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265 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I10-Beamline for Advanced Dichroism	Quenching and restoration of orbital angular momentum through a dynamic bond in a cobalt(II) complex Sheng-qun Su , Shu-qi Wu , Michael L. Baker , Peter Bencok , Nobuaki Azuma , Yuji Miyazaki , Motohiro Nakano , Soonchul Kang , Yoshihito Shiota , Kazunari Yoshizawa , Shinji Kanegawa , Osamu Sato Journal Of The American Chemical Society DOI: 10.1021/jacs.0c02257 Diamond Proposal Number(s): [17723] Show Abstract ▼ Abstract: Orbital angular momentum plays a vital role in various applications, especially magnetic and spintronic properties. There-fore, controlling orbital angular momentum is of paramount importance to both fundamental science and new technologi-cal applications. Many attempts have been made to modulate the ligand-field induced quenching effects of orbital angular momentum to manipulate magnetic properties. However, to date, reported changes in the magnitude of orbital angular momentum are small in both molecular and solid-state magnetic materials. Moreover, no effective methods currently exist to modulate orbital angular momentum. Here, we report a dynamic bond approach to realize a large change in orbital angu-lar momentum. We have developed a Co(II) complex that exhibits coordination number switching between six and seven. This cooperative dynamic bond switching induces considerable modulation of the ligand field, thereby leading to substantial quenching and restoration of the orbital angular momentum. This switching mechanism is entirely different from those of spin-crossover and valence tautomeric compounds, which exhibit switching in spin multiplicity.	Jun 2020
I19-Small Molecule Single Crystal Diffraction	An expandable hydrogen-bonded organic framework characterized by three-dimensional electron diffraction Peng Cui , Erik Svensson Grape , Peter R. Spackman , Yue Wu , Rob Clowes , Graeme M. Day , A. Ken Inge , Marc A. Little , Andrew I. Cooper Journal Of The American Chemical Society DOI: 10.1021/jacs.0c04885 Diamond Proposal Number(s): [23666] Show Abstract ▼ Abstract: A molecular crystal of a 2-D hydrogen-bonded organic framework (HOF) undergoes an unusual structural transformation after solvent removal from the crystal pores during activation. The conformationally flexible host molecule, ABTPA, adapts its molecular conformation during activation to initiate a framework expansion. The microcrystalline activated phase was characterized by three-dimensional electron diffraction (3D ED), which revealed that ABTPA uses out-of-plane anthracene units as adaptive structural anchors. These units change orientation to generate an expanded, lower density framework material in the activated structure. The porous HOF, ABTPA-2, has robust dynamic porosity (SABET = 1183 m2 g-1) and exhibits negative area thermal expansion. We use crystal structure prediction (CSP) to understand the underlying energetics behind the structural transformation and discuss the challenges facing CSP for such flexible molecules.	Jun 2020
I19-Small Molecule Single Crystal Diffraction	Photochemical unmasking of polyyne rotaxanes Steffen Woltering , Przemyslaw Gawel , Kirsten E. Christensen , Amber L. Thompson , Harry L. Anderson Journal Of The American Chemical Society DOI: 10.1021/jacs.0c05308 Diamond Proposal Number(s): [20876] Show Abstract ▼ Abstract: Bulky photo-labile masked alkyne equivalents (MAEs) are needed for the synthesis of polyyne polyrotaxanes, as insulated molecular wires and as stabilized forms of the linear polymeric allotrope of carbon, carbyne. We have synthesized a novel MAE based on phenanthrene and compared it with an indane-based MAE. Photochemical unmasking of model compounds was studied at different wavelengths (250 nm and 350 nm), and key products were identified by NMR spectroscopy and X-ray crystallography. UV irradiation at 250 nm leads to unmasking of both MAEs. Irradiation of the phenanthrene system at 350 nm results in quantitative dimerization via [2+2] cycloaddition to form a [3]-ladderane; irradiation of this ladderane at 250 nm generates a dihydrotriphenylene, which can be oxidized easily to a triphenylene. Irradiation of the indane-based MAE at 350 nm in the presence of traces of oxygen forms an endoperoxide and a bisepoxide. Both MAEs have been incorporated into rotaxanes via copper-mediated active metal template Glaser or Cadiot-Chodkiewicz coupling. The identity of the rotaxanes was confirmed by NMR spectroscopy and mass spectrometry. The phenanthrene rotaxane decomposes during attempted photochemical unmasking, whereas photolysis of the indane rotaxane results in unmasking of the polyyne thread to form a rotaxane with a chain of 16 sp-hybridized carbon atoms. This approach opens avenues towards the synthesis of encapsulated carbon allotropes.	Jun 2020
