6 research outputs found
Gold Fusion: From Au<sub>25</sub>(SR)<sub>18</sub> to Au<sub>38</sub>(SR)<sub>24</sub>, the Most Unexpected Transformation of a Very Stable Nanocluster
The
study of the molecular cluster Au<sub>25</sub>(SR)<sub>18</sub> 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 Au<sub>25</sub>(SR)<sub>18</sub><sup>0</sup> undergoes a spontaneous bimolecular
fusion to form another benchmark gold nanocluster, Au<sub>38</sub>(SR)<sub>24</sub>. We tested this reaction with a series of Au<sub>25</sub> clusters. The fusion was confirmed and characterized by
UV–vis absorption spectroscopy, ESI mass spectrometry, <sup>1</sup>H and <sup>13</sup>C 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 Au<sub>25</sub>(SR)<sub>18</sub><sup>0</sup> 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 Au<sub>13</sub> 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 H<sub>2</sub>O<sub>2</sub>
The effects of oxidative stress induced
by H<sub>2</sub>O<sub>2</sub> were tested in liquid cultures in the
fumonisin-producing fungus Fusarium verticillioides. The quantitative analysis of fumonisins B<sub>1</sub>, B<sub>2</sub>, B<sub>3</sub>, and B<sub>4</sub> 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 H<sub>2</sub>O<sub>2</sub> 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
× 10<sup>6</sup> 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>-CNC<sub>6</sub>H<sub>4</sub>O)<sub>2</sub>Y (diNC-1:
Y = PÂ(O)ÂPh; diNC-2:
Y = <i>o</i>-CÂ(O)ÂC<sub>6</sub>H<sub>4</sub>CÂ(O); diNC-3:
Y = <i>m</i>-CÂ(O)ÂC<sub>6</sub>H<sub>4</sub>CÂ(O); diNC-4:
Y = CÂ(O)ÂC<sub>2</sub>H<sub>4</sub>CÂ(O); diNC-5: Y = <i>trans</i>-CÂ(O)ÂC<sub>2</sub>H<sub>2</sub>CÂ(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 platinumÂ(II) complexes of general formula [PtX<sub>2</sub>(diNC)]<sub>1,2</sub> (X = Cl, Me; diNC = diisocyanide ligand)
were isolated by simple substitution of 1,5-cyclooctadiene in the
starting [PtX<sub>2</sub>(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)Â[<i>cis</i>-PtCl<sub>2</sub>(PPh<sub>3</sub>)]<sub>2</sub>} 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>-CNC<sub>6</sub>H<sub>4</sub>O)<sub>2</sub>Y (diNC-1:
Y = PÂ(O)ÂPh; diNC-2:
Y = <i>o</i>-CÂ(O)ÂC<sub>6</sub>H<sub>4</sub>CÂ(O); diNC-3:
Y = <i>m</i>-CÂ(O)ÂC<sub>6</sub>H<sub>4</sub>CÂ(O); diNC-4:
Y = CÂ(O)ÂC<sub>2</sub>H<sub>4</sub>CÂ(O); diNC-5: Y = <i>trans</i>-CÂ(O)ÂC<sub>2</sub>H<sub>2</sub>CÂ(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 platinumÂ(II) complexes of general formula [PtX<sub>2</sub>(diNC)]<sub>1,2</sub> (X = Cl, Me; diNC = diisocyanide ligand)
were isolated by simple substitution of 1,5-cyclooctadiene in the
starting [PtX<sub>2</sub>(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)Â[<i>cis</i>-PtCl<sub>2</sub>(PPh<sub>3</sub>)]<sub>2</sub>} 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