bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anion Effects in (BEDT‐TTF)2X Salts: Symmetry Induced Superstructures
Authors: Kistenmacher Thomas J. 
Published: November 2013

AbstractThe structural and electrical properties of a series of (BEDT‐TTF)2X salts are systematized in terms of a substructure‐superstructure relationship which is induced by variation in anion symmetry and pictorially represented as a crystallographic family tree. Importantly, it is recognized that the ambient‐pressure superconductors α‐(BEDT‐TTF)2I3, α‐(BEDT‐TTF)2IBr2, and α‐(BEDT‐TTF)2AuI2 have crystal structures coincident with the parent subcell of this crystallographic family tree. Moreover, all first‐generation supercells (doubling of any one subcell vector) are exclusively populated by salts with non‐centrosymmetric anions of tetrahedral symmetry, and, apparently, second‐generation supercells (doubling of any two subcell vectors) are populated by salts with centrosymmetric anions of octahedral symmetry. Finally, trends in structural properties with anion size are briefly considered.
Functionalized Bilayer Membranes as Artificial Transaminase: Modification of the Active Site and Its Consequence in Catalytic Efficiency
Authors: Murakami Yukito , Kikuchi Jun‐Ichi , Akiyoshi Kazunari , Shiratori Nobuyuki 
Published: November 2013

AbstractThe transamination reaction of l‐phenylalanine with pyruvate as catalyzed by the artificial transaminase formed with synthetic bilayer aggregates was examined in aqueous media under mild kinetic conditions. Each catalyst system was constructed with a combination of a synthetic peptide lipid, a hydrophobic vitamin B6 derivative, and metal ions. Modification of the active site in the present artificial transaminase was performed by changing a combination of molecular components constituting the catalytic system. While the catalytic activity was scarcely influenced by differences in aggregate structure, single‐ or multi‐walled bilayer, and in copper‐(II) concentration, molecular structures of the hydrophobic vitamin B6 and an amino acid residue of the peptide lipid had significant effects on the reactivity.
P‐450 Type Activation of Dioxygen by Heterogenized Metal Porphyrins: Comparison with the Corresponding Homogeneous Systems
Authors: Fukuzumi Shunichi , Mochizuki Seiji , Tanaka Toshio 
Published: November 2013

AbstractThe protons of silanol groups on a silica or silica‐alumina surface are replaced by metal(III) porphyrin cations, FeTPP+, MnTPP+, and CoTPP+ (TPP = tetraphenylporphyrin). The heterogenized iron(III) or manganese(III) porphyrin supported on silica thus prepared can activate dioxygen in the presence of excess amounts of NaBH4 and cyclohexene, affording cyclohexanol and cyclohex‐2‐ene‐1‐ol in a 4:1 ratio, which is the same as the ratio observed in the known P‐450 type oxidation of cyclohexene catalyzed by a homogeneous manganese porphyrin (MnTPPCl) in the presence of NaBH4 used as an electron source. The heterogenized iron(III) porphyrin shows a reactivity comparable with that of the corresponding heterogenized manganese(III) porphyrin. On the other hand, substitution of the heterogenized iron(III) porphyrin by the corresponding homogeneous catalyst, FeTPPCl, results in drastic change in the product ratio; the ratio of cyclohexanol to cyclohex‐2‐ene‐l‐ol is reversed, suggesting that the oxidation of cyclohexene proceeds via radical chain autoxidation reactions. The catalytic activity for the P‐450 type oxidation is diminished while FeTPPCl is converted to the μ‐oxo‐dimer (FeTPP)2O. Cobalt(III) porphyrin in a homogeneous system also affords the autoxidation products. Such a mechanistic difference between the homogeneous and heterogeneous metal porphyrins in the oxidation of cyclohexene by dioxygen has been confirmed by kinetic studies in which the P‐450 type oxidation and autoxidation obey different kinetics.
Fourier Transform EPR Measurement of Homogeneous Electron Transfer Rates
Authors: Angerhofer A. , Massoth R.J. , Bowman M.K. 
Published: November 2013

