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Crystal Growth & Design

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https://www.readbyqxmd.com/read/29018306/solid-phase-deracemization-of-an-atropisomer
#1
Anthonius H J Engwerda, Pim van Schayik, Henjo Jagtenberg, Hugo Meekes, Floris P J T Rutjes, Elias Vlieg
The scope of Viedma ripening and temperature cycling with respect to chiral molecules has remained mostly limited to molecules with a single stereogenic center, while racemization proceeds through inversion at that particular stereocenter. In this article we demonstrate for the first time that atropisomers, chiral rotamers that possess an axis of chirality, can be successfully deracemized in the solid phase by either applying temperature cycling or Viedma ripening.
October 4, 2017: Crystal Growth & Design
https://www.readbyqxmd.com/read/29018305/unraveling-complexity-in-the-solid-form-screening-of-a-pharmaceutical-salt-why-so-many-forms-why-so-few
#2
Doris E Braun, Sreenivas R Lingireddy, Mark D Beidelschies, Rui Guo, Peter Müller, Sarah L Price, Susan M Reutzel-Edens
The solid form landscape of 5-HT2a antagonist 3-(4-(benzo[d]isoxazole-3-yl)piperazin-1-yl)-2,2-dimethylpropanoic acid hydrochloride (B5HCl) proved difficult to establish. Many crystalline materials were produced by solid form screening, but few forms readily grew high quality crystals to afford a clear picture or understanding of the solid form landscape. Careful control of crystallization conditions, a range of experimental methods, computational modeling of solvate structures, and crystal structure prediction were required to see potential arrangements of the salt in its crystal forms...
October 4, 2017: Crystal Growth & Design
https://www.readbyqxmd.com/read/28966560/crystal-nucleation-using-surface-energy-modified-glass-substrates
#3
Kyle A Nordquist, Kevin M Schaab, Jierui Sha, Andrew H Bond
Systematic surface energy modifications to glass substrates can induce nucleation and improve crystallization outcomes for small molecule active pharmaceutical ingredients (APIs) and proteins. A comparatively broad probe for function is presented in which various APIs, proteins, organic solvents, aqueous media, surface energy motifs, crystallization methods, form factors, and flat and convex surface energy modifications were examined. Replicate studies (n ≥ 6) have demonstrated an average reduction in crystallization onset times of 52(4)% (alternatively 52 ± 4%) for acetylsalicylic acid from 91% isopropyl alcohol using two very different techniques: bulk cooling to 0 °C using flat surface energy modifications or microdomain cooling to 4 °C from the interior of a glass capillary having convex surface energy modifications that were immersed in the solution...
August 2, 2017: Crystal Growth & Design
https://www.readbyqxmd.com/read/28794692/deracemization-of-a-racemic-allylic-sulfoxide-using-viedma-ripening
#4
Anthonius H J Engwerda, Niels Koning, Paul Tinnemans, Hugo Meekes, F Matthias Bickelhaupt, Floris P J T Rutjes, Elias Vlieg
Despite the importance of enantiopure chiral sulfoxides, few methods exist that allow for their deracemization. Here, we show that an enantiopure sulfoxide can be produced from the corresponding racemate using Viedma ripening involving rearrangement-induced racemization. The suitable candidate for Viedma ripening was identified from a library of 24 chiral sulfoxides through X-ray structure determination. Starting from the racemic sulfoxide, an unprecedented application of a 2,3-sigmatropic rearrangement type racemization in a Viedma ripening process allowed for complete deracemization...
August 2, 2017: Crystal Growth & Design
https://www.readbyqxmd.com/read/28729813/novel-design-integrating-a-microwave-applicator-into-a-crystallizer-for-rapid-temperature-cycling-a-direct-nucleation-control-study
#5
Rohit Kacker, Marilena Radoiu, Herman J M Kramer
The control of nucleation in crystallization processes is a challenging task due to the often lacking knowledge on the process kinetics. Inflexible (predetermined) control strategies fail to grow the nucleated crystals to the desired quality because of the variability in the process conditions, disturbances, and the stochastic nature of crystal nucleation. Previously, the concept of microwave assisted direct nucleation control (DNC) was demonstrated in a laboratory setup to control the crystal size distribution in a batch crystallization process by manipulating the number of particles in the system...
