Search results for "surface"

Structure and Shear Response of Janus Colloid–Polymer Mixtures in Solution

2020

We investigate the structure and rheological properties of dilute colloid-polymer mixtures at rest and under shear via molecular simulations that take into account hydrodynamic interactions. Mixtures of amphiphilic Janus colloids (JCs) and hydrophobic/amphiphilic polymers are considered for various solvent qualities and polymer concentrations. Free polymers, small polymer droplets, and hybrid aggregates coexist in mixtures with slightly hydrophobic homopolymers. As the solvent quality worsens, all polymers aggregate into small droplets, covered and stabilized by the JCs. In mixtures with amphiphilic polymers, we observe the coexistence of free polymers, purely polymeric micelles, and hybrid…

A synthetic hexapeptide (Argireline) with antiwrinkle activity

2008

Botulinum neurotoxins (BoNTs) represent a revolution in cosmetic science because of their remarkable and long-lasting antiwrinkle activity. However, their high neurotoxicity seriously limits their use. Thus, there is a need to design and validate non-toxic molecules that mimic the action of BoNTs. The hexapeptide Ac-EEMQRR-NH2 (coined Argireline) was identified as a result of a rational design programme. Noteworthy, skin topography analysis of an oil/water (O/W) emulsion containing 10% of the hexapeptide on healthy women volunteers reduced wrinkle depth up to 30% upon 30 days treatment. Analysis of the mechanism of action showed that Argireline significantly inhibited neurotransmitter relea…

Characterization of β-B-Agostic Isomers in Zirconocene Amidoborane Complexes

2009

The reaction of Cp(x)(2)ZrCl(2) (Cp(x) = Cp, Cp*) with ammonia borane in presence of n-butyllithium yielded Cp(2)Zr(Cl)NH(2)BH(3) and Cp(x)(2)Zr(H)NH(2)BH(3). These derivatives are isoelectronic with the ethyl zirconocene chloride and hydride, respectively, and feature a chelating amidoborane ligand coordinating through a Zr-N bond and a Zr-H-B bridge. In solution, each of the complexes consists of an equilibrium mixture of two isomers differing in the orientation of the amidoborane ligand with respect to the Zr-X bond (X = H, Cl), while in the solid state, only one isomer was observed. Such isomers have not been characterized for any metal complexes containing the isoelectronic beta-agosti…

Soil microbial biomass and activity under different agricultural management systems in a semiarid Mediterranean agroecosystem

2010

Abstract A field experiment was carried out in a semiarid agricultural Mediterranean area located at the “El Teularet” experimental field in the Enguera Sierra (Valencia, southeast Spain) to assess the influence of different agricultural management systems on indicators of soil biological quality and activity (microbial biomass C, basal respiration, C mineralization coefficients, metabolic quotient (qCO2), respiratory quotient (RQ: moles CO2 evolved/moles O2 consumed), soluble C and dehydrogenase, urease, protease-BAA, phosphatase and β-glucosidase activities), one year after treatment establishment. The management practices assayed were as follows: application of the herbicides paraquat, g…

Monolayer Properties of Hydrophobic .alpha.-Helical Peptides Having Various End Groups at the Air/Water Interface

1994

Continuum-uniform approach calculations of the solubility of hydrocarbons in water

1993

Abstract The ransfer free energies from gas phase to water for some hydrocarbons are calculated by means of a continuum-uniform model of the solvent. For the calculation of the cavitation energy a model based on the surface tension is proposed. The calculated values are compared with the experimental free energies obtained with and without a corrective factor that accounts for the difference in the solute—solvent sizes. Good agreement between the theoretical free energies and the corrected experimental data is obtained. Our calculations seem to show that the hydrophobic effect is directly related to the molecular surface area.

Preparation and characterisation of Na 2 S and ZnSO 4 nanoparticles in water/sodium bis(2-ethylhexyl)sulphosuccinate/ n -heptane microemulsions

2001

The preparation procedure for nanoparticles of the water-soluble salts Na2S and ZnSO4, two commonly used reagents to synthesise ZnS nanoparticles, by evaporation of volatile components of salt-containing water-in-oil microemulsions is described. In suitable conditions, the evaporation leads to the formation of dry salt–surfactant composites and to the formation of Na2S or ZnSO4 nanoparticles. It was found that the salt–surfactant composites can be totally redissolved in a dry apolar organic solvent allowing the formation of virtually water-free solutions containing a considerable amount of the water-soluble salts. The presence of nanoparticles in these solutions and in the composites has be…

Photochemical Functionalization of Allyl Benzoates by C-H Insertion

2013

The photoreactivity of allyl benzoates, containing an electron-rich double bond, has been explored by irradiation at 305 nm in different solvents. Solvent addition products arising from an insertion of the alpha H–C bonds of THF, dioxane, and i-PrOH to the allylic double bond was realized. The observed reactivity depended on reaction conditions and substitution pattern of the substrate. A DFT study on this unusual reaction was performed allowing the formulation of two mechanistic pathways.

Evaluation and comparison of tailor-made stationary phases based on spherical silica-based beads for capillary electrochromatography via peptide sepa…

2004

Small cyclic peptides have been employed to elucidate the performance of novel sorbents as stationary phases in capillary electrochromatography (CEC). In this paper chain length dependencies for ordinary liquid chromatographic sorbents are reported together with findings acquired on beads specifically designed to suit CEC. The latter, tailor-made, spherical, porous silica exhibits a distinguished surface modification to meet the criteria anticipated to enhance performance profiles in CEC. With well-characterised peptides resembling the analytes, probing of the CEC system in a systematic manner (predominantly via the organic modifier content of the background electrolyte (BE)) reveals insigh…

Comparison of an indirect format ELISA on modified graphite and polystyrene surfaces against triazines.

2006

An indirect format enzyme-linked immuno-sorbent assay (ELISA) on graphite rods (Ø 0.8 mm x 20 mm) and, for comparison, on microtiter plates has been developed against terbuthylazine. For this purpose, a series of 2-aminoalkyl-4-chloro-6-terbuthyl-s-triazine-2,6- diamine ELISA haptens with alkyl spacer lengths of 2, 4, 6, and 8 CH2 groups has been synthesized. The graphite rods or the microtiter plates were covered by a polymerized glutaraldehyde network, and the ELISA haptens have been coupled by imino coupling to the free aldehyde groups of that network. ε-Aminocaproic acid has been used as an agent to block unspecific binding sites. The ELISA was run in a competitive mode, where the immob…