Perfluoropolyether-Silica Hybrids: Preparation and Surface Characterization

,-Triethoxysilane terminated perfluoropolyether-polycaprolactone block copolymers, TXCL(x)Si, were synthesised, characterised and subsequently reacted with tetraethoxysilane to prepare transparent organic-inorganic hybrid materials by using the sol–gel process. Surface characterization was carried out through contact angle measurements. All the materials investigated (independently on both the reaction time of the sol–gel reaction before coating application and the bulk organic-inorganic ratio) showed a strong hydrophobic character when compared with non-fluorinated and fully inorganic control materials. The highest water contact angles were obtained when TXCL(x)Si oligomer used for the preparation of the hybrid contained short hydrogenated polycaprolactone segments. In all cases, the surface tension values indicated that the very surface at the air-coating interface showed almost completely perfluoropolyether segments.     

Mapping and identification of protein-protein interactions by two-dimensional far-Western immunoblotting

Studies of protein-protein interactions have proved to be a useful approach to link proteins of unknown function to known cellular processes. In this study we have combined several existing methods to attempt the comprehensive identification of substrates for poorly characterized human protein tyrosine phosphatases (PTPs). We took advantage of so-called "substrate trapping" mutants, a procedure originally described by Flint et al. (Proc. Natl. Acad. Sci. USA 1997, 94, 1680-1685) to identify binding partners of cloned PTPs. This procedure was adapted to a proteome-wide approach to probe for candidate substrates in cellular extracts that were separated by two-dimensional (2-D) gel electrophoresis and blotted onto membranes. Protein-protein interactions were revealed by far-Western immunoblotting and positive binding proteins were subsequently identified from silver-stained gels using tandem mass spectrometry. With this method we were able to identify possible substrates for PTPs without using any radio-labeled cDNA or protein probes and showed that they corresponded to tyrosine phosphorylated proteins. We believe that this method could be generally applied to identify possible protein-protein interactions.     

The Fascinating Chemistry of α-Haloamides

The aim of this review is to highlight the rich chemistry of α-haloamides originally mainly used to discover new C−N, C−O and C−S bond forming reactions, and later widely employed in C−C cross-coupling reactions with C(sp³), C(sp²) and C(sp) coupling partners. Radical-mediated transformations of α-haloamides bearing a suitable located unsaturated bond has proven to be a straightforward alternative to access diverse cyclic compounds by means of either radical initiators, transition metal redox catalysis or visible light photoredox catalysis. On the other hand, cycloadditions with α-halohydroxamate-based azaoxyallyl cations have garnered significant attention. Moreover, in view of the important role in life and materials science of difluoroalkylated compounds, a wide range of catalysts has been developed for the efficient incorporation of difluoroacetamido moieties into activated as well as unactivated substrates.     

Chemical Characterization of Plant Extracts and Evaluation of their Nematicidal and Phytotoxic Potential

Nacobbus aberrans ranks among the “top ten” plant-parasitic nematodes of phytosanitary importance. It causes significant losses in commercial interest crops in America and is a potential risk in the European Union. The nematicidal and phytotoxic activities of seven plant extracts against N. aberrans and Solanum lycopersicum were evaluated in vitro, respectively. The chemical nature of three nematicidal extracts (EC_50,48h ≤ 113 µg mL⁻¹) was studied through NMR analysis. Plant extracts showed nematicidal activity on second-stage juveniles (J2): (≥87%) at 1000 µg mL⁻¹ after 72 h, and their EC₅₀ values were 71.4–468.1 and 31.5–299.8 µg mL⁻¹ after 24 and 48 h, respectively. Extracts with the best nematicidal potential (EC_50,48h < 113 µg mL⁻¹) were those from Adenophyllum aurantium, Alloispermum integrifolium, and Tournefortia densiflora, which inhibited L. esculentum seed growth by 100% at 20 µg mL⁻¹. Stigmasterol (1), β-sitosterol (2), and α-terthienyl (3) were identified from A. aurantium, while 1, 2, lutein (4), centaurin (5), patuletin-7-β-O-glucoside (6), pendulin (7), and penduletin (8) were identified from A. integrifolium. From T. densiflora extract, allantoin (9), 9-O-angeloyl-retronecine (10), and its N-oxide (11) were identified. The present research is the first to report the effect of T. densiflora, A. integrifolium, and A. aurantium against N. aberrans and chemically characterized nematicidal extracts that may provide alternative sources of botanical nematicides.     

