Search results for "SOLVENT"

A comparative study between cosolvent and cononsolvent ternary polymer systems through the preferential adsorption coefficient

1993

Sorption equilibrium of polystyrene and poly (dimethyl siloxane) in mixed solvents has been monitored by means of the preferential adsorption coefficient experimentally determined from intensity light scattering measurements. The pairs of solvents used to dissolve each polymer sample have been selected for the purpose to perform cosolvent and cononsolvent ternary polymer systems. Flory-Huggins formalism including ternary interactions has been used to predict the sorption equilibrium for the cosolvent system and, for the first time, for cononsolvent ones. Moreover, the proportionality between binary and ternary interactions, recognized by Pouchly, is also corroborated for both ternary polyme…

Polymer brushes in solvents of variable quality: Molecular dynamics simulations using explicit solvent

2007

The structure and thermodynamic properties of a system of end-grafted flexible polymer chains grafted to a flat substrate and exposed to a solvent of variable quality are studied by molecular dynamics methods. The macromolecules are described by a coarse-grained bead-spring model, and the solvent molecules by pointlike particles, assuming Lennard-Jones-type interactions between pairs of monomers (epsilon(pp)), solvent molecules (epsilon(ss)), and solvent monomer (epsilon(ps)), respectively. Varying the grafting density sigma(g) and some of these energy parameters, we obtain density profiles of solvent particles and monomers, study structural properties of the chain (gyration radius componen…

Photooxidations of Alkenes in Fluorinated Constrained Media:  Fluoro-organically Modified NaY as Improved Reactors for Singlet Oxygen “Ene” Reactions

2007

Creating a stationary fluorinated environment inside the zeolite cavity can increase the reactivity observed for intrazeolite photooxidation of alkenes. Exchanging the zeolite with fluorinated organic cations is a much more effective strategy than simply using a fluorinated solvent for slurry irradiations. Use of cations containing C-F bonds is also more efficient than use of deuterated cations for creation of a singlet oxygen friendly environment where the quenching processes are slowed down. Doping the zeolite with fluoro-organic cation 4 resulted in an increase in the singlet oxygen lifetime to 12 micros.

Enhancing reactivity of carbonyl compounds via hydrogen-bond formation. A DFT study of the hetero-Diels-Alder reaction between butadiene derivative a…

2003

To examine how hydrogen-bond (HB) formation involving chloroform solvent molecules influences the chemical reactivity of ketones, the hetero-Diels-Alder reaction of N,N-dimethyl-1-amino-3-methoxy-1,3-butadiene and acetone has been studied by using density functional theory (DFT) at the B3LYP/6-31G level. The effects of the chloroform on the activation energies have been modeled by means of discrete-continuum models. In the gas phase, the formation of specific HB between acetone and one and two chloroform molecules decreases the activation barriers from 19.3 to 13.6 and 8.5 kcal/mol, respectively. Inclusion of solvent effects by means of combined discrete and polarizable continuum models yie…

Enhanced Skin Permeation of Estradiol by Dimethyl Sulfoxide Containing Transdermal Patches.

2021

Dimethyl sulfoxide is a well-known and widely used dermal penetration enhancer. Its incorporation in transdermal patches would be highly desirable

Gold Redox Catalytic Cycles for the Oxidative Coupling of Alkynes

2011

[EN] Au(I)/Au(III) catalytic cycles are catalytically competent to perform the oxidative coupling of alkynes in the homogeneous phase at room temperature and without any protecting atmosphere. Selectfluor as oxidant, wet acetonitrile as solvent, and sodium carbonate as base are the reagents of choice. Both aromatic and alkyl alkynes can be coupled, and mechanistic studies reveal that at least two gold species having different oxidation states are implicated in the key step of the coupling.

1985

Viscosity measurements were carried out as a function of pressure and temperature with solutions of 8 wt.-% PVC (Mw ≈ 75 000) in ten thermodynamically good solvents by means of a Searle-type viscometer. A rollingxyhball viscometer was used for the investigation of the pure solvents. In all cases the viscosity increases in a more or less exponential manner when the pressure is raised. The viscosity ratio f1000 = η1000 bar/η1bar can be varied by the choice of the solvent from ca. 2 (tetrahydrofuran) to 3,0 (cyclohexanone) at 40°C. For a constant temperature of 40°C, the volumes of activation for the viscous flow of the solutions, V≠, or f1000 exceed that of the pure solvent, by typically 25%.…

Use of reversed-phase C18 Sep-Pak cartridges for the purification and concentration of sepiapterin and other pteridines

1985

Abstract Several pteridines have been tested for their ability to bind to C 18 Sep-Pak. Riboflavin, sepiapterin, deoxysepiapterin, 6-acetyl-7,8-dihydropterin, 6-acetyldihydrohomopterin and 3′-hydroxysepiapterin were strongly retained and all but 6-acetyldihydrohomopterin quantitatively recovered upon elution with 2 ml of methanol. The effect of the concentration and volume of the sample, pH and salt concentration on the retention of sepiapterin have been studied. The procedure was very useful for the purification, desalting, solvent exchange and concentration of pteridines having high affinity for the cartridge. C 18 Sep-Pak has been applied succesfully to sample clean-up prior to high-perf…

Solvent-free ruthenium-catalysed triflate coupling as a convenient method for selective azole-o-C-H monoarylation.

2019

Metal-catalysed ortho-directed C–H functionalization usually faces selectivity issues in the competition between mono- and disubstitution processes. We report herein the ruthenium-catalysed N-directed C–H monoarylation of arylpyrazoles with a selectivity of up to 96% or that generally reaches values above 80%. This selectivity is an effect of solvent-free conditions associated with sulfonate reagents, in the absence of frequently used acidic additives.

Solvent-Free Synthesis of a Pillared Three-Dimensional Coordination Polymer with Magnetic Ordering

2015

A new magnetic coordination polymer, [Fe(bipy)(im)2] (bipy = 4,4-bipyridine and im = imidazole), has been synthesized in a solvent-free reaction. Structural analysis reveals a pillared 3D coordination polymer composed by neutral layers, formed by iron(II) and imidazolate linkers, interconnected by bipy ligands which serve as pillars. Magnetic measurements show that the material magnetically orders at low temperatures (Tc = 14.5 K) as a weak ferromagnet, likely due to a spin canting.