bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Chemistry of Precipitation in Israel
Authors: Singer Arieh 
Published: November 2013

AbstractRecent concerns about the rapid deterioration in the quality of water resources in Israel, in addition to the widely documented anthropogenic acidification of precipitation in many parts of the world, have put a “state of the art” review of our knowledge of the chemistry of precipitation in Israel on the order of the day. Electrolyte content in precipitation in Israel is inversely related to average annual precipitation, and thus is 3–6 times higher in southern than in central Israel. The major reason for these differences is the differential enrichment in components of continental origin, such as Ca2+ and HCO3−. The chemical composition of precipitation is determined by the balance between components of marine and continental origin. Na+ and Cl− are the major ions contributed by sea spray, and therefore most of the precipitation exhibits Na/Cl (molar) ratios close to that of seawater. Precipitation in the southern parts of the country is an exception. Other ions of partly marine origin are Mg2+, SO42−, K+, and, to a limited extent, Ca2+. Marine contribution to precipitation decreases with distance from the sea. The most important component of continental origin in precipitation in Israel is Ca2+, similar to precipitation in other semiarid areas surrounding the Mediterranean. Calcium in precipitation is often associated with dryfall (dust) originating in North African desert areas. NH4+ concentration levels are relatively low, and thus, the importance of this ion as an acidity‐neutralizing agent is small compared to central/northern Europe. Precipitation in Israel is neutral to mildly alkaline, with an average pH of 6.5 ± 0.8. Mildly alkaline rain is the rule in central and southern Israel. In the Golan Heights, Galilee, and the northern coastal region, most of the precipitation events are acidic. On Mt. Carmel, 40% of the rain events examined during three rainy seasons were strongly acid, and in more than 65% of the events, pH was ≤5.6. Acidity in precipitation in Israel is determined primarily by excess SO42−. Nitrates have only a subordinate role. Synoptic analysis as well as sulfur isotopic data suggest that the excess sulfate is a long‐range import from over the Mediterranean Sea, either of anthropogenic European or of biogenic/marine dimethyl sulfide (DMS) origin. In southern Israel, an isotopic amount effect was observed, whereby rain in rainier years was isotopically lighter δ18O than precipitation in the less rainy years. δ34S values of precipitation were found to be in the range of 0–15‰, thus indicating that precipitation sulfate consisted of a mixture of marine and nonmarine sulfate. Cl and Sr isotope ratios in precipitation were determined as well.
Atmospheric Wet Depositions in Tropical America
Authors: Sanhueza Eugenio , Santana Magaly 
Published: November 2013

AbstractThe chemical composition of wet depositions at a “natural” regional scale and in local polluted areas in tropical America is reviewed. The available data indicate that at large regional scales, atmospheric wet depositions in tropical America are little affected by anthropogenic emissions, and that rain concentrations of non‐sea‐salt sulfate (SO4*), NO3−, and NH4* are much lower than the ones observed at midlatitudes in the northern hemisphere. The regional acidity of rainwater (pH −5) is mainly due to formic and acetic acids; however, the sources of these acids (probably natural) are not well identified as yet. Some “local‐regional” problems are observed in Brazil and Venezuela, and it is likely that other tropical urban‐industrial areas also present anthropogenic acidification of rain, but no measurements have been made. Since most soils in tropical America are sensitive to acid deposition, the evaluation in areas affected by local urban‐industrial emissions should be emphasized.
Acetone in the Urban Atmosphere: A Study in Denver, Colorado
Authors: Anderson Larry G. , Lanning John A. , Wolfe Pamela 
Published: November 2013

AbstractWe report 4‐h average concentration data for acetone, formaldehyde, acetaldehyde, and carbon monoxide measured in downtown Denver, Colorado, USA from January through December 1993. The correlations between these carbonyl compounds and CO measurements suggest that motor vehicles are a significant source for all three carbonyls, particularly during the winter. The diurnal character of the concentrations of formaldehyde and acetaldehyde suggests that there is at least a small net photochemical source for these compounds during the summer. The diurnal character of the acetone concentration suggests that there is a significant net photochemical source for acetone during the summer. An analysis of the initial photochemical production and loss processes for these carbonyls under typical atmospheric conditions suggests that the production and loss processes for formaldehyde nearly balance. This same analysis for the other carbonyls suggests that there should be a large net photochemical source for both acetaldehyde and acetone. Such a large photochemical source is not observed for acetaldehyde. Acetone is relatively unreactive in the atmosphere on a timescale of urban or regional interest. Thus, atmospheric measurements of acetone concentrations may serve as a useful indicator of the photochemical age or degree of photochemical processing of an air mass.
Ozone Levels in Central Israel
Authors: Peleg Mordechai , Luria Menachem , Setter Ilan , Perner Dieter , Russell Patricia 
Published: November 2013

