Chiral poly(alkyl phenylpropiolate)s −{(C6H5)CC[CO2(CH2)2OCOR*]}n−with R* =(S)-(+)-[1-(6-methoxy-2-naphthyl)ethyl (P1), (1R,2S,5R)-(−)-menthoxymethyl (P2), (S)-(+)-(α-acetoxy)benzyl (P3), and cholesteryloxy (P4) were synthesized, and their structures and properties were investigated. The monomers [C6H5C⋮CCO2(CH2)2OCOR*; 1−4] were prepared by esterifications of stereogenic acids 8−10 or chloroformate (11) with 3-hydroxyethyl phenylpropiolate (7) in high yields. Polymerizations of 1−4 were effected by MoCl5−Ph4Sn at 60 or 80 °C, and polymers with high molecular weights (Mw up to ∼100 × 103) were obtained in moderate yields. The polymers were characterized by IR, NMR, TGA, UV, and CD analyses. All of the polymers are stable, losing little of their weights when heated to ≥300 °C and undergoing no chain scissions when annealed in air at ≥150 °C. The macromolecular chains take helical conformations with preferred handedness, and their helical chirality can be reversibly tuned by solvent or temperature to varying extents.
The relationship between oral contraceptives (OC) and breast-cancer risk was analysed using data from a case-control study conducted between June 1991 and February 1994 in 6 Italian centres on 1,991 patients below age 65 with histologically confirmed incident breast cancer and 1,899 controls admitted to hospital for a wide range of acute, non-neoplastic, non-hormone-related diseases. "Ever OC use" was reported by 18% of cases versus 14% of controls, corresponding to a multivariate odds ratio (OR) of 1.1 (95%) confidence interval, Cl 0.9 to 1.4). The ORs were 1.3 for use lasting < 1 year, 1.1 for 1 to 4 years, 0.9 for 5 to 8 years, and 1.2 for over 8 years. With reference to age at first use, there was some indication that the OR was elevated in women who had started use before age 30, but not in those starting at a later age. With reference to time since last OC use, the OR was above unity for women who had stopped for less than 10 years (1.6 for 1 to 4 years; 1.7 for 5 to 9 years), but the OR declined to unity for women who had stopped OC use for 10 years or longer. The OR for women who had stopped OC use for less than 10 years was consistently elevated across strata of selected covariates, and was directly related to the duration of use (OR 1.3 for < 5 years, 1.7, for > or = 5 years). In contrast, the OR was 0.6, for use lasting > or = 5 years in women who had stopped for 10 years or more. The elevated OR for women who had recently stopped OC use, together with the absence of association (or the suggestion of some protection) for those who had stopped for 10 years or more is consistent with the pattern of breast-cancer risk observed after a full-term pregnancy, and provides important reassurance on a public health level on the long-term impact of OCs on breast carcinogenesis.
The proportions of gastric cancer cases attributable (or attributable risks, AR) to consumption of traditional foods (i.e., pasta, rice and maize), low intake of beta-carotene and vitamin C, short duration of use of an electric refrigerator, low educational level, and family history of gastric cancer were computed using data from a case-control study conducted in Northern Italy. Between 1985 and June 1993 a total of 746 incident, histologically confirmed gastric cancer cases and 2,053 controls admitted to the same network of hospitals for acute, nonneoplastic, non-digestive-tract diseases, unrelated to long-term modifications of diet, were interviewed. The ARs were 48% for low intake of beta-carotene, 40% for high consumption of traditional foods, and 16% for low intake of vitamin C. Overall, these 3 dietary factors explained 73% of the gastric cancer cases in the population. Five percent of all cases were attributable to less than 30 years' use of an electric refrigerator, 15% to low educational level, and 5% to family history of gastric cancer. In individuals over age 60, a greater proportion of cases was attributable to traditional foods, low education and late adoption of electric refrigeration (58% vs. 32% aged under 60), suggesting that correlates of lower social class, influenced lifestyle, and dietary habits more markedly in earlier than in more recent generations. According to our estimates, over 3 quarters of the gastric cancer cases in this area are explainable in terms of the risk factors considered. Increased consumption of vitamin C and beta-carotene, and reduced consumption of traditional foods, would help to avoid over 10,000 out of 14,000 stomach-cancer deaths in Italy every year. Consequently, stomach cancer, which is still the third leading cause of cancer death in Italy, would represent only about 2% of all cancer deaths.
