bluuebunny/crossref_metadata_2025_split huggingface dataset:
19F NMR Spectroscopy Tagging and Paramagnetic Relaxation Enhancement‐Based Conformation Analysis of Intrinsically Disordered Protein Complexes
Authors: Somlyay Máté , Ledolter Karin , Kitzler Manuel , Sandford Graham , Cobb Steven L. , Konrat Robert 
Published: September 2019

AbstractThe combination of 19F NMR spectroscopy tagging and paramagnetic relaxation enhancement (PRE) NMR spectroscopy experiments was evaluated as a versatile method to probe protein–protein interactions and conformational changes of intrinsically disordered proteins upon complex formation. The feasibility of the approach is illustrated with an application to the Myc‐Max protein complex; this is an oncogenic transcription factor that binds enhancer box DNA fragments. The single cysteine residue of Myc was tagged with highly fluorinated [19F]3,5‐bis(trifluoromethyl)benzyl bromide. Structural dynamics of the protein complex were monitored through intermolecular PREs between 19F‐Myc and paramagnetic (1‐oxyl‐2,2,5,5‐tetramethyl‐Δ3‐pyrroline‐3‐methyl)methanethiosulfonate (MTSL)‐tagged) Max. The 19F R2 relaxation rates obtained with three differently MTSL‐tagged Max mutants revealed novel insights into the differential structural dynamics of Myc‐Max bound to DNA and the tumour suppressor breast cancer antigen 1. Given its ease of implementation, fruitful applications of this strategy to structural biology and inhibitor screening can be envisaged.
Optimization of the Inverted Emulsion Method for High‐Yield Production of Biomimetic Giant Unilamellar Vesicles
Authors: Moga Akanksha , Yandrapalli Naresh , Dimova Rumiana , Robinson Tom 
Published: September 2019

AbstractIn the field of bottom‐up synthetic biology, lipid vesicles provide an important role in the construction of artificial cells. Giant unilamellar vesicles (GUVs), due to their membrane's similarity to natural biomembranes, have been widely used as cellular mimics. So far, several methods exist for the production of GUVs with the possibility to encapsulate biological macromolecules. The inverted emulsion‐based method is one such technique, which has great potential for rapid production of GUVs with high encapsulation efficiencies for large biomolecules. However, the lack of understanding of various parameters that affect production yields has resulted in sparse adaptation within the membrane and bottom‐up synthetic biology research communities. Here, we optimize various parameters of the inverted emulsion‐based method to maximize the production of GUVs. We demonstrate that the density difference between the emulsion droplets, oil phase, and the outer aqueous phase plays a crucial role in vesicle formation. We also investigated the impact that centrifugation speed/time, lipid concentration, pH, temperature, and emulsion droplet volume has on vesicle yield and size. Compared to conventional electroformation, our preparation method was not found to significantly alter the membrane mechanical properties. Finally, we optimize the parameters to minimize the time from workbench to microscope and in this way open up the possibility of time‐sensitive experiments. In conclusion, our findings will promote the usage of the inverted emulsion method for basic membrane biophysics studies as well as the development of GUVs for use as future artificial cells.
Catalytic CO2 Reduction with Boron‐ and Aluminum Hydrides
Authors: Franz Daniel , Jandl Christian , Stark Claire , Inoue Shigeyoshi 
Published: September 2019

AbstractThe previously reported dimeric NHI aluminum dihydrides 1 a,b, as well as the bis(NHI) aluminum dihydride salt 9+[OTs]−, the bis(NHI) boron dihydride salt 10+[OTs]−, and the “free” bis(NHI) ligand 12 were investigated with regard to their activity as a homogenous (pre)catalyst in the hydroboration (i. e. catalytic reduction) of carbon dioxide (CO2) in chloroform under mild conditions (i. e. room temperature, 1 atm; NHI=N‐heterocyclic imine, Ts=tosyl). Borane dimethylsulfide complex and catecholborane were used as a hydride source. Surprisingly, the less sterically hindered 1 a exhibited lower catalytic activity than the bulkier 1 b. A similarly unexpected discrepancy was found with the lower catalytic activity of 10+ in comparison to the one of the bis(NHI) 12. The latter is incorporated as the ligand to the boron center in 10+. To elucidate possible mechanisms for CO2 reduction the compounds were subjected to stoichiometric reactivity studies with the borane or CO2. Aluminum carboxylates 4, 6, and 7+ with two, four, and one formate group per two aluminum centers were isolated. Also, the boron formate salt 11+[OTs]− was characterized. Selected metal formates were subjected to stoichiometric reactions with boranes and/or tested as a catalyst. We conclude that each type of catalyst (1 a,b, 9+, 10+, 12) follows an individual mechanistic pathway for CO2 reduction.
Solving the Catalytic Mechanism of Tryptophan Synthase: an Emergent Drug Target in the Treatment of Tuberculosis
Authors: Teixeira Carla S. Silva , Ramos Maria J. , Sousa Sérgio F. , Cerqueira Nuno M. F. S. A. 
Published: September 2019

