I19-Small Molecule Single Crystal Diffraction
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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.
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Aug 2019
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[11397]
Open Access
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.
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Aug 2019
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I16-Materials and Magnetism
I22-Small angle scattering & Diffraction
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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.
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Jul 2019
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I04-1-Macromolecular Crystallography (fixed wavelength)
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Diamond Proposal Number(s):
[12346]
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.
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Jul 2019
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I19-Small Molecule Single Crystal Diffraction
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Javier
Castella-gil
,
Samuel
Mañas-valero
,
Inigo
Vitórica-yrezábal
,
Duarte
Ananias
,
João
Rocha
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Raul
Santiago
,
Stefan T.
Bromley
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José J.
Baldoví
,
Eugenio
Coronado
,
Manuel
Souto
,
Guillermo
Minguez Espallargas
Diamond Proposal Number(s):
[17379]
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.
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Jul 2019
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I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[13467]
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.
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May 2019
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I04-1-Macromolecular Crystallography (fixed wavelength)
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Diamond Proposal Number(s):
[9948]
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.
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Apr 2019
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I04-1-Macromolecular Crystallography (fixed wavelength)
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Diamond Proposal Number(s):
[14331]
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.
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Apr 2019
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[13639]
Abstract: This study details attempts to access N‐heterocyclic carbenes (NHCs) featuring the diazaborolyl group, {(HCNDipp)2B}, as one or both of the N‐bound substituents. Attempts to isolate N‐heterocyclic carbenes based around imidazolylidene or related heterocycles, are characterized by facile N‐to‐C migration of the boryl substituent. In the cases of imidazolium precursors bearing one N‐bound diazaboryl group and one methyl substituent, deprotonation leads to the generation of the target carbenes, which can be characterized in situ by NMR measurements, and trapped by reactions with metal fragments and elemental selenium. The half‐lives of the free carbenes at room temperature range from 4‐50 h (depending on the pattern of ancillary substituents) with N‐to‐C2 migration of the boryl function being shown to be the predominant rearrangement pathway. Kinetic studies show this to be a first order process that occurs with an entropy of activation close to zero. DFT calculations imply that an intramolecular 1,2‐shift is mechanistically feasible, with calculated activation energies of the order of 90‐100 kJ mol‐1 reflecting the retention of significant aromatic character in the imidazole ring in the transition state. Trapping of the carbene allows for evaluation of steric and electronic properties via systems of the type LAuCl, LRh(CO)2Cl and LSe. A highly unsymmetrical (but nonetheless bulky) steric profile and moderately enhanced σ‐donor capabilities (compared to IMes) are revealed.
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Dec 2018
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[15059]
Abstract: Two new heteroleptic metal‐organic framework materials show strong adsorption of H2 and ethanol. [Co2(L1)(bdc)2], where L1=N1,N4‐bis(4‐pyridinylmethyl)‐2,5‐dimethylbenzene‐1,4‐diamine and bdc is benzene‐1,4‐dicarboxylate, has a twofold interpenetrating pillared layer structure with pcu topology. It has a stepped, hysteretic EtOH adsorption that can be related to complicated phase and structural transformation behaviour that occurs on de‐solvation and re‐solvation, including major conformational changes to the geometry of the flexible L1 ligand. [Co2(L1)(bpdc)2], where bpdc=biphenyl‐4,4′‐dicarboxylate, has a unique six‐connected self‐catenating framework structure. Solvation changes occur without significant structural change and a partially‐hydrolysed material binds its own decomposition products as guests.
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Dec 2018
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