bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metallic and Mott Insulating Spin‐Frustrated Antiferromagnetic States in Ionic Fullerene Complexes with a Two‐Dimensional Hexagonal C60.− Packing Motif
Authors: Konarev Dmitri V. , Khasanov Salavat S. , Otsuka Akihiro , Maesato Mitsuhiko , Uruichi Mikio , Yakushi Kyuya , Shevchun Artem F. , Yamochi Hideki , Saito Gunzi , Lyubovskaya Rimma N. 
Published: May 2014

Abstract(MDABCO+)(C60.−)(TPC) (1), in which MDABCO+ is N‐methyldiazabicyclooctanium, TPC is triptycene, and both have threefold symmetry, is a rare example of a fullerene‐based quasi‐2D metal and contains closely packed hexagonal fullerene layers with interfullerene center‐to‐center distances of 10.07 Å at 300 K. Evidence for the metallic nature of 1 was obtained by optical and microwave conductivity measurements on single crystals. The metal is characterized by a nontypical Drude response and relatively large optical mass (m*/m0=6.7). The latter indicates a narrow‐band nature, which is consistent with the calculated bandwidth of 0.10–0.15 eV. The coexistence of metallic and antiferromagnetic nonmetallic 2D layers was observed in 1 above 200–230 K. It was assumed that the nonmetallic layers undergo a transition to the metallic state below 200 K due to ordering of the fullerene and cationic sublattices. New layered complex (MQ+)(C60.−)(TPC) (2) with a hexagonal arrangement of C60.− was obtained by increasing the interfullerene distance with the bulkier N‐methylquinuclidinium cations (MQ+) having threefold symmetry. The structure of 2 is characterized by increased interfullerene center‐to‐center distances in the layers (10.124, 10.155, and 10.177 Å at 250 K). Unit‐cell doubling parallel to the 2D layer (along the b axis) was observed at low temperatures. In contrast to metallic 1, 2 exhibits a nonmetallic spin‐frustrated state with an antiferromagnetic interaction of spins (the Weiss temperature is −27 K) and no magnetic ordering down to 1.9 K. It was supposed that the expanded interfullerene distances in the triangular arrangement decrease the bandwidth and suppress metallic conductivity in 2, and thus a Mott–Hubbard insulating state with antiferromagnetically frustrated spins results.
Modified SWCNTs with Amphoteric Redox and Solubilizing Properties
Authors: Rodríguez‐Pérez Laura , García Raúl , Herranz María Ángeles , Martín Nazario 
Published: May 2014

AbstractA complementary double‐covalent functionalization of single‐wall carbon nanotubes (SWCNTs) that involves both solubilizing ionic liquids and electroactive moieties is reported. Our strategy is a simple and efficient methodology based on the stepwise functionalization of the nanotube surface with two different organic moieties. In a first instance, oxidized SWCNTs are amidated with ionic liquid precursors, and further treated with n‐butyl bromide to afford SWCNTs functionalized with 1‐butylimidazolium bromide. This approach allows tuneable polarity induced by anion exchange, which has an effect on the relative solubility of the modified SWCNTs in water. Subsequently, a 1,3‐dipolar cycloaddition reaction was performed to introduce the electron‐acceptor 11,11,12,12‐tetracyano‐9,10‐anthra‐para‐quinodimethane (TCAQ) unit on the SWCNTs. Furthermore, to evaluate the influence of the functional group position, the TCAQ electroactive molecule was anchored through an esterification reaction onto previously oxidized SWCNTs, followed by the Tour reaction to introduce the ionic liquid functions. IR and Raman spectroscopies, thermogravimetric analysis (TGA), UV/Vis/NIR spectroscopy, transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS) were employed and clearly confirmed the double‐covalent functionalization of the SWCNTs.
Ru‐Catalyzed Branched versus Linear Selective C3‐Alkylation of 2‐Aroylbenzofurans with Acrylates via CH Activation
Authors: Kommagalla Yadagiri , Srinivas Kolluru , Ramana Chepuri V. 
Published: May 2014

