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Nature Chemistry

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https://www.readbyqxmd.com/read/27995927/mechanism-of-o2-diffusion-and-reduction-in-fefe-hydrogenases
#1
Adam Kubas, Christophe Orain, David De Sancho, Laure Saujet, Matteo Sensi, Charles Gauquelin, Isabelle Meynial-Salles, Philippe Soucaille, Hervé Bottin, Carole Baffert, Vincent Fourmond, Robert B Best, Jochen Blumberger, Christophe Léger
FeFe hydrogenases are the most efficient H2-producing enzymes. However, inactivation by O2 remains an obstacle that prevents them being used in many biotechnological devices. Here, we combine electrochemistry, site-directed mutagenesis, molecular dynamics and quantum chemical calculations to uncover the molecular mechanism of O2 diffusion within the enzyme and its reactions at the active site. We propose that the partial reversibility of the reaction with O2 results from the four-electron reduction of O2 to water...
January 2017: Nature Chemistry
https://www.readbyqxmd.com/read/27995926/suppression-of-kasha-s-rule-as-a-mechanism-for-fluorescent-molecular-rotors-and-aggregation-induced-emission
#2
Hai Qian, Morgan E Cousins, Erik H Horak, Audrey Wakefield, Matthew D Liptak, Ivan Aprahamian
Although there are some proposed explanations for aggregation-induced emission, a phenomenon with applications that range from biosensors to organic light-emitting diodes, current understanding of the quantum-mechanical origin of this photophysical behaviour is limited. To address this issue, we assessed the emission properties of a series of BF2-hydrazone-based dyes as a function of solvent viscosity. These molecules turned out to be highly efficient fluorescent molecular rotors. This property, in addition to them being aggregation-induced emission luminogens, enabled us to probe deeper into their emission mechanism...
January 2017: Nature Chemistry
https://www.readbyqxmd.com/read/27995925/fusing-tetrapyrroles-to-graphene-edges-by-surface-assisted-covalent-coupling
#3
Yuanqin He, Manuela Garnica, Felix Bischoff, Jacob Ducke, Marie-Laure Bocquet, Matthias Batzill, Willi Auwärter, Johannes V Barth
Surface-assisted covalent linking of precursor molecules enables the fabrication of low-dimensional nanostructures, which include graphene nanoribbons. One approach to building functional multicomponent systems involves the lateral anchoring of organic heteromolecules to graphene. Here we demonstrate the dehydrogenative coupling of single porphines to graphene edges on the same metal substrate as used for graphene synthesis. The covalent linkages are visualized by scanning probe techniques with submolecular resolution, which directly reveals bonding motifs and electronic features...
January 2017: Nature Chemistry
https://www.readbyqxmd.com/read/27995922/lack-of-evidence-for-phase-only-control-of-retinal-photoisomerization-in-the-strict-one-photon-limit
#4
M Liebel, P Kukura
The concept of shaping electric fields to steer light-induced processes coherently has fascinated scientists for decades. Despite early theoretical considerations that ruled out one-photon coherent control (CC), several experimental studies reported that molecular responses are sensitive to the shape of the excitation field in the weak-field limit. These observations were largely attributed to the presence of rapid-decay channels, but experimental verification is lacking. Here, we test this hypothesis by investigating the degree of achievable control over the photoisomerization of the retinal protonated Schiff-base in bacteriorhodopsin, isorhodopsin and rhodopsin, all of which exhibit similar chromophores but different isomerization yields and excited-state lifetimes...
January 2017: Nature Chemistry
https://www.readbyqxmd.com/read/27995921/reticular-synthesis-of-porous-molecular-1d-nanotubes-and-3d-networks
#5
A G Slater, M A Little, A Pulido, S Y Chong, D Holden, L Chen, C Morgan, X Wu, G Cheng, R Clowes, M E Briggs, T Hasell, K E Jelfs, G M Day, A I Cooper
Synthetic control over pore size and pore connectivity is the crowning achievement for porous metal-organic frameworks (MOFs). The same level of control has not been achieved for molecular crystals, which are not defined by strong, directional intermolecular coordination bonds. Hence, molecular crystallization is inherently less controllable than framework crystallization, and there are fewer examples of 'reticular synthesis', in which multiple building blocks can be assembled according to a common assembly motif...
