György Mészáros

The structure of liquid tetrachlorides CCl4,SiCl4,GeCl4,TiCl4,VCl4, and SnCl4

Neutron diffraction measurements have been carried out for determining the total structure factor of liquid CCl4, SiCl4, GeCl4, TiCl4, VCl4, and SnCl4. The data were interpreted using the reverse Monte Carlo method, where the procedure started from results of molecular dynamics calculations. It is demonstrated that simple repulsive interatomic potential models are suitable for describing the most important structural features qualitatively. Based on detailed analyses of particle configurations, it is shown that “corner-to-face” type near-neighbor arrangements, that have been promoted for the interpretation of these structures over the last 20 years, are actually very rare, their occurrence being around 5% only. Instead, the dominance of “corner-to-corner” type orientational correlations is found.

cAMP dependent inhibition of thromboxane A2, prostacyclin and PGF2α synthesis in mouse hepatocytes

The role of cAMP dependent regulation in thromboxane A2, prostacyclin and PGF2 alpha synthesis (measured by radioimmunoassay) was investigated in isolated mouse hepatocytes and in microsomal membranes prepared from these cells. In isolated hepatocytes N6,O2-dibutyryl cAMP inhibited the formation of all the three derivatives, while calcium ionophore A 23187 stimulated their synthesis. Addition of the dissociated catalytic subunit of cAMP dependent protein kinase and ATP to microsomal membranes inhibited the production of TXA2, PGI2 and PGF2 alpha by about 50% and this inhibition was counteracted by the combined addition of heat stable inhibitor protein of cAMP dependent protein kinase. It is concluded that in parenchymal liver cells cAMP dependent phosphorylation is directly involved in the inhibition of prostanoid synthesis.

Temporal correlations and structural memory effects in break junction measurements

We review data analysis techniques that can be used to study temporal correlations among conductance traces in break junction measurements. We show that temporal histograms are a simple but efficient tool to check the temporal homogeneity of the conductance traces, or to follow spontaneous or triggered temporal variations, like structural modifications in trained contacts, or the emergence of single-molecule signatures after molecule dosing. To statistically analyze the presence and the decay time of temporal correlations, we introduce shifted correlation plots. Finally, we demonstrate that correlations between opening and subsequent closing traces may indicate structural memory effects in atomic-sized metallic and molecular junctions. Applying these methods on measured and simulated gold metallic contacts as a test system, we show that the surface diffusion induced flattening of the broken junctions helps to produce statistically independent conductance traces at room temperature, whereas at low temperature repeating tendencies are observed as long as the contacts are not closed to sufficiently high conductance setpoints. Applying opening-closing correlation analysis on Pt-CO-Pt single-molecule junctions, we demonstrate pronounced contact memory effects and recovery of the molecule for junctions breaking before atomic chains are formed. However, if chains are pulled the random relaxation of the chain and molecule after rupture prevents opening-closing correlations.