Several different charge transfer and Ce3+ localization scenarios for Rh–CeO2(111)

We present DFT+U based electronic structure calculations in a p(3x3) slab supercell, for low coverages of atomically dispersed Rh interacting with the CeO2(111) surface, comparing Rh as an adatom, and as a dopant substituted into the surface layer. We find that, energetically, a Rh atom approaching a ceria(111) surface with both sparse O and Ce vacancies present strongly prefers to heal the Ce vacancies, but next it prefers to adsorb on a stoichiometric region rather than healing an O vacancy. In the adatom system, Rh is oxidized by electron transfer to a 4f orbital on one Ce ion in the surface layer, which is then nominally converted from Ce4+ → Ce3+ (i.e. Rh adatoms are single donors). We show that there are a number of different local minima, with Ce3+ localization at 1st, 2nd or 3rd nearest neighbour Ce sites. The second neighbour is the most stable, but all are close in energy. In the Rh-doped system (Rh replaces Ce), Rh is oxidized by charge transfer to neighbouring O atoms, and Rh doping leads to deep acceptor and donor states. Rh is not stable in the O sublattice. Moreover, based on vacancy formation energies, we find that oxygen vacancy formation is strongly enhanced in the vicinity of Rh dopants, but slightly suppressed in the vicinity of Rh adatoms

Pharmacology of the nicotinic acetylcholine receptor from fetal rat muscle expressed in Xenopus Oocytes

The fetal rat muscle nicotinic acetylcholine receptor was expressed in Xenopus oocytes. Using the voltage-clamp technique, the response to a range of agonists was measured, listed in order of (decreasing) activity efficacy: anatoxin greater-than or equal to epibatidine > acetylcholine > DMPP (1,1-dimethyl-4-phenylpiperazinium) >> cytisine > pyrantel > nicotine > coniine > tubocurare > lobeline. The agonist responses were compared with the steric and electrostatic properties of the molecules, using molecular modelling. Single-channel currents were measured in outside-out patches for acetylcholine, nicotine, cytisine, anatoxin and epibatidine. The conductance of the single channels was independent of the type of agonist. The mean open times were characteristic of the agonist applied. Tubocurare, better known for its antagonist properties, was also a partial agonist. Single-channel currents were also observed for tubocurare, and for methyllycaconitine in patches with a very high density of the muscle nicotinic acetylcholine receptor, and these were blocked by small alpha, Greek-bungarotoxin. The agonist properties of physostigmine, galanthamine and their methyl derivatives were also investigated. The conductance of the channels observed in outside-out patches was similar to that obtained for the classical agonists. The single-channel currents observed for physostigmine, galanthamine and their methyl derivatives were blocked by small alpha, Greek-bungarotoxin, methyllycaconitine and mecamylamine, in contrast to previously reported studies on neuronal and adult muscle nicotinic acetylcholine receptors

pdb

PDB file WT.pdb contains the last frame from 10 ns molecular dynamics simulation alpha7-AChBP chimera (PDB 3SQ6). Only two adjacent subunits were subjected to simulations. PDB files with names E185V, E189G, F187S, L119D, Q117T, R186I, S184N and Y118W contain the last frame from molecular dynamics simulation of alpha7-AChBP chimera with the respective mutations (residues numbered according to human alpha7 nAChR). PDB files F104.pdb and V104_mutant.pdb contain structures in which 104th residue of alpha7 AChBP chimera was changed either to phenylalanine (as in actual human alpha7 nAChR) or to valine (as in alpha9 nAChR)

Role of acetylcholine receptor subunits in gating of the channel

The Torpedo and calf acetylcholine receptors and hybrids composed of subunits from the two species have been produced in Xenopus oocytes by the use of the cloned complementary DNAs. Single-channel current measurements indicate that these receptors form channels of similar conductance but with different gating behaviour