bluuebunny/crossref_metadata_2025_split huggingface dataset:
Capillary Condensation and Surface Flow in Microporous Vycor Glass
Authors: Abeles Benjamin , Chen Liang Fan , Johnson Jack W. , Drake J.M. 
Published: November 2013

AbstractDepending on the size of the pores and on the temperature and pressure of the fluid, flow in microporous materials can be through gas diffusion, surface diffusion, and viscous liquid flow driven by capillary forces or by hydraulic pressure. We have studied these flow regimes with toluene in untreated Vycor glass with a pore radius of 31 Å and Vycor glass with a pore radius of 21 Å whose pores were derivatized with C18H38. The observed increase in viscosity with decreasing pore size is ascribed to the attractive interaction of the monolayer adsorbed on the pore walls. The surface diffusion coefficient at 22°C is 5 × 10−5 cm2 s−1 for both the derivatized and underivatized Vycor, with an activation energy of 3 kcal in the temperature range 22–100°C.
Polymers in Slabs, Slits, and Pores
Authors: Whittington Stuart G. , Soteros Christine E. 
Published: November 2013

AbstractWhen a polymer is subject to a geometrical constraint, such as being confined to a pore, there may be a loss in configurational entropy. If a linear polymer is in dilute solution in a good solvent, then it can be modelled as a self‐avoiding walk on a lattice and, in this case, it is possible to make rigorous statements about this entropy loss. We shall discuss some of these results for self‐avoiding walks in a half‐space, a slab, a prism, etc. We then examine the dependence of this entropy loss on the architecture of the polymer and ask if ring or star or comb polymers all lose the same amount of entropy when confined in the same way. It turns out that this depends on the nature of the confinement. We also look at the case where a polymer interacts with a surface and investigate how the adsorption behavior depends on the architecture of the polymer. The behavior is strikingly different in two and in three dimensions.
An Enantioselective Total Synthesis of (+)‐Elenoic Acid and the Non‐Natural Enantiomers of Tetrahydroalstonine, Aricine, and Reserpinine
Authors: Hölscher Peter , Knölker Hans‐Joachim , Winterfeldt Ekkehard 
Published: November 2013

AbstractA simple enantioselective synthesis of (+)epi‐elenoic acid is reported and its transformation into (+)‐elenoic acid is described. Well‐established procedures transform these compounds into the antipodes of tetrahydroalstonine, aricine, and reserpinine.
Polarizing Nuclear Spins Via Photo‐Excited Triplet States
Authors: Schmidt J. , van den Heuvel D.J. , Henstra A. , Lin T.‐S. , Wenckebach W. Th. 
Published: November 2013

AbstractIn this paper we discuss two methods to achieve high nuclear polarizations at room temperature using pulsed EPR techniques and triplet spins which are optically excited by a laser pulse. The results of our experiments, which are performed on a single crystal of napthalene doped with pentacene, show that an unusually high proton spin polarization can be achieved and that the transfer occurs in a time determined by the dipolar interaction between the electron spins of the pentacene guests and the proton spins on the surrounding napthalene molecules.
On Multiple Quantum NMR of Coupled Spins in Solids
Authors: Ba Yong , Veeman Wiebren S. 
Published: November 2013

AbstractIt is shown that odd‐order multiple quantum coherences can be generated and detected in a system of dipolar coupled spins in a solid. The odd‐order multiple quantum coherences can be detected in various ways. In one particular experiment positive‐ and negative‐order quantum coherences can be distinguished. The theory is demonstrated by experiments on adamantane.
Macromolecule Structure Refinement by Relaxation Matrix Analysis of 2D NOE Spectra: Effect of Differential Internal Motion on Internuclear Distance Determination in Proteins
Authors: Kumar Anil , James Thomas L. , Levy George C. 
Published: November 2013

