I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Open Access
Abstract: The benzyl-substituted phosphine–boranes PhCH2P(BH3)R2 [R = iPr (1H), Ph (2H), Cy (3H)] are accessible through either the reaction between R2PCl and PhCH2MgBr, followed by treatment with BH3·SMe2 or the reaction between R2P(BH)3Li and PhCH2Br. Treatment of 1H, 2H, or 3H with nBuLi, PhCH2Na, or PhCH2K gave the corresponding alkali metal complexes [{iPr2P(BH3)CHPh}Li(THF)]2 (1Li), [{Ph2P(BH3)CHPh}Li(OEt2)2] (2Li), [{Cy2P(BH3)CHPh}Li(TMEDA)] (3Li), [iPr2P(BH3)CHPh]Na (1Na), [{Ph2P(BH3)CHPh}Na(THF)2]2 (2Na), [Cy2P(BH3)CHPh]Na(THF)0.5 (3Na), [{iPr2P(BH3)CHPh}K]∞ (1K), [{Ph2P(BH3)CHPh}K(THF)]∞ (2K), and [{Cy2P(BH3)CHPh}K.0.5PhMe]∞ (3K). X-ray crystallography revealed that, while 2Li and 3Li crystallize as monomers, 1Li and 2Na crystallize as borane-bridged dimers. The potassium complexes 1K, 2K, and 3K all crystallize with polymeric structures, in which the monomer units are linked to each other through a range of both bridging BH3 groups and multihapto interactions between the potassium cations and the aromatic rings. The reactions between two equivalents of either 1Li or 3Li and Cp2Sn gave the corresponding dialkylstannylenes [{R2P(BH3)CHPh}2Sn] [R = iPr (1Sn), Cy (3Sn)]. These compounds were isolated as mixtures of the rac and meso diastereomers. X-ray crystallography reveals that rac-1Sn and rac-3Sn crystallize as discrete monomers each exhibiting two agostic-type B–H···Sn contacts.
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Jan 2024
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I19-Small Molecule Single Crystal Diffraction
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Bernhard
Kepplinger
,
Lina
Mardiana
,
Joseph
Cowell
,
Stephanie
Morton-Laing
,
Yousef
Dashti
,
Corinne
Wills
,
Emma C. L.
Marrs
,
John D.
Perry
,
Joe
Gray
,
Michael
Goodfellow
,
Jeff
Errington
,
Michael R.
Probert
,
William
Clegg
,
Jonathan
Bogaerts
,
Wouter
Herrebout
,
Nick E. E.
Allenby
,
Michael J.
Hall
Diamond Proposal Number(s):
[6749, 11145]
Open Access
Abstract: A genomic and bioactivity informed analysis of the metabolome of the extremophile Amycolatopsis sp. DEM30355 has allowed for the discovery and isolation of the polyketide antibiotic tatiomicin. Identification of the biosynthetic gene cluster was confirmed by heterologous expression in Streptomyces coelicolor M1152. Structural elucidation, including absolute stereochemical assignment, was performed using complementary crystallographic, spectroscopic and computational methods. Tatiomicin shows antibiotic activity against Gram‑positive bacteria, including methicillin‑resistant Staphylococcus aureus (MRSA). Cytological profiling experiments suggest a putative antibiotic mode‑of‑action, involving membrane depolarisation and chromosomal decondensation of the target bacteria.
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Sep 2022
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: Herein we present a rearomative diastereoselective etherification/amination reaction of 2,3,9,9a-tetrahydro-
1H-carbazoles, themselves accessible via the Diels-Alder reaction of N-protected 3-vinyl-1H-indoles. We
have developed a one-pot rearomative bromination/nucleophilic substitution reaction sequence employing both
O- and N-centred nucleophiles, inverting the typical reactivity of 2,3,9,9a-tetrahydro-1H-carbazoles at the
4-position. Alcohols or secondary amines can be incorporated allowing access to the corresponding 4-substituted-
2,3,4,9-tetrahydro-1H-carbazoles, the diastereoselectivity of the reaction being controlled by the nature of
the nucleophile and the reaction conditions.
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Apr 2021
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[6302]
Abstract: The reaction between two equivalents of {(Me3Si)2CH}(Ph)PH(BH3) (1) and Bu2Mg, followed by two
equivalents of BH3·SMe2, gives the corresponding phosphido-bis(borane) complex, which may be crystallised as two distinct chemical species: the complex [{(Me3Si)2CH}(Ph)P(BH3)2]2Mg(THF)4·THF (2a), and two
different THF solvates (1 : 1 and 1 : 2) of the solvent-separated ion triples [{(Me3Si)2CH}(Ph)P(BH3)2]2[Mg
(THF)6]·THF (2b) and [{(Me3Si)2CH}(Ph)P(BH3)2]2[Mg(THF)6]·2THF (2c). Similar reactions between two
equivalents of 1 and either (4-tBuC6H4CH2)2Ca(THF)4 or [(Me3Si)2CH]2Sr(THF)2, followed by two equivalents of BH3·SMe2, give the heavier alkali metal complexes [{(Me3Si)2CH}(Ph)P(BH3)2]2M(THF)4 [M = Ca (3),
Sr (4)]. Surprisingly, compounds 2a, 3 and 4 adopt almost identical structures in the solid state, which
differ only in the geometrical arrangement of the phosphido-bis(borane) ligands and the hapticity of the
borane groups.