AbstractMeasurements performed during the early summer months of 1988–1991 at a rural site in central Israel, some 50 km east of the highly urbanized coastal region, have shown that during the afternoon hours the area was often under the influence of ozone mixing ratios above the Israel ambient standard (117 ppbv) and occasionally even above 150 ppbv. Analysis of air mass back trajectories has shown that only those air masses passing over the Tel Aviv metropolitan area cause elevated ozone mixing ratios at the rural site. This highly urbanized region emits large amounts of precursors which are entrapped in the air parcels entering Israel under the predominantly westerly wind flows. As these air masses travel inland, sufficient time is available (3–5 h) to allow the photochemical reactions to generate ozone before reaching the rural site. The above hypothesis is further supported by the fact that parallel to the increase of ozone at the rural site, elevated carbon monoxide (up to 0.8 ppmv) and other trace gases were also observed. A significant correlation (R2 > 0.8) was found to exist between the ozone mixing ratio and the NOx concentrations in photochemically aged air masses. In several cases an excess of up to 12 ozone molecules was formed for each NOx molecule present.
Soft Matter in a Tight Spot: Nanorheology of Confined Liquids and Block Copolymers
Authors: Granick Steve , Demirel A. Levent , Cai Lenore L. , Peanasky John 
Published: November 2013

AbstractThe linear frequency‐dependent shear rheology and force–distance profiles of molecularly‐thin fluids of very different structure were contrasted: a globular molecule octamethylcyclotetrasiloxane (OMCTS), branched alkanes (3‐methylundecane and squalane), and a polymer brush in near‐theta solution (polystyrene‐polyvinylpyridine). In each case the data suggest a prolongation of the longest relaxation time (τ1) with increasing compression. At frequencies ω > 1/τ1 the shear response was “solid‐like”, but at ω < 1/τ1 it was “liquid‐like”. OMCTS under mild compression exhibited seeming power‐law viscoelastic behavior with G′(ω) = G″(ω) over a wide frequency range. Of the branched‐molecule fluids, 3‐methylundecane exhibited oscillatory force–distance profiles; this confirms prior computer simulations. But squalane (6 pendant methyl groups in an alkane chain 24 carbons long) showed one sole broad attractive minimum. Polymer brushes in a near‐theta solvent exhibited changes qualitatively similar to those OMCTS, in particular, a smooth progression of longest relaxation time, generating a transition from “liquid‐like” to “solid‐like” shear rheology with decreasing film thickness. The common trend of shear response in these systems, in spite of important differences in molecular structure and force–distance profiles, is emphasized.
Application of FTIR Spectroscopy to the Structural Study on the Function of Bacteriorhodopsin
Authors: Maeda Akio 
Published: November 2013

AbstractDifference FTIR spectroscopy of the photointermediates of bacteriorhodopsin is informative for changes in H‐bonding, the protonation states, and the bond orientation of functional residues such as C=O, N‐H, and O‐H of the chromophore, protein residues, peptide bonds, and internal water molecules. The vibrational bands of the chromophore are found at frequencies similar to those observed by resonance Raman spectra. Moreover, FTIR gives clear results on the N— in‐plane bending vibration and C14–C15 stretching vibrational modes, both of which are useful for the analysis of the structure of the chromophore. The protonation states and H‐bonding changes of intramembrane protonated aspartic acid residues can be revealed only by FTIR spectroscopy, in combination with proper isotope labeling and site‐directed mutagenesis. The results with Asp‐96 and Asp‐85 in the L, M, and N photointermediates were especially useful for understanding the proton transfer mechanism. Besides amino acid groups in the protein, peptide C=O vibrations were assigned to a specific bond by the use of site‐directed isotope labeling. Water molecules which undergo structural changes upon photoreaction were attributed specifically to those interacting with particular protein residues by mutational studies. On the basis of these FTIR studies, the role of the L intermediate is emphasized as the key intermediate that creates the conditions for the proton transfer reaction from the Schiff base to Asp‐85 and subsequent proton uptake reactions in the cytoplasmic domain.
Atomically‐Resolved Investigations of Surface Reaction Chemistry by Scanning Tunneling Microscopy
Authors: Hamers Robert J. , Chen X. , Frank E.R. , Higgins S.R. , Shan J. , Wang Y. 
Published: November 2013