January 2017: Nature Chemistry
https://www.readbyqxmd.com/read/27995918/multistep-nucleation-of-nanocrystals-in-aqueous-solution
#6
N Duane Loh, Soumyo Sen, Michel Bosman, Shu Fen Tan, Jun Zhong, Christian A Nijhuis, Petr Král, Paul Matsudaira, Utkur Mirsaidov
The nucleation and growth of solids from solutions impacts many natural processes and is fundamental to applications in materials engineering and medicine. For a crystalline solid, the nucleus is a nanoscale cluster of ordered atoms that forms through mechanisms still poorly understood. In particular, it is unclear whether a nucleus forms spontaneously from solution via a single- or multiple-step process. Here, using in situ electron microscopy, we show how gold and silver nanocrystals nucleate from supersaturated aqueous solutions in three distinct steps: spinodal decomposition into solute-rich and solute-poor liquid phases, nucleation of amorphous nanoclusters within the metal-rich liquid phase, followed by crystallization of these amorphous clusters...
January 2017: Nature Chemistry
https://www.readbyqxmd.com/read/27995916/emergence-of-a-catalytic-tetrad-during-evolution-of-a-highly-active-artificial-aldolase
#7
Richard Obexer, Alexei Godina, Xavier Garrabou, Peer R E Mittl, David Baker, Andrew D Griffiths, Donald Hilvert
Designing catalysts that achieve the rates and selectivities of natural enzymes is a long-standing goal in protein chemistry. Here, we show that an ultrahigh-throughput droplet-based microfluidic screening platform can be used to improve a previously optimized artificial aldolase by an additional factor of 30 to give a >10(9) rate enhancement that rivals the efficiency of class I aldolases. The resulting enzyme catalyses a reversible aldol reaction with high stereoselectivity and tolerates a broad range of substrates...
January 2017: Nature Chemistry
https://www.readbyqxmd.com/read/27995915/an-infrared-spectroscopy-approach-to-follow-%C3%AE-sheet-formation-in-peptide-amyloid-assemblies
#8
Jongcheol Seo, Waldemar Hoffmann, Stephan Warnke, Xing Huang, Sandy Gewinner, Wieland Schöllkopf, Michael T Bowers, Gert von Helden, Kevin Pagel
Amyloidogenic peptides and proteins play a crucial role in a variety of neurodegenerative disorders such as Alzheimer's and Parkinson's disease. These proteins undergo a spontaneous transition from a soluble, often partially folded form, into insoluble amyloid fibrils that are rich in β-sheets. Increasing evidence suggests that highly dynamic, polydisperse folding intermediates, which occur during fibril formation, are the toxic species in the amyloid-related diseases. Traditional condensed-phase methods are of limited use for characterizing these states because they typically only provide ensemble averages rather than information about individual oligomers...
January 2017: Nature Chemistry
https://www.readbyqxmd.com/read/27995914/breaking-scaling-relations-to-achieve-low-temperature-ammonia-synthesis-through-lih-mediated-nitrogen-transfer-and-hydrogenation
#9
Peikun Wang, Fei Chang, Wenbo Gao, Jianping Guo, Guotao Wu, Teng He, Ping Chen
Ammonia synthesis under mild conditions is a goal that has been long sought after. Previous investigations have shown that adsorption and transition-state energies of intermediates in this process on transition metals (TMs) scale with each other. This prevents the independent optimization of these energies that would result in the ideal catalyst: one that activates reactants well, but binds intermediates relatively weakly. Here we demonstrate that these scaling relations can be broken by intervening in the TM-mediated catalysis with a second catalytic site, LiH...
January 2017: Nature Chemistry
https://www.readbyqxmd.com/read/27995912/conformer-specific-hydrogen-atom-tunnelling-in-trifluoromethylhydroxycarbene
#10
Artur Mardyukov, Henrik Quanz, Peter R Schreiner
Conformational control of organic reactions is at the heart of the biomolecular sciences. To achieve a particular reactivity, one of many conformers may be selected, for instance, by a (bio)catalyst, as the geometrically most suited and appropriately reactive species. The equilibration of energetically close-lying conformers is typically assumed to be facile and less energetically taxing than the reaction under consideration itself: this is termed the 'Curtin-Hammett principle'. Here, we show that the trans conformer of trifluoromethylhydroxycarbene preferentially rearranges through a facile quantum-mechanical hydrogen tunnelling pathway, while its cis conformer is entirely unreactive...
