bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cascade Olefin Isomerization/Intramolecular Diels–Alder Reaction Catalyzed by N‐Heterocyclic Carbenes
Authors: Kowalczyk Marcin , Lupton David W. 
Published: April 2014

AbstractThe addition of an N‐heterocyclic carbene to the carbonyl group of an α,β,γ,δ‐unsaturated enol ester affords a hemiacetal azolium intermediate that enables a cascade olefin isomerization/Diels–Alder reaction, for which mechanistic studies implicate Lewis base catalysis. Preliminary studies into the utility of the products have been undertaken with reductive and oxidative cleavage, giving materials for potential use in complex‐target synthesis.
Gold‐Catalyzed Synthesis of Functionalized Pyridines by Using 2H‐Azirines as Synthetic Equivalents of Alkenyl Nitrenes
Authors: Prechter Agnes , Henrion Guilhem , Faudot dit Bel Pierre , Gagosz Fabien 
Published: April 2014

Abstract2H‐Azirines are easily synthesized from the corresponding ketones and, despite possessing a CN bond embedded in a strained three‐membered cycle, they are sufficiently stable to be isolated, stored, and manipulated. 2H‐Azirines can be regarded as valuable synthetic equivalents of alkenyl nitrenes, however, reactions capitalizing on the cyclic strain of the heterocyclic motif and involving the cleavage of the CN single bond remain surprisingly limited. A gold‐catalyzed reaction that allows the formation of polysubstituted functionalized pyridines from easily accessible 2‐propargyl 2H‐azirine derivatives was developed. This transformation, which corresponds to an unprecedented intramolecular transfer of an alkenyl nitrene to an alkyne, proceeds with low catalyst loading, is efficient, and exhibits a high functional‐group tolerance and a wide substrate scope.
CH Bond Functionalization through Intramolecular Hydride Transfer
Authors: Haibach Michael C. , Seidel Daniel 
Published: April 2014

AbstractKnown for over a century, reactions that involve intramolecular hydride‐transfer events have experienced a recent resurgence. Undoubtedly responsible for the increased interest in this research area is the realization that hydride shifts represent an attractive avenue for CH bond functionalization. The redox‐neutral nature of these complexity‐enhancing transformations makes them ideal for sustainable reaction development. This Review summarizes recent progress in this field while highlighting key historical contributions.
Construction of a Live‐Attenuated HIV‐1 Vaccine through Genetic Code Expansion
Authors: Wang Nanxi , Li Yue , Niu Wei , Sun Ming , Cerny Ronald , Li Qingsheng , Guo Jiantao 
Published: April 2014

AbstractA safe and effective vaccine against human immunodeficiency virus type 1 (HIV‐1) is urgently needed to combat the worldwide AIDS pandemic, but still remains elusive. The fact that uncontrolled replication of an attenuated vaccine can lead to regaining of its virulence creates safety concerns precluding many vaccines from clinical application. We introduce a novel approach to control HIV‐1 replication, which entails the manipulation of essential HIV‐1 protein biosynthesis through unnatural amino acid (UAA*)‐mediated suppression of genome‐encoded blank codon. We successfully demonstrate that HIV‐1 replication can be precisely turned on and off in vitro.
Specroelectrochemical, switching kinetics, and chronoamperometric studies of dibenzyl derivative of poly(3,4‐propylenedioxythiophene) thin‐film‐based electrochromic device
Authors: Lakshmanan Raja , Raja Palani Prabhu , Shivaprakash Narayanapura Channegowda , Nair Sindhu Sukumaran 
Published: April 2014