AbstractThe carbonyl‐directed C3H activation and alkylation of 2‐aroylbenzo[b]furans with acrylates occurs selectively either in a linear or branched fashion, depending on the catalyst employed; [Ru(p‐cymene)Cl2]2 or Ru(PPh3)3Cl2, respectively. Two alternate pathways—funded upon the differences in steric and electronic preferences of these two complexes—is proposed for the selectivity of linear versus branched products.
Modulating Aβ33–42 Peptide Assembly by Graphene Oxide
Authors: Li Qiang , Liu Lei , Zhang Shuai , Xu Meng , Wang Xueqin , Wang Chen , Besenbacher Flemming , Dong Mingdong 
Published: May 2014

AbstractGraphene oxide (GO) is utilized as the modulator to tune the formation and development of amyloid fibrils (Aβ33–42). Atomic force microscopy temporal evolution measurements reveal that the initial binding between the peptide monomer and the large available surface of the GO sheets can redirect the assembly pathway of amyloid beta. The results support the possibility to develop graphene‐based materials to inhibit amyloidosis.
Thermodynamic and Kinetic Study of Scandium(III) Complexes of DTPA and DOTA: A Step Toward Scandium Radiopharmaceuticals
Authors: Pniok Miroslav , Kubíček Vojtěch , Havlíčková Jana , Kotek Jan , Sabatie‐Gogová Andrea , Plutnar Jan , Huclier‐Markai Sandrine , Hermann Petr 
Published: May 2014

AbstractDiethylenetriamine‐N,N,N′,N′′,N′′‐pentaacetic acid (DTPA) and 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA) scandium(III) complexes were investigated in the solution and solid state. Three 45Sc NMR spectroscopic references suitable for aqueous solutions were suggested: 0.1 M Sc(ClO4)3 in 1 M aq. HClO4 (δSc=0.0 ppm), 0.1 M ScCl3 in 1 M aq. HCl (δSc=1.75 ppm) and 0.01 M [Sc(ox)4]5− (ox2−=oxalato) in 1 M aq. K2C2O4 (δSc=8.31 ppm). In solution, [Sc(dtpa)]2− complex (δSc=83 ppm, ▵ν=770 Hz) has a rather symmetric ligand field unlike highly unsymmetrical donor atom arrangement in [Sc(dota)]− anion (δSc=100 ppm, ▵ν=4300 Hz). The solid‐state structure of K8[Sc2(ox)7]⋅13 H2O contains two [Sc(ox)3]3− units bridged by twice “side‐on” coordinated oxalate anion with Sc3+ ion in a dodecahedral O8 arrangement. Structures of [Sc(dtpa)]2− and [Sc(dota)]− in [(Hguanidine)]2[Sc(dtpa)]⋅3 H2O and K[Sc(dota)][H6dota]Cl2⋅4 H2O, respectively, are analogous to those of trivalent lanthanide complexes with the same ligands. The [Sc(dota)]− unit exhibits twisted square‐antiprismatic arrangement without an axial ligand (TSA′ isomer) and [Sc(dota)]− and (H6dota)2+ units are bridged by a K+ cation. A surprisingly high value of the last DOTA dissociation constant (pKa=12.9) was determined by potentiometry and confirmed by using NMR spectroscopy. Stability constants of scandium(III) complexes (log KScL 27.43 and 30.79 for DTPA and DOTA, respectively) were determined from potentiometric and 45Sc NMR spectroscopic data. Both complexes are fully formed even below pH 2. Complexation of DOTA with the Sc3+ ion is much faster than with trivalent lanthanides. Proton‐assisted decomplexation of the [Sc(dota)]− complex (τ1/2=45 h; 1 M aq. HCl, 25 °C) is much slower than that for [Ln(dota)]− complexes. Therefore, DOTA and its derivatives seem to be very suitable ligands for scandium radioisotopes.
A Family of “Click” Nucleosides for Metal‐Mediated Base Pairing: Unravelling the Principles of Highly Stabilizing Metal‐Mediated Base Pairs
Authors: Richters Tim , Krug Olga , Kösters Jutta , Hepp Alexander , Müller Jens 
Published: May 2014

