bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tremorgenic Indole Alkaloids. 10. An Improved Asymmetric Synthesis of a Tricyclic Common Intermediate
Authors: Smith Amos B. , Hartz Richard A. , Spoors P. Grant , Rainier Jon D. 
Published: November 2013

AbstractAn efficient third‐generation asymmetric synthesis of tricyclic lactone (+)‐1, designed to serve as the common intermediate for construction of the indole tremorgens, has been developed. The major challenge was stereocontrolled introduction of the vicinal quaternary methyl groups. Our initial approaches employed enolate chemistry to install the second methyl moiety; herein we exploit instead a hydroxyl‐directed Simmons‐Smith cyclopropanation followed by reductive opening of the three‐membered ring. The new 15‐step synthesis proceeds in 8.3% overall yield, nearly an eightfold increase over the second‐generation route, and is amenable to large‐scale production of (+)‐1.magnified image
Asymmetric Sequential Michael Addition–N–Heterocyclization Reactions Involving Chiral Imines
Authors: D'angelo Jean , Cavé Christian , Desmaële Didier 
Published: November 2013

AbstractThe reaction of chiral imines ent‐14, 27, and 31 with α‐chloroacrylonitrile 6, maleic anhydride 9, and citraconic anhydride 35 has been investigated. Addition of imine 27 to 6 furnished, after NaBH3CN‐reduction of the crude product, the bicyclic derivative 28 as a single isomer. When the same protocol was applied to imine ent‐14, a mixture of adducts 29 and 30 was obtained. Addition of imine 31 to 6 gave the annulated pyrrole 32. Condensation of imine 27 with maleic anhydride 9 afforded compound 33 as a single isomer. Addition of imine ent‐14 to citraconic anhydride 35 led, after esterification of the crude product with CH2N2, to a mixture of adducts 36 and 37. The mechanism of these aza‐annulations was discussed on the basis of the regio‐ and stereoselectivities observed.
A Convenient Method for the Preparation of Disaccharides by Transglycosylation of Methyl Glycosides
Authors: Uchiro Hiromi , Kurusu Nobuyuki , Mukaiyama Teruaki 
Published: November 2013

AbstractTransglycosylation of methyl glycosides with various glycosyl acceptors using a Sn(OTf)2–Me3SiCl promoter system in the presence of molecular sieves 5A afforded the corresponding glycosides. Several useful disaccharides are effectively prepared in good yields with moderate to good stereoselectivities.
Recent Developments in the Synthesis of Annonaceous Acetogenins
Authors: Marshall James A. , Hinkle Kevin W. , Hagedorn Chad E. 
Published: November 2013

AbstractSynthetic routes to various bis‐THF annonaceous acetogenins and prototypes thereof are reviewed. These C35–C37 long‐chain diethers exhibit a remarkable range of biological activities. The core unit, with six oxygenated stereogenic centers, provides a challenging target for asymmetric synthesis.
Electrochemical Deposition of Hydrosulfide and Ethanethiolate Adlayers on Silver(111). Voltammetric Measurement of Structural Phase Transitions During Adlayer Formation
Authors: Stevenson Keith J. , Hatchett David W. , White Henry S. 
Published: November 2013

AbstractReversible, oxidative adsorption of hydrosulfide (HS−) and ethanethiolate (CH3CH2S−) on highly‐ordered, Ag(111) electrodes in aqueous 0.5 M NaOH solutions is reported. Oxidation of HS− and CH3CH2S− results in adlayer formation, as determined by voltammetry, coulometry, and in‐situ electrochemical quartz‐crystal measurements. The voltammetric response of Ag(111) in HS− solutions displays three characteristic waves. Two waves correspond to the reversible 1‐e− oxidative adsorption of HS”, resulting in the formation of a Ag‐SH adlayer. The third wave corresponds to the kinetically‐slow 1‐e− oxidation of the Ag‐SH adlayer, yielding an underpotential deposited monolayer of Ag2S. The voltammetric response observed in CH3CH2S− solutions is qualitatively similar to that of HS−, displaying two well‐resolved waves corresponding to oxidative adsorption. The observation of two voltammetric waves is suggestive of a mechanism of CH3CH2S− adlayer formation involving at least two distinct structural phases. However, unlike the situation for HS”, the resulting Ag‐SCH2CH3 adlayer is unable to undergo a second oxidative transition. The free energies of adsorption of HS” and CH3CH2S− on Ag(111) are measured to be ca. −23 kcal/mol.
Spectroelectrochemical Investigations of the Spreading of 4‐Pentadecyl Pyridine onto the Au(111) Electrode
Authors: Sagara Takamasa , Zamlynny Vlad , Bizzotto Dan , Mcalees Alan , Mccrindle Robert , Lipkowski Jacek 
Published: November 2013

