I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[22240]
Open Access
Abstract: Wide-dose-range 2D radiochromic films for radiotherapy, such as GAFchromic EBT, are based on the lithium salt of 10,12-pentacosadiynoic acid (Li-PCDA) as the photosensitive component. We show that there are two solid forms of Li-PCDA—a monohydrated form A and an anhydrous form B. The form used in commercial GAFchromic films is form A due to its short needle-shaped crystals, which provide favorable coating properties. Form B provides an enhanced photoresponse compared to that of form A, but adopts a long needle crystal morphology, which is difficult to process. The two forms were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, CP-MAS 13C solid-state NMR spectroscopy, and thermogravimetric analysis. In sum, these data suggest a chelating bridging bidentate coordination mode for the lithium ions. The sodium salt of PCDA (Na-PCDA) is also reported, which is an ionic cocrystal with a formula of Na+PCDA–·3PCDA. The PCDA and PCDA– ligands display monodentate and bridging bidentate coordination to the sodium ion in contrast to the coordination sphere of the Li-PCDA forms. In contrast to its lithium analogues, Na-PCDA is photostable.
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Mar 2021
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[16117, 222240]
Open Access
Abstract: In this work we develop photoreactive cocrystals/salts of a commercially-important diacetylene, 10,12-pentacosadiynoic acid (PCDA, 1) and report the first X-ray crystal structures of PCDA based systems. The topochemical reactivity of the system is modified depending on the coformer used and correlates with the structural parameters. Crystallisation of 1 with 4,4′-azopyridine (2), 4,4′-bipyridyl (3), and trans-1,2-bis(4-pyridyl)ethylene (4) results in unreactive 2[thin space (1/6-em)]:[thin space (1/6-em)]1 cocrystals or a salt in the case of 4,4′-bipiperidine (5). However, salt formation with morpholine (6), diethylamine (7), and n-butylamine (8), results in highly photoreactive salts 12·7 and 1·8 whose reactivity can be explained using topochemical criteria. The salt 1·6 is also highly photoreactive and is compared to a model morpholinium butanoate salt. Resonance Raman spectroscopy reveals structural details of the photopolymer including its conformational disorder in comparison to less photoactive alkali metal salts and the extent of solid state conversion can be monitored by CP-MAS NMR spectroscopy. We also report an unusual catalysis in which amine evaporation from photopolymerised PCDA ammonium salts effectively acts as a catalyst for polymerisation of PCDA itself. The new photoreactive salts exhibit more reactivity but decreased conjugation compared to the commercial lithium salt and are of considerable practical potential in terms of tunable colours and greater range in UV, X-ray, and γ-ray dosimetry applications.
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Jul 2020
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: We report the application of supramolecular gel and microemulsion droplet crystallisation methodologies to isoniazid crystallization. Tailored gelators have been designed with isoniazid mimetic functionality in an attempt to control crystal morphology and polymorphic behaviour. Microemulsion crystallisation was investigated to achieve thermodynamic control over drug crystallisation. Both techniques resulted in only a single form of isoniazid implying that it is genuinely monomorphic.
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Feb 2018
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[11145]
Abstract: A series of l-histidine-derived monoureas are described which exhibit versatile organogelation peroperties when the substituent directly attached to the urea is an aliphatic group. Arylureas exhibit a tendency to bind chloride anion.
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Feb 2018
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: This paper reports the characterization of the composition and morphology of mineral formation on glass and plastic (polymethylmethacrylate) substrates in a dishwasher environment and the identification of suitable phosphate-free mineral crystallization inhibitors as environmentally benign candidates to replace the currently used phosphate-containing inhibitor 1-hydroxyethane 1,1-diphosphoric acid (HEDP). Screening of the calcium carbonate crystallization inhibition performance of twenty-eight different compounds resulted in the identification of two phosphate-free, cyclic polycarboxylic acid inhibitors, which were found in combination to be effective replacements. Each inhibitor proved to be highly substrate specific with all-cis-cyclohexane-1,2,3,4,5,6-hexacarboxylic acid (CHHCA) preventing deposition on glass (where calcite is the dominant polymorph) and cis,cis,cis,cis-cyclopentane-1,2,3,4-tetracarboxylic acid (CPTCA) inhibiting aragonite deposition on polymethylmethacrylate (PMMA). When used in combination, these two species prevented all forms of calcium carbonate deposition on both substrate types. The underlying inhibition mechanism and structural requirements of an efficient calcium carbonate inhibitor are also discussed.
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Jan 2018
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: Lamellar supramolecular assemblies are a common feature of fibrous gels formed by molecules such as peptides and ureas. Competition between gelation and crystallization is highly solvent dependent and can be governed by the dynamics of nascent lamellae in solution. We hypothesize that gel fibrils are formed when the scrolling of lamellae outpaces multilayer stacking. Crystallographic data on model picolyl bis(urea)s were correlated with their gelation properties. Most structures are lamellar, and gels involving fibrous aggregates form concomitantly alongside crystalline solvates. A distinguishing feature of these solvate crystals is that the lamellae have unequal numbers of picolyl groups on opposite faces. Atomistic molecular dynamics simulations show that this asymmetry causes isolated lamellae to scroll spontaneously into fibrils, whereas symmetrical lamellae adopt flat, crumpled, or saddle-like morphologies. Scrolling represents a general mechanism for gel formation, affording networks of unbranched fibers with monodisperse diameters dictated by the equilibrium curvature of the folding lamellae.