AbstractInterproton distances obtained from NMR experiments are used to determine the high‐resolution structure of biopolymers. The accuracy of internuclear distances extracted from proton homonuclear 2D NOE spectra can be improved by using a complete relaxation matrix analysis, taking into account all proton dipole‐dipole interactions as well as internal motions. The effect of internal motion on interproton distances, determined from the 2D NOE cross‐peak intensities, has been examined using a new version of the mardigras program, which iteratively determines interproton distances from experimental 2D NOE peak intensities using the complete relaxation matrix. The internal motion has been specified by the ‘model‐free’ approach in terms of an overall correlation time, local correlation times, and order parameters. Using a simulation for the 58‐residue protein bovine pancreatic trypsin inhibitor (BPTI), it is shown that if the local order parameter and correlation time for a given residue differ substantially (but within the experimentally determined range of values) from the average order parameter and correlation time, the error in the interproton distance may be as large as 0.6 Å.
A Picosecond Study of the Photophysics of CdS Clusters Grown in situ in Reversed Micelles
Authors: Barzykin Alexander V. , Fox Marye Anne 
Published: November 2013

AbstractA study of the dynamics of the electronic states of CdS semiconductor clusters grown in situ in reversed micelles via picosecond pump‐probe technique reveals efficient transient bleaching of the excitonic absorption. This effect is attributable mainly to hole localization near the trapped electron, with no evidence of electron ejection (forming a solvated electron) detectable despite the apparent proximity of the cluster to the included water pool. Bleaching efficiency is cluster‐size dependent, and recovery kinetics are governed by the nature of the particle surface. Similar decay behavior is observed in cluster fluorescence. Generally, the decay is characterized by two components, the faster attributed to recombination of a mobile, detrapped electron with a trapped hole, and the slower to an exchange interaction between trapped carriers. The observed strong multiexponentionality of the decay results from a distribution in trap energy levels, as well as from a distribution of distances between traps on the cluster surface. By varying preparation conditions, particles of different sizes with different surface defects can be grown in reversed micelles in a reproducible way so that their electronic properties can be controlled.
Size‐Quantized Semiconductor Particulate Films Generated in situ at Monolayers
Authors: Fendler Janos H. 
Published: November 2013

AbstractMethodologies for the in situ generation of size‐quantized semiconductor particulate films (SQSPFs) are described. Cadmium, zinc, lead, and copper sulfides have been generated from their divalent metal ion precursors electrostatically attached to well‐compressed, negatively charged monolayers by the infusion of hydrogen sulfide. Cadmium selenide has been generated at positively charged dioctadecyldimethylammonium bromide monolayers floating on an aqueous subphase which contained appropriate concentrations of sodium selenosulfate and cadmium nitrilotriacetate. SQSPFs have been characterized by absorption spectra, electron microscopy, scanning tunneling microscopy, X‐ray diffraction, and electrochemical measurements. Evidence is presented for the oriented growth and preparation‐dependent rectification behavior of SQSPFs.
Formation and Photoreaction of PbI2, HgI2, and BiI3 Layered Ultrasmall Particles
Authors: Nosaka Yoshio , Fukuyama Toshiaki , Horiuchi Masato , Fujii Nobuyuki 
Published: November 2013

AbstractFormation of ultrasmall particles of PbI2 in methanol was observed by means of stroboscopic stopped‐flow spectroscopy. Pulse‐laser induced electron transfer from PbI2, HgI2, and BiI3 to viologens was measured for various laser intensities and for various viologen concentrations. The electron transfer yields were 0.24, 0.08, and 0.03 for HgI2, PbI2, and BiI3, respectively. The laser‐intensity dependence differed from the previous observation for CdS and showed that the low yield is not attributable to the direct electron‐hole recombination in the particle.
Ultrafast Torsional Relaxation from the Barrier Region for an Excited‐State Isomerization in Solution: 9‐Carbonylanthracenes
Authors: Johnson Alan E. , Jarzęba WŁOdztmierz , Walker Gilbert C. , Barbara Paul F. 
Published: November 2013

AbstractThe class of compounds containing a carbonyl group substituted at the 9 position of anthracene have been studied as new model systems for torsional isomerization in solution. Franck‐Condon excitation yields an excited‐state distribution near the barrier for isomerization in S1. Using time‐resolved fluorescence spectroscopy, we have determined that the relaxation from the barrier region is subpicosecond for three different compounds in all solvents studied. In fact, the relaxation seems to be almost independent of solvent at room temperature, indicating that most of the local friction felt by the twisting carbonyl is internal friction rather than solvent friction. Apparently the small carbonyl is effectively shielded from the solvent by the anthracene ring so the solvent friction is not strong. In contrast to the weak solvent coupling, previously reported gas‐phase spectra indicate that the torsion may be strongly coupled to the other vibrational modes of the molecule. Energy flow out of the torsion into these other vibrational modes appears to occur on the subpicosecond time scale.
The Lowest Singlet and Triplet States of o‐Benzyne: Spin‐Coupled Interpretation of the Electronic Structure at CAS SCF Equilibrium Geometries
Authors: Karadakov Peter B. , Gerratt Joseph , Raos Guido , Cooper David L. , Raimondi Mario 
Published: November 2013