AbstractTryptophan Synthase (TSase) is an emergent therapeutic target in the treatment of tuberculosis. Interest in TSase as a drug target arose from the fact that this enzyme is not present in humans, while in bacteria, like M. tuberculosis, it catalyses the last two steps in the tryptophan biosynthetic pathway. Several inhibitors of TSase have recently been developed, with promising results. However, the exact catalytic mechanism of this enzyme has remained unexplained at the atomic level. The fact that TSase is a multifunctional enzyme, with two dimers, each one with two independent active sites, interconnected by a 25 Å tunnel, has made it a challenging enzyme, from the catalytic point of view. QM/MM calculations were used to analyze and explain the two steps catalyzed by this enzyme. The results provide an atomic‐level clarification of the full catalytic mechanism of this enzyme, offering also important clues for the development of new inhibitors against tuberculosis.
The Ampoule Method: A Pathway towards Controllable Synthesis of Electrocatalysts for Water Electrolysis
Authors: Zhao Yongqiang , Jin Bo , Vasileff Anthony , Shi Bingyang , Jiao Yan , Qiao Shi‐Zhang 
Published: September 2019

AbstractThe ampoule method provides a promising pathway towards the controllable synthesis of novel electrocatalysts for water electrolysis due to its straightforward manipulation of reaction conditions, accessible experimental design, and controlled environment. This Concept introduces the development of the ampoule method and anticipates its application in electrocatalyst synthesis for water electrolysis. First, the history, device configuration, and merits of the ampoule method are briefly introduced. Afterwards, typical materials synthesized by the ampoule method are discussed. Then, recent process in applying the ampoule method to synthesize electrocatalysts for water electrolysis is highlighted. Finally, opportunities and potentials of this method in facilitating electrocatalyst synthesis for water electrolysis are discussed.
The Effects of Exposed Specific Facets and Sulfation on the Surface Acidity of Cu2O Solids
Authors: Wu Yanan , Huang Daofeng , Fu Yingyi , Zhang Li , Liu Shixi , Tang Gangfeng , Ren Yuanhang , Ye Lin , Chen Xueying , Yue Bin , He Heyong 
Published: September 2019

AbstractCuprous oxide microcrystals with {111}, {111}/{100}, and {100} exposed facets were synthesized. 31P MAS NMR using trimethylphosphine as the probe molecule was employed to study the acidic properties of samples. It was found that the total acidic density of samples increases evidently after sulfation compared with the pristine cuprous oxide microcrystals. During sulfation, new {100} facets are formed at the expense of {111} facets and lead to the generation of two Lewis acid sites due to the different binding states of SO42− on {111} and {100} facets. Moreover, DFT calculation was used to illustrate the binding models of SO42− on {111} and {100} facets. Also, a Pechmann condensation reaction was applied to study the acidic catalytic activity of these samples. It was found that the sulfated {111} facet has better activity due to its higher Lewis acid density compared with the sulfated {100} facet.
Tunable Fullerene Affinity of Cages, Bowls and Rings Assembled by PdII Coordination Sphere Engineering
Authors: Chen Bin , Horiuchi Shinnosuke , Holstein Julian J. , Tessarolo Jacopo , Clever Guido H. 
Published: September 2019

