Search results for "aqueous solution"
showing 10 items of 1610 documents
Encapsulation of hydrophilic and lipophilized catechin into nanoparticles through emulsion electrospraying
2017
In this work, we investigated the potential of emulsion electrospraying that contained bacterial cellulose and proteins for the encapsulation of epigallocatechin gallate (EGCG). Specifically, two different catechins, hydrophilic (H-EGCG) or lipophilized (L-EGCG), were encapsulated either on the aqueous or the oily phase of the emulsions in order to compare the antioxidants’ stability. Emulsion properties in terms of stability, droplet size, bulk and interfacial viscosity were studied combined with the evaluation of the properties of the produced particles, namely the morphology and size of the particles, the encapsulation efficiency (EE) of catechin and the stability of the EGCG within the …
Synthesis, Characterization, and Catalysis of β3-[(CoIIO4)W11O31(O2)4],10- the First Keggin-Based True Heteropoly Dioxygen (Peroxo) Anion. Spectrosco…
1999
Reactions of hydrogen peroxide with several lacunary polyoxometalates of the 1:11 series, XW11O39m- (X = Co3+, Ga3+, Fe3+, Si4+, and P5+), are reported. Synthetic pathways to new polyoxotungstates incorporating dioxygen moieties (peroxo and/or superoxo) are developed. The key step involves treating lacunary precursors with H2O2 in strongly buffered aqueous solutions. Upon reaction of H2O2 with α-[Co3+W11O39],9- (a) the central tetrahedral Co3+ is reduced to Co2+ and (b) each of the four unshared oxygens surrounding the vacancy are replaced by a peroxide group, yielding salts of the tetraperoxide anion β3-[(Co2+O4)W11O31(O2)4]10- (1). These results are unequivocally established by a combinat…
A quantum mechanics-molecular mechanics study of dissociative electron transfer : The methylchloride radical anion in aqueous solution
2002
The dissociative electron transfer reaction CH3Cl+e−→CH3•+Cl− in aqueous solution is studied by using a QM/MM method. In this work the quantum subsystem (a methylchloride molecule plus an electron) is described using density functional theory while the solvent (300 water molecules) is described using the TIP3P classical potential. By means of molecular dynamics simulations and the thermodynamic integration technique we obtained the potential of mean force (PMF) for the carbon–chlorine bond dissociation of the neutral and radical anion species. Combining these two free energy curves we found a quadratic dependence of the activation free energy on the reaction free energy in agreement with Ma…
Structure Sensitivity of 2-Methyl-3-butyn-2-ol Hydrogenation on Pd: Computational and Experimental Modeling
2014
In the frame of DFT paradigms, the adsorption of 2-methyl-3-butyn-2-ol (MBY) and 2-methyl-3-buten-2-ol (MBE) on a Pd-30 cluster, including both {100} and {111} faces, was studied along with the pathways involved in the hydrogenation, taking place on plane and low coordination (corner/edge) sites of given MBY/Pd-30 and MBE/Pd-30 surface configurations. The calculated energetics, further validated by gas-phase and water-assisted gas-phase MBY and MBE hydrogenation, performed on well-defined size and shape-controlled Pd nanoparticles supported on SiO2, were able to explain the origin of the structure sensitivity and the high selectivity characterizing the title reaction when occurring in aqueo…
Water and oxoanion encapsulation chemistry in a 1H-pyrazole azacryptand
2019
Anion complexes of the cryptand built with the tripodal amine tris(2-aminoethyl)amine, known as tren, with water and several oxoanions of biological and environmental interest (nitrate, sulfate, phosphate, perchlorate and arsenate) have been crystallized from aqueous solution and resolved with single-crystal X-ray diffraction. All crystals show guest species encapsulated in the interior of the cavity as well as, in some cases, sitting in the grooves defined by the arms of the macrocycle. Hydrogen bonding and electrostatic interactions play a major role in anion binding to the host. The macrocycle is able to encapsulate anions in a wide range of protonation degrees. Solution studies have bee…
