bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fine Tuning of the Anisotropy Barrier by Ligand Substitution Observed in Linear {Dy2Ni2} Clusters
Authors: Li Yan , Shang Qiu , Zhang Yi‐Quan , Yang En‐Cui , Zhao Xiao‐Jun 
Published: November 2016

AbstractThree new heterometallic single‐molecule magnets (SMMs), [Dy2Ni2(bipy)2(RC6H4COO)10] [bipy=2,2′‐bipyridine, R=H (1), CH3 (2), and NO2 (3)], are synthesized solvothermally with different 3‐substituted benzoate ligands (RC6H4COO−), and are characterized both structurally and magnetically. Structural analyses reveal that the three entities are structurally analogous, exhibiting an approximately linear {Dy2Ni2} core bridged by ten carboxylate moieties from the RC6H4COO− ligands. A noncoordinating substituent group attached on the phenyl ring results in minor geometry distortions of 1–3, but causes a significant decrease in the Mulliken atomic charge on the axially shortest O donor through inductive and/or conjugative effects. Weak intramolecular ferromagnetic (for DyIII⋅⋅⋅DyIII) and antiferromagnetic (for DyIII⋅⋅⋅NiII) interactions with slightly different coupling strengths are observed in 1–3 at low temperatures, and the effective anisotropy barriers to block the magnetization reversal are 39.9, 25.9, and 2.8 cm−1, respectively, under zero direct‐current field. Ab initio calculations reveal that ligand substitution by the noncoordinating electron‐withdrawing/electron‐donating group can give rise to good modulation of the energy gap between the two lowest Kramers doublets, as well as the orientation of the local easy axis of the DyIII ion magnetization. The directions of the local easy axis of the DyIII ion can further influence the dipole spin–spin interaction and the molecular anisotropy of the entire molecule, which, together with the energy separation between the ground and first excited ground states, become the significant factors determining the effective anisotropy barrier heights of 1–3. These important results demonstrate that the charge distributions of the ligand‐field environments play essential roles in SMM performance, which should be considered seriously and utilized efficiently during the rational design of new, more feasible and practical SMMs.
Chirality Transfer in Gold(I)‐Catalysed Hydroalkoxylation of 1,3‐Disubstituted Allenes
Authors: Webster Stacey , Sutherland Daniel R. , Lee Ai‐Lan 
Published: November 2016

AbstractGold(I)‐catalysed intermolecular hydroalkoxylation of enantioenriched 1,3‐disubstituted allenes was previously reported to occur with poor chirality transfer due to rapid allene racemisation. The first intermolecular hydroalkoxylation of allenes with efficient chirality transfer is reported here, exploiting conditions that suppress allene racemisation. A full substrate scope study reveals that excellent regio‐ and stereoselectivities are achieved when a σ‐withdrawing substituent is present.
meso–meso‐Linked Diarylamine‐Fused Porphyrin Dimers
Authors: Fukui Norihito , Yorimitsu Hideki , Osuka Atsuhiro 
Published: November 2016

AbstractA meso–meso‐linked diphenylamine‐fused porphyrin dimer and its methoxy‐substituted analogue were synthesized from a meso–meso‐linked porphyrin dimer by a reaction sequence involving Ir‐catalyzed β‐selective borylation, iodination, meso‐chlorination, and SNAr reactions with diarylamines followed by electron‐transfer‐mediated intramolecular double C−H/C−I coupling. While these dimers commonly display characteristic split Soret bands and small oxidation potentials, they produced different products upon oxidation with tris(4‐bromophenyl)aminium hexachloroantimonate. Namely, the diphenylamine‐fused porphyrin dimer was converted into a dicationic closed‐shell quinonoidal dimer, while the methoxy‐substituted dimer gave a meso–meso, β‐β doubly linked porphyrin dimer.
Modelling Chemical Reasoning to Predict and Invent Reactions
Authors: Segler Marwin H. S. , Waller Mark P. 
Published: November 2016

