Novel DFO-functionalized mesoporous silica for iron sensing. Part 2. Experimental detection of free iron concentration (pFe) in urine samples.

Successful in vivo chelation treatment of iron(iii) overload pathologies requires that a significant fraction of the administered drug actually chelates the toxic metal. Increased mobilization of the iron(iii) in experiments on animals or humans, most often evaluated from urinary output, is usually used as an assessment tool for chelation therapy. Alternatively, the efficiency of a drug is estimated by calculating the complexing ability of a chelating agent towards Fe(iii). The latter is calculated by the pFe value, defined as the negative logarithm of the concentration of the free metal ion in a solution containing 10 µM total ligand and 1 µM total metal at a physiological pH of 7.4. In theory, pFe has to be calculated taking into account all the complexation equilibria involving the metal and the possible ligands. Nevertheless, complexation reactions in complex systems such as serum and urine may hardly be accurately modelled by computer software. The experimental determination of the bioavailable fraction of iron(iii) in biological fluids would therefore be of the utmost relevance in the clinical practice. The efficiency of the therapy could be more easily estimated as well as the course of overload pathologies. In this context, the aim of the present work was the development of a sensor to assess the free iron directly in biological fluids (urine) of patients under treatment with chelating agents. In the proposed device (DFO-MS), the strong iron chelator deferoxamine (DFO) is immobilized on the MCM-41 mesoporous silica. The characterization of the iron(iii) sorption on DFO-MS was undertaken, firstly in 0.1 M KNO3, then directly in urine samples, in order to identify the sorption mechanism. The stoichiometry of the reaction in the solid phase was found to be: with an exchange constant (average value) of log ßex = 40(1). The application of DFO-MS to assess pFe in SPU (Simulating Pathology Urine) samples was also considered. The results obtained were very promising for a future validation and subsequent application of the sensor in samples of patients undergoing chelation therapy.

Supramolecular receptors in solid phase: developing sensors for anionic radionuclides.

New solid-phases for the binding, separation and extraction of perrhenate and pertechnetate (ReO(4)(-) and TcO(4)(-)) from water solutions have been developed from a selective molecular receptor. Host compounds being capable of encapsulating these oxoanions are of great interest. The azacryptand, containing two tripodal tetra-amine subunits covalently linked by p-xylyl spacers, is known to display high affinity for ReO(4)(-) and TcO(4)(-) in water. The syntheses of new solid phases, obtained by fixing the receptor on mesoporous silica MCM-41 and Amberlite CG50 supports, are here described. FT-IR, micro-Raman, elemental analysis (CHN), sorption isotherms, (29)Si MAS NMR, and SEM/EDS were employed for solids characterisation. Promising performances were found for silica derivatives, for which the amount of the receptor fixed on silica ranged from 0.2 to 0.3 mmol g(-1). The perrhenate sorption mechanism was investigated with the aim to select the conditions for application in batch and fixed bed column systems.