bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tuning the Surface Chemistry of Pd by Atomic C and H: A Microscopic Picture
Authors: Aleksandrov Hristiyan A. , Viñes Francesc , Ludwig Wiebke , Schauermann Swetlana , Neyman Konstantin M. 
Published: November 2012

AbstractPalladium is crucial for industry‐related applications such as heterogeneous catalysis, energy production, and hydrogen technologies. In many processes, atomic H and C species are proposed to be present in the surface/near‐surface area of Pd, thus noticeably affecting its chemical activity. This study provides a detail and unified view on the interactions of the H and C species with Pd nanoparticles (NPs), which is indispensable for insight into their catalytic properties. Density functional calculations of the interplay of C and H atoms at various concentrations and sites on suitable Pd NPs have been performed, accompanied by catalysis‐relevant experiments on oxide‐supported bare and C‐modified Pd NPs. It is shown that on a Pd79NP a subsurface C atom destabilizes nearby atoms H at low coverage. Our experiments confirm that H atoms bind more weakly on C‐containing Pd NPs than on C‐free NPs. Various factors related to the presence of both H and C atoms on a Pd79surface, which may influence the penetration of H atoms from the surface into the subsurface area, have been investigated. Carbon atoms facilitate the subsurface penetration of atomic H both thermodynamically and kinetically when the surface is densely covered by H atoms. Moreover, subsurface H atoms are also energetically favored, even in the absence of C atoms, when several facets of the NP are covered by H atoms.
Adsorption‐Induced Restructuring and Early Stages of Carbon‐Nanotube Growth on Ni Nanoparticles
Authors: Wang Yuexia , Barcaro Giovanni , Negreiros Fabio R. , Visart de Bocarmé Thierry , Moors Mathieu , Kruse Norbert , Hou Marc , Fortunelli Alessandro 
Published: November 2012

AbstractCarbon adsorption on various Ni surfaces is investigated as a function of coverage via a combination of first‐principles simulations and field emission microscope experiments. It is found that carbon can be efficiently stored as subsurface carbides, but with different energetics on differently oriented surfaces depending on their compactness and density of adsorption sites. In the resulting morphological reshaping, {113} facets are predicted to grow at the expense of {111} and {100} facets, in excellent agreement with experimental observations. Moreover, at high coverage on the {113} surface the carbon adsorption energy passes through a maximum after which a structural crossover is realized such that carbon atoms tend to ascend to the surface to form one‐dimensional chains (which are the precursors of graphitic nanostructures). This rationalizes the experimental observation of an incubation time between carbon storage and the beginning of catalytic growth, and provides insight into the early stages (nucleation mechanism) of carbon nanotubes on Ni nanoparticles.
Copper(I) and Silver(I) Bis(trifluoromethanesulfonyl)imide and Their Interaction with an Arene, Diverse Olefins, and an NTf2−‐Based Ionic Liquid
Authors: Stricker Marion , Oelkers Benjamin , Rosenau Carl Philipp , Sundermeyer Jörg 
Published: November 2012

AbstractThe chemistry of coinage metal bis(triflyl)imides of technological interest, CuNTf2 and AgNTf2, their synthesis and complexes with excess of comparatively weakly coordinating NTf2− as well as with ether, olefins, and the arene mesitylene are described. The existence of the solvent‐free pure phase [CuNTf2]∞ has not been evidenced so far. Contrary to the literature, in which the preparation of [CuNTf2]∞ is supposed to be carried out by reacting mesityl copper, [Cu(Mes)]5, and HNTf2, we found that in fact this reaction leads reproducibly to the interesting copper diarene sandwich complex [Cu(η3‐MesH)2][Cu(NTf2)2] (1) (MesH=1,3,5‐trimethylbenzene). The unexpectedly stable molecular etherate [Cu(Et2O)(NTf2)] (2) turned out to be the best precursor for CuNTf2 having only an inert and easily exchangeable solvent ligand. The coordination mode of NTf2− in 1 and 2 as well as in the hitherto unknown crystalline phase of [AgNTf2]∞ (3) is described. The complex formation, which takes place when dissolving 2 or 3 in the room temperature ionic liquid (RTIL) [emim]NTf2 ([emim]+=1‐ethyl‐3‐methylimidazolium), has been studied. Furthermore, the reaction of 1–3 towards the diolefins 1,5‐cyclooctadiene (COD), 2,5‐norbornadiene (NBD) and isoprene (2‐methylbuta‐1,3‐diene) and towards ethylene has been investigated. The products 4–13 of these conversions have been isolated and fully characterized by NMR‐ and IR spectroscopies, mass spectrometry, and elemental‐ and XRD analyses. The potential of [Cu(η3‐MesH)2][Cu(NTf2)2] (1), [Cu(Et2O)(NTf2)] (2) and [AgNTf2]∞ (3) as well as of [emim][M(NTf2)2] (M=Cu 4, Ag 5) as chemisorbers for ethylene was studied by NMR spectroscopy.
Synthesis and Two‐Photon Absorption Property Characterizations of Small Dendritic Chromophores Containing Functionalized Quinoxaliniod Heterocycles
Authors: Lin Tzu‐Chau , Lee Ying‐Hsuan , Liu Che‐Yu , Huang Bor‐Rong , Tsai Ming‐Yu , Huang Yu‐Jhen , Lin Ja‐Hon , Shen Yu‐Kai , Wu Cheng‐Yu 
Published: November 2012

