Dario Battistel

Electrochemical Mapping Reveals Direct Correlation between Heterogeneous Electron-Transfer Kinetics and Local Density of States in Diamond Electrodes

Conducting carbon materials: a multi-microscopy approach shows that local heterogeneous electron-transfer rates at conducting diamond electrodes correlate with the local density of electronic states. This model of electroactivity is of considerable value for the rational design of conducting diamond electrochemical technologies, and also provides key general insights on electrode structure controls in electrochemical kinetics.

Simple and clear evidence for positive feedback limitation by bipolar behavior during scanning electrochemical microscopy of unbiased conductors.

On the basis of an experimentally validated simple theoretical model, it is demonstrated unambiguously that when an unbiased conductor is probed by a scanning electrochemical tip (scanning electrochemical microscopy, SECM), it performs as a bipolar electrode. Though already envisioned in most recent SECM theories, this phenomenon is generally overlooked in SECM experimental investigations. However, as is shown here, this may alter significantly positive feedback measurements when the probed conductor is not much larger than the tip.

In Situ Scanning Electrochemical Microscopy (SECM) Detection of Metal Dissolution during Zinc Corrosion by Means of Mercury Sphere‐Cap Microelectrode Tips

This work presents a scanning electrochemical microscopy (SECM)-based in situ corrosion probing methodology that is capable of monitoring the release of zinc species in corrosion processes. It is based on the use of Hg-coated Pt microelectrodes as SECM tips, which offer a wider negative potential range than bare platinum or other noble-metal tips. This allows for the reduction of zinc ions at the tip to be investigated with low interference from hydrogen evolution and oxygen reduction from aqueous solutions. The processes involved in the corrosion of zinc during its immersion in chloride-containing solutions were successfully monitored by scanning the SECM tip, set at an adequate potential, across the sample either in one direction or in the X-Y plane parallel to its surface. In this way, it was possible to detect the anodic and cathodic sites at which the dissolution of zinc and the reduction of oxygen occurred, respectively. Additionally, cyclic voltammetry (CV) or constant potential measurements were used to monitor the release of zinc species collected at the tip during an SECM scan.

Iron-binding characterization and polysaccharide production by Klebsiella oxytoca strain isolated from mine acid drainage

Aims:  To investigate Klebsiella oxytoca strain BAS‐10 growth on ferric citrate under anaerobic conditions for exopolysaccharide (EPS) production and localization on cell followed by the purification and the EPS determination of the iron‐binding stability constant to EPS or biotechnological applications.

Characterisation of biosynthesised silver nanoparticles by scanning electrochemical microscopy (SECM) and voltammetry.

Silver nanoparticles (AgNPs) were biosynthesised by a Klebsiella oxytoca strain BAS-10, which, during its growth, is known to produce a branched exopolysaccharide (EPS). Klebsiella oxytoca cultures, treated with AgNO3 and grown under either aerobic or anaerobic conditions, produced silver nanoparticles embedded in EPS (AgNPs-EPS) containing different amounts of Ag(0) and Ag(I) forms. The average size of the AgNPs-EPS was determined by transmission electron microscopy, while the relative abundance of Ag(0)- or Ag(I)-containing AgNPs-EPS was established by scanning electrochemical microscopy (SECM). Moreover, the release of silver(I) species from the various types of AgNPs-EPS was investigated by combining SECM with anodic stripping voltammetry. These measurements allowed obtaining information on the kinetic of silver ions release from AgNPs-EPS and their concentration profiles at the substrate/water interface.

A Rapid Electrochemical Procedure for the Detection of Hg(0) Produced by Mercuric-Reductase: Application for Monitoring Hg- resistant Bacteria Activity.

In this work, gold microelectrodes are employed as traps for the detection of volatilized metallic mercury produced by mercuric reductase (MerA) extracted from an Hg-resistant Pseudomonas putida strain FB1. The enzymatic reduction of Hg (II) to Hg (0) was induced by NADPH cofactor added to the samples. The amount of Hg(0) accumulated on the gold microelectrode surface was determined by anodic stripping voltammetry (ASV) after transferring the gold microelectrode in an aqueous solution containing 0.1 M HNO(3) + 1 M KNO(3). Electrochemical measurements were combined with spectrofluorometric assays of NADPH consumption to derive an analytical expression for the detection of a relative MerA activity of different samples with respect to that of P. putida. The method developed here was employed for the rapid determination of MerA produced by bacteria harbored in soft tissues of clams (Ruditapes philippinarum), collected in high Hg polluted sediments of Northern Adriatic Sea in Italy.

Fire and human record at Lake Victoria, East Africa, during the Early Iron Age: Did humans or climate cause massive ecosystem changes?

Organic molecular markers determined in a sediment core (V95-1A-1P) from Lake Victoria (East Africa) were used to reconstruct the history of human impact and regional fire activity during the Early Iron Age (~2400 to ~1100 yr BP). Fire history was reconstructed using levoglucosan and polycyclic aromatic hydrocarbons (PAHs) as markers for biomass burning that demonstrate two distinct fire periods peaking at 1450–1700 and 1850–2050 cal. yr BP. A partial correlation between levoglucosan and PAHs is interpreted as different transport behaviors and burn temperatures affecting the proxies. A fecal sterol index (CoP-Index) indicates the presence of humans near the lakeshore, where the CoP-Index lags a few centuries behind the fire peaks. The CoP-Index peaks between 1850 and1950 cal. yr BP and between 1400 and 1500 cal. yr BP. Retene, a PAH that indicates softwood combustion, differs from other PAHs and levoglucosan by abruptly increasing at ~1650 cal. yr BP and remaining high until 1200 cal. yr BP. This increase may potentially signal human activity in that the development of metallurgy and/or ceramic production requires highly efficient fuels. However, this increase in retene occurs at the same time as severe drought events centered at ~1500 and ~2000 yr BP where the droughts and associated woodland to grassland transition may have resulted in more intense fires. The grassland expansion could have created favorable conditions for human activities and triggered settlement growth that in turn may have created a positive feedback for further landscape opening.

