Effective Guanidine‐Catalyzed Synthesis of Carbonate and Carbamate Derivatives from Propargyl Alcohols in Supercritical Carbon Dioxide

The reactions of propargyl alcohols with carbon dioxide in supercritical carbon dioxide or in acetonitrile with gaseous carbon dioxide in the presence of organic bases as catalysts have been examined. Bicyclic guanidines are effective catalysts for the formation of α‐methylene cyclic carbonates under mild reaction conditions. Oxoalkyl carbonates, oxoalkyl carbamates or α‐methyleneoxazolidinones are obtained in high yields and good selectivities in one‐step starting from propargyl alcohols and an external nucleophile (alcohols or amines) using bicyclic guanidines as catalysts in supercritical carbon dioxide. Propargylic diols under the same reaction conditions underwent a rearrangement process instead of carbon dioxide insertion whereas in the presence of an external nucleophile the formation of oxocarbonates, oxocarbamates or cyclic carbamates was achieved in satisfactory yields.     

High performance PA6/CNTs nanohybrid fibers prepared in the melt

Commercial and home-made carbon nanotubes (CNTs) were plasma treated under oxygen atmosphere and then added to polyamide 6 (PA6) in order to prepare fibres by melt spinning. For comparison, pristine nanofillers were used too. The effect of functionalization and of filler characteristics on the morphological, rheological, mechanical and electrical properties of the fibres was studied by TEM and SEM, rheological measurements, tensile and electrical conductivity tests. The results demonstrated that the functionalization led to a better mechanical performance and the morphological analysis confirmed that the adhesion, the dispersion and the alignment of the nanotubes within the polymer matrix were improved when using functionalized CNTs. Electrical tests marked that functionalization slightly reduced the conductivity of the materials.     

Hydrogen plasma treatment of very thin p-type nanocrystalline Si films grown by RF-PECVD in the presence of B(CH3)3

We have characterized the structure and electrical properties of p-type nanocrystalline silicon films prepared by radio-frequency plasma-enhanced chemical vapor deposition and explored optimization methods of such layers for potential applications in thin-film solar cells. Particular attention was paid to the characterization of very thin (∼20 nm) films. The cross-sectional morphology of the layers was studied by fitting the ellipsometry spectra using a multilayer model. The results suggest that the crystallization process in a high-pressure growth regime is mostly realized through a subsurface mechanism in the absence of the incubation layer at the substrate-film interface. Hydrogen plasma treatment of a 22-nm-thick film improved its electrical properties (conductivity increased more than ten times) owing to hydrogen insertion and Si structure rearrangements throughout the entire thickness of the film.     

Equilibrium Isotherms,Thermodynamics, and Kinetic Studies for the Adsorption of Food Azo Dyes onto Chitosan Films

The adsorption of FD&C red 2 and FD&C yellow 5 onto chitosan films (CFs) was evaluated by equilibrium isotherms, thermodynamics, and kinetic studies. The effects of temperature (298–328 K), initial dye concentration (50–300 mg L^?1), stirring rate (50–350 rpm), and contact time (0–120 min) were investigated at pH of 2.0 and 100 mg L^?1 of CFs. The dye concentration was determined by spectrophotometry. Freundlich and Langmuir models were used to represent the equilibrium data. The Langmuir model was the more adequate to represent the equilibrium data (R² > 0.99 and average relative error <2.50%) and the maximum adsorption capacities were 494.13 and 480.00 mg g^?1 for FD&C red 2 and FD&C yellow 5, respectively, obtained at 298 K. The R_L values ranged from 0.044 to 0.145. The adsorption was exothermic, spontaneous, and favorable. For the FD&C red 2, 90% of saturation was attained at 120 min and the Elovich model was the more appropriate. For the FD&C yellow 5, 95% of saturation was attained at 20 min and the pseudo first-order model was the more adequate to fit the kinetic data. CFs were easily separated from the liquid phase after the adsorption process, providing benefits for industrial applications, and its application range can be extended for azo dyes.     

Surface modification of cellulosic fibres for multi-purpose TiO2 based nanocomposites

Vegetable cellulose fibres have been surface modified using the hydrolysis of tetraethoxysilane (TEOS), octyltrimethoxysilane (OTMS) or phenyltrimethoxysilane (PTMS), followed by the layer-by-layer deposition of previously synthesized TiO₂ nanoparticles. Raman, FTIR and ²⁹Si Solid State NMR spectroscopies, and SEM were used to characterize the resulting nanocomposites. Water contact angle measurements were performed and the results indicate a quite distinct behaviour depending on the employed surface modification procedure. We anticipate that some of the cellulose-based composite materials have potential to be used in self-cleaning surfaces and reinforcing agents in polymer matrices, namely due to their hydrophobic surface and photostability when exposed to solar radiation.     

Homo- and copolymers of furan–maleic anhydride and furan–dimethylacetylene dicarboxylate adducts via aqueous ring-opening metathesis polymerization

Homo- and copolymers of the Diels-Alder adduct of furan with maleic anhydride (F-MA) and of furan with dimethylacetylene dicarboxylate (F-DMAD) were synthesized by aqueous ring-opening metathesis polymerization and characterized by IR, NMR, and DSC. Microstructural product analyses by ¹³C-NMR indicated the copolymer composition to be 50 : 50 of each of the monomers when an equimolar mixture of RuCl₃ and K₂RuCl₅, was used as the catalyst, with the cis-form predominant for poly(F-MA) and the trans-form predominant for poly(F-DMAD). On the practical side, the acidic and ester functionality of the copolymer would lend itself to be both blendable (and selectively extractable) with some already existing petroleum-based acrylate polymers. © 1993 John Wiley & Sons, Inc.     

A re-evaluation of the concept of homophilic interactions?

In this histochemical study on the ocular lens, the authors test for the presence of various sorts of the (unsaturated) polycyclic aromatic hydrocarbon (PAH) in 66, both clear and cataractous human lenses. A statistically significant greater amount of PAH is found in the cataractous lenses studied (p < 0.01), with two kind of PAH, phenanthrene and 1,2-benzoanthracene, appearing exclusively in lenses with cataracts. The authors put forward a hypothesis on the cataractogenic effect of PAH on the basis of its interference with lens metabolism and the subsequent production and release of free-radicals.     

DNA index by flow cytometric analysis: an additional prognostic factor in advanced ovarian carcinoma without residual disease after primary operation

Prediction of duration of a patient's stay in the ICU after cardiac surgery is difficult. In 652 consecutive adult patients undergoing elective coronary artery bypass graft (CABG) surgery, we analysed prospectively preoperative and immediate postoperative variables thought to influence duration of stay in the ICU. With univariate analysis, we found that age, preoperative left ventricular ejection fraction, bypass time, aortic cross-clamp time, blood transfusions and the number of inotropic agents administered in the immediate postoperative period (for at least 6 h) were significant correlates of duration of stay in the ICU. However, logistic regression analysis showed that the number of inotropes was the most important determinant of stay in the ICU, with an overall prediction accuracy of 94.8%. The main cause of prolonged stay in the ICU (more than 2 days) was low cardiac output syndrome. We conclude that analysis of perioperative variables enhanced our ability to accurately predict duration of stay in the ICU in cardiac surgery patients. The number of inotropic agents administered during the first 6 h after operation was the most important determinant of duration of stay in the ICU.