AbstractFourier‐Transform Electron Paramagnetic Resonance has measured the rates of homogeneous electron transfer reactions involving duroquinone radical anions. The radicals are generated by laser photolysis of duroquinone in methanol solution containing 10% triethylamine. The duroquinone concentration was varied over a factor of 1000. The rate constant for electron transfer between the radical anion and the neutral duroquinone is 1.5×108M−1s−1 and the intrinsic spin relaxation rates, T−11 and T−12 are 0.32 MHz and 0.44 MHz, respectively. Two‐Dimensional magnetization transfer spectra show that the reaction is a homogeneous electron transfer reaction. The electron transfer rates are measured by two novel pulse sequences designed for more efficient data acquisition in samples with no unresolved inhomogeneous broadening. These two sequences result in a more rapid, accurate determination of the second‐order chemical rate constant since the second‐order rate constant is obtained directly and is not derived from a single measurement of a pseudo‐first‐order rate. The transient duroquinone radical anions studied here appear to have the same T1, T2 and electron transfer rates as stable duroquinone radical anions in alkaline solutions.
Using Magnetic Resonance of Protons to Image Flowing Blood
Authors: Thomas Dixon W. 
Published: November 2013

AbstractPhysicians often request angiograms or images of arteries. Conventional angiography requires catheterizing a patient, injecting an iodine compound into an artery, and X‐ray photography. All 3 steps have hazards and, compared to clinical nuclear magnetic resonance (NMR) examinations, the procedure is painful, time consuming, and expensive. Iodine distinguishes blood from other tissues in conventional angiography; blood motion serves the same purpose in several recent NMR experiments reviewed here. Blood spins can be inverted upstream of a region of interest. After they flow downstream, blood will be labeled in the region of interest. Comparing NMR images made with and without labeling identifies blood. Alternatively, equal and opposite magnetic field gradient pulses can mark moving blood by changing the phase of its magnetization. The second gradient cancels the phase effect of the first for spins which are still in the same place, thus only blood is affected. Two images with different blood phases are compared. The blood phases may differ because gradients used to produce the images differ or because blood velocities differ owing to different synchronization with the heart. Results of several NMR experiments are presented. All have much lower quality and higher convenience than the conventional X‐ray method.
Geometry‐Directed Generation and Synthetic Application of α‐Lithio Oxime Ethers
Authors: Shatzmiller Shimon , Lidor Rami , Shalom Eytan , Bahar Naim Menashe Eliezer 
Published: November 2013

AbstractSeveral mono‐ and di‐O‐alkyloximes have been regioselectively transformed to the syn α‐lithio derivatives by treatment with n‐butyllithium. The control of oxime ether geometry served to control regioselectivity in α‐lithiation and subsequent carbon‐carbon (alkylation, oxidative coupling) and carbon‐halogen bond formation reactions. The geometry‐directed α‐lithiation‐dimerization sequence was used for the synthesis of large ring compounds.
Synthesis and Enzymic Conversion of Isobutanoyl‐carba(dethia)‐Coenzyme A
Authors: Brendelberger Günter , Rétey János 
Published: November 2013

AbstractAcyl coenzyme A analogues in which the sulphur is replaced by methylene are stable to hydrolysis and can be used to investigate enzymatic reaction mechanisms. With this idea in mind we synthesized isobutanoyl‐carba(dethia)‐coenzyme A (isobutanoyl‐CH2CoA) and monitored its reaction in enzymatic systems. A cell‐free extract of Pseudomonas putida (ATCC 21244) complemented with FAD, phenazine methosulphate, and DCIP catalyzed the conversion of isobutanoyl‐CH2CoA into methacryloyl‐CH2CoA and β‐hydroxyisobutanoyl‐CH2CoA. The latter could not be further oxidized to the aldehyde and carboxyl level, indicating that these oxidations normally occur after hydrolysis of the CoA ester.
Mechanistic Studies on the [2 + 2] Photocycloaddition of Deuterium‐Labeled Olefins
Authors: Becker Dan , Haddad Nizar 
Published: November 2013

AbstractThe mechanism of intramolecular [2 + 2] photocycloaddition of 1b has been investigated. Structure determination of deuterium‐labeled photoadducts was accomplished by 2H NMR.
Dynamics, Spectra, and Relaxation Phenomena of Excess Electrons in Clusters
Authors: Barnett Robert N. , Landman Uzi , Rajagopal Gunaretnam , Nitzan Abraham 
Published: November 2013

AbstractIn this paper, we review quantum simulation methods for studies of coupled quantum‐classical systems and their applications in investigations of dynamics, spectra, and relaxation phenomena of excess electrons in polar molecular and ionic clusters.
Resonances, Cross Sections, and Partial Widths by the Complex Coordinate Method
Authors: Moiseyev Nimrod 
Published: November 2013

AbstractThe Complex Coordinate Method (CCM) is reviewed, emphasizing the theoretical aspects and properties of the complex‐scaled Hamiltonian. It is shown that the CCM not only enables the calculation of resonance positions and widths by computational techniques that had originally been developed for bound states, but also can be used as a powerful tool in the calculation of scattering cross sections and partial widths.
Aspects of the Softness and Hardness Concepts of Density‐Functional Theory
Authors: Harbola Manoj K. , Chattaraj Pratim K. , Parr Robert G. 
Published: November 2013