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Oct 2017
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: The solution hydration behavior of a series of lactam-based kinetic clathrate hydrate inhibitors (KHIs) has been studied in order to determine mechanistic insight into their KHI performance. IR and 1H NMR spectroscopic titration data were compared across a series of mono- and bis(lactam) model compounds, and solid-phase hydration behavior was examined by Dynamic Vapour Sorption. The structures of several of the model compounds have been investigated by X-ray crystallography. The work reveals insight into the very low crystallinity and high hygroscopicity of these materials which is linked to their performance as KHIs. Analysis of water binding in sour gas systems, containing H2S and CO2, reveals no effect on the water affinity of the lactams suggesting that sour gas components do not inhibit KHI performance, but rather promote clathrate hydrate formation.
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Apr 2017
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I19-Small Molecule Single Crystal Diffraction
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Oday A.
Al-owaedi
,
David C.
Milan
,
Marie-christine
Oerthel
,
Sören
Bock
,
Dmitry S.
Yufit
,
Judith A. K.
Howard
,
Simon J.
Higgins
,
Richard J.
Nichols
,
Colin J.
Lambert
,
Martin R.
Bryce
,
Paul J.
Low
Diamond Proposal Number(s):
[6749]
Open Access
Abstract: The single-molecule conductance of metal complexes of the general forms trans-Ru(C≡CArC≡CY)2(dppe)2 and trans-Pt(C≡CArC≡CY)2(PPh3)2 (Ar = 1,4-C6H2-2,5-(OC6H13)2; Y = 4-C5H4N, 4-C6H4SMe) have been determined using the STM I(s) technique. The complexes display high conductance (Y = 4-C5H4N, M = Ru (0.4 ± 0.18 nS), Pt (0.8 ± 0.5 nS); Y = 4-C6H5SMe, M = Ru (1.4 ± 0.4 nS), Pt (1.8 ± 0.6 nS)) for molecular structures of ca. 3 nm in length, which has been attributed to transport processes arising from tunneling through the tails of LUMO states.
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Sep 2016
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[6749]
Abstract: The Pd(PPh3)4/CuI-cocatalyzed reaction of
Ru(CñMCCñMCH)(PPh3)2Cp (2) with aryl iodides, Ar-I (3,
Ar = C6H4CN-4 (a); C6H4Me-4 (b); C6H4OMe-4 (c); 2,3-
dihydrobenzo[b]thiophene (d); C5H4N (e)) proceeds
smoothly in diisopropylamine and under an inert atmosphere
to give the substituted buta-1,3-diynyl complexes Ru(CñM
CCñMCAr)(PPh3)2Cp (4a-e) in moderate to good yield. The
procedure allows the rapid preparation of a range of metal
complexes of arylbuta-1,3-diynyl ligands without necessitating
the prior synthesis of the individual buta-1,3-diynes as ligand
precursors. Similar reaction of 2 with half an equivalent of 1,4-
diiodobenzene affords the bimetallic derivative {Ru-
(PPh3)2Cp}2(Ê-CñMCCñMC-1,4-C6H4−CñMCCñMC) (5). In
the presence of atmospheric oxygen, homocoupling of the diynyl reagent 2 takes place to provide the octa-1,3,5,7-tetrayndiyl
complex {Ru(PPh3)2Cp}2(Ê-CñMCCñMCCñMCCñMC) (6). Crystallographically determined molecular structures are reported
for five complexes (4a, 4b, 4d, 5, and 6). Quantum chemical calculations indicate that the HOMOs are mainly located on the
C4−C6H4−C4 and C8 bridges for 5 and 6, respectively, while spectroelectrochemical (UV−vis−NIR and IR) studies on 6
establish that oxidation takes place at the C8 bridge, likely followed by cyclodimerization reactions of the bridging ligand.
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Jun 2015
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[6749]
Abstract: The synthesis and characterization of a series of cobalt compounds,
coordinated by the redox-active macrocyclic biquinazoline ligand, Mabiq [2−4:6−8-
bis(3,3,4,4-tetramethyldihydropyrrolo)-10−15-(2,2′-biquinazolino)-[15]-1,3,5,8,10,14-hexaene-
1,3,7,9,11,14-N6], is presented. The series includes the monometallic Co(Mabiq)Cl2
(1), Co(Mabiq)Cl (2), and Co(Mabiq) (4), with formal metal oxidation states of 3+ →
1+. A binuclear cobaltous compound, Co2(Mabiq)Cl3 (3), also was obtained, providing
the first evidence for the ability of the Mabiq ligand to coordinate two metal ions. The
electronic structures of the paramagnetic 2 and 3 were examined by electron paramagnetic
resonance spectroscopy and magnetic susceptibility studies. The CoII ion that resides in
the N4-macrocylic cavity of 2 and 3 adopts a low-spin S = 1/2 configuration. The
bypirimidine functionality in 3 additionally coordinates a high-spin S = 3/2 cobaltous ion in
a tetrahedral environment. The two metal ions in 3 are weakly coupled by magnetometry.
The square-planar, low-valent 4 offers one of a limited number of examples of structurally
characterized N4-macrocyclic CoI compounds. Spectroscopic and density functional theory computational data suggest that a
CoII(Mabiq•) description may be a reasonable alternative to the CoI formalism for this compound.
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Jun 2015
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