AbstractFor metal‐mediated host compounds, the development of strategies to reduce symmetry and introduce multiple functionalities in a non‐statistical way is a challenging task. We show that the introduction of steric stress around the coordination environment of square‐planar PdII cations and bis‐monodentate nitrogen donor ligands allows to control the size and shape of the assembled product, from [Pd2L4] cages over [Pd2L3] bowl‐shaped structures to [Pd2L2] rings. Therefore, banana‐shaped ligand backbones were equipped with pyridines, two different quinoline isomers and acridine, the latter three introducing steric congestion through hydrogen substituents on annelated benzene rings. Differing behavior of the four resulting hosts towards the binding of C60 and C70 fullerenes was studied and related to structural differences by NMR spectroscopy, mass spectrometry and single crystal X‐ray diffraction. The three cages based on pyridine, 6‐quinoline or 3‐quinoline donors were found to either bind C60, C70 or no fullerene at all.
Twisting the TAPPs: Bay‐Substituted Non‐planar Tetraazapero‐pyrenes and their Reduced Anions
Authors: Günther Benjamin A. R. , Höfener Sebastian , Zschieschang Ute , Wadepohl Hubert , Klauk Hagen , Gade Lutz H. 
Published: September 2019

AbstractA new synthesis of tetraazaperopyrenes (TAPPs) starting from a halogenated perylene derivative 3,4,9,10‐ tetrabromo‐1,6,7,12‐tetrachloroperylene (1) gave access to bay‐substituted TAPPs for the first time. Selective lithiation of the bromine‐positions and subsequent addition of tosyl azide led to the formation of the tetraazidotetrachloroperylene (2), which was subsequently reduced by addition of sodium borohydride to the corresponding tetraaminotetrachloroperylene (3). Oxidation to its semiquinoidal form 4 and subsequent cyclization with acid chlorides gave rise to a series of bay‐chlorinated TAPPs. Whereas the aromatic core of the previously studied ortho‐substituted TAPPs was found to be planar, the steric pressure of the two chlorine substituents on each side leads to the twist of the peropyrene core of approximately 30 degrees, a structural feature also observed in other bay‐substituted perylene derivatives. An experimental and computational analysis reveals that introducing chloride substituents at these positions leads to slightly increased electron affinities (EA) enabling the selective generation and characterization of the reduced mono‐anionic radicals and closed shell di‐anionic species. These anions were isolated and characterized by UV/Vis spectroscopy and EPR or NMR, respectively. Processing of the bay‐chlorinated TAPPs in n‐channel organic TFTs revealed electron mobilities of 0.001 to 0.003 cm2 V−1 s−1. These reduced electron mobilities compared to the ortho‐halogenated TAPPs are thought to be rooted in the less densely packed solid‐state structures.
Synthesis of Anthracene Derivatives with Azaacene‐Containing Iptycene Wings and the Utilization as a Dopant for Solution‐Processed Organic Light‐Emitting Diodes
Authors: Hayashi Hironobu , Kato Yuki , Matsumoto Akinobu , Shikita So , Aizawa Naoya , Suzuki Mitsuharu , Aratani Naoki , Yasuda Takuma , Yamada Hiroko 
Published: September 2019

AbstractSubstituted acene derivatives are regarded as promising materials for organic electronic devices such as organic light‐emitting diodes (OLEDs). In particular, anthracene derivatives are known to exhibit good fluorescence property, with the air stability and solubility in common organic solvents expected to give advantages for solution‐processed device fabrication. In this study, a series of bistriisopropylsilyl(TIPS)ethynyl anthracene derivatives with azaacene‐containing iptycene wings have been synthesized by using condensation reactions. Effects of size of azaacenes on optical properties and packing structures were investigated. UV/Vis absorption and fluorescence spectra indicate that the π‐elongation of iptycene units has small effects on the overall π‐system, which is also supported by electrochemical measurements. Secondly, single‐crystal X‐ray analysis implies that the molecules likely have interactions with the iptycene units of adjacent molecules, while the iptycene wings and TIPSethynyl groups can prevent the central anthracene unit from undesirable non‐radiative energy loss. Finally, the most emissive derivative was used as a dopant for solution‐processed OLEDs, showing obvious electroluminescence with a luminance of over 920 cd m−2.
Computer Modelling and Synthesis of Deoxy and Monohydroxy Analogues of a Ribitylaminouracil Bacterial Metabolite that Potently Activates Human T Cells
Authors: Ler Geraldine J. M. , Xu Weijun , Mak Jeffrey Y. W. , Liu Ligong , Bernhardt Paul V. , Fairlie David P. 
Published: September 2019