AbstractThe ability to reason beyond established knowledge allows organic chemists to solve synthetic problems and invent novel transformations. Herein, we propose a model that mimics chemical reasoning, and formalises reaction prediction as finding missing links in a knowledge graph. We have constructed a knowledge graph containing 14.4 million molecules and 8.2 million binary reactions, which represents the bulk of all chemical reactions ever published in the scientific literature. Our model outperforms a rule‐based expert system in the reaction prediction task for 180 000 randomly selected binary reactions. The data‐driven model generalises even beyond known reaction types, and is thus capable of effectively (re‐)discovering novel transformations (even including transition metal‐catalysed reactions). Our model enables computers to infer hypotheses about reactivity and reactions by only considering the intrinsic local structure of the graph and because each single reaction prediction is typically achieved in a sub‐second time frame, the model can be used as a high‐throughput generator of reaction hypotheses for reaction discovery.
Control of the Termination Mechanism in Radical Polymerization by Viscosity: Selective Disproportionation in Viscous Media
Authors: Nakamura Yasuyuki , Ogihara Tasuku , Hatano Sayaka , Abe Manabu , Yamago Shigeru 
Published: November 2016

AbstractThe termination mechanism of radical polymerization, that is, disproportionation (Disp) versus combination (Comb), determines the chain length and end‐group structure of the resulting polymer as well as polymer properties, and yet factors governing the mechanism are still unclear. Furthermore, no attempts have been made to control the mechanism. Here, the effects of temperature and viscosity on the termination of methyl methacrylate (MMA) and styrene (St) polymerization were elucidated by using small molecular model‐radicals and the corresponding polymer radicals in various solvents. The results showed that Disp was preferred over Comb if the temperature was decreased and the viscosity of the media was increased for all the radicals examined. Although the temperature effect on the Disp/Comb selectivity is counterintuitive because Disp should be favored entropically over Comb considering the decrease in the number of polymer chains in Comb, the results clearly showed that the observed inverse temperature effect was a result of the viscosity effect. Disp was favored over Comb at lower temperatures and in more viscous solvents because the transition state leading to Disp is more flexible than that for Comb. Because of the significant viscosity effect, Disp selectively occurred in highly viscous solvents; the Disp/Comb selectivity was 97/3 in both MMA and St termination. For the first time, the termination mechanism was intentionally controlled and such a high Disp selectivity was observed. In particular, the termination mechanism in St is described as Comb in textbooks, but nearly complete inversion of the selectivity from Comb to Disp is realized by simply changing the viscosity of the media.
Advanced Magnetic Resonance Techniques for the Structural Characterization of Aminoxyl Radicals and Their Inorganic–Organic Nanocomposite Systems
Authors: Eckert Hellmut 
Published: November 2016

AbstractElectron and nuclear spins are extremely sensitive probes of their local structural and dynamic surroundings. Their Zeeman energy levels are modified by different types of local magnetic and electric fields created by their structural environment, which influence their magnetic resonance condition. For this reason, electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectroscopies have become extremely powerful tools of structural analysis, which are being widely used for the structural characterization of complex solids. Following a brief introduction into the basic theoretical foundations the most commonly used techniques and their application towards the structural characterization of paramagnetic solids based on aminoxyl radicals and their inorganic–organic nanocomposites will be described. Both ESR and NMR observables are useful for monitoring intermolecular interactions between unpaired electron spins, which are particularly important for the design of organically based ferromagnetic systems. ESR and NMR methods based on this effect can be used for monitoring the synthesis of polynitroxides and for evaluating the catalytic function of aminoxyl intercalation compounds. Finally, the sensitivity of ESR signals to motional dynamics can be exploited for characterizing molecule‐surface interactions in nanocomposite systems. In the context of the latter work recently developed signal enhancement strategies are described, using polarization transfer from electron spins to nuclear spins for NMR spectroscopic detection.
1H‐ und 13C‐NMR‐Spektroskopie
Authors: Findeisen Matthias , Siehl Hans‐Ullrich , Berger Stefan 
Published: November 2016

AbstractDer gegenwärtige Stand der Routine 1D 1H‐ und 13C‐NMR‐Spektroskopie wird geschildert. Nach einer knappen Einführung in die zu Grunde liegende Theorie werden die zurzeit verfügbaren Spektrometer und Softwaresysteme diskutiert. Anhand eines Beispiels aus der Naturstoffchemie wird die Vorgehensweise bei der Analyse der Spektren erläutert.
Positive cooperativity of CaSiO3 and platinum‐tin catalyst in reaction of acetic acid to ethanol
Authors: Zhang Jianqiang , Luo Jian , Gao Jun , Liu Dianhua 
Published: November 2016