AbstractResearch by our group aimed at studying the chemistry of surfaces with atomic‐resolution scanning tunneling microscopy is reviewed. Three areas of application are discussed: semiconductor surface chemistry, adsorption processes at metals, and in situ studies of dissolution and oxidation‐reduction chemistry of minerals.
Thermally‐Induced Changes in Bonding Properties of C60 on Si(100)‐2×1 Surfaces
Authors: Yao Xiaowei , Chen Dong , Ruskell Todd G. , Workman Richard K. , Sarid Dror 
Published: November 2013

AbstractThe co‐adsorption of pre‐ and post‐annealed C60 molecules on Si(100)‐2×1 surfaces has been investigated using scanning tunneling microscopy in ultrahigh vacuum. The images reveal that the adsorption characteristics of the post‐annealed adsorbates are different from their pre‐annealed counterparts. The post‐annealed C60 molecules bond either to the top of the dimer rows or to the missing dimer defects, while the pre‐annealed molecules predominantly occupy the four‐dimer sites in the troughs. The apparent size and height of post‐annealed C60 molecules are smaller than those of the pre‐annealed ones. Our observations suggest that the post‐annealed C60 molecules are chemisorbed on the surface, because the molecules covalently bond to Si atoms during the sample annealing. In contrast, the adsorption of the pre‐annealed C60 molecules can be explained by a dipole‐induced‐dipole interaction between the molecules and the Si(100) surface, i.e., physisorption.
Chemically‐Specific Probes for the Atomic Force Microscope
Authors: Lee Gil U , Chrisey Linda A. , O'Ferrall C. Elizabeth , Pilloff Daniel E. , Turner Noel H. , Colton Richard J. 
Published: November 2013

AbstractThe atomic force microscope (AFM) measures force and displacement with high sensitivity and submillisecond temporal resolution. By functionalizing the AFM probe with specific chemical groups or macromolecules it is possible to characterize the chemical and physical properties of single molecules on the nanometer scale. In this paper we discuss the key issues that must be addressed when designing and characterizing a successful immobilization chemistry, and describe the chemistry we developed to covalently immobilize oligonucleotides in a specific orientation.
Catalytic Antibody Structures: An Early Assessment
Authors: Haynes Matthew R. , Heine Andreas , Wilson Ian A. 
Published: November 2013

AbstractThe three‐dimensional structures of four catalytic antibodies, three of which were complexed with transition‐state analogs, have been determined by X‐ray crystallographic methods. An additional catalytic antibody structure has been deduced using homology modeling methods, and the information derived from the resulting model has been the basis for site‐directed mutagenesis experiments. Analysis of these crystal structures suggests that the primary source of catalytic activity in three of the antibodies is primarily shape and charge complementarity between the combining sites and the transition‐state‐analog haptens. The fourth structure may contain a modified “catalytic triad,” with histidine, serine, and tyrosine side chains positioned so that they could participate in the chemical transformation. Otherwise, the abzyme structures are representative of antibody structures in general, and do not possess any particularly unusual features that would suggest a classification outside the normal range of variation expected within the immunoglobulin family. Rather, the catalytic activity of these antibodies can be explained entirely on the basis of the local arrangement of residues that line the binding sites for their haptenic antigens. In addition, the structures provide strong evidence that the conserved immunoglobulin framework can provide a highly suitable context to serve as the basis for a generalized, programmable catalyst.
Antibody‐Catalyzed Uni‐ and Multi‐Substrate Reactions Compared Using Transition‐State Binding (KTS)
Authors: Reymond Jean‐Louis , Chen Yuanwei 
Published: November 2013

AbstractCatalytic antibody technology is based on the equivalence between catalysis, transition‐state binding, and transition‐state analog binding. This simple concept has attracted enormous creativity to the field. Unfortunately a similar degree of simplicity is usually not evident in kinetic analyses of antibody‐catalyzed reactions. In particular, the rate enhancement kcat/kuncat does not allow one to compare reactions of different orders. Here we propose a simple language based on expressing KTS, the dissociation constant of the antibody‐transition‐state complex, together with a drawing for the corresponding transition‐state. The constant KTS was introduced by Kurz in 1963 as a quantitative expression for Pauling's formulation of catalysis. A small value of KTS describes tight transition‐state binding, and thus efficient catalysis. We show that this analysis allows a unified and remarkably simple description of antibody‐catalyzed reactions with very different levels of complexity. It also enforces a proper formulation of the “uncatalyzed” reaction, which has a critical influence in assessing catalytic efficiency. Comparing KTS with Ki, the dissociation constant of the antibody‐hapten complex, shows how far binding to a designed hapten translates into catalysis.
The Unimolecular Decomposition of Cyclobutanol: Experimental and Theoretical Study
Authors: Tanaka Seiji , Tomariguchi Susumu , Saito Ko , Takahashi Osamu , Tabayashi Kiyohiko 
Published: November 2013