AbstractThe adsorption of 4‐pentadecyl‐pyridine (C15‐4‐Py) onto the Au(111) electrode was investigated with the help of electrochemical and spectroscopic techniques. Electrochemical studies demonstrated that a film of C15‐4‐Py spreads onto the metal surface at potentials close to the potential of zero charge (pzc) and desorbs from the electrode surface at potentials which are sufficiently negative. The character of C15–4‐Py adsorption resembles adsorption of pyridine molecules at the Au(111) electrode, indicating that the film properties are to a large extent determined by the interaction between the pyridine moiety and the metal surface. Addition of 25 mol%) of 10‐decyl‐9‐[2‐(4‐pyridyl)ethyl]anthracene(DPEA), a dye molecule, to the C15–4‐Py film only slightly modified its properties but allowed the use of spectroscopic methods to study the film properties. Fluorescence spectroscopy and light scattering experiments were employed to study the potential‐induced desorption and adsorption of the surfactant molecules. Using spectroelectrochemical techniques we have demonstrated that the desorption of the film and its readsorption involves the formation of micelles in the subsurface region and spreading of the micelles onto the electrode surface. A general mechanism of spreading of insoluble surfactants onto electrode surfaces has been proposed.
Characterization and Electroanalytical Application of ω‐Mercaptoalkanesulfonic Acid Monolayers on Gold
Authors: Turyan Iva , Mandler Daniel 
Published: November 2013

AbstractSelf‐assembled monolayers (SAMs) of ω‐mercaptoalkanesulfonic acid on gold surfaces have been studied by electrochemistry and other surface techniques. In spite of the fact that these monolayers are disorganized, i.e., of “brush” type, they are impermeable to inorganic anions due to their high negative charge. Moreover, we find that an ω‐mercaptodecanesulfonic acid (MDS) monolayer is also impermeable to organic species, regardless of their charge, because of its high hydrophilicity. The combination of these properties made it possible to apply gold electrodes modified with MDS for the determination of iron(III) ions in the presence of organic species that are either electroactive throughout the same potential window or form strong complexes with iron(III).
Preparation of Self‐Assembled Monolayers from Micellar Solutions
Authors: Liu Jian , Kaifer Angel E. 
Published: November 2013

AbstractThe self‐assembly of alkanethiols on gold surfaces from micellar aqueous solutions was investigated using Triton X‐100, sodium dodecylsulfate, and cetyltrimethylammonium bromide as representative nonionic, anionic, and cationic surfactants, respectively. The surfactant solutions solubilized the otherwise water‐insoluble alkanethiols, which self‐assembled on gold to form organized assemblies very similar to those prepared using the conventional procedures, i.e., exposure of the gold surface to a nonaqueous solution of the alkanethiol. The resulting derivatized gold electrodes exhibited typical electrochemical properties, such as low capacitance values and substantial blocking of the voltammetric reduction of Ru(NH3)63+. The concentration of surfactant was found to have a profound effect on the rate of alkanethiol chemisorption.
Electrochemical Formation of CdSe Monolayers on the Low Index Planes of Au
Authors: Lister Tedd E. , Colletti Lisa P. , Stickney John L. 
Published: November 2013

AbstractThe electrochemical analog of atomic layer epitaxy (ALE) is being studied. ALE is a method for growing thin films of materials using a cycle of surface limited reactions. The surface limited reactions control the deposition by limiting the growth to an atomic layer at a time. In electrochemistry, a surface limited deposition is generally referred to as underpotential deposition (UPD), and UPD is used to form the atomic layers in electrochemical ALE (ECALE). The work presented here is an atomic level study of the deposition of the first few monolayers of CdSe via ECALE: by the alternated UPD of atomic layers of Se and Cd on the low index planes of Au. UPD of Se resulted in the formation of ordered structures on each of the low index planes of Au, as observed by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The subsequent UPD of Cd resulted in CdSe deposits which exhibited 1:1 stoichiometry, as determined by coulometry and Auger electron spectroscopy (AES). The following LEED patterns were observed for the CdSe monolayers: Au(111)(√7×√7)R19.1°, Au(111)(3×3), Au(110)(2×3), and the Au(100)(√2×2√2)R45°. Similar LEED patterns were observed on each surface for deposits formed using up to three ECALE cycles. In situ STM studies of Cd deposition on Se‐covered Au(111) indicated the formation of a (3×3) structure, consistent with LEED results, and with previous TEM studies. The same LEED patterns were also observed for CdSe monolayers where Cd was deposited as the first atomic layer. AES indicated that the element deposited first remained on the bottom, and that deposited second remained on top.
Spectroscopic Characterization of Supersonic Molecular Beams
Authors: Vaida Veronica , Frost Gregory J. , Goss Lisa M. 
Published: November 2013

