bluuebunny/crossref_metadata_2025_split huggingface dataset:
Predicting the Relative Stability of Simple versus ansa‐Sandwich Systems Across Groups: Structure, Bonding, and (In)Stability in Tris(sandwich)benzene Complexes
Authors: Donald Kelling J. , Bober Matthew 
Published: January 2011

AbstractWe examine theoretically the bonding and thermodynamic stability of a proposed class of tris(sandwich)benzene complexes with the general formula C6(RMR′)3. In these systems, a single central (benzene) ring is flanked by three distorted 18‐electron sandwich fragments with M = Groups 6, 7, or 8 metals, and R and R′ = Ph or cyclopentadienyl (Cp) substituents. Remarkably, the computed free energy changes for the binding of the metal atoms to the organic fragments in 1) the ansa‐(C6(RMR′)3) complexes and 2) the simple (RMR′) sandwich complexes—for all the Groups 6, 7, and 8 metals—conform to the linear relationship: [ΔGbind(C6(RMR′)3)]/3 = ${\beta {{\Delta G\hfill \atop 1\hfill}}}$[ΔGbind(RMR′)]+${\beta {{\Delta G\hfill \atop 2\hfill}}}$ (R=0.989). The bonding and relative stabilities of these unusual tris(sandwich) and simple sandwich complexes are assessed at the B3PW91 level of theory employing small‐core relativistic MDF pseudopotentials and the corresponding basis sets for all the metals. The possible existence of strain‐induced bond localization (the so‐called Mills–Nixon effect) in the C6(RMR′)3 complexes and the aromaticity at the central benzene ring in C6(RMR′)3 are investigated. Despite the strain on the central ring, no bond fixation is observed. The tris(sandwich) complexes of Groups 6, 7, and 8 are all thermodynamically stable, relative to the free M atoms and organic fragments, with increasing stability as M gets heavier (going down the groups). The equation above also enables us to predict, by extrapolation, the (in)stabilities of the C6(RMR′)3 complexes of several other transition metals and helps us to better understand thermodynamic aspects of the ansa effect. Similar functions likely apply for other ansa variants of sandwich complexes.
Critical In Vitro Evaluation of Responsive MRI Contrast Agents for Calcium and Zinc
Authors: Mishra Anurag , Logothetis Nikos K. , Parker David 
Published: January 2011

AbstractThe synthesis of two gadolinium(III) complexes that exhibit an increase in proton relaxivity in the presence of added Ca2+ or Zn2+ ions is reported. The complexes increase their hydration state from zero to one following metal‐ion binding, confirmed by spectral measurements on the corresponding EuIII complexes. At a field of 1.4 T and 310 K, modulation of relaxivity of the order of 30–40 % was observed in mouse serum in each case. The dissociation constants for Ca2+ and Zn2+ binding were sensitive to the presence of added bicarbonate, and were 450 μM (Ca2+) and 200 μM (Zn2+) in serum. Such systems may, therefore, be considered for use as magnetic resonance imaging (MRI) contrast agents to track the restoration of changes in metal‐ion concentration in the cerebrospinal fluid of the brain, following neural stimulation.
Aurophilicity: The Effect of the Neutral Ligand L on [{ClAuL}2] Systems
Authors: Muñiz Jesús , Wang Cong , Pyykkö Pekka 
Published: January 2011

AbstractThe effect of the ligand L on the aurophilic AuI⋅⋅⋅AuI closed‐shell interaction in perpendicular [{ClAuL}2] model systems is investigated. An analogous study of the effect of the halide X (here Cl) exists, and showed a correlation with the softness of the ligand X. In this work, we study the correlation with L=N‐heterocyclic carbenes (NHC), cyclic diphosphinocarbenes (PHC), NF3, CO, methyl isocyanide CNMe, PF3, SH2, NH3, H2O, pyridine, triazene, the carbodiphosphorene model C(PH3)2, C3H2, and the related model systems CN2 or CP2. The NHCs yield stronger interactions than PH3. The spatial orientation of certain ligands in a “paddle” configuration plays an important role on the strength of the interaction. All are examples on aurophilicity.
Efficient Charge Separation in TiO2 Films Sensitized with Ruthenium(II)–Polypyridyl Complexes: Hole Stabilization by Ligand‐Localized Charge‐Transfer States
Authors: Verma Sandeep , Kar Prasenjit , Das Amitava , Ghosh Hirendra N. 
Published: January 2011