January 2017: Nature Chemistry
https://www.readbyqxmd.com/read/27995911/homochiral-polymerization-driven-selective-growth-of-graphene-nanoribbons
#11
Hiroshi Sakaguchi, Shaotang Song, Takahiro Kojima, Takahiro Nakae
The surface-assisted bottom-up fabrication of graphene nanoribbons (GNRs), which consists of the radical polymerization of precursors followed by dehydrogenation, has attracted attention because of the method's ability to control the edges and widths of the resulting ribbon. Although these reactions on a metal surface are believed to be catalytic, the mechanism has remained unknown. Here, we demonstrate 'conformation-controlled surface catalysis': the two-zone chemical vapour deposition of a 'Z-bar-linkage' precursor, which represents two terphenyl units linked in a 'Z' shape, results in the efficient formation of acene-type GNRs with a width of 1...
January 2017: Nature Chemistry
https://www.readbyqxmd.com/read/27995924/structure-prediction-encoding-evolution-of-porous-solids
#12
Caroline Mellot-Draznieks, Anthony K Cheetham
No abstract text is available yet for this article.
December 20, 2016: Nature Chemistry
https://www.readbyqxmd.com/read/27995923/bridging-the-gaps-in-18-f-pet-tracer-development
#13
Michael G Campbell, Joel Mercier, Christophe Genicot, Véronique Gouverneur, Jacob M Hooker, Tobias Ritter
No abstract text is available yet for this article.
December 20, 2016: Nature Chemistry
https://www.readbyqxmd.com/read/27995920/interplay-between-defects-disorder-and-flexibility-in-metal-organic-frameworks
#14
Thomas D Bennett, Anthony K Cheetham, Alain H Fuchs, François-Xavier Coudert
Metal-organic frameworks are a novel family of chemically diverse materials, which are of interest across engineering, physics, chemistry, biology and medicine-based disciplines. Since the development of the field in its current form more than two decades ago, priority has been placed on the synthesis of new structures. However, more recently, a clear trend has emerged in shifting the emphasis from material design to exploring the chemical and physical properties of structures already known. In particular, although such nanoporous materials were traditionally seen as rigid crystalline structures, there is growing evidence that large-scale flexibility, the presence of defects and long-range disorder are not the exception in metal-organic frameworks, but the rule...
December 20, 2016: Nature Chemistry
https://www.readbyqxmd.com/read/27995919/c-h-activation-complex-peptides-made-simple
#15
Sean Bartlett, David R Spring
No abstract text is available yet for this article.
December 20, 2016: Nature Chemistry
https://www.readbyqxmd.com/read/27995917/bioinorganic-chemistry-nitrate-no-more
#16
Marshall Brennan
No abstract text is available yet for this article.
December 20, 2016: Nature Chemistry
https://www.readbyqxmd.com/read/27995913/chemists-boldly-go
#17
Michelle Francl, Michael Donnay
No abstract text is available yet for this article.
December 20, 2016: Nature Chemistry
https://www.readbyqxmd.com/read/27995910/a-portrait-of-cadmium
#18
Nadezda V Tarakina, Bart Verberck
No abstract text is available yet for this article.
December 20, 2016: Nature Chemistry
https://www.readbyqxmd.com/read/27874873/enabling-singlet-fission-by-controlling-intramolecular-charge-transfer-in-%C3%AF-stacked-covalent-terrylenediimide-dimers
#19
Eric A Margulies, Claire E Miller, Yilei Wu, Lin Ma, George C Schatz, Ryan M Young, Michael R Wasielewski
When an assembly of two or more molecules absorbs a photon to form a singlet exciton, and the energetics and intermolecular interactions are favourable, the singlet exciton can rapidly and spontaneously produce two triplet excitons by singlet fission. To understand this process is important because it may prove to be technologically significant for enhancing solar-cell performance. Theory strongly suggests that charge-transfer states are involved in singlet fission, but their role has remained an intriguing puzzle and, up until now, no molecular system has provided clear evidence for such a state...
December 2016: Nature Chemistry
https://www.readbyqxmd.com/read/27874872/mechanically-controlled-quantum-interference-in-individual-%C3%AF-stacked-dimers
#20
Riccardo Frisenda, Vera A E C Janssen, Ferdinand C Grozema, Herre S J van der Zant, Nicolas Renaud
Recent observations of destructive quantum interference in single-molecule junctions confirm the role of quantum effects in the electronic conductance properties of molecular systems. These effects are central to a broad range of chemical and biological processes and may be beneficial for the design of single-molecule electronic components to exploit the intrinsic quantum effects that occur at the molecular scale. Here we show that destructive interference can be turned on or off within the same molecular system by mechanically controlling its conformation...
December 2016: Nature Chemistry
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