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93 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
I19-Small Molecule Single Crystal Diffraction	One guest or two? A crystallographic and solution study of guest binding in a cubic coordination cage Christopher Taylor , Stephen Argent , Michael Ludden , Jerico Piper , Cristina Mozaceanu , Sarah Barnett , Michael Ward Chemistry - A European Journal DOI: 10.1002/chem.201905499 Diamond Proposal Number(s): [19876] Show Abstract ▼ Abstract: A crystallographic investigation of a series of host/guest complexes in which small‐molecule organic guests occupy the central cavity of an approximately cubic M 8 L 12 coordination cage has revealed some unexpected behaviour. Whilst some guests form 1:1 H•G complexes as we have seen before, an extensive family of bicyclic guests – including some substituted coumarins and various saturated analogues – form 1:2 H•G 2 complexes in the solid state, despite the fact that solution titrations are consistent with 1:1 complex formation, and the combined volume of the pair of guests significantly exceeds the Rebek 55±9% packing for optimal guest binding, with packing coefficients of up to 87%. Re‐examination of solution titration data for guest binding in two cases showed that, although conventional fluorescence titrations are consistent with 1:1 binding model, alternative forms of analysis – Job plot and an NMR titration – at higher concentrations do provide evidence for 1:2 H•G 2 complex formation. The observation of guests binding in pairs in some cases opens up new possibilities for altered reactivity of bound guests, and also highlights the recently‐articulated difficulties associated with determining stoichiometry of supramolecular complexes in solution.	Dec 2019
I19-Small Molecule Single Crystal Diffraction	Coordination cage catalysed hydrolysis of organophosphates: cavity or surface based? Christopher Taylor , Alexander Metherell , Stephen Argent , Fatma Ashour , Nicholas Williams , Michael Ward Chemistry – A European Journal DOI: 10.1002/chem.201904708 Diamond Proposal Number(s): [19876] Show Abstract ▼ Abstract: The hydrophobic central cavity of a water‐soluble M8L12 cubic coordination cage can accommodate a range of phospho‐diester and phospho‐triester guests such as the insecticide 'dichlorvos' (2,2‐dichlorovinyl dimethyl phosphate) and the chemical warfare agent analogue diisopropyl chlorophosphate. The accumulation of hydroxide ions around the cationic cage surface due to ion‐pairing in solution generates a high local pH around the cage, resulting in catalysed hydrolysis of the phospho‐triester guests. A series of control experiments unexpectedly demonstrates that – in marked contrast to previous cases – it is not necessary for the phospho‐triester substrates to be bound inside the cavity for catalysed hydrolysis to occur. This suggests that catalysis can occur on the exterior surface of the cage as well as the interior surface, with the exterior‐binding catalysis pathway dominating here because of the small binding constants for these phospho‐triester substrates in the cage cavity. These observations suggest that cationic but hydrophobic surfaces could act as quite general catalysts in water by bringing substrates into contact with the surface (via the hydrophobic effect) where there is also a high local concentration of anions (due to ion‐pairing / electrostatic effects).	Nov 2019
I19-Small Molecule Single Crystal Diffraction	A tris(3‐pyridyl)stannane as a building block for heterobimetallic coordination polymers and supramolecular cages Dominic Wright , Eric Yang , Alex J. Plajer , Álvaro García-romero , Andrew D. Bond , Tanya Ronson , Celedonio M. Álvarez , Raúl García-rodríguez , Annie L. Colebatch Chemistry – A European Journal DOI: 10.1002/chem.201903498 Diamond Proposal Number(s): [15768] Show Abstract ▼ Abstract: The systematic assembly of supramolecular arrangements is a persistent challenge in modern coordination chemistry, especially where further aspects of complexity are concerned, as in the case of large molecular mixed‐metal arrangements. One targeted approach to such heterometallic complexes is to engineer metal‐based donor ligands of the correct geometry to build 3‐D arrangements upon coordination to other metals. This simple idea has, however, only rarely been applied to main group metal‐based ligand systems. Here we show that the new, bench‐stable tris(3‐pyridyl)stannane ligand PhSn(3‐Py)3 (3‐Py = 3‐pyridyl) provides simple access to a range of heterometallic Sn(IV)/transition metal complexes, and that the presence of weakly coordinating counteranions can be used to build discrete molecular arrangements involving anion encapsulation. This work therefore provides a building strategy in this area, which parallels that of supramolecular transition metal chemistry.	Aug 2019
