The Role of Phosphate Binding in Purine Nucleoside Phosphorylase of Helicobacter pylori

Purine nucleoside phosphorylase (PNP) is an essential enzyme in the purine salvage pathway of Helicobacter pylori. Since H. pylori lacks the ability to synthesize purine nucleosides de novo, inhibition of this enzyme could stop the growth of this bacterium. However, for the design of successful inhibitors the details of the mechanism of this enzyme should be fully understood. PNPs catalyze cleavage of the glycosidic bond of purine nucleosides, and phosphate is one of the substrates. It is thought that binding of phosphate induces the conformational change as a necessary initial step in the catalysis. This conformational change is manifested in closing of either one of the six active sites in the homohexameric PNPs. It is unclear whether the binding of phosphate is sufficient or just a necessary condition for the closing of the active site. In this paper we conducted an experiment to check this by soaking the crystals of the apo form of the enzyme in increasing concentrations of phosphate. This work is licensed under a Creative Commons Attribution 4.0 International License

Charge state control of F16CoPc on h-BN/Cu(111)

International audienceThe use of molecular materials in solar cells and nano-electronics demands a fundamental understanding and control of their electronic properties. Particularly relevant is the molecular response to the environment, that is, the interaction with the support and adjacent molecules, as well as the influence of electrostatic gating. Here, the control of molecular level alignment and charge states of fluorinated cobalt phthalocyanines (F16CoPc) on atomically thin hexagonal boron nitride (h-BN) sheets on Cu(111) is reported using scanning tunneling microscopy (STM) and spectroscopy (STS), as well as atomic force microscopy (AFM) and complementary density functional theory (DFT) calculations. Three parameters that govern the electronic level alignment of F16CoPc orbitals are investigated: i) template-induced gating by the work function variation of the h-BN/Cu(111) substrate, ii) gating by the STM tip, and iii) screening by neighboring molecules. The interplay of these parameters influences the charge distribution in the studied molecular arrangements and thus provides the possibility to tune their physicochemical behavior, for instance, the response toward electronic or optical excitation, charge transport, or binding of axial adducts

A Tunable Two-impurity Kondo system in an atomic point contact

Two magnetic atoms, one attached to the tip of a Scanning Tunneling Microscope (STM) and one adsorbed on a metal surface, each constituting a Kondo system, have been proposed as one of the simplest conceivable systems potentially exhibiting quantum critical behaviour. We have succeeded in implementing this concept experimentally for cobalt dimers clamped between an STM tip and a gold surface. Control of the tip-sample distance with sub-picometer resolution allows us to tune the interaction between the two cobalt atoms with unprecedented precision. Electronic transport measurements on this two-impurity Kondo system reveal a rich physical scenario which is governed by a crossover from local Kondo screening to non-local singlet formation due to antiferromagnetic coupling as a function of separation of the cobalt atoms.Comment: 22 pages, 5 figure

Molecular self-assembly at nanometer scale modulated surfaces:Trimesic acid on Ag(111), Cu(111) and Ag/Cu(111)

A modulated substrate strongly influences the self-assembly of trimesic acid: from disorder at room temperature to perfect order upon annealing.</p

Unraveling the electronic structure of cobalt oxide nanoislands on Au(111)

This study utilizes spatially resolved low temperature scanning tunneling microscopy and spectroscopy to investigate cobalt oxide nanoislands on Au(111) single crystal surfaces. The electronic structure of bilayer, trilayer and multilayer islands is measured, and the findings are correlated with structural variations across the islands, at oxygen defect lines on the islands and at the island step edges. Of particular importance is the identification of electronic features below the Fermi level unique to certain island edges, that are well-known to exhibit increased chemical reactivity. The results advance the understanding of the electronic properties of surface supported cobalt oxide nanostructures, which are known to be important for catalytic applications. Furthermore, on the trilayer island structures a distinct peak in the density of states at the Fermi level is measured that adds to theoretical predictions of superconductivity in CoO2 layers