Salting coefficient of triethanolamine in major seawater salts

Activity coefficient of triethanolamine (TEA) in major seawater salts (NaCl, KCl, CaCl2 and MgCl2) has been determinated using the distribution method. It increases slowly in KCl, remains almost constant in NaCl and decreases in the other salts. Pitzer model has been used to fit the experimental data and the corresponding interaction parameters have been determinated

Potentiometric characterisation of cyclodextrin inclusion complexes of local anaesthetics

The complexation of several local anaesthetics by β and γ-cyclodextrins was studied by potentiometry with glass electrode. Tetracaine and dibucaine complexation constants were determined at 25°C in the presence of 0.1 M of NaCl. It was found that prilocaine and lidocaine complexes cannot be detected.Ministerio de Educacion y Ciencia; CTQ2005-07428/BQUMinisterio de Ciencia e Innovacion; CTQ2008-04429/BQ

A further study of acetylacetone nitrosation

The nitrosation of acetylacetone (AcAc) has been revised in an aqueous acid medium of perchloric acid and buffers of mono-, di-, or tri-chloroacetic acid. The results show that in the presence of buffers, under conditions of [nit] ≪ [AcAc] (nit = sodium nitrite) the reaction cannot be studied by UV-Vis spectroscopy, contrary to the recently published paper by García-Rio et al. (J. Org. Chem., 2008, 73, 8198). The present study also corroborates the previously published mechanism of AcAc nitrosation, where no base-catalysis was observed. Contrarily, the low effect of buffers was attributed to the formation of nitrosyl chloro-, dichloro- or trichloro-acetate salts that are new nitrosating agents.Ministerio de Ciencia e Innovación; CTQ2008-04429/BQ

Micellar effects on aromatic esters hydrolysis

The alkaline hydrolysis of two aromatic esters, 2-naphthyl acetate (2NA) and phenyl acetate (PhA) has been tackled in this work. The reaction has been followed in water and in the presence of cationic surfactants with different chain lengths: dodecyltrimethylammonium bromide (DTABr), tetradecyltrimethylammonium bromide (TTABr), and hexadecyltrimethylammonium bromide (CTABr) and the corresponding hydroxides (DTAOH, TTAOH and CTAOH) at 25. °C. The pseudo-first order rate constants increase with surfactant concentration in the presence of surfactants with reactive counter-ions, while a maximum is reached for bromide surfactants with a constant concentration of hydroxyl ion. Both, the association equilibrium constants of 2NA and PhA with micelles and the rate constant in this medium were determined. The degree of counter-ion association to micelles was considered as a variable parameter, using the adsorption equilibrium of bromide and hydroxide ions to the micelle.Ministerio de Educación y Ciencia; CTQ2005-07428/BQUMinisterio de Ciencia e Innovación; CTQ2008-04429/BQ

Fluorescence study of tetracaine–cyclodextrin inclusion complexes

The steady-state fluorescence emission from the local anaesthetic tetracaine (TCA) in water-solvent mixtures and in the presence of α-, β- and γ-cyclodextrin (CD) was investigated at various pH values. Emission was observed from the locally and the intramolecular charge transfer excited states. The TCA-CD system was found to be characterised by 1:1 associate in every case. The association constants of each complex were determined.Ministerio de Educación y Ciencia; CTQ2005-07428/BQUMinisterio de Ciencia e Innovación; CTQ2008-04429/BQ

Iron(III) complexation by Vanchrobactin, a siderophore of the bacterial fish pathogen Vibrio anguillarum

The bacterial fish pathogen Vibrio anguillarum serotype O2 strain RV22 produces the mono catecholate siderophore Vanchrobactin (Vb) under conditions of iron deficiency. Vb contains two potential bidentate coordination sites: catecholate and salicylate groups. The iron(iii) coordination properties of Vb is investigated in aqueous solutions using spectrophotometric and potentiometric methods. The stepwise equilibrium constants (logK) for successive addition of Vb dianion to a ferric ion are 19.9; 13.3, and 9.5, respectively, for an overall association constant of 42.7. Based on the previous results, we estimated the equilibrium concentration of free iron(iii) under physiological conditions for pH 7.4 solution containing 10-6 M total iron and 10-5 M total Vb as pFe = 20 (=-log[Fe3+]). The Vb model compounds catechol (Cat) and 2,4-dihydroxy-N-(2-hydroxyethyl)benzamide (Dhb) have also been examined, and the obtained results show that the interaction of the whole system of Vb that contains the ferric-chelating groups of both Dhb and Cat, is synergically greater than the separate parts; i.e. Vb is the best chelating agent either in acid or basic media. In summary, bacteria employing Vb-mediated iron transport thus are able to compete effectively for iron with other microorganisms within which they live.Ministerio de Educación y Ciencia; CTQ2008-04429Ministerio de Educación y Ciencia; CTQ2005-00793Galicia. Consellería de Economía e Industria; 10PXIB103157P

Kinetic and Equilibrium Study of the Reaction of Nitroprusside and Hydroxide Ions: Influence of Ionic Strength Using Pitzer Model

[Abstract] A kinetic and equilibrium study of the addition reaction of hydroxide ions to nitroprusside has been carried out in this paper. Rate and equilibrium constants at different salt concentrations (up to 4 mol/kg) were obtained and the influence of ionic strength was studied by means of Pitzer equations. This model is of special interest because it is able to explain the experimental behaviour at high ionic strength, when Debye-Huckel limiting law is no longer valid

Equilibrium constants of triethanolamine in major seawater salts

Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl2 or CaCl2), with binary mixtures of MgCl2 and CaCl2, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl2, while it is increased by the other electrolytes used in this work

The salting coefficient and size of alkylamines in saline media at different temperatures: estimation from Pitzer equations and the mean spherical approximation

The renewed theoretical interest in the proton transfer associated to the amino group together with the scarcity of acid-base studies of amines in moderate to concentrated saline media focussed our attention on the study of the basicities of some alkylamines, namely monomethyl, dimethyl and trimethylamine, in aqueous saline solutions of KCl at various temperatures. A non-conventional analysis of stoichiometric equilibrium constants versus ionic strength data is carried out. On one hand, Pitzer’s model is easily applied to calculate the salting coefficient and the thermodynamic equilibrium constant of the alkylamines. On the other hand, the mean spherical approximation has the advantage over the Debye–Hückel based theories that it can account for effects produced by species of different sizes. Here, it is applied to predict the dependence of the salting behavior on the size of the alkylamines.Xunta de Galicia; XUGA 10310B9