Use of liquid chromatography–high‐resolution mass spectrometry for isolation and characterization of hydrolyzed fumonisins and relevant analysis in maize‐based products

The synthesis of partially hydrolyzed fumonisins (PHFB₁ and PHFB₂) and hydrolyzed fumonisins (HFB₁ and HFB₂) by chemical hydrolysis of pure fumonisins (FB₁ and FB₂) is reported together with the isolation and characterization by liquid chromatography–high‐resolution mass spectrometry (LC–HRMS). Two structural isomers of partially hydrolyzed forms of FB₁ and FB₂ were identified, namely PHFB_1a and PHFB_1b and PHFB_2a and PHFB_2b. Reaction yields were 21% for PHFB₁ (sum of the two isomers), 52% for HFB₁, 31% for PHFB₂ (sum of the two isomers) and 30% for HFB₂. Purity of each isolated compound was >98%. An LC–HRMS method for the simultaneous determination of fumonisins and their partially and totally hydrolyzed derivatives was applied to 24 naturally contaminated samples of maize and maize‐based products. The majority of samples (18 out of 24) were contaminated with fumonisins B₁ and B₂. Fumonisins co‐occurred with both partially hydrolyzed and hydrolyzed fumonisins in four nixtamalized samples (three masa flours and one tortilla chips). Co‐occurrence of fumonisins with partially hydrolyzed fumonisins was also recorded in one sample of maize kernels and four samples of maize‐based products (i.e. maize meal, cous‐cous, corn‐cakes and cornflakes). Mycotoxins levels ranged from 60 to 5700 µg/kg for fumonisins (sum of FB₁ and FB₂), from 10 to 210 µg/kg for partially hydrolyzed fumonisins (sum of PHFB₁ and PHFB₂) and from 30 to 200 µg/kg for hydrolyzed fumonisins (sum of HFB₁ and HFB₂). This is the first report of the isolation of PHFB₂ and the co‐occurrence of FB_1, FB₂, PHFB₁, PHFB₂, HFB₁ and HFB₂ in maize products. Considering the growing use of nixtamalized and maize‐based products, the monitoring of fumonisins and their partially and totally hydrolyzed forms in these products may represent an important contributing factor in evaluating the relevant human risk exposure. Copyright © 2014 John Wiley & Sons, Ltd.     

Determination of fumonisins B1 and B2 in corn-based foods for infants and young children by LC with immunoaffinity column cleanup: interlaboratory validation study

A liquid chromatographic method for the determination of fumonisins B1 (FB1) and B2 (FB2) in corn-based foods for infants and young children was subjected to an interlaboratory validation study involving 11 laboratories. Five blind duplicate sample pairs of each matrix were analyzed to establish the accuracy, repeatability, and reproducibility of the method. Mass fractions in the baby food samples ranged from 89.1 to 384.4 microg/kg FB1 and from 22.5 to 73.6 microg/kg FB2. The method involved a warm extraction with citrate phosphate buffer-methanol-acetonitrile (50 + 25 + 25, v/v/v), a cleanup through an immunoaffinity column, and an end-determination of fumonisins by LC after automated precolumn derivatization with o-phthaldialdehyde reagent. RSDs for within-laboratory repeatability (RSDr) ranged from 6.8 to 23.5% for FB1 and 7.6 to 22.9% for FB2. RSDs for between-laboratory reproducibility (RSDR) ranged from 15.4 to 26.2% for FB1 and 21.6 to 36.3% for FB2. Mean FB1 recoveries from baby foods spiked at 100.0 and 250.0 microg/kg were 89 and 96%, respectively; for FB2 spiked foods at 25.0 and 62.5 microg/kg recoveries were 90 and 85%, respectively. HorRat values ranged from 0.8 to 1.2 for FB1, whereas for FB2 they ranged from 0.9 to 1.4 when calculated according to Horwitz, and from 1.0 to 1.7 when calculated according to Thompson, indicating an acceptable among-laboratory precision for all matrixes (HorRat values <2).     