AbstractIn the density‐functional theory of the ground state of an electronic system there arise the concepts of softness, hardness, local softness, and local hardness. Definitions of these quantities are reviewed, and then local softness and local hardness are discussed in some detail. The local softness of a species, the derivative magnified image, is a measure of the chemical reactivity of a site in the molecule. From it can be obtained the total global absolute softness in the sense of Pearson and a normalized chemical reactivity index of frontier type. Several formulas for s(r) are obtained, including new fluctuation formulas, and its determinative role in chemisorption, catalysis, and frontier‐controlled charge‐transfer processes is briefly discussed. Local hardness is a corresponding appropriately defined functional derivative η(r) = [δμ/δp(r)]v(r). Difficulties associated with ambiguities in this definition are discussed and resolved. It is concluded that for most purposes the best working formula for local hardness is magnified image, where η(r, r′) is the hardness kernel; magnified image, where F[p] is the usual Hohenberg‐Kohn functional and f(r) is the Fukui function. With this definition, η(r) = η, a constant which is the global hardness. Just as the chemical potential equalizes in the ground state, so does the hardness. It is demonstrated that hardness can be taken to be an average of orbital contributions.
Interaction of Carbohydrates with Phosphatidylcholine Inverse Micelles
Authors: Wachtel Ellen , Federman Silvina , Greenspoon Noam 
Published: November 2013

AbstractSmall angle X‐ray scattering experiments indicate that egg phosphatidylcholine dissolved in benzene at a concentration of 12–50 mM organizes into approximately isometric inverse micelles with a size that depends upon the amount of water present. These inverse micelles can serve as self‐assembled hosts for monosaccharide derivatives. For a given amount of water, addition of carbohydrates causes an increase in the micelle size. In contrast, cyclohexane solutions of egg phosphatidylcholine contain highly anisotropic structures, possibly elongated rods. Monosaccharide derivatives can be extracted into these structures and are bound, at low water content, to the polar head groups. Upon addition of water the sugar is probably displaced from the polar head groups and gains some motional freedom in the water pool which is formed. This fact indicates that the polar head group of phosphatidylcholine interacts, probably by means of hydrogen bond formation, with monosaccharides and brings about their solubilization in nonpolar solvents.
Optical Nuclear Polarization of Deuterium Spins: Mechanisms and Applications in Solid State NMR
Authors: Allgeier Jürgen , Buntkowsky Gerd , Hentrich Sven , Hoffmann Werner , Vieth Hans‐Martin 
Published: November 2013

AbstractA gain in detection sensitivity of more than three orders of magnitude has been achieved in high resolution solid state 2H NMR of monocrystalline systems by applying optical nuclear polarization (ONP) via excited triplet states. The method is demonstrated for crystals of fluorene doped with optically active guest molecules which have localized triplet states and for the 1: 1 mixed crystal of anthracene/tetracyanobenzene with excitonic states. The factors determining the efficiency of ONP are discussed and compared to the case of proton spin systems.
Single and Multiple Quantum NMR Relaxation Times of Sodium and Potassium in Red Blood Cells
Authors: Shinar Hadassah , Eliav Uzi , Navon Gil 
Published: November 2013

AbstractThe two components T2f and T2s of the transverse magnetization decay curve of 23Na in dog erythrocytes were measured using the triple quantum filtered spectra. It was shown that this technique, in spite of its inferior sensitivity, may be used for systems where T2f and T2s are not very different. Thus it was possible to measure the effect of 2, 3‐diphosphoglycerate (2, 3 DPG) depletion on the intracellular 23Na relaxation rates. The effect found indicates some contribution of hemoglobin‐2, 3‐DPG complexes to the 23Na relaxation in intact erythrocytes. 39K relaxation times were measured in human and chicken erythrocytes. The results indicate binding similar to that of 23Na. Finally, a decrease of the cellular volume of erythrocytes was found to shorten 23Na relaxation times. The result was interpreted as due to an increase in intracellular concentration of proteins.
Kinetic Basicities of Aqueous Binary Mixtures: A Surprisingly Good Linear Correlation with the Gas Phase Basicity of the Organic Cosolvent
Authors: Pines Ehud , Fleming Graham R. 
Published: November 2013