AbstractA general spectroscopic method is described by which samples prepared in supersonic molecular beams can be characterized independently in their ground and excited electronic states. The centerpiece of this experiment is a Fourier transform spectrometer operating at high resolution in the infrared, visible, and ultraviolet. This method is illustrated with studies of the NO2 and OClO radicals prepared in supersonic molecular beams at temperatures and pressures characteristic of the Earth's atmosphere.This general spectroscopic method is discussed by analogy with low‐ and high‐resolution studies of electronic states which in limited cases have been used to characterize sample conditions in supersonic molecular beam experiments.
Heteroepitaxy of Diamond on Cubic Boron Nitride
Authors: Koizumi Satoshi 
Published: November 2013

AbstractThe epitaxial growth process of diamond from the gas phase on a cubic boron nitride (c‐BN) {111} surface has been investigated. At the initial growth stage, carbon adsorption progressed on a boron‐terminated surface of c‐BN ({111}B). The coordination of the carbon atoms was found to be the same as that observed in diamond, as confirmed by electron energy loss spectroscopy (EELS). The epitaxial growth of diamond particles has been observed after formation of the carbon layer. On the other hand, on the nitrogen‐terminated surface ({111}N), neither stable adsorption of carbon nor nucleation of diamond has been observed. The stability of adsorbed carbon atoms in the chemical vapor deposition (CVD) ambient, in which large amounts of atomic hydrogen are supplied to the substrate heated at high temperature, is quite important for the nucleation of diamond. Using cross‐sectional transmission electron microscopy (TEM), numerous crystal defects were observed, both in c‐BN and diamond. Formation of the epitaxial diamond particles has been observed especially at defect sites on c‐BN. The misfit dislocation has been observed near the interface with the diamond particle. Even though there exist misfit dislocations that relieve the stress caused by the lattice mismatch between diamond and c‐BN, the epitaxial film involved retains a tensile strain of about 0.29% for a film thickness of about 200 nm.
Diamond Electrodes
Authors: Tenne Reshef , Lévy‐Clément Claude 
Published: November 2013

AbstractWith their unique chemical stability and high electron mobility, boron‐doped thin diamond films are likely to have favorable properties for a number of electrochemical applications. A review of the recent developments in this field is presented with critical evaluation of the experimental data. In particular, the relationship between the material's characteristics and the electrochemical behavior of the electrodes is discussed in detail. A number of potential applications for these electrodes are presented: for dimensionally stable electrodes in highly corrosive environments, for discharging toxic effluents, and for electrochemical sensors.
Applications of Conformal CVD Diamond Films
Authors: Rotter Shlomo 
Published: November 2013

AbstractA method for enhanced nucleation of diamond growth on non‐diamond substrates is introduced via the results obtained in a wide variety of applications. The exact details of the method are still proprietary, but the outcome, as demonstrated in this paper, is unique and promises to be of great practical use. The main feature of the growth following the nucleation step is a very high density of nucleation sites which instantly started to grow over any structured surface in a perfectly conformal fashion.
Laser‐Excited Photothermal Lens Spectrometry in a Low‐Volume Cylindrical Sample Cell
Authors: Bialkowski Stephen E. 
Published: November 2013

AbstractA new apparatus for performing laser‐excited photothermal lens spectroscopy is described. The apparatus uses a sub‐microliter cylindrical sample cell, chopped laser excitation, and a continuous probe laser to perform photothermal lens spectrometry. The sample is irradiated with a constant irradiance beam, and the photothermal lens forms due to thermal diffusion through the sample cell walls. Solutions for the thermal diffusion equations predict a parabolic temperature change under continuous irradiation. Experimental results are obtained for organic and inorganic complexes in ethanol solution and compared to those obtained using a standard sample cell. Results for dicyclopentadienyl iron solutions excited with 10mW 514.5 nm Ar+ laser radiation show that the cylindrical sample cell signal is 32% of that obtained using the standard sample cell. This ratio is in reasonable agreement with that expected based on thermal diffusion models. Results obtained for ruthenium tris‐bipyridyl chloride and perchlorate salts are not stable with respect to irradiation time. The latter results suggest that a significant amount of ruthenium tris‐bipyridyl complex is photolyzed with the mild irradiation conditions used in these experiments.
The Surface Chemistry of Hydrocarbons on Transition Metal Surfaces: A Critical Review
Authors: Zaera Francisco 
Published: November 2013