AbstractCatalytic hydrogenation of acetic acid to ethanol was investigated in a fixed‐bed micro‐reactor with calcium silicate‐modified platinum‐tin catalyst at mild reaction condition. The modified catalyst exhibited excellent performance for the ethanol synthesis process at relatively low pressure. According to the results of H2‐pulse chemisorption experiments, the introduction of calcium silicate promoted the dispersion of platinum particles. The NH3‐TPD and H2‐TPR results showed the decrease of acid content on catalyst surface and the enhancement of reducibility after the CaSiO3 modification. Additionally, the results of XPS indicated that Sn (0) was emergent and Pt (2+) was sharply decreased after reduction. Both the H2‐TPR and XPS results supported the formation of Pt‐Sn alloy during the reduction process at 623 K. The Pt‐Sn alloy changed the electron density and benefited the free hydrogen dissociation and hydrogenation. The enhancement of reaction temperature and pressure both promoted acetic acid conversion. The kinetic model of power‐function type was established to describe the process of hydrogenation. The results of residual analysis confirmed that the raised kinetic model for acetic acid to ethanol reaction was suitable.
Rhodium(III)/Amine Synergistically Catalyzed Enantioselective Alkylation of Aldehydes with α,β‐Unsaturated 2‐Acyl Imidazoles
Authors: Gong Jun , Li Kuan , Qurban Saira , Kang Qiang 
Published: November 2016

AbstractA synergistic catalysis combination of chiral‐at‐metal rhodium complex and amine catalyst was developed for enantioselective alkylation of aldehydes with α,β‐unsaturated 2‐acyl imidazoles. The corresponding adducts were obtained in good yields with excellent enantioselectivities (up to 99% ee).
Quantifying the suitability of CIE D50 and a simulators based on LED light sources
Authors: Gu H.T. , Pointer M.R. , Liu X.Y. , Ronnier Luo M. 
Published: November 2016

AbstractIn this study, two psychophysical experiments, colour‐difference assessment and colour‐appearance estimation, were conducted to investigate the perceived quality of four CIE illuminant simulators, including two simulators based on LED light sources. The perceived colour‐differences of 30 metameric pairs, seen under the different simulators, were evaluated by 10 colour‐normal observers using the gray scale method and the colour appearance of the colour inconstant sample in each pair assessed in a magnitude estimation method. Colorimetric measures revealed that LED simulators can achieve the desired quality according to the relevant ISO and CIE standards. The results of the experiments showed that an LED simulator outperformed the conventional fluorescent lamp‐based simulator for the CIE illuminant D50 condition. In addition, an LED simulator worked almost equally well as a conventional simulator for simulating CIE illuminant A. These findings strongly indicated the good quality of LED simulators based on a limited number of channels, and the superiority of LED technology. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 408–418, 2017
New Method to Study Ion–Molecule Reactions at Low Temperatures and Application to the Reaction
Authors: Allmendinger Pitt , Deiglmayr Johannes , Schullian Otto , Höveler Katharina , Agner Josef A. , Schmutz Hansjürg , Merkt Frédéric 
Published: November 2016

AbstractStudies of ion–molecule reactions at low temperatures are difficult because stray electric fields in the reaction volume affect the kinetic energy of charged reaction partners. We describe a new experimental approach to study ion–molecule reactions at low temperatures and present, as example, a measurement of the
reaction with the
ion prepared in a single rovibrational state at collision energies in the range Ecol/kB=5–60 K. To reach such low‐collision energies, we use a merged‐beam approach and observe the reaction within the orbit of a Rydberg electron, which shields the ions from stray fields. The first beam is a supersonic beam of pure ground‐state H2 molecules and the second is a supersonic beam of H2 molecules excited to Rydberg–Stark states of principal quantum number n selected in the range 20–40. Initially, the two beams propagate along axes separated by an angle of 10°. To merge the two beams, the Rydberg molecules in the latter beam are deflected using a surface‐electrode Rydberg–Stark deflector. The collision energies of the merged beams are determined by measuring the velocity distributions of the two beams and they are adjusted by changing the temperature of the pulsed valve used to generate the ground‐state H2 beam and by adapting the electric‐potential functions applied to the electrodes of the deflector. The collision energy is varied down to below Ecol/kB=10 K, that is, below Ecol≈1 meV, with an energy resolution of 100 μeV. We demonstrate that the Rydberg electron acts as a spectator and does not affect the cross sections, which are found to closely follow a classical Langevin‐capture model in the collision energy range investigated. Because all neutral atoms and molecules can be excited to Rydberg states, this method of studying ion–molecule reactions is applicable to other reactions involving singly charged cations.
Insights into the Gelating Abilities of Ricinelaidic Acid and its Ammonium Salts: How do Stereochemistry, Charge, and Chain Lengths Control Gelation of a Long‐Chain Alkenoic Acid?
Authors: Zhang Mohan , Weiss Richard G. 
Published: November 2016

