bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessing student engagement and self‐regulated learning in a medical gross anatomy course
Authors: Pizzimenti Marc A. , Axelson Rick D.
Published: May 2014

In courses with large enrollment, faculty members sometimes struggle with an understanding of how individual students are engaging in their courses. Information about the level of student engagement that instructors would likely find most useful can be linked to: (1) the learning strategies that students are using; (2) the barriers to learning that students are encountering; and (3) whether the course materials and activities are yielding the intended learning outcomes. This study drew upon self‐regulated learning theory (SRL) to specify relevant information about learning engagement, and how the measures of particular scales might prove useful for student/faculty reflection. We tested the quality of such information as collected via the Motivated Strategies for Learning Questionnaire (MSLQ). MSLQ items were administered through a web‐based survey to 150 students in a first‐year medical gross anatomy course. The resulting 66 responses (44% response rate) were examined for information quality (internal reliability and predictive validity) and usefulness of the results to the course instructor. Students' final grades in the course were correlated with their MSLQ scale scores to assess the predictive validity of the measures. These results were consistent with the course design and expectations, showing that greater use of learning strategies such as elaboration and critical thinking was associated with higher levels of performance in the course. Motivation subscales for learning were also correlated with the higher levels of performance in the course. The extent to which these scales capture valid and reliable information in other institutional settings and courses needs further investigation. Anat Sci Educ 8: 104–110. © 2014 American Association of Anatomists.
Measuring academic influence: Not all citations are equal
Authors: Zhu Xiaodan , Turney Peter , Lemire Daniel , Vellino André
Published: May 2014

The importance of a research article is routinely measured by counting how many times it has been cited. However, treating all citations with equal weight ignores the wide variety of functions that citations perform. We want to automatically identify the subset of references in a bibliography that have a central academic influence on the citing paper. For this purpose, we examine the effectiveness of a variety of features for determining the academic influence of a citation. By asking authors to identify the key references in their own work, we created a data set in which citations were labeled according to their academic influence. Using automatic feature selection with supervised machine learning, we found a model for predicting academic influence that achieves good performance on this data set using only four features. The best features, among those we evaluated, were those based on the number of times a reference is mentioned in the body of a citing paper. The performance of these features inspired us to design an influence‐primed h‐index (the hip‐index). Unlike the conventional h‐index, it weights citations by how many times a reference is mentioned. According to our experiments, the hip‐index is a better indicator of researcher performance than the conventional h‐index.
Tuning the Self‐Assembly of Oligothiophenes on Chemical Vapor Deposition Graphene: Effect of Functional Group, Solvent, and Substrate
Authors: Sun Xiuling , Mu Youbing , Zhang Jia , Wang Xiaona , Hu Pingan , Wan Xiaobo , Guo Zongxia , Lei Shengbin
Published: May 2014

Tuning and characterizing the interfacial structure of organic semiconductors on graphene is essential for graphene‐based devices. Regulation of the supramolecular assembling structure of oligothiophenes on graphene by changing functional groups attached to the backbone of oligothiophenes is described and the assembling behavior is compared with that on the basal plane of highly oriented pyrolytic graphite. It reveals that terminal functional groups attached to the conjugated backbone of oligothiophene can entirely change the assembling structures. Significant solvent and substrate effects have also been confirmed by comparing the assembling structures of oligothiophenes deposited from tetrahydrofuran, 1,2,4‐trichlorobenzene, and octanoic acid onto graphene and graphite.
Fabrication of Predominantly Mn4+‐Doped TiO2 Nanoparticles under Equilibrium Conditions and Their Application as Visible‐Light Photocatalyts
Authors: Wang Lijie , Fan Jiajie , Cao Zetan , Zheng Yichao , Yao Zhiqiang , Shao Guosheng , Hu Junhua
Published: May 2014