AbstractA family of artificial nucleosides has been developed by applying the CuI‐catalyzed Huisgen 1,3‐dipolar cycloaddition. Starting from 2‐deoxy‐β‐D‐glycosyl azide as a common precursor, three bidentate nucleosides have been synthesized. The 1,2,3‐triazole involved in all three nucleobases is complemented by 1,2,4‐triazole (TriTri), pyrazole (TriPyr), or pyridine (TriPy). Molecular structures of two metal complexes indicate that metal‐mediated base pairs of TriPyr may not be fully planar. An investigation of DNA oligonucleotide duplexes comprising the new “click” nucleosides showed that they can bind AgI to form metal‐mediated base pairs. In particular the mispair formed from TriPy and the previously established imidazole nucleoside is significantly stabilized in the presence of AgI. A comparison of different oligonucleotide sequences allowed the determination of general factors involved in the stabilization of nucleic acids duplexes with metal‐mediated base pairs.
Enantioselective Transformation of Allyl Carbonates into Branched Allyl Carbamates by Using Amines and Recycling CO2 under Iridium Catalysis
Authors: Zheng Sheng‐Cai , Zhang Min , Zhao Xiao‐Ming 
Published: May 2014

AbstractEnantioselective transformation of allyl carbonates into branched allyl carbamates by using amines and recycling CO2 in the presence of an Ir complex and K3PO4 was accomplished. This provided branched allyl carbamates in fair to excellent yields with up to 98:2 regioselectivity and 93 % ee. The role of CO2 in this transformation is discussed as well.
Stereoelectronic Basis for the Kinetic Resolution of N‐Heterocycles with Chiral Acylating Reagents
Authors: Hsieh Sheng‐Ying , Wanner Benedikt , Wheeler Philip , Beauchemin André M. , Rovis Tomislav , Bode Jeffrey W. 
Published: May 2014

AbstractThe kinetic resolution of N‐heterocycles with chiral acylating agents reveals a previously unrecognized stereoelectronic effect in amine acylation. Combined with a new achiral hydroxamate, this effect makes possible the resolution of various N‐heterocycles by using easily prepared reagents. A transition‐state model to rationalize the stereochemical outcome of this kinetic resolution is also proposed.
Deoxyribonucleoside‐Modified Squaraines as Near‐IR Viscosity Sensors
Authors: Zhang Yuanwei , Yue Xiling , Kim Bosung , Yao Sheng , Belfield Kevin D. 
Published: May 2014

AbstractDeoxyribonucleoside‐modified squaraines were synthesized by Sonogashira coupling reactions using an unsymmetrical, terminal alkynylated benzothiazolium squaraine dye. These non‐natural nucleosides exhibited fluorescent ‘turn‐on’ properties in viscous conditions with an enhancement of >300‐fold. The viscosity‐dependent fluorescence enhancement was attributed to a combination of hampering both molecular aggregation and intramolecular bond rotation of the squaraine probe. Fluorescence microscopy allowed visualization of highly viscous regions during various stages of cellular mitosis.
Structure–Activity Relationship of Trifluoromethyl‐Containing Metallocenes: Electrochemistry, Lipophilicity, Cytotoxicity, and ROS Production
Authors: Maschke Marcus , Alborzinia Hamed , Lieb Max , Wölfl Stefan , Metzler‐Nolte Nils 
Published: May 2014