I19-Small Molecule Single Crystal Diffraction	Multiple‐porphyrin functionalized hexabenzocoronenes Norbert Jux , Max M. Martin , Dominik Lungerich , Frank Hampel , Jens Langer , Tanya K. Ronson Chemistry – A European Journal DOI: 10.1002/chem.201903113 Diamond Proposal Number(s): [11397] Open Access Show Abstract ▼ Abstract: Porphyrin‐hexabenzocoronene architectures serve as good model compounds to study light harvesting systems. Herein, the synthesis of porphyrin functionalized hexa‐peri‐hexa‐benzocoronenes (HBCs), in which one or more porphyrins are covalently linked to a central HBC core, is presented. Therefore, a series of hexaphenylbenzenes (HPBs) was prepared and reacted under oxidative Scholl conditions. The transformation to the respective HBC derivatives worked well with mono‐ and tri‐porphyrin substituted HPBs. However, if more porphyrins are attached to the HPB core, Scholl oxidations are hampered or completely suppressed. Hence, a change of the synthetic strategy was necessary to first pre‐forming the HBC core, followed by the introduction of the porphyrins. All products were fully characterized, including, if possible, single crystal XRD. UV/Vis absorption spectra of porphyrin‐HBCs showed, depending on the number of porphyrins as well as with respect to the substitution pattern, variations in their spectral features with strong distortions of the porphyrins’ B‐band.	Aug 2019
I16-Materials and Magnetism I22-Small angle scattering & Diffraction	New type of columnar liquid crystal superlattice in double‐taper ionic minidendrons Ya-xin Li , Fang-fang Fan , Jie Wang , Liliana Cseh , Min Xue , Xiang-bing Zeng , Goran Ungar Chemistry – A European Journal DOI: 10.1002/chem.201902639 Show Abstract ▼ Abstract: Wedge‐shaped molecules, such as dendrons, are among the most important building blocks for directed supramolecular self‐assembly. Here we present a new approach aimed at widening the range and complexity of potential mesophases by introducing double‐tapered mesogens. Two series of compounds are presented, both alkali metal salts (Li, Na, Cs) of 3,4,5‐tris‐alkoxybenzoic acid with a second tapered tris‐alkoxyaryl group attached at the end of an alkoxy chain. The double‐tapered compounds all display an unusual hexagonal columnar phase consisting of one ionic and three non‐ionic columns per unit cell. The cation size has an unexpectedly drastic effect on unit cell size. Unlike most columnars, the current phases show unusually high dimensional stability on heating, and high stiffness in spite of being 80‐85% aliphatic, attributed to their molecular topology. The described approach may lead to co‐assemblies of multifunctional materials, e.g. parallel p‐ and n‐semiconducting nanowires or parallel ionic and electronic conductors.	Jul 2019
I04-1-Macromolecular Crystallography (fixed wavelength)	19F‐NMR monitoring of reversible protein post‐translational modifications: Class D β‐lactamase carbamylation and inhibition Emma Van Groesen , Christopher T. Lohans , Jurgen Brem , Kristina M. J. Aertker , Timothy D. W. Claridge , Christopher Schofield Chemistry – A European Journal DOI: 10.1002/chem.201902529 Diamond Proposal Number(s): [12346] Show Abstract ▼ Abstract: Bacterial production of β‐lactamases with carbapenemase activity is a global health threat. The active sites of class D carbapenemases such as OXA‐48, which is of major clinical importance, uniquely contain a carbamylated lysine residue which is essential for catalysis. Although there is significant interest in characterizing this post‐translational modification, and it is a promising inhibition target, protein carbamylation is challenging to monitor in solution. We report the use of 19F‐NMR spectroscopy to monitor the carbamylation state of 19F‐labelled OXA‐48. This method was used to investigate the interactions of OXA‐48 with clinically used serine β‐ lactamase inhibitors, including avibactam and vaborbactam. Crystallographic studies on 19F‐labelled OXA‐48 provide a structural rationale for the sensitivity of the 19F‐label to active site interactions. The overall results demonstrate the use of 19F‐NMR to monitor reversible covalent post‐translational modifications.	Jul 2019
I19-Small Molecule Single Crystal Diffraction	Electronic, structural and functional versatility in tetrathiafulvalene-lanthanide metal-organic frameworks Javier Castella-gil , Samuel Mañas-valero , Inigo Vitórica-yrezábal , Duarte Ananias , João Rocha , Raul Santiago , Stefan T. Bromley , José J. Baldoví , Eugenio Coronado , Manuel Souto , Guillermo Minguez Espallargas Chemistry - A European Journal DOI: 10.1002/chem.201902855 Diamond Proposal Number(s): [17379] Show Abstract ▼ Abstract: Tetrathiafulvalene‐lanthanide (TTF‐Ln) metal–organic frameworks (MOFs) are an interesting class of multifunctional materials in which porosity can be combined with electronic properties such as electrical conductivity, redox activity, luminescence and magnetism. Herein a new family of isostructural TTF‐Ln MOFs is reported, denoted as MUV‐5(Ln) (Ln=Gd, Tb, Dy, Ho, Er), exhibiting semiconducting properties as a consequence of the short intermolecular S⋅⋅⋅S contacts established along the chain direction between partially oxidised TTF moieties. In addition, this family shows photoluminescence properties and single‐molecule magnetic behaviour, finding near‐infrared (NIR) photoluminescence in the Yb/Er derivative and slow relaxation of the magnetisation in the Dy and Er derivatives. As such properties are dependent on the electronic structure of the lanthanide ion, the immense structural, electronic and functional versatility of this class of materials is emphasised.	Jul 2019