The chemical state of a transition‐metal dopant in TiO2 can intrinsically determine the performance of the doped material in applications such as photocatalysis and photovoltaics. In this study, manganese‐doped TiO2 is fabricated by a near‐equilibrium process, in which the TiO2 precursor powder precipitates from a hydrothermally obtained transparent mother solution. The doping level and subsequent thermal treatment influence the morphology and crystallization of the TiO2 samples. FTIR spectroscopy and X‐ray photoelectron spectroscopy analyses indicate that the manganese dopant is substitutionally incorporated by replacing Ti4+ cations. The absorption band edge can be gradually shifted to 1.8 eV by increasing the nominal manganese content to 10 at %. Manganese atoms doped into the titanium lattice are associated with the dominant 4+ valence oxidation state, which introduces two curved, intermediate bands within the band gap and results in a significant enhancement in photoabsorption and the quantity of photogenerated hydroxyl radicals. Additionally, the high photocatalytic performance of manganese‐doped TiO2 is also attributed to the low oxygen content, owing to the equilibrium fabrication conditions. This work provides an important strategy to control the chemical and defect states of dopants by using an equilibrium fabrication process.
The Synthesis of Dendritic EDOT–Peptide Conjugates and their Multistimuli‐Responsive Self‐Assembly into Supramolecular Nanorods and Fibers in Water
Authors: Ahlers Patrick , Frisch Hendrik , Spitzer Daniel , Vobecka Zuzana , Vilela Filipe , Besenius Pol
Published: May 2014

We report the synthesis of amphiphilic dendritic EDOT–peptide conjugates and discuss their stimuli‐responsive self‐assembly into polyanionic nanorods in water. In order to expand the general concept of frustrated growth, whereby attractive supramolecular interactions within the enlarged π‐system of the hydrophobic core of a dendritic peptide are hampered by repulsive interactions in the hydrophilic periphery, we show that changes in the pH and ionic strength are both able to independently trigger the self‐assembly of the dendritic monomers into supramolecular nanorods and nanofibers. These transitions are analyzed using circular dichroism and fluorescence spectroscopic methods, and the resulting supramolecular polymers are characterized by transmission electron microscopy.
Mapping Collaboration Networks in the World of Autism Research
Authors: Goldstein Neal D. , Tager‐Flusberg Helen , Lee Brian K.
Published: May 2014

In the era of globalization and with the emergence of autism spectrum disorder as a global concern, the landscape of autism research has expanded to encompass much of the world. Here, we seek to provide an overview of the world of autism research, by documenting collaboration underlying the International Meeting for Autism Research (IMFAR), the pre‐eminent annual scientific meeting devoted to the presentation of the latest autism research. We analyzed published abstracts presented at IMFAR meetings, between 2008 and 2013, to determine patterns of collaboration. We described collaboration networks on the individual, institutional, and international levels, and visually depicted these results on spatial network maps. Consistent with findings from other scientific disciplines, we found that collaboration is correlated with research productivity. Collaborative hotspots of autism research throughout the years were clustered on the East and West coasts of the U.S., Canada, and northern Europe. In years when conferences were held outside of North America, the proportion of abstracts from Europe and Asia increased. While IMFAR has traditionally been dominated by a large North American presence, greater global representation may be attained by shifting meeting locations to other regions of the world. Autism Res 2015, 8: 1–8. © 2014 International Society for Autism Research, Wiley Periodicals, Inc.
Verification of a new biocompatible single‐use film formulation with optimized additive content for multiple bioprocess applications
Authors: Jurkiewicz Elke , Husemann Ute , Greller Gerhard , Barbaroux Magali , Fenge Christel
Published: May 2014

