Julián J. Garrido

RETENTION MECHANISMS OF Cd ON ILLITE

The adsorption of metals by clay minerals is a complex process involving different mechanisms, and is controlled by different variables which can interact. The aim of this work was to study the retention mechanisms of Cd on illite. We obtained Cd adsorption isotherms at constant pH, adsorption edges as a function of pH, adsorption isotherms at 5, 25 and 45°C (pH = 7), and response surfaces of the simultaneous effect of pH, initial concentration, ionic strength, and temperature on the retention of Cd on illite. Below pH 6, adsorption of Cd on illite is via ion exchange with H3O+ and Na+ ions which saturate the exchange sites, the exchange with Na+ being the main mechanism between pH 4.5 and 6.0. For pH values >6, the effect of ionic strength on the amount of Cd2+ retained decreased with pH, being negligible at pH 8; the proton stoichiometry was greater than for pH values <6 and an increase in the temperature favored the retention of Cd. These facts are compatible with a more specific process involving hydrolyzed species, in which Cd can associate with illite as an inner sphere complex.

A fiber-optic sensor to detect volatile organic compounds based on a porous silica xerogel film

Fiber-optic sensors are increasingly used for the determination of volatile organic compounds (VOCs) in air matrices. This paper provides experimental results on the sensitivity of a fiber-optic sensor that uses a film of a porous silica xerogel as the sensing element. This film was synthesized by the sol-gel process and affixed to the end of the optical fiber by the dip-coating technique. This intrinsic sensor works in reflection mode, and the transduction takes place in the light that travels through the core of the fiber. The VOCs included in this research cover a wide range of compounds with different functional groups and polarities. The highest sensitivity was for 2-propanol (13.1±1.4 M(-1) nm(-1)), followed by toluene (11.4±1.4 M(-1) nm(-1)), and 1-butylamine (9.5±0.4 M(-1) nm(-1)). Acetone and cyclohexane had the lowest sensitivity of all studied VOCs. Limits of detection varied between 9.1×10(-5) M for 1-butylamine and 1.6×10(-3) M for ethanol. Silanol groups on the xerogel surface act as weak acids and interact strongly with molecules that contain OH groups like alcohols, π-electrons like toluene, or a lone pair of electrons like toluene. Stronger interaction of methanol and ethanol with the silanol groups on the film led to some irreversible adsorption of these analytes at room temperature.

Polynuclear mesityl-gold and -gold-silver derivatives. Crystal structure of [Ag(μ-dppm)2{Au(mes)}2]C1O4 · 3CH2Cl2 (dppm = bis(diphenylphosphino)methane, mes=mesityl)

Abstract The reaction of the complex [Au(mes)dppm] (mes = mesityl, dppm = PPH2CH2PPh2) with [Au(tht)2]SO3CF3 (tht = tetrahydrothiophene) or AgClO4 in molar ratio 2:1 afforded trinuclear derivatives [M(μ-dppm)2{Au(mes)}2]A (M = Au, A = SO3CF3 (1); M = Ag, A = C1O4 (2)). The structure of [Ag(μ-dppm)2{Au(mes)}2]ClO4 has been determined by a single-crystal X-ray diffraction study, which shows AuAg distances of 2.944(2) and 2.946(2) A.

Influence of prefermentation clarification on the higher alcohol contents of wines

Abstract Nitrogenous compounds and the amount of solids have an effect on both the metabolic pathway and on the concentration of higher alcohols (HA) in wines. In this study, the influence of two prefermentation clarification treatments (static sedimentation and vacuum filtration) on the concentration of nitrogen which can be assimilated and glucose consumption have been studied with respect to HA concentration of wines. The results show that total HA decreased with increasing must clarification level, and the clarification is more of a determining factor than amino nitrogen. No relation has been found in these complex mediums between Leu concentration and the formation of isoamyl alcohol nor between Val and isobutyl alcohol. The concentration of n-propyl alcohol was unrelated to concentration and consumption of Thr and Gaba. There seems to be a relationship between slower glucose consumption in filtered musts and lower HA concentration in wines.

Application of gold complexes in the development of sensors for volatile organic compounds

Two different kinds of sensors have been developed by using the same kind of vapochromic complexes. The vapochromic materials [Au2Ag2(C6F5)4L2]n have different colours depending on the ligand L. These materials change, reversibly, their optical properties, colour and fluorescence, in the presence of the vapours of volatile organic compounds (VOCs). For practical applications, two different ways of fixing the vapochromic material to the optical fibre have been used: the sol-gel technique and the electrostatic self-assembly method (ESA). With the first technique the sensors can even be used to detect VOCs in aqueous solutions, and using the second method it has been possible to develop nanosensors.

