Thickness-dependent optical band gap in one-dimensional Ca3Co2O6 nanometric films

Recent studies on the physical properties of Ca₃Co₂O₆ nanometric samples have shown that their properties are significantly different from those of the bulk samples. The origin of this change is not trivial. We have carried out optical measurements on Ca₃Co₂O₆ thin films with different thicknesses in order to characterize their electronic structure using optical spectroscopy measurements. The absorption spectra show a dependence on the film thickness that is correlated to the grain size in the polycrystalline layers. We found that the optical band gap increases from 1.3 to 1.55 eV when the thickness changes from 35 to 100 nm. The change in the band gap evolution with the film thickness is discussed in terms of both the amorphous effect and the grain size in the Ca₃Co₂O₆ thin films. Finally, we show that these results are consistent with recent measurements concerning magnetic and electrical properties of Ca₃Co₂O₆ nanometric samples.     

Chemoenzymatic synthesis of l-tyrosine derivative for a transketolase assay

We have prepared an l-tyrosine derivative bearing a d-threo ketose moiety by a convenient chemoenzymatic route. This compound is of potential interest for developing stereospecific assays for enzymes catalyzing C-C bond cleavage such as transketolase. We showed in vitro by analytical studies (LC/MS and ³¹P NMR) that this compound can release l-tyrosine in the presence of wild type TK extract and bovine serum albumin. This assay is the first step towards a mutant TK selection test that could be developed for yeast cells auxotrophic for l-tyrosine.     

Multiple Ligand and Cell-Dependent States of Lateral Mobility of Plasmalemmal G Protein-Coupled Cholecystokinin Receptors

Lateral movement of receptor molecules in the plane of the plasmalemma has important implications for signal transduction and receptor regulation, yet mechanisms affecting such movement are not well understood. We have studied the lateral mobility of the G protein-coupled cholecystokinin (CCK) receptor expressed in the natural milieu of the rat pancreatic acinar cell and in a model cell system, the CHO-CCKR cell, after occupation with fluorescent agonist and antagonist. Lateral diffusion characteristics were distinct in each type of cell and for receptors occupied by each type of ligand, fluorescent agonist, rhodamine-Gly-[(Nle^28,31)CCK-26-33], and fluorescent antagonist, rhodamine-Gly-[(D-Trp³⁰,Nle^28,31)CCK-26-32]-phenethyl ester. Multiple states of mobility were detected for CCK receptors. The slowest population of mobile receptors on the CHO-CCKR cells moved at similar rates when occupied by both antagonist and agonist, while the faster-moving populations moved at a faster rate when occupied with antagonist than with agonist. The fastest component of mobile receptors may reflect unconstrained interactions of the antagonist-occupied receptors with signaling or anchoring structures, while the slowest component may represent the fraction of ligand-occupied receptors that ultimately undergo internalization. The intermediate mobility states may reflect receptor interactions with signal transduction and regulatory machinery. While only a single population of mobile receptors was demonstrable on the acinar cells, increased ligand concentrations (agonist and antagonist) resulted in increased percentages of mobile receptors, suggesting a stoichiometric limitation of immobilizing molecular constraints. Inhibition of protein kinase C had no significant effect on the lateral mobility of agonist-occupied CCK receptors.     

Manifolds: Hausdorffness versus homogeneity

We analyze the relationship between Hausdorffness and homogeneity in the frame of manifolds not confined to be Hausdorff. We exhibit examples of homogeneous non-Hausdorff manifolds and prove that a Lindelöf homogeneous manifold is Hausdorff.