July 5, 2017: Crystal Growth & Design
https://www.readbyqxmd.com/read/28615995/additive-enhanced-creeping-of-sodium-chloride-crystals
#6
Eleanor R Townsend, Willem J P van Enckevort, Jan A M Meijer, Elias Vlieg
This article investigates the mechanism behind the creeping of sodium chloride induced by additives. Here, an experimental approach is complemented with theoretical considerations to describe how creeping patterns of brine evolve and how the introduction of additives into the solution affects the morphology of the resultant crystals. We have found that these additives cause kinetic roughening and morphological instability mainly due to the reduction of surface free energy. There was also a marked increase in three-dimensional nucleation of the NaCl crystals and thus branching...
June 7, 2017: Crystal Growth & Design
https://www.readbyqxmd.com/read/28867966/investigation-of-the-evolution-of-crystal-size-and-shape-during-temperature-cycling-and-in-the-presence-of-a-polymeric-additive-using-combined-process-analytical-technologies
#7
Elena Simone, Anneke R Klapwijk, Chick C Wilson, Zoltan K Nagy
Crystal size and shape can be manipulated to enhance the qualities of the final product. In this work the steady-state shape and size of succinic acid crystals, with and without a polymeric additive (Pluronic P123) at 350 mL, scale is reported. The effect of the amplitude of cycles as well as the heating/cooling rates is described, and convergent cycling (direct nucleation control) is compared to static cycling. The results show that the shape of succinic acid crystals changes from plate- to diamond-like after multiple cycling steps, and that the time required for this morphology change to occur is strongly related to the type of cycling...
April 5, 2017: Crystal Growth & Design
https://www.readbyqxmd.com/read/28670205/why-do-hydrates-solvates-form-in-small-neutral-organic-molecules-exploring-the-crystal-form-landscapes-of-the-alkaloids-brucine-and-strychnine
#8
Doris E Braun, Ulrich J Griesser
Computational methods were used to generate and explore the crystal structure landscapes of the two alkaloids strychnine and brucine. The computed structures were analyzed and rationalized by correlating the modelling results to a rich pool of available experimental data. Despite their structural similarity, the two compounds show marked differences in the formation of solid forms. For strychnine only one anhydrous form is reported in the literature and two new solvates from 1,4-dioxane were detected in the course of this work...
November 2, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/28261000/a-versatile-system-for-high-throughput-in-situ-x-ray-screening-and-data-collection-of-soluble-and-membrane-protein-crystals
#9
Jana Broecker, Viviane Klingel, Wei-Lin Ou, Aidin R Balo, David J Kissick, Craig M Ogata, Anling Kuo, Oliver P Ernst
In recent years, in situ data collection has been a major focus of progress in protein crystallography. Here, we introduce the Mylar in situ method using Mylar-based sandwich plates that are inexpensive, easy to make and handle, and show significantly less background scattering than other setups. A variety of cognate holders for patches of Mylar in situ sandwich films corresponding to one or more wells makes the method robust and versatile, allows for storage and shipping of entire wells, and enables automated crystal imaging, screening, and goniometer-based X-ray diffraction data-collection at room temperature and under cryogenic conditions for soluble and membrane-protein crystals grown in or transferred to these plates...
November 2, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/27829821/enhanced-nmr-discrimination-of-pharmaceutically-relevant-molecular-crystal-forms-through-fragment-based-ab-initio-chemical-shift-predictions
#10
Joshua D Hartman, Graeme M Day, Gregory J O Beran
Chemical shift prediction plays an important role in the determination or validation of crystal structures with solid-state nuclear magnetic resonance (NMR) spectroscopy. One of the fundamental theoretical challenges lies in discriminating variations in chemical shifts resulting from different crystallographic environments. Fragment-based electronic structure methods provide an alternative to the widely used plane wave gauge-including projector augmented wave (GIPAW) density functional technique for chemical shift prediction...
