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Abstract: Experimental and computational searches for the crystal structures of the five commercially available isomers of dichloronitrobenzene and 3,4-dinitrochlorobenzene were performed to assess the relationship between functional group interactions and steric requirements in determining the solid forms. Experimentally, this resulted in the first crystal structure determination of 2,4-dichloronitrobenzene, two solvates of 3,4-dichloronitrobenzene and one of 3,4-dinitrochlorobenzene. Additionally, low temperature redeterminations of the crystal structures were obtained for 2,5-dichloronitrobenzene, 3,4-dichloronitrobenzene, and both the ?- and ?-forms of 3,4-dinitrochlorobenzene. The searches for energetically feasible structures of each of these compounds showed a wide variety of distributions leading to varying degrees of clarity of prediction of the solid state behavior. These range from 2,3-dichloronitrobenzene, which only adopts the crystal structure that was clearly the most thermodynamically stable of all five isomers, through complex systems, which show a range of low energy minima indicating possible polymorphism and solvate formation, to 2,4-dichloronitrobenzene, which can conformationally distort and adopts a complicated Z? = 2 crystal structure.
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Jan 2008
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Abstract: The structural response of the nootropic drug piracetam (2-oxo-pyrrolidineacetamide) to both direct compression and high-pressure recrystallization from aqueous solution is reported. Crystals obtained by these methods have been characterized in situ by single-crystal X-ray diffraction. Compression of form II between pressures of 0.45-0.70 GPa caused a reversible, single- crystal to single-crystal transition to give a new polymorph, form V. Crystallization from a dilute aqueous solution of piracetam at a pressure of 0.6 GPa via crystallization of high-pressure ice-VI resulted in the formation of a previously unreported dihydrate. The molecular packing arrangements of these new structures are compared with the known polymorphs and hydrates of piracetam. This study highlights how the systematic variation of pressure is a powerful method for the exploration of polymorphism and solvate formation and has the potential to add a further dimension to polymorph screening of pharmaceuticals.
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May 2007
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Open Access
Abstract: Reaction of zinc(II) chloride with the ligand N,N‘-{2,4-(di-2-pyridylamino)-1,3,5-triazin-6-yl}-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (oxodendtriz) in acetonitrile/methanol results in the formation the tetranuclear complex [Zn4(oxodendtriz)Cl8](CH3CN)2(H2O)1.5. Notably, its crystal structure reveals unique π-interactions with the first experimental evidence of electron-rich/electron-poor molecule pairing, which is corroborated by computational studies. In addition, infinite helical water chains with both right- and left-handed configurations are present in the crystal lattice.
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May 2006
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Abstract: Systematic investigation of the reactions of the system AlCl3·6H2O/pyridine-2,4,6-tricarboxylic acid (H3PTC)/pyridine in water yielded two new compounds, both containing the dimeric {AlPTC(μ-OH)(H2O)}22– unit. With long reaction times, the framework compound [Al(μ-OH){AlPTC(μ-OH)(H2O)}2]·2H2O (CAU-16, compound 1) is obtained, the first example of a framework compound with a metal–organic cluster linker, and bearing the MIL-53 network. Although the compound does not breathe, as other MIL-53 compounds do, it has a maximum uptake of CO2 of 1.76(2) mmol g–1 at 196 K. With shorter reaction times, the molecular compound {Al(HPTC)(μ-OH)(H2O)}2 (2) was prepared, leading to the proposal of a crystallization scheme for the Al3+-pyridine-2,4,6,-tricarboxylic acid system. To determine whether further framework compounds bearing hybrid metal cluster linkers could be prepared, systematic high-throughput investigations of pyridine-2,4,6-tricarboxylic acid in water with Ga3+ and In3+ were undertaken. These yielded two chain-type compounds, GaPTC(H2O)2 (3) and InPTC(H2O)2 (4), with different coordination chemistries. Optimized syntheses for compounds 1, 2, and 4 are reported.
