of arylene moieties incorporated.     

Site-directed mutagenesis of the putative active site residues of 3C proteinase of coxsackievirus B3: evidence of a functional relationship with trypsin-like serine proteinases

Picornavirus 3C proteinases (3C^pro) are cysteine proteinasesbut recent sequence analyses have shown that they are relatedto trypsin-like serine proteinases. Two models of 3C^pro structurehave been presented. Both models indicate that residues His40and Cysl47 are members of the catalytic triad but the modelsdiffer in the designation of the third member of the catalytictriad, which is assigned as either Glu71 or Asp85. To test theimportance of these four residues in the catalytic activityof 3C^pro of coxsackievirus B3, a member of the enterovirus subgroupof the picornavirus family, single amino acid substitutionswere introduced at each of the four sites. All of these mutationsresulted in the reduction or inactivation of autocatalytic cleavageof the 3C precursor protein expressed in Escherichia coli, suggestingthat all of these residues are essential for the proteolyticreaction. The substitution of Cysl47 with Ala abolished 3C^proactivity while the mutant in which Cysl47 was replaced withSer retained reduced proteolytic activity both in cis and intrans. Our results strongly support the proposal that Cysl47of 3C^pro functions as a nucleophile analogous to Serl95 of trypsin-likeserine proteinases.     

Preparation and cured properties of novel cycloaliphatic epoxy resins

Preparation and characterization of novel cycloaliphatic epoxy resins, which are derived from octadienyl compounds, were studied. From a model peracetic acid epoxidation reaction using 2,7-octadienyl acetate-1, the structure of the liquid resins is estimated to be mainly terminal epoxides and some amount of inner epoxide depending on the epoxide content. The epoxy resins offer lower toxicity and lower vapor pressure. The reactivity of the resin with acid anhydrides is moderate but faster than that of traditional cyclohexane epoxide-type resins and slower than that of the glycidyl ester-type resins. This reactivity was also examined using model compounds. The heat deflection temperature of the hexahydro-phthalic anhydride-cured resins is shown to be directly proportional to the number of epoxy groups in the molecules. The flexural strength of the cured resins is nearly equivalent to that of the commercial resins, although the flexural elongation of the resins is larger than that of the rigid cyclohexane epoxide-type resins. The thermal stability of the cured resins is comparable to typical rigid cycloaliphatic resins; furthermore, high water resistance of the cured resins is suggested to be attributed to the hydrophobic character of the C₈ chain by cross-linking. © 1993 John Wiley & Sons, Inc.     

Remarks on Muscle Contraction Mechanism II. Isometric Tension Transient and Isotonic Velocity Transient

Mitsui and Ohshima (2008) criticized the power-stroke model for muscle contraction and proposed a new model. In the new model, about 41% of the myosin heads are bound to actin filaments, and each bound head forms a complex MA(3) with three actin molecules A1, A2 and A3 forming the crossbridge. The complex translates along the actin filament cooperating with each other. The new model well explained the experimental data on the steady filament sliding. As an extension of the study, the isometric tension transient and isotonic velocity transient are investigated. Statistical ensemble of crossbridges is introduced, and variation of the binding probability of myosin head to A1 is considered. When the binding probability to A1 is zero, the Hill-type force-velocity relation is resulted in. When the binding probability to A1 becomes finite, the deviation from the Hill-type force-velocity relation takes place, as observed by Edman (1988). The characteristics of the isometric tension transient observed by Ford, Huxley and Simmons (1977) and of the isotonic velocity transient observed by Civan and Podolsky (1966) are theoretically reproduced. Ratios of the extensibility are estimated as 0.22 for the crossbridge, 0.26 for the myosin filament and 0.52 for the actin filament, in consistency with the values determined by X-ray diffraction by Wakabayashi et al. (1994).     

Synthesis and properties of poly(tetramethyl-1,6-silpyrenylenesiloxane) derivative with phenyl groups on pyrenylene moiety

Poly(tetramethyl-1,6-silpyrenylenesiloxane) derivative with phenyl groups on pyrenylene moieties (P1) was prepared via polycondensation of disilanol monomer, i.e. 1,6-bis(dimethylhydroxysilyl)-3,8-diphenylpyrene (M1). P1 exhibited the very high glass transition temperature (T _g) of 191 °C. The temperature at 5% weight loss (T _d5) of P1 was 482 °C, indicating the relatively good thermostability of P1. P1 exhibited the bathochromic effect in the absorption and fluorescence spectra, indicating the expansion of π-conjugation by introducing phenyl groups onto pyrene skeleton as well as the σ–π and σ*–π* conjugation between pyrene and silyl moieties. In addition, P1 exhibited relatively weak excimer emission because of the inhibition of the excimer formation of pyrene skeleton by introduction of bulky phenyl groups onto pyrene skeleton. The fluorescence quantum yields (Φ_Fs) of M1 and P1 in chloroform were determined to be 0.46 and 0.37, respectively. It was revealed that M1 and P1 exhibited the higher fluorescence intensity than 1,6-diphenylpyrene, owing to the effect of the introduction of silyl moieties onto pyrene skeleton.     

Synthesis and properties of novel poly(tetramethylsilnaphthylenesiloxane) derivatives

Novel poly(tetramethylsilnaphthylenesiloxane) derivatives were synthesized and characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), and X-ray diffraction analyses. Poly(tetramethylsilnaphthylenesiloxane) derivatives were obtained by condensation polymerization of the corresponding disilanol derivatives, i.e. 1,4-, 1,5-, 2,6-, and 2,7-bis(dimethylhydroxysilyl)naphthalenes, which were prepared by the Grignard reaction using chlorodimethylsilane and the corresponding dibromonaphthalene derivatives followed by the hydrolyses, catalyzed by palladium on charcoal. The obtained poly(tetramethyl-1,5-silnaphthylenesiloxane) was insoluble in common organic solvents; however, the other polymers exhibited the good solubility in common organic solvents, such as tetrahydrofuran (THF), chloroform, dichloromethane, and toluene. The introduction of tetramethyl-1,5-silnaphthylenesiloxane units into the resulting polymer was confirmed by ¹H NMR spectrum of the copolymer obtained by condensation copolymerization of 1,5-bis(dimethylhydroxysilyl)naphthalene with 1,4-bis(dimethylhydroxysilyl)naphthalene. It was revealed from the DSC and X-ray diffraction measurements that poly(tetramethyl-1,5-silnaphthylenesiloxane) and poly(tetramethyl-2,6-silnaphthylenesiloxane) exhibited the crystallinity; however, poly(tetramethyl-1,4-silnaphthylenesiloxane) and poly(tetramethyl-2,7-silnaphthylenesiloxane) were amorphous. The glass transition temperature (T_g) and the temperature at 5% weight loss (T_d5) of poly(tetramethylsilnaphthylenesiloxane) derivatives with dimethylsilyl group at 1-position of the naphthylene moiety were higher than those at 2-position of the naphthylene moiety. The T_g and melting point (T_m) of the present polymers were higher than those of poly(tetramethyl-1,4-silphenylenesiloxane).