Role of the caffeic acid oxidation products on the iron mobilization at the soil-root interface

Previous results show that the reduction of Fe(III) by caffeiic acid (CAF) is strongly influenced by the pH of the reaction medium (DEIANA et al., 1995). In particular, it has been found that al pH > 3.8 the reducing activity of CAF towards the Fe(III) ions in solution is low, but it increases when Fe(III) is complexed as Fe(III)-polygalacturonate. The mobilization of the Fe(II) ions, which form upon the Fe(III) reduction, has been shown to depend mainly on the nature of the Fe(III)-polygalacturonate complexes (DEIANA et al., 1994a). In particular, it bas been observed a high redox activity of CAF towards Fe(III) when the metal ion is coordinated by the carboxilic groups of the macromolecule. The Fe(III) reduction has been found to decrease when an oxydrilic group was inserted in the Fe(III) coordination sphere. The Fe(II) produced partly diffuses into the external solution and partly is still strongly held by the polysaccharidic matrix. The oxidation of CAF by Fe(III) gives rise to the formation of products (OP) with different polymerization degree, some of which are similar to those found in natural systems (DEIANA et al., 1994b). In order to determine the role of these products in the Fe(III) reduction as well as in the mobilization of the Fe(II) produced it was set up an electrochemical method to synthetize these products (DEIANA et al., 1994b). Here are reported some results about the interaction which establish between the CAF oxidation products and iron in both oxidized and reduced form

Performance of two potentiometric fluoride determination methods in hard dental tissue

A comparison between two ion selective electrode (ISE) potentiometric methods is reported for determining the amount of fluoride in hard dental tissue after placement of fluoride-releasing dental restorations. The two methods are: (1) the direct method involving linear calibration (LC), and (2) a spiking method involving multiple standard additions (MA). Results showed that measurements performed by the LC method underestimate the amount of fluoride released by up to 30%. Recovery tests demonstrated that the use of MA and blank correction procedures is useful for an accurate and sensitive ISE determination of fluoride in hard dental tissues

Sorption of chrysoidine by row cork and cork entrapped in calcium alginate beads

Abstract Azo-dyes, molecules characterised by the presence of the azo-group (–N N–), are widely used in textile, leather, rubber, plastic, and food industries. Water-soluble azo-dyes are greatly resistant to biodegradation, and are characterised by a high thermal and photo stability due to their complex structures. The release of these molecules into the environment is of crucial concern due to their toxic, mutagenic and carcinogenic characteristics. Biosorption has been demonstrated an effective method to remove pollutants from wastewaters thus solving ecological tasks, being a low cost process and the sorbent biodegradable. The main requirements of an efficient sorbent are thermal, chemical and mechanical stability, and rapid sorption. In this work, the ability of both row cork and the same sorbent entrapped in a biopolymeric gel of calcium alginate, on the removal of chrysoidine from aqueous solutions was examined. The influence on the sorption of pH, initial dye concentration, and particle size, as well as the efficiency of the entrapment, have been investigated. The maximum sorption was found for cork samples of fine particle size (FC), in both row and entrapped forms, at pH 7; conversely, at pH 4 the difference is significant (0.12 mmol/g for row cork and 0.20 mmol/g for entrapped cork), evoking a cooperation of alginate in binding the positively charged chrysoidine molecule

Polimeri conduttori e metallopolimeri redox

Il nostro gruppo di ricerca è da anni attivo nella sintesi e caratterizzazione elettrochimica di polimeri conduttori a base tiofenica. In particolare la nostra attenzione è rivolta verso materiali costituiti da un backbone di tipo tertiofenico, che consente la polimerizzazione nelle posizioni 2 e 5, e da unità chelanti all’azoto, (terpiridine o fenantroline), che possono consentire la coordinazione con metalli di transizione all’interno del polimero ed incrementarne ulteriormente le proprietà conduttive

Mesoporous Titania powders: the role of precursors, ligand addition and calcination rate on their morphology, crystalline structure and photocatalytic activity