AbstractA series of star‐shaped multi‐polar chromophores (compounds 1–3) containing functionalized quinoxaline and quinoxalinoid (indenoquinoxaline and pyridopyrazine) units has been synthesized and characterized for their two‐photon absorption (2PA) properties both in the femtosecond and the nanosecond time domain. Under our experimental conditions, these model fluorophores are found to manifest strong and wide‐dispersed two‐photon absorption in the near‐infrared region. It is demonstrated that molecular structures with multi‐branched π frameworks incorporating properly functionalized quinoxalinoid units would possess large molecular nonlinear absorptivities within the studied spectral range. Effective optical‐power attenuation and stabilization behaviors in the nanosecond time domain of a selected representative dye molecule (i.e., compound 2) from this model compound set were also investigated and the results indicate that such structural motif could be a useful approach for the molecular design toward strong two‐photon‐absorbing material systems for quick‐responsive and broadband optical‐suppressing‐related applications, particularly to confront long laser pulses.
Simple Bipolar Hosts with High Glass Transition Temperatures Based on 1,8‐Disubstituted Carbazole for Efficient Blue and Green Electrophosphorescent Devices with “Ideal” Turn‐on Voltage
Authors: Huang Hong , Wang Yixin , Pan Biao , Yang Xiao , Wang Lei , Chen Jiangshan , Ma Dongge , Yang Chuluo 
Published: November 2012

AbstractTwo hybrids based on 1,8‐disubstituted carbazole, 1,8‐OXDCz and 1,8‐mBICz, have been designed and synthesized through a facile process. The incorporation of oxadiazole or N‐phenylbenzimidazole moieties at the 1,8‐positions of carbazole greatly improves its morphological stability, giving glass transition temperatures (Tg) as high as 138 and 154 °C, respectively. Blue phosphorescent organic light‐emitting devices (PhOLEDs) with 1,8‐mBICz exhibit almost the same performance as a similarly structured device based on the mCP host, and green PhOLEDs employing the new host material 1,8‐OXDCz exhibit an ideal turn‐on voltage (2.5 V at 1.58 cd m−2), a maximum current efficiency (ηc,max) of 73.9 cd A−1, and a power efficiency (ηp,max) of 89.7 lm W−1. These results are among the best performances of [Ir(ppy)3]‐based devices with simple device configurations.
Halogen Bonding from a Hard and Soft Acids and Bases Perspective: Investigation by Using Density Functional Theory Reactivity Indices
Authors: Pinter Balazs , Nagels Nick , Herrebout Wouter A. , De Proft Frank 
Published: November 2012

AbstractHalogen bonds between the trifluoromethyl halides CF3Cl, CF3Br and CF3I, and dimethyl ether, dimethyl sulfide, trimethylamine and trimethyl phosphine were investigated using Pearson’s hard and soft acids and bases (HSAB) concept with conceptual DFT reactivity indices, the Ziegler–Rauk‐type energy‐decomposition analysis, the natural orbital for chemical valence (NOCV) framework and the non‐covalent interaction (NCI) index. It is found that the relative importance of electrostatic and orbital (charge transfer) interactions varies as a function of both the donor and acceptor molecules. Hard and soft interactions were distinguished and characterised by atomic charges, electrophilicity and local softness indices. Dual‐descriptor plots indicate an orbital σ hole on the halogen similar to the electrostatic σ hole manifested in the molecular electrostatic potential. The predicted high halogen‐bond‐acceptor affinity of N‐heterocyclic carbenes was evidenced in the highest complexation energy for the hitherto unknown CF3I⋅NHC complex. The dominant NOCV orbital represents an electron‐density deformation according to a n→σ*‐type interaction. The characteristic signal found in the reduced density gradient versus electron‐density diagram corresponds to the non‐covalent interaction between contact atoms in the NCI plots, which is the manifestation of halogen bonding within the NCI theory. The unexpected CX bond strengthening observed in several cases was rationalised within the molecular orbital framework.
Charge‐Neutral Amidinate‐Containing Iridium Complexes Capable of Efficient Photocatalytic Water Reduction
Authors: Yu Zhen‐Tao , Yuan Yong‐Jun , Cai Jian‐Guang , Zou Zhi‐Gang 
Published: November 2012

