Adsorption and charge transfer interactions of bi-isonicotinic acid on Ag(111)

The adsorption and charge transfer dynamics of the organic molecule bi-isonicotinic acid (4,4′-dicarboxy-2,2′-bipyridine) on single crystal Ag(111) has been studied using synchrotron radiation-based photoemission, x-ray absorption and resonant core spectroscopies. Measurements for multilayer and monolayer coverage are used to determine the nature of the molecule-surface interactions and the molecular orientation. An experimental density of states for the monolayer with respect to the underlying metal surface is obtained by combining x-ray absorption spectroscopy at the N 1s edge and valence photoemission to measure the unoccupied and occupied valence states, respectively. This shows that the lowest unoccupied molecular orbital in the core-excited state lies energetically below the Fermi level of the surface allowing charge transfer from the metal into this orbital. Resonant photoelectron spectroscopy was used to probe this charge transfer in the context of super-spectator and super-Auger electron transitions. The results presented provide a novel interpretation of resonant core-level spectroscopy to explore ultra-fast charge transfer between an adsorbed organic molecule and a metal surface through the observation of electrons from the metal surface playing a direct role in the core-hole decay of the core-excited molecule

Exploring ultra-fast charge transfer and vibronic coupling with N 1s RIXS maps of an aromatic molecule coupled to a semiconductor

We present for the first time two-dimensional resonant inelastic x-ray scattering (RIXS) maps of multilayer and monolayer biisonicotinic acid adsorbed on the rutile TiO2(110) single crystal surface. This enables the elastic channel to be followed over the lowest unoccupied molecular orbitals resonantly excited at the N 1s absorption edge. The data also reveals ultra-fast intramolecular vibronic coupling, particularly during excitation into the LUMO-derived resonance. Both elastic scattering and the vibronic coupling loss features are expected to contain the channel in which the originally excited electron is directly involved in the core-hole decay process. This allows RIXS data for a molecule coupled to a wide bandgap semiconductor to be considered in the same way as the core-hole clock implementation of resonant photoemission spectroscopy (RPES). However, contrary to RPES measurements, we find no evidence for depletion of the participator channel under the conditions of ultra-fast charge transfer from the molecule to the substrate densities of states, on the timescale of the core-hole lifetime. These results suggest that the radiative core-hole decay processes in RIXS are not significantly modified by charge transfer on the femtosecond timescale in this system

Charge transfer from an adsorbed ruthenium-based photosensitizer through an ultra-thin aluminium oxide layer and into a metallic substrate

The interaction of the dye molecule N3 (cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4′-dicarbo-xylato)-ruthenium(II)) with the ultra-thin oxide layer on a AlNi(110) substrate, has been studied using synchrotron radiation based photoelectron spectroscopy, resonant photoemission spectroscopy, and near edge X-ray absorption fine structure spectroscopy. Calibrated X-ray absorption and valence band spectra of the monolayer and multilayer coverages reveal that charge transfer is possible from the molecule to the AlNi(110) substrate via tunnelling through the ultra-thin oxide layer and into the conduction band edge of the substrate. This charge transfer mechanism is possible from the LUMO+2 and 3 in the excited state but not from the LUMO, therefore enabling core-hole clock analysis, which gives an upper limit of 6.0 ± 2.5 fs for the transfer time. This indicates that ultra-thin oxide layers are a viable material for use in dye-sensitized solar cells, which may lead to reduced recombination effects and improved efficiencies of future devices

An in situ exploration of subsurface defect migration to a liquid water‐exposed rutile TiO2(110) surface by XPS

The ability of titanium dioixide to split water into OH− and H+ species is heavily dependent on the behaviour of defects in the crystal structure at or near the surface. We present an in situ study of defect migration in rutile TiO2(110) conducted using X‐ray photoelectron spectroscopy (XPS). First, surface and subsurface defects were created in the crystal by argon ion sputtering. Subsequent in situ exposure of the defective crystal to liquid water healed the surface defects, whereas the subsurface remained defective. The sample was then annealed while XPS was used to monitor the concentration of titanium defects. At low annealing temperatures, Ti3+ was observed to migrate from the subsurface to the surface. Further annealing gradually restored the surface and subsurface to the defect‐free Ti4+ form, during which the changes in abundance of Ti1+, Ti2+ and Ti3+ defects are discussed

A soft x-ray probe of a titania photoelectrode sensitized with a triphenylamine dye

We present a thorough soft x-ray photoelectron spectroscopy (XPS) study of a mesoporous titanium dioxide electrode sensitized with the dye 4-(diphenylamino)phenylcyanoacrylic acid, referred to as “L0.” Supported by calculations, the suite of XPS, x-ray absorption spectroscopy, and resonant photoelectron spectroscopy allows us to examine bonding interactions between the dye and the surface and the frontier electronic structure at the molecule-oxide interface. While placing these measurements in the context of existing literature, this paper is intended as a useful reference for further studies of more complex triphenylamine based sensitizers

