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The Halloysite (Al2Si2O5(OH)4·2H2O) is an abundant and cheap clay and is considered one of the most promising nano structured and naturally occurring clay mineral. Large deposits of this material are present in France, Belgium, China, New Zealand and USA [1,2]. Among the spheroidal, tubular or platy morphologies, the tubular is the most common and abundant one. Typically, halloysite nanotubes (HNTs) are formed by 15 – 20 aluminosilicate layers, having a length of 1 ± 0.5 μm, and inner and outer diameters of 10 – 15 nm and 50 -70 nm, respectively [1]. In each layer, the SiOH and the AlOH groups are disposed on the external and the internal surfaces, respectively. As consequence, in each nanotube and in a large pH range, there is a charge separation between the inner and the outer surfaces. In particular, the inner surface is positively charged because of protonation of AlOH groups and the outer surface is negatively charged because of the gradual deprotonation of SiOH groups at pH higher than 2. This charge separation is one of the most important features for the HNTs versatility and is strictly dependent on the acid – base properties of their functional groups. In this work, the protonation / deprotonation of SiOH and AlOH groups of HNTs is evaluated by ISE-H+ potentiometric titrations of HNTs aqueous suspensions in different ionic media and ionic strengths (0.025 ≤ I / mol L-1 ≤ 0.750) and in a wide pH range (2 – 11), at T = 25°C.ISE-H+ potentiometric titration data have been processed by using the same models successfully used in a previous work for carboxylic and phenol groups of humic and fulvic substances [3]. Moreover, the change of superficial charge with the changing of pH was also evaluated by ζ potential measurements.Correlations between the ζ potential trend and the distribution of protonated and deprotonated species of HNTs were found.

The great part of municipal solid wastes is worldwide stored in sanitary landfills. The interaction of organic and inorganic wastes with rainwater produces in the landfill a leachate of extremely variable composition. It depends on several variables such as the type of wastes, the age of landfill, the pH, the redox potential, etc [1-2]. Four are the recognized categories of pollutants in landfill leachate: inorganic macrocomponents, dissolved organic matter (DOM), heavy metals and xenobiotic organic compounds [3]. In particular, heavy metals (arsenic, cadmium, copper, lead, mercury, etc.) are usually present at concentration of few ppb and up to some ppm. A variable but consistent fraction of DOM is constituted by humic and fulvic-like compounds, formed through a series of biological and chemical processes that involve DOM, especially during the methanogenic phase of wastes decomposition [3]. The great number of binding sites in humic like substances, mainly carboxylic and phenolic groups, are responsible of the high sequestering ability of leachate towards metal ions. As consequence, the speciation scheme of all the toxic metal ions contained in the landfill is strictly influenced by the amount and composition of DOM fraction in leachate. Due to the imperfections or the possible damages of landfill liners, the leachate can contaminate superficial and ground waters in proximity of the landfill causing serious environmental pollution and human health risks. In a previous study the presence and the amount of landfill leachate, also in trace, on some groundwater samples collected in proximity of Bellolampo landfill was evaluated [4]. The obtained results showed a leachate concentration of ~ 130 μg L-1. Landfill of Bellolampo is a solid waste sanitary landfill near Palermo (Sicily). The landfill has been created in 1960s and become a controlled dump site in 1980s. Previous ICP-OES measurements on Bellolampo leachate have been shown a Pb, Cd and Cu concentrations in the ranges 0.05 - 2.3, 0.02 - 0.12 and 0.02 - 0.6 mg L-1 respectively. The environmental and health risks related to the presence of toxic heavy metal ions in leachate depends on the species that metals form with the other components and at the conditions of the contaminated groundwater, with particular attention to the amount of free metal ions, the most dangerous among their possible species in aqueous solution. For this reason, the study of the sequestering ability of landfill leachate towards toxic metal ions is of fundamental importance to establish the environmental impact of leachate contamination. Here we present a potentiometric and voltammetric (Differential Pulse Anodic Stripping Voltammetry, DP-ASV) study on the acid-base properties and on the sequestering ability of leachate samples collected in Bellolampo landfill towards Cd(II), Pb(II) and Cu(II) ions. The voltammetric and potentiometric titrations were carried out in NaCl aqueous solution, at I = 0.1 mol L-1 in order to simulate the mean experimental conditions typical of groundwaters. The acid – base properties of the filtered leachate were compared to those of the soluble fraction of humic substances, with carboxylic and phenolic groups as main binding sites of the macromolecules. Two units namely leach1 and leach2 containing COOH and phenol OH groups, respectively were considered and the Diprotic Like model has been used to process the ISE-H+ potentiometric data [5]. The voltammetric titrations of toxic metal ions solutions with leachate (diluted or as it is) were carried out adjusting the pH of titrand solutions at 5. The results shown an appreciable sequestering ability of leachate towards the heavy metal ions considered and an estimation of the metal complexes stability has been done by calculating rough metal – leachate formation constants.