AbstractThe catalytic chemical conversion of hydrocarbons on transition metals is at the heart of a good number of processes of industrial importance, including oil and food processing, pharmacological synthesis, manufacturing of specialty chemicals, and polymer production, to name a few. This is an old field that has advanced in great measure by process development work based on trial and error. It has only been in the last few decades, with the advent of a battery of new surface‐sensitive techniques, that it has been possible to address the fundamental questions on the basic chemistry behind those hydrocarbon conversion reactions. In this review we highlight some of the main ideas advanced in this field by modern surface‐science studies. Particular emphasis is given here to the pioneering work of Professor Somorjai's group as well as our more recent contributions. A discussion is provided on the state of the art of the knowledge available in terms of the elementary steps involved in the transformations of hydrocarbons on metals, as obtained in experiments performed under well‐controlled vacuum conditions; on the connection between that knowledge and the reactions that may prevail under the atmospheric pressures encountered in real catalytic processes; and on the key questions that remain unanswered to date and the possible future directions in this area of research.
The Rotational State Distributions of Photodesorbed Ammonia as a Local Probe of Corrugation
Authors: Bornscheuer Karl‐Heinz , Binetti Marcello , Hasselbrink Eckart 
Published: November 2013

AbstractPhotodesorption of ammonia follows a curved reaction path. Electronic excitation of, or electron attachment to, the adsorbate molecule leads to a transition from the pyramidal ground state to an excited state with planar geometry. During the short residence time in the excited state, the hydrogen atoms are accelerated towards the surface, resulting in an inversion of the molecule and a strong repulsion from the surface which eventually leads to desorption. In this paper, we present evidence that in the inverted geometry the molecule feels the corrugation of the surface potential on rotation around its symmetry axis. This gives rise to a strong torque in cases where the 3‐fold symmetry of the molecule is not matched by the lattice symmetry, resulting in energy transfer to the rotational degrees of freedom. Secondly, it is demonstrated that when both ammonia and oxygen are coadsorbed on a Ru surface, in which case the rotation of adsorbed NH3 is frustrated, a large fraction of the zero point energy is released as rotational energy.
Realistic Surface Science Models of Supported Catalysts: The Chromium Oxide Ethylene Polymerization Catalyst
Authors: Thüne P.C. , Niemantsverdriet J.W. 
Published: November 2013

AbstractDepositing catalytically active particles onto flat, thin oxide films which have electric conductivity forms an attractive way to make supported catalysts suitable for surface science investigations. Here we describe the development of a model system for the chromium oxide on silica catalyst used in industry for the polymerization of ethylene, the so‐called Phillips catalyst. The model system, consisting of molecularly dispersed chromium ions, deposited by wet chemical impregnation on a thin silica film and anchored to it by treating it in oxygen, displays a representative activity for polyethylene formation.
Laser Diagnostics of Combustion Processes: From Chemical Dynamics to Technical Devices
Authors: Ebert Volker , Schulz Christof , Volpp Hans‐Robert , Wolfrum Jürgen , Monkhouse Penelope 
Published: November 2013

AbstractLaser‐based in situ diagnostic techniques with high temporal, spectral, and spatial resolution have become valuable tools to study the molecular dynamics of gas‐phase and heterogeneous reactions as well as complex technical combustion processes. Results of recent experiments will be presented in which laser‐induced fluorescence, sum‐frequency generation surface vibrational spectroscopy, Rayleigh scattering, excimer laser‐induced fragmentation fluorescence, and high‐resolution tunable diode laser absorption spectroscopy were applied to investigate elementary chemical gas‐phase and catalytic combustion reactions, internal combustion engine processes, as well as coal combustion and waste incineration.
The Sulfinatodehalogenation Reaction
Authors: Huang Wei‐Yuan , Wu Fan‐Hong 
Published: November 2013

