Search results for " effect"

Characterization of interaction between tricyclic structures containing pharmaceuticals, their models and humic substances.

2011

Their persistence and wide consumption identify pharmaceuticals as “emerging pollutants”. The complexation of pharmaceuticals containing adamantine ring structures and their model substances with humic acids (HA) of different origins was compared using fluorescence spectroscopy as a function of pH, humic acid concentration, ionic strength, and molecular mass of HA. Binding constants between the studied pharmaceuticals and humic acids were calculated. A combination of dynamic and static quenching processes as indicated by nonlinear Stern-Volmer plots and high Kd values were positively correlated with the concentration of carboxyl groups in the studied humic acids. For basic functional group-…

Characterization of a fiber-reinforced new fully aromatic liquid crystalline polymer

1998

A new rigid liquid crystalline polymer that demonstrates good mechanical and thermomechanical properties and acceptable processing temperature has been recently synthesized and characterized. The melting temperature and some thermomechanical properties do not seem, however, suitable for use in some applications at high temperature or in the presence of aggressive fluids. The use of appropriate inorganic fillers can overcome these shortcomings. In this work the new LCP, polymerized in a bench-scale apparatus, and the same sample filled with carbon fibers are characterized. The properties of the carbon fiber filled LCP are compared with those of another filled wholly aromatic commercial LCP,…

Triboelectrification of nanocomposites using identical polymer matrixes with different concentrations of nanoparticle fillers

2021

In this study, we investigate triboelectrification in polymer-based nanocomposites using identical polymer matrixes containing different concentrations of nanoparticles (NPs). The triboelectric surface charge density on polymer layers increased as the difference in nanoparticle filler concentration between the two triboelectric layers escalated, despite the fact that the polymer matrix was the same in both layers. This effect was observed in tests of various polymer types and filler NPs. Our mechanical experiments and finite element analysis simulations confirmed that polymeric triboelectrification is related to the surface viscoelastic deformation that occurs during mechanical contact and …

Risk Assessment of "Other Substances" – L-leucine, L-isoleucine and L-valine, the Branched Chain Amino Acids (BCAA)

2018

Behaviour of modified and unmodified polybutadienes in the semidilute regime

1997

Abstract The association behaviour of polybutadiene modified with 4-phenyl-l,2,4-triazoline-3,5-dione was studied in semidilute solution through static (SLS) and dynamic light scattering (DLS). The results were compared with the unmodified polybutadiene, whose behavior in semidilute solution was also studied as function of the molecular weight. At higher concentrations a small-angle excess scattering in SLS and a slow mode motion in DLS were observed both for modified and unmodified polybutadienes suggesting the presence of large clusters. Increasing the polymer concentration, the mass fraction of the slow motion increases up to values near 1, indicating a proximity to the gel point. For po…

A DFT study of the role of the Lewis acid catalysts in the [3 + 2] cycloaddition reaction of the electrophilic nitrone isomer of methyl glyoxylate ox…

2015

The molecular mechanism and stereoselectivity of the BF3 Lewis acid catalyzed [3 + 2] cycloaddition (32CA) reaction between C-methoxycarbonyl nitrone and cyclopentene has been theoretically studied using DFT methods at the MPWB1K/6-31G(d) computational level. The BF3 catalyst accelerates the 32CA reaction by decreasing the activation energy leading to the formation of the trans cycloadduct as the kinetic product, in agreement with the experimental data. Inclusion of solvent effects slightly increases the activation energy and decreases the exothermic character of the 32CA reaction as a consequence of a better solvation of nitrone than the transition state and the cycloadduct. The use of the…

Density functional theory study of the mechanism of the proline-catalyzed intermolecular aldol reaction

2002

Transition structures associated with the C-C bond-formation step of the proline-catalyzed intermolecular aldol reaction between acetone and isobutyraldehyde have been studies using density functional theory methods at the B3LYP/6-31G** computational level. A continuum model has been selected to represent solvent effects. For this step, which is the stereocontrolling and rate-determining step, four reactive channels corresponding to the syn and anti arrangement of the active methylene of the enamine relative to the carboxylic acid group of l-proline and the re and si attack modes to both faces of the aldehyde carbonyl group have been analyzed. The B3LYP/6-31G** energies are in good agreemen…

Collapse of Linear Polyelectrolyte Chains in a Poor Solvent: When Does a Collapsing Polyelectrolyte Collect its Counterions?

2008

To better understand the collapse of polyions in poor solvent conditions the effective charge and the solvent quality of the hypothetically uncharged polymer backbone need to be known. In the present work this is achieved by utilizing poly-2-vinylpyridine quaternized to 4.3% with ethylbromide. Conductivity and light scattering measurements were utilized to study the polyion collapse in isorefractive solvent/nonsolvent mixtures consisting of 1-propanol and 2-pentanone, respectively, at nearly constant dielectric constant. The solvent quality of the uncharged polyion could be quantified which, for the first time, allowed the experimental investigation of the effect of the electrostatic intera…

Non-classical CH⋯O hydrogen-bond determining the regio- and stereoselectivity in the [3 + 2] cycloaddition reaction of (Z)-C-phenyl-N-methylnitrone w…

2015

The role of the ester groups in the regio- and stereoselectivities of the zw-type [3 + 2] cycloaddition (32CA) reaction of C-phenyl-N-methylnitrone with dimethyl 2-benzylidenecyclopropane-1,1-dicarboxylate (BCPC) has been studied using DFT methods at the MPWB1K/6-31G(d) level. The possible ortho/meta regioisomeric channels and the endo/exo stereoselective approach modes were explored and characterized. Analysis of the relative energies associated with the different reaction pathways indicates that the presence of the two CO2Me groups in the cyclopropane ring has a remarkable effect on selectivities favouring the ortho/endo path, in good agreement with the experimental data. Inclusion of sol…

Size Exclusion Chromatography of Proteins on Improved Bonded Silica Columns

1985

Publisher Summary This chapter discusses the size exclusion chromatography (SEC) of proteins on improved bonded silica columns. Over the past few years, the use of high performance liquid chromatography (HPLC) has been extended to protein chemistry as a powerful separation and isolation technique. A spectrum of variants providing high resolution potential—ion exchange, reversed phase, hydrophobic interaction, affinity, and size exclusion—is available. Of these, SEC is the simplest with respect to method development and equipment design: proteins are separated according to their size in a short and predictable time span under isocratic conditions. The SEC columns are packed with micro-partic…