Single‐use bioprocessing bags and bioreactors gained significant importance in the industry as they offer a number of advantages over traditional stainless steel solutions. However, there is continued concern that the plastic materials might release potentially toxic substances negatively impacting cell growth and product titers, or even compromise drug safety when using single‐use bags for intermediate or drug substance storage. In this study, we have focused on the in vitro detection of potentially cytotoxic leachables originating from the recently developed new polyethylene (PE) multilayer film called S80. This new film was developed to guarantee biocompatibility for multiple bioprocess applications, for example, storage of process fluids, mixing, and cell culture bioreactors. For this purpose, we examined a protein‐free cell culture medium that had been used to extract leachables from freshly gamma‐irradiated sample bags in a standardized cell culture assay. We investigated sample bags from films generated to establish the operating ranges of the film extrusion process. Further, we studied sample bags of different age after gamma‐irradiation and finally, we performed extended media extraction trials at cold room conditions using sample bags. In contrast to a nonoptimized film formulation, our data demonstrate no cytotoxic effect of the S80 polymer film formulation under any of the investigated conditions. The S80 film formulation is based on an optimized PE polymer composition and additive package. Full traceability alongside specifications and controls of all critical raw materials, and process controls of the manufacturing process, that is, film extrusion and gamma‐irradiation, have been established to ensure lot‐to‐lot consistency. © 2014 The Authors. Published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers Biotechnol. Prog., 30:1171–1176, 2014
Biosynthesis of Colabomycin E, a New Manumycin‐Family Metabolite, Involves an Unusual Chain‐Length Factor
Authors: Petříčková Kateřina , Pospíšil Stanislav , Kuzma Marek , Tylová Tereza , Jágr Michal , Tomek Petr , Chroňáková Alica , Brabcová Eva , Anděra Ladislav , Krištůfek Václav , Petříček Miroslav
Published: May 2014

Colabomycin E is a new member of the manumycin‐type metabolites produced by the strain Streptomyces aureus SOK1/5‐04 and identified by genetic screening from a library of streptomycete strains. The structures of colabomycin E and accompanying congeners were resolved. The entire biosynthetic gene cluster was cloned and expressed in Streptomyces lividans. Bioinformatic analysis and mutagenic studies identified components of the biosynthetic pathway that are involved in the formation of both polyketide chains. Recombinant polyketide synthases (PKSs) assembled from the components of colabomycin E and asukamycin biosynthetic routes catalyzing the biosynthesis of “lower” carbon chains were constructed and expressed in S. aureus SOK1/5‐04 ΔcolC11–14 deletion mutant. Analysis of the metabolites produced by recombinant strains provided evidence that in both biosynthetic pathways the length of the lower carbon chain is controlled by an unusual chain‐length factor supporting biosynthesis either of a triketide in asukamycin or of a tetraketide in colabomycin E. Biological activity assays indicated that colabomycin E significantly inhibited IL‐1β release from THP‐1 cells and might thus potentially act as an anti‐inflammatory agent.
Two‐Face, Two‐Turn α‐Helix Mimetics Based on a Cross‐Acridine Scaffold: Analogues of the Bim BH3 Domain
Authors: Li Xiangqian , Wang Ziqian , Feng Yingang , Song Ting , Su Pengchen , Chen Chengbin , Chai Gaobo , Yang Ying , Zhang Zhichao
Published: May 2014

The design of a cross‐acridine scaffold mimicking the i, i+3, i+5, and i+7 residues distributed over a two‐face, two‐turn α‐helix is described. Docking studies and 2D 1H,15N HSQC NMR spectroscopy provide compelling evidence that compound 3 d accurately reproduces the arrangement of four hotspots in the Bim BH3 peptide to permit binding to the Mcl‐1 and Bcl‐2 proteins (Ki 0.079 and 0.056 μM, respectively). Furthermore, the hotspot mutation could also be mimicked by individual or multiple deletions of side chains on the scaffold.
Facile Synthesis of Native and Protease‐Resistant Ubiquitylated Peptides
Authors: Weller Caroline E. , Huang Wei , Chatterjee Champak
Published: May 2014