AbstractWe report the synthesis of trifluoromethylated metallocenes (M=Fe, Ru) and related metal‐free compounds for comparison of their biological properties with the aim to establish structure–activity relationships toward the anti‐proliferative activity of this compound class. All new compounds were comprehensively characterized by NMR spectroscopy (1H, 13C, 19F), mass spectrometry, IR spectroscopy, and elemental analysis. A single‐crystal X‐ray structure was obtained on the Ru derivative, 1‐(1‐hydroxy‐1‐hexafluoromethylethyl)ruthenocene (3). The cytotoxicity of all compounds was tested on MCF‐7, HT‐29, and PT‐45 cells, and IC50 values as low as 12 μM were observed. Both the metallocene moiety and the hydroxy function are crucial for cytotoxicity. In addition, the activity decreased sharply even if only one trifluoromethyl group was replaced with a methyl group. Electrochemical investigations by cyclic voltammetry revealed that all CF3‐containing compounds are harder to oxidize than the unsubstituted metallocenes. Moreover, log P determination by RP‐HPLC showed the fluorinated derivatives to have higher lipophilicity, with log P values up to 4.6. At the same time, the generation of reactive oxygen species (ROS) in Jurkat cells by these compounds was investigated by flow cytometry. Strong ROS production was shown exclusively for the bis‐CF3 derivative 1‐(1‐hydroxy‐1‐hexafluoromethylethyl)ferrocene (1) after 6 and 24 h. Also on the Jurkat cell line, only compound 1 strongly induces necrosis after 24 and 48 h, as shown by annexin V/propidium iodide staining. No induction of apoptosis was observed. We propose that compound 1 is more efficiently incorporated into cancer cells relative to all other derivatives, causing significant induction of oxidative stress within the cell, which ultimately leads to cell death.
A Detailed Study of Antibacterial 3‐Acyltetramic Acids and 3‐Acylpiperidine‐2,4‐diones
Authors: Jeong Yong‐Chul , Bikadi Zsolt , Hazai Eszter , Moloney Mark G. 
Published: May 2014

AbstractInspired by the core fragment of antibacterial natural products such as streptolydigin, 3‐acyltetramic acids and 3‐acylpiperidine‐2,4‐diones have been synthesised from the core heterocycle by direct acylation with the substituted carboxylic acids using a strategy which permits ready access to a structurally diverse compound library. The antibacterial activity of these systems has been established against a panel of Gram‐positive and Gram‐negative bacteria, with activity mostly against the former, which in some cases is very potent. Data consistent with modes of action against undecaprenylpyrophosphate synthase (UPPS) and/or RNA polymerase (RNAP) for a small subset of the library has been obtained. The most active compounds have been shown to exhibit binding at known binding sites of streptolydigin and myxopyronin at UPPS and RNAP. These systems offer potential for their antibacterial activity, and further demonstrate the use of natural products as biologically validated starting points for drug discovery.
Synthesis, Characterization, and in vitro Antiproliferative Activity of [Salophene]platinum(II) Complexes
Authors: Proetto Maria T. , Liu Wukun , Molchanov Andrey , Sheldrick William S. , Hagenbach Adelheid , Abram Ulrich , Gust Ronald 
Published: May 2014

AbstractA series of methoxy‐ and fluorine‐substituted [salophene]platinum(II) complexes (salophene=N,N′‐bis(salicylidene)‐1,2‐phenylenediamine) were synthesized and characterized by 1H NMR spectroscopy and mass spectrometry. The structure was confirmed on the example of [5‐OCH3‐salophene]platinum(II) (4‐Pt) by crystal structure analysis. The cytotoxicity of all complexes against MCF‐7 cells showed strong dependence on the kind of substituent and its position on the salicylidene moiety, whereas 1‐Pt (H), 3‐Pt (4‐OCH3), and 6‐Pt (3‐F) exhibited high antiproliferative effects (IC50<2 μM). Drug lipophilicity and cellular accumulation were analyzed in an attempt to explain the differences in antitumor potency. To gain insight into their mode of action, DNA interaction studies were performed, in which compounds such as 1‐Pt acted as non‐DNA‐binding platinum anticancer drugs, as neither intercalation nor DNA covalent binding were detected.
Polymer‐Coated PtCo Nanoparticles Deposited on Diblock Copolymer Templates: Chemical Selectivity versus Topographical Effects
Authors: Metwalli E. , Krisch I. , Markovits I. , Rawolle M. , Ruderer M. A. , Guo S. , Wyrzgol S. , Jentys A. , Perlich J. , Lercher J. A. , Müller‐Buschbaum P. 
Published: May 2014

