FOX, Current State and Possibilities

Černý, Radovan; Favre‐Nicolin, V.; Rohlíček, Ján; Hušák, M.

doi:10.3390/cryst7100322

Cited by 10 publications

(3 citation statements)

References 28 publications

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“…The model of the crystal structure was generated using the global optimization technique implemented in FOX. 32 , 33 Figure 11 presents the Rietveld refinement result for SM_D diffractogram by utilizing GSAS-II software. 34 In the Rietveld refinement, standard restraints were applied to bond lengths and angles, as well as planar restraints to the aromatic parts of the molecule.…”

Section: Resultsmentioning

confidence: 99%

“…The experimental diffraction data were indexed in an orthorhombic cell applying the successive dichotomy method DICVOL04 as implemented in Expo2014 software. 29 − 31 The global optimization technique using FOX 32 , 33 with the application of a safinamide and methanesulfonate molecule model was applied. Multiple runs of calculations were performed with 8 × 10 6 trials per run, and the best obtained solution was selected based on the smallest data fitting discrepancies, as well as the general sense of the calculated model was chosen for the structure refinement stage.…”

Section: Methodsmentioning

confidence: 99%

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Solid-State Study of the Structure, Dynamics, and Thermal Processes of Safinamide Mesylate─A New Generation Drug for the Treatment of Neurodegenerative Diseases

et al. 2021

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Safinamide mesylate ( SM ), the pure active pharmaceutical ingredient (API) recently used in Parkinson disease treatment, recrystallized employing water–ethanol mixture of solvents (vol/vol 1:9) gives a different crystallographic form compared to SM in Xadago tablets. Pure SM crystallizes as a hemihydrate in the monoclinic system with the P 2 1 space group. Its crystal and molecular structure were determined by means of cryo X-ray crystallography at 100 K. SM in the Xadago tablet exists in anhydrous form in the orthorhombic crystallographic system with the P 2 1 2 1 2 1 space group. The water migration and thermal processes in the crystal lattice were monitored by solid-state NMR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. SM in Xadago in the high-humidity environment undergoes phase transformation to the P 2 1 form which can be easily reversed just by heating up to 80 °C. For the commercial form of the API, there is also a reversible thermal transformation observed between Z ′ = 1 ↔ Z ′ = 3 crystallographic forms in the 0–20 °C temperature range. Analysis of molecular motion in the crystal lattice proves that the observed conformational polymorphism is forced by intramolecular dynamics. All above-mentioned processes were analyzed and described employing the NMR crystallography approach with the support of advanced theoretical calculations.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Solid-State Study of the Structure, Dynamics, and Thermal Processes of Safinamide Mesylate─A New Generation Drug for the Treatment of Neurodegenerative Diseases

et al. 2021

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“…They allow defining additional conditions for the studied crystal structure, which is handled as additional observation. For example, the model can be restricted by several specifying torsion angles or by rigid groups as it is already implemented in existing software [6,7]. All these additional observations aim to make it possible to find a solution or at least significantly reduce the calculation time.Another observation that may increase the probability of finding the correct solution is the information about intermolecular distances in the crystal structure.…”

mentioning

confidence: 99%

Use of intermolecular distances from ssNMR in crystal structure determination from powder diffraction data

Rohlíček¹,

Kobera²,

Hušák³

et al. 2021

Acta Cryst Sect A

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The steady-state in the field of software allowing the application of different approaches for crystal structure determination [1,2] could give the impression that the determination of the crystal structure from the powder diffraction data is a common and straightforward task that does not deserve additional attention. However, looking at crystal structures determined from powder diffraction data, one can estimate the limit of the method. In the words of degrees of freedom, the current limit is around 40. The two most complex crystal structures found in the CSD database [3,4], and also many others, were solved using the direct-space methods [5]. Simply said, the direct-space methods find the structural model by changing the position and shape of the molecular fragments in the asymmetric part of the unit cell. They allow defining additional conditions for the studied crystal structure, which is handled as additional observation. For example, the model can be restricted by several specifying torsion angles or by rigid groups as it is already implemented in existing software [6,7]. All these additional observations aim to make it possible to find a solution or at least significantly reduce the calculation time.Another observation that may increase the probability of finding the correct solution is the information about intermolecular distances in the crystal structure. This information can be obtained by performing a specific ssNMR measurement which usually offers a list of short-range interactions between atoms. We decided to implement such a possibility to the already existing software FOX [5], and we tested it on several compounds. First of all, we tested it on the already solved crystal structures. We defined intermolecular distances between several selected atoms with various precisions, and we used them as additional restrictions that influenced the final cost function. We then tested it on a compound with an unknown crystal structure, for which we obtained estimated intermolecular distances from the ssNMR. We used these additional observations for the structure solution process from X-ray powder diffraction data.

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