7 research outputs found
The adsorption and decomposition of carbon monoxide on Ni(100) and the oxidation of the surface carbide by oxygen
The interaction of carbon monoxide with Ni(100) has been studied by ellipsometry and Auger electron spectroscopy. Bombardment by electrons of a relatively high energy (2500 eV) leads to the disproportionation of the adsorbed CO (2 COad â Cad + CO2g ). The rate of oxidation of this surface carbide is , where hc is the carbon 272 eV Auger peak height, n=0.5 and the apparent activation energy Eact =13.3 kcal/mole. This relation is valid at 200â400°C and at oxygen pressures of 5 Ă 10â9â8 Ă 10â7 Torr
A nonlinear method of removing harmonic noise in geophysical data
A nonlinear, adaptive method to remove the harmonic noise that commonly resides in geophysical data is proposed in this study. This filtering method is based on the ensemble empirical mode decomposition algorithm in conjunction with the logarithmic transform. We present a synthetic model study to investigate the capability of signal reconstruction from the decomposed data, and compare the results with those derived from other 2-D adaptive filters. Applications to the real seismic data acquired by using an ocean bottom seismograph and to a shot gather of the ground penetrating radar demonstrate the robustness of this method. Our work proposes a concept that instead of Fourier-based approaches, the harmonic noise removal in geophysical data can be achieved effectively by using an alternative nonlinear adaptive data analysis method, which has been applied extensively in other scientific studies
Ready Synthetic Access to Enantiopure Allylic α<sub>(F)</sub>-Branched Fluoroalkenes
Convenient access to homochiral fluoroalkenes is described via a JuliaâKocienski olefination reaction. The required homochiral fluorosulfone is synthesized by a Mitsunobu reaction from readily available enantiopure secondary alcohols
Total Synthesis of (â)-Luminacin D
A second-generation synthesis of
(â)-luminacin D based on
an early stage introduction of the trisubstituted epoxide group is
reported, allowing access to the natural product in an improved yield
and a reduced number of steps (5.4%, 17 steps vs 2.6%, 19 steps).
A full account of the optimization work is provided, with the reversal
of stereoselection in the formation of the C4 alcohol in equally excellent
diastereoselectivity as the key improvement
Total Synthesis of (â)-Luminacin D
A second-generation synthesis of
(â)-luminacin D based on
an early stage introduction of the trisubstituted epoxide group is
reported, allowing access to the natural product in an improved yield
and a reduced number of steps (5.4%, 17 steps vs 2.6%, 19 steps).
A full account of the optimization work is provided, with the reversal
of stereoselection in the formation of the C4 alcohol in equally excellent
diastereoselectivity as the key improvement
Stereoselectivity of the HondaâReformatsky Reaction in Reactions with Ethyl Bromodifluoroacetate with αâOxygenated Sulfinylimines
The
Reformatsky reaction of ethyl bromodifluoroacetate to α-oxygenated
sulfinylimines is described. Using HondaâReformatsky conditions,
the reaction proceeds with double diastereodifferentiation, with the
configuration of the sulfinyl group determining the stereochemical
course of the reaction. Excellent diastereoselectivities (>94:6)
are
obtained for the matched cases. In contrast, reaction with sulfinylimines
derived from unsubstituted alkanals proceeded with virtually no diastereoselectivity
Effects of Sugar Functional Groups, Hydrophobicity, and Fluorination on CarbohydrateâDNA Stacking Interactions in Water
Carbohydrateâaromatic interactions
are highly relevant for
many biological processes. Nevertheless, experimental data in aqueous
solution relating structure and energetics for sugarâarene
stacking interactions are very scarce. Here, we evaluate how structural
variations in a monosaccharide including carboxyl, <i>N</i>-acetyl, fluorine, and methyl groups affect stacking interactions
with aromatic DNA bases. We find small differences on stacking interaction
among the natural carbohydrates examined. The presence of fluorine
atoms within the pyranose ring slightly increases the interaction
with the CâG DNA base pair. Carbohydrate hydrophobicity is
the most determinant factor. However, gradual increase in hydrophobicity
of the carbohydrate does not translate directly into a steady growth
in stacking interaction. The energetics correlates better with the
amount of apolar surface buried upon sugar stacking on top of the
aromatic DNA base pair