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Oct 2014
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Abstract: We report the solid-state structural properties and phase transition behaviour of 1,4-dibromo-2,3,5,6-tetramethylbenzene, demonstrating that this material undergoes an order-disorder phase transition below ambient temperature (at ca. 156 K on cooling and ca. 159 K on heating). In both the high-temperature and low-temperature phases, the crystal structure is based on π-stacking of the molecules. In the high-temperature phase, the bromine and methyl groups are located with essentially equal probability in each of the six substituent positions, and it is shown by natural-abundance solid-state 2H NMR spectroscopy that, at ambient temperature, this disorder is dynamic via rapid molecular reorientation about an axis perpendicular to the aromatic ring. In the low-temperature phase, the bromine and methyl substituents occupy preferred sites within the crystal structure, with the distribution of site occupancies becoming progressively more ordered on decreasing temperature.
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Mar 2019
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B18-Core EXAFS
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Diamond Proposal Number(s):
[8269]
Abstract: Calcite formation via an amorphous calcium carbonate (ACC) precursor phase potentially offers a method for enhanced incorporation of incompatible trace metals, including Sr2+. In batch crystallisation experiments where CaCl2 was rapidly mixed with Na2CO3 solutions the Sr2+ : Me2+ ratio was varied from 0.001 to 0.1; and, the pathway of calcite precipitation was directed by either the presence or absence of high Mg2+ concentrations (i.e. using a Mg2+ : total Me2+ ratio of 0.1). In the Mg-free experiments crystallisation proceeded via ACC → vaterite → calcite and average Kd Sr values were between 0.44-0.74. At low Sr2+ concentrations (Sr2+ : Me2+ ratio ≤ 0.01) EXAFS analysis revealed that the Sr2+ was incorporated into calcite in the 6 fold coordinate Ca2+ site. However, at higher Sr2+ concentrations (Sr2+ : Me2+ ratio = 0.1), Sr2+ was incorporated into calcite in a 9-fold site with a local coordination similar to Ca2+ in aragonite, but calcite-like at longer distances (i.e. > 3.5 Å). In the high-Mg experiments the reaction proceeded via an ACC → calcite pathway with higher Kd Sr of 0.90-0.97 due to the presence of Mg2+ stabilising the ACC phase and promoting rapid calcite nucleation in conjunction with higher Sr2+ incorporation. Increased Sr2+ concentrations also coincided with higher Mg2+ uptake in these experiments. Sr2+ was incorporated into calcite in a 9-fold coordinate site in all the high-Mg experiments regardless of initial Sr2+ concentrations, likely as a result of very rapid crystallisation kinetics and the presence of smaller Mg2+ ions compensating for the addition of larger Sr2+ ions in the calcite lattice. These experiments show that the enhanced uptake of Sr2+ ions can be achieved by calcite precipitation via ACC, and may offer a rapid, low temperature, low-cost, method for removal of several incompatible Me2+ ions (e.g. Pb2+, Ba2+, Sr2+) during effluent treatment.
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Jan 2017
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B18-Core EXAFS
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Diamond Proposal Number(s):
[17060]
Abstract: Sr-containing calcium carbonates were precipitated from solutions containing Ca(OH)2, SrCl2 and Na2CO3 in a reactor where constant solution composition was maintained. The total concentration of divalent ions was same in all experiments, but the Sr/Ca ratio was varied between 0.002 and 0.86, and the pH value was between 12.02 and 12.25. All solutions were oversaturated with respect to calcite (SIcalcite = 1.2-1.5). Calcite was the only product formed at low Sr/Ca ratios, but at Sr/Ca ≥ 0.45 strontianite was detected in some systems. Sr-rich precipitate was observed in both a surface layer on (6.9-6 µm) rhombic calcite seed crystals and as smaller (> 3.64-1.96 µm) calcite crystals that were elongated along their C-axis. The degree of crystal elongation increased with the Sr/Ca ratio in those crystals. Precipitates recovered from low Sr/Ca ratio experiments exhibited an XRD spectrum identical to that of rhombic calcite, however the peaks attributed to Sr-containing calcite shifted progressively to lower 2θ values with increasing solution Sr/Ca ratio, indicating increased lattice volume. Sr K-edge EXAFS analysis of the precipitates showed that the shift in morphology and lattice volume is accompanied by a change in the local coordination of Sr2+ in calcite. The Sr-O bond lengths were similar to the Ca-O bond lengths in calcite, but Sr-O coordination increased from 6 fold in crystals containing 0.21 Wt. % Sr, to 8 fold in crystals containing 9.47 Wt. % Sr, and the Sr-Ca coordination decreased from 6 and 6 (for the first and second Sr-Ca shells respectively) to 4 and 1. It is suggested that Sr2+ undergoes preferential incorporation at obtuse (+) growth sites on the calcite surface due to its large ionic radius (1.13 Å), and this increases the growth rate parallel to the C-axis, resulting in the observed elongation in this direction.
