Ben Warner

Histamine receptors that influence blockage of the normal human nasal airway

1 The aim of this study was to investigate the mechanisms by which histamine causes nasal blockage. Histamine, 40–800 μg, intranasally into each nostril, induced significant blockage of the nasal airway in normal human subjects, as measured by acoustic rhinometry. 2 Oral pretreatment with cetirizine, 5–30 mg, the H1 antagonist, failed to reverse completely the nasal blockage induced by histamine, 400 μg. 3 Dimaprit, 50–200 μg, the H2 agonist, intranasally, caused nasal blockage, which was reversed by oral pretreatment with ranitidine, 75 mg, the H2 antagonist. 4 A combination of cetirizine, 20 mg, and ranitidine, 75 mg, caused greater inhibition of the nasal blockage caused by histamine, 400 μg, than cetirizine alone. In the presence of both antagonists, there was residual histamine‐induced nasal blockage. 5 R‐α‐methylhistamine (R‐α‐MeH), 100–600 μg, the H3 agonist, intranasally, caused nasal blockage, which was not inhibited by either cetirizine or ranitidine. 6 Thioperamide, 700 μg, the H3 antagonist, intranasally, reversed the R‐α‐MeH‐induced nasal blockage. Thioperamide alone had no significant action on the nasal blockage induced by histamine, 400 and 1000 μg, but, in the presence of cetirizine, 20 mg, thioperamide further reduced the histamine‐induced nasal blockage. 7 Corynanthine, 2 mg, the α1‐adrenoceptor antagonist, administered intranasally, caused nasal blockage. 8 Corynanthine produced a greater increase in nasal blockage when in combination with bradykinin compared to its combination with R‐α‐MeH. 9 There appears to be a contribution of H1, H2 and H3 receptors to histamine‐induced nasal blockage in normal human subjects. The sympathetic nervous system actively maintains nasal patency and we suggest that activation of nasal H3 receptors may downregulate sympathetic activity.

Tunable magnetoresistance in an asymmetrically coupled single-molecule junction

Phenomena that are highly sensitive to magnetic fields can be exploited in sensors and non-volatile memories. The scaling of such phenomena down to the single-molecule level may enable novel spintronic devices. Here, we report magnetoresistance in a single-molecule junction arising from negative differential resistance that shifts in a magnetic field at a rate two orders of magnitude larger than Zeeman shifts. This sensitivity to the magnetic field produces two voltage-tunable forms of magnetoresistance, which can be selected via the applied bias. The negative differential resistance is caused by transient charging of an iron phthalocyanine (FePc) molecule on a single layer of copper nitride (Cu2N) on a Cu(001) surface, and occurs at voltages corresponding to the alignment of sharp resonances in the filled and empty molecular states with the Cu(001) Fermi energy. An asymmetric voltage-divider effect enhances the apparent voltage shift of the negative differential resistance with magnetic field, which inherently is on the scale of the Zeeman energy. These results illustrate the impact that asymmetric coupling to metallic electrodes can have on transport through molecules, and highlight how this coupling can be used to develop molecular spintronic applications.

Sub-molecular modulation of a 4f driven Kondo resonance by surface-induced asymmetry

Coupling between a magnetic impurity and an external bath can give rise to many-body quantum phenomena, including Kondo and Hunds impurity states in metals, and Yu-Shiba-Rusinov states in superconductors. While advances have been made in probing the magnetic properties of d-shell impurities on surfaces, the confinement of f orbitals makes them difficult to access directly. Here we show that a 4f driven Kondo resonance can be modulated spatially by asymmetric coupling between a metallic surface and a molecule containing a 4f-like moment. Strong hybridization of dysprosium double-decker phthalocyanine with Cu(001) induces Kondo screening of the central magnetic moment. Misalignment between the symmetry axes of the molecule and the surface induces asymmetry in the molecules electronic structure, spatially mediating electronic access to the magnetic moment through the Kondo resonance. This work demonstrates the important role that molecular ligands have in mediating electronic and magnetic coupling and in accessing many-body quantum states.

Guided Molecular Assembly on a Locally Reactive 2D Material

Atomically precise engineering of the position of molecular adsorbates on surfaces of 2D materials is key to their development in applications ranging from catalysis to single-molecule spintronics. Here, stable room-temperature templating of individual molecules with localized electronic states on the surface of a locally reactive 2D material, silicene grown on ZrB2 , is demonstrated. Using a combination of scanning tunneling microscopy and density functional theory, it is shown that the binding of iron phthalocyanine (FePc) molecules is mediated via the strong chemisorption of the central Fe atom to the sp3 -like dangling bond of Si atoms in the linear silicene domain boundaries. Since the planar Pc ligand couples to the Fe atom mostly through the in-plane d orbitals, localized electronic states resembling those of the free molecule can be resolved. Furthermore, rotation of the molecule is restrained because of charge rearrangement induced by the bonding. These results highlight how nanoscale changes can induce reactivity in 2D materials, which can provide unique surface interactions for enabling novel forms of guided molecular assembly.

Figure 1 Inset.pxp

(A) STM topographic image of FePc molecules on silicene/ZrB2 (17.53 nm x 8.71nm; Vset = -1 V, Iset = 0.5 nA). The cross-shaped molecules adsorb at the edges of the stripeddomains. The linear nature of these domains enables the creation chains of molecules on thesurface. The frontier molecular orbital can also be observed. In the inset, white lines havebeen added between the silicene ‘up’ atoms to highlight the lattice and purple lines mark thebinding angle. (B) Same topographic image at positive bias (Vset = +1 V, Iset = 0.5 nA). Themolecules now have a triangular profile, and the domain boundaries, as well as kinks thatappear when a domain boundary shifts to a neighboring row of Si ‘up’ atoms, are more clearlyresolved