Relativistic magnetotransport in graphene

We study the thermal and electric transport of a fluid of interacting Dirac fermions as they arise in single-layer graphene. We include Coulomb interactions, a dilute density of charged impurities and the presence of a magnetic field to describe both the static and the low frequency response as a function of temperature T and chemical potential mu. In the critical regime mu << T where both bands above and below the Dirac point contribute to transport we find pronounced deviations from Fermi liquid behavior, universal, collision-dominated values for transport coefficients and a cyclotron resonance of collective nature. In the collision-dominated high temperature regime the linear thermoelectric transport coefficients are shown to obey the constraints of relativistic magnetohydrodynamics which we derive microscopically from Boltzmann theory. The latter also allows us to describe the crossover to disorder-dominated Fermi liquid behavior at large doping and low temperatures, as well as the crossover to the ballistic regime at high fields.Comment: Proceedings of the Landau Memorial Conference 200

Internal dynamics of the 3-Pyrroline-N-Oxide ring in spin-labeled proteins

Site-directed spin labeling is a versatile tool to study structure as well as dynamics of proteins using EPR spectroscopy. Methanethiosulfonate (MTS) spin labels tethered through a disulfide linkage to an engineered cysteine residue were used in a large number of studies to extract structural as well as dynamic information on the protein from the rotational dynamics of the nitroxide moiety. The ring itself was always considered to be a rigid body. In this contribution, we present a combination of high-resolution X-ray crystallography and EPR spectroscopy of spin-labeled protein single crystals demonstrating that the nitroxide ring inverts fast at ambient temperature while exhibiting nonplanar conformations at low temperature. We have used quantum chemical calculations to explore the potential energy that determines the ring dynamics as well as the impact of the geometry on the magnetic parameters probed by EPR spectroscopy

The Chiral Herbicide Beflubutamid (II): Enantioselective Degradation and Enantiomerization in Soil, and Formation/Degradation of Chiral Metabolites

Beflubutamid is a chiral soil herbicide currently marketed as racemate against dicotyledonous weeds in cereals. Biotests have shown that (−)-beflubutamid is at least 1000× more active than (+)-beflubutamid. Potential substitution of the racemate by (−)-beflubutamid should therefore be further considered. Here, we investigated the degradation behavior in soils and formation and degradation of two chiral metabolites. Laboratory incubation experiments were performed with an alkaline and an acidic soil. The compounds were analyzed by enantioselective GC-MS. Degradation rate constants were determined by kinetic modeling. In the alkaline soil, degradation of beflubutamid was slightly enantioselective, with slower degradation of the herbicidally active (−)-enantiomer. In the acidic soil, however, both enantiomers were degraded at similar rates. In contrast, degradation of a phenoxybutanamide metabolite was highly enantioselective. Chiral stability of beflubutamid and its metabolites was studied in separate incubations with the pure enantiomers in the same soils. In these experiments, (−)-beflubutamid was not converted to the nonactive (+)-enantiomer and vice versa. Significant enantiomerization was, however, observed for the major metabolite, a phenoxybutanoic acid. With regard to biological activity and behavior in soils, enantiopure (−)-beflubutamid definitively has the potential to substitute for the racemic herbicide

Surface Interactions Surpass Carbon–Carbon Bond: Understanding and Control of the Scission Behavior of Core–Shell Polymer Brushes on Surfaces

A tapping-mode AFM investigation of core–shell cylindrical polymer brushes (CPBs) on mica shows that they can be ruptured upon spin-coating. Three different CPBs were synthesized, having a methacrylate backbone, carrying branches of poly[oligo(ethylene glycol)methacrylate] (POEGMA), POEGMA-<i>block</i>-poly[2-(dimethylamino)ethyl methacrylate] (POEGMA-<i>b-</i>PDMAEMA), and POEGMA-<i>block</i>-poly[2-(methacryloyloxy)ethyl trimethylammoniumiodide] (POEGMA-<i>b</i>-PMETAI). The polymer backbone of core–shell CPB with POEGMA-<i>b</i>-PDMAEMA or POEGMA-<i>b</i>-PMETAI branches is ruptured upon drying on a mica surface, while they are stable in aqueous solution. We propose that the scission behavior is induced by Coulomb interactions between PDMAEMA or PMETAI corona and the solid surface and that this interaction is stronger than one or more carbon–carbon single bonds. We control this scission behavior by tuning the surface interactions through switching the surface nature, varying pH, or adding multivalent counterions. Our study demonstrates that core–shell CPB serves as a template to directly compare the weak intermolecular forces with the strong carbon–carbon covalent bonds

Direct Sampling and Analysis of Atmospheric Particulate Organic Matter by Proton-Transfer-Reaction Mass Spectrometry

We report on a new method for analyzing atmospheric submicrometer particulate organic matter which combines direct particle sampling and volatilization with online chemical ionization mass spectrometric analysis. Technically, the method relies on the combined use of a CHARON (“<i>Chemical Analysis of Aerosol Online</i>”) particle inlet and a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS). Laboratory studies on target analytes showed that the ionization conditions in the PTR-ToF-MS lead to extensive fragmentation of levoglucosan and <i>cis</i>-pinonic acid, while protonated oleic acid and 5α-cholestane molecules remain intact. Potential problems and biases in quantitative and qualitative analyses are discussed. Side-by-side atmospheric comparison measurements of total particulate organic mass and levoglucosan with an aerosol mass spectrometer (AMS) were in good agreement. Complex and clearly distinct organic mass spectra were obtained from atmospheric measurements in three European cities (Lyon, Valencia, Innsbruck). Data visualization in reduced-parameter frameworks (e.g., oxidation state of carbon vs carbon number) revealed that the CHARON-PTR-ToF-MS technique adds significant analytical capabilities for characterizing particulate organic carbon in the Earth’s atmosphere. Positive matrix factorization (PMF) was used for apportioning sources of atmospheric particles in late fall in Innsbruck. The <i>m</i>/<i>z</i> signatures of known source marker compounds (levoglucosan and resin acids, polycyclic aromatic hydrocarbons, nicotine) in the mass spectra were used to assign PMF factors to biomass burning, traffic, and smoking emission sources