AbstractA remarkably good correlation between the rate of proton transfer from excited protonated 1‐aminopyrene and the gas phase basicities of the organic component in water: organic solvent binary mixtures has been found. We suggest that use of anilinium acids minimizes the effect of anion solvation and Coulomb interactions and enables the influence of the organic cosolvent on the proton transfer to be clearly observed. The model proposed is one in which the proton is always transferred to a water molecule and a concerted proton transfer to a water molecule solvated by the organic cosolvent also occurs. The cosolvent influence is then on this latter species via hydrogen bond interactions. The correlation holds in pure water but not in pure organic solvents where, clearly, the proton must be transferred to the organic molecule.
Transition Structures of the Electrocyclic Reactions of cis,cis,cis‐1,3,5‐Cyclooctatriene
Authors: Thomas Bert E. , Evanseck Jeffrey D. , Houk Kendall N. 
Published: November 2013

AbstractThe electrocyclic reactions of cis,cis,cis‐1,3,5‐cyclooctatriene have been studied using ab initio molecular orbital theory. cis,cis,cis‐1,3,5‐cyclooctatriene can undergo an electrocyclic ring opening in a conrotatory fashion to form cis,cis‐1,3,5,7‐octatetraene and a disrotatory electrocyclization to form bicyclo[4.2.0]octa‐2,4‐diene. The transition structures for these electrocyclic reactions have been located. Geometry optimizations employed restricted Hartree‐Fock calculations and the 3–21G and 6–31G* basis sets. Electron correlation energies were calculated using second‐order, and in some cases fourth‐order, Møller‐Plesset theory. Scaled RHF/6–31G* force constants were employed in the prediction of secondary deuterium isotope effects for the conrotatory ring opening. The ground state of cis,cis,cis‐1,3,5‐cyclooctatriene exists in a twist‐boat conformation with staggering at the saturated linkage. The transition structure for the conrotatory electrocyclic ring opening to form cis,cis‐1,3,5,7‐octatetraene has a helical structure, which has implications for the stereoselectivities of ring closure of 1‐substituted‐cis,cis‐1,3,5,7‐octatetraenes. The disrotatory transition structure for the electrocyclization to form bicyclo[4.2.0]octa‐2,4‐diene is strongly distorted from Cs symmetry, in contrast to the transition structure for the disrotatory electrocyclization of cis‐1,3,5‐hexatriene. This distortion is caused by staggering about the saturated linkage.
Ab Initio Molecular Orbital Study of Electronic and Geometrical Structures of MCH2+ Complex and its Reactivity with H2, Where M = Co, Rh, and Ir
Authors: Musaev Djamaladdin G. , Morokuma Keiji 
Published: November 2013

AbstractBy using CASSCF (for optimization of geometries) and MR‐SDGI‐CASSCF (for energies) methods we have studied and compared the mechanism of reaction MCH2+ + H2, as well as the electronic and geometrical structure of the MCH2+ complex, where M = Co, Rh, and Ir. It has been found that the mechanisms of reaction MCH2+ + H2 → M+ + CH4 (1) for M = Co and Rh are similar and follow the path: MCH2++H2 → (H2)MCH2+ → [TS1, H2‐activation] → MCH4+ → M+ + CH4. The key step is activation of the H‐H bond, which has a barrier about twice as high for M = Co as for M = Rh; reaction (1) occurs more easily for M = Rh than M = Co. M = Ir completely changes the mechanism of reaction (1), which now follows the path: IrCH2+(3A2) + H2 → (H2) IrCH2+(3A2) → [TS1, H2‐activation] → (H)2 IrCH2+(1A') → [TS2, H‐migration] → HIrCH3+(3A) → [TS3, CH4‐elimination] → IrCH4+(3A2) → Ir+(5F, s1d7) + CH4. The reaction (1) is exothermic for M = Co and Rh, but endothermic for M = Ir. For M = Co and Rh, the reverse reaction M+ + CH4 can give only one product MCH4+ and does not proceed further easily; for M = Co, at elevated temperature CoCH4+may give CoH+ and CoCH3+. However, for M = Ir the reverse reaction can proceed further to give hydridomethyl HIrCH3+ and bishydrido (H)2CH2+ complexes, as well as IrCH4+.
Atmospheric Chemistry of 2‐Ethyl Acrolein
Authors: Grosjean Daniel , Grosjean Eric , Williams Edwin L. 
Published: November 2013

