Adsorption and self-organization of CuOEP on heterogeneous surfaces : tuning the molecule-substrate interaction

The adsorption and self-organization of copper(II) octaethyl porphyrin (CuOEP) have been studied in detail on heterogeneous surfaces by Scanning Tunnelling Microscopy (STM), Low Energy Electron Diffraction (LEED) and Ultraviolet Photoelectron Spectroscopy (UPS). The research has been focussed both on the adsorption of CuOEP on clean metals as well as on ultrathin sodium chloride films grown on metals. For this reason, in a first stage, the growth of NaCl films on Cu(111), Ag(111) and Ag(001) has been carefully investigated. For submonolayer coverages the samples show the formation of NaCl islands with a characteristic rectangular shape, which coexist with clean metal regions. Salt structurestoML thick can be identified. CuOEP molecules have been deposited on the so prepared heterogeneous salt-metal surfaces. STM reveals that the molecules self organize in ordered monolayers on the bare metal areas as well as on the NaCl islands. Series of observations performed by increasing the CuOEP coverage in steps fromtoML revealed that the assembly develops in a hierarchical fashion. Molecules sequentially adsorb and assemble first on the bare metal, then on the 1-layer and 2-layer thick NaCl areas. From these observations it can be inferred that the adsorption energy of CuOEP decreases by introducing an insulator layer and by increasing its thickness. Moreover, the investigation of the STM appearance of CuOEP as a function of the bias voltage, indicates a weaker adsorbate-substrate interaction on the NaCl/metal system than on the bare metal. The adsorption of CuOEP on the clean metal has been further investigated by LEED and UPS. Combining LEED and STM, the structure of the molecular layer formed on Cu(111), Ag(111) and Ag(001) is determined. Information on the adsorption conformation of CuOEP has also been gained by high resolution STM. In these measurements several intramolecular features can be recognized and they fit very well with simulated STM images based on DFT calculations. The theoretical predictions of the molecular orbital energies fit also very well with the UPS measurements. In particular the position and the relative intensity of HOMO and HOMO-1 levels show a very good agreement between experiment and calculation. UPS has also been used to measure the work function change of the various metal substrates upon CuOEP adsorption. These experiments prove that, for all metal investigated, a charge transfer from the molecule to the substrate takes place. This charge transfer is found to depend on the work function of the substrate. In particular the comparison between the Ag(111) and Ag(001) cases demonstrates that the observed work function change does not depend only on the chemistry of the substrate but also on the details of the surface electronic structure

Influence of reactor surface materials on the ozone zero phenomenon

It is long known that for highly efficient ozone production in a dielectric barrier discharge (DBD), it is beneficial to add a small quantity of nitrogen to the oxygen feed gas. When operated in very pure oxygen without any significant nitrogen content, the ozone formation even drops to zero under certain operating conditions. This is known in the field as the “ozone zero phenomenon”, or OZP. The exact mechanisms of said effect, however, are still not understood and a subject of ongoing research. In the present work, we investigated the influence of different reactor surface materials, and their changes when exposed to plasma, on their influence on ozone formation under different nitrogen conditions. The metal powder deposited on the reactor surfaces by sputtering effects was found to have a buffering effect on the time scale needed for the OZP to fully develop. We conclude that the surface of the DBD reactor, in particular the available surface area for nitrogen compounds to adsorb to, is the crucial element in understanding the processes behind the OZP

A neurochemical map of the developing amphioxus nervous system

Abstract Background Amphioxus, representing the most basal group of living chordates, is the best available proxy for the last invertebrate ancestor of the chordates. Although the central nervous system (CNS) of amphioxus comprises only about 20,000 neurons (as compared to billions in vertebrates), the developmental genetics and neuroanatomy of amphioxus are strikingly vertebrate-like. In the present study, we mapped the distribution of amphioxus CNS cells producing distinctive neurochemicals. To this end, we cloned genes encoding biosynthetic enzymes and/or transporters of the most common neurotransmitters and assayed their developmental expression in the embryo and early larva. Results By single and double in situ hybridization experiments, we identified glutamatergic, GABAergic/glycinergic, serotonergic and cholinergic neurons in developing amphioxus. In addition to characterizing the distribution of excitatory and inhibitory neurons in the developing amphioxus CNS, we observed that cholinergic and GABAergic/glycinergic neurons are segmentally arranged in the hindbrain, whereas serotonergic, glutamatergic and dopaminergic neurons are restricted to specific regions of the cerebral vesicle and the hindbrain. We were further able to identify discrete groups of GABAergic and glutamatergic interneurons and cholinergic motoneurons at the level of the primary motor center (PMC), the major integrative center of sensory and motor stimuli of the amphioxus nerve cord. Conclusions In this study, we assessed neuronal differentiation in the developing amphioxus nervous system and compiled the first neurochemical map of the amphioxus CNS. This map is a first step towards a full characterization of the neurotransmitter signature of previously described nerve cell types in the amphioxus CNS, such as motoneurons and interneurons.</p

