Sn-Beta zeolites with borate salts catalyse the epimerization of carbohydrates via an intramolecular carbon shift

Carbohydrate epimerization is an essential technology for the widespread production of rare sugars. In contrast to other enzymes, most epimerases are only active on sugars substituted with phosphate or nucleotide groups, thus drastically restricting their use. Here we show that Sn-Beta zeolite in the presence of sodium tetraborate catalyses the selective epimerization of aldoses in aqueous media. Specifically, a 5 wt% aldose (for example, glucose, xylose or arabinose) solution with a 4:1 aldose:sodium tetraborate molar ratio reacted with catalytic amounts of Sn-Beta yields near-equilibrium epimerization product distributions. The reaction proceeds by way of a 1,2 carbon shift wherein the bond between C-2 and C-3 is cleaved and a new bond between C-1 and C-3 is formed, with C-1 moving to the C-2 position with an inverted configuration. This work provides a general method of performing carbohydrate epimerizations that surmounts the main disadvantages of current enzymatic and inorganic processes.National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Award DMR-0819762)DuPont MIT Alliance (Graduate Research Fellowship)National Institutes of Health (U.S.) (Grant EB-001960)National Institutes of Health (U.S.) (Grant EB-002026)National Science Foundation (U.S.). Graduate Research Fellowship Program (Grant 1122374

Interconnect performance and scaling strategy for the 22 nm node and beyond

After four decades of continuous scaling on the CMOS technology, many innovations have been realized for improving interconnects RC performance since the emergence of copper. However, wire resistance has become a dominant factor on interconnect RC performance at the 22nm node. Optimization of metal aspect ratio and barrier thickness are important directions for mitigating the increase of wire resistance. In addition to reducing the dielectric constant of the ULK MD, reducing the dielectric constant of the copper capping layer and the transitional layer of the ULK MD are approaches for lowering the parasitic capacitance. In order to further boost interconnect performance, an air-gap integration is an option for reducing the capacitance without scaling metal thickness. Therefore, conventional scaling can be extended to the next generation. © 2009 Materials Research Society.link_to_subscribed_fulltex