Effects of micelle nature and concentration on the acid dissociation constants of the metal extractor PADA

The pyridine-2-azo-p-dimethylaniline (PADA) ligand presents two acid dissociation constants, being pKa1 related to the pyridinium and pKa2 related to the anilinium residue. These have been measured by spectrophotometric titrations in aqueous solutions containing either the anionic (SDS), or the non–ionic (Triton X-100) or the cationic (DTAC) surfactants. The pKai shifts of the charged systems from that of the PADA/Triton X-100 reference (∆pKai0) are compared. For PADA/DTAC ∆pKa10 = 0.05 and ∆pKa20 = 0.6. For PADA/SDS ∆pKa10 = 2.1 and ∆pKa20 = 2.1 both yielding the value of -126 mV for the surface potential (ψ) of SDS. The ψ value, lying between the calculated Stern potential and the zeta potential, indicates that the dye is located on the SDS micelles between the fixed and the shear layer. In contrast, the behaviour of PADA/DTAC is explained assuming that the positively charged deprotonation sites of PADA are forced to protrude towards the bulk solvent by the positive charges of DTAC micelles. The shifts of the apparent pKai from the aqueous values (∆pKaiw) have also been analysed. Concerning PADA/Triton X-100, the shifts ∆pKa1w = -0.1 and ∆pKa2w = -0.9 are rationalized in terms of dielectric constant reduction at the reaction sites. Concerning PADA/DTAC, ∆pKa1w= -0.05 and ∆pKa2w= -0.3 whereas, for PADA/SDS, ∆pKa1w = 2.0 and ∆pKa2w = 1.2. The pKa2w values decrease on raising the surfactant concentrations for all the investigated systems. This behaviour is explained assuming that the increase of the overall micellar surface and, by consequence, of the reaction sites number, results in a site dilution effect which disfavours proton association. The addition of NaCl induces changes of pKa1 and pKa2 which are explained in terms of (large) reduction of ψ for PADA/SDS and of (small) reduction of the dielectric constant for the other systems

The effect of impregnation strategy on methane dry reforming activity of Ce promoted Pt/ZrO2

Cataloged from PDF version of article.Dry reforming of methane has been studied over Pt/ZrO2 catalysts promoted with Ce for different temperatures and feed compositions. The influence of the impregnation strategy and the cerium amount on the activity and stability of the catalysts were investigated. The results have shown that introduction of 1 wt.% Ce to the Pt/ZrO2 catalyst via coimpregnation method led to the highest catalytic activity and stability. 1 wt.%Ce-1 wt.%Pt/ZrO2 catalyst prepared by sequential impregnation displayed inferior CH4 and CO2 conversion performances with lowest H-2/CO production ratios. 1 wt.%Ce-1 wt.%Pt/ZrO2 catalyst prepared by coimpregnation showed the highest activity even for the feed with high CH4/CO2 ratio. The reason for high activity was explained by the intensive interaction between Pt and Ce phases for coimpregnated sample, which had been verified by X-ray photoelectron spectroscopy and Energy Dispersive X-Ray analyses. Strong and extensive Pt-Ce surface interaction results in an increase in the number of Ce3+ sites and enhances the dispersion of Pt. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved

A sense of things to come: Future research directions in sensory marketing

The exciting exploration on sensory marketing presented in this book is just the foundation upon which to build future research. There are myriad unexplored questions and innumerable directions in which to take this research. Our goal in this chapter is not to provide an exhaustive array of these future directions, but rather to stimulate the reader into exploring new ideas. We present possible future directions for each sense individually (vision, audition, smell, touch, taste), and conclude with ideas for future research addressing the interplay among multiple senses within consumer behavior

Interaction of the Pd(II) complex of 5,10,15,20-tetrakis(1-methyl-4-pyridiyl)-porphyne with natural DNA

A mechanistic, thermodynamic and kinetic analysis of the binding of the Pd(II)/5,10,15,20-tetrakis(1-methyl-4-pyridiyl)-porphyrine metal complex is done. Fluorescence and absorbance titrations under different conditions of temperature and salt content concur in indicating that the binding is strong. Kinetic and equilibrium parameters for the complex interaction with the nucleic acid are obtained and the binding mechanism is discussed. An intercalative binding is found to be active

Developing an open geographic data model and analysis tools for disaster management: landslide case

Disaster management aims to reduce catastrophic losses of disasters. Geographic information technologies support disaster management activities for effective and collaborative data management considering the complex nature of disasters. This study with an original conceptual approach aims to develop interoperable geographic data model and analysis tools to manage geographic data sets coming from different sources. For landslide disaster, 39 scenario-based activities were analysed with the required data according to user needs in a cycle of activities at mitigation, preparedness, response, and recovery phases. An interoperable geographic data model for disaster management (ADYS), enabling up-to-date exchange of geographic data, was designed, compliant with the standards of ISO/TC211 Geographic Information/Geomatics, Open Geospatial Consortium (OGC), and the Turkish National GIS (TUCBS). An open source and free analysis toolbox was developed and tested in the case study of activities such as landslide hazard analysis and a disaster warning system to support the Provincial Disaster Management Centres of Turkey. Open data models and analysis tools make effective activity management and data sharing possible. However, transforming data sets into data exchange formats is laborious