AbstractThe electronic structure of the X̃1A1 and ã3B2states of o‐benzyne is analyzed by means of spin‐coupled (SC) wave functions involving eight active orbitals: two at the dehydro centers, in the plane of the ring, and six π orbitals, inherited from benzene. The equilibrium geometries of the two states, at which all calculations have been carried out, result from separate full geometry optimizations employing ‘8 in 8’ complete active space self‐consistent field (CAS SCF) wave functions incorporating an analogous core‐valence partitioning. The diradical character of the ground state of o‐benzyne, as approximated by the singlet SC wave function, is reflected in the low value of the overlap (0.46) between the two in‐plane sp2‐like SC orbitals at the dehydro centers, which are just 1.274 Å apart, and in the nonnegligible extent of triplet coupling between the spins of the electrons in these orbitals — ca. 6.4% of the total spin function for the valence electrons (expressed in the Serber spin basis) is made up of spin eigenfunctions, in which these electrons enter as a triplet pair. The geometry of the ground state is found to have an aryne‐like character, which is further confirmed by the pattern of alternation of the overlaps between neighboring 71 valence orbitals, and by the domination of the total spin function for the valence electrons (expressed in the Rumer spin basis) by the spin‐coupling patterns corresponding to an arynic structure.
Ethynylvinylidene
Authors: Collins Charlene L. , Hu Ching‐Han , Yamaguchi Yukio , Schaefer Henry F. 
Published: November 2013

AbstractEthynylvinylidene, an energetically low‐lying isomer of diacetylene, has been studied using ab initio molecular electronic structure theory. Geometries of diacetylene, ethynylvinylidene, and the transition state between them have been optimized using the double‐ζ plus polarization (DZP) and triple‐ζ plus double polarization function (TZ2P) basis sets with the self‐consistent field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double substitutions (CCSD), and CCSD with perturbatively included connected triple substitutions [CCSD(T)] methods. At the TZ2P CCSD(T) level of theory only single point energies have been determined at the TZ2P CCSD geometries. Harmonic vibrational frequencies and infrared (IR) intensities are reported for the three stationary points at the DZP SCF, TZ2P SCF, and DZP CISD levels of theory. For ethynylvinylidene, rotational constants, dipole moments, and dipole moment components along the principal axes are also given. This isomer is found to be an extremely shallow minimum on the C4H2 potential energy surface, and the classical barrier to rearrangement (to diacetylene) is vanishingly small at the highest level of theory.
Addition of Methyl Radical to Substituted Alkenes: A Theoretical Study of the Reaction Mechanism
Authors: Wong Ming Wah , Pross Addy , Radom Leo 
Published: November 2013

AbstractAb initio calculations at the QCISD(T)/6–311G**level have been carried out to study the addition of the methyl radical to a series of substituted alkenes, and the results analyzed with the aid of the curve‐crossing model. It is found that (a) reaction exothermicity is the main factor that dominates reactivity, (b) polar contributions to the transition states are generally small and of minor energetic consequences, and (c) the general observation that π‐electron‐accepting substituents in the alkene enhance reactivity is a secondary correlation that is a consequence of the effect of these substituents on reaction exothermicity. There is no evidence for the prevalent view that the methyl radical is generally nucleophilic towards alkenes.
NDDO‐Based CI Methods for the Prediction of Electronic Spectra and Sum‐Over‐States Molecular Hyperpolarization
Authors: Clark Timothy , Chandrasekhar Jayaraman 
Published: November 2013