AbstractThe gelating abilities of ricinelaidic acid (d‐REA), the trans‐isomer of ricinoleic acid (d‐RA), and a series of its alkylammonium and alkane‐α,ω‐diammonium salts have been examined in a wide range of organic liquids. The gelation efficiency of the trans acid is much better than that of the cis, although neither is as efficient as is the completely saturated molecular gelator analogue, (R)‐12‐hydroxystearic acid (d‐12HSA). The formation of ammonium salts also improves the gelation ability of d‐REA in high polarity liquids. The gelating properties are highly dependent upon the chain length of the alkyl group of the alkylammonium salts, but not very dependent on the chain length of the alkane‐α,ω‐diammonium salts. Structural insights from Fourier transform infrared spectroscopy and powder X‐ray diffraction indicate that the absence or presence of unsaturation, the incorporation of (charged) ammonium centers, and the different chain lengths of the alkylammonium salts lead to different packing arrangements and different strengths of H‐bonding interactions within the gel assemblies of the d‐REA derivatives. Insights into the relationships among the various systematic structural changes to d‐REA and the properties of their aggregated structures, including the gel states, are provided.
The Role of Entropy in Nanoparticle Agglomeration
Authors: Kätelhön Enno , Sokolov Stanislav V. , Bartlett Thomas R. , Compton Richard G. 
Published: November 2016

AbstractAgglomeration processes in non‐interacting particle systems can be understood from a thermodynamic point of view. If the enthalpy of agglomeration is negligible, the distribution of agglomeration states adopts the state of highest entropy. Herein, we provide the exact analytical solution to the mole fractions of agglomerates comprising i monomers, xi=2−i.
New Mechanism for the Reduction of Vanadyl Acetylacetonate to Vanadium Acetylacetonate for Room Temperature Flow Batteries
Authors: Shamie Jack S. , Liu Caihong , Shaw Leon L. , Sprenkle Vincent L. 
Published: November 2016

AbstractIn this study, a new mechanism for the reduction of vanadyl acetylacetonate, VO(acac)2, to vanadium acetylacetonate, V(acac)3, is introduced. V(acac)3 has been studied for use in redox flow batteries (RFBs) for some time; however, contamination by moisture leads to the formation of VO(acac)2. In previous work, once this transformation occurs, it is no longer reversible because there is a requirement for extreme low potentials for the reduction to occur. Here, we propose that, in the presence of excess acetylacetone (Hacac) and free protons (H+), the reduction can take place between 2.25 and 1.5 V versus Na/Na+ via a one‐electron‐transfer reduction. This reduction can take place in situ during discharge in a novel hybrid Na‐based flow battery (HNFB) with a molten Na–Cs alloy as the anode. The in situ recovery of V(acac)3 during discharge is shown to allow the Coulombic efficiency of the HNFB to be ≈100 % with little or no capacity decay over cycles. In addition, utilizing two‐electron‐transfer redox reactions (i.e., V3+/V4+ and V2+/V3+ redox couples) per V ion to increase the energy density of RFBs becomes possible owing to the in situ recovery of V(acac)3 during discharge. The concept of in situ recovery of material can lead to more advances in maintaining the cycle life of RFBs in the future.
Regioselectivity and Reaction Mechanism of Ru‐Catalyzed Hydrogenolysis of Squalane and Model Alkanes
Authors: Nakagawa Yoshinao , Oya Shin‐ichi , Kanno Daisuke , Nakaji Yosuke , Tamura Masazumi , Tomishige Keiichi 
Published: November 2016

AbstractThe dependence of the C−C hydrogenolysis activity on reaction parameters and the structure of the substrate alkanes was investigated for Ru/CeO2 catalyst with very small (dispersion: H/Ru=0.89) Ru particles. The substrate concentration and reaction temperature did not have a significant effect on the selectivity pattern, except that methane production was promoted at high temperatures. However, the hydrogen pressure had a marked effect on the selectivity pattern. Ctertiary−C bond dissociation, terminal Csecondary−Cprimary bond dissociation, and fragmentation to form excess methane had negative reaction order with respect to hydrogen partial pressure, whereas Csecondary−Csecondary bond dissociation had an approximately zero reaction order. Therefore, a high hydrogen pressure is essential for the regioselective hydrogenolysis of Csecondary−Csecondary bonds in squalane. Ru/SiO2 catalyst with larger Ru particles showed similar changes in the product distribution during the change in hydrogen pressure. The reaction mechanism for each type of C−C bond dissociation is proposed based on reactivity trends and DFT calculations. The proposed intermediate species for the internal Csecondary−Csecondary dissociation, terminal Csecondary−Cprimary dissociation, and Ctertiary−C dissociation is alkyls, alkylidynes, and alkenes, respectively.
Understanding the Reaction Mechanism of Glycerol Hydrogenolysis over a CuCr2O4Catalyst
Authors: Yun Yang Sik , Kim Tae Yong , Yun Danim , Lee Kyung Rok , Han Jeong Woo , Yi Jongheop 
Published: November 2016