(meso-Tetrakis(1-methyl-4-pyridinium)porphyrinato)Pd(II) complex: kinetics of formation and DNA binding

Absorbance variation in time, connected to complex formation, is spectrophotometrically observed at two different temperatures. Spectra broadening upon reaction suggests some aggregation of the formed metal complex. Due to the presence of high metal ion amounts respect to ligand (pseudo-first order conditions) the curves can be analysed by a mono-exponential equation, yielding for each curve amplitude (amp) and reciprocal relaxation time (1/t) parameters. The initial rate (slope of the very first part of the plot) can also be obtained. Constancy of the curves amplitude and zero intercept of the 1/t vs. [Pd] plot indicate a quantitative process taking place (kd = 0). The slope of the dilogarithmic plot of the initial rates values is equal to one, indicating a first order reaction respect to palladium in agreement with formation of a 1:1 complex. The above considerations are true both at 25 °C and at 40°C.Addition of DNA produces bathochromic and hypochromic effects consistent with intercalation of the metal complex between DNA base pairs. However, the non-perfect isosbestic points suggest non-simple equilibria i.e. complex mechanism of interaction. Calculations on the binding isotherm resulting form titrations indicate quantitative binding, even in the presence of relatively high salt content (1.0 M NaCl)

The interaction mechanism of gold(III) with the metal extractant PADA in DTAC micellar medium and applications to gold(III) extraction

The kinetics of binding of Au(III), initially present as AuCl4 -, to the azo-dye ligand pyridine-2-azo-p-dimethylaniline (PADA) in dodecyltrimethylammonium chloride (DTAC) micellar solution have been investigated as a preliminary study on gold micellar extraction and recovery. PADA (Figure 1) is endowed with excellent hydrophobic properties, which make it an ideal carrier for the transport of the metal ions from water to micelle, allowing the metal extraction process to be carried out. The kinetic study enables the mechanism of the binding reaction to be worked out under different investigated medium conditions, showing that in the presence of the DTAC micellar pseudo-phase the reaction is strongly accelerated (catalytic effect) compared to water. The results concur in suggesting that differently oxydrilated forms, originated from the starting AuCl4-, are reactive and, in DTAC at low pH, also the aquoform AuCl3(H2O) reacts with PADA, whereas the tetrachlorocomplex apparently does not react, except that in water at relatively low pH. The characteristics of the water/micelle system have been also exploited, for the purpose of extracting and recovering gold, by applying the micellar enhanced ultrafiltration (MEUF) procedure. Using MEUF the negative AuCl4- ion is extracted with yields near to 100% by DTAC, owing to direct adsorption on the micelle surface. The recovery step has been accomplished adding an electrolyte (NaCl) solution, which lowers the surface potential of the micelle, thus favoring the recovery process. Ammonia has been also added in order to convert the gold(III) chlorocomplexes into the ammonia complex, which is repelled from the positively charged DTAC surface and can be recovered. A recovery yield of 86% has been achieved, which provides a promising basis for the extraction of gold from water using the surfactant DTAC

Gold-Copper Extraction and Separation by Micellar Enhanced Ultrafiltration

This study presents a method for separation and extraction of gold(III) and copper(II). The extraction and recovery of polluting and precious metals from waste fluids has recently gained increasing importance. It should be noted that, besides to its main use in jewellery and investment, applications of gold are rapily and widely expanding so that the gold recovery from waste fluids or waste scraps is becoming important. On the other hand, the risk potential of copper in the environment gains in significance due to application and special properties of copper with respect to toxicity and complexing ability with humic substances.4 Studies on metal extraction suggest that surfactant based metodologies could be effective in the removal of these ions from waste fluids

Metal-Complex Formation and DNA Interaction of 5,10,15,20-Tetrakis(1-methyl-4-pyridiy1)-porphine: Study of the Mechanistic Aspects

The macrocyclic porphyrin 5,10,15,20-tetrakis(1-methyl-4-pyridiyl)-porphine is studied in its ability to coordinate Cu(II) even at very low pH values and to interact, as a copper complex, with calf-thymus (CT-DNA). The kinetics and equilibria for metal-ligand complexes formation are spectrophotometrically studied, particularly focussing on the mechanistic information provided by the kinetic approach. The rate constants of complex formation is much lower than that of water exchange at Cu(II), this behavior is ascribed to an equilibrium between two porphyrin populations, only one of them being reactive. Concerning the interaction of the copper-porphyrin complex (D) with CT-DNA, it has been found that the complex binds to G-C base pairs by intercalation while forms external complex with the A-T base pairs. The kinetic results agree with a reaction mechanism that takes into account the slow shuffling from an AT-bound form (DAT) to a GC-bound form (DGC) of the copper complex (D), finally leading to a more stable DGC* intercalated form. Kinetic and equilibrium parameters for the copper complex binding to the nucleic acid are obtained, and the binding mechanism is discussed. A mechanism is proposed where D reacts simultaneously with (G-C) and (A-T) base pairs. The resulting bound forms interconvert according to a "shuffling" process, which involves formation of an intermediate (DGC) form. (C) 2009 Wiley Periodicals, Inc