Development and use of lentiviral vectors pseudotyped with influenza B haemagglutinins: application to vaccine immunogenicity, mAb potency and sero-surveillance studies

Influenza B viruses cause respiratory disease epidemics in human populations and are included in seasonal influenza vaccines. Serological methods are employed to evaluate vaccine immunogenicity prior to licensure. However, the haemagglutination inhibition assay, which represents the gold standard for assessing the immunogenicity of influenza vaccines, has been shown to be relatively insensitive for the detection of antibodies against influenza B viruses. Furthermore, this assay, and the serial radial haemolysis assay are not able to detect stalk-directed cross-reactive antibodies. For these reasons there is a need to develop new assays that can overcome these limitations. The use of replication-defective viruses, such as lentiviral vectors pseudotyped with influenza A haemagglutinins, in microneutralization assays is a safe and sensitive alternative to study antibody responses elicited by natural infection or vaccination. We have produced Influenza B haemagglutinin-pseudotypes using plasmid-directed transfection. To activate influenza B haemagglutinin, we have explored the use of proteases by adding relevant encoding plasmids to the transfection mixture. When tested for their ability to transduce target cells, the newly produced influenza B pseudotypes exhibit tropism for different cell lines. Subsequently the pseudotypes were evaluated as surrogate antigens in microneutralization assays using reference sera, monoclonal antibodies, human sera collected during a vaccine immunogenicity study and surveillance sera from seals. The influenza B pseudotype virus neutralization assay was found to effectively detect neutralizing and cross-reactive responses despite lack of significant correlation with the haemagglutinin inhibition assay

Metabolic Roles of Uncultivated Bacterioplankton Lineages in the Northern Gulf of Mexico "Dead Zone".

This is the final version of the article. Available from American Society for Microbiology via the DOI in this record.Marine regions that have seasonal to long-term low dissolved oxygen (DO) concentrations, sometimes called "dead zones," are increasing in number and severity around the globe with deleterious effects on ecology and economics. One of the largest of these coastal dead zones occurs on the continental shelf of the northern Gulf of Mexico (nGOM), which results from eutrophication-enhanced bacterioplankton respiration and strong seasonal stratification. Previous research in this dead zone revealed the presence of multiple cosmopolitan bacterioplankton lineages that have eluded cultivation, and thus their metabolic roles in this ecosystem remain unknown. We used a coupled shotgun metagenomic and metatranscriptomic approach to determine the metabolic potential of Marine Group II Euryarchaeota, SAR406, and SAR202. We recovered multiple high-quality, nearly complete genomes from all three groups as well as candidate phyla usually associated with anoxic environments-Parcubacteria (OD1) and Peregrinibacteria Two additional groups with putative assignments to ACD39 and PAUC34f supplement the metabolic contributions by uncultivated taxa. Our results indicate active metabolism in all groups, including prevalent aerobic respiration, with concurrent expression of genes for nitrate reduction in SAR406 and SAR202, and dissimilatory nitrite reduction to ammonia and sulfur reduction by SAR406. We also report a variety of active heterotrophic carbon processing mechanisms, including degradation of complex carbohydrate compounds by SAR406, SAR202, ACD39, and PAUC34f. Together, these data help constrain the metabolic contributions from uncultivated groups in the nGOM during periods of low DO and suggest roles for these organisms in the breakdown of complex organic matter.IMPORTANCE Dead zones receive their name primarily from the reduction of eukaryotic macrobiota (demersal fish, shrimp, etc.) that are also key coastal fisheries. Excess nutrients contributed from anthropogenic activity such as fertilizer runoff result in algal blooms and therefore ample new carbon for aerobic microbial metabolism. Combined with strong stratification, microbial respiration reduces oxygen in shelf bottom waters to levels unfit for many animals (termed hypoxia). The nGOM shelf remains one of the largest eutrophication-driven hypoxic zones in the world, yet despite its potential as a model study system, the microbial metabolisms underlying and resulting from this phenomenon-many of which occur in bacterioplankton from poorly understood lineages-have received only preliminary study. Our work details the metabolic potential and gene expression activity for uncultivated lineages across several low DO sites in the nGOM, improving our understanding of the active biogeochemical cycling mediated by these "microbial dark matter" taxa during hypoxia

On the suitability of high vacuum electrospray deposition for the fabrication of molecular electronic devices

We present a series of three studies investigating the potential application of high vacuum electrospray deposition to construct molecular electronic devices. Through the use of time of flight secondary ion mass spectrometry we explore the use of this novel deposition technique to fabricating multilayer structures using materials that are compatible with the same solvents and films containing a mixture of molecules from orthogonal solvents. Using x-ray photoelectron spectroscopy we study the deposition of a polymer blend using electrospray and find evidence of preferential deposition of one of the components