Abstract5‐(2‐Oxopropylideneamino)‐6‐d‐ribitylaminouracil (5‐OP‐RU) is a natural product formed during bacterial synthesis of vitamin B2. It potently activates mucosal associated invariant T (MAIT) cells and has immunomodulatory, inflammatory, and anticancer properties. This highly polar and unstable compound forms a remarkably stable Schiff base with a lysine residue in major histocompatibility complex class I–related protein (MR1) expressed in antigen‐presenting cells. Inspired by the importance of the ribityl moiety of 5‐OP‐RU for binding to both MR1 and the T cell receptor (TCR) on MAIT cells, each OH was removed in silico. DFT calculations and MD simulations revealed a very stable hydrogen bond between the C3′−OH and uracil N1H, which profoundly restricts flexibility and positioning of each ribityl‐OH, potentially impacting their interactions with MR1 and TCR. By using deoxygenation strategies and kinetically controlled imine formation, four monodeoxyribityl and four monohydroxyalkyl analogues of 5‐OP‐RU were synthesised as new tools for probing T cell activation mechanisms.
Synthesis of Functionalized Tetrahydropyridines by SnCl4‐Mediated [4+2] Cycloaddition between Donor–Acceptor Cyclobutanes and Nitriles
Authors: Tong David , Wu Jackie , Bazinski Nathan , Koo Donghyun , Vemula Naresh , Pagenkopf Brian L. 
Published: September 2019

AbstractCycloadditions of strained carbocycles promoted by Lewis acids are powerful methods to construct heterocyclic frameworks. In fact, the formal [3+2] cycloadditions of donor–acceptor (DA) cyclopropanes with nitriles has seen particular success in synthesis. In this work, we report on the first [4+2] cycloaddition of nitriles with DA cyclobutanes by Lewis acid activation. Tetrahydropyridine derivatives were obtained in up to 91 % yield from various aryl‐activated cyclobutane diesters and aliphatic or aromatic nitriles.
Pep‐Lipid Cubosomes and Vesicles Compartmentalized by Micelles from Self‐Assembly of Multiple Neuroprotective Building Blocks Including a Large Peptide Hormone PACAP‐DHA
Authors: Angelova Angelina , Drechsler Markus , Garamus Vasil M. , Angelov Borislav 
Published: September 2019

AbstractStructural control over design and formation of self‐assembled nanomaterials for neuroprotection and neuroregeneration is crucial for their application in nanomedicine. Here a synthetic construct of the pituitary adenylate cyclase‐activating polypeptide (PACAP38) coupled to a docosahexaenoic acid (DHA: an ω‐3 polyunsaturated fatty acid (PUFA)) is designed towards the creation of compartmentalized liquid crystalline assemblies of neuroprotective compounds. The hormone PACAP38 is a ligand of the class B PAC1 G‐protein‐coupled receptor (GPCR), whereas DHA is a lipid trophic factor. The lipidated peptide PACAP‐DHA is co‐assembled into hierarchical nanostructures elaborated from hybrid vesicle‐micelle reservoirs as well into PEGylated cubosomes composed of multiple neuroprotective building blocks. The resulting nanostructures are determined by synchrotron small‐angle X‐ray scattering (BioSAXS) and cryogenic transmission electron microscopy (cryo‐TEM). Multicompartment topologies are obtained in a two‐fold approach: (i) intriguing compartmentalized vesicles, which embed pep‐lipid micelles forming nanopatterns, and (ii) multidomain pep‐lipid cubosomes. Both kinds of topologies are favorable for sustained‐release applications in combination therapies of neurodegeneration. The organizational complexity of the scaffolds involving the lipidated high‐molecular weight peptide hormone is beyond the one that has been reached with small lipid‐like peptide surfactants.
Building Blocks for High‐Efficiency Organic Photovoltaics: Interplay of Molecular, Crystal, and Electronic Properties in Post‐Fullerene ITIC Ensembles
Authors: Swick Steven M. , Gebraad Tim , Jones Leighton , Fu Bo , Aldrich Thomas J. , Kohlstedt Kevin L. , Schatz George C. , Facchetti Antonio , Marks Tobin J. 
Published: September 2019