November 2, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/28670204/stoichiometric-and-non-stoichiometric-hydrates-of-brucine
#11
Doris E Braun, Ulrich J Griesser
The complex interplay of temperature and water activity (aw) / relative humidity (RH) on the solid form stability and transformation pathways of three hydrates (HyA, HyB and HyC), an isostructural dehydrate (HyAdehy ), an anhydrate (AH) and amorphous brucine has been elucidated and the transformation enthalpies quantified. The dihydrate (HyA) shows a non-stoichimetric (de)hydration behavior at RH < 40% at 25 °C and the removal of the water molecules results in an isomorphic dehydrate structure. The metastable dehydration product converts to AH upon storage at driest conditions or to HyA if exposed to moisture...
October 5, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/28808430/amelogenin-affects-brushite-crystal-morphology-and-promotes-its-phase-transformation-to-monetite
#12
Dongni Ren, Qichao Ruan, Jinhui Tao, Jonathan Lo, Steven Nutt, Janet Moradian-Oldak
Amelogenin protein is involved in organized apatite crystallization during enamel formation. Brushite (CaHPO4·2H2O), one of the precursors of hydroxyapatite mineralization in vitro, has been used for fabrication of biomaterials for hard tissue repair. In order to explore its potential application in biomimetic material synthesis, we studied the influence of the enamel protein amelogenin on brushite morphology and phase transformation to monetite. Our results show that amelogenin can adsorb onto the surface of brushite, leading to the formation of layered morphology on the (010) face...
September 7, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/27512345/role-of-caco3%C3%A2-neutral-pair-in-calcium-carbonate-crystallization
#13
Damiano Genovese, Marco Montalti, Fermín Otálora, Jaime Gómez-Morales, María Sancho-Tomás, Giuseppe Falini, Juan Manuel García-Ruiz
The molecular structure of the units that get incorporated into the nuclei of the crystalline phase and sustain their growth is a fundamental issue in the pathway from a supersaturated solution to the formation of crystals. Using a fluorescent dye we have recorded the variation of the pH value in time along a gel where CaCl2 and NaHCO3 counter-diffuse to crystallize CaCO3. The same pH-space-time distribution maps were also computationally obtained using a chemical speciation code (phreeqc). Using data arising from this model we investigated the space-time evolution of the activity of the single species (ions and ion pairs) involved in the crystallization process...
August 3, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/29056873/characterization-of-protein-nanocrystals-based-on-the-reversibility-of-crystallization
#14
Katerina Dörner, Jose M Martin-Garcia, Christopher Kupitz, Zhen Gong, T Conn Mallet, Liqing Chen, Rebekka M Wachter, Petra Fromme
A new approach is described to screen for protein nanocrystals based on the reversibility of crystallization. Methods to characterize nanocrystals are in strong need to facilitate sample preparation for serial femtosecond X-ray nanocrystallography (SFX). SFX enables protein structure determination by collecting X-ray diffraction from nano- and microcrystals using a free electron laser. This technique is especially valuable for challenging proteins as for example membrane proteins and is in general a powerful method to overcome the radiation damage problem and to perform time-resolved structure analysis...
July 6, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/27418882/surface-induced-phase-of-tyrian-purple-6-6-dibromoindigo-thin-film-formation-and-stability
#15
Magdalena Truger, Otello M Roscioni, Christian Röthel, Dominik Kriegner, Clemens Simbrunner, Rizwan Ahmed, Eric D Głowacki, Josef Simbrunner, Ingo Salzmann, Anna Maria Coclite, Andrew O F Jones, Roland Resel
The appearance of surface-induced phases of molecular crystals is a frequently observed phenomenon in organic electronics. However, despite their fundamental importance, the origin of such phases is not yet fully resolved. The organic molecule 6,6'-dibromoindigo (Tyrian purple) forms two polymorphs within thin films. At growth temperatures of 150 °C, the well-known bulk structure forms, while at a substrate temperature of 50 °C, a surface-induced phase is observed instead. In the present work, the crystal structure of the surface-induced polymorph is solved by a combined experimental and theoretical approach using grazing incidence X-ray diffraction and molecular dynamics simulations...