ABSTRACTThe dibenzyl derivative of poly(3,4‐propylenedioxythiophene) (PProDOT‐Bz2) thin film is deposited onto ITO‐coated glass substrate by electropolymerization technique. The electropolymerization of ProDOT‐Bz2 is carried out by a three‐electrode electrochemical cell. The cyclic voltammogram shows the redox properties of electrochemically prepared films deposited at different scan rates. The thin films prepared were characterized for its morphological properties to study the homogeniety. Classic six‐layer structure of PProDOT‐Bz2 electrochromic device using this material was fabricated and reported for the first and its characterizations such as spectroelectrochemical, switching kinetics, and chronoamperometric studies are performed. The color contrast of the thin film and the device achieved are 64 and 40%, respectively, at λmax (628 nm). The switching time is recorded and the observed values are 5 s from the coloring state to the bleaching state and vice versa. The chronoamperometry shows that the device performed up to 400 cycles, and it is capable of working up to 35 cycles without any degradation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40717.
Polyols and polyurethane foams from acid‐catalyzed biomass liquefaction by crude glycerol: Effects of crude glycerol impurities
Authors: Hu Shengjun , Li Yebo 
Published: April 2014

ABSTRACTThe effects of crude glycerol impurities on acid‐catalyzed biomass liquefaction by crude glycerol were investigated. Salts (i.e., NaCl and Na2SO4) decreased biomass conversion ratios and negatively affected the properties of polyols produced. Regression models were developed and validated as appropriate for describing the relationships between organic impurities and biomass conversion ratios and between organic impurities and the hydroxyl number of polyols. Polyols produced from crude glycerol containing 0–45% organic impurities showed the hydroxyl number varying from 1301 to 700 mg KOH/g, acid number from 19 to 28 mg KOH/g, viscosity from 2.4 to 29.2 Pa s, and molecular weight (Mw) from 244 to 550 g/mol. Crude glycerol containing 40–50 wt % of organic impurities was suitable to produce polyols with suitable properties for rigid and/or semi‐rigid polyurethane (PU) foam applications. The produced PU foams showed density and compressive strength comparable to those derived from petrochemical solvent‐based liquefaction processes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40739.
Friction and wear properties of dumbbell‐shaped jute fiber‐reinforced friction materials
Authors: Ma Yunhai , Liu Yucheng , Ma Shengsheng , Wang Hubiao , Gao Zhihui , Sun Junjie , Tong Jin , Guo Li 
Published: April 2014

ABSTRACTThe surfaces of jute fibers (Corchorus capsularis L.) were processed to have different dumbbell‐shaped spacing (5 mm, 10 mm, 15 mm, and 20 mm), and the physical properties of the modified surfaces of the jute fibers were evaluated in this study. The dumbbell‐shaped jute fiber (DJF)‐reinforced friction materials were prepared through compression mold. The friction and wear performance of the DJF were tested using a friction material tester at constant speed. The results showed that the dumbbell‐shaped spacing has less influence on the friction coefficients of friction materials. The friction coefficients of DJF have bigger fluctuation compared with that of straight fiber during the temperature‐increasing procedure. The wear rate of DJF with dumbbell‐shaped spacing of 15 mm was the lowest, except for that when the temperatures were about 200–250°C. Morphologies of wear surfaces of DJF were observed using scanning electron microscopy and the friction characteristics were analyzed. The results showed that reinforced with DJFs in the friction materials can reduce the specific wear rate and the variation in friction coefficient compared with that of straight jute fibers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40748.
Facile Synthesis of Ultrathin Lepidocrocite Nanosheets from Layered Precursors
Authors: Yang Yijun , Zhong Yeteng , Wang Xi , Ma Ying , Yao Jiannian 
Published: April 2014

AbstractUltrathin two‐dimensional nanosheets have been widely studied because of their peculiar properties and promising applications. As a typical layered material, successful exfoliation of freestanding ultrathin lepidocrocite (γ‐FeOOH) nanosheets from the bulk material has not been reported to date. Herein, we report a facile synthetic route to prepare ultrathin lepidocrocite nanosheets with a thickness of approximately 2–3 nm from FeOx–propanediol layered precursors through weakening of the hydrogen bonds during the crystallization process. The ultrathin morphology and single‐crystal structure of the nanosheets were confirmed by transmission electron microscopy, X‐ray diffraction, and atomic force microscopy. The formation process of these nanosheets demonstrated simultaneous exfoliation and crystallization of lepidocrocite in basic aqueous solution. The obtained ultrathin nanosheets exhibited a much lower Néel temperature (18.3 K) than bulk lepidocrocite and weak ferromagnetic behavior below this temperature.
Fibroblast growth factor signaling and inhibition in non‐small cell lung cancer and their role in squamous cell tumors
Authors: Salgia Ravi 
Published: April 2014