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Dec 2020
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I19-Small Molecule Single Crystal Diffraction
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Jonathan
Bould
,
Kamil
Lang
,
Kaplan
Kirakci
,
Luis
Cerdán
,
Daniel
Roca-Sanjuán
,
Antonio
Francés-Monerris
,
William
Clegg
,
Paul G.
Waddell
,
Marcel
Fuciman
,
Tomáš
Polívka
,
Michael G. S.
Londesborough
Diamond Proposal Number(s):
[22240]
Abstract: We present the first examples of alkylated derivatives of the macropolyhedral boron hydride, anti-B18H22, which is the gain medium in the first borane laser. This new series of ten highly stable and colorless organic–inorganic hybrid clusters are capable of the conversion of UVA irradiation to blue light with fluorescence quantum yields of unity. This study gives a comprehensive description of their synthesis, isolation, and structural characterization together with a delineation of their photophysical properties using a combined theoretical and experimental approach. Treatment of anti-B18H221 with RI (where R = Me or Et) in the presence of AlCl3 gives a series of alkylated derivatives, Rx-anti-B18H22–x (where x = 2 to 6), compounds 2–6, in which the 18-vertex octadecaborane cluster architectures are preserved and yet undergo a linear “polyhedral swelling”, depending on the number of cluster alkyl substituents. The use of dichloromethane solvent in the synthetic procedure leads to dichlorination of the borane cluster and increased alkylation to give Me11-anti-B18H9Cl211, Me12-anti-B18H8Cl212, and Me13-anti-B18H7Cl213. All new alkyl derivatives are highly stable, extremely efficient (ΦF = 0.76–1.0) blue fluorophores (λems = 423–427 nm) and are soluble in a wide range of organic solvents and also a polystyrene matrix. The Et4-anti-B18H18 derivative 4b crystallizes from pentane solution in two phases with consequent multiabsorption and multiemission photophysical properties. An ultrafast transient UV–vis absorption spectroscopic study of compounds 4a and 4b reveals that an efficient excited-state absorption at the emission wavelength inhibits the laser performance of these otherwise remarkable luminescent molecules. All these new compounds add to the growing portfolio of octadecaborane-based luminescent species, and in an effort to broaden the perspective on their highly emissive photophysical properties, we highlight emerging patterns that successive substitutions have on the molecular size of the 18-vertex borane cluster structure and the distribution of the electron density within.
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Nov 2020
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[11145]
Open Access
Abstract: This feature article is derived from the author’s presentation of the Lonsdale Lecture at the BCA Spring Meeting in 2018. One of the research results for which Kathleen Lonsdale is best known was her 1929 demonstration that the benzene ring in crystalline hexamethylbenzene is planar and has essentially hexagonal
symmetry, resolving decades of dispute among organic chemists. More recent crystallographic studies of hexamethylbenzene have shown that there are actually small deviations from planarity. Such deviations for aromatic compounds may be due to electronic, steric, and/or intermolecular factors.
Some substituted benzene molecules display remarkably large deviations, both from a planar ring structure and from regular hexagonal angular geometry around the ring. Starting from this specific connection with Kathleen Lonsdale’s
research, a number of stories are recounted of structural distortions and deviations from expected results and explanations that have been suggested for them, across a wide range of chemical topics including macrocycles, metal clusters, unusual coordination geometry and isomerism. On the way we find genuine surprises and results that have led to new understanding, but also examples of poor experiments, misinterpretation of data, scientific bias and preconceived ideas, incompetence and even deliberate fraud. Some aspects of structure validation are discussed. While showcasing some interesting research in its own right, this account also serves an educational purpose.