I04-1-Macromolecular Crystallography (fixed wavelength)	Aerobic photocatalytic H2 production by a [NiFe] hydrogenase engineered to place a silver nanocluster in the electron relay Liyun Zhang , Giorgio Morello , Stephen Carr , Fraser A. Armstrong Journal Of The American Chemical Society DOI: 10.1021/jacs.0c04302 Diamond Proposal Number(s): [18069] Show Abstract ▼ Abstract: Hydrogenase-1 (Hyd-1) from E. coli poses a conundrum regarding the properties of electrocatalytic reversibility and associated bidirectionality now established for many redox enzymes. Its excellent H2-oxidizing activity begins only once a substantial overpo-tential is applied, and it cannot produce H2. A major reason for its unidirectional behavior is that the reduction potentials of its electron-relaying FeS clusters are too positive relative to the 2H+/H2 couple at neutral pH; consequently, electrons held within the enzyme lack the energy to drive H2 production. However, Hyd-1 is O2-tolerant and even functions in air. Changing a tyrosine (Y) or threonine (T), located on the protein surface within 10 Å of the distal [4Fe-4S] and medial [3Fe-4S] clusters, to cysteine (C), allows site-selective attachment of a silver nanocluster (AgNC), the reduced or photoexcited state of which is a powerful reduct-ant. The AgNC provides a new additional redox site, capturing externally-supplied electrons with sufficiently high energy to drive H2 production. Assemblies of Y’227C (or T’225C) with AgNCs/PMAA (PMAA = polymethylacrylate templating several AgNC) are also electroactive for H2 production at a TiO2 electrode. A colloidal system for visible-light photo-H2 generation is made by building the hybrid enzyme into a heterostructure with TiO2 and graphitic carbon nitride (g-C3N4), the resulting scaffold promoting uptake of electrons excited at the AgNC. Each hydrogenase produces 40 molecules of H2 per second and sustains 20% activity in air.	Jun 2020
I19-Small Molecule Single Crystal Diffraction	A transformation network culminating in a heteroleptic Cd6L6L'2 twisted trigonal prism Dawei Zhang , Tanya K. Ronson , Lin Xu , Jonathan R. Nitschke Journal Of The American Chemical Society DOI: 10.1021/jacs.0c03798 Diamond Proposal Number(s): [11397] Show Abstract ▼ Abstract: Transformations between three-dimensional metallosupramolecular assemblies can enable switching between the different functions of these structures. Here we report a network of such transformations, based upon a subcomponent displacement strategy. The flow through this network is directed by the relative reactivities of different amines, aldehydes, and di(2-pyridyl)ketone. The network provides access to an unprecedented heteroleptic Cd6L6L'2 twisted trigonal prism. The principles underpinning this network thus allow for the design of diverse structural transformations, converting one helicate into another, a helicate into a tetrahedron, a tetrahedron into a different tetrahedron, and a tetrahedron into the new trigonal prismatic structure type. The selective conversion from one host to another also enabled the uptake of a desired guest from a mixture of guests.	May 2020
I19-Small Molecule Single Crystal Diffraction	An S 10-symmetric 5-fold interlocked [2]catenane Tanya K. Ronson , Yujia Wang , Kim Baldridge , Jay S. Siegel , Jonathan R. Nitschke Journal Of The American Chemical Society DOI: 10.1021/jacs.0c03349 Diamond Proposal Number(s): [15768] Show Abstract ▼ Abstract: The reaction of sym-pentakis(4-aminothiophenyl)corannulene with 2-formyl-6-methyl-pyridine and CuI or 2-formyl-1,10-phenanthroline and MII (Co or Zn) yields an S10-symmetric five-fold interlocked [2]catenane of two interpenetrating [CuI5L2]5+ cages or D5-symmetric [MII5L2]10+ cages, respectively. The new structures were characterized by X-ray crystallography, NMR spectroscopy and mass spectrometry. Density functional theory computations point to dispersive energies on par with traditional covalent bond energies. Subcomponent exchange reactions favored formation of the [CoII5L2]10+ cage over the [CuI10L4]10+ catenane. The single cage and catenane each co-crystalized with a guest corannulene to form a bowl-in-bowl sub-structure.	May 2020
I19-Small Molecule Single Crystal Diffraction	Single-step enantioselective synthesis of mechanically planar chiral [2]rotaxanes using a chiral leaving group strategy Chong Tian , Stephen D. P. Fielden , Borja Pérez-saavedra , Iñigo J. Vitorica-yrezabal , David Leigh Journal Of The American Chemical Society DOI: 10.1021/jacs.0c03447 Show Abstract ▼ Abstract: We report a one-step enantioselective synthesis of mechanically planar chiral [2]rotaxanes. Previous studies of such molecules have generally involved the separation of enantiomers from racemic mixtures or the preparation and separation of diastereomeric intermediates followed by post-assembly modification to remove other sources of chirality. Here, we demonstrate a simple asymmetric metal-free active template rotaxane synthesis using a primary amine, an activated ester with a chiral leaving group, and an achiral crown ether lacking rotational symmetry. Mechanically planar chiral rotaxanes are obtained directly in up to 50% enantiomeric excess. The rotaxanes were characterized by NMR spectroscopy, high-resolution mass spectrometry, chiral HPLC, single crystal X-ray diffraction, and circular dichroism. Either rotaxane enantiomer could be prepared selectively by incorporating pseudoenantiomeric cinchona alkaloids into the chiral leaving group.	May 2020