AbstractWith the introduction of targeted agents primarily applicable to non‐small cell lung cancer (NSCLC) of adenocarcinoma histology, there is a heightened unmet need in the squamous cell carcinoma population. Targeting the angiogenic fibroblast growth factor (FGF)/FGF receptor (FGFR) signaling pathway is among the strategies being explored in squamous NSCLC; these efforts are supported by growth‐promoting effects of FGF signaling in preclinical studies (including interactions with other pathways) and observations suggesting that FGF/FGFR‐related aberrations may be more common in squamous versus adenocarcinoma and other histologies. A number of different anti‐FGF/FGFR approaches have shown promise in preclinical studies. Clinical trials of two multitargeted tyrosine kinase inhibitors are restricting enrollment to patients with squamous NSCLC: a phase I/II trial of nintedanib added to first‐line gemcitabine/cisplatin and a phase II trial of ponatinib for previously treated advanced disease, with the latter requiring not only squamous disease but also a confirmed FGFR kinase amplification or mutation. There are several ongoing clinical trials of multitargeted agents in general NSCLC populations, including but not limited to patients with squamous disease. Other FGF/FGFR‐targeted agents are in earlier clinical development. While results are awaited from these clinical investigations in squamous NSCLC and other disease settings, additional research is needed to elucidate the role of FGF/FGFR signaling in the biology of NSCLC of different histologies.
Interesse von Jugendlichen an Naturwissenschaften
Authors: Dierks Pay Ove , Höffler Tim , Parchmann Ilka 
Published: April 2014

AbstractInteresse ist von großer Bedeutung für die Lernmotivation und die spätere Studien‐ oder Berufswahl. In diesem Beitrag wird der aktuelle Stand der Forschung zum Interesse allgemein und spezifisch an den Naturwissenschaften dargelegt. Ergänzend wird eine Adaption des „RIASEC‐Modells“ nach John L. Holland zur Charakterisierung von Interessen in den Naturwissenschaften vorgestellt. Darauf aufbauend gibt dieser Beitrag einen zusammenfassenden Überblick über Ansätze schulischer und außerschulischer Förderangebote.
Stereoselective Reduction of 1‐O‐Isopropyloxygenipin Enhances Its Neuroprotective Activity in Neuronal Cells from Apoptosis Induced by Sodium Nitroprusside
Authors: Wang Rikang , Yang Jian , Liao Sufen , Xiao Gaokeng , Luo Jun , Zhang Lang , Little Peter J. , Chen Heru , Zheng Wenhua 
Published: April 2014

AbstractGenipin is a Chinese herbal medicine with both neuroprotective and neuritogenic activity. Because of its unstable nature, efforts have been to develop more stable genipin derivatives with improved biological activities. Among the new compounds reported in the literature, (1R)‐isopropyloxygenipin (IPRG001) is a more stable but less active compound compared with the parent, genipin. Here, two new IPRG001 derivatives generated by stereoselective reduction of the C6=C7 double bond were synthesized. The 1R and 1S isomers of (4aS,7S,7aS)‐methyl‐7‐(hydroxymethyl)‐1‐isopropoxy‐1,4a,5,6,7,7a‐hexahydrocyclopenta[c]pyran‐4‐carboxylate (CHR20 and CHR21) were shown to be very stable both in high‐glucose cell culture medium and in mice serum at 37 °C. Evaluation using an MTT assay and Hoechst staining showed that CHR20 and CHR21 promote the survival of rat adrenal pheochromocytoma (PC12) and retinal neuronal (RGC‐5) cells from injury induced by sodium nitroprusside (SNP). The neuroprotective effects of CHR20 and CHR21 were greater than both isomers of IPRG001, the parent compounds. These results indicate that reduction of 1‐O‐isopropyloxygenipin enhances its neuroprotective activity without affecting its stability.
Synthesis and Biological Evaluation of Imidazo[2,1‐b][1,3,4]thiadiazole‐Linked Oxindoles as Potent Tubulin Polymerization Inhibitors
Authors: Kamal Ahmed , Rao M. P. Narasimha , Das Pompi , Swapna P. , Polepalli Sowjanya , Nimbarte Vijaykumar D. , Mullagiri Kishore , Kovvuri Jeshma , Jain Nishant 
Published: April 2014