Sorption of 4-ethylguaiacol and 4-ethylphenol on yeast cell walls, using a synthetic wine.

4-Ethylphenol (4-EP) and 4-ethylguaiacol (4-EG) are the identified volatile phenolic compounds associated with off-odour in wine. The aim of this work was to investigate the kinetics and thermodynamics of sorption of 4-EG and 4-EP by yeast cell walls, using a synthetic wine. Results showed that the sorption capacity by yeast cell walls for 4-EG was greater than that for 4-EP and that the kinetics of 4-EG were quicker, although the unions were weaker than in the case of 4-EP. The retention of these compounds was by means of specific chemical sorption. The process of sorption of these compounds to the yeast walls could be due to their binding to the residual lipids, as well as to interaction of 4-EP and 4-EG (positively charged compounds), with the functional groups of the mannoproteins and the free amino acids of the surface of the cell walls.

Synthesis of new tetrathiafulvalenes with aromatic substituents and related metallic dithiolene complexes

Synthesis of square-planar complexes and the corresponding TTFs derivatives with 4-(substituted)1,2-dithiolene as ligands can be achieved starting from the corresponding thione or ketone in an ethoxide solution. Complexes of Ni(II) and Au(III) have been prepared using 4-(p-Cyanophenyl) and 4-(4-pyridil)1,3-dithiole-2-thione as precursors.

Influence of vacuum filtration of Viura must on the concentration of fatty acids and their utilization in fermentation

Fatty acids such as palmitoleic, oleic, linoleic and linolenic along with sterols constitute growth or survival factors for yeast. The objective of this work was to study the influence of vacuum filtration of Viura must on fatty acid contents and their use during fermentation. The results were compared with unclarified must, the control. Filtration drastically reduced the total fatty acid concentration (81.5%) and especially unsaturated fatty acids (97.1% of linoleic, and 100% of linolenic), as well as the minor saturated acids, arachidic and behenic. In the first half of fermentation, fatty acids were excreted in the filtered must (76.8%) whereas they were consumed in the control (46.8%). In the second half of fermentation, there was greater consumption in the control sample (74.5%) than in the filtered sample (37.4%).

Trimethylsilylmethyl gold(I) complexes. X-ray structure of [Au(CH2SiMe3)PPh2CH2PPh2Me]ClO4 · 0.25CH2Cl2

Abstract The reaction of [AuCl(L)] (L = AsPh 3 or PPh 3 ) with Mg(CH 2 SiMe 3 )Cl gives the neutral complexes [Au(CH 2 SiMe 3 )L] [L = ASPh 3 ( 1 ) or PPh 3 ( 2 )]. Complex 1 undergoes substitution reactions with monodentate ligands to afford mononuclear complexes [Au(CH 2 SiMe 3 )PPh 3 ] or [Au(CH 2 SiMe 3 )L′]ClO 4 [L′ = PPh 2 CH 2 PPh 2 Me ( 3 ) or PPh 2 CH 2 PPh 2 CH 2 C 6 F 5 ( 4 )]. If a potentially bidentate ligand is used, the latter reaction gives mononuclear or dinuclear complexes, [Au(CH 2 SiMe 3 )dppe] (dppe = PPh 2 CH 2 CH 2 PPh 2 ) ( 5 ) or [(Me 3 SiCH 2 )Au(L-L)Au(CH 2 SiMe 3 )] [L-L = dppm ( 6 ) or dppe ( 7 )] (dppm = PPh 2 CH 2 PPh 2 ), depending on the molar ratio. The structure of [Au(CH 2 SiMe 3 )PPh 2 CH 2 PPh 2 Me]ClO 4 has been established by an X-ray diffraction study.

Sedimentation clarification of Garnacha musts. Consumption of amino acids during fermentation and aging

Given the importance of finding good methods for the clarification of musts, the aim of this study was to observe the influence of sedimentation on the consumption of amino acids and the other nitrogenous compounds during fermentation and aging of obtained wines. Garnacha grapes were selected and original must was taken as a control. In decanted Garnacha musts, the reduction in the fermentation rates was not due to the deficiency of assimilable nitrogen (ammonium and amino nitrogen). In the first half of fermentation, basic amino acids were consumed similarly in both musts, however, the neutral and dicarboxylic acids were consumed more in the decanted must. In the latter part of fermentation, there was a greater liberation, in general, of amino acids in the decanted must, probably due to the lesser tolerance of yeast to ethanol in the clarified medium.