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Apr 2018
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Controls
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Matthew W.
Bowler
,
Uwe
Mueller
,
Manfred S.
Weiss
,
Juan
Sanchez-weatherby
,
Thomas
Sorensen
,
Marjolein M. G. M.
Thunnissen
,
Thomas
Ursby
,
Alexandre
Gobbo
,
Silvia
Russi
,
Michael G.
Bowler
,
Sandor
Brockhauser
,
Olof
Svensson
,
Florent
Cipriani
Open Access
Abstract: Controlled dehydration of macromolecular crystals can lead to significant
improvements in crystalline order, which often manifests itself in higher diffraction
quality. Devices that can accurately control the humidity surrounding crystals on a
beamline have led to this technique being increasingly adopted as experiments become
easier and more reproducible. However, these experiments are often carried out by trial
and error, and in order to facilitate and streamline them four European synchrotrons
have established a collaboration around the HC1b dehydration device. The MAX IV
Laboratory, Diamond Light Source, BESSY II, and the EMBL Grenoble Outstation/
ESRF have pooled information gathered from user experiments, and on the use of the
device, to propose a set of guidelines for these experiments. Here, we present the status
and automation of the installations, advice on how best to perform experiments using
the device, and an analysis of successful experiments that begins to show some trends in
the type of protocols required by some systems. The dehydration methods shown are
applicable to any device that allows control of the relative humidity of the air
surrounding a macromolecular crystal.
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Mar 2015
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I02-Macromolecular Crystallography
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Diamond Proposal Number(s):
[8425]
Abstract: Nucleation is a critical step determining the outcome of the entire crystallization process. Finding an effective nucleant for protein crystallization is of utmost importance for structural biology. The latter relies on good-quality crystals to solve the three-dimensional structures of macromolecules. In this study we show that crystalline barium sulfate (BaSO4) with an etched and/or ionic liquid (IL)-functionalized surface (1) can induce protein nucleation at concentrations well below the concentration needed to promote crystal growth under control conditions, (2) can shorten the nucleation time, (3) can increase the growth rate, and finally (4) may help to improve the protein crystal morphology. These effects were shown for lysozyme, RNase A, trypsin, proteinase K, myoglobin, and hemoglobin. Therefore, the use of BaSO4 particles enables us to reduce the amount of protein in crystallization trials and increases the chance of obtaining protein crystals of the desired quality. In the context of the underlying mechanism, it is shown that the protein–solid contact formation is governed by the interaction of the polar compartments of the biomacromolecule with the support. The tendency of a protein to concentrate near the solid surface is enhanced by both the hydrophobicity of the protein and that of the surface (tuned by the functionalizing IL). These mechanisms of interaction of biomacromolecules with inorganic hydrophilic solids correspond to the principles of amphiphilic IL–mineral interactions.
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Jun 2015
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I03-Macromolecular Crystallography
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Abstract: A new strategy is proposed for batch crystallization of proteins in solution-growth or gel-growth by using the batch method inside capillary tubes applying magnetic fields. Four proteins with differing proportions of alpha-helices and beta-sheets and crystallized in five different crystallographic space groups are studied, allowing an analysis of the anisotropy of the diamagnetic susceptibility of the peptide bond its well as the polarity of the space groups in the presence of a strong magnetic field of 11.75 T. The crystal quality is shown to be improved by using a strong magnetic field to orient protein molecules, and gel-growth (high concentrations of agar) to control the transport phenomena as well as crystal growth. Sonic advantages to increase the crystal quality for crystals from marginal conditions for X-ray diffraction, and disadvantages of the use of solution- and gel-growth (low concentration of agar) in magnetic Fields, and their plausible applications to high resolution X-ray crystallography are discussed.
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Dec 2009
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