Halloysite is one of the most interesting nano-structured clay materials. It is similar to kaolin but has a hollow tubular structure that can be attributable to particular crystallization conditions. Typically, halloysite nanotubes (HNTs) are formed by 15 – 20 aluminosilicate layers, has a length of 1 ± 0.5 μm and inner and outer diameters of 1 - 30 and 30 - 50 nm, respectively [1,2]. In each layer the SiOH and the AlOH groups are disposed on the external and the internal surfaces, respectively. The particular structure of HNTs makes this kind of material very useful for different purposes in several fields. Among the various applications, worth of mention are: i) their use as additive for devices in the capture tumor cells in blood; ii) nanoparticles for the entrapment and controlled release of active molecules; ii) additive agents in wound and personal care; iv) sorbents for water contaminants etc [1,2]. In all these applications, the knowledge of the acid-base properties of HNTs is of fundamental importance. The acid-base properties of HNTs have been studied by ISE-H+ potentiometric titrations in NaCl medium, in the range 0.025 ≤ I / mol L-1 ≤ 0.750 and at T = 25°C. Two functional groups indicated with HNT1 (SiOH) and HNT2 (AlOH) were considered in the analysis of the experimental data. Potentiometric data were processed with four different models previously used for the study of the acid - base properties of natural and synthetic polyelectrolytes: Högfeldt, Linear, modified Henderson-Hasselbalch and diprotic like models [3]. The results obtained with the four models for the protonation constants of HNT1 groups of HNTs were in good accordance, whilst the acid-base properties of HNT2 groups were well defined by one protonation constant calculated by processing the potentiometric titration data with the computer programs STACO and BSTAC.

In the last decade nanoparticles have assumed more and more importance because of their particular properties mainly due to the nanometer-scale dimensions that confer them a large surface/volume ratio. Among nanomaterials one of the most studied is the halloysite that, as well as the other natural clay minerals is safe for human and environmental friendly. Halloysite is abundant and cheap and is present in large deposits worldwide like those in New Zealand, France, Belgium and China [1,2]. It is similar to kaolin but has a hollow tubular structure that can be attributable to particular crystallization conditions. Typically, halloysite nanotubes (HNTs) are formed by 15 – 20 aluminosilicate layers, has a length of 1 ± 0.5 μm and inner and outer diameters of ~15 and 50 -70 nm, respectively [1,2]. In each layer the SiOH and the AlOH groups are disposed on the external and the internal surfaces, respectively. As consequence, the chemistry of the lumen and of the outer surface of HNTs is completely different. In particular, in each nanotube the inner surface is positively charged and the outer surface has an excess of negative charges in a wide pH range. The particular structure of HNTs makes this kind of clay mineral very useful for different purposes and several papers and reviews have been published on their different applications [1-3]. The behavior of HNTs in all these applications is strictly related to their acid-base properties that here have been studied by ISE-H+ potentiometric titrations in several interacting and non interacting ionic media, in the range 0.025 ≤ I mol L-1 ≤ 1.000, at T = 25°C. Two functional groups indicated with HNT1 (SiOH) and HNT2 (AlOH) were considered in the analysis of the experimental data. Potentiometric data related to the HNT1 groups were processed with four different models previously used for the study of the acid-base properties of natural and synthetic polyelectrolytes: Högfeldt, Linear, modified Henderson-Hasselbalch and diprotic like models [4]. The acid – base behavior of HNT2 groups were well defined by one protonation constant calculated by processing the potentiometric titration data with the computer programs STACO and BSTAC.

