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 (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Leitfähige Kohlenstoffmaterialien: Eine Kombination von Mikroskopietechniken zeigt, dass die lokalen heterogenen Elektronentransferraten leitfähiger Diamant‐Elektroden mit der lokalen Dichte elektronischer Zustände korrelieren. Dieses Elektroaktivitätsmodell ist für die Entwicklung von elektrochemischen Methoden basierend auf leitfähigem Diamant bedeutsam und zeigt den Einfluss der Elektrodenstruktur auf die elektrochemische Kinetik (siehe Bild).

Monolayers and bilayers of lipid mixtures self-assembled on mercury form spontaneously gel-phase (solid ordered, s o ) and liquid-ordered (l o ) microdomains, thanks to the fluidity imparted to these films by the liquid metal support. The differential capacity of the hydrocarbon tail region of monolayers of mixtures of two lipid components of high and low transition temperature T m , increases during the transition from the liquid disordered (l d ) phase to the coexistence of l d and s o phases. Addition of cholesterol to this binary mixture causes a decrease in differential capacity. This behavior is explained by regarding the capacity as a measure of the total perimeter of the s o microdomains, due to the mismatch between these microdomains and the l d phase. Cholesterol removes this mismatch by converting the anisotropic s o microdomains into isotropic l o microdomains (rafts). This allows differential capacity measurements by electrochemical impedance spectroscopy to follow phase transitions in lipid mixtures. The coexistance of l d , l o and s o phases is confirmed by images of a distal lipid monolayer self-assembled on top of a thiolipid monolayer tethered to a mercury microcap, by using two-photon fluorescence lifetime imaging microscopy (2P-FLIM).

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.Methods and Results:Klebsiella oxytoca ferments ferric citrate under anaerobic conditions and produces a ferric hydrogel, whereas ferrous ions were formed in solution. During growth, cells precipitate and a hydrogel formation was observed: the organic material was constituted of an EPS bound to Fe(III) ions, this was found by chemical analyses of the iron species and transmission electron microscopy of the cell cultures. Iron binding to EPS was studied by cyclic voltammetric measurements, either directly on the hydrogel or in an aqueous solutions containing Fe(III)-citrate and purified Fe(III)-EPS. From the voltammetric data, the stability constant for the Fe(III)-EPS complex can be assumed to have values of approx. 1012–1013. It was estimated that this is higher than for the Fe(III)-citrate complex.Conclusions:The production of Fe(III)-EPS under anaerobic conditions is a strategy for the strain to survive in mine drainages and other acidic conditions. This physiological feature can be used to produce large amounts of valuable Fe(III)-EPS, starting from a low cost substrate such as Fe(III)-citrate.Significant and Impact of the Study:The data herein demonstrates that an interesting metal-binding molecule can be produced as a novel catalyst for a variety of potential applications and the EPS itself is a valuable source for rhamnose purification.

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.

Deforestation associated with the initial settlement of New Zealand is a dramatic example of how humans can alter landscapes through fire. However, evidence linking early human presence and land-cover change is inferential in most continental sites. We employed a multi-proxy approach to reconstruct anthropogenic land use in New Zealand’s South Island over the last millennium using fecal and plant sterols as indicators of human activity and monosaccharide anhydrides, polycyclic aromatic hydrocarbons, charcoal and pollen as tracers of fire and vegetation change in lake-sediment cores. Our data provide a direct record of local human presence in Lake Kirkpatrick and Lake Diamond watersheds at the time of deforestation and a new and stronger case of human agency linked with forest clearance. The first detection of human presence matches charcoal and biomarker evidence for initial burning at c. AD 1350. Sterols decreased shortly after to values suggesting the sporadic presence of people and then rose to unprecedented levels after the European settlement. Our results confirm that initial human arrival in New Zealand was associated with brief and intense burning activities. Testing our approach in a context of well-established fire history provides a new tool for understanding cause-effect relationships in more complex continental reconstructions.

Silver nanoparticles (AgNPs), embedded into a specific exopolysaccharide (EPS), were produced by Klebsiella oxytoca DSM 29614 by adding AgNO3 to the cultures during exponential growth phase. In particular, under aerobic or anaerobic conditions, two types of silver nanoparticles, named AgNPs-EPS(aer) and the AgNPs-EPS(anaer), were produced respectively. The effects on bacterial cells was demonstrated by using Escherichia coli K12 and Kocuria rhizophila ATCC 9341 (ex Micrococcus luteus) as Gram-negative and Gram-positive tester strains, respectively. The best antimicrobial activity was observed for AgNPs-EPS(aer), in terms of minimum inhibitory concentrations and minimum bactericidal concentrations. Observations by transmission electron microscopy showed that the cell morphology of both tester strains changed during the exposition to AgNPs-EPS(aer). In particular, an electron-dense wrapped filament was observed in E. coli cytoplasm after 3 h of AgNPs-EPS(aer) exposition, apparently due to silver accumulation in DNA, and both E. coli and K. rhizophila cells were lysed after 18 h of exposure to AgNPs-EPS(aer). The DNA breakage in E. coli cells was confirmed by the comparison of 3-D fluorescence spectra fingerprints of DNA. Finally the accumulation of silver on DNA of E. coli was confirmed directly by a significant Ag(+) release from DNA, using the scanning electrochemical microscopy and the voltammetric determinations.

No abstract