Plasmonic Scissors for Molecular Design

Heterogeneous catalysts play an important role in surface catalytic reactions, but selective bond breaking and control of reaction products in catalytic processes remain significant challenges. High‐vacuum tip‐enhanced Raman spectroscopy (HV‐TERS) is one of the best candidates to realize surface catalytic reactions. Herein, HV‐TERS was employed in a new method to control dissociation by using hot electrons, generated from plasmon decay, as plasmonic scissors. In this method, the N?N bond in 4,4′‐dimercaptoazobenzene was selectively dissociated by plasmonic scissors, and the reaction products formed from the radical fragment (SC₆H₅N) were controlled by varying the pH value. Under acidic conditions, p‐aminothiophenol was produced from the radical fragment by attachment of hydrogen ions, whereas under alkaline conditions, 4‐nitrobenzenethiol was obtained by attachment of oxygen ions to the substrate.     

Thermal stability and electronic structure of atomically uniform Pb films on Si(111)

Atomically uniform Pb films are successfully prepared on Si(111), despite a large lattice mismatch. Angle-resolved photoemission measurements of the electronic structure show layer-resolved quantum well states which can be correlated with dramatic variations in thermal stability. The odd film thicknesses N = 5, 7, and 9 monolayers show sharp quantum well states. The even film thicknesses N = 6 and 8 do not, but are much more stable than the odd film thicknesses. This correlation is discussed in terms of a total energy calculation and Friedel-like oscillations in properties.     

SOME NEW CLASSES OF ALMOST PERIODIC FUNCTIONS

In this paper classes of almost periodic functions are formed whlch lie between those established by W. Stepanoff and by H. Burkill.     

Use of high-performance thin layer chromatography by the American Herbal Pharmacopoeia

TLC characterizations are among the key identity tests in most pharmacopoeial monographs. Pharmacopoeial standards are typically used by industry as a basis for meeting QC requirements and current good manufacturing practices (cGMPs). TLC is a relatively low-cost, highly versatile tool for developing specifications for raw materials, as well as for the various preparations for which pharmacopoeial standards are created. In addition to its use in the development of identity tests, TLC is a valuable tool for screening plant samples that pharmacopoeias must review in the development of monographs and botanical reference materials (BRMs). Specifically, HPTLC is the ideal TLC technique for these purposes because of its increased accuracy, reproducibility, and ability to document the results, compared with standard TLC. Because of this, HPTLC technologies are also the most appropriate TLC technique for conformity with GMPs. This article highlights the manner in which HPTLC is used by the American Herbal Pharmacopoeia (AHP) in the development of AHP monograph identity standards, the identification of adulterating species, and the development of AHP-verified BRMs.     

A Similarity Solution for Oil Lens Redistribution Including Capillary Forces and Oil Entrapment

Redistribution of a LNAPL lens (oil) at the phreatic surface is described using a multi-phase flow model, with emphasis on the effect of oil entrapment by water. The flow process is analyzed under the assumption that the vertical capillary and gravitational forces balance. Vertical integration leads to explicit functions which approximate the relations between the free oil volume per unit lateral area and the vertically averaged oil relative permeability on the one hand and the vertical position of the interface between zones with either two or three phases on the other hand. A linear relation between the trapped and free oil volume per unit lateral area approximates the vertically integrated nonlinear expression for the trapped oil saturation. The resulting differential equation admits a similarity solution describing the lateral spreading of free oil and the amount and location of trapped oil. Comparison with illustrative numerical computations, which are based on the nonreduced flow model in a two-dimensional planar or axisymmetric domain, shows that the analytical solution provides a good approximation of the free oil distribution at all later times.     

Effect of O2 on the adsorption of SO2 on carbon-supported Pt electrocatalysts

Adsorption of SO(2) in the presence of O(2) on Pt/C catalysts often used as electrocatalysts has been investigated by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The amounts of SO(2) adsorption on Pt/C in the presence of O(2) were much higher than those in the absence of O(2) (SO(2)-N(2)) and from the carbon support (Vulcan XC-72) alone. Adsorption is dependent on oxygen concentration over the range 0-20% but reaches saturation at 20% O(2). The spillover of SO(2) from Pt to the carbon support has been proposed for 10, 20, and 40% Pt loadings, characterized by desorption temperatures of approximately 150 and 260 °C for SO(2) adsorbed on Pt and carbon, respectively. Adsorbed Pt-S, C-S, C-SO(x), and Pt-SO(4) species were identified by XPS as S-containing species on both Pt and carbon. Both TPD and XPS indicate that the carbon support plays a major role in SO(2) adsorption, primarily as SO(x) (x = 3, 4). The bonding of S and SO(x) on the carbon support was strong enough that back diffusion to the Pt surface did not occur.     

α-Azido bisphosphonates: synthesis and nucleotide analogues

The first examples of α-azido bisphosphonates [(RO)(2)P(O)](2)CXN(3) (1, R = i-Pr, X = Me; 2, R = i-Pr, X = H; 3, R = H, X = Me; 4, R = H, X = H) and corresponding β,γ-CXN(3) dGTP (5-6) and α,β-CXN(3) dATP (7-8) analogues are described. The individual diastereomers of 7 (7a/b) were obtained by HPLC separation of the dADP synthetic precursor (14a/b).     

The Reduction and Nitration of 1-Keto and 4-Keto-1,2,3,4-Tetrahydrophenanthrene

The reduction and nitration of 1-keto and 4-keto-1,2,3,4-tetrahydrophenanthrene were investigated. The structures of the products were confirmed by spectroscopic data.     

Neutral currents and stellar cooling

If weak neutral currents couple with the strengths suggested by recent experiments, then stellar cooling via neutrino pair emission from thermally excited nuclear states may be significant in white dwarfs with central temperature ?10^8° K. At higher temperatures, other neutrino cooling processes are more important. In the sun, the decay of thermally excited ⁵⁷Fe nuclei may produce a moderately large, but probably unobservable, low-energy flux of ν_μ, $\text{g}\text{?}\text{n}{}_{\mathrm{\mu }}$, ν_e, and $\text{g}\text{?}\text{n}{}_{\mathrm{e}}$ neutrinos.