Here we present room-temperature spin-dependent charge transport measurements in single-molecule junctions made of metalloporphyrin-based supramolecular assemblies. They displayl arge conductance switching for magnetoresistance in as ingle-molecule junction. The magnetoresistance depends acutely on the probed electron pathway through the supramolecular wire:those involving the metal center showed marked magnetoresistance effects as opposed to those exclusively involving the porphyrin ring which present nearly complete absence of spin-dependent charge transport. The molecular junction magnetoresistance is highly anisotropic, being observable when the magnetization of the ferromagnetic junction electrode is oriented along the main molecular junction axis,a nd almost suppressed when it is perpendicular. The key ingredients for the abovee ffect to manifest are the electronic structure of the paramagnetic metalloporphyrin, and the spinterface created at the molecule-electrode contact.
In contrast with conventional single-molecule junctions, in which the current flows parallel to the long axis or plane of a molecule, we investigate the transport properties of M(II)-5,15-diphenylporphyrin (M-DPP) single-molecule junctions (M=Co, Ni, Cu, or Zn divalent metal ions), in which the current flows perpendicular to the plane of the porphyrin. Novel STM-based conductance measurements combined with quantum transport calculations demonstrate that current-perpendicular-to-the-plane (CPP) junctions have three-orders-of-magnitude higher electrical conductances than their current-in-plane (CIP) counterparts, ranging from 2.10−2 G0 for Ni-DPP up to 8.10−2 G0 for Zn-DPP. The metal ion in the center of the DPP skeletons is strongly coordinated with the nitrogens of the pyridyl coated electrodes, with a binding energy that is sensitive to the choice of metal ion. We find that the binding energies of Zn-DPP and Co-DPP are significantly higher than those of Ni-DPP and Cu-DPP. Therefore when combined with its higher conductance, we identify Zn-DPP as the favoured candidate for high-conductance CPP single-molecule devices.
The ability to design surfaces with reversible, high affinity protein binding sites represents a significant step forward in the advancement of analytical methods for diverse biochemical and biomedical applications. Herein, we report a dynamic supramolecular strategy to directly assemble proteins on surfaces based on multivalent host-guest interactions. The host-guest interactions are achieved by one-step nanofabrication of a well-oriented β-cyclodextrin host-derived self-assembled monolayer on gold (β-CD-SAM) that forms specific inclusion complexes with hydrophobic amino acids located on the protein's surface. Cytochrome C, insulin, -chymotrypsin and RNase A are used as model guest proteins. Surface plasmon resonance (SPR) and static time of flight secondary ion mass spectrometry (ToF-SIMS) studies demonstrate that all four proteins interact with the β-CD-SAM in a specific manner via the hydrophobic amino acids on the surface of the protein. The β-CD-SAMs bind the proteins with high nanomolar to single-digit micromolar dissociation constants (KD). Importantly, while the proteins can be captured with high affinity, their release from the surface can be achieved under very mild conditions. Our results expose the great advantages of using a supramolecular approach for controlling protein immobilization, in which the strategy described herein provides unprecedented opportunities to create advanced bioanalytic and biosensor technologies.
Here we present room-temperature spin-dependent charge transport measurements in single-molecule junctions made of metalloporphyrin-based supramolecular assemblies. They displayl arge conductance switching for magnetoresistance in as ingle-molecule junction. The magnetoresistance depends acutely on the probed electron pathway through the supramolecular wire:those involving the metal center showed marked magnetoresistance effects as opposed to those exclusively involving the porphyrin ring which present nearly complete absence of spin-dependent charge transport. The molecular junction magnetoresistance is highly anisotropic, being observable when the magnetization of the ferromagnetic junction electrode is oriented along the main molecular junction axis,a nd almost suppressed when it is perpendicular. The key ingredients for the abovee ffect to manifest are the electronic structure of the paramagnetic metalloporphyrin, and the spinterface created at the molecule-electrode contact.
IntroduzioneMolte affermazioni sono state fatte circa cambiamenti che si manifestano nelle origini e negli sviluppi del conflitto politico nelle società occidentali, e nell'Europa occidentale in particolare. Tali cambiamenti sono stati chiamati, con un termine collettivo ora di moda rna inappropriato, la «fine delle ideologie». Le affermazioni possono essere cosí condensate: le tradizionali linee di divisione in classi economiche e forse anche sociali si sono venute sfumando con la rapida crescita di una «nuova classe media» e l'aumento del tenore di vita nelle nazioni dell'Europa occidentale.I fattori locali, regionali, etnici e religiosi sono diminuiti d’importanza in quanto basi fondamentali di affiliazione politica in molti paesi, mentre ha luogo una « mobilitazione sociale » e le masse vengono sempre piú integrate nelle loro rispettive culture politiche nazionali. A ciò contribuiscono lo stesso sviluppo economico e sociale, il diffondersi dei mezzi di comunicazione, la proliferazione delle associazioni volontarie, e l’aumento dei poteri dell’esecutivo e delle sue responsabilità nella salute, nel benessere, nella sicurezza sociale nonché nelle attività economiche in generale.
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