AbstractNDDO‐based (AM1) configuration interaction (CI) calculations have been used to calculate the wavelength and oscillator strengths of electronic absorptions in organic molecules and the results used in a sum‐over‐states treatment to calculate second‐order hyperpolarizabilities. The results for both spectra and hyperpolarizabilities are of acceptable quality as long as a suitable CI‐expansion is used. We have found that using an active space of eight electrons in eight orbitals and including all single and pair‐double excitations in the CI leads to results that agree well with experiment and that do not change significantly with increasing active space for most organic molecules. Calculated second‐order hyperpolarizabilities using this type of CI within a sum‐over‐states calculation appear to be of useful accuracy.
Radiative and Nonradiative Decay of Electronically Excited HNF and DNF
Authors: Chen Jing , Dagdigian Paul J. 
Published: November 2013

AbstractDecay lifetimes for a range of HNF and DNF levels in their excited Ã 2A' electronic states, in specific K' stacks and in some cases in individual N' rotational levels, are reported. Above a threshold energy, these lifetimes are found to drop, in a K'‐ and N'‐dependent way, below the extrapolated purely radiative lifetimes. This reduction in lifetime is ascribed to the onset of nonradiative, predissociative decay. Lifetimes for individual N' rotational levels in the HNF(Ã2A') (0,4,0) and DNF(Ã2A') (0,6,0) vibrational manifolds are also reported. These are found to fluctuate in a seemingly random manner vs. N', reflecting the variation of the coupling to the dissociation continuum. The implications of these results and, from other experiments, the direct observation of NH(X3Σ−) and ND(X3Σ−) photofragments for the dynamics of the nonradiative decay of electronically excited HNF and DNF are discussed.
Photofragment Translational Spectroscopy of Fluorinated Halomethanes
Authors: Felder Peter , Yang Xuefeng , Baum Georg , Huber Robert 
Published: November 2013

AbstractThe primary and secondary dissociation processes of CF2Br2 and CF2BrI have been studied by photofragment translational spectroscopy in a pulsed molecular beam. The photolysis of CF2Br2 at 193 nm produces mainly the fragment pair CF2Br + Br and, in a competing primary process, CF2 + Br2. The CF2Br radicals are formed with sufficient internal energy to overcome the barrier of the unimolecular secondary dissociation to CF2+ Br. The photodissociation of CF2BrI at 248 nm also proceeds along two decay pathways involving the fission of the weak C‐I bond and the stronger C‐Br bond, respectively. The former reaction produces spin‐orbit excited iodine atoms I(2P1/2) and stable CF2Br radicals, whereas the latter reaction produces unstable CF2I radicals. The results of this study are compared with those of other workers, and an account of the ultraviolet photochemistry of fluorinated halomethanes is given.
Effective Methods for Estimation of Binding Energies in Computer‐Aided Drug Design
Authors: Warshel A. , Tao H. , Fothergill M. , Chu Z.‐T. 
Published: November 2013

AbstractThe development of an efficient and accurate method for computer‐aided drug design presents a major challenge for computational chemistry. The present work addresses this challenge by examining the accuracy and speed of several alternative strategies. Previous studies of the binding of ligands to the MC603 antibody and new studies of ligand binding to endothiapepsin are considered. It is found that the semimacroscopic version of the Protein Dipoles Langevin Dipoles method (the PDLD/S method) approach can provide qualitative results with reasonable execution times. Much more time is required for the linear response approximation, although it yields accurate results in some cases. Overall, it is still not clear what generation of computers will be needed for reliable and fast drug screening. Nevertheless, computer simulation is clearly useful for correlation X‐ray structures of enzyme‐inhibitor complexes with the corresponding binding energies.
Measurement of NOx, SO2, SPM, and O3 at a High Altitude Station in Northwestern Turkey
Authors: Tuncel Semra G. , Baykal A. Hadi , Tuncel Gürdal , Özer Ulviye 
Published: November 2013

