A molecular probe for the optical detection of biogenic amines

A coumarin derivative was employed for the detection of biogenic amines in buffered aqueous solution by UV-Vis or fluorescence spectroscopy. Incorporated in a polymeric matrix, the dye can also be used for the optical detection of gaseous amines.     

A simple fluorescence assay for the detection of fluoride in water at neutral pH

A simple assay for the detection of fluoride in water by fluorescence spectroscopy was developed. The assay is based on commercially available reagents and allows sensing of fluoride in the low millimolar concentration range with high selectivity over other anions.     

Subsurface examination of a foliar biofilm using scanning electron- and focused-ion-beam microscopy

The dual beam scanning electron microscope, equipped with both a focused ion- and scanning electron-beam (FIB SEM) is a novel tool for the exploration of the subsurface structure of biological tissues. The FIB can remove a predetermined amount of material from a selected site to allow for subsurface exploration and when coupled with SEM or scanning ion-beam microscopy (SIM) could be suitable to examine the subsurface structure of bacterial biofilms on the leaf surface. The suitability of chemical and cryofixation was examined for use with the FIB SEM to examine bacterial biofilms on leaf surfaces. The biological control agent, Burkholderia pyroccinia FP62, that rapidly colonizes the leaf surface and forms biofilms, was inoculated onto geranium leaves and incubated in a greenhouse for 7 or 14 days. Cryofixation was not suitable for examination of leaf biofilms because it created a frozen layer over the leaf surface that cracked when exposed to the electron beam and the protective cap required for FIB milling could not be accurately deposited. With chemically fixed samples, it was possible to precisely FIB mill a single cross section (5μm) or sequential cross sections from a single site without any damage to the surrounding surface. Biofilms, 7 days post-inoculation (DPI), were composed of 2-5 bacterial cell layers while biofilms 14 DPI ranged from 5 to greater than 30 cell layers. Empty spaces between bacteria cells in the subsurface structure were observed in biofilms 7- and 14-DPI. Sequential cross sections inferred that the empty spaces were often continuous between FP62 cells and could possibly make up a network of channels throughout the biofilm. FIB SEM was a useful tool to observe the subsurface composition of a foliar biofilm.     

Site-directed methyl group labeling as an NMR probe of structure and dynamics in supramolecular protein systems: applications to the proteasome and to the ClpP protease

Methyl groups are powerful reporters of structure, motion, and function in NMR studies of supramolecular protein assemblies. Their utility can be hindered, however, by spectral overlap, difficulties with assignment or lack of probes in biologically important regions of the molecule studied. Here we show that (13)CH(3)-S- labeling of Cys side chains using (13)C-methyl-methanethiosulfonate ((13)C-MMTS) (IUPAC name: methylsulfonylsulfanylmethane) provides a convenient probe of molecular structure and dynamics. The methodology is demonstrated with an application focusing on the gating residues of the Thermoplasma acidophilum proteasome, where it is shown that the (13)CH(3)-S- label reports faithfully on the conformational heterogeneity and dynamics in this region of the complex. A second and related application involves labeling with (13)C-MMTS at the N-termini of the subunits comprising the E. coli ClpP protease that reveals multiple conformations of gating residues in this complex as well. These N-terminal residues adopt a single conformation upon gate opening.     

Estimation of lake water - groundwater interactions in meromictic mining lakes by modelling isotope signatures of lake water

A method is presented to assess lake water-groundwater interactions by modelling isotope signatures of lake water using meteorological parameters and field data. The modelling of delta(18)O and deltaD variations offers information about the groundwater influx into a meromictic Lusatian mining lake. Therefore, a water balance model is combined with an isotope water balance model to estimate analogies between simulated and measured isotope signatures within the lake water body. The model is operated with different evaporation rates to predict delta(18)O and deltaD values in a lake that is only controlled by weather conditions with neither groundwater inflow nor outflow. Comparisons between modelled and measured isotope values show whether the lake is fed by the groundwater or not. Furthermore, our investigations show that an adaptation of the Craig and Gordon model [H. Craig, L.I. Gordon. Deuterium and oxygen-18 variations in the ocean and the marine atmosphere. In Stable Isotopes in Oceanographic Studies and Paleotemperature, Spoleto, E. Tongiorgi (Ed.), pp. 9-130, Consiglio Nazionale delle Ricerche, Laboratorio di Geologia Nucleare, Pisa (1965).] to specific conditions in temperate regions seems necessary.     

Superconductivity in hydrogenated carbon nanostructures

We present an application of density functional theory for superconductors to superconductivity in hydrogenated carbon nanotubes and fullerane (hydrogenated fullerene). We show that these systems are chemically similar to graphane (hydrogenated graphene) and like graphane, upon hole doping, develop a strong electron phonon coupling. This could lead to superconducting states with critical temperatures approaching 100 K, however this possibility depends crucially on if and how metallization is achieved.     

Head-to-Tail Dimerization of N-Heterocyclic Diazoolefins

The head-to-tail dimerization of N-heterocyclic diazoolefins is described. The products of these formal (3+3) cycloaddition reactions are strongly reducing quinoidal tetrazines. Oxidation of the tetrazines occurs in a stepwise fashion, and we were able to isolate a stable radical cation and diamagnetic dications. The latter are also accessible by oxidative dimerization of diazoolefins.