Magnetic and superconducting interactions couple electrons together to form complex states of matter. We show that, at the atomic scale, both types of interactions can coexist and compete to influence the ground state of a localized magnetic moment. Local spectroscopy at 4.5 kelvin shows that the spin-1 system formed by manganese-phthalocyanine (MnPc) adsorbed on Pb(111) can lie in two different magnetic ground states. These are determined by the balance between Kondo screening and superconducting pair-breaking interactions. Both ground states alternate at nanometer length scales to form a Moiré-like superstructure. The quantum phase transition connecting the two (singlet and doublet) ground states is thus tuned by small changes in the molecule-lead interaction.

Large π-conjugated molecules, when in contact with a metal surface, usually retain a finite electronic gap and, in this sense, stay semiconducting. In some cases, however, the metallic character of the underlying substrate is seen to extend onto the first molecular layer. Here, we develop a chemical rationale for this intriguing phenomenon. In many reported instances, we find that the conjugation length of the organic semiconductors increases significantly through the bonding of specific substituents to the metal surface and through the concomitant rehybridization of the entire backbone structure. The molecules at the interface are thus converted into different chemical species with a strongly reduced electronic gap. This mechanism of surface-induced aromatic stabilization helps molecules to overcome competing phenomena that tend to keep the metal Fermi level between their frontier orbitals. Our findings aid in the design of stable precursors for metallic molecular monolayers, and thus enable new routes for the chemical engineering of metal surfaces.

We study heating and heat dissipation of a single C60 molecule in the junction of a scanning tunneling microscope (STM) by measuring the electron current required to thermally decompose the fullerene cage. The power for decomposition varies with electron energy and reflects the molecular resonance structure. When the STM tip contacts the fullerene the molecule can sustain much larger currents. Transport simulations explain these effects by molecular heating due to resonant electronphonon coupling and molecular cooling by vibrational decay into the tip upon contact formation.The paradigm of molecular electronics is the use of a single molecule as an electronic device [1]. This concept is sustained on the basis that a single molecule (or a molecular thin film) should withstand the flow of electron current densities as large as 10 10 A/m 2 without degrading. A fraction of these electrons heat the molecular junction through inelastic scattering with the molecule [2]. The temperature at the junction is a consequence of an equilibrium between heating due to electron flow and heat dissipation out of the junction. The former is dominated by the coupling of electronic molecular states with molecular vibrons [2,3,4]. The latter depends on the strength of the vibrational coupling between the "hot" molecular vibrons and the bath degrees of freedom of the "cold" electrodes.Theoretical studies predicted that current-induced heating in molecular junctions can be large enough to affect the reliability of molecular devices [2]. However, experimental access to this information is very limited. Recent studies of the thermally activated force during molecular detachment from a lead [5,6] and of structural fluctuation during attachment to it [7] reveal that the temperature of a molecular junction can reach several hundred degrees under normal working conditions, thus revealing that present devices work on the limit of practical operability [8]. Heat dissipation away from the junction becomes an important issue.In this work, we characterize the mechanisms of heating and heat dissipation induced by the flow of current across a single molecule. Our approach is based on detecting the limiting electron current inducing molecular decomposition at varying applied source-drain bias (i.e. the maximum power one molecule can sustain). We use a low temperature scanning tunneling microscope (STM) to control the flow of electrons through a single C 60 molecule at an increasing rate until the molecule decomposes. By comparing the power applied for decomposition (P dec ) in tunneling regime and in contact with the STM tip we find that it depends significantly on two factors: i) P dec decreases when molecular resonances participate in the transport, evidencing that they enhance the heating; ii) P dec increases as the molecule is contacted to the source and drain electrodes, revealing the heat dissipation by phonon coupling to the leads. A good contact between the single-molecule (SM) device and the leads is hence an important requirement for its ope...

The ring-opening/closing reaction between spiropyran (SP) and merocyanine (MC) is a prototypical thermally and optically induced reversible reaction. However, MC molecules in solution are thermodynamically unstable at room temperature and thus return to the parent closed form on short time scales. Here we report contrary behavior of a submonolayer of these molecules adsorbed on a Au(111) surface. At 300 K, a thermally induced ring-opening reaction takes place on the gold surface, converting the initial highly ordered SP islands into MC dimer chains. We have found that the thermally induced ring-opening reaction has an activation barrier similar to that in solution. However, on the metal surface, the MC structures turn out to be the most stable phase. On the basis of the experimentally determined molecular structure of each molecular phase, we ascribe the suppression of the back reaction to a stabilization of the planar MC form on the metal surface as a consequence of its conjugated structure and large electric dipole moment. The metal surface thus plays a crucial role in the ring-opening reaction and can be used to alter the stability of the two isomers.

BackgroundProtein kinases constitute a particularly large protein family in Arabidopsis with important functions in cellular signal transduction networks. At the same time Arabidopsis is a model plant with high frequencies of gene duplications. Here, we have conducted a systematic analysis of the Arabidopsis kinase complement, the kinome, with particular focus on gene duplication events. We matched Arabidopsis proteins to a Hidden-Markov Model of eukaryotic kinases and computed a phylogeny of 942 Arabidopsis protein kinase domains and mapped their origin by gene duplication.ResultsThe phylogeny showed two major clades of receptor kinases and soluble kinases, each of which was divided into functional subclades. Based on this phylogeny, association of yet uncharacterized kinases to families was possible which extended functional annotation of unknowns. Classification of gene duplications within these protein kinases revealed that representatives of cytosolic subfamilies showed a tendency to maintain segmentally duplicated genes, while some subfamilies of the receptor kinases were enriched for tandem duplicates. Although functional diversification is observed throughout most subfamilies, some instances of functional conservation among genes transposed from the same ancestor were observed. In general, a significant enrichment of essential genes was found among genes encoding for protein kinases.ConclusionsThe inferred phylogeny allowed classification and annotation of yet uncharacterized kinases. The prediction and analysis of syntenic blocks and duplication events within gene families of interest can be used to link functional biology to insights from an evolutionary viewpoint. The approach undertaken here can be applied to any gene family in any organism with an annotated genome.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-548) contains supplementary material, which is available to authorized users.

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Codeposition of C60 and the three-dimensional molecular hydrocarbon 1,3,5,7-tetraphenyladamantane (TPA) on Au(111) leads to the spontaneous formation of molecular nanostructures in which each fullerene is locked into a specific orientation by three surrounding TPA. Scanning tunneling spectroscopy shows that the electronic coupling of C60 with the surface is significantly reduced in these nanostructures, enhancing the free-molecule properties. As evidenced by density functional theory simulations, the nanostructures are stabilized by 18 local electrostatic forces between C60 and TPA, resulting in a lifting of the C60 cage from the surface.

Spiropyran is a prototype molecular switch which undergoes a reversible ring-opening reaction by photoinduced cleavage of a C-O bond in the spiropyran (SP) to the merocyanine (MC) isomer. While the electronic states and switching behavior are well characterized in solution, adsorption on metal surfaces crucially affects these properties. Using two-photon photoemission and scanning tunneling spectroscopy, we resolve the molecular energy levels on a Au(111) surface of both isomeric forms. Illumination at various wavelengths does not yield any observable switching rate, thus evidencing a very small upper limit of the quantum efficiency. Electron-induced switching from the SP to the MC isomer via generation of a negative ion resonance can be detected with a quantum yield of (2.2 ± 0.2) × 10(-10) events/electron in tunneling spectroscopy. In contrast, the back reaction could not be observed. This study reveals that the switching properties of surface-bound molecular switches can be very different compared with free molecules, reflecting the strong influence of the interaction with the metal substrate.