AbstractWe have studied the interfacial electron‐transfer dynamics on TiO2 film sensitized with synthesized ruthenium(II)–polypyridyl complexes—[RuII(bpy)2(L1)] (1) and [RuII(bpy)(L1)(L2)] (2), in which bpy=2,2′‐bipyridyl, L1=4‐[2‐(4′‐methyl‐2,2′‐bipyridinyl‐4‐yl)vinyl]benzene‐1,2‐diol, and L2=4‐(N,N‐dimethylaminophenyl)‐2,2′‐bipyridine—by using femtosecond transient absorption spectroscopy. The presence of electron‐donor L2 and electron‐acceptor L1 ligands in complex 2 introduces lower energetic ligand‐to‐ligand charge‐transfer (LLCT) excited states in addition to metal‐to‐ligand (ML) CT manifolds of complex 2. On photoexcitation, a pulse‐width‐limited (<100 fs) electron injection from populating LLCT and MLCT states are observed on account of strong catecholate binding on the TiO2 surface. The hole is transferred directly or stepwise to the electron‐donor ligand (L2) as a consequence of electron injection from LLCT and MLCT states, respectively. This results an increased spatial charge separation between the hole residing at the electron‐donor (L2) ligand and the electron injected in TiO2 nanoparticles (NPs). Thus, we observed a significant slow back‐electron‐transfer (BET) process in the 2/TiO2 system relative to the 1/TiO2 system. Our results suggest that RuII–polypyridyl complexes comprising LLCT states can be a better photosensitizer for improved electron injection yield and slow BET processes in comparison with RuII–polypyridyl complexes comprising MLCT states only.
Identification of Ligands for the Tau Exon 10 Splicing Regulatory Element RNA by Using Dynamic Combinatorial Chemistry
Authors: López‐Senín Paula , Gómez‐Pinto Irene , Grandas Anna , Marchán Vicente 
Published: January 2011

AbstractWe describe the use of dynamic combinatorial chemistry (DCC) to identify ligands for the stem‐loop structure located at the exon 10‐5′‐intron junction of Tau pre‐mRNA, which is involved in the onset of several tauopathies including frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP‐17). A series of ligands that combine the small aminoglycoside neamine and heteroaromatic moieties (azaquinolone and two acridines) have been identified by using DCC. These compounds effectively bind the stem‐loop RNA target (the concentration required for 50 % RNA response (EC50): 2–58 μM), as determined by fluorescence titration experiments. Importantly, most of them are able to stabilize both the wild‐type and the +3 and +14 mutated sequences associated with the development of FTDP‐17 without producing a significant change in the overall structure of the RNA (as analyzed by circular dichroism (CD) spectroscopy), which is a key factor for recognition by the splicing regulatory machinery. A good correlation has been found between the affinity of the ligands for the target and their ability to stabilize the RNA secondary structure.
Dendritic Oligothiophenes Terminated with Tris(alkyloxy)phenylethynyl Tails: Synthesis, Physical Properties, and Self‐Assembly
Authors: Ma Chang‐Qi , Pisula Wojciech , Weber Cornelia , Feng Xin‐Liang , Müllen Klaus , Bäuerle Peter 
Published: January 2011