AbstractThe reaction mechanism of glycerol hydrogenolysis to 1,2‐propanediol over a spinel CuCr2O4catalyst was investigated by using DFT calculations. Theoretical models were developed from the results of experimental characterization. Adsorption configurations and energetics of the reactant, intermediates, final product, and transition states were calculated on Cu(1 1 1) and CuCr2O4(1 0 0). Based on our DFT results, we found that the formation of acetol is preferred to that of 3‐hydroxypropionaldehyde thermodynamically and kinetically on both surfaces. For glycerol hydrogenolysis to 1,2‐propanediol, the CuCr2O4surface is less exothermic but more kinetically favorable than the Cu surface. The low activation barrier during the reaction on the CuCr2O4surface is attributed to the unique surface structure; the cubic spinel structure provides a stable adsorption site on which reactants are allowed to be dehydrated and hydrogenated easily with the characteristic adsorption configuration. The role of the Cu and Cr atoms in a CuCr2O4surface were revealed. The results of reaction tests supported our theoretical calculations.
Mutiphase oscillator using dissipatively coupled transmission lines with regularly spaced tunnel diodes
Authors: Narahara Koichi 
Published: November 2016

SummaryA generation scheme is proposed for multiphase oscillatory signals based on mutual synchronization of the oscillating pulse edges developed in point‐coupled transmission lines periodically loaded with tunnel diodes (TDs). When supplied with an appropriate voltage at the end of a TD line, a pulse edge is shown to exhibit a spatially extended limit‐cycle oscillation on the line. When two TD lines are dissipatively coupled, such edge oscillations are mutually synchronized such that two edges simultaneously pass the connecting cells. Based on this observation, the scheme employs multiple point‐coupled TD lines, wherein the first and last lines are linked at the same position. Its design criterion is obtained by applying the phase reduction method to the transmission equation of a TD line. In addition, several time‐domain calculations demonstrate the validity of the scheme. Copyright © 2016 John Wiley & Sons, Ltd.
Fine‐needle aspiration biopsy of pancreatic neuroendocrine tumors: Correlation between Ki‐67 index in cytological samples and clinical behavior
Authors: Díaz del Arco Cristina , Esteban López‐Jamar J. Miguel , Ortega Medina Luis , Díaz Pérez J. Ángel , Fernández Aceñero Ma Jesús 
Published: November 2016

BackgroundMitotic count in hematoxylin‐eosin stained slides and Ki‐67 index allow stratification of patients for prognosis and therapeutic decision making in pancreatic neuroendocrine tumors (PNETs). However, the utility of Ki‐67 determination in cytological material and its association to PNET prognosis are under discussion.MethodsWe have retrospectively reviewed all cases of EUS‐FNA cytology of pancreatic lesions performed in the Hospital Clínico San Carlos (Madrid) between 2006 and 2016. We have analyzed the potential association between the Ki‐67 estimation in PNET cytological material and patient outcomes.ResultsWe identified 24 PNET cases. Mean age was 56.8 years and most patients were males (54%). PNETs were mainly located in the head and tail of the pancreas and the mean tumor size was 36 mm. Cell block from cytology was available in 12 cases (50%), and there were 19 G1, 2 G2, and 3 G3 tumors. All cases graded as G2 (2 patients) or G3 (three patients) on cytology were stage IV, and the 19 cases graded as G1 ranged from stages IA to IV. All patients with G2 tumors on cytology died due to PNET. Of the three patients with G3 lesions, two died of disease and the other died 2 months after diagnosis from causes other than PNET. 78% of the patients with G1 tumors are stable and currently being followed‐up.ConclusionHigher Ki‐67 index in cytology specimens portends a worse outcome, although some G1 tumors may progress or cause death. Diagn. Cytopathol. 2017;45:29–35. © 2016 Wiley Periodicals, Inc.