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Nov 2020
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[16117]
Abstract: The reaction of K[arachno-B9H14] with [NiCl2(dppe)] produces four new 19-vertex macropolyhedral metallaboranes that result from borane cluster fusion: [9′-(dppe)-9′-Ni-anti-B18H20] (1) and isomeric [11′-(dppe)-11′-Ni-syn-B18H20] (2), together with the chlorine-substituted derivative of 1, [5′-Cl-9′-(dppe)-9′-Ni-anti-B18H19] (3), and the 18-vertex cluster compound [7′-(dppe)-7′-anti-NiB17H21] (4). Two closo 10-vertex single-cluster species, [1-(dppe)-1-closo-NiB9H7Cl2] (5) and [1-(dppe)-1-closo-NiB9H7Cl(OH)] (6), were also isolated from the reaction. The production of the metalated syn-octadecaborane isomer 2 from the fusion of two arachno-nonaborate clusters is the first such case to be observed; in all other reported cases fusion has resulted in products with the anti-octadecaboranyl bis-nido configuration.
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Sep 2019
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[748, 987, 1747, 2871, 6302, 6749, 8682, 11145, 14380, 16117, 21953]
Abstract: A historical account is given of the 25-year development of dedicated synchrotron beamlines for single-crystal diffraction as applied to the so-called small-molecule fields of chemistry and materials science. Designs have drawn on previous successful models in macromolecular crystallography, with appropriate modifications in view of the different properties and behaviour of the respective sample types. Key factors in making these facilities attractive and productive for users include familiarity of operational procedures and the availability of experimental techniques and features normally found in local chemical crystallography laboratories, especially for the handling of samples and processing of diffraction data. Beamlines dedicated to single-crystal diffraction rather than shared with other techniques can be optimized for effective and efficient use. The experience gained from the original design, development and exploitation of stations 9.8 and 16.2SMX at the Daresbury Laboratory Synchrotron Radiation Source and beamline 11.3.1 at the Advanced Light Source have led to highly productive current facilities at ALS beamline 12.2.1 and Diamond Light Source beamline I19, including the recent introduction of remote-access operation. Such facilities have generated and continue to provide major impact in academic and commercial research that could otherwise not be achieved, including patents and applications in pharmaceuticals, energy and gas storage systems, and government policy.
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Apr 2019
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[16117]
Open Access
Abstract: The silver-nucleoside complex [Ag(I)-(N3-cytidine)2], 1, self-assembles to form a supramolecular metal-mediated base-pair array analogous to those seen in metallo-DNA. A combination of complementary hydrogen-bonding, hydrophobic and argentophilic interaction drive the formation of a double-helix with a continuous silver core. These features are essentially retained in the corresponding organogel which exhibits thixotropic self-healing that can be attributed to the reversible nature of the intermolecular interactions. Electrical measurements on 1 show that despite having Ag···Ag distances within <5% of the metallic radii, the material is electrically insulating. This is due to the electronic structure which features filled valence bands and a large band gap and, hence, such Ag(I)-DNA systems should not be considered molecular nanowires. However, photo-reduced samples of gel exhibit luminescence confirming that these poly-cytidine sequences appropriately pre-configure silver ions for the formation of quantum-confined metal clusters in line with contemporary views on DNA-templated clusters.
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Feb 2019
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I19-Small Molecule Single Crystal Diffraction
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Hamed
Mosaei
,
Vadim
Molodtsov
,
Bernhard
Kepplinger
,
John
Harbottle
,
Christopher William
Moon
,
Rose Elizabeth
Jeeves
,
Lucia
Ceccaroni
,
Yeonoh
Shin
,
Stephanie
Morton-Laing
,
Emma Claire Louise
Marrs
,
Corinne
Wills
,
William
Clegg
,
Yulia
Yuzenkova
,
John David
Perry
,
Joanna
Bacon
,
Jeff
Errington
,
Nicholas Edward Ellis
Allenby
,
Michael John
Hall
,
Katsuhiko S.
Murakami
,
Nikolay
Zenkin
Diamond Proposal Number(s):
[8682]
Open Access
Abstract: Antibiotic-resistant bacterial pathogens pose an urgent healthcare threat, prompting a demand for new medicines. We report the mode of action of the natural ansamycin antibiotic kanglemycin A (KglA). KglA binds bacterial RNA polymerase at the rifampicin-binding pocket but maintains potency against RNA polymerases containing rifampicin-resistant mutations. KglA has antibiotic activity against rifampicin-resistant Gram-positive bacteria and multidrug-resistant Mycobacterium tuberculosis (MDR-M. tuberculosis). The X-ray crystal structures of KglA with the Escherichia coli RNA polymerase holoenzyme and Thermus thermophilus RNA polymerase-promoter complex reveal an altered—compared with rifampicin—conformation of KglA within the rifampicin-binding pocket. Unique deoxysugar and succinate ansa bridge substituents make additional contacts with a separate, hydrophobic pocket of RNA polymerase and preclude the formation of initial dinucleotides, respectively. Previous ansa-chain modifications in the rifamycin series have proven unsuccessful. Thus, KglA represents a key starting point for the development of a new class of ansa-chain derivatized ansamycins to tackle rifampicin resistance.
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Sep 2018
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