Direct immersion solid‐phase microextraction with gas chromatography and mass spectrometry for the determination of specific biomarkers of human sweat in melted snow

To provide a reliable tool for investigating diffusion processes of the specific components of the human odor 3-hydroxy-3-methylhexanoic acid and 3-methyl-3-sulfanylhexan-1-ol through the snowpack, we developed and optimized an analytical method based on direct immersion solid-phase microextraction followed by gas chromatography with mass spectrometry. Direct immersion solid-phase microextraction was performed using polyacrylate fibers placed in aqueous solutions containing 3-hydroxy-3-methylhexanoic acid and 3-methyl-3-sulfanylhexan-1-ol. After optimization, absorption times of 120 min provided a good balance to shorten the analysis time and to obtain suitable amounts of extractable analytes. The extraction efficiency was improved by increasing the ionic strength of the solution. Although the absolute extraction efficiency ranged between 10 and 12% for 3-hydroxy-3-methylhexanoic acid and 2-3% for 3-methyl-3-sulfanylhexan-1-ol, this method was suitable for analyzing 3-hydroxy-3-methylhexanoic acid and 3-methyl-3-sulfanylhexan-1-ol concentrations of at least 0.04 and 0.20 ng/mL, respectively. The precision of the direct immersion solid-phase microextraction method ranged between 8 and 16%. The variability within a batch of six fibers was 10-18%. The accuracy of the method provided values of 88-95 and 86-101% for 3-hydroxy-3-methylhexanoic acid and 3-methyl-3-sulfanylhexan-1-ol, respectively. The limit of detection (and quantification) was 0.01 ng/mL (0.04 ng/mL) for 3-hydroxy-3-methylhexanoic acid and 0.06 ng/mL (0.20 ng/mL) for 3-methyl-3-sulfanylhexan-1-ol. The signal versus concentration was linear for both compounds (r(2) = 0.973-0.979). The stability of these two compounds showed that 3-hydroxy-3-methylhexanoic acid was more stable in water than 3-methyl-3-sulfanylhexan-1-ol. We applied the method to environmental samples in correspondence with an olfactory target buried previously.

Mononuclear and heterodinuclear phenanthrolinedione complexes of d- and f-block elements‡

Abstract1,10-Phenanthroline-5,6-dione (Phd) complexes of group 3 and lanthanide elements having formulae Ln(hfac)3(Phd) (Ln = Y, Eu, Yb; hfac = hexafluoroacetylacetonate) were synthesised and characterised. Complexes of d-block elements of the type [MCl(Phd)(p-cymene)]+ (M = Ru, Os) were also prepared. In all these species, coordination of the polydentate ligand occurs by the N-donor moieties, as indicated by DFT calculations. The novel compounds were tested, together with fac-ReBr(Phd)(CO)3, as precursors for the preparation of heterobimetallic d/f derivatives. The reaction of the rhenium complex with yttrium or lanthanide anhydrous triflate salts led to the formation of the complexes ReBr(CO)3(N,N′-Phd-O,O′)Ln(OTf)3(THF) (Ln = Y, Eu, Yb), where the trivalent ions interacted with the quinonoid moiety. The redox properties of the rhenium centre were strongly affected by the coordination of Ln(OTf)3, as observed by comparing the cyclic voltammetry measurements carried out on fac-ReBr(Phd)(CO)3 and on ReBr(CO)3(N,N′-Phd-O,O′)Y(OTf)3.

A thin ice layer segregates two distinct fungal communities in Antarctic brines from Tarn Flat (Northern Victoria Land)

Brines are hypersaline solutions which have been found within the Antarctic permafrost from the Tarn Flat area (Northern Victoria Land). Here, an investigation on the possible presence and diversity of fungal life within those peculiar ecosystems has been carried out for the first time. Brines samples were collected at 4- and 5-meter depths (TF1 and TF2, respectively), from two brines separated by a thin ice layer. The samples were analyzed via Illumina MiSeq targeting the ITS region specific for both yeasts and filamentous fungi. An unexpected high alpha diversity was found. Beta diversity analysis revealed that the two brines were inhabited by two phylogenetically diverse fungal communities (Unifrac value: 0.56, p value < 0.01; Martin’s P-test p-value < 0.001) characterized by several specialist taxa. The most abundant fungal genera were Candida sp., Leucosporidium sp., Naganishia sp. and Sporobolomyces sp. in TF1, and Leucosporidium sp., Malassezia sp., Naganishia sp. and Sporobolomyces sp. in TF2. A few hypotheses on such differentiation have been done: i) the different chemical and physical composition of the brines; ii) the presence in situ of a thin layer of ice, acting as a physical barrier; and iii) the diverse geological origin of the brines.