AbstractThe atmospheric oxidation of the unsaturated aldehyde 2‐ethyl acrolein, CH2=C(C2H5)CHO, has been studied in laboratory experiments involving the reaction of ozone with 2‐ethyl acrolein in the dark (with cyclohexane added to scavenge the hydroxyl radical), and the sunlight irradiation of 2‐ethyl acrolein with NO in air. The major carbonyl products of the 2‐ethyl acrolein reaction with ozone are formaldehyde, acetaldehyde, and the dicarbonyl ethylglyoxal, CH3CH2COCHO. Sunlight irradiation of 2‐ethyl acrolein and NO led to the formation of three carbonyls (formaldehyde, acetaldehyde, and ethylglyoxal) and three peroxyacyl nitrates, (RC(O)OONO2), including PAN (R = CH3), PPN (R = C2H5), and the unsaturated compound EPAN (R = CH2=C(C2H5)). Mechanisms are outlined for the reactions of ozone and of the hydroxyl radical with 2‐ethyl acrolein. These mechanisms are consistent with the observed carbonyl and peroxyacyl nitrate products. Thermal decomposition, a major atmospheric removal process for peroxyacyl nitrates, has been studied for EPAN. The decomposition rate of EPAN relative to that of PAN is 0.59–0.73 at 292–294 K and 1 atm of air. Atmospheric implications of these results are discussed.
A Preliminary Apportionment of the Sources of Fine Particulates Impacting on the Israeli Coast
Authors: Gertler Alan W. 
Published: November 2013

AbstractThe Chemical Mass Balance (CMB) receptor model was used to apportion the sources of PM2.5 aerosol (particulate matter with aerodynamic diameter <2.5 μm) sampled during a limited period at Caesarea, a site located in northern Israel along the Mediterranean coast, from late May to early June, 1993, a period corresponding to the time of year when air mass transport from Europe is frequent. Observed PM2.5 concentrations averaged 25.5 μg/m3 during the sampling period, with sulfate accounting for the majority (>50%) of the total observed mass. Source contribution estimates predicted by the CMB receptor model were similar for all periods, with predicted ammonium sulfate, mobile source, coal‐fired power plants, marine aerosol, and residual oil combustion contributions of 74, 14, 9, 3, and 0.3%, respectively. Transport (coupled with transformation) sources accounted for almost 97% of the ambient particulate loadings observed in this preliminary study.
Glass Transition Behavior in Ultra‐Thin Polystyrene Films
Authors: Keddie J.L. , Jones R.A.L. 
Published: November 2013

AbstractWe have used ellipsometry to measure the glass transition temperature (Tg) of ultra‐thin films of polystyrene (PS) (less than 20 nm thick) obtained by spin‐casting from solution onto silicon substrates. We find that Tg in these ultra‐thin films is depressed from the bulk value in qualitative accord with our earlier results on thicker films of PS. In films as thin as 8 nm, the depression from the bulk value of Tg is 35 K. We have also prepared ultra‐thins by grafting PS‐COOH on the native oxide of Si and by spin‐casting PS‐COOH onto Si. Here we have been able to measure the Tg of 5‐nm films in which we find a Tg depression of 10 K. We tentatively ascribe the smaller value of Tg depression for these grafted chains to the constraining effect of the anchor.
Role of Surface‐Anchored Polymer Chains in Adhesion and Slippage
Authors: Léger L. , Hervet H. , Marciano Y. , Deruelle M. , Massey G. 
Published: November 2013

AbstractWhen in contact with an attractive wall, polymer chains tend to form thick, surface‐anchored layers with an internal structure which can be controlled. We present and analyze experiments conducted on model systems aimed at understanding how such surface‐anchored polymer layers can act as adhesion promoters or can induce wall slip. For both situations, the key parameter is the degree of interdigitation between the surface layer and the bulk polymer system, either an elastomer or a melt. We analyze how this degree of interdigitation governs the optimum enhancement in the adhesion energy between the solid wall and an elastomer, and how it is at the origin of the very different wall slip regimes observed experimentally.
Reactions on Single‐Crystal Metal Surfaces Studied with Scanning Tunneling Microscopy
Authors: Murray P.W. , Besenbacher F. , Stensgaard I. 
Published: November 2013

AbstractA review is given of scanning tunneling microscopy (STM) studies of reactions between different chemical species on metal surfaces. Results presented for a variety of systems show that STM can give unique insight at the atomic level into the mechanistic details of surface reactions and decomposition of molecules. This is illustated with a number of examples of reactions occuring on single‐crystal metal surfaces, such as Ni(110), Cu(110), Ag (110), Rh (110), and Pt(111). The ability of the local STM probe to study the influence of defect sites on reactivity is highlighted, and similarities and differences in reactivity of different systems are discussed. Finally, the application of STM to enhance reactivity via tip interactions is addressed.