Search results for "Organo"
showing 10 items of 1460 documents
First Evidence of Proline Acting as a Bifunctional Catalyst in the Baylis–Hillman Reaction Between Alkyl Vinyl Ketones and Aryl Aldehydes
2008
Proline in the presence of sodium hydrogen carbonate has been found to be an effective catalyst for the Baylis–Hillman reaction between methyl or ethyl vinyl ketone and aryl aldehydes. Screening of several amine catalysts showed that an ionizable carboxylic function directly linked to the secondary amine catalyst plays an important role in the synthesis of the desired product in good yield. The data obtained has allowed us to suggest, for the first time, that proline, sarcosine, pipecolinic acid and homoproline may act as bifunctional catalysts via a bicyclic enaminolactone species as intermediate. Quantum-mechanical calculations (PM3/COSMO and ab initio 3-21G/COSMO) support this mechanism …
ChemInform Abstract: Catalytic Enantioselective Addition of Terminal Alkynes to Aromatic Aldehydes Using Zinc-Hydroxyamide Complexes.
2010
A mandelamide ligand, derived from (S)-mandelic acid and (S)-phenylethanamine, catalyzes the addition of aryl-, alkyl- and silyl-alkynylzinc reagents to aromatic and heteroaromatic aldehydes with good yields and good to high enantioselectivities.
Reversible Solvent‐Exchange‐Driven Transformations in Multifunctional Coordination Polymers Based on Copper‐Containing Organosulfur Ligands
2014
The preparation by simple direct synthesis of a series of coordination polymers based on copper with chloride or bromide and dipyrimidinedisulfide is reported. The structural characterisations of these compounds reveal a rich structural variety as a result of the number of coordination modes available to the organosulfur ligand, in combination with the bridging capabilities of the halides. Interestingly, some of the polymers displayed fully reversible solvent exchange/removal crystal-to-crystal 2D to 0D and 2D to 2D transformations. These materials show multifunctional electronic properties. Thus, some of them are semiconductors and present weak antiferromagnetic interactions, and the CuI/C…
Fluidity of liposome membranes doped with organic tin compounds: ESR study.
2008
The kinetics of change in the fluidity of liposome membranes, obtained in the process of sonication of Egg Yolk Lecithin (EYL), with the admixture of organic tin compounds, was investigated. Five compounds were selected for the research: three differed in the length of hydrocarbon chains, (CH(3))(4)Sn, (C(2)H(5))(4)Sn, and (C(3)H(7))(3)SnCl, whereas two differed in the number of aromatic rings, (C(6)H(5))(2)SnCl(2) and (C(6)H(5))(3)SnCl. The concentration of the compounds in proportion to EYL was 2 mol-%. Electron Spin (paramagnetic) Resonance (ESR) was applied using two spin probes TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and 16-DOXYL-stearic acid methyl ester (2-ethyl-2-(15-methoxy-15…
Time-resolved rheology as a tool to monitor the progress of polymer degradation in the melt state – Part II: Thermal and thermo-oxidative degradation…
2015
Abstract Thermal and thermo-oxidative degradation of nanocomposites based on polyamide 11 (PA11) and organo-modified clay (Cloisite® 30B) are studied in the melt state (T = 215 °C) via time-resolved mechanical spectroscopy (TRMS). The goal is assessing the potentiality of rheological analysis for studying polymer degradation in complex systems such as polymer nanocomposites, whose rheological response stems from the combination of the contributions of polymer and nanoparticles. We prove that a thorough analysis grounded on TRMS allows to isolate the effect of degradation of the polymer matrix, whose progress can be hence profitably monitored. Essentially the same degradation mechanisms as i…
Langmuir–Blodgett films based on inorganic molecular complexes with magnetic or optical properties
2005
Langmuir and Langmuir–Blodgett (LB) films of a great variety of molecular metal complexes with interesting magnetic or optical properties have been prepared in the last few years. Some of the results obtained by our group and others are summarized in this article. (i) LB films of polyoxometalates (POM) were first prepared taking advantage of the adsorption properties of these cluster anions along a positively charged monolayer of an organic surfactant spread in water. A correct choice of the POM allowed the preparation of LB films with magnetic, electrochromic, or luminescent properties. Besides this semiamphiphilic method, two new methods to prepare LB films of POMs have been developed by …
Metabolomics approach to studying minimally processed peach (Prunus persica) fruit
2012
Fresh-cut fruit products for both retail and food service applications have increasingly appeared in the market place in recent years. Among different fruit types, peaches can be used and are highly appreciated as fresh-cut product although their commercial success is limited due to their short shelf-life and the quick onset of wounding-related physiological reactions. In this work we analyzed the technological and physiological changes induced by fresh-cut preparation in three different types of peach cultivars: 'Fayette' (melting), 'Wilhelmina' (non-melting) and 'Ghiaccio3' (stony hard). We performed a metabolite targeting profiling to focus on the changes in organic acid levels, importan…
On the interlayer spacing collapse of Cloisite (R) 30B organoclay
2011
Abstract When used as a nanofiller for the preparation of polymer/clay nanocomposites (PCNs), Cloisite® 30B (30B) often undergoes a d-spacing collapse, as demonstrated by a shift to wider angles of the XRD basal reflection. Such collapse has been variously attributed to organoclay contamination or, more often, to thermal degradation of the organic modifier with expulsion of the volatile products from the galleries. In this work, several PCNs loaded with 30B have been prepared by melt compounding, using different polymer matrices, and have subsequently been subjected to dissolution in appropriate solvents followed by precipitation in excess non-solvent and room temperature drying. An XRD ana…
Effect of an organoclay on the photochemical transformations of a PBAT/PLA blend and morpho-chemical features of crosslinked networks
2021
Abstract In this work, we report the effect of an organoclay on the photochemical weathering of nanocomposites based on a poly(butylene adipate-co-terephthalate) (PBAT)/poly(lactic acid) (PLA) blend. The evolution of physicochemical properties was monitored by integrating spectroscopic, mechanical, and morphological analyses. A robust relationship was found between the molecular transformations of the polymer macromolecules and the morpho-mechanical properties of irradiated films. Moreover, the analysis of insoluble fractions extracted from nanocomposites pointed out that free-standing, porous structures, displaying an unprecedented thickness as great as 100 µm, were formed, thus unambiguou…
Mössbauer Spectroscopy and Organotin Polymers
2008
Mössbauer spectroscopy allows the structural analysis of certain metal atoms situated in complex structures. Briefly, Mössbauer spectroscopy is a resonant absorption spectroscopy that is observed best in isotopes having long lived, low-lying excited nuclear energy states. The largest recoil-free resonant cross-section is found for 57Fe. Currently, Mössbauer spectroscopy is being used on Mars to identify iron compounds that are present in the Martian landscape. There are over 20,000 entries in SciFinder for Mössbauer spectroscopy, of which the two largest entries are for iron and tin containing compounds. There are only about 100 entries for organotin compounds, with only a handful related t…