Study of the interference effects in an optical cavity for organic light-emitting diode applications

The interference effects generated in a bottom-emitting electroluminescent device fabricated on a polymer underlayer introduced with the aim of improving the anode roughness have been studied. The analysis of the interference fringes at different detection angles and the spatial coherence demonstrates that this phenomenon is due to multiple internal reflections that propagate in the polymer layer. This effect can be eliminated by modifying the polymer thickness and the incidence angle of the electromagnetic radiation at the anode-polymer interface. Inkjet etching technology is adopted for microcavities-shaped polymer structuring to destroy the resonator effect of the optical cavity.     

The chemical behaviour of the azido group bonded to copper(I): Synthesis and reactivity of thiothiatriazolato and alkynyl complexes

The copper(I) azido-derivatives, (PPh₃)(phen)CuN₃ (Ia) and (PPh₃)(TMP)CuN₃ (Ib) (phen = 1,10-phenanthroline; TMP = 3,4,7,8-tetramethyl-1,10-phenanthroline), obtained from [(PPh₃)₂CuN₃]₂ and the bidentate ligand (biL), react with CS₂ to give the thiothiatriazolato-copper(I) complexes, (PPh₃)(phen)Cu$\text{NC(S)SNN}$ (IIa) and (PPh₃)(TMP)Cu$\text{NC(S)SNN}$ (IIb). The preparation of IIa and IIb occurs only when free triphenylphosphine is present in the reaction medium. The isothiocyanate complexes, (PPh₃)(biL)Cu(NCS) (biL = phen, IIIa; biL = TMP, IIIb) are formed, instead of IIa and IIb, when free PPh₃ is not added to the reaction medium. The complexes IIIa and IIIb are also obtained when CH₂Cl₂ solutions of IIa and IIb are stirred for 15 h in the absence of light; if longer reaction times are used, the dimeric isothiocyanato complexes [(biL)Cu(NCS)]₂ are formed. Compounds IIa and IIb react with PhCOCl to give (PPh₃)(biL)CuCl and 4-benzoyl-1,2,3,4-thiatriazole-5-thione, PhCO$\text{NC(S)SNN}$.Treatment of Ia and Ib, or [(PPh₃)₂CuN₃]₂, with COS did not lead to isolation of characterizable products. An unsaturated molecule such as ethyl propriolate, EtO₂CCCH, does not behave as a 1,3-dipolarophile in its reactions with Ia and Ib, the alkynyl derivatives [(biL)Cu₂(CCCO₂Et)₂]_n (_n is probably 2; biL = phen, IVa; biL = TMP, IVb), being obtained. Similarly the azido-complex [(PPh₃)₂CuN₃]₂ reacts with ethyl propiolate to give the asymmetric binuclear alkynyl derivative, (PPh₃)₃Cu₂(CCCO₂Et)₂ (V). The reaction of V with hydrogen chloride gives EtO₂CCCH and the known complex (PPh₃)₃Cu₂Cl₂, confirming the above formulation. The reactions of V with neutral ligands such as TMP, phen and CyNC have also been studied, leading to the isolation of new copper(I) alkynyl-derivatives.     

Synthesis and crystal structure of [(PhenH)(PhenH2)][BiCl6]·2H2O with different o-phenanthroline protonations

The reaction between bismuthate oxide and phen (1,10-phenanthroline) in acid medium led to the isolation of the unusual [(PhenH)(PhenH₂)][BiCl₆]·2H₂O derivative, which has been characterized by X-ray analysis and IR spectroscopy. The compound crystallizes in the triclinic space group with a = 8.313(2), b = 9.349(2), c = 9.807(3) Å, = 86.39(3), = 110.27(3) and = 106.48(3)°. The crystal structure is made of [BiCl₆]^3– anions and [(PhenH)(PhenH₂)]³⁺ cations. A network of hydrogen bond interactions involving the two clathrated water molecules, the phenanthroline moiety and the chlorines characterizes the entire structure.     