AbstractA series of imidazo[2,1‐b][1,3,4]thiadiazole‐linked oxindoles composed of an A, B, C and D ring system were synthesized and investigated for anti‐proliferative activity in various human cancer cell lines; test compounds were variously substituted at rings C and D. Among them, compounds 7 ((E)‐5‐fluoro‐3‐((6‐p‐tolyl‐2‐(3,4,5‐trimethoxyphenyl)‐imidazo[2,1‐b][1,3,4]thiadiazol‐5‐yl)methylene)indolin‐2‐one), 11 ((E)‐3‐((6‐p‐tolyl‐2‐(3,4,5‐trimethoxyphenyl)imidazo[2,1‐b][1,3,4]thiadiazol‐5‐yl)methylene)indolin‐2‐one), and 15 ((E)‐6‐chloro‐3‐((6‐phenyl‐2‐(3,4,5‐trimethoxyphenyl)imidazo[2,1‐b][1,3,4]thiadiazol‐5‐yl)methylene)indolin‐2‐one) exhibited potent anti‐proliferative activity. Treatment with these three compounds resulted in accumulation of cells in G2/M phase, inhibition of tubulin assembly, and increased cyclin‐B1 protein levels. Compound 7 displayed potent cytotoxicity, with an IC50 range of 1.1–1.6 μM, and inhibited tubulin polymerization with an IC50 value (0.15 μM) lower than that of combretastatin A‐4 (1.16 μM). Docking studies reveal that compounds 7 and 11 bind with αAsn101, βThr179, and βCys241 in the colchicine binding site of tubulin.
The Integrin Ligand c(RGDf(NMe)Nal) Reduces Neointimal Hyperplasia in a Polymer‐Free Drug‐Eluting Stent System
Authors: Rechenmacher Florian , Steigerwald Kristin , Laufer Burkhardt , Neubauer Stefanie , Kapp Tobias G. , Li Liang , Mas‐Moruno Carlos , Joner Michael , Kessler Horst 
Published: April 2014

AbstractThe use of highly active and selective integrin ligands in combination with stent implantation is emerging as a promising alternative to the release of classical immunosuppressive drugs by current drug‐eluting stents (DES), which has been associated with delayed vascular healing and late stent thrombosis. Herein we present the development and biological evaluation of the integrin ligand c(RGDf(NMe)Nal) as a potent anti‐proliferative molecule that targets coronary artery smooth muscle cells (CASMCs). This peptide showed an antagonistic activity for αvβ3 and αvβ5 in the low‐nanomolar range, and selectivity against the platelet receptor αIIbβ3. In vitro, it efficiently inhibited the proliferation of CASMCs, displaying higher potency than the anti‐tumor drug candidate cilengitide. This peptide was then loaded into a polymer‐free bare metal stent (BMS), and its release studied at different time points. Up to seven days of elution, the peptide‐coated stents retained high anti‐proliferative activity toward CASMCs. Finally, the peptide was examined in vivo in a polymer‐free DES system in a rabbit iliac artery model. After 28 days of implantation, histopathological analysis revealed that the peptide clearly decreased neointimal growth and improved vessel healing and re‐endothelialization compared with the FDA‐approved Cypher DES. Our study shows that this type of lipophilic integrin ligand, when eluted from a polymer‐free stent system, has the potential to successfully decrease in‐stent restenosis in the absence of delayed vascular healing.
A negotiation‐based method for task allocation with time constraints in open grid environments
Authors: Kong Yan , Zhang Minjie , Ye Dayong 
Published: April 2014