AbstractThree‐dimensional (3D) π‐conjugated dendritic oligothiophenes up to a third generation have been functionalized with tris(decyloxy)phenylethynyl tails at the periphery. The first‐generation compounds (3 T‐p‐Ph‐C10 and 6 T‐p‐Ph‐C10) were synthesized by palladium‐catalyzed Sonogashira coupling reactions, whereas the higher generation products were synthesized by palladium‐catalyzed Suzuki coupling reactions in a divergent approach. The optical and electrochemical properties were investigated by UV/Vis absorption, fluorescence spectroscopy, and cyclic voltammetry. The results revealed that the terminal tris(alkyloxy)phenylethynyl groups are conjugated to the branched oligothiophene core, yielding redshifted absorption and fluorescence spectra and reduced optical band gaps relative to the dendritic oligothiophene core. A structural study revealed a close relationship between the type of supramolecular organization and the size of the oligothiophene core. The first‐generation compounds 3 T‐p‐Ph‐C10 and 6 T‐p‐Ph‐C10 displayed columnar phases in the bulk state, which was confirmed by two‐dimensional wide‐angle X‐ray scattering (2D WAXS) measurements. The self‐assembly into columnar stacks has mainly been attributed to phase separation between the rigid thiophene cores and the flexible side‐chains assisted by minor π‐stacking interactions between the conjugated dendritic oligothiophene units. The high‐generation compounds, however, showed less ordered structures in the solid state.
Density Functional Calculations on the Distribution, Acidity, and Catalysis of TiIV and TiIII Ions in MCM‐22 Zeolite
Authors: Yang Gang , Zhou Lijun , Liu Xianchun , Han Xiuwen , Bao Xinhe 
Published: January 2011

AbstractIsolated Ti species in zeolites show unique catalytic activities for a variety of chemical reactions. In this work, density functional calculations were used to explore three current concerns: 1) the distributions of TiIV and TiIII ions in the MCM‐22 zeolite; 2) the Lewis acidity of the TiIV and TiIII sites; and 3) activation of alkane CH bonds by photocatalysis with Ti‐doped zeolites. Neither the TiIV nor TiIII ions are randomly distributed in the MCM‐22 zeolite. The orders of relative stability are very close for the eight TiIV and TiIII sites, and the T3 site is the most probable in both cases. The wavelengths for TiIV–TiIII excitations were calculated to lie in the range λ=246.9–290.2 nm. The Ti3IV site shows Lewis acidity toward NH3 in two different modes, and these two modes can coexist with each other. The calculated TiIV coordination numbers, TiIVO bond elongations, and charge transfers caused by NH3 adsorption are in good agreement with previous results. Similarly, two different NH3 adsorption modes exist for the Ti3III site; the site that exhibits radical transfer from the lattice O to N atoms is preferred due to the higher adsorption energy. This indicates that the Ti3III site does not show Lewis acidity, in contrast to the Ti3IV site. At the Ti3III site, the energy barrier for activating the methane CH bond was calculated to be 33.3 kJ mol−1 and is greatly reduced by replacing the hydrogen atoms with methyl groups. In addition, the reactivity is improved when switching from MCM‐22 to TS‐1 zeolite. The studies on the various Ti species reveal that lattice O atoms rather than TiIII radicals are crucial to the activation of alkane CH bonds. This work provides new insights into and aids understanding of the catalysis by isolated Ti species in zeolites.
Heuristic Chemistry—Addition Reactions
Authors: Graulich Nicole , Hopf Henning , Schreiner Peter R. 
Published: January 2011

AbstractOrganic chemistry is often considered a difficult subject requiring great effort to achieve expert status. Only once this level has been reached, judging, deciding, and recalling chemical information will be fast and guided by heuristic strategies. These principles, used intuitively, improve the efficiency and speed of problem‐solving and decision‐making procedures. Establishing these strategies in teaching and learning chemistry should significantly help students acquire well‐structured procedural knowledge early in their education. In an attempt to improve conceptual thinking in teaching organic chemistry, in this contribution we develop a heuristic view of addition reactions and propose a new way of perceiving this class of organic reactions.
Development of Fluorescent Glucose Bioprobes and Their Application on Real‐Time and Quantitative Monitoring of Glucose Uptake in Living Cells
Authors: Lee Hyang Yeon , Lee Jae Jeong , Park Jongmin , Park Seung Bum 
Published: January 2011

