Interactions between cyclodextrins and fluorescent T-2 and HT-2 toxin derivatives: a physico-chemical study

T-2 and HT-2 toxins are mycotoxins produced by several Fusarium species that are commonly found in various cereal grains, including oats, barley, wheat and maize. Intake estimates indicate that the presence of these mycotoxins in the diet can be of concern for public health. In this work, the inclusion processes occurring between fluorescent anthracene-derivatives of T-2 and HT-2 toxins and different cyclodextrin (CD) molecules were investigated in aqueous solutions by means of UV–Vis absorption, fluorescence emission and dynamic light scattering. Binding constant values and chemico-physical parameters were calculated. It was found that β-CDs give stronger inclusion reactions with both T-2 and HT-2 derivatives, as stated by important emission intensity increments. Such interactions were found to be fundamentally enthalpy-driven. Among β-CDs, the effect of the methylation at hydroxyl groups was tested: as a result, the di-methyl form of β-CD was found to induce the best fluorescence intensity enhancements.     

Steric and Electronic Effects on the Configurational Stability of Residual Chiral Phosphorus‐Centered Three‐Bladed Propellers: Tris‐aryl Phosphane Oxides

A series of tris‐aryl phosphane oxides existing as residual enantiomers or diastereoisomers with substituents on the aryl rings differing in size and electronic properties were synthesized and characterized. Their electronic properties were evaluated on the basis of their electrochemical oxidation and reduction potentials together with those of the corresponding “blade bromides” (i.e., the naphthalene derivatives displaying the same substitution pattern of the tris‐naphthyl phosphane oxide blades, with a bromo substituent where the phosphorus atom is located) determined by CV. The residual stereoisomeric phosphane oxides were isolated in a stereochemically pure state and were found to be highly configurationally stable at room temperature (stereoisomerization barriers of about 27 kcal mol^?1). The chiroptical properties of the residual stereoisomers and the assignments of absolute configuration are discussed. The configurational stability of residual tris‐aryl phosphane oxides was found to be scarcely influenced by the electronic properties of the substituents present on the aromatic rings constituting the blades, while steric effects play the most relevant role. Detailed theoretical calculations are in agreement with the experimental results and also contribute to a rational interpretation of the stereodynamics of these systems.     

Epoxide Opening versus Silica Condensation during Sol–Gel Hybrid Biomaterial Synthesis

Hybrid organic–inorganic solids represent an important class of engineering materials, usually prepared by sol–gel processes by cross‐reaction between organic and inorganic precursors. The choice of the two components and control of the reaction conditions (especially pH value) allow the synthesis of hybrid materials with novel properties and functionalities. 3‐Glycidoxypropyltrimethoxysilane (GPTMS) is one of the most commonly used organic silanes for hybrid‐material fabrication. Herein, the reactivity of GPTMS in water at different pH values (pH 2–11) was deeply investigated for the first time by solution‐state multinuclear NMR spectroscopic and mass spectrometric analysis. The extent of the different and competing reactions that take place as a function of the pH value was elucidated. The NMR spectroscopic and mass spectrometric data clearly indicate that the pH value determines the kinetics of epoxide hydrolysis versus silicon condensation. Under slighly acidic conditions, the epoxy‐ring hydrolysis is kinetically more favourable than the formation of the silica network. In contrast, under basic conditions, silicon condensation is the main reaction that takes place. Full characterisation of the formed intermediates was carried out by using NMR spectroscopic and mass spectrometric analysis. These results indicate that strict control of the pH values allows tuning of the reactivity of the organic and inorganic moities, thus laying the foundations for the design and synthesis of sol–gel hybrid biomaterials with tuneable properties.     

Surfactant Hydrogels for the Dispersion of Carbon‐Nanotube‐Based Catalysts

Novel hydrogel phases based on positively charged and zwitterionic surfactants, namely, N‐[p‐(n‐dodecyloxybenzyl)]‐N,N,N‐trimethylammonium bromide (pDOTABr) and p‐dodecyloxybenzyldimethylamine oxide (pDOAO), which combine pristine carbon nanotubes (CNTs), were obtained, thus leading to stable dispersions and enhanced cross‐linked networks. The composite hydrogel featuring a well‐defined nanostructured morphology and an overall positively charged surface was shown to efficiently immobilise a polyanionic and redox‐active tetraruthenium‐substituted polyoxometalate (Ru₄POM) by complementary charge interactions. The resulting hybrid gel has been characterised by electron microscopy techniques, whereas the electrostatic‐directed assembly has been monitored by means of fluorescence spectroscopy and ζ‐potential tests. This protocol offers a straightforward supramolecular strategy for the design of novel aqueous‐based electrocatalytic soft materials, thereby improving the processability of CNTs while tuning their interfacial decoration with multiple catalytic domains. Electrochemical evidence confirms that the activity of the catalyst is preserved within the gel media.     