AbstractMetal–polymer hybrid films are prepared by deposition of polymer‐coated PtCo nanoparticles onto block copolymer templates. For templating, a thin film of the lamella‐forming diblock copolymer poly(styrene‐b‐methyl methacrylate) P(S‐b‐MMA) is chemically etched and a topographical surface relief with 3 nm height difference is created. Two types of polymer‐grafted PtCo nanoparticles are compared to explore the impact of chemical selectivity versus the topographical effect of the nanotemplate. A preferable wetting of the polystyrene (PS) domains with poly(styrenesulfonate) (PSS)‐coated PtCo nanoparticles (instead of residing in the space between the domains) is observed. Our investigation reveals that the interaction between PSS‐coated nanoparticles and PS domains dominates over the topographical effects of the polymer surface. In contrast, a non‐selective deposition of poly(N‐vinyl‐2‐pyrrolidone) (PVP)‐coated PtCo nanoparticles and the formation of large metal‐particle aggregates on the film is observed.
Conical Intersections and Low‐Lying Electronic States of Tetrafluoroethylene
Authors: Mullinax J. Wayne , Sokolov Alexander Yu , Schaefer Henry F. 
Published: May 2014

AbstractThe low‐lying electronic states of tetrafluoroethylene (C2F4) are characterized theoretically for the first time using equation‐of‐motion coupled cluster theory (EOM‐CCSD), and complete active space self‐consistent field (CASSCF) and second‐order perturbation theory (CASPT2). Computations are performed for vertical excitation energies, equilibrium geometries, minimum‐energy conical intersections, and potential energy curves along three geometric coordinates: 1) twisting of the FCCF dihedral angle, 2) pyramidalization of the CF2 group, and 3) migration of a fluorine atom resulting in an ethylidene‐like (CF3CF) structure. The results suggest two relaxation pathways from the Rydberg‐3s excited electronic state to the ground state. These relaxation pathways are discussed in conjunction with the femtosecond photoionization spectroscopy results of Trushin et al. [ChemPhysChem­ 2004, 5, 1389].
Chiral Discrimination in Dimers of Diphosphines PH2PH2and PH2PHF
Authors: Azofra Luis M. , Alkorta Ibon , Elguero José 
Published: May 2014

AbstractA theoretical study of the conformational profile of two diphosphines, PH2PH2and PH2PHF, is carried using second‐order Møller–Plesset perturbation theory (MP2) computational methods. The chiral minima found are used to build homo‐ and heterochiral dimers. Six minima are found for the (PH2PH2)2dimers and 27 for the (PH2PHF)2dimers. Pnicogen and hydrogen bonds, the non‐covalent forces that stabilize the complexes, are characterized by Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) methodologies. Those with several pnicogen bonds are more stable than those with hydrogen bonds. The chirodiastaltic energies amount to a total of 1.77 kJ mol−1for theRa:RaversusRa:Sa(PH2PH2)2dimers, 0.81 kJ mol−1for theRSa:RSaversusRSa:SRa(PH2PHF)2dimers, and 2.93 kJ mol−1for theRRa:RRaversusRRa:SSa(PH2PHF)2dimers. In the first and second cases, the heterochiral complex is favored whereas in the third case, the homochiral complex is favored.
Quantitative Analysis of Molecular Interaction Potentials of Ionic Liquid Anions Using Multi‐Functionalized Stationary Phases in HPLC
Authors: Cho Chul‐Woong , Stolte Stefan , Ranke Johannes , Preiss Ulrich , Krossing Ingo , Thöming Jorg 
Published: May 2014

AbstractThe molecular interaction potentials, including S (dipolarity/polarizability), A (hydrogen bonding acidity), and B (hydrogen bonding basicity), of anions are experimentally determined using multi‐functionalized stationary phases in high‐performance liquid chromatography (HPLC) systems. We employ three different multi‐functionalized stationary phase columns (Obelisc R, Obelisc N, and Acclaim Trinity‐P1) combined with two ingredients, namely, acetonitrile (ACN) and methanol (MeOH). These conditions can cause neutral, cationic, and anionic compounds to be retained. By using the retention characteristics of calibration compounds, including cations, anions, and neutral compounds, system parameters including the ionic interaction terms (zcZc, zaZa) are evaluated using multiple linear regression, resulting in a standard deviation (SD) of 0.090–0.158 log units. Based on the system parameters and retention characteristics of the anions of interest, their molecular interaction potentials are characterized on the same scale for neutral and cationic molecules. Furthermore, to verify the determined molecular interaction potentials, we predict anion hydrophobicity. The results show that the determined S, A, and B, together with the computable descriptors E (excess molar refraction) and V (McGowan volume), can predict anion hydrophobicity with R2=0.982 and SD=0.167 (dimensionless).
Understanding the Unusual Adsorption Behavior in Hierarchical Zeolite Nanosheets
Authors: Bai Peng , Olson David H. , Tsapatsis Michael , Siepmann J. Ilja 
Published: May 2014