Synthesis, solid state and solution studies of cobalt(II) complexes with 2-hydroxyiminopropanoic acid
2013
Abstract This paper describes the synthesis of the Zn(II) complex with H2L = 2-hydroxyiminopropanoic acid. The final structure incorporated two linear dimeric anions with two Zn2+ atoms, which are linked by a carbonate anion into a tetranuclear unit. In each dinuclear unit, the two Zn(II) ions are coordinated by three molecules of the doubly deprotonated ligand in two different coordination modes. This result is confirmed both by X-ray crystallography and by ESI-MS investigations of the crystals dissolved in water. Equilibrium studies of the zinc(II) complexes formed by H2L in aqueous solution based on independent pH-metric titrations and zinc ion-selective electrode (ISE) titrations indica…
Role of Water During Crystallization of Amorphous Cobalt Phosphate Nanoparticles
2016
The transformation of amorphous precursors into crystalline solids and the associated mechanisms are still poorly understood. We illuminate the formation and reactivity of an amorphous cobalt phosphate hydrate precursor and the role of water for its crystallization process. Amorphous cobalt phosphate hydrate nanoparticles (ACP) with diameters of ∼20 nm were prepared in the absence of additives from aqueous solutions at low concentrations and with short reaction times. To avoid the kinetically controlled transformation of metastable ACP into crystalline Co3(PO4)2 × 8 H2O (CPO) its separation must be fast. The crystallinity of ACP could be controlled through the temperature during precipitati…
Die Dissoziationskonstanten von 2,3?-und 2,4?-Dihydroxydiphenylmethanderivaten
1974
The pK-values of the first and second degree of dissociation of 2.3′-dihydroxy-6′-methyl-3.5-dinitro-diphenylmethane, 2.3′-dihydroxy-6′-methyl-5-nitro-diphenylmethane, 2.3′-dihydroxy-5.6′-dimethyl-3-nitro-diphenylmethane, 2.4′-dihydroxy-3′. 5′-dimethyl-3.5-dinitro-diphenylmethane, 2.4′-dihydroxy-3′. 5′-dimethyl-5-nitro-diphenylmethane and 2.4′-dihydroxy-3′.5.5′-trimethyl-3-nitrodiphenylmethane were determined in aqueous solution at 25°C by the spectrophotometric method. The observed pK-values are compared with those of 2-methyl-4.6-dinitro-phenol, 2-methyl-4-nitrophenol, 2.4-dimethyl-6-nitrophenol, 3.4-dimethylphenol and 2.4.6-trimethylphenol which serve as model compounds for the single ph…
A study of dimethyltin(IV)-L-cysteinate in aqueous solution
1988
The in vivo activity of some R2Sn-L-cysteinate complexes (R = Me, Et, n-Bu) against murine P-388 leukaemia has been tested. Only the Et2Sn(IV) complex showed a marginal positive effect. Trigonal bipyramidal tin environments with two carbon (R) atoms and the sulfur atom in the equatorial plane and oxygen (carboxylate) and nitrogen (NH2) in apical positions have been proposed for the solid compexes (R = Me, Et, n-Bu, Ph) on the basis of experimental Mossbauer parameters and infrared (IR) data. Aqueous solutions of the Me2SnL-cysteinate have been studied by IR, 1H NMR and 119Sn Mossbauer spectroscopy (in frozen solution) at different pH values to identify the Me2Sn(IV) species present. At pH >…
Speciation of Organic Matter in Natural Waters-interaction of polyacrylates and polymethacrylates with major cation components of seawater
2004
Abstract The speciation of some high molecular weight polycarboxylates was studied in different ionic media. Polyacrylates here investigated ( W =2.0, 5.1 and 20.0 kDa) form weak species with alkali metal cations ( K =10 2 mol l −1 , t =25 °C, I =0 mol l −1 ) and quite stable complexes with alkaline earth metal cations ( K >10 6 mol l −1 , t =25 °C, I =0 mol l −1 ). Results are reported from experiments performed in a multicomponent electrolyte solution simulating the major composition of seawater (artificial seawater). Protonation constants in this medium are expressed as a polynomial function of S 1/2 ( S =salinity) and the sharp lowering with respect to values obtained in non-interacting…