Mechanism of protonation of [Pt(3)(mu-PBu(t)(2))3(H)(CO)2], yielding the hydride-bridged [Pt(3)(mu-PBu(t)(2))2(mu-H)(PBu(t)(2)H)(CO)2]OTf (Tf=CF(3)SO(2)), and the spectroscopic and theoretical characterization of a kinetic intermediate

The reaction of the Pt(I)Pt(I)Pt(II) triangulo cluster Pt(3)(micro-PBu(t)()(2))(3)(H)(CO)(2) (1) with TfOH (Tf = CF(3)SO(2)) affords the hydride-bridged cationic derivative [Pt(3)(mu-PBu(t)()(2))(2)(mu-H)(PBu(t)()(2)H)(CO)(2)]OTf (2). With TfOD the reaction gives selectively [Pt(3)(mu-PBu(t)(2))(2)(mu-D)(PBu(t)(2)H)(CO)(2)]OTf (2-D(1)), implying that the proton is transferred to a metal center while a P-H bond is formed by the reductive coupling of one of the bridging phosphides and the terminal hydride ligand of the reagent. The reaction proceeds through the formation of a thermally unstable kinetic intermediate which was characterized at low temperatures, and was suggested to be the CO-hydrogen-bonded (or protonated) [Pt(3)(mu-PBu(t)(2))(3)(H)(CO)(2)].HOTf (3). An ab initio theoretical study predicts a hydrogen-bonded complex or a proton-transfer tight ion pair as a possible candidate for the structure of the kinetic intermediate.     

Dynamics of individual single-walled carbon nanotubes in water by real-time visualization

Individual single-walled carbon nanotubes (SWNTs) in aqueous suspension are visualized directly by fluorescence video microscopy. The fluorescent tagging is simple, biocompatible, and does not modify the SWNTs. The dynamics of individual SWNTs in water are observed and quantified for the first time. We measure the confined rotational diffusion coefficient and find it in reasonable agreement with predictions based on confined diffusion of dilute Brownian rods. We determine the critical concentration at which SWNTs in suspensions start interacting. By analyzing the fluctuating shape of SWNTs in the 3 to 5 microm range, we determine that their persistence length ranges between 32 and 174 microm, in agreement with theoretical estimates; thus, commonly available SWNTs in liquids can be considered as rigid Brownian rods in the absence of imposed external fields or self-attractive forces.     

Elementary scales and the lack of Fourier paradox for Fourier fluids

Focusing on the Fourier fluids in the liquid state, which are characterized by linear thermal constitutive equation and low compressibility, this short note proposes a discrete approach based on the elementary scales, which allows removing the so-called Fourier paradox in classical continuum thermomechanics. As a corollary, the adopted line of reasoning allows highlighting some features on the elementary scales.

     

Energy and angular momentum sharing in dissipative collisions

Primary and secondary masses of heavy reaction products have been deduced from kinematics and E-ToF measurements, respectively, for the direct and reverse collisions of ⁹³Nb and ¹¹⁶Sn at 25 AMeV. Light charged particles have also been measured in coincidence with the heavy fragments. Direct experimental evidence of the correlation of energy-sharing with net mass transfer has been found using information from both the heavy fragments and the light charged particles. The ratio of hydrogen and helium multiplicities points to a further correlation of angular momentum sharing with net mass transfer. Received: 18 September 2000 / Accepted: 2 December 2000     

Analysis of glycosyl phosphatidylinositol-anchored proteins by two-dimensional gel electrophoresis

The aim of this study was to characterize mammalian glycosyl phosphatidylinositol (GPI)-anchored proteins y two-dimensional gel electrophoresis using immobilized pH gradients. Analysis was performed on detergent-resistant membrane fractions of baby hamster kidney (BHK) cells, since such fractions have previously been shown to be highly enriched in GPI-anchored proteins. Although the GPI-anchored proteins were readily separated by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), these proteins were undetectable on two-dimensional (2-D) gels, even though these gels unambiguously revealed high enrichment of known hydrophobic proteins of detergent-resistant membranes such as caveolin-1 and flotillin-1 (identified by Western blotting and tandem mass spectrometry, respectively). Proper separation of GPI-anchored proteins required cleavage of the lipid tail with phosphatidylinositol-specific phospholipase C, presumably to avoid interference of the hydrophobic phospholipid moiety of GPI-anchors during isoelectric focusing. Using this strategy, BHK cells were observed to contain at least six GPI-anchored proteins. Each protein was also present as multiple isoforms with different isoelectric points and apparent molecular weights, consistent with extensive but differential N-glycosylation. Pretreatment with N-glycosidase F indeed caused the different isoforms of each protein to collapse into a single spot. In addition, quantitative removal of N-linked sugars greatly facilitated the detection of heavily glycosylated proteins and enabled sequencing by nanoelectrospray-tandem mass spectrometry as illustrated for the GPI-anchored protein, Thy-1.