Showing papers in "Chemical Reviews in 1992"

Measurement of interfacial processes at electrode surfaces with the electrochemical quartz crystal microbalance

Abstract: I. Introductlon The last 10-15 years have seen electrochemista applying more and more sophisticated instrumental techniques to studies of electrode surfaces, both because of the increased availability of powerful new tools for interfacial characterization and because of an increased emphasis in modern electrochemical research on detailed characterization of the structure and composition of the interface. Many methods have been newly applied to the study of electrochemical interfaces' during this time. One of these methods is based on quartz crystal microbalance (QCM) technology. The

Large clusters and colloids. Metals in the embryonic state

Abstract: Ligand stabilized transition metal clusters and colloids in the size range of 1–15 nm show size dependent quantization phenomena. Quantum size effects become the more evident the smaller the particle is. Whereas particles >2 nm behave like quantum dots only at low temperatures, the 1.4 nm Au55 cluster follows quantum mechanical rules even at room temperature. First steps to organize clusters and colloids three- (3D), two- (2D) and one- (1D) dimensionally have been performed. 3D arrays are reached by using spacer molecules to link the clusters and to enlarge the distances between them. 2D assemblies are realized in cluster and colloid monolayers on chemically modified surfaces. One-dimensional cluster wires become available by using nanoporous aluminum oxide membranes as templates.

Electron transfer in ruthenium-modified proteins

Abstract: Photochemical techniques have been used to measure the kinetics of intramolecular electron transfer in Ru(bpy)2(im)(His)2(+)-modified (bpy = 2,2'-bipyridine; im = imidazole) cytochrome c and azurin. A driving-force study with the His33 derivatives of cytochrome c indicates that the reorganization energy (lambda) for Fe2+-->Ru3+ ET reactions is 0.8 eV. Reductions of the ferriheme by either an excited complex, *Ru2+, or a reduced complex, Ru+, are anomalously fast and may involve formation of an electronically excited ferroheme. The distance dependence of Fe2+-->Ru3+ and Cu+-->Ru3+ electron transfer in 12 different Ru-modified cytochromes and azurins has been analyzed using a tunneling-pathway model. The ET rates in 10 of the 12 systems exhibit an exponential dependence on metal-metal separation (decay constant of 1.06 A-1) that is consistent with prediction of the pathway model.

Asymmetric hydroxylation of enolates with N-sulfonyloxaziridines

Abstract: Franklin A. Davis was born in Des Moines. Iowa. He recelved his B.S. degree in 1962 from the University of WiScOnsln and was granted e Ph.D. degree in 1966 from Syracuse University working under Donald C. Dimer. After two years with Michael J. S. Dewar as a Welch PoSMoctoral Fellow at the University of Texas he joined the facuity at Drexel University in 1968 where he is currently the George S. Sasin Professor of Organic Chemistry. I n 1980 he received Drexel University's Research Achievement Award and in 1982 the PhiladelDhia ACS Section Award. Dr. Davis' research Interests lie in the area of asymmetric synthesis. molecular recognMon.and new syntheticmethodspartkularlyrelatedtoenalF tioselective oxidations. me development of new methods for the regioand stereoselective fluorination of organic molecules is a recent focus

Chromium-catalyzed oxidations in organic synthesis

Abstract: Chromium oxidations have been widely explored since the very beginning of organic chemistry, and the topic remains of current interest as exemplified by the extensive number of papers in which at least one step involves the w e of an oxochromium(V1) reagent. This is primarily due to the wide variety of oxidizable functions by the proper choice of reagent. A plethora of chromium reagents and procedures have been proposed and they have been extensively described in reviews and books.‘J These methods, in which the oxidative ability and selectivity have now been in part evaluated by computer assistance,3 imply either the w e of stoichiometric quantities or large excesses of poisonous chromium reagents? The metallic byproduct residues are also toxic, and furthermore, their presence often makes the workup difficult. Considering cost and environmental factors, it would be advantageous to use catalytic methods. Such a system is illustrated in Scheme 1 where “Cr” is the catalyst (chromium salt or complex), YO the oxygen source, and S and SO the organic substrate, respectively, before and after oxidation. To be of interest, the process has to employ an inexpensive YO and the byproduct Y has to be easily disposable or recyclable. Furthermore, the synthetic organic chemist engaged in a laboratory scale experiment would prefer to test the