I04-Macromolecular Crystallography	A histidine residue and a tetranuclear cuprous‐thiolate cluster dominate the copper loading landscape of a copper storage protein from Streptomyces lividans Megan L. Straw , Michael A. Hough , Michael T. Wilson , Jonathan A. R. Worrall Chemistry – A European Journal DOI: 10.1002/chem.201901411 Diamond Proposal Number(s): [13467] Show Abstract ▼ Abstract: The chemical basis for protecting organisms against the toxic effect imposed by excess cuprous ions is to constrain this through high‐affinity binding sites that employ cuprous‐thiolate coordination chemistries. In bacteria, a family of cysteine rich four helix‐bundle proteins utilise thiolate chemistry to bind up to 80 cuprous ions. These proteins have been termed copper storage proteins (Csp). The present study investigates cuprous ion loading to the Csp from Streptomyces lividans (SlCsp) using a combination of X‐ray crystallography, site‐directed mutagenesis and stopped‐flow reaction kinetics with either aquatic cuprous ions or a chelating donor. We illustrate that at low cuprous ion concentrations, copper is loaded exclusively into an outer core region of SlCsp via one end of the four helix‐bundle, facilitated by a set of three histidine residues. X‐ray crystallography reveals the existence of polynuclear cuprous‐thiolate clusters culminating in the assembly of a tetranuclear [Cu4(μ2‐S‐Cys)4(Νδ1‐His)] cluster in the outer core. As more cuprous ions are loaded, the cysteine lined inner core of SlCsp fills with cuprous ions but in a fluxional and dynamic manner with no evidence for the assembly of further intermediate polynuclear cuprous‐thiolate clusters as observed in the outer core. Using site‐directed mutagenesis a key role for His107 in the efficient loading of cuprous ions from a donor is established. A model of copper loading to SlCsp is proposed and discussed.	May 2019
I04-1-Macromolecular Crystallography (fixed wavelength)	A GAP‐GTPase‐GDP‐Pi intermediate crystal structure analyzed by DFT shows GTP hydrolysis involves serial proton transfers Yi Jin , Robert W. Molt Jr. , Erika Pellegrini Chemistry – A European Journal DOI: 10.1002/chem.201901627 Diamond Proposal Number(s): [9948] Show Abstract ▼ Abstract: Cell signaling by small G proteins uses an ON to OFF signal based on conformational changes following the hydrolysis of GTP to GDP and release of dihydrogen phosphate (Pi). The catalytic mechanism of GTP hydrolysis by RhoA is strongly accelerated by a GAP protein and is now well defined, but timing of inorganic phosphate release and signal change remains unresolved. We have generated a quaternary complex for RhoA‐GAP‐GDP‐Pi. Its 1.75 Å crystal structure shows geometry for ionic and hydrogen bond coordination of GDP and Pi in an intermediate state. It enables the selection of a QM core for DFT exploration of a 20 H‐bonded network. This identifies serial locations of the two mobile protons from the original nucleophilic water molecule, showing how they move in three rational steps to form a stable quaternary complex. It also suggests how two additional proton transfer steps can facilitate Pi release.	Apr 2019
I04-1-Macromolecular Crystallography (fixed wavelength)	Construction of a shape‐diverse fragment set: Design, synthesis and screen against Aurora‐A kinase Rong Zhang , Patrick J. Mcintyre , Patrick M. Collins , Daniel J. Foley , Christopher Arthur , Frank Von Delft , Richard Bayliss , Stuart Warriner , Adam Nelson Chemistry – A European Journal 73 DOI: 10.1002/chem.201900815 Diamond Proposal Number(s): [14331] Show Abstract ▼ Abstract: Historically, chemists have explored chemical space in a highly uneven and unsystematic manner. As an example, the shape diversity of existing fragment sets does not generally reflect that of all theoretically possible fragments. To assess experimentally the added value of increased three dimensionality, a shape‐diverse fragment set was designed and collated. The set was assembled by both using commercially available fragments and harnessing unified synthetic approaches to sp3‐rich molecular scaffolds. The resulting set of 80 fragments was highly three‐dimensional, and its shape diversity was significantly enriched by twenty synthesised fragments. The fragment set was screened by high‐throughput protein crystallography against Aurora‐A kinase, revealing four hits that targeted the binding site of allosteric regulators. In the longer term, it is envisaged that the fragment set could be screened against a range of functionally diverse proteins, allowing the added value of more shape‐diverse screening collections to be more fully assessed.	Apr 2019

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