AbstractTwo new charge‐neutral iridium complexes, [Ir(tfm‐ppy)2(N,N′‐diisopropyl‐benzamidinate)] (1) and [Ir(tfm‐ppy)2(N,N′‐diisopropyl‐4‐diethylamino‐3,5‐dimethyl‐benzamidinate)] (2) (tfm‐ppy=4‐trifluoromethyl‐2‐phenylpyridine) containing an amidinate ligand and two phenylpyridine ligands were designed and characterised. The photophysical properties, electrochemical behaviours and emission quenching properties of these species were investigated. In concert with the cobalt catalyst [Co(bpy)3]2+, members of this new class of iridium complexes enable the photocatalytic generation of hydrogen from mixed aqueous solutions via an oxidative quenching pathway and display long‐term photostability under constant illumination over 72 h; one of these species achieved a relatively high turnover number of 1880 during this time period. In the case of complex 1, the three‐component homogeneous photocatalytic system proved to be more efficient than a related system containing a charged complex, [Ir(tfm‐ppy)2(dtb‐bpy)]+ (3, dtb‐bpy=4,4′‐di‐tert‐butyl‐2,2′‐dipyridyl). In combination with a rhodium complex as a water reduction catalyst, the performances of the systems using both complexes were also evaluated, and these systems exhibited a more efficient catalytic propensity for water splitting than did the cobalt‐based systems that have been studied previously.
Selective Dimerization of Lewis‐Acid/Base‐Stabilized Phosphanylalanes
Authors: Bodensteiner Michael , Timoshkin Alexey Y. , Peresypkina Eugenia V. , Vogel Ulf , Scheer Manfred 
Published: November 2012

AbstractThe reaction of [{(CO)5W}PRH2] (R=H, Ph) with H3Al⋅NR3 (R=Et, Me) leads to the formation of four‐membered heterocyclic compounds [({(CO)5W}P(H)AlH⋅ NEt3)2] and [({(CO)5W}PhPAlH⋅ NMe3)2]. Upon dissolving the solid compounds, fast equilibria between the isomers are observed on the NMR timescale. Further insight into the stability and reactivity of the isomers was gained by applying theoretical methods. DFT calculations predict that hydrogen elimination in the case of [({(CO)5W}PhPAlH⋅NMe3)2] may be reversible.
7,7,8,8‐Tetraaryl‐o‐quinodimethane Stabilized by Dibenzo Annulation: A Helical π‐Electron System That Exhibits Electrochromic and Unique Chiroptical Properties
Authors: Suzuki Takanori , Sakano Yuto , Iwai Tomohiro , Iwashita Shinichi , Miura Youhei , Katoono Ryo , Kawai Hidetoshi , Fujiwara Kenshu , Tsuji Yasushi , Fukushima Takanori 
Published: November 2012

AbstractWhen two benzene rings are fused to a tetraaryl‐o‐quinodimethane skeleton, sterically hindered helical molecules 1 acquire a high thermodynamic stability. Because the tetraarylbutadiene subunit contains electron‐donating alkoxy groups, 1 undergo reversible two‐electron oxidation to 22+, which can be isolated as deeply colored stable salts. Intramolecular transfer of the point chirality (e.g., sec‐butyl) on the aryl groups to helicity induces a diastereomeric preference in dications 2 b2+ and 2 c2+, which represents an efficient method for enhancing circular‐dichroism signals. Thus, those redox pairs can serve as new electrochiroptical response systems. X‐ray analysis of dication 22+ revealed π–π stacking interaction of the diarylmethylium moieties, which is also present in solution. The stacking geometry is the key contributor to the chirosolvatochromic response.
Direct Conjugate Addition of Alkynes with α,β‐Unsaturated Carbonyl Compounds Catalyzed by NCN‐Pincer Ru Complexes
Authors: Ito Jun‐ichi , Fujii Kohei , Nishiyama Hisao 
Published: November 2012

