Frozen low-spin interface in ultrathin Fe films on Cu(111)

In ultrathin film systems, it is a major challenge to understand how a thickness-driven phase transition proceeds along the cross-sectional direction of the films. We use ultrathin Fe films on Cu(111) as a prototype system to demonstrate how to obtain such information using an in situ scanning tunneling microscope and the surface magneto-optical Kerr effect. The magnetization depth profile of a thickness-driven low-spin to high-spin magnetic phase transition is deduced from the experimental data, which leads us to conclude that a low-spin Fe layer at the Fe/Cu interface stays live upon the phase transition. The magnetically live low-spin phase is believed to be induced by a frozen fcc Fe layer that survives a thickness-driven fcc-->bcc structural transition.     

Photoemission from condensed layers of H2 on Cu and Au

We have measured the photoemission of monolayers as well as thick films of H₂ molecules condensed onto Cu and Au. The adsorbed monolayer exhibits a relaxation energy of 1.75 eV whereas we see a bandlike 1s state for thick layers having a bandwidth of 1.2 eV. We also observe energy loss features which are in agreement with previous electron energy loss and optical absorption studies.     

Sequential allylic C-H amination/vinylic C-H arylation: a strategy for unnatural amino acid synthesis from α-olefins

Tandem reaction sequences that selectively convert multiple C-H bonds of abundant hydrocarbon feedstocks to functionalized materials enable rapid buildup of molecular complexity in an economical way. A tandem C-H amination/vinylic C-H arylation reaction sequence is described under Pd(II)/sulfoxide-catalysis that furnishes a wide range of α- and β-homophenylalanine precursors from commodity α-olefins and readily available aryl boronic acids. General routes to enantiopure amino acid esters and densely functionalized homophenylalanine derivatives are demonstrated.     

Solvent density effects on the solvation behavior and configurational structure of bare and passivated 38-atom gold nanoparticle in supercritical ethane

In exploring the effects of solvent density on the mode and the degree of solvation of the bare and passivated 38-atom gold particle in supercritical ethane, we have extended the molecular dynamics simulations of the system, reported previously,(34) to cover a range of isotherms in the T > T(c) regime, where T(c) is the critical temperature of the solvent. Consonant with our previous observations, the modes of solvation of the bare and the passivated particle, deduced from the radial distribution of the solvent about the metal core center of mass, are found to be vastly different from each other at all solvent densities: while the molecules solvating the bare particle form a well-defined, two-region layer around it, those solvating the passivated particle are loosely dispersed in the passivating layer. For the bare particle, the degree of solvation (vartheta) as a function of solvent density passes through a maximum occurring in the close vicinity of the critical point, consistent with our previous results and in agreement with Debenedetti's theoretical analysis,(22,23) which predicts a solvation enhancement effect in the critical region for systems where the unlike solvent/solute interaction is much stronger than the solvent/solvent interaction. Taking the degree of solvation (vartheta) as a measure of solvent quality, we have investigated how the solvent quality would vary along the solvent-density isotherms. In the solvent-density regime rho > rho(c), the solvent quality is found to be a decreasing function of the density as a result of progressive dominance of the excluded volume effect over the attractive particle/solvent interactions. The particle/solvent affinity is greatly reduced in the presence of the passivating layer, resulting in considerable shrinkage of the good-solvent-quality domain in the supercritical regime. The solvent environment and the presence of the passivating chains produce significant disorder in the equilibrium structure assumed by the nanoparticle core.     

Quantitative determination of major active components in Ginkgo biloba dietary supplements by liquid chromatography/mass spectrometry

A reversed-phase high-performance liquid chromatography/electrospray ionisation mass spectrometry (RP-HPLC/ESI-MS) method was developed and validated for the simultaneous determination of ten major active components in Ginkgo biloba extract (bilobalide, ginkgolides A, B, C, quercetin, kaempferol, isorhamnetin, rutin hydrate, quercetin-3-beta-D-glucoside and quercitrin hydrate) which have not been previously reported to be quantified in a single analysis. The ten components exhibit baseline separation in 50 min by C18 chromatography using a water/1:1 (v/v) methanol/acetonitrile gradient. Quantitation was performed using negative ESI-MS in selected ion monitoring (SIM) mode. Good reproducibility and recovery were obtained by this method. The sensitivity of both UV and different mass spectrometry modes (full scan, selected ion monitoring (SIM), and selected reaction monitoring (SRM)) were compared and both quantitation with and without internal standard were evaluated. The analysis of Ginkgo biloba commercial products showed remarkable variations in the rutin and quercetin content as well as the terpene lactone contents although all the products satisfy the conventional quality control method.     

Tantalus,the First Dedicated Synchrotron Radiation Source

Tantalus began as a 240 MeV electron storage ring that served as a testbed for the next-generation accelerator (which eventually would become Fermilab) [1 There are several more extensive papers on the history of Tantalus: David W. Lynch, “The Early Years of Tantalus,” Synch. Rad. News 5, 16 (1992); David W. Lynch, “Tantalus, a 240 MeV Dedicated Source of Synchrotron Radiation, 1968-1986,” J. Synchrotron Rad. 4, 334 (1997); Giorgio Margaritondo, “The Evolution of a Dedicated Synchrotron Light Source,” Physics Today, May (2008), 37.[Taylor &; Francis Online] , [Google Scholar], 2 List of acronyms: AEC–Atomic Energy Commission (evolved into today's Department of Energy); AFOSR–Air Force Office of Scientific Research; NSF–National Science Foundation; FFAG–fixed-field alternating gradient; UHV–ultrahigh vacuum; OSHA–Occupational Safety and Health Administration; EDC–energy distribution curve; CIS–constant initial state; CFS–constant final state; NAS–National Academy of Sciences. [Google Scholar]]. It was to be injected from the 40 MeV FFAG synchrotron that was already operating. Before its completion, funding from the AEC was discontinued. During the time it was in financial limbo, a report from an NAS study group suggested using Tantalus as a source of VUV synchrotron radiation for spectroscopy and possibly other techniques. The AFOSR eventually funded the completion and early use of Tantalus.