Ammonium salt catalyzed oxidation of organosulfides to organosulfoxydes

The selective oxidation of aromatic and aliphatic organosulfides with H₂O₂/H₂O catalyzed by metal free ammonium salts has been explored. Reactions were performed using 2.5–5 mol % of catalyst loadings, isolating the corresponding sulfoxides in good to excellent yields (75–93%) and high selectivity.     

Free-radical selective functionalization of 1,4-naphthoquinones by perfluorodiacyl peroxides

Perfluoroalkyl radicals, generated by thermal decomposition of perfluorodiacyl peroxides, react selectively with quinone rings of 1,4-naphthoquinones. In the presence of a non-conjugated alkene such as 1-hexene, perfluoroalkyl radicals add to the double bonds of the olefin forming a radical adduct, which selectively adds to the naphthoquinone ring. Several perfluorodiacyl peroxides have been synthesized and used for the direct and alkene-mediated functionalization of naphthoquinones. Geometrical parameters and electron density topology of all perfluorodiacyl peroxides have been calculated by the density functional formalism and quantum theory of atoms in molecules to attempt a rationalization of the experimental reactivity.     

Separation of complex sugar mixtures on a hydrolytically stable bidentate urea‐type stationary phase for hydrophilic interaction near ultra high performance liquid chromatography

A stationary phase bearing both bridged bis‐ureido and free amino groups (USP‐HILIC‐NH₂–2.5SP) for high‐speed hydrophilic interaction liquid chromatography separations was prepared using a one‐pot two‐step procedure starting from 2.5 μm totally porous silica particles. Highly polar compounds, such as polyols, hydroxybenzoic acids, and sugars, were successfully analyzed in shorter times and with higher peak efficiency, when compared to results obtained with a bidentate urea‐type column packed with 5 μm particles. Increased sugarophilicity and better peak shape were attested for the USP‐HILIC‐NH₂–2.5SP column (100 × 3.2 mm id) when compared with two commercially available UHPLC columns, namely an acquity BEH amide packed with totally porous 1.7 μm microparticles and a HILIC Kinetex column packed with core–shell 2.6 μm particles. Finally, the new column was employed in the separation of complex mixture of sugars (mono‐, di‐, and oligosaccharides) and in the analysis of beer samples. The resulting chromatograms showed good selectivity and overall resolution, while the catalyzing effect of the free amino moieties resulted in excellent peak shapes and in the absence of split peaks due to sugar anomerization phenomena.     

Promotion of Förster Resonance Energy Transfer in a Saponite Clay Containing Luminescent Polyhedral Oligomeric Silsesquioxane and Rhodamine Dye

A new hybrid photostable saponite clay with embedded donor–acceptor dyes was prepared and characterized in this work. The saponite is intercalated with a luminescent polyhedral oligomeric silsesquioxane, which transfers the photoexcitation energy directly to an acceptor dye (rhodamine B). The obtained composite material was characterized by means of XRD, TEM microscopy, and UV/Vis and photoluminescence spectroscopy. A physicochemical study showed that the system behaved as an efficient Förster resonance energy transfer pair, owing to the very good spectral overlap of donor emission (λ_em=510–540 nm) and acceptor absorption in the λ=530–570 nm range. The hybrid material represents the first example of a photonic antenna based on a synthetic saponite clay and can be considered a step forward in the search for new, efficient, and stable materials suitable for light‐harvesting applications.     

A priori error estimates for nonstationary optimal control problems with gradient state constraints

We are concerned with the discretization of semilinear parabolic optimization problems subject to constraints on the first derivative of the solution of the PDE. Constructing sequences of feasible controls for the dG(0)-cG(1) discretization of the problem and relying on a quadratric growth condtion, we show convergence orders as temporal and spatial mesh tends to zero. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)