AbstractAccurate single‐crystal X‐ray diffraction data offer a unique opportunity to compare and contrast the atomistic details of bulk heterojunction photovoltaic small‐molecule acceptor structure and packing, as well as provide an essential starting point for computational electronic structure and charge transport analysis. Herein, we report diffraction‐derived crystal structures and computational analyses on the n‐type semiconductors which enable some of the highest efficiency organic solar cells produced to date, 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene (ITIC) and seven derivatives (including three new crystal structures: 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐propylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene (ITIC‐C3), 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(3‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene (m‐ITIC‐C6), and 3,9‐bis(2‐methylene‐((3‐(1,1‐dicyanomethylene)‐6,7‐difluoro)‐indanone))‐5,5,11,11‐tetrakis(4‐butylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene (ITIC‐C4‐4F). IDTT acceptors typically pack in a face‐to‐face fashion with π–π distances ranging from 3.28–3.95 Å. Additionally, edge‐to‐face packing is observed with S⋯π interactions as short as 3.21–3.24 Å. Moreover, ITIC end group identities and side chain substituents influence the nature and strength of noncovalent interactions (e. g. H‐bonding, π–π) and thus correlate with the observed packing motif, electronic structure, and charge transport properties of the crystals. Density functional theory (DFT) calculations reveal relatively large nearest‐neighbor intermolecular π‐π electronic couplings (5.85–56.8 meV) and correlate the nature of the band structure with the dispersion interactions in the single crystals and core–end group polarization effects. Overall, this combined experimental and theoretical work reveals key insights into crystal engineering strategies for indacenodithienothiophene (IDTT) acceptors, as well as general design rules for high‐efficiency post‐fullerene small molecule acceptors.
Modified Graphitic Carbon Nitride Nanosheets for Efficient Photocatalytic Hydrogen Evolution
Authors: Zhou Xunfu , Zhu Yating , Gao Qiongzhi , Zhang Shengsen , Ge Chunyu , Yang Siyuan , Zhong Xinhua , Fang Yueping 
Published: September 2019

AbstractConsiderable research efforts have been devoted to develop noble‐metal‐free cocatalysts coupled with semiconductors for highly efficient photocatalytic H2 evolution as part of the challenge toward solar‐to‐fuel conversion. Herein, a new cocatalyst with excellent activity in the electrocatalytic H2 evolution reaction (HER) that is based on Co sheathed in N‐doped graphitic carbon nanosheets (Co@NC) was fabricated by a surfactant‐assisted pyrolysis approach and then coupled with g‐C3N4 nanosheets to construct a 2 D‐2 D g‐C3N4/Co@NC composite photocatalyst by a simple grinding method. As a result of advantages in effective electrocatalytic HER activity, suitable electronic band structure, and rapid interfacial charge transfer brought about by the 2 D‐2 D spatial configuration, the g‐C3N4/Co@NC photocatalyst that contained 4 wt % Co@NC presented a high photocatalytic H2 generation rate of 15.67 μmol h−1 under visible‐light irradiation (λ≥400 nm), which was 104.5 times higher than that of pristine g‐C3N4. The optimum g‐C3N4/Co@NC photocatalyst showed a high apparent quantum efficiency of 10.82 % at λ=400 nm.
Community carbon and water exchange responses to warming and precipitation enhancement in sandy grassland along a restoration gradient
Authors: Luo Yayong , Zuo Xiaoan , Li Yulin , Zhang Tonghui , Zhang Rui , Chen Juanli , Lv Peng , Zhao Xueyong 
Published: September 2019

AbstractTemperature increasing and precipitation alteration are predicted to occur in arid and semiarid lands; however, the response mechanism of carbon and water exchange at community level is still unclear in semiarid sandy land. We investigated the responses of carbon and water exchanges to warming and precipitation enhancement along a sand dune restoration gradient: mobile sand dunes (MD), semifixed sand dunes (SFD), and fixed sand dunes (FD). The average net ecosystem productivity (NEP) and evapotranspiration (ET) between May and August increased by 98% and 59%, respectively, from MD to SFD, while they had no significant differences between FD and the other two habitats. Warming inhibited ecosystem NEP, ET, and water use efficiency (WUE) by 69%, 49% (p < .001), and 80%, respectively, in SFD, while it nearly had no significant effects in MD and FD. However, precipitation addition by 30% nearly had no significant effects on community NEP, ET, and WUE, except for warming treatment in FD. In general, precipitation addition of 30% may still not be enough to prevent drought stress for growth of plants, due to with low water holding capacity and high evaporation rates in sandy land. Temperature increase magnified drought stress as it increased evapotranspiration rates especially in summer. In addition, community NEP, ET, and WUE were usually influenced by interactions between habitats and temperature, as well as the interactions among habitats, temperature, and precipitation. Species differences in each habitat along the restoration gradient may alter climate sensitivity of sandy land. These results will support in understanding and the prediction of the impacts of warming and precipitation change in semiarid sandy grassland.