AbstractNCN‐pincer Ru‐complexes containing bis(oxazolinyl)phenyl ligands serve as suitable catalysts in the direct conjugate additions of α,β‐unsaturated carbonyl compounds, including ketones, esters, and amides, as well as vinylphosphonates, giving various β‐alkynyl carbonyl and phosphonate compounds. A bis(oxazolinyl)phenyl (phebox)–Ru complex also catalyzes the asymmetric conjugate addition of an alkyne with a β‐substituted, α,β‐unsaturated ketone to produce a chiral β‐alkynyl ketone.
Periadolescent maturation of the prefrontal cortex is sex‐specific and is disrupted by prenatal stress
Authors: Markham Julie A. , Mullins Sylvina E. , Koenig James I. 
Published: November 2012

AbstractThe prefrontal cortex (PFC) undergoes dramatic, sex‐specific maturation during adolescence. Adolescence is a vulnerable window for developing mental illnesses that show significant sexual dimorphisms. Gestational stress is associated with increased risk for both schizophrenia, which is more common among men, and cognitive deficits. We have shown that male, but not female, rats exposed to prenatal stress develop postpubertal deficits in cognitive behaviors supported by the prefrontal cortex. Here we tested the hypothesis that repeated variable prenatal stress during the third week of rat gestation disrupts periadolescent development of prefrontal neurons in a sex‐specific fashion. Using Golgi‐Cox stained tissue, we compared dendritic arborization and spine density of prelimbic layer III neurons in prenatally stressed and control animals at juvenile (day 20), prepubertal (day 30), postpubertal (day 56), and adult (day 90) ages (N = 115). Dendritic ramification followed a sex‐specific pattern that was disrupted during adolescence in prenatally stressed males, but not in females. In contrast, the impact of prenatal stress on the female PFC was not evident until adulthood. Prenatal stress also caused reductions in brain and body weights, and the latter effect was more pronounced among males. Additionally, there was a trend toward reduced testosterone levels for adult prenatally stressed males. Our findings indicate that, similarly to humans, the rat PFC undergoes sex‐specific development during adolescence and furthermore that this process is disrupted by prenatal stress. These findings may be relevant to both the development of normal sex differences in cognition as well as differential male–female vulnerability to psychiatric conditions. J. Comp. J. Comp. Neurol. 521:1828–1843, 2013. © 2012 Wiley Periodicals, Inc.
De novo expression of neurokinin‐1 receptors by spinoparabrachial lamina I pyramidal neurons following a peripheral nerve lesion
Authors: Saeed Abeer W. , Ribeiro‐da‐Silva Alfredo 
Published: November 2012

AbstractLamina I of the spinal dorsal horn is a major site of integration and transmission to higher centers of nociceptive information from the periphery. One important primary afferent population that transmits such information to the spinal cord expresses substance P (SP). These fibers terminate in contact with lamina I projection neurons that express the SP receptor, also known as the neurokinin‐1 receptor (NK‐1r). Three types of lamina I projection neurons have been described: multipolar, fusiform, and pyramidal. Most neurons of the first two types are thought to be nociceptive and express the NK‐1r, whereas most pyramidal neurons are nonnociceptive and do not express the NK‐1r. In this immunocytochemical and behavioral study, we induced a neuropathic pain‐like condition in the rat by means of a polyethylene cuff placed around in the sciatic nerve. We document that this lesion led to a de novo expression of NK‐1r on pyramidal neurons as well as a significant increase in SP‐immunoreactive innervation onto these neurons. These phenotypic changes were evident at the time of onset of neuropathic pain‐related behavior. Additionally, we show that, after a noxious stimulus (intradermal capsaicin injection), these NK‐1r on pyramidal neurons were internalized, providing evidence that these neurons become responsive to peripheral noxious stimulation. We suggest that the changes following nerve lesion in the phenotype and innervation pattern of pyramidal neurons are of significance for neuropathic pain and/or limb temperature regulation. J. Comp. Neurol. 521:1915–1928, 2013. © 2012 Wiley Periodicals, Inc.
Halogen‐Bonding Interactions with π Systems: CCSD(T), MP2, and DFT Calculations
Authors: Forni Alessandra , Pieraccini Stefano , Rendine Stefano , Gabas Fabio , Sironi Maurizio 
Published: November 2012