The reversible post‐translational modification of eukaryotic proteins by ubiquitin regulates key cellular processes including protein degradation and gene transcription. Studies of the mechanistic roles for protein ubiquitylation require quantities of homogenously modified substrates that are typically inaccessible from natural sources or by enzymatic ubiquitylation in vitro. Therefore, we developed a facile and scalable methodology for site‐specific chemical ubiquitylation. Our semisynthetic strategy utilized a temporary ligation auxiliary, 2‐(aminooxy)ethanethiol, to direct ubiquitylation to specific lysine residues in peptide substrates. Mild reductive removal of the auxiliary after ligation yielded ubiquitylated peptides with the native isopeptide linkage. Alternatively, retention of the ligation auxiliary yielded protease‐resistant analogues of ubiquitylated peptides. Importantly, our strategy was fully compatible with the presence of protein thiol groups, as demonstrated by the synthesis of peptides modified by the human small ubiquitin‐related modifier 3 protein.
High Catalytic Synergism between the Components of the Rhenium Complex@Silver Hybrid Material in Alkene Epoxidations
Authors: Indra Arindam , Greiner Mark , Gericke Axel Knop , Schlögl Robert , Avnir David , Driess Matthias
Published: May 2014

The immobilization of a water‐soluble rhenium complex in metallic silver matrices has resulted in a highly efficient catalyst for epoxidation, which has better epoxidation catalytic activity than the individual components. This unprecedented synergism could be obtained only by using the novel immobilization methodology, and not by using the standard adsorption process. The composite catalyst has been fully characterized (by using XRD, TEM, SEM, energy‐dispersive X‐ray spectroscopy, and atomic X‐ray mapping), and the synergism has originated as a result of the proximity of the two components. Photoemission spectroscopic studies confirm the presence of +6 and +7 oxidation states of rhenium in metallic silver in the active catalyst.
NH3 Oxidation Mechanism over Cu/SAPO‐34 Catalysts Prepared by Different Methods
Authors: Yu Tie , Wang Jun , Huang Yu , Shen Meiqing , Li Wei , Wang Jianqiang
Published: May 2014

NH3 oxidation mechanism and its inhibition effect on the selective catalytic reduction of NOx by NH3 (NH3–SCR) reaction over two series of Cu/SAPO‐34 catalysts were studied. It was found that the different NO conversions were induced by the diverse NH3 oxidation degree. X‐ray diffraction, scanning electron microscopy, H2 temperature‐programmed reduction (H2–TPR), and CO diffuse reflectance infrared Fourier transform spectroscopy (CO–DRIFTS) analyses were conducted to estimate the Cu species distribution. The TPR results showed that the CuO species was dominant in impregnated Cu/SAPO‐34 samples, and the ion‐exchanged Cu/SAPO‐34 samples contained more isolated Cu2+ species. Furthermore, H2–TPR, electron paramagnetic resonance, and CO–DRIFTS analyses were utilized to quantify the CuO, Cu2+, and Cu+ species. The results together with the kinetic results revealed the CuO is the active site for NH3 oxidation, and the NH3 oxidation over Cu/SAPO‐34 sample consists two steps: (a) NO production; (b) further NO consumption by adsorbed NH3 species on Cu2+ sites. Finally, the inhibition of NH3 oxidation on NH3–SCR activity was explained and the NO conversion at high temperature was related to the Cu2+/CuO ratio in Cu/SAPO‐34 sample.
Poly(γ‐glutamic acid)/Silica Hybrids with Calcium Incorporated in the Silica Network by Use of a Calcium Alkoxide Precursor
Authors: Poologasundarampillai Gowsihan , Yu Bobo , Tsigkou Olga , Wang Daming , Romer Frederik , Bhakhri Vineet , Giuliani Finn , Stevens Molly M. , McPhail David S. , Smith Mark E. , Hanna John V. , Jones Julian R.
Published: May 2014

