Borazine Promoted Growth of Highly Oriented Thin Films.

We report on a phenomenon, where thin films sputter-deposited on single-crystalline Al2O3(0001) substrates exposed to borazine─a precursor commonly used for the synthesis of hexagonal boron nitride layers─are more highly oriented than those grown on bare Al2O3(0001) under the same conditions. We observed this phenomenon in face-centered cubic Pd, body-centered cubic Mo, and trigonal Ta2C thin films grown on Al2O3(0001). Interestingly, intermittent exposure to borazine during the growth of Ta2C thin films on Ta2C yields better crystallinity than direct deposition of monolithic Ta2C. We attribute these rather unusual results to a combination of both enhanced adatom mobilities on, and epitaxial registry with, surfaces exposed to borazine during the deposition. We expect that our approach can potentially help improve the crystalline quality of thin films deposited on a variety of substrates.

Orthovanadate stimulates cAMP phosphodiesterase 3 activity in isolated rat hepatocytes through mitogen-activated protein kinase activation dependent on cAMP-dependent protein kinase.

Orthovanadate (vanadate) as well as insulin stimulated phosphodiesterase 3 (PDE3) in the particulate fraction of rat hepatocytes. The vanadate-induced activations of PDE3 and mitogen-activated protein kinase (MAPK) were inhibited by H-89 and PD98059, suggesting that the MAPK activation via cAMP-dependent protein kinase (PKA) and MAPK kinase is involved in the vanadate action. On the other hand, the insulin-induced activations of PDE3 and Akt were inhibited by wortmannin, suggesting involvement of the Akt activation via phosphatidylinositol 3-kinase (PI3K) in the insulin action. The vanadate-induced activations of PKA and PDE3 were inhibited in part by propranolol or genistein, suggesting that vanadate may exert its actions via dual signaling pathways of beta-adrenergic receptors and receptor tyrosine kinases of growth factors. Vanadate, in contrast to insulin, did not promote the phosphorylation of insulin receptor substrate-1. The vanadate-induced increase in the phosphorylation of a main isoform of MAPKs, p44 protein, was detected by immunoblotting migration patterns of SDS-PAGE. A partially purified PDE3 activity was increased by addition of MAPK or Akt to the reaction mixture, suggesting that MAPK as well as Akt acts upstream of PDE3. The activation of PDE3 by insulin was independent of a transient increase in the MAPK activity, probably due to the dephosphorylated inactivation mediated by the induced activation of MAPK phosphatases (MKPs). Vanadate did not affect the MKP activity. These results indicate that vanadate stimulates the particulate PDE3 activity by activating mainly p44 MAPK via a PKA-dependent process, and that it differs from insulin with regard to a phosphorylation cascade of PDE3 activation.