The increase of the worldwide demand of “Platinum group elements” (PGE) for application in several fields such as industry, medicine, jewellery and, especially, in catalyst converter production, caused a noticeable increasing of PGE concentration in the environment. Though palladium, among the anthropogenic PGE, is not the most abundant one, it is the most hazardous since it undergoes easily and quickly oxidation to palladium(II) when in contact with soils, with a consequent increase of its mobility in the environment. The presence of complexing agents, which form soluble complex species with palladium(II), favours the mobility of the ion with an increase of its availability to plants, animals and humans. Among anthropogenic complexing molecules, an important role is played by synthetic aminopolycarboxylic chelating agents (usually called with the acronym APC) whose concentration in the environment is progressively increasing owing to their considerable use in several fields (agriculture, industry, medicine) and a low biodegradability of most of them. The interaction of these ligands with palladium(II) ion leads to the formation of soluble complex species whose stability influences strongly the availability of palladium(II) in the environment. With the aim to assess the strength of interaction of Pd2+ with aminopolycarboxylic ligands, here we report the results of a systematic study, , on the formation of palladium(II) complex species with five APCs [ethylenediamine-N,N,N’,N’-tetraacetate (EDTA), (S,S)-Ethylenediamine-N,N′-disuccinic acid (S,S-EDDS), Nitrilotriacetate (NTA) and diethylenetriamine-N,N,N’,N’’,N’’-pentaacetate (DTPA) and triethylenetetraamine-N,N,N’,N’’,N’’’,N’’’-hexaacetate (TTHA)]. Owing to the high stability of the Pd2+ - APC complex species, the calculation of their stability constants was very difficult and was possible only by combining the results obtained from two series of ISE-H+ potentiometric titration (in NaNO3 and in mixed NaNO3 /NaI ionic medium) and from ISE-H+ potentiometric /spectrophotometric titrations (in NaClO4). As expected, the stability of Pd-APC complex species is function of the number of carboxylic and amino groups present in the ligand molecules (e.g., logKPd(APC) = 37.00, 36.31, 23.60, 23.07 and 17.82 for TTHA, DTPA, EDTA, S,S-EDDS and NTA in Na+ ionic media, at I = 0.1 mol L-1 and T = 25°C). Results obtained on the stability of species in the Pd- S,S-EDDS show that this ligand, which is the most biodegradable APC ligand, can be used successfully as environmental friendly chelating agent in substitution of the other less degradable APCs in all their application fields. From the stability data of the Pd2+ - APCs the sequestration capacity [expressed as pL50, i.e. the –log (APC concentration] necessary to bind the 50% of the metal ion) of the ligands under investigation towards palladium(II) ion was determined in the pH range considered. The pL50 is easily correlated to important physico-chemical parameters (pH, ionic strength, temperature, etc.) as shown in the Figure, were the dependence on pH of pL50 of the APCs towards Pd2+ ion is reported. As can be seen, TTHA and DTPA show almost the same sequestering ability in the pH range 2 – 10, clearly higher than that of EDTA, S,S-EDDS and NTA where a minor number of amino and carboxylic groups is present in the molecule.