Unique Formation of a Crystal Phase Containing Cyclic Oligomers and Helical Polymers of the Same Monomeric Fragment

The yellow, microcrystalline compound [Cu(pymo)] (Hpymo=2-hydroxypyrimidine) has been characterized with the newly emerging technique of ab initio X-ray powder diffraction. A unique and unprecedented crystal phase containing cyclic oligomers and infinite helical polymers (see picture) of the same monomeric fragment is selectively formed upon reaction of [Cu(CH₃CN)₄][BF₄] and Hpymo with NEt₃.     

The innovative method of high accuracy interferometric calibration of the Precision Laser Inclinometer

In this report a high accuracy method for an interferometric calibration of the Precision Laser Inclinometer (PLI) is proposed. The method is based on the simultaneous measurement of: (a) the PLI base calibration slope (angle), set by a piezoelectric positioner, via laser interferometry and (b) the PLI response signal. A calibration coefficient of 322.5 ± 1.9 μrad/V has been determined experimentally in an interval [4 × 10^–7, 4 × 10^–6] rad in which there is a linear dependence between the PLI-signal and the calibration angle.     

Metal imidazolato polymers: synthesis, characterization and crystal structure of new silver(I) triphenylphosphine derivatives

When the polymeric complex [Ag(im)]_n (Him = imidazole) is reacted with PPh₃ (PPh₃ = triphenylphosphine), it yields the [Ag₂(μ₂-im)₂(PPh₃)₃]_n and [Ag(μ₂-im)(PPh₃)₂]_n species, shown to contain wavy chains of metal ions, singly bridged by N,N′-exo-bidentate imidazolate ligands. The former, crystallised as the CH₂Cl₂ solvate, contains two non-equivalent silver(I) ions, differing in the number of coordinated phosphines (one, in trigonal planar stereochemistry, or two, having tetrahedral geometry). The latter has a unique independent silver(I) ion in a tetrahedral environment, with two coordinated PPh₃ ligands. The reactivity of known silver(I) azolates with PPh₃, as well as the solution behaviour and (when available) the crystal structures of the corresponding derivatives are taken into consideration for a due comparison.     

Nuclear magnetic resonance approaches to brain function studies

The fast developing and newly emerging nuclear magnetic resonance methods for functional brain imaging are discussed. The main features of blood-oxygen-level-dependent (BOLD) imaging and perfusion imaging are exposed together with their limitations. The combination of localized spectroscopy with magnetic resonance imaging (MRI) and neuronal activation provide the crucial metabolic information, which is complementary to the physiological data given by BOLD and perfusion imaging. Finally, the diffusion tensor imaging and the nonlinear MRI, with the perspective of getting information about the “architecture” of the axonal connections and of the macrostructures are discussed.     

Filled Polysilsesquioxanes: A New Approach to Chemical Sensing

Summary : In an attempt to investigate new polymeric materials as constituents of an e-nose we focus our attention on a new emerging class of versatile three-dimensional polyhedral silicon polymers, called polysilsesquioxanes, containing nanosized inorganic cages. Such hybrid amphiphilic materials offer exceptional opportunities to create composites with singular properties. In particular we found that the polyhedral organosilsesquioxane (POSS) cages covalently attached to the polymer backbone as side-chain act as an “internal” filler with a nanometric homogeneous dispersion. We show how it is possible to fabricate sensing devices based on selected POSS matrix and, by a suitable choice of other “external” home-made fillers, (e.g. graphite, copper, silicon, zinc and their alloys) obtained by mechanical milling the response of the resulting composites towards different classes of compounds can be tuned. In particular we fabricated a new high sensitive relative humidity device, exhibiting a fivefold response change for relative humidity changing in the range 0% to 100%. This behaviour can not be modelled on the basis of the matrix swelling operating mechanism. Rather, the combined effect of the matrix and the filler has to be invoked in order to explain the formation of nanopores inside the material that are responsible of the porous behavior of our sensors.