We evaluate the influence of the use of different titania precursors, calcination rate, and ligand addition on the morphology, texture and phase content of synthesized mesoporous titania samples, parameters which, in turn, can play a key role in titania photocatalytic performances. The powders, obtained through the evaporation-induced self-assembly method, are characterized by means of ex situ X-Ray Powder Diffraction (XRPD) measurements, N2 physisorption isotherms and transmission electron microscopy. The precursors are selected basing on two different approaches: the acid-base pair, using TiCl4 and Ti(OBu)4, and a more classic route with Ti(OiPr)4 and HCl. For both precursors, different specimens were prepared by resorting to different calcination rates and with and without the addition of acetylacetone, that creates coordinated species with lower hydrolysis rates, and with different calcination rates. Each sample was employed as photoanode and tested in the water splitting reaction by recording I-V curves and comparing the results with commercial P25 powders. The complex data framework suggests that a narrow pore size distribution, due to the use of acetylacetone, plays a major role in the photoactivity, leading to a current density value higher than that of P25

Processi di trasferimento ionico nella rizosfera: ruolo dell'acido caffeico e dei suoi prodotti di ossidazione nella mobilizzazione del ferro da networks di acido poligalatturonico

Dottorato di ricerca in chimica agraria. 8. ciclo. A.a. 1992-95. Tutore S. DeianaConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Numerical methods in synthesis and analysis of electrochemical responses

Though literature reports the trends of the significant quantities of the responses for different potential controlled techniques for many different types of mechanisms, direct comparisons between experimental and theoretical responses are often necessary. For an experimenter who wants to calculate a theoretical response, numerical methods are particularly appealing. In particular, digital simulation methods based on finite difference expressions of the differential equations accounting for diffusion and kinetics of the electrode process are probably the simplest numerical techniques to use. Many different models have been proposed. Nonuniform space or space-time discretizations have been suggested to speed up the simulation procedure. As to the analysis of the response, more or less trivial treatments (filtering of noise, background subtraction, convolution or deconvolution procedures, etc.) can lead to signals where the significant quantities can be estimated more accurately. The qualitative and quantitative definition of the operative mechanism can be in part or completely computerized. A key point consists of some general optimization method, such as the Simplex

Analysis of cyclic voltammetric responses by Fourier transform-based deconvolution and convolution procedures

Numerical procedures for processing linear sweep and cyclic voltammetric responses are suggested in order to (1) deconvolve a sequence accounting for diffusion from the original signals; (2) convolve these with the same sequence. Deconvolution and convolution operations are performed via the Fourier transform method. Responses obtained by simulation of uncomplicated reversible, quasi-reversible and irreversible charge transfers are considered. The values of the parameters characterizing deconvolution and convolution responses are computed and discussed; a comparison is made with the corresponding parameters of the original current/potential curves, as well as with data reported in the literature for nernstian and totally irreversible charge transfers, obtained by following different mathematical procedures

Electrochemical and spectroelectrochemical study of copper complexes with 1,10-phenanthrolines

The redox behaviour of a series of copper(II) complexes with different phenanthrolines (1:2 metal to ligand) in dimethylformamide solvent is reported. Cyclic voltammetry, controlled potential coulometry and spectroelectrochemistry in the visible region have been used. Accurate values for the formal potential of the copper(II)/ copper(I) couples could be computed by spectroelectrochemistry, also in those cases in which the systems are poorly reversible. Two further reductions lead to neutral and anionic copper species, respectively. The nature of the substituents on the phenanthroline ligands has been found to affect strongly the redox potential of the former couples, while a less marked influence on the latter ones has been evidenced. On the other hand, differences in the ligands induce very different kinetic stability of the copper complexes formed in the more cathodic processes

Platinum complexes with N---N---C ligands: syntheses, electrochemical and spectroscopic characterisations of platinum(II) and relevant electroreduced species

A series of cyclometallated platinum(II) species with N---N---C ligands (N---N---C=ortho-C-deprotonated form of 6-benzyl-substituted 2,2′-bipyridines) and different fourth monodentate ligands (Cl−, I−, CN−, CO, PPh3, Py, MeCN) has been investigated electrochemically, with particular emphasis to the analysis of the relatively stable one-electron reduced species. EPR spectra have been recorded at different temperatures on the electroreduced solutions. The analyses were supported by a systematic comparison with simulated spectra and allowed a definition of the interaction of the additional unpaired electron with the 195Pt, 14N, and 1H nuclei present in the molecule. Attention has been also paid to the effects of the ligands on the thermodynamics (E1/2,r) of the reduction, as well as to some reactivity aspects of the substrates that could be shown by voltammetric tests. A number of these compounds have been synthesised for the first time, so that a full characterisation has been performed