AbstractHierarchical zeolites are advanced materials possessing the catalytic and adsorption properties of conventional zeolites while eliminating their transport limitations through the introduction of mesopores. Recent experiments comparing the adsorption in hierarchical self‐pillared pentasils (SPP) and silicalite‐1 (MFI) revealed an interesting crossover in sorbate loading for branched or long‐chain alkanes but not for shorter linear alkanes, but an explanation for this behavior is not readily available through experimental probes due to the complications arising from the presence of multiple adsorption sites. Here we present a molecular simulation study on the adsorption of alkane isomers and show that a multi‐step mechanism, found here for all molecules, is responsible for the observed phenomena.
Silver Arrays Inside DNA Duplexes Constructed from Silver(I)‐Mediated Pyrrolo‐dC–Pyrrolo‐dC Base Pairs
Authors: Mei Hui , Yang Haozhe , Röhl Ingo , Seela Frank 
Published: May 2014

AbstractTuneable silver arrays inside DNA duplexes were constructed by multiple incorporations of pyrrolo‐dC–pyrrolo‐dC base pairs. A short array with six silver ions was built within a DNA template. The size and positioning of the array is programmable and depends on the incorporation site of the modified base pairs. Always two silver ions were captured by one pyrrolo‐dC–pyrrolo‐dC pair as confirmed by melting experiments, UV and fluorescence titration experiments as well as ESI mass spectra. The silver‐mediated pyrrolo‐dC–pyrrolo‐dC base pairs with phenyl residues in the 6‐position were significantly more stable than those containing methyl substitutions. The caged silver ions are released from duplex DNA by sodium iodide but not by chloride or bromide anions, thus indicating very high stability of the metal–DNA complex.
Grafting Transition Metal–Organic Fragments onto W/Ta Mixed‐Addendum Nanoclusters for Broad‐Spectrum‐Driven Photocatalysis
Authors: Zhang Tian‐Zhan , Yao Shuang , Zhang Zhi‐Ming , Lu Ying , Li Yang‐Guang , Wang En‐Bo 
Published: May 2014

AbstractTwo new transition‐metal (TM)‐containing polytantalotungstates, CsNa2H[Cu(bpy)(H2O)3]3{[Cu(bpy)2]2[Cu(bpy)(H2O)2]3[Ta4O6(SiW9Ta3O40)4]}⋅17 H2O (1) and K4Na4H4[Ta4O6(SiW9Ta3O40)4][Cu(apy)(H2O)2]4⋅42 H2O (2) (bpy=2,2′‐bipyridine, apy=3‐aminopyridine), have been synthesised under hydrothermal conditions. Both compounds 1 and 2 were determined and characterised by single‐crystal X‐ray diffraction analysis, thermogravimetric analysis, IR spectroscopy, UV/Vis spectroscopy and elemental analysis. Compounds 1 and 2 contain W/Ta mixed‐addendum nanoclusters decorated by TM–organic fragments. Compounds 1 and 2 are the first TM‐containing polytantalotungstates promise a more diverse set of structures of the polytantalotungstate family. The obtained materials can harvest a wide spectrum of solar light, from UV to near‐infrared (NIR) wavelength. Photocatalytic study revealed that compounds 1 and 2 exhibited UV‐ and visible‐light‐driven photocatalytic water splitting activity. Compound 1 could also be used as a catalyst for the photocatalytic decomposition of 2,4‐dichlorophenol in water with NIR‐light irradiation. This is the first NIR photocatalyst obtained in polyoxometalate chemistry.