Gold Fusion: From Au₂₅(SR)₁₈ to Au₃₈(SR)₂₄, the Most Unexpected Transformation of a Very Stable Nanocluster

The study of the molecular cluster Au₂₅(SR)₁₈ has provided a wealth of fundamental insights into the properties of clusters protected by thiolated ligands (SR). This is also because this cluster has been particularly stable under a number of experimental conditions. Very unexpectedly, we found that paramagnetic Au₂₅(SR)₁₈⁰ undergoes a spontaneous bimolecular fusion to form another benchmark gold nanocluster, Au₃₈(SR)₂₄. We tested this reaction with a series of Au₂₅ clusters. The fusion was confirmed and characterized by UV–vis absorption spectroscopy, ESI mass spectrometry, ¹H and ¹³C NMR spectroscopy, and electrochemistry. NMR evidences the presence of four types of ligand and, for the same proton type, double signals caused by the diastereotopicity arising from the chirality of the capping shell. This effect propagates up to the third carbon atom along the ligand chain. Electrochemistry provides a particularly convenient way to study the evolution process and determine the fusion rate constant, which decreases as the ligand length increases. No reaction is observed for the anionic clusters, whereas the radical nature of Au₂₅(SR)₁₈⁰ appears to play an important role. This transformation of a stable cluster into a larger stable cluster without addition of any co-reagent also features the bottom-up assembly of the Au₁₃ building block in solution. This very unexpected result could modify our view of the relative stability of molecular gold nanoclusters

In Vitro Production of Fumonisins by Fusarium verticillioides under Oxidative Stress Induced by H₂O₂

The effects of oxidative stress induced by H₂O₂ were tested in liquid cultures in the fumonisin-producing fungus Fusarium verticillioides. The quantitative analysis of fumonisins B₁, B₂, B₃, and B₄ was achieved by means of liquid chromatography coupled to high-resolution mass spectrometry. Two effects in F. verticillioides, consisting of different abilities to produce fumonisins in response to oxidative stress, were identified. Following H₂O₂ addition, two F. verticillioides strains produced significantly more fumonisin (>300%) while three other strains produced significantly less (<20%) in comparison to control cultures. Transcriptional studies with seven biosynthetic genes showed a significant increase in transcript levels in the strain that made more fumonisin and either no or minimal changes in the strain that made less fumonisin. Our data indicate the important role of oxidative stress toward the modulation of the fumonisin biosynthesis and suggest the necessity to verify the presence of such divergent behavior in F. verticillioides populations under natural conditions

Electrochemosensor for Trace Analysis of Perfluorooctanesulfonate in Water Based on a Molecularly Imprinted Poly(<i>o</i>‑phenylenediamine) Polymer

This work is aimed at developing an electrochemical sensor for the sensitive and selective detection of trace levels of perfluorooctanesulfonate (PFOS) in water. Contamination of waters by perfluorinated alkyl substances (PFAS) is a problem of global concern due to their suspected toxicity and ability to bioaccumulate. PFOS is the perfluorinated compound of major concern, as it has the lowest suggested control concentrations. The sensor reported here is based on a gold electrode modified with a thin coating of a molecularly imprinted polymer (MIP), prepared by anodic electropolymerization of <i>o</i>-phenylenediamine (o-PD) in the presence of PFOS as the template. Activation of the sensor is achieved by template removal with suitable a solvent mixture. Voltammetry, a quartz crystal microbalance, scanning electron microscopy and elemental analysis were used to monitor the electropolymerization process, template removal, and binding of the analyte. Ferrocenecarboxylic acid (FcCOOH) has been exploited as an electrochemical probe able to generate analytically useful voltammetric signals by competing for the binding sites with PFOS, as the latter is not electroactive. The sensor has a low detection limit (0.04 nM), a satisfactory selectivity, and is reproducible and repeatable, giving analytical results in good agreement with those obtained by HPLC-MS/MS analyses

Management of a Toxic Cyanobacterium Bloom (<i>Planktothrix rubescens</i>) Affecting an Italian Drinking Water Basin: A Case Study

