Atomically-thin Layers Research Articles

Atomic morphology and chemical reactions of the reactive wetting front

Morphology at the reactive wetting front during spreading was first observed in situ at an atomic scale using a high resolution transmission electron microscope. Two typical nanomorphologies of an Ag–Cu–Ti molten alloy were observed on a SiC substrate depending on the nucleation position of the reaction product, TiC. In the case of the precursor atomic thin layer spreading ahead of the droplet of the molten alloy, the TiC nucleated in the thick region of the precursor, which was a few nm behind the tip of the precursor layer. In contrast, molten alloy spreading with TiC growing simultaneously at the tip was also observed. In this case, the precursor layer on SiC did not exist. Nucleation and growth rate of the reaction product were related to the tip morphology.

Isolation and characterization of microcystins (heptapeptide hepatotoxins) from Portuguese strains of Microcystis aeruginosa KUTZ. emend ELEKIN mssub: 1994-12-29

Ten toxic strains of the freshwater cyanobacteria Microcystis aeruginosa KUTZ. emend ELEKIN were isolated from natural lakes and reservoirs of North and Central Portugal. Strains were grown in Z8 medium, cells harvested and freeze-dried prior to toxin extraction. Toxins were isolated by reverse phase HPLC and characterized by HPLC amino acid analysis, fast atom bombardment mass spectrometry and thin layer chromatography. One to four microcystins were purified from each strain and a total of six different toxins were isolated. MCYST-LR is the most common and the dominant microcystin in all the isolated strains. MCYST-LA, MCYST-RR and MCYST-YR are also important while, MCYST-AR and [D-Asp 3 ]MCYST-LR occurred as minor components. There seems to occur a significant difference in average cell size between natural lake and reservoir strains together with a tendency to the preferential occurrence of MCYST-LA in natural lakes strains and MCYST-YR in the reservoir strains.