No abstract

In this paper, the results obtained by five independent methods for the quantification of fumonisins B(1), B(2), and B(3) in raw maize are reported. Five naturally contaminated maize samples and a reference material were analyzed in three different laboratories. Although each method was validated and common calibrants were used, a poor agreement about fumonisin contamination levels was obtained. In order to investigate the interactions among analyte and matrix leading to this lack of consistency, the occurrence of fumonisin derivatives was checked. Significant amounts of hidden fumonisins were detected for all the considered samples. Furthermore, the application of an in vitro digestion protocol to raw maize allowed for a higher recovery of native fumonisins, suggesting that the interaction occurring among analytes and matrix macromolecules is associative rather than covalent. Depending on the analytical method as well as the maize sample, only 37-68% of the total fumonisin concentrations were found to be extractable from the samples. These results are particularly impressive and significant in the case of the certified reference material, underlying the actual difficulties in ascertaining the trueness of a method for fumonisin determination, opening thus an important issue for risk assessment.

No abstract

A modified cyclodextrin containing a dansyldiethylenetriamine metal-binding group (6-deoxy-6-N-(N‘‘-dansyldiethylenetriamino)-β-cyclodextrin, CD-dien-DNS) was synthesized. The conformation of CD-dien-DNS was studied by 2D NMR (ROESY spectra) in D2O, by circular dichroism, and by fluorescence. The results were compared with those previously obtained with the analogous 6-deoxy-6-N-(N‘-dansylethylenediamino)-β-cyclodextrin (CD-en-DNS) and were consistent with the self-inclusion of the dansyl group within the macrocycle cavity. However, the orientation of the dansyl group for CD-dien-DNS was found to be equatorial, whereas for CD-en-DNS it was axial, suggesting a dependence of the orientation of the dansyl group upon the length of the linker. In the presence of lipophilic organic molecules, CD-dien-DNS showed sensing properties similar to those observed for CD-en-DNS, suggesting a similar “in-out” movement of the dansyl group, due to competitive inclusion of the guest. Unlike CD-en-DNS, CD-dien-DNS was found to be a fluorescent chemosensor for copper(II) ion, with a linear response up to a 1:1 molar ratio, suggesting that a more flexible conformation of the linker and the presence of additional binding sites allow binding of the metal ion by the amino and sulfonamidate groups. Good selectivity for Cu(II), when compared with Fe(II), Co(II), Ni(II), and Zn(II), was observed. The CD-dien-DNS copper(II) complex was shown to behave as a chemosensor for bifunctional molecules, such as amino acids. In fact, upon addition of alanine, tryptophan, and thyroxine, the negligible fluorescence intensity of Cu(CD-dien-DNS) complex was “switched on”, with a response dependent on the amino acid side chain.

No abstract