Molecular Assembly and Self-Assembly: Molecular Nanoscience for Future Technologies

In this review the emerging science of single molecules is discussed from the perspective of nanoscale molecular functions and devices. New methods for the controlled assembly of well-defined molecular nanostructures are presented: self assembly and single molecular positioning. The observation and selective modification of conformation, electronics, and molecular mechanics of individual molecules and molecular assemblies by scanning probes are demonstrated. To complement this scientific review, some of the possible consequences and visions for future developments are discussed, as far as they derive from the presented systems. Here, the prospects of nanoscale science to stimulate technological evolution are exemplified

The GABAergic-like system in the marine demosponge <i>Chondrilla nucula</i>

Gamma-amino butyric acid (GABA) is believed to be the principal inhibitory neurotransmitter in the mammalian central nervous system, a function that has been extended to a number of invertebrate systems. The presence of GABA in the marine demosponge Chondrilla nucula was verified using immunofluorescence detection and high-pressure liquid chromatography. A strong GABA-like immunoreactivity (IR) was found associated with choanocytes, exopinacocytes, endopinacocytes lining inhalant, and exhalant canals, as well as in archaeocytes scattered in the mesohyl. The capacity to synthesize GABA from glutamate and to transport it into the vesicles was confirmed by the presence in C. nucula of glutamate decarboxylase (GAD) and vesicular GABA transporters (vGATs), respectively. GAD-like and vGAT-like IR show the same distribution as GABA-like IR. Supporting the similarity between sponge and mammalian proteins, bands with an apparent molecular weight of about 65-67 kDa and 57 kDa were detected using antibodies raised against mammalian GAD and vGAT, respectively. A functional metabotropic GABAB-like receptor is also present in C. nucula. Indeed, both GABAB R1 and R2 isoforms were detected by immunoblot and immunofluorescence. Also in this case, IR was found in choanocytes, exopinacocytes, and endopinacocytes. The content of GABA in C. nucula amounts to 1225.75 ± 79 pmol/mg proteins and GABA is released into the medium when sponge cells are depolarized. In conclusion, this study is the first indication of the existence of the GABA biosynthetic enzyme GAD and of the GABA transporter vGAT in sponges, as well as the first demonstration that the neurotransmitter GABA is released extracellularly

The GABAergic-like system in the marine demosponge Chondrilla nucula

Gamma-amino butyric acid (GABA) is believed to be the principal inhibitory neurotransmitter in the mammalian central nervous system, a function that has been extended to a number of invertebrate systems. The presence of GABA in the marine demosponge Chondrilla nucula was verified using immunofluorescence detection and high-pressure liquid chromatography. A strong GABA-like immunoreactivity (IR) was found associated with choanocytes, exopinacocytes, endopinacocytes lining inhalant, and exhalant canals, as well as in archaeocytes scattered in the mesohyl. The capacity to synthesize GABA from glutamate and to transport it into the vesicles was confirmed by the presence in C. nucula of glutamate decarboxylase (GAD) and vesicular GABA transporters (vGATs), respectively. GAD-like and vGAT-like IR show the same distribution as GABA-like IR. Supporting the similarity between sponge and mammalian proteins, bands with an apparent molecular weight of about 65-67 kDa and 57 kDa were detected using antibodies raised against mammalian GAD and vGAT, respectively. A functional metabotropic GABA(B)-like receptor is also present in C. nucula. Indeed, both GABA(B) R1 and R2 isoforms were detected by immunoblot and immunofluorescence. Also in this case, IR was found in choanocytes, exopinacocytes, and endopinacocytes. The content of GABA in C. nucula amounts to 1225.75 +/- 79 pmol/mg proteins and GABA is released into the medium when sponge cells are depolarized. In conclusion, this study is the first indication of the existence of the GABA biosynthetic enzyme GAD and of the GABA transporter vGAT in sponges, as well as the first demonstration that the neurotransmitter GABA is released extracellularly