SummaryThis paper addresses the task allocation problem in an open, dynamic grid environments and service‐oriented environments. In such environments, both grid/service providers and consumers can be modelled as intelligent agents. These agents can leave and enter the environment freely at any time. Task allocation under time constraints becomes a challenging issue in such environments because it is difficult to apply a central controller during the allocation process due to the openness and dynamism of the environments. This paper proposes a negotiation‐based method for task allocation under time constraints in an open, dynamic grid environment, where both consumer and provider agents can freely enter or leave the environment. In this method, there is no central controller available, and agents negotiate with each other for task allocation based only on local views. The experimental results show that the proposed method can outperform the current methods in terms of the success rate of task allocation and the total profit obtained from the allocated tasks by agents under different time constraints. Copyright © 2014 John Wiley & Sons, Ltd.
Diagnosis of the Redox Levels of TCNQF4 Compounds Using Vibrational Spectroscopy
Authors: Haworth Naomi L. , Lu Jinzhen , Vo Nguyen , Le Thanh Hai , Thompson Christopher D. , Bond Alan M. , Martin Lisandra L. 
Published: April 2014

AbstractThe vibrational spectroscopy of TCNQF40, TCNQF41− and TCNQF42− has been investigated by means of density functional theory. Band assignments in infrared and Raman spectra have been clarified and a series of diagnostics developed for redox level characterisation of TCNQF4 compounds. In the CC stretching region (1460–1600 cm−1), TCNQF40 and TCNQF41− show two bands, with the more energetic being at 1600 cm−1 in TCNQF40 and at approximately 1535 cm−1 in TCNQF41−; in TCNQF42− both modes absorb below 1500 cm−1, often merging to give a single band. In the CF and endocyclic CC stretching region (1290 and 1360 cm−1), TCNQF40 and TCNQF41− show strong bands, whereas TCNQF42− absorbs weakly or not at all. (Additional bands, e.g. from co‐crystallised solvent molecules, may complicate this region.) In the nitrile stretching region (2000–2250 cm−1), modes are highly sensitive to nitrile coordination by metal cations. All three redox levels can produce bands above 2200 cm−1, however bands below 2150 cm−1 are usually due to TCNQF42−. This sensitivity to coordination is likely to affect the spectra of many organic molecular ions.
Silver Coordination Polymers Based on p‐Cyanophenylsilanes as Ligands
Authors: Blankschein Bianca , Schulz Axel , Villinger Alexander , Wustrack Ronald 
Published: April 2014

AbstractDifferently substituted p‐cyanophenylsilanes, Me4−nSi(C6H4CN)n, (n=2, 3, 4), PhSi(C6H4CN)3, cycHexSi(C6H4CN)3 (cycHex=cyclohexyl), and MePhSi(C6H4CN)2, were prepared and fully characterized. Their coordination behavior was studied by utilizing silver salts of the type AgX (X=O3SCF3−, CO2CF3−), which led to coordination polymers. One‐dimensional chains were observed for the bidentate p‐cyanophenylsilane ligands, whereas two‐ and three‐dimensional networks, including macrometalacycles, were found for the tridentate ligand. Treatment of AgO2CCF3 with the tetradentate ligand Si(C6H4CN)4 led to the formation of a diamond‐like three‐dimensional network with two interpenetrating nets linked by bridging Ag2(CF3CO2)2 dimers. X‐ray structures show a wide range of close Ag⋅⋅⋅Ag distances in the polymers, which are dependent on the ligand and the anion utilized.
Fe3O4/Carbon Hybrid Nanoparticle Electrodes for High‐Capacity Electrochemical Capacitors
Authors: Lee Jun Seop , Shin Dong Hoon , Jun Jaemoon , Lee Choonghyeon , Jang Jyongsik 
Published: April 2014

