Thermal control of the defunctionalization of supported Au25(glutathione)18 catalysts for benzyl alcohol oxidation.

Au25(SG)18 (SG - glutathione) clusters deposited on ZrO2 nanoparticles have been used as a catalyst for benzyl alcohol oxidation. Calcination was performed at different temperatures to study the ligand and particle size effect on the catalytic activity. In contrast to most gold nanoclusters which have to be completely defunctionalized for maximum catalytic activity, the partially defunctionalized Au25(SG)18@ZrO2 catalyst, thermally treated at 300 °C, exhibits full conversion of benzyl alcohol within 15 h under atmospheric pressure with 94% selectivity towards benzaldehyde.

Competitive Ligand Exchange and Dissociation in Ru Indenyl Complexes.

Kinetic profiles obtained from monitoring the solution-phase substitution chemistry of [Ru(η5-indenyl)(NCPh)(PPh3)2]+ (1) by both electrospray ionization mass spectrometry and 31P{1H} NMR are essentially identical, despite an enormous difference in sample concentrations for these complementary techniques. These studies demonstrate dissociative substitution of the NCPh ligand in 1. Competition experiments using different secondary phosphine reagents provide a ranking of phosphine donor abilities at this relatively crowded half-sandwich complex: PEt2H > PPh2H ≫ PCy2H. The impact of steric congestion at Ru is evident also in reactions of 1 with tertiary phosphines; initial substitution products [Ru(η5-indenyl)(PR3)(PPh3)2]+ rapidly lose PPh3, enabling competitive re-coordination of NCPh. Further solution experiments, relevant to the use of 1 in catalytic hydrophosphination, show that PPh2H out-competes PPh2CH2CH2CO2Bu t (the product of hydrophosphination of tert-butyl acrylate by PPh2H) for coordination to Ru, even in the presence of a 10-fold excess of the tertiary phosphine. Additional information on relative phosphine binding strengths was obtained from gas-phase MS/MS experiments, including collision-induced dissociation experiments on the mixed phosphine complexes [Ru(η5-indenyl)PP'P″]+, which ultimately appear in solution during the secondary phosphine competition experiments. Unexpectedly, unsaturated complexes [Ru(η5-indenyl)(PR2H)(PPh3)]+, generated in the gas-phase, undergo preferential loss of PR2H. We propose that competing orthometallation of PPh3 is responsible for the surprising stability of the [Ru(η5-indenyl)(PPh3)]+ fragment under these conditions.

DA-6034 Induces [Ca(2+)]i Increase in Epithelial Cells.

DA-6034, a eupatilin derivative of flavonoid, has shown potent effects on the protection of gastric mucosa and induced the increases in fluid and glycoprotein secretion in human and rat corneal and conjunctival cells, suggesting that it might be considered as a drug for the treatment of dry eye. However, whether DA-6034 induces Ca(2+) signaling and its underlying mechanism in epithelial cells are not known. In the present study, we investigated the mechanism for actions of DA-6034 in Ca(2+) signaling pathways of the epithelial cells (conjunctival and corneal cells) from human donor eyes and mouse salivary gland epithelial cells. DA-6034 activated Ca(2+)-activated Cl(-) channels (CaCCs) and increased intracellular calcium concentrations ([Ca(2+)]i) in primary cultured human conjunctival cells. DA-6034 also increased [Ca(2+)]i in mouse salivary gland cells and human corneal epithelial cells. [Ca(2+)]i increase of DA-6034 was dependent on the Ca(2+) entry from extracellular and Ca(2+) release from internal Ca(2+) stores. Interestingly, these effects of DA-6034 were related to ryanodine receptors (RyRs) but not phospholipase C/inositol 1,4,5-triphosphate (IP3) pathway and lysosomal Ca(2+) stores. These results suggest that DA-6034 induces Ca(2+) signaling via extracellular Ca(2+) entry and RyRs-sensitive Ca(2+) release from internal Ca(2+) stores in epithelial cells.