Dynamical effects and conductance asymmetry in metal-insulator-metal systems with different electrodes

We investigated the electron tunneling process in a planar system consisting of two semi-infinite metal electrodes of different dielectric properties separated by a narrow vacuum gap. This system can be viewed as a model of a metal-insulator-metal structure, or even as a very rough model of scanning tunneling microscopy. We used a local limit of a self-consistent dynamic calculation to evaluate effective tunneling barriers, and discussed the influence of different screening properties of the metallic electrodes on these barriers as well as on the conductance. We found that the barriers are significantly additionally lowered due to the difference in the charge fluctuation frequencies of the electrodes, and that the conductance minimum in such systems is shifted to a nonzero value. We compared our results with some measurements of I-V characteristics and work functions and found that our calculations contribute to the understanding of the observed conductance asymmetry

Synthetic Studies in the Chloramphenicol Series. III. Synthesis of threo-DL-Chloramphenicol from DL-Serine Ethyl Ether

A synthesis of threo-DL-chloramphenicol (I) from a-phthalimido-~-ethoxy-DL-propiophenone (II) is described. The crude ketone II obtained from a-phthalimido-~-ethoxy-DL-propionyl chloride via Friedel-Crafts reaction was reduced with aluminium isopropoxide to give a yield of 17.2 % of the corresponding carbinol III. This carbinol gave in a series of reactions threo -DL-chloramphenicol in an overall yield of 2.4 %

MAGE-A3/4 and NY-ESO-1 antigens expression in metastatic esophageal squamous cell carcinoma

In the present study we analyzed immunohistochemical expression of MAGE-A 3/4 and NY-ESO-1 in 55 samples of esophageal squamous cell carcinomas (ESCC) and their respective lymph node metastases. To our knowledge this is the first study to assess and compare the expression of these antigens in ESCC lymph node metastases

Optically Active Trisulphides and Tetrasulphides Related to L-Cystine

A . description is ,given of the preparation and properties of optically active bis(2-carboxy - 2- phthalimidoethyl) disulphide (Ia), [a]D-275°, bis(2-carboxy -2.:phthalimidoethyl) trisulphide (lb) , ,[a]D -4720 and bis(2-c arboxy -2-phthalimidoethyl) tetrasulphide (le), [a]D:--3880. The starting material for these compounds was N - -phthaloyl-L-cysteine (II), [a]D-64° prepared from L-cysteine hydrocl).loride and sodium o- carbethoxythiobenzoa te