Current materials used for bone regeneration are usually bioactive ceramics or glasses. Although they bond to bone, they are brittle. There is a need for new materials that can combine bioactivity with toughness and controlled biodegradation. Sol‐gel hybrids have the potential to do this through their nanoscale interpenetrating networks (IPN) of inorganic and organic components. Poly(γ‐glutamic acid) (γ‐PGA) was introduced into the sol‐gel process to produce a hybrid of γ‐PGA and bioactive silica. Calcium is an important element for bone regeneration but calcium sources that are used traditionally in the sol‐gel process, such as Ca salts, do not allow Ca incorporation into the silicate network during low‐temperature processing. The hypothesis for this study was that using calcium methoxyethoxide (CME) as the Ca source would allow Ca incorporation into the silicate component of the hybrid at room temperature. The produced hybrids would have improved mechanical properties and controlled degradation compared with hybrids of calcium chloride (CaCl2), in which the Ca is not incorporated into the silicate network. Class II hybrids, with covalent bonds between the inorganic and organic species, were synthesised by using organosilane. Calcium incorporation in both the organic and inorganic IPNs of the hybrid was improved when CME was used. This was clearly observed by using FTIR and solid‐state NMR spectroscopy, which showed ionic cross‐linking of γ‐PGA by Ca and a lower degree of condensation of the Si species compared with the hybrids made with CaCl2 as the Ca source. The ionic cross‐linking of γ‐PGA by Ca resulted in excellent compressive strength and reduced elastic modulus as measured by compressive testing and nanoindentation, respectively. All hybrids showed bioactivity as hydroxyapatite (HA) was formed after immersion in simulated body fluid (SBF).
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

(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

A 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

The 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

Graphene 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

Diethylenetriamine‐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

A 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

Enantioselective 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

The 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

Deoxyribonucleoside‐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

We 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

Inspired 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

A 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

Metal–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

The 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

A 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

The 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

Hierarchical 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

Tuneable 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

Two 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.
Study of gemcitabine‐sensitive/resistant cancer cells by cell cloning and synchrotron FTIR microspectroscopy
Authors: Rutter Abigail V. , Siddique Muhammad R. , Filik Jacob , Sandt Christophe , Dumas Paul , Cinque Gianfelice , Sockalingum Ganesh D. , Yang Ying , Sulé‐Suso Josep
Published: May 2014

Over the last few years, significant scientific insight on the effects of chemotherapy drugs at cellular level using synchrotron‐based FTIR (S‐FTIR) microspectroscopy has been obtained. The work carried out so far has identified spectral differences in cancer cells before and after the addition of drugs. However, this had to account for the following issues. First, chemotherapy agents cause both chemical and morphological changes in cells, the latter being responsible for changes in the spectral profile not correlated with biochemical characteristics. Second, as the work has been carried out in mixed populations of cells (resistant and sensitive), it is important to distinguish the spectral differences which are due to sensitivity/resistance to those due to cell morphology and/or cell mixture. Here, we successfully cloned resistant and sensitive lung cancer cells to a chemotherapy drug. This allowed us to study a more uniform population and, more important, allowed us to study sensitive and resistant cells prior to the addition of the drug with S‐FTIR microscopy. Principal component analysis (PCA) did not detect major differences in resistant cells prior to and after adding the drug. However, PCA separated sensitive cells prior to and after the addition of the drug. This would indicate that the spectral differences between cells prior to and after adding a drug might reside on those more or less sensitive cells that have been able to remain alive when they were collected to be studied with S‐FTIR microspectroscopy. This is a proof of concept and a feasibility study showing a methodology that opens a new way to identify the effects of drugs on more homogeneous cell populations using vibrational spectroscopy. © 2014 International Society for Advancement of Cytometry
Indirect CD4+ T‐cell‐mediated elimination of MHC IINEG tumor cells is spatially restricted and fails to prevent escape of antigen‐negative cells
Authors: Tveita Anders A. , Schjesvold Fredrik H. , Sundnes Olav , Haabeth Ole Audun W. , Haraldsen Guttorm , Bogen Bjarne
Published: May 2014

