Ligand Binding to MacromoleculesAllosteric and sequential models of cooperativity Many biochemical processes involve the binding of ligands to macromolecules; for example, substrates or inhibitors to enzymes, and oxygen to myoglobin or hemoglobin. The simplest cases of ligand binding can be handled easily by application of elementary thermodynamics, but more complicated problems, such as those involving cooperativity, can become extremely tedious.Our purpose is to describe a simpler way of attacking such
Magnetic molecule-surface hybrids are ideal building blocks for molecular spintronic devices due to their appealing tailorable magnetic properties and nanoscale size. So far, assemblies of interacting molecular-surface hybrids needed for spintronic functionality were generated by depositing aromatic molecules onto transition-metal surfaces, resulting in a random arrangement of hybrid magnets due to the inherent and strong hybridization. Here, we demonstrate the formation of multiple intramolecular subunits within a single molecule-surface hybrid by means of spin-polarized scanning tunneling microscopy experiments and ab initio density functional theory calculations. This novel effect is realized by depositing a polycyclic aromatic molecule on a magnetic surface. A highly asymmetric chiral adsorption position induces different structural, electronic, and magnetic properties in each aromatic ring of the molecule. In particular, the induced molecular spin polarization near the Fermi energy varies among the rings due to site-and spin-dependent molecule-surface hybridization. Our results showcase a possible organic chemistry route of tailoring geometrically welldefined assemblies of magnetically distinguishable subunits in molecule-surface hybrids.
The polynuclear coordination compounds [Co II 3 Co III 2 (Hbda) 2 (bda) 2 (ib) 6 ]$2MeCN (1) and [Ni II 4 (Hbda) 3 (ib) 5 (MeCN)] (2) (H 2 bda ¼ N-butyldiethanolamine, ib ¼ isobutyrate) are prepared under aerobic conditions using an identical synthetic protocol that solely differs in the employed transition metal (Co II vs. Ni II ). Whereas compound 1 displays a mixed-valent, pentanuclear, horseshoe-shaped structure with alternating Co(II) and Co(III) ions, compound 2 presents a tetrahedrally-shaped Ni(II) structural motif where four nickel centers are bridged by three O atoms to afford a lacunary Ni 4 O 3 cubane, a motif hitherto only observed as a substructure of higher-nuclearity coordination clusters and polyoxometalates. Both compounds are thermally surprisingly stable (>130 C). 1 exhibits weak antiferromagnetic exchange interactions; 2 shows a ferromagnetic coupled triangle of three Ni centers interacting antiferromagnetically with a single Ni apex. Fig. 4 Temperature dependence of c m T at 0.1 T of compound 2; inset: molar magnetization M m vs. B at 2.0 K: experimental data (open circles), least-squares fit (red solid lines).This journal is
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