An extraordinary bloom of <i>Planktothrix rubescens</i>, which can produce microcystins (MCs), was observed in early 2009 in the Occhito basin, used even as a source of drinking water in Southern Italy. Several activities, coordinated by a task force, were implemented to assess and manage the risk associated to drinking water contaminated by cyanobacteria. Main actions were: evaluation of analytical protocols for screening and confirmatory purpose, monitoring the drinking water supply chain, training of operators, a dedicated web site for risk communication. ELISA assay was considered suitable for health authorities as screening method for MCs and to optimize frequency of sampling according to alert levels, and as internal control for the water supplier. A liquid chromatography-tandem mass spectrometric method able to quantify 9 MCs was optimized with the aim of supporting health authorities in a comprehensive risk evaluation based on the relative toxicity of different congeners. Short, medium, and long-term corrective actions were implemented to mitigate the health risk. Preoxidation with chlorine dioxide followed by flocculation and settling have been shown to be effective in removing MCs in the water treatment plant. Over two years, despite the high levels of cyanobacteria (up to 160 × 10⁶ cells/L) and MCs (28.4 μg/L) initially reached in surface waters, the drinking water distribution was never limited

Platinum(II) Complexes with Novel Diisocyanide Ligands: Catalysts in Alkyne Hydroarylation

A series of novel diisocyanide ligands (<i>o</i>-CNC₆H₄O)₂Y (diNC-1: Y = P­(O)­Ph; diNC-2: Y = <i>o</i>-C­(O)­C₆H₄C­(O); diNC-3: Y = <i>m</i>-C­(O)­C₆H₄C­(O); diNC-4: Y = C­(O)­C₂H₄C­(O); diNC-5: Y = <i>trans</i>-C­(O)­C₂H₂C­(O)) was successfully synthesized by reaction of lithium 2-isocyanophenate (generated in situ from benzoxazole and <i>n</i>-BuLi) and a diacylic or phosphonic dichloride. The corresponding platinum­(II) complexes of general formula [PtX₂(diNC)]_1,2 (X = Cl, Me; diNC = diisocyanide ligand) were isolated by simple substitution of 1,5-cyclooctadiene in the starting [PtX₂(COD)] complexes. The structure of the complexes, mononuclear or dinuclear, was confirmed by single-crystal X-ray analysis. A dinuclear complex of formula {(μ-diNC)­[<i>cis</i>-PtCl₂(PPh₃)]₂} could also be obtained with the diisocyanide ligand having a rigid fumaryl bridge and consequently the isocyanide moieties pointing in opposite directions. All the complexes were employed as catalysts in the hydroarylation of alkynes, showing generally good activity and selectivity toward the <i>trans</i>-hydroarylation product. With <i>N</i>-methylindole as aromatic substrate the major product was instead a heterocycle:alkyne 2:1 adduct

Platinum(II) Complexes with Novel Diisocyanide Ligands: Catalysts in Alkyne Hydroarylation

A series of novel diisocyanide ligands (<i>o</i>-CNC₆H₄O)₂Y (diNC-1: Y = P­(O)­Ph; diNC-2: Y = <i>o</i>-C­(O)­C₆H₄C­(O); diNC-3: Y = <i>m</i>-C­(O)­C₆H₄C­(O); diNC-4: Y = C­(O)­C₂H₄C­(O); diNC-5: Y = <i>trans</i>-C­(O)­C₂H₂C­(O)) was successfully synthesized by reaction of lithium 2-isocyanophenate (generated in situ from benzoxazole and <i>n</i>-BuLi) and a diacylic or phosphonic dichloride. The corresponding platinum­(II) complexes of general formula [PtX₂(diNC)]_1,2 (X = Cl, Me; diNC = diisocyanide ligand) were isolated by simple substitution of 1,5-cyclooctadiene in the starting [PtX₂(COD)] complexes. The structure of the complexes, mononuclear or dinuclear, was confirmed by single-crystal X-ray analysis. A dinuclear complex of formula {(μ-diNC)­[<i>cis</i>-PtCl₂(PPh₃)]₂} could also be obtained with the diisocyanide ligand having a rigid fumaryl bridge and consequently the isocyanide moieties pointing in opposite directions. All the complexes were employed as catalysts in the hydroarylation of alkynes, showing generally good activity and selectivity toward the <i>trans</i>-hydroarylation product. With <i>N</i>-methylindole as aromatic substrate the major product was instead a heterocycle:alkyne 2:1 adduct