AbstractHalogen bonding is a noncovalent interaction between a halogen atom and a nucleophilic site. Interactions involving the π electrons of aromatic rings have received, up to now, little attention, despite the large number of systems in which they are present. We report binding energies of the interaction between either NCX or PhX (X=F, Cl, Br, I) and the aromatic benzene system as determined with the coupled cluster with perturbative triple excitations method [CCSD(T)] extrapolated at the complete basis set limit. Results are compared with those obtained by Møller–Plesset perturbation theory to second order (MP2) and density functional theory (DFT) calculations by using some of the most common functionals. Results show the important role of DFT in studying this interaction.
Synthesis, growth, morphology of the semiorganic nonlinear optical crystal L‐glutamic acid hydrochloride and its structural, thermal and SHG characterizations
Authors: Dhanasekaran P. , Srinivasan K. 
Published: November 2012

AbstractOne of the halide derivatives of L‐glutamic acid which was identified as a semiorganic nonlinear optical material, L‐glutamic acid hydrochloride [HOOC(CH2)2CH(NH2)COOH.HCl], was grown as bulk single crystal and its significant properties were characterized. The stoichiometric title compound was synthesized and the solubility of its recrystallized form in DD water was determined in the temperature range 30–80 °C by gravimetric method. Structural confirmation was carried out by powder X‐ray diffraction study through lattice parameter verification. Optical quality smaller dimension single crystals were grown from aqueous solution by self nucleation through slow evaporation of solvent method and a large dimension single crystal was grown by slow cooling method with reversible seed rotation technique. Morphological importances of different growth facets of the as grown crystals were studied through optical goniometry. Unit cell structure of the grown crystal was refined by single crystal X‐ray diffraction analysis, functional groups present in the crystal responsible for various modes of vibrations were confirmed by FTIR spectroscopy analysis, thermal stability of the grown crytal was analysed by TG/DTA and DSC and second harmonic generation (SHG) of a fundamental Nd:YAG laser beam by Kurtz technique. Results indicate that the grown crystal is in stoichiometric composition and has significant improvement in its thermal and SHG properties when compared to pure L‐glutamic acid polymorphs.
Scalable and efficient key management for Mobile WiMAX networks
Authors: Gilanian Sadeghi Mohammad Mehdi , Mohd Ali Borhanuddin , Ma Maode , Ab Manan Jamalul‐lail 
Published: November 2012

SUMMARYEfficiency and security are two critical but often conflicting issues in Multicast and Broadcast Service of IEEE 802.16e technology. Hence, it is vital to ensure an optimal scenario where neither security concerns, nor operational efficiency of the network is compromised. This paper proposes a new key management scheme called Scalable and Efficient Key Management Protocol, which uses a binary tree structure together with a B‐tree of order 2 structure. It focuses on improving key management performance of the existing techniques in terms of efficiency and scalability, without a loss in security. Scalable and Efficient Key Management Protocol dynamically establishes subgroups based on the current number of Mobile Stations in a WiMAX Base Station's coverage area. This will optimize the communications, computational and storage costs of the network. In addition, the scheme guarantees strong network scalability. Both analytical and simulation approaches have been carried out, and the results showed that the proposed scheme exhibits superior performance in terms of efficiency and scalability compared with existing schemes. Copyright © 2012 John Wiley & Sons, Ltd.
Modeling and analysis of access transparency and scalability in P2P distributed systems
Authors: Mousavi Khaneghah E. , Mirtaheri S. L. , Sharifi M. , Minaei Bidgoli B. 
Published: November 2012

SUMMARYPeer‐to‐peer (P2P) systems have been developed with the goal of providing support for transparent and efficient sharing of scalable distributed resources wherein size scalability is limited by the costs of all types of transparencies, especially data access transparency, which are due to the need for frequent data exchanges between peers and other related communication overheads. We present a model that formulates the relationship between scalability and data access transparency in P2P distributed systems to figure out how large these systems can be scaled up, given the overheads of establishing data access transparency. To validate our model and show how our model can be deployed in real life, we consider a real P2P distributed system as a case study and evaluate how CPU utilization, bandwidth, and data request frequency parameters of our model relate to the amount of effort required by the system management to establish data access transparency. We then calculate the strength of the coefficient of correlation of scalability and data access transparency in the system. The degree of strength of this coefficient allows the system designer to decide at design time whether to allow the use of the model in the management of system at runtime or not. Copyright © 2012 John Wiley & Sons, Ltd.