Rheology of hydrophobically modified polyacrylamide-co-poly(acrylic acid) on addition of surfactant and variation of solution pH

Constant shear and shear dependent viscosity measurements are reported in aqueous systems of co- and terpolymers of acrylamide (AM), N-n-alkylacrylamide (C10, C12, and C14 alkyl groups), and acrylic acid (AA) with added anionic surfactant sodium dodecyl sulfate (SDS). The results are presented as three-dimensional plots of viscosity vs surfactant concentration and pH at constant shear rate or viscosity vs shear rate and surfactant concentration at constant pH. For terpolymers incorporating AA, a strong viscosity maximum is observed at intermediate pH values (pH 4-6) where the AA groups are partially ionized and at SDS concentrations close to the critical micelle concentration. At high pH, all AA incorporating terpolymer solutions with SDS are strongly shear thinning, but at pH 3-4 the systems of terpolymers with SDS are strongly shear thickening at low shear, followed by a shear-thinning region at high shear. These results are explained in terms of surfactant-mediated network formation with polymer coil expansion and hydrogen bonding between partially ionized AA groups as additional factors.     

Cooperative C-F...Si interaction in optically active helical polysilanes

Cooperative amplification of the C-F...Si weak interaction between side chains and the main chain was found to afford rigid rodlike helical polysilanes with a preferential screw sense.     

Phosphorylation of phospholipase D1 and the modulation of its interaction with RhoA by cAMP-dependent protein kinase

Agents that elevate cellular cAMP are known to inhibit the activation of phospholipase D (PLD). We investigated whether PLD can be phosphorylated by cAMP-dependent protein kinase (PKA) and PKA-mediated phosphorylation affects the interaction between PLD and RhoA, a membrane regulator of PLD. PLD1, but not PLD2 was found to be phosphorylated in vivo by the treatment of dibutyryl cAMP (dbcAMP) and in vitro by PKA. PKA inhibitor (KT5720) abolished the dbcAMP-induced phosphorylation of PLD1, but dibutyryl cGMP (dbcGMP) failed to phosphorylate PLD1. The association between PLD1 and Val14RhoA in an immunoprecipitation assay was abolished by both dbcAMP and dbcGMP. Moreover, RhoA but not PLD1 was dissociated from the membrane to the cytosolic fraction in dbcAMP-treated cells. These results suggest that both PLD1 and RhoA are phosphorylated by PKA and the interaction between PLD1 and RhoA is inhibited by the phosphorylation of RhoA rather than by the phosphorylation of PLD1.     

Biomedical significance of endothelial cell specific growth factor, angiopoietin

Until recently, vascular endothelial growth factor (VEGF) was the only growth factor proven to be specific and critical for blood vessel formation. Other long-known factors, such as the fibroblast growth factors (FGFs), platelet-derived growth factor, or transforming growth factor-beta, had profound effects in endothelial cells. But such factors were nonspecific, in that they could act on many other cells, and it seemed unlikely that these growth factors would be effective targets for treatment of endothelial cell diseases. A recently discovered endothelial cell specific growth factor, angiopoietin, has greatly contributed to our understanding of the development, physiology, and pathology of endothelial cells (Davis et al., 1996; Yancopoulos et al., 2000). The recent studies that identified and characterized the physiological and pathological roles of angiopoietin have allowed us to widen and deepen our knowledge about blood vessel formation and vascular endothelial function. Therefore, in this review, we describe the biomedical significance of these endothelial cell growth factors, the angiopoietins, in the vascular system under normal and pathological states.     

Synthesis of 6-substituted 1-alkoxy-5-alkyluracils

Synthesis of 6-substituted 1-alkoxy-5-alkyluracils 2a-c have been achieved from readily accessible 2-alkyl-3,3-di(methylthio)acryloyl chlorides 4a,b in high overall yields. Treatment of 4a,b with silver cyanate followed by reaction of the resulting isocyanates 5a,b with an appropriate alkoxyamine afforded N-alkoxy-N′-[2-alkyl-3,3-di(methylthio)acryloyl]ureas 6a,b in 85–88% yields. Cyclization of 6a,b in acetic acid containing methanesulfonic acid followed by oxidation with 3-chloroperoxybenzoic acid gave high yields of 1-alkoxy-5-alkyl-6-(methylsulfonyl)uracils 9a,b. Nucleophillic addition-elimination reaction of 9a,b with sodium azide, phenylthiol, or phenylselenol produced 6-azido-1-butoxythymine ( 2a , 98%), 5-ethyl-1-(2-phenoxyethoxy)-6-(phenylthio)uracil ( 2b , 95%), or 5-ethyl-1-(2-phenoxyethoxy)-6-(phenylselenenyl)uracil ( 2c , 91%).     

Deposition of a Continuous and Conformal Copper Seed Layer by a Large-Area Electron Cyclotron Resonance Plasma Source with Embedded Lisitano Antenna

To deposit copper seed layer on ultra large scale integration devices, a large-area (Ø 378 mm) electron cyclotron resonance plasma has been generated by using permanent magnets-embedded Lisitano antenna. The plasma source operates in the pressure range of 0.2–1.5 mTorr with microwave power range of 500–2,000 W. By using a Langmuir probe, the electron density and temperature have been measured near the DC sputter target position. Measurements indicate argon plasmas having electron densities of ~5 × 10¹⁰/cm and electron temperatures of 5 eV with 750 W microwave power at gas pressures of 0.5 mTorr. Using this plasma source and a DC sputter, we obtained excellent conformal copper seed layer with high aspect ratios of 12:1. This is in contrast with conventional methods using magnetron sputter, which has aspect ratios of 2–3:1. Also, improvements are observed in the smoothness (root mean square roughness of 1.345 nm), uniformity (2.5 % at 300 mm wafer), and sidewall symmetricity (more than 95 %) of the copper seed layer.