AbstractWe developed a novel fluorescent glucose bioprobe, GB2‐Cy3, for the real‐time and quantitative monitoring of glucose uptake in living cells. We synthesized a series of fluorescent glucose analogues by adding Cy3 fluorophores to the α‐anomeric position of D‐glucose through various linkers. Systematic and quantitative analysis of these Cy3‐labeled glucose analogues revealed that GB2‐Cy3 was the ideal fluorescent glucose bioprobe. The cellular uptake of this probe competed with the cellular uptake of D‐glucose in the media and was mediated by a glucose‐specific transport system, and not by passive diffusion. Flow cytometry and fluorescence microscopy analyses revealed that GB2‐Cy3 is ten times more sensitive than 2‐NBDG, a leading fluorescent glucose bioprobe. GB2‐Cy3 can also be utilized for the quantitative flow cytometry monitoring of glucose uptake in metabolically active C2C12 myocytes under various treatment conditions. As opposed to a glucose uptake assay performed by using radioisotope‐labeled deoxy‐D‐glucose and a scintillation counter, GB2‐Cy3 allows the real‐time monitoring of glucose uptake in living cells under various experimental conditions by using fluorescence microscopy or confocal laser scanning microscopy (CLSM). Therefore, we believe that GB2‐Cy3 can be utilized in high‐content screening (HCS) for the discovery of novel therapeutic agents and for making significant advances in biomedical studies and diagnosis of various diseases, especially metabolic diseases.
Desilication Mechanism Revisited: Highly Mesoporous All‐Silica Zeolites Enabled Through Pore‐Directing Agents
Authors: Verboekend Danny , Pérez‐Ramírez Javier 
Published: January 2011

AbstractThe role of pore‐directing agents (PDAs) in the introduction of hierarchical porosity in silicalite‐1 in alkaline medium was investigated. By incorporation of various PDAs in aqueous NaOH, homogenously distributed mesopores were introduced in 2.5 μm silicalite‐1 crystals. It was proven for the first time that framework aluminum is not a prerequisite for the introduction of intracrystalline mesoporosity by desilication. The pore‐directing role is not directly exerted by framework trivalent cations metals, but by species on the external surface of the zeolite. The inclusion of metal complexes (Al(OH)4−, Ga(OH)4−) and tetraalkyl ammonium cations (tetramethyl ammonium (TMA+), tetrapropyl ammonium (TPA+)) in the alkaline solution led to distinct mesopore surface areas (up to 286 m2 g−1) and pore sizes centered in the range of 5–20 nm. In the case alkaline treatment was performed in the presence of Al(OH)4−, all aluminum partially integrated in the zeolite giving rise to both Lewis and Brønsted acidity. Apart from the concentration and location, the affinity of the PDA to the zeolite surface plays a crucial role in the pore formation process. If the PDA is attracted too strongly (e.g., TMA+), the dissolution is reduced dramatically. When the pore‐directing agent is not attracted to the zeolite’s external surface, excessive dissolution occurs (standard alkaline treatment). TPA+ proved to be the most effective PDA as its presence led to high mesopore surface areas (>200 m2 g−1) over a broad range of PDA concentrations (0.003–0.1 M). Importantly, our results enable to extend the suitability of desilication for controlled mesopore formation to all‐silica zeolites.
Enzyme‐Inspired Controlled Release of Cucurbit[7]uril Nanovalves by Using Magnetic Mesoporous Silica
Authors: Liu Jinshui , Du Xuezhong , Zhang Xianfeng 
Published: January 2011