AbstractThe thermal decomposition of cyclobutanol has been investigated behind incident and reflected shock waves at temperatures between 950 K and 1450 K in the total density region (1.5 × 10−6 – 1.5 × 10−5) mol/cm3. A strong absorption by an intermediate was observed at the wavelength of 193 nm. By comparing the kinetics with that of pyruvic acid, this absorption was identified to be that of vinyl alcohol. The kinetic parameters of vinyl alcohol, both for the production and the decomposition, were determined. The production rate constant was in agreement with that obtained by Back (Can J. Chem. 1982, 60, 2357), who monitored the ethylene production. The total decomposition mechanism of cyclobutanol was discussed on the basis of MO calculations. It was shown that vinyl alcohol was produced through a biradical before it isomerized to acetaldehyde.
Reaction of Silane with Atomic Oxygen at High Temperatures
Authors: Iida Daisuke , Koshi Mitsuo , Matsui Hiroyuki 
Published: November 2013

AbstractThe reaction of silane with atomic oxygen (3P) was investigated by the shock‐tube–laser‐photolysis method over the temperature range of 900–1170 K. Oxygen atoms were produced by the ArF laser photolysis of SO2 behind reflected shock waves and monitored with atomic resonance absorption spectroscopy. The rate constant for the SiH4 + O reaction was evaluated by taking the possible contribution of the consecutive reaction into consideration. The Arrhenius temperature coefficient was determined to be Ea= 26.6 kJ mol−1, which is much higher than the experimental activation energies obtained at lower temperatures. Rate constants calculated by a transition state theory with the reaction barrier height of E0= 10.2 kJ mol−1 agreed well with both the present and the previous experimental results for a wide temperature range.
Real Gas Corrections in Shock Tube Studies at High Pressures
Authors: Davidson David F. , Hanson Ronald K. 
Published: November 2013

AbstractReaction kinetics studies at high pressure in shock tubes can be significantly affected by the influence of real gas effects on state variables. The effect on the temperature, pressure, and density can be calculated by solving the shock wave equations using real gas equations of state (EOS). We present a method to solve the shock wave equations in a straightforward way by taking advantage of the recently‐developed real gas properties package by Schmitt et al. (U. of Iowa Rep. UIME PPB 93–006, 1994). The solutions of these equations for shock waves in pure argon are presented. We find that the reflected shock temperatures and densities can be significantly different from those predicted by using an ideal gas EOS. Using the Peng‐Robinson EOS, for example, the calculated real gas reflected shock temperature is less than the ideal gas temperature by 83 K per 1000 atm. An illustrative example of the effect of real gas corrections on a rate coefficient determination is also presented.
Functionalized [2]Rotaxanes
Authors: Asakawa Masumi , Ashton Peter R. , Iqbal Sayeedha , Quick Andrew , Stoddart J. Fraser , Tinker Nigel D. , White Andrew J.P. , Williams David J. 
Published: November 2013

AbstractThe synthesis of a series of dumbbell‐shaped compounds, which can act as a host (e.g., toward alkali metal cations) and as a guest (e.g., toward cyclobis(paraquat‐p‐phenylene)) in a supramolecular context is described. The self‐assembly of [2]pseudorotaxanes and [2]rotaxanes, in which cyclobis(paraquat‐p‐phenylene) encircles polyether chains intercepted in their middles by a hydroquinone ring and terminated at each end by 12‐crown‐4, 15‐crown‐5, monoaza‐18‐crown‐6, 18‐crown‐6, or adamantyl groups, is achieved using either threading, clipping, or slipping procedures. All the [2]pseudorotaxanes and [2]rotaxanes are characterized in solution by spectroscopic means and, in the case of two of the [2]rotaxanes, by X‐ray crystal structures in the solid state. In the presence of metal ions, [2]pseudorotaxanes carrying 12‐crown‐4 or 15‐crown‐5 stoppers can be disassembled in solution. The research shows how one kind of complexation can affect another kind of complexation—manifesting itself in a physical change in the system and so acting as a prototype of a potential molecular device.
Alignment Photoregulation of a Nematic Liquid Crystal by Surface Adsorption of Aminoalkylated Azobenzenes
Authors: Ueda Masahide , Kudo Kazuaki , Ichimura Kunihiro 
Published: November 2013