July 6, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/28663717/computational-and-experimental-characterization-of-five-crystal-forms-of-thymine-packing-polymorphism-polytypism-disorder-and-stoichiometric-0-8-hydrate
#16
Doris E Braun, Thomas Gelbrich, Klaus Wurst, Ulrich J Griesser
New polymorphs of thymine emerged in an experimental search for solid forms, which was guided by the computationally generated crystal energy landscape. Three of the four anhydrates (AH) are homeoenergetic (A° - C) and their packing modes differ only in the location of oxygen and hydrogen atoms. AHs A° and B are ordered phases, whereas AH C shows disorder (X-ray diffuse scattering). Anhydrates AHs A° and B are ordered phases, whereas AH C shows disorder (X-ray diffuse scattering). Analysis of the crystal energy landscape for alternative AH C hydrogen bonded ribbon motifs identified a number of different packing modes, whose 3D structures were calculated to deviate by less than 0...
June 1, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/27175105/crystallization-of-carbamazepine-in-proximity-to-its-precursor-iminostilbene-and-a-silica-surface
#17
Paul Christian, Christian Röthel, Martin Tazreiter, Andreas Zimmer, Ingo Salzmann, Roland Resel, Oliver Werzer
Amorphous films of the anticonvulsant drug carbamazepine are easily accessible by various methods, while the crystallization into specific polymorphs represents a challenging and time-consuming task. In this work, the crystallization of drop cast carbamazepine at silica surfaces is investigated by atomic force microscopy and both in situ and ex situ grazing incidence X-ray diffraction. The pristine films grow with low crystallization rates into a triclinic polymorph, exhibiting poor orientational order within films...
May 4, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/27175104/detergent-mediated-formation-of-%C3%AE-hematin-heme-crystallization-promoted-by-detergents-implicates-nanostructure-formation-for-use-as-a-biological-mimic
#18
Rebecca D Sandlin, Kim Y Fong, Renata Stiebler, Christopher P Gulka, Jenny E Nesbitt, Matheus P Oliveira, Marcus F Oliveira, David W Wright
Hemozoin is a unique biomineral that results from the sequestration of toxic free heme liberated as a consequence of hemoglobin degradation in the malaria parasite. Synthetic neutral lipid droplets (SNLDs) and phospholipids were previously shown to support the rapid formation of β-hematin, abiological hemozoin, under physiologically relevant pH and temperature, though the mechanism by which heme crystallization occurs remains unclear. Detergents are particularly interesting as a template because they are amphiphilic molecules that spontaneously organize into nanostructures and have been previously shown to mediate β-hematin formation...
May 4, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/27081373/supramolecular-synthons-will-giant-rigid-superspheres-do
#19
Eugenia Peresypkina, Alexander Virovets, Manfred Scheer
For the first time, the concept of supramolecular synthons was applied to giant rigid superspheres based on pentaphosphaferrocene [Cp(R)Fe(η(5)-P5)] (R = Me, Et) and Cu(I) halides, which reach 2.1-3.0 nm in diameter. Two supramolecular synthons, σ-π and π-π, are discovered based on halogen···Cp(R) and Cp*···Cp* specific interactions, respectively. The geometry of the synthons is reproducible in a series of crystal structures of various supramolecules. The σ-π synthon alone is realized more frequently for Br-containing superspheres...
April 6, 2016: Crystal Growth & Design
https://www.readbyqxmd.com/read/27065755/self-assembled-multilayers-of-silica-nanospheres-for-defect-reduction-in-non-and-semipolar-gallium-nitride-epitaxial-layers
#20
Tongtong Zhu, Tao Ding, Fengzai Tang, Yisong Han, Muhammad Ali, Tom Badcock, Menno J Kappers, Andrew J Shields, Stoyan K Smoukov, Rachel A Oliver
Non- and semipolar GaN have great potential to improve the efficiency of light emitting devices due to much reduced internal electric fields. However, heteroepitaxial GaN growth in these crystal orientations suffers from very high dislocation and stacking faults densities. Here, we report a facile method to obtain low defect density non- and semipolar heteroepitaxial GaN via selective area epitaxy using self-assembled multilayers of silica nanospheres (MSN). Nonpolar (11-20) and semipolar (11-22) GaN layers with high crystal quality have been achieved by epitaxial integration of the MSN and a simple one-step overgrowth process, by which both dislocation and basal plane stacking fault densities can be significantly reduced...
February 3, 2016: Crystal Growth & Design
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