AbstractThe controlled release of drugs by biostimuli is highly desirable under physiological conditions for their potential use in advanced applications. The enzyme‐inspired controlled release of cucurbituril nanovalves by using magnetic mesoporous silica nanoparticles (MSNs) in near‐neutral aqueous solutions is reported for the first time. The encirclement of cucurbit[7]uril (CB[7]) onto the protonated 1,4‐butanediamine stalks tethered to the external surfaces of superparamagnetic Fe3O4‐embedded mesoporous silica particles leads to tight blocking of the nanopores. The supramolecular nanovalves are activated by the enzymatic decarboxylation products of lysine, cadaverine (in the protonated form), which has a high affinity for CB[7], so that the encapsulated guest molecules, calcein, in the nanopores are released into the bulk solution. The release of calcein can be controlled in small portions on command by alternating changes in enzymatic decarboxylation products and CB[7]. The amino acid derived polyamines have long been associated with cell growth and cancers. The guest molecules released from the delivery system of magnetic MSNs can act not only on sensing probes for levels of decarboxylases and polyamines, but also on efficacious drugs to specific tissues and cells for regulation of polyamine synthesis.
Nickel‐Catalyzed, Cascade Cycloadditions of 1‐Ethynyl‐8‐halonaphthalenes with Nitriles: Synthesis, Structure, and Physical Properties of New Pyrroloarenes
Authors: Wu Tsun‐Cheng , Tai Chia‐Cheng , Tiao Hsin‐Chieh , Kuo Ming‐Yu , Wu Yao‐Ting 
Published: January 2011

AbstractThe reaction of 1‐ethynyl‐8‐halonaphthalenes 1 with nitriles in the presence of the catalytic system [NiBr2(dppe)]/Zn (dppe=1,2‐bis(diphenylphosphino)ethane) is found to produce unusual pyrroloarenes 2. The carbon–nitrogen triple bond in nitrile is activated twice, and five new bonds are formed in a one‐pot transformation, which causes a pyrrole and two six‐membered rings to be generated simultaneously. The scope and limitations of this reaction are examined. Similarly, alkyl‐bridged diynes also furnish the corresponding polycycles. Diaryl‐substituted cycloadducts 2 (R1=Ar) are fluxional, because of the restriction in rotation of the aryl groups. The rotational barrier is studied by performing 1H NMR experiments at various temperatures. The structures of several compounds are determined by X‐ray crystallographic analysis. The photophysical and electrochemical properties of the pyrroloarenes are also investigated.
Epibranchial placode‐derived neurons produce BDNF required for early sensory neuron development
Authors: Harlow Danielle E. , Yang Hui , Williams Trevor , Barlow Linda A. 
Published: January 2011

AbstractIn mice, BDNF provided by the developing taste epithelium is required for gustatory neuron survival following target innervation. However, we find that expression of BDNF, as detected by BDNF‐driven β‐galactosidase, begins in the cranial ganglia before its expression in the central (hindbrain) or peripheral (taste papillae) targets of these sensory neurons, and before gustatory ganglion cells innervate either target. To test early BDNF function, we examined the ganglia of bdnf null mice before target innervation, and found that while initial neuron survival is unaltered, early neuron development is disrupted. In addition, fate mapping analysis in mice demonstrates that murine cranial ganglia arise from two embryonic populations, i.e., epibranchial placodes and neural crest, as has been described for these ganglia in non‐mammalian vertebrates. Only placodal neurons produce BDNF, however, which indicates that prior to innervation, early ganglionic BDNF produced by placode‐derived cells promotes gustatory neuron development. Developmental Dynamics 240:309–323, 2011. © 2011 Wiley‐Liss, Inc.
Synthesis of a [3Fe2S] Cluster with Low Redox Potential from [2Fe2S] Hydrogenase Models: Electrochemical and Photochemical Generation of Hydrogen
Authors: Gao Weiming , Sun Junliang , Li Mingrun , Åkermark Torbjörn , Romare Kristina , Sun Licheng , Åkermark Björn 
Published: January 2011

