Adsorption of ethynyl-cyclopropyl-cyclooctyne (ECCO), an alkyne-functionalized cyclooctyne, on Si(0 0 1) was studied by means of x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Together, XPS and STM results clearly indicate chemoselective adsorption of ECCO on Si(0 0 1) via a [2+2] cycloaddition of the strained triple bond of cyclooctyne without reaction of the ethynyl group. The results are compared to the adsorption of acetylene on Si(0 0 1): C 2 H 2 adsorbs on Si(0 0 1) via a precursor-mediated reaction channel as it was shown by means of temperature dependent measurements of the sticking probability as well as by means of STM experiments at variable temperature. On the other hand, cyclooctyne adsorbs on Si(0 0 1) via a direct reaction channel. This qualitative difference in the reaction pathways of the two functionalities leads to the observed chemoselective adsorption of ECCO via the strained triple bond of cyclooctyne. As the ethynyl group stays intact, monolayers of ECCO on Si(0 0 1) form a well defined interface between the silicon substrate and further organic molecular layers which can be attached to the ethynyl functionality.
Ants are a biodiverse group of insects that have evolved toxic venom containing many undiscovered bioactive molecules. In this study, we found that the venom of the ruby ant Myrmica rubra is a rich source of peptides. LC-MS analysis revealed the presence of 142 different peptides varying in molecular weight, sequence length, and hydrophobicity. One of the most abundant peaks was selected for further biochemical and functional characterization. Combined Edman degradation and de novo peptide sequencing revealed the presence of a novel decapeptide (myrmicitoxin) with the amino acid sequence NH2-IDPKLLESLA-CONH2. The decapeptide was named U-MYRTX-MRArub1 and verified against a synthetic standard. The amidated peptide was tested in a synthetic form to determine the antimicrobial activity towards the bacterial pathogens and insecticidal potential against pea aphids (Acyrthosiphon pisum). This peptide did not show antimicrobial activity but it significantly reduced the survival of aphids. It also increased the sensitivity of the aphids to two commonly used chemical insecticides (imidacloprid and methomyl). Since ant venom research is still in its infancy, the findings of this first study on venom peptides derived from M. rubra highlight these insects as an important and rich source for discovery of novel lead structures with potential application in pest control.
Ant venoms contain many small, linear peptides, an untapped source of bioactive peptide toxins. The control of agricultural insect pests currently depends primarily on chemical insecticides, but their intensive use damages the environment and human health, and encourages the emergence of resistant pest populations. This has promoted interest in animal venoms as a source of alternative, environmentally-friendly bio-insecticides. We tested the crude venom of the predatory ant, Manica rubida, and observed severe fitness costs in the parthenogenetic pea aphid (Acyrthosiphon pisum), a common agricultural pest. Therefore, we explored the M. rubida venom peptidome and identified a novel decapeptide U-MYRTX-MANr1 (NH2-IDPKVLESLV-CONH2) using a combination of Edman degradation and de novo peptide sequencing. Although this myrmicitoxin was inactive against bacteria and fungi, it reduced aphid survival and reproduction. Furthermore, both crude venom and U-MYRTX-MANr1 reversibly paralyzed injected aphids and induced a loss of body fluids. Components of M. rubida venom may act on various biological targets including ion channels and hemolymph coagulation proteins, as previously shown for other ant venom toxins. The remarkable insecticidal activity of M. rubida venom suggests it may be a promising source of additional bio-insecticide leads.
The reaction of a methyl-substituted benzylazide on the silicon (001) surface was investigated by means of X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density functional theory (DFT)-based computations. It was found that the reaction takes place via an intermediate state, which could be experimentally observed at low temperatures. XPS analysis showed that at temperatures of 150 K and above, the azide further reacts on the silicon surface via abstraction of N 2 . The final state sees the remaining nitrogen atom of the adsorbate binding covalently to the surface. In the STM images, this final state is associated with two different adsorption configurations. In comparison with DFT calculations, these two configurations are assigned to the molecule being bound via the nitrogen atom only and to a configuration with the molecule bound to the substrate via the nitrogen atom and carbon ring simultaneously.
Adsorption of methanol on Si(001) was studied by means of X-ray photoelectron spectroscopy (XPS), molecular beam techniques, and scanning tunneling microscopy (STM) at surface temperatures between 50 and 800 K. Even at lowest temperatures, only the final reaction products, i.e., a silicon bound methoxy group and a Si−H entity, were observed in the XPS and STM experiments. However, the initial sticking probability drops with increasing surface temperature, indicating that the reaction proceeds via an intermediate state. Two final configurations with the dissociation products adsorbed either on one or two silicon dimers were observed; their branching ratio does not change with temperature, indicating very similar, low conversion barriers for the two pathways.
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