The moiré potential serves as a periodic quantum confinement for optically generated excitons, creating spatially ordered zero-dimensional quantum systems. However, a broad emission spectrum resulting from inhomogeneity among moiré potentials hinders the investigation of their intrinsic properties. In this study, we demonstrated a method for the optical observation of quantum coherence and interference of a single moiré exciton in a twisted semiconducting heterobilayer beyond the diffraction limit of light. We observed a single and sharp photoluminescence peak from a single moiré exciton following nanofabrication. Our findings revealed the extended duration of quantum coherence in a single moiré exciton, persisting beyond 10 ps, and an accelerated decoherence process with increasing temperature and excitation power density. Moreover, quantum interference experiments revealed the coupling between moiré excitons in different moiré potential minima. The observed quantum coherence and interference of moiré exciton will facilitate potential applications of moiré quantum systems in quantum technologies.
Read moreThis paper presents a method for chemical functionalization of CNTs through the combined process of UV/O3 treatment and silanization process. FT-IR and TEM were employed to characterize the changes in surface functionalities and morphology. The results indicate improved dispersion and attachment of silane molecules on the surface of CNTs. Epoxy matrix nanocomposites containing functionalized CNTs showed much better dispersion with associated higher mechanical properties than those without functionalization. These findings confirmed the improved interfacial interactions due to covalent bonding between the functionalized CNTs and epoxy resin.
Read moreIn article number 2300068, Dominique Ausserré, Fabien Vialla and co-workers combine Backside Absorbing Layer Microscopy (BALM) and an original self-calibrating image analysis procedure to achieve simple, accurate monolayer counting in exfoliated 2D material stacks. The authors demonstrate characterization of flakes from 1 to >30 monolayer thickness with the challenging case of transparent hexagonal boron nitride (hBN).
Read moreIn the present work, we investigated self-assembling of a poly(phenylacetylene) carrying L-valine pendants (PPA-Val) in a water/methanol solution, upon evaporation of the solution on mica, and on the water surface. With intercalation of a fluorescence probe of Ru(phen)2(dppx)2+ (phen = 1,10-phenanthroline, dppx=7,8-dimethyldipyridophenazine) into the hydrophobic cavities associated by the PPA-Val chains, their helical structures were directly detected in solution with an in situ fluorescence microscope. Helical aggregates were observed with AFM upon evaporation of the solvents, suggesting that the helical structures in the solution are the building blocks of the helical aggregates. Self-assembling structures of PPA-Val on the water surface were, however, very different from that formed upon evaporation of its THF solution on the mica surface. The polymer chains associated into a monolayer of extended fibers on the water surface, whereas superhelical fibers formed on the mica surface. Water molecules play a critical role in inducing the polymer to form diverse morphological structures in its bulk solution and on its surface. In solution, the isotropic hydrophobic effect drove the polymer chains to form superhelical aggregates, while on the water surface, the hydrophobic effect concentrated mainly on the lateral part of the polymer, thus giving a monolayer of extended fibers.
Read moreWe present a single-molecule study demonstrating that resonant charge transport through vibronic states takes place in molecules that are strongly anchored at an electrode. The molecules are adsorbed on a CuN/Cu(100) surface, with the molecular terminal group attaching to the Cu ridge. We use a scanning tunneling microscope to inject charges into the highest occupied molecular orbital and excite vibronic transitions. The charges are then transferred in a single-electron process through either a single or a double intramolecular channel, depending on molecular adsorption configuration. These phenomena are explained in terms of localized molecular orbitals and an effective intramolecular barrier.
