Search results for "aqueous solution"

Small angle scattering study of poly(methylmethacrylate)-blockpoly(ethylene oxide) block co-polymer in aqueous solution

2005

A combined Small Angle X ray (SAXS) and Neutron (SANS) Scattering study of aqueous solutions of a symmetric block copolymer consisting of poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO) moieties is presented. The polymer forms slightly polydisperse spherical micelles in a wide range of concentration (0.03 – 6.7 w/V) and temperature (20°C ≤ T ≤ 65°C). A good description of the SANS data is obtained using a polydisperse core-shell model with a structure factor for a modified hard sphere potential. By increasing the concentration at constant T we observed a decrease of the aggregation number and an increase of solvation of PEO groups in the shell, opposite to what happens by in…

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.

Insights into catanionic vesicles thermal transition by NMR spectroscopy

2012

Oppositely charged ionic surfactants can self-assemble into hollow structures, called catanionic vesicles, where the anionic-cationic surfactant pair assumes a double-tailed zwitterionic attitude. In the present work, multilamellar- to-unilamellar thermal transition of a mixed aqueous system of sodium dodecyl sulphate (SDS) and cetyl trimethyl ammonium bromide (CTAB), with a slight excess of the anionic one, has been investigated by 1H, 2H, 14N NMR spectra and 23Na transverse relaxation measurements. It has been inferred that an increase of the temperature enhances the SDS counterion dissociation, which can be considered as one of the driving forces of the mentioned transition. Moreover, in…

Application of the negative staining technique to both aqueous and organic solvent solutions of polymer particles

1999

Abstract Transmission electron microscopy (TEM) imaging of several different polymers in aqueous and organic solutions using the negative staining technique is demonstrated, to emphasise the possibilities of this specimen preparation technique for polymer science. Negative stains can readily be prepared in both water and organic solvents (e.g. dimethyl formamide (DMF), dimethyl sulfoxide (DMSO) and tetrahydrofurane (THF)). Polymer particle size, size distribution and shape seen in negative stain correlates well with those of unstained materials. The particle surface and smaller particles (e.g. 10–20 nm) are more clearly defined in the presence of a negative stain. The inherent problems of s…

Fractionated precipitation of acid macropolyanions by dialysis, a simple method for the estimation of DNA in complex biological samples.

1976

Abstract After efficient extraction by para-aminosalicylate, (hopping, grinding and eventual sonication, the macropolyanions are transformed into their cetyltrimethylammonium salts. These have differing solubilities, strongly depending on ionic strength. The cationic detergent-macropolyanionic salts are solubilized by high salt concentration. Salt is then dialysed out, rendering the polyanions highly insoluble in a sequential fashion. The insolubilized components are determined quantitatively by monitoring turbidity, which in case of DNA is strictly proportionate to its concentration. This relation is not affected by other components. This makes DNA determination possible even in crude aque…

Oxygen atom transfer catalysis by dioxidomolybdenum(VI) complexes of pyridyl aminophenolate ligands

2021

Abstract A series of new cationic dioxidomolybdenum(VI) complexes [MoO2(Ln)]PF6 (2–5) with the tripodal tetradentate pyridyl aminophenolate ligands HL2-HL5 have been synthesized and characterized. Ligands HL2-HL4 carry substituents in the 4-position of the phenolate ring, viz. Cl, Br and NO2, respectively, whereas the ligand HL5, N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N,N-bis(2-pyridylmethyl)amine, is a derivative of 3,5-di-tert-butylsalicylaldehyde. X-ray crystal structures of complexes 2, 3 and 5 reveal that they have a distorted octahedral geometry with the bonding parameters around the metal centres being practically similar. Stoichiometric oxygen atom transfer (OAT) properties of 5 with…

High oxidation state aqueous organometallics. Formation and structure of an oxo-centred Cp*MoV trinuclear cation by chemical reduction of Cp*2Mo2O5

2002

International audience; Reduction of Cp*2Mo2O5 by zinc/CF3CO2H in MeOH–H2O yields a salt which is composed of [Cp*3Mo3O4(O2CCF3)3]+ and [Zn2(O2CCF3)6]2− ions after crystallisation from THF–Et2O.

Iron(II) Complexes with Scorpiand-Like Macrocyclic Polyamines: Kinetico-Mechanistic Aspects of Complex Formation and Oxidative Dehydrogenation of Coo…

2017

The Fe(II) coordination chemistry of a pyridinophane tren-derived scorpiand type ligand containing a pyridine ring in the pendant arm is explored by potentiometry, X-ray, NMR, and kinetics methods. Equilibrium studies in water show the formation of a stable [FeL]2+ complex that converts to monoprotonated and monohydroxylated species when the pH is changed. A [Fe(H–2L)]2+ complex containing an hexacoordinated dehydrogenated ligand has been isolated, and its crystal structure shows the formation of an imine bond involving the aliphatic nitrogen of the pendant arm. This complex is low spin Fe(II) both in the solid state and in solution, as revealed by the Fe–N bond lengths and by the NMR spect…

2020

The pH-responsive nature of two self-assembled NDI-peptide amphiphile conjugates is reported. The diethoxy substituted NDI showed a pH-dependent assembly behaviour, as expected. In contrast, the isopropylamino- and ethoxy-substituted NDI based supramolecular polymer was stable at acidic and basic aqueous conditions. This finding highlights how subtle changes in the molecular design of π-stacked chromophore-peptide conjugates have a drastic impact on their equilibrium structure and ultimately functional properties.

The Catalytic Effect of Fluoroalcohol Mixtures Depends on Domain Formation

2017

In the present contribution, we investigated catalytically active mixtures of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and aqueous H2O2 by molecular dynamics simulations. It is clearly observable that the HFIP molecule strongly binds to the H2O2, which is necessary for the desired catalytic reaction to occur. Upon the addition of the substrate cyclooctene to the solution, this interaction is enhanced, which suggests that the catalytic activity is increased by the presence of the hydrocarbon. We could clearly observe the microheterogeneous structure of the mixture, which is the result of the separation of the hydroxyl groups, water, and H2O2 from the fluorinated alkyl moiety in the form of l…