AbstractSulfinatodehalogenation is a simple and efficient reaction for the synthesis of polyfluoroalkane‐sulfinates and sulfonates. The reaction can also be applied for the polyfluoroalkylation of organic compounds. A brief account is given of its development and scope, reaction mechanism, and applications in organic synthesis.
Influence of Electrostatic Interactions on Complexes with Short O···O Hydrogen Bonds in Basic Salts of Pyridine Betaines and Acid Salts of ω‐Phenyloalkanocarboxylic Acids
Authors: Szafran Mirosław , Kowalczyk Iwona , Barczyński Piotr 
Published: November 2013

AbstractThe isostructural complexes [C5H5N+(CH2)nCOO]2HX and [C6H5(CH2)nCOO]2HK (n = 1–4), which differ in their counterions and charge on the ring, were synthesized, and their powder FT‐IR spectra analyzed. All complexes containing a charged pyridine ring are of Hadži type iii, characterized by an intense broad (continuum) absorption below 1600 cm−1typical of a short‐strong hydrogen bond (SSHB) with a delocalized proton and a singlevC=O band. The positively charged nitrogen atoms interact electrostatically with the X−ion and, additionally, with one of the oxygen atoms of the carboxylic group, producing a more or less symmetric environment of the H‐bonded proton, and stabilizing the SSHB. The broad absorption of [C6H5CH2COO]2HK is very similar to that of other pyridine complexes. Upon addition of methylene groups the broad absorption moves to higher wavenumbers, the O···O distance is elongated, and the H‐bonded proton becomes more localized. In the spectrum of [C6H5(CH2)4COO]2HK thevC=O andvasCOO bands were found at 1704 and 1641 cm−1, respectively, which shows that the H‐bonded proton is asymmetrically located. The observed variation of absorption with the number of CH2groups reflects changes of contacts between the K+ion and COO−groups.
Covalent and Ionic States of Strong Acids at the Ice Surface
Authors: Devlin J. Paul , Uras Nevin , Rahman Mohammed , Buch Victoria 
Published: November 2013

AbstractThe relationship between the degree of ionization and the environment of a strong acid is of basic scientific interest. Often this relationship reduces to the interdependence of ion/acid hydration and proton transfer. Despite the presence of pure water, the surface of crystalline ice, particularly at cryogenic temperatures, is one of limited (controlled?) availability of water of hydration. Here, the detailed nature of the ice surface and the states of strong acids adsorbed to ice at cryogenic temperatures are examined. These subjects are of special current interest since the ability to model the complex chemistry that occurs on the surfaces of water‐rich particles in the atmosphere, particularly in the stratosphere over the polar regions, requires a valid concept of the acid‐ice interface. Our combined spectroscopic and simulation studies have identified the surface of free‐standing ice particles as badly disordered, with a range of water‐ring sizes and an increased level of H‐bond saturation relative to an ordered ice surface. FT‐IR results are reported for the interaction of the surface of such ice particles with submonolayer amounts of adsorbed DCl, DBr, and HNO3 and for multilayer exposure to DCl. The DCl and DBr adsorbed states demonstrate behavior familiar from observations on strongly bound molecular adsorbates. Two methods have been devised for exposure of the nanocrystals to HNO3 One gives an ionic state initially, while the initial state of the other approach is molecular. In both instances, the system is observed to evolve, with time/warming, towards a common mixed molecular–ionic adsorbed state.
Femtosecond Intramolecular Double Proton Transfer in Solution
Authors: Glasbeek Max 
Published: November 2013

AbstractA review is given of our recent femtosecond fluorescence upconversion studies of photoexcited [2,2′‐bipyridyl]‐3,3′‐diol (BP(OH)2), and a few derivative compounds thereof. For BP(OH)2 in liquid solution, concerted and consecutive intramolecular double proton transfers are found to occur concurrently. The concerted (one‐step) process takes place in less than 100 fs. The consecutive two‐step process (with a first step in less than 100 fs and a second step of a few picoseconds) is solvent and excitation wavelength dependent. From the results we infer that the excited‐state double proton transfer in BP(OH)2 is promoted by low‐frequency vibrational stretching and bending modes. Proton transfer dynamics was also studied for BP(OH)2 in sol‐gel glasses. Residual amounts of methanol and water in the pores of the sol‐gel glass are found to still solvate the probe molecule and to affect the proton transfer dynamics. Finally, some results of fluorescence upconversion experiments for 6‐Me‐BPOH (6‐methyl‐[2,2′‐bipyridyl]‐3′‐ol) and BP(OH)2‐6‐COOMe (methyl‐3,3′‐dihydroxy‐[2,2′‐bipyridyl]‐6‐carboxylate) are presented for comparison. It appears that the latter compound in the excited state exhibits a single proton transfer only.