AbstractIn the attempted replacement of carbon monoxide by thebis(phosphane) dppv in a dinuclear [2Fe2S] complex, a trinuclear [3Fe2S] complex with two bis(phosphane) ligands was unexpectedly obtained. On protonation, this gave a bridged hydride complex with an unusually low potential for the reduction of protons to molecular hydrogen. The redox potential also appears sufficiently positive for direct electron transfer from an excited [Ru(bpy)3]2+ sensitizer.
Growth and biomass production with enhanced β‐glucan and dietary fibre contents of Ganoderma australe ATHUM 4345 in a batch‐stirred tank bioreactor
Authors: Papaspyridi Lefki‐Maria , Katapodis Petros , Gonou‐Zagou Zacharoula , Kapsanaki‐Gotsi Evangelia , Christakopoulos Paul 
Published: January 2011

AbstractIn this study we maximized biomass production by the basidiomycete Ganoderma australe ATHUM 4345, a species of pharmaceutical interest as it is a valuable source of nutraceuticals, including dietary fibers and glucans. We used the Biolog FF MicroPlate to screen 95 different carbon sources for growth monitoring. The pattern of substrate catabolism forms a substrate assimilation fingerprint, which is useful in selecting components for media optimization of maximum biomass production. Response surface methodology, based on the central composite design was applied to explore the optimum concentrations of carbon and nitrogen sources of culture medium in shake flask cultures. When the improved culture medium was tested in a 20‐L stirred tank bioreactor, using 13.7 g/L glucose and 30.0 g/L yeast extract, high biomass yields (10.1±0.4 g/L) and productivity of 0.09 g L−1 h−1 were obtained. The yield coefficients for total glucan and dietary fibers on biomass formed were 94.82±6 and 341.15±12.3 mg/g mycelium dry weight, respectively.
Asset allocation in the Athens stock exchange: a variance sensitivity analysis
Authors: Diamandis Panayiotis F. , Drakos Anastassios A. , Kouretas Georgios P. , Zarangas Leonidas P. 
Published: January 2011

ABSTRACTThis paper provides an analysis of asset allocation using univariate portfolio GARCH models applied on daily data for the period January 1999 to December 2009 on stocks traded in the Athens Stock Exchange, a recently monitored emerging market. Our analysis adopts the variance sensitivity analysis (VSA) methodology due to Manganelli (2004) and we are able to recover from the univariate approach the multivariate dimension of the portfolio allocation problem. The main results of the analysis are: First, we demonstrate that using a two asset portfolio consisting of blue chips traded in the Greek capital market the estimated variance is a parabolic and convex function of the estimated weights providing evidence that diversification produces significant gains in terms of risk reduction. Second, based on the shape of the first and second derivatives the model misspecification due to the fitting univariate GARCH models is insignificant. Third, we compare the performance of VSA against that of three popular multivariate GARCH models and it is shown that the adopted methodology provides more efficient results than the competing models. The gains in efficiency get larger as the size of the portfolio increases. Finally, with the application of the Kupiec's test for out‐of‐sample forecasting performance we demonstrate that the VSA outperforms all three alternative models at both the 95% and 99% confidence interval independently of the trading position. Copyright © 2011 John Wiley & Sons, Ltd.
A PANEL DATA APPROACH FOR PROGRAM EVALUATION: MEASURING THE BENEFITS OF POLITICAL AND ECONOMIC INTEGRATION OF HONG KONG WITH MAINLAND CHINA
Authors: Hsiao Cheng , Steve Ching H. , Ki Wan Shui 
Published: January 2011

SUMMARYWe propose a simple‐to‐implement panel data method to evaluate the impacts of social policy. The basic idea is to exploit the dependence among cross‐sectional units to construct the counterfactuals. The cross‐sectional correlations are attributed to the presence of some (unobserved) common factors. However, instead of trying to estimate the unobserved factors, we propose to use observed data. We use a panel of 24 countries to evaluate the impact of political and economic integration of Hong Kong with mainland China. We find that the political integration hardly had any impact on the growth of the Hong Kong economy. However, the economic integration has raised Hong Kong's annual real GDP by about 4%. Copyright © 2011 John Wiley & Sons, Ltd.