Tumor‐specific Th1 cells can activate tumor‐infiltrating macrophages that eliminate MHC class II negative (MHC IINEG) tumor cells. Activated M1‐like macrophages lack antigen (Ag) receptors, and are presumably unable to discriminate and thus kill both Ag‐positive (AgPOS) and Ag‐negative (AgNEG) tumor cells (bystander killing). The lack of specificity of macrophage‐mediated cytotoxicity might be of clinical importance as it could provide a means of avoiding tumor escape. Here, we have tested this idea using mixed populations of AgPOS and AgNEG tumor cells in a TCR‐transgenic model in which CD4+ T cells recognize a secreted tumor‐specific antigen. Surprisingly, while AgPOS tumor cells were recognized and rejected, AgNEG cells grew unimpeded and formed tumors. We further demonstrated that macrophage‐mediated cytotoxicity was spatially restricted to areas dominated by AgPOS tumor cells, sparing AgNEG tumor cells in the vicinity. As a consequence, macrophage tumoricidal activity did not confer bystander killing in vivo. The present results offer novel insight into the mechanisms of indirect Th1‐mediated elimination of MHC IINEG tumor cells.
Efficient Palladium(II) Precatalysts Bearing 4,5‐Dicyanoimidazol‐2‐ylidene for the Mizoroki–Heck Reaction
Authors: Baier Heiko , Metzner Philipp , Körzdörfer Thomas , Kelling Alexandra , Holdt Hans‐Jürgen
Published: May 2014

The new N‐heterocyclic carbene (NHC) complex [PdCl2{(CN)2IMes}(PPh3)] (2) ({(CN)2IMes}: 4,5‐dicyano‐1,3‐dimesitylimidazol‐2‐ylidene) and the NHC palladacycle [PdCl(dmba){(CN)2IMes}] (3) (dmba: N,N‐dimethylbenzylamine) have been synthesized by thermolysis of 4,5‐dicyano‐1,3‐dimesityl‐2‐(pentafluorophenyl)imidazoline (1) in the presence of suitable palladium(II) precursors. The acyclic complex 2 was formed by ligand exchange using the mononuclear precursor [PdCl2(PPh3)2] and the palladacycle 3 was formed by cleavage of the dinuclear chloro‐bridged precursor [Pd(μ‐Cl)(dmba)]2. The new NHC precursor 1‐benzyl‐4,5‐dicyano‐2‐(pentafluorophenyl)‐3‐picolylimidazoline (5) was formed by condensation of pentafluorobenzaldehyde with N‐benzyl‐N′‐picolyldiaminomaleonitrile (4). The NHC palladacycle [PdCl2{(CN)2IBzPic}] (6) ({(CN)2IBzPic}: 1‐benzyl‐4,5‐dicyano‐3‐picolylimidazol‐2‐ylidene) was prepared by in situ thermolysis of 5 in the presence of [PdCl2(PhCN)2]. The three palladium(II) complexes were characterized by NMR and IR spectroscopy, mass spectrometry and elemental analysis. In addition, the molecular structures of 2 and 3 were determined by X‐ray diffraction. The π‐acidity of (CN)2IBzPic was compared with (CN)2IMes and perviously reported π‐acidic imidazol‐2‐ylidenes by NBO analysis. The Mizoroki–Heck (MH) reactions of various aryl halides with n‐butyl acrylate were performed in the presence of complexes 2, 3 and 6. The new precatalysts showed high activity in the MH reactions giving good‐to‐excellent product yields with 0.1 mol‐% precatalyst. The nature of the catalytically active species of 2, 3 and 6 was investigated by poisoning experiments with mercury and transmission electron microscopy. It was found that palladium nanoparticles formed from the precatalysts were involved in the catalytic process.