AbstractTemporal variation of NO, NO2, SO2, SPM (suspended particulate matter), and O3 were measured at a high altitude station in the northwestern part of Turkey. The long‐ and short‐term trends in the concentrations of measured parameters were investigated to understand sources contributing to the observed concentrations of these pollutants. Higher concentrations of O3 during summer months were consistent with higher photochemical production with increased solar flux. Seasonal patterns observed in other parameters were consistent with their source strengths during different periods of the year. O3 showed a peak at approximately 3 pm, together with SO2 and NO2. SPM, on the other hand, showed a different diurnal pattern with a maximum concentration occurring during night hours. The main sources of O3, SO2, and NO2 on Mt. Uludag were found to be transported from the town of Bursa and from a nearby ski resort. The vehicular activities on the road which connects the town of Bursa to the ski resort are also an observable source of O3 and its precursors, but not of SO2 and SPM. High concentrations of O3 were observed during night hours. Unlike daytime peaks, these peaks were sporadic and did not correlate with the SO2 and NO2. These night‐time O3 concentrations were suspected to be due to injection from the stratosphere.
Solubilization of Proteins in Membranes
Authors: Dan N. , Safran S.A. 
Published: November 2013

AbstractThe solubility of proteins in membranes depends both on the protein properties and membrane characteristics. In this paper, we calculate the concentration of membrane inclusions as a function of their concentration in solution and the physical properties of the membrane. We find that the membrane deformation plays a key role in determining the adsorption. When there is no thickness mismatch between the inclusions and the membrane, the effective adsorption energy decreases with the lipid spontaneous curvature and hence strongly favors protein adsorption into the membrane.
Trace Element Characteristics of Central Anatolian Obsidian Flows and Their Relevence to Pre‐History
Authors: Yellin Joseph 
Published: November 2013

AbstractThis report concerns the chemical characterization of obsidian sources from Central Anatolia by neutron activation analysis. The sources covered in this study were Göllü Dağ, Hotamiş Dağ, Köru Dağ, Nenezi Dağ, and Çatköy. The study reported here was undertaken with the object of obtaining an accurate “fingerprint” of the compositions of obsidian sources that would permit tracing the origin of archaeological obsidian artifacts to their sources, and in particular, archaeological obsidian recovered from prehistoric sites in Israel. The extent of the sampling within the sources was more thorough than hitherto reported and the results are of high precision and accuracy.
Properties and Photoactivity of Rhodopsin Mutants
Authors: Sakmar Thomas P. , Fahmy Karim 
Published: November 2013

AbstractA variety of spectroscopic and biochemical studies of recombinant site‐directed mutants of rhodopsin and related visual pigments have been carried out. These studies have elucidated key structural elements common to visual pigments, such as a conserved disulfide bond. In addition, systematic analysis of the chromophore‐binding pocket in rhodopsin and cone pigments has led to an improved understanding of the mechanism of the opsin‐shift, and of particular molecular determinants underlying color vision in humans. Identification of conformational changes which occur upon rhodopsin photoactivation has been of particular recent concern. Assignment of these molecular alterations to specific regions in the receptor has been attempted by studying native opsin regenerated with synthetic retinal analogues or recombinant opsins regenerated with 11‐cis‐retinal. Individual molecular groups that undergo structural alterations during photoactivation have been identified. Analysis of particular mutant pigments in which specific groups are locked into their respective “on” or “off” states has provided a framework to identify determinants of the active conformation as well as the minimal number of intramolecular transitions required to switch between inactive and active conformations. A simple model for the active state of rhodopsin can be compared to structural models of its ground state to localize chromophore‐protein interactions that may be important in the photoactivation mechanism.
The Photocycles of Bacteriorhodopsin
Authors: Lanyi Janos K. , Váró György 
Published: November 2013

AbstractThe photoisomerization of all‐trans‐retinal of bacteriorhodopsin to 13‐cis gives rise to a series of unstable states that thermally interconvert on the picosecond to millisecond timescale, and ultimately decay back to the initial state. Since this “photocycle” drives the translocation of a proton from the cytoplasmic to the extracellular side of the membrane, its detailed description is essential to understand the mechanism of the ion transport. The interconversions of the intermediates of the cycle, K610, L550, M410, N560, and O640, proceed with complex multiphasic kinetics, and there is much disagreement over the interpretation of this. However, many groups have described the photocycle as a single reaction sequence with several reversible reactions, some pH‐dependent. Through the use of time‐resolved spectroscopy and site‐specific mutations, such a scheme provides a reasonable model for how the retinal Schiff base first transfers its proton to Asp‐85, followed by release of a proton to the extracellular side; then the Schiff base is reprotonated from Asp‐96, and proton uptake from the cytoplasmic surface restores the initial protonation state of Asp‐96, while the retinal reisomerizes to all‐trans.