Read moreSuspensions containing quaternized poly(pyridylacetylene) (PPyA) and AgX (X = Br and I) were obtained by simply mixing PPyA with water soluble silver salts. The suspensions were stable in the dark at room temperature, and could be cast into uniform films. After exposure to UV-light for sufficient time, Ag nanoparticles were in situ generated in the polymer matrix via photochemical reaction. By adjusting the Ag+ contents and the halide counterions, the size of Ag particles, the conductivity of the composite films, and the surface morphology of the composites were tuned. The quaternized PPyA absorbed UV-light efficiently and the photogenerated halogen caused fast degradation of the polymers. Thus the photo-chemical process concomitantly resulted in the formation of Ag nanoparticles and highly porous films. These properties offer the composite materials potential in the construction of UV-eroding conductive patterns, embedded metal nanostructures, and porous films for loading metal particles as catalyst.
Read moreA new silole derivative, 1,2,3,4,5-pentaphenyl-1-(8-phenyl-1,7-octadiynyl)silole, is synthesized, characterized, and used as the electron-transport/emission layers in organic light-emitting diodes. Blue emission at 492 nm is observed, with a maximum luminance of 10 460 cd/m/sup 2/ at 18 V. The respective maximum current and power efficiencies are 8.47 cd/A and 3.8lm/W. A triple-layer composite cathode was used, consisting of tris(8-hydroxy-quinolne)aluminum (Alq/sub 3/) lithium fluoride and aluminum. The dependence of emission efficiency on the thickness of TPD and Alq/sub 3/ is investigated and explained.
Read moreAbstract Van der Waals heterostructures are fabricated by layer-by-layer assembly of individual two-dimensional materials and can be used to create a wide range of electronic devices. However, current assembly techniques typically use polymeric supports, which limit the cleanliness—and thus the electronic performance—of such devices. Here, we report a polymer-free technique for assembling van der Waals heterostructures using flexible silicon nitride membranes. Eliminating the polymeric supports allows the heterostructures to be fabricated in harsher environmental conditions (incompatible with a polymer) such as at temperatures of up to 600 °C, in organic solvents and in ultra-high vacuum. The resulting heterostructures have high-quality interfaces without interlayer contamination and exhibit strong electronic and optoelectronic behaviour. We use the technique to assemble twisted-graphene heterostructures in ultra-high vacuum, resulting in a tenfold improvement in moiré superlattice homogeneity compared to conventional transfer techniques.
Read morePoly(phenylacetylene)s bearing monosaccharide pendant groups are synthesized in high yields by [Rh(nbd)Cl]<sub>2</sub> catalyst. The polymers have high molecular weights and give satisfactory spectroscopic data corresponding to their molecular structures. They are thermally quite stable (≥ 300°C) and show strong circular dichroism signals in the visible spectral region owing to the helicity of the polyene backbone. The monosaccharide-containing polyacetylenes are cytophilic and can stimulate the growth of living cells.
Read moreInterfacial electron-transfer (ET) reactions underpin the interconversion of electrical and chemical energy. It is known that the electronic state of electrodes strongly influences ET rates because of differences in the electronic density of states (DOS) across metals, semimetals, and semiconductors. Here, by controlling interlayer twists in well-defined trilayer graphene moirés, we show that ET rates are strikingly dependent on electronic localization in each atomic layer and not the overall DOS. The large degree of tunability inherent to moiré electrodes leads to local ET kinetics that range over 3 orders of magnitude across different constructions of only three atomic layers, even exceeding rates at bulk metals. Our results demonstrate that beyond the ensemble DOS, electronic localization is critical in facilitating interfacial ET, with implications for understanding the origin of high interfacial reactivity typically exhibited by defects at electrode-electrolyte interfaces.
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