AbstractFe3O4/carbon hybrid nanoparticles (FeCHNPs) were fabricated using dual‐nozzle electrospraying, vapor deposition polymerization (VDP), and carbonization. FeOOH nanoneedles decorated with polypyrrole (PPy) nanoparticles (FePNPs) were fabricated by electrospraying pristine PPy mixed with FeCl3 solution, followed by heating stirring reaction. A PPy coating was then formed on the FeOOH nanoneedles through a VDP process. FeCHNPs were produced through carbonization of PPy and FeOOH phase transitions. These hybrid carbon nanoparticles (NPs) were used to build electrodes of electrochemical capacitors. The specific capacitance of the FeCHNPs was 455 F g−1, which is larger than that of pristine PPy NPs (105 F g−1) or other hybrid PPy NPs. Furthermore, the FeCHNP‐based capacitors exhibited better cycle stability during charge–discharge cycling than other hybrid NP capacitors. This is because the carbon layer on the Fe3O4 surface formed a protective coating, preventing damage to the electrode materials during the charge–discharge processes. This fabrication technique is an effective approach for forming stable carbon/metal oxide nanostructures for energy storage applications.
Rapid Trifluoromethylation and Perfluoroalkylation of Five‐Membered Heterocycles by Photoredox Catalysis in Continuous Flow
Authors: Straathof Natan J. W. , Gemoets Hannes P. L. , Wang Xiao , Schouten Jaap C. , Hessel Volker , Noël Timothy 
Published: April 2014

AbstractTrifluoromethylated and perfluoroalkylated heterocycles are important building blocks for the synthesis of numerous pharmaceutical products, agrochemicals and are widely applied in material sciences. To date, trifluoromethylated and perfluoroalkylated hetero‐aromatic systems can be prepared utilizing visible light photoredox catalysis methodologies in batch. While several limitations are associated with these batch protocols, the application of microflow technology could greatly enhance and intensify these reactions. A simple and straightforward photocatalytic trifluoromethylation and perfluoroalkylation method has been developed in continuous microflow, using commercially available photocatalysts and microflow components. A selection of five‐membered hetero‐aromatics were successfully trifluoromethylated (12 examples) and perfluoroalkylated (5 examples) within several minutes (8–20 min).
Thermochromic and Piezochromic Effects of CoII–Imidazole‐Based Supramolecular Gels as Logic Gates
Authors: Jung Sung Ho , Moon Jong Hun , Lee Jin Yong , Jung Jong Hwa 
Published: April 2014

AbstractWe demonstrate that the imidazole‐based ligand 1 efficiently produces a coordination polymer gel by simple mixing with Co2+ ion. When the molar ratio of CoCl2 to ligand 1 was less < 1, a red sol was obtained, indicating the formation of an octahedral (Oh) complex species as occurs with Co(NO3)2. In contrast to G1, when the amount of CoCl2 employed was more than 1 equiv., the color of the gel changed from red to blue (G2), indicating the formation of mainly a tetrahedral (Td) complex species. The ionochromic and the piezochromic effects of imidazole‐based suprmolecular gel with Co2+ were investigated. These effects of supramolecular gel were controlled by various anions of cobalt, which are due to coordination geometric change of gels. Interestingly, the ionochromic and piezochromic effects of G1 act as AND and OR logic gates in the solid and the gel state.
Sulfur–Carbon Bond Formation through Ring‐Opening of Triazolothiadiazole with Organometallics
Authors: Othman Raja Ben , Massip Stéphane , Marchivie Mathieu , Jarry Christian , Vercouillie Johnny , Chalon Sylvie , Guillaumet Gérald , Suzenet Franck , Routier Sylvain 
Published: April 2014

AbstractAn efficient and convenient method was developed for the formation of S‐substituted thiotriazoles through an unprecedented organometallic addition and subsequent ring‐opening sequence of 3‐substituted [1,2,4]triazolo[3,4‐b][1,3,4]thiadiazole. The method is applicable to a wide range of substrates containing different functional groups and furnishes excellent yields of the corresponding N‐unsubstituted 3‐ or 5‐alkyl, aryl, alkynyl and alkenyl sulfanyl‐1,2,4‐triazole products.