Poster al 96th Scientific Assembly and Annual Meeting oft he Radiological Society of North America - RSNA 2010 Chicago 28 novembre – 3 dicembre 2010

L’interesse nei confronti della chimica di coordinazione del mercurio(II) deriva dalla sua tossicità intrinseca. Sebbene tutte le forme di mercurio siano tossiche, gli effetti sull’ambiente e sull’uomo sono in genere legati alle trasformazioni ambientali di Hg inorganico a metilmercurio. L’elevata tossicità del metilmercurio(II) per gli esseri umani deriva dall’affinità del mercurio(II) nei confronti di residui cisteinil solfuri. I tioli a basso peso molecolare costituiscono i vettori per il trasporto e la distribuzione di mercurio nell’organismo umano a causa del fenomeno del "mimetismo molecolare”. Uno studio della chimica in soluzione del metilmercurio(II) in presenza di tali leganti fornisce pertanto informazioni utili circa la natura e l'entità delle interazioni tra di essi. Tali informazioni possono essere utilizzate per valutare metodi di rimozione del metallo da sistemi biologici attraverso l’uso di agenti chelanti (chelation therapy). In questo lavoro viene riportato uno studio delle capacità complessanti di leganti zolfo donatori nei confronti di CH3Hg+. I leganti considerati sono: l’acido 2 mercaptopropanoico (o tiolattico, tla), l’acido 3-mercaptopropanoico (mpa), l’acido 2-mercaptosuccinico (o tiomalico, tma), la penicilammina (pen), la cisteina (cys) e il glutatione (gsh). Lo studio è stato eseguito mediante diverse tecniche strumentali: la potenziometria (ISE-H+) al fine di determinare le costanti di formazione dei complessi per i diversi sistemi CH3Hg+-legante; la calorimetria per determinare le relative entalpie di formazione; la spettroscopia 1H NMR e la spettrometria di massa-elettrospray (ESI-MS) per confermare i modelli di speciazione proposti e per ottenere informazioni strutturali. Gli studi sono stati condotti in NaNO3 a I = 0.1 mol L-1 e a t = 25 °C, in presenza di ioduro quale legante competitivo. Per i sistemi CH3Hg+ -tma, -pen e -gsh è stata inoltre studiata la dipendenza dei parametri termodinamici di formazione dei complessi dalla forza ionica nell’intervallo 0 ≤ I ≤ 1 mol L-1 (NaNO3). I dati sperimentali hanno messo in evidenza la formazione per tutti i sistemi della specie ML con una elevata stabilità (logβ = 16.06-17.94) e della specie MLH, oltre a MLH2 (per pen e gsh) e MLOH (per tla, mpa e tma). La capacità sequestrante è espressa mediante il parametro pL50 che definisce la quantità di legante necessaria per sequestrare il 50% di ione metallico presente in soluzione.

The formation of complexes species of the dioxouranium(VI) ion with aspartic and glutamic acids was studied in the pH range of 3 to 6 at 25 °C by potentiometric measurements (H+-glass electrode). Results gave evidence for the formation of the following species: (UO2)A0, (UO2)AH+, and (UO2)2A(OH)2 0 (A2- ) a glutamic or aspartic ligand). Investigations were carried out in a NaCl ionic medium at I (0.1, 0.25, 0.5, and 1.0) mol L-1. The dependence on ionic strength of the formation constants was analyzed by the specific ion interaction theory (SIT) model. The formation constants at infinite dilution, obtained using this model, are log â110 ) 8.53 ( 0.03, 8.37 ( 0.05; log â111 ) 13.60 ( 0.05, 13.42 ( 0.02; and log â21-2 ) 3.31 ( 0.05, 2.98 ( 0.03 for glutamate and aspartate, respectively, where indexes for the overall formation constant âpqr refer to the equilibrium pUO22+ + qA2- + rH+ ) (UO2)p(A)qHr(2p - 2q + r). The specific interaction coefficients are also reported. A mononuclear hydroxo species (UO2)A(OH)-, of great interest for very low naturally occurring concentrations of uranium(VI), was hypothesized, with equilibrium constant log K [(UO2)A0 + H2O ) (UO2)A(OH)-])-5.4 at t ) 25 °C and I ) 0 mol L-1. Speciation profiles for different concentrations of UO22+ in the presence of both amino acids are discussed.