AbstractAdsorption behavior of azobenzenes having an aminoalkyl residue onto a silica surface is described. Immersion of a silica plate in a benzene solution of an aminoalkylated azobenzene resulted in efficient adsorption to form face‐to‐face aggregates which are converted into monomeric states by partial desorption. Silica plates adsorbing the azobenzene bearing an aminoalkyl residue were employed to achieve the surface‐assisted photoregulation of alignment of a nematic liquid crystal between homeotropic and planar modes. Based on these observations, a convenient method to prepare command surfaces for the orientational photoregulation of liquid crystals was presented by filling a liquid crystal containing an aminoalkylated azobenzene into an empty cell composed of clear silica plates.
Sugar‐Induced Chiral Orientation of Boronic‐Acid‐Appended Amphiphile Clusters Formed in the Dipalmitoylphosphatidylcholine (DPPC) Membrane
Authors: Kimura Taro , Takeuchi Masayuki , Hamachi Itaru , Shinkai Seiji 
Published: November 2013

AbstractA boronic‐acid‐appended amphiphile bearing an azobenzene chromophore in the chain center (3) was synthesized. Although 3 could not form the membrane‐like, ordered aggregate by itself, it formed a phase‐separated aggregate in a dipalmitoylphosphatidylcholine (DPPC) matrix membrane. When saccharides were added, the boronic acid group reversibly formed the saccharide complexes, and 3 in the DPPC matrix membrane became CD‐active with the appearance of exciton‐coupling bands. Comparison of the saccharide absolute configuration with the CD intensity established that the saccharide possessing the OH group (as 3‐OH, 4‐OH, and 5‐CH2OH) in the same side as the cis‐1,2‐diol gives the strong CD band. Judging from the structure of 3–saccharide complexes, these “same‐side” OH groups can enjoy intermolecular hydrogen‐bonding interactions, which eventually induce the chiral orientation of azobenzene chromophores. This is a novel membrane system useful to read out the information stored in the saccharide structure and to create novel membrane structures by added saccharides.
Triplet EPR Dynamics of Randomly Oriented Dications and Dianions of Tetraoxaporphyrinoids
Authors: Berman Assia , Levanon Haim , Vogel Emanuel 
Published: November 2013

AbstractThis paper deals with the photoexcited triplet state of several tetraoxaporphyrinoids studied by time‐resolved electron paramagnetic resonance (EPR). The porphyrinoids studied are tetraoxa[18]porphyrin (1a++), octaethyl‐tetraoxa[18]porphyrin (1b++), tetra‐n‐butyl tetraoxa[18]porphyrin (1c++), octaethyl‐tetraoxa[26]porphyrin (2++), and tetraoxa[18]porphycene (3++), all of them as per‐chlorate salts. To qualify as stable aromatic 18π‐ (or 26π‐) electron systems, they must exist as dications. Analysis of the triplet EPR spectra is characterized by unique features not found in their parent porphyrins and porphycenes. While in the case of the axially‐symmetric tetraphenylporphyrin, the triplet EPR spectra indicate deviation from axial symmetry, the tetraoxaporphyrin 1a++ exhibits, as expected, a vanishing E‐term of the zero‐field splitting (ZFS) tensor. A conspicuous difference is found between the triplet EPR spectra of the dications and the dianions of all tetraoxa compounds. The results are discussed in terms of the electronic structures of the porphyrinoids.
A Biomimetic Approach to Taxol: Stereoselective Synthesis of a 12‐Membered Ring Ene‐Epoxide
Authors: Takahashi Takashi , Okabe Tadashi , Iwamoto Hajime , Hirose Yoichiro , Yamada Haruo , Doi Takayuki , Usui Shuji , Fukazawa Yoshimasa 
Published: November 2013

AbstractThe stereoselective synthesis of a taxol intermediate via a biomimetic route is described. Aldol condensation of γ‐butyrolactone and citral derivatives generated three stereogenic centers at positions C1, C2, and C11 corresponding to taxol. Intramolecular alkylation of the cyanohydrin ether efficiently formed the 12‐membered ring system in which stereoselective reduction, followed by directed epoxidation, afforded the key intermediate epoxide.