I03-Macromolecular Crystallography I04-Macromolecular Crystallography	Alkynyl benzoxazines and dihydroquinazolines as cysteine targeting covalent warheads and their application in identification of selective irreversible kinase inhibitors Kirsten Mcaulay , Emily A. Hoyt , Morgan Thomas , Marianne Schimpl , Michael S. Bodnarchuk , Hilary J. Lewis , Derek Barratt , Deepa Bhavsar , David M. Robinson , Michael J. Deery , Derek Ogg , Gonçalo J. I. Bernardes , Richard A. Ward , Michael J. Waring , Jason G. Kettle Journal Of The American Chemical Society DOI: 10.1021/jacs.9b13391 Diamond Proposal Number(s): [12419, 20015] Show Abstract ▼ Abstract: With a resurgence in interest in covalent drugs, there is need to identify new moieties capable of cysteine bond formation that are differentiated from commonly employed systems such as acrylamide. Herein, we report on the discovery of new alkynyl benzoxazine and dihydroquinazoline moieties capable of covalent reaction with cysteine. Their utility as alternative electrophilic warheads for chemical biological probes and drug molecules is demonstrated through site-selective protein modification and incorporation into kinase drug scaffolds. A potent covalent inhibitor of JAK3 kinase was identified with superior selectivity across the kinome and improvements in in vitro pharmacokinetic profile relative to the related acrylamide-based inhibitor. In addition, the use of a novel heterocycle as cysteine reactive warhead is employed to target Cys788 in c-KIT where acrylamide has previously failed to form covalent interactions. These new reactive and selective heterocyclic warheads supplement the current repertoire for cysteine covalent modification whilst avoiding some of the limitations generally associated with established moieties.	May 2020
I19-Small Molecule Single Crystal Diffraction	Narcissistic, integrative and kinetic self-sorting within a system of coordination cages Felix J. Rizzuto , Jonathan R. Nitschke Journal Of The American Chemical Society DOI: 10.1021/jacs.0c02444 Diamond Proposal Number(s): [11397] Show Abstract ▼ Abstract: Many useful principles of self-assembly have been elucidated through studies of systems where multiple components combine to create a single structure. More complex systems, where multiple product structures self-assemble in parallel from a shared set of precursors, are also of great interest, as biological systems exhibit this behavior. The greater complexity of such systems leads to an increased likelihood that discrete species will not be formed, however. Here we show how the kinetics of self-assembly govern the formation of multiple metal-organic architectures from a mixture of five building blocks, preventing the formation of a discrete structure of intermediate size. By varying ligand symmetry, denticity and orientation, we explore how five distinct polyhedra – a tetrahedron, an octahedron, a cube, a cuboctahedron and a triangular prism – assemble in concert around CoII template ions. The underlying rules dictating the organization of assemblies into specific shapes are deciphered, explaining the formation of only three discrete entities when five could form in principle.	Apr 2020
B22-Multimode InfraRed imaging And Microspectroscopy	Polyamorphism mirrors polymorphism in the liquid–liquid transition of a molecular liquid Finlay Walton , John Bolling , Andrew Farrell , Jamie Macewen , Christopher D. Syme , Mario González-jiménez , Hans Martin Senn , Claire Wilson , Gianfelice Cinque , Klaas Wynne Journal Of The American Chemical Society DOI: 10.1021/jacs.0c01712 Diamond Proposal Number(s): [20351] Show Abstract ▼ Abstract: Liquid-liquid transitions between two amorphous phases in a single-component liquid have courted controversy. All known examples of liquid–liquid transitions in molecular liquids have been observed in the supercooled state suggesting an intimate connection with vitrification and locally favored structures inhibiting crystallization. However, there is precious little information about the local molecular packing in supercooled liquids meaning that the order parameter of the transition is still unknown. Here, we investigate the liquid–liquid transition in triphenyl phosphite and show that it is caused by the competition between liquid structures that mirror two crystal polymorphs. The liquid–liquid transition is found to be between a geometrically frustrated liquid to a dynamically frustrated glass. These results indicate a general link between polymorphism and polyamorphism and will lead to a much greater understanding of the physical basis of liquid–liquid transitions and allow the systematic discovery of other examples.	Apr 2020

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