Search results for "solvation"
showing 10 items of 157 documents
Anatase nanoparticles boundaries resulting from titanium tetrachloride hydrolysis
2017
An important factor that governs solar energy transformation into electrical or chemical energy, when using nanoparticles-based devices, is the spatial location of traps limiting electron transport. Evidences have been presented indicating that the electron diffusion is strongly influenced by nanoparticle boundaries, whose characteristics depend on the particles preparation. In the present work we have studied the role of hydrated excess proton structures in the formation of anatase nanoparticles boundaries in samples prepared by TiCl4 hydrolysis at low temperature and strong acidic conditions. The samples, constituted by anatase nanocrystals but, mainly, by amorphous titania, are studied b…
NMR Spectroscopic Evidence for the Intermediacy of XeF3− in XeF2/F− Exchange, Attempted Syntheses and Thermochemistry of XeF3− Salts, and Theoretical…
2010
The existence of the trifluoroxenate(II) anion, XeF(3)(-), had been postulated in a prior NMR study of the exchange between fluoride ion and XeF(2) in CH(3)CN solution. The enthalpy of activation for this exchange, ΔH(⧧), has now been determined by use of single selective inversion (19)F NMR spectroscopy to be 74.1 ± 5.0 kJ mol(-1) (0.18 M) and 56.9 ± 6.7 kJ mol(-1) (0.36 M) for equimolar amounts of [N(CH(3))(4)][F] and XeF(2) in CH(3)CN solvent. Although the XeF(3)(-) anion has been observed in the gas phase, attempts to prepare the Cs(+) and N(CH(3))(4)(+) salts of XeF(3)(-) have been unsuccessful, and are attributed to the low fluoride ion affinity of XeF(2) and fluoride ion solvation in…
Supramolecular interactions of hexacyanocobaltate(III) with polyamine receptors containing a terminal anthracene sensor
2003
Abstract The fluorescence emission properties of a series of chemosensors containing a polyamine receptor bearing an anthracene signaling unit were studied. The fluorescence emission intensity is dependent on the protonation degree of the receptor, the fully protonated form exhibiting the highest emission intensity. By removing protons from the nitrogens a quenching effect can be observed, due to an electron-transfer from the amine to the excited fluorophore. The rate constant of the quenching process is exponentially dependent on the distance of the nitrogen from which the electron is transferred (β=0.6 A−1). The ability of the chemosensors for signaling anions was tested through the model…
Theoretical electronic spectra of 2-aminopurine in vapor and in water
2006
The accurate quantum chemical CASSCF and CASPT2 methods combined with a Monte Carlo procedure to mimic solvation effects have been used in the calculation of the spectroscopic properties of two tautomers of 2-aminopurine (2AP). Absorption and emission spectra have been simulated both in vacuum and in aqueous environment. State and transition energies and properties have been obtained with high accuracy, leading to the assignment of the most important spectroscopic features. The lowest-lying 1 (,*) ( 1 La) state has been determined as responsible for the first band in the absorption spectrum and also for the strong fluorescence observed for the system in water. The combined approach used in …
Estimation of free energies of anion transfer from solid-state electrochemistry of alkynyl-based Au(I) dinuclear and Au(I)–Cu(I) cluster complexes co…
2011
A method is presented to determine the free energy for anion transfer between two solvents. This is based on solid-state electrochemistry of alkynyl-based dinuclear Au(I) complexes (AuC2R)2PPh2C6H4PPh2 (L1: R=Fc; L2: R=C6H4Fc) and heterometallic Au(I)–Cu(I) [{Au3Cu2 (C2R)6}Au3(PPh2C6H4PPh2)3](PF6)2 (L3: R=Fc; L4: R=C6H4Fc) complexes. These compounds exhibit a reversible ferrocenyl-centred solid-state oxidation processes involving anion insertion in contact with aqueous, MeOH and MeCN electrolytes. Voltammetric data can be used for a direct measurement of the free energy of ion transfer using midpeak potentials in solutions of suitable salts in the solvents separately or in mixtures of the s…
Rheological study and thermodynamic analysis of the binary system (water/ethanol): Influence of concentration
2004
Water is the most widely used solvent in the chemical and pharmaceutical industry, since it is the most physiological and best tolerated excipient. However, in some cases water cannot be used as a solvent because the active substance or solute is insoluble or only slightly soluble in water. For this and other reasons, nonwater solvents may be used possessing the common characteristic of being soluble or mixable in water; as a result, such solvents can be used to prepare binary or tertiary mixtures, etc., with different purposes such as increasing water solubility, or modifying the viscosity or absorption of the dissolved substance, for example. Ethanol, along with other alcohols either alon…
Origin of peak asymmetry and the effect of temperature on solute retention in enantiomer separations on imprinted chiral stationary phases
1995
Abstract In enantiomer separations of d - and l -phenylalanine anlilide ( d,l -PA) on l -PA-imprinted chiral stationary phases (CSPs), the use of an aqueous buffer-organic solvent mixture as mobile phase resulted in improved column efficiency compared with what has previously been observed using mobile phases containing acetic acid as modifier. The dependence of the chromatographic parameters on flow-rate and sample load was studied. A strong dependence of the asymmetry factor ( A s ) of the l -form on sample load and a weak dependence on flow-rate indicate that the non-linear adsorption isotherm is the main reason for the broad peaks observed in this system. Depending on the method used fo…
Viscous Synergy of Pure Monoalcohol Mixtures in Water and Its Relation to Concentration
2004
Pure or aqueous alcohols are the solvents most widely used in industry, including in the manufacture of pharmaceuticals and cosmetic products. However, water–alcohol mixtures generate hydrogen-bonded molecular associations that lead to volume contraction and an increase in viscosity greater than that expected in the absence of any interaction between the components of the mixture. This phenomenon is referred to as viscous synergy. The present study investigates viscous synergy in monoalcohol systems containing up to five carbon atoms, since beyond hexanol all alcohols are practically insoluble in water. In all cases, determinations were made of the proportions of water and alcohol for which…
Physical origin of Na+/Cl− selectivity of tight junctions between epithelial cells. Nonlocal electrostatic approach
2020
Abstract Tight junctions (TJs) of epithelial cells play a key role in regulation of the ion exchange between NaCl solutions separated by the layer of these cells. Their functioning is based on a strong difference in the permeabilities of these channels for Na+ and Cl− ion migrational fluxes owing to specific properties of the protein network inside TJs. It has been assumed in this study that this phenomenon originates from combination of two effects related to this specific TJ protein (claudin) which segments are partially located inside the TJ space. First, their ionogenic groups create a negative charge distributed inside TJs, thus inducing a difference between the Na+ and Cl− concentrati…
Ionic partition diagram of tetraphenylporphyrin at the water|1,2-dichloroethane interface
2011
diagram of 5,10,15,20-tetraphenyl-21H,23H-porphine (H2TPP) at the water|1,2-dichloroethane interface using a simple Born solvation model. This zone diagram shows under which form this porphyrin is present, i.e. neutral, monoprotonated or diprotonated, and in which phase i.e. either in the aqueous or the organic phase as a function of the aqueous pH and the interface polarisation that can be controlled externally or by the distribution of supporting electrolytes. This diagram explains why the monoprotonated form has been difficult to observe when doing biphasic pH titrations