Crystal forms of betulin. Polymorphysm or pseudopolymorphysm?

Porins represent a group of channel forming proteins that facilitate diffusion of small solutes across the outer membrane of Gram-negative bacteria, while excluding large molecules (>650 Da). Planar membranes reconstituted from purified matrix porin (OmpF protein) trimers and phospholipids have allowed quantitative functional studies of the voltage-dependent channels and revealed concerted activation of triplets. Under the same reconstitution conditions but using high protein concentrations porin aggregated to 2D lattices suitable for electron microscopy and image processing. Depending on the lipid-to- protein ratio three different crystal packing arrangements were observed: a large (a = 93 Å) and a small (a = 79 Å) hexagonal and a rectangular (a = 79 Å b = 139 Å) form with p3 symmetry for the hexagonal arrays. In all crystal forms distinct stain filled triplet indentations could be seen and were found to be morphologically identical within a resolution of (22 Å). It is tempting to correlate stain triplets with triple channels, but the proof of this hypothesis requires an analysis of the structure in 3 dimensions.

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Crystal forms

Physics Subject Headings (PhySH) ◽

10.29172/b23c6297-9e2d-413e-84ae-84e597abac27 ◽

2018 ◽

Keyword(s):

Crystal Forms

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Crystal Forms of Semisynthetic Ergot Alkaloid Terguride

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc20020479 ◽

2002 ◽

Vol 67 (4) ◽

pp. 479-489 ◽

Cited By ~ 4

Author(s):

Michal Hušák ◽

Bohumil Kratochvíl ◽

Ivana Císařová ◽

Ladislav Cvak ◽

Alexandr Jegorov ◽

...

Keyword(s):

Crystal Structure ◽

Ergot Alkaloid ◽

Simplified Model ◽

Quantum Mechanical ◽

Quantum Mechanical Calculations ◽

X Ray Diffraction ◽

Torsion Angles ◽

Crystal Forms ◽

X Ray ◽

Independent Molecules

Two new structures of semisynthetic ergot alkaloid terguride created by unusual number of symmetry-independent molecules were determined by X-ray diffraction methods at 150 K. Form A (monoclinic, P212121, Z = 12) contains three symmetry-independent terguride molecules and two molecules of water in the asymmetric part of the unit cell. The form CA (monoclinic, P21, Z = 8) is an anhydrate remarkable by the presence of four symmetry-independent molecules in the crystal structure. Conformations of twelve symmetry-independent molecules that were found in four already described terguride structures are compared with torsion angles obtained by ab initio quantum-mechanical calculations for the simplified model of N-cyclohexyl-N'-diethylurea.

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Monitoring protein precipitates by in-house X-ray powder diffraction

Powder Diffraction ◽

10.1017/s0885715613000833 ◽

2013 ◽

Vol 28 (S2) ◽

pp. S458-S469 ◽

Cited By ~ 1

Author(s):

Kenny Ståhl ◽

Christian G. Frankær ◽

Jakob Petersen ◽

Pernille Harris

Keyword(s):

Powder Diffraction ◽

Protein Crystal ◽

Data Sets ◽

Crystal Forms ◽

X Ray ◽

Cell Parameters ◽

X Ray Scattering ◽

Source Organism ◽

Peak Asymmetry ◽

Overlapping Peaks

Powder diffraction from protein powders using in-house diffractometers is an effective tool for identification and monitoring of protein crystal forms and artifacts. As an alternative to conventional powder diffractometers a single crystal diffractometer equipped with an X-ray micro-source can be used to collect powder patterns from 1 µl samples. Using a small-angle X-ray scattering (SAXS) camera it is possible to collect data within minutes. A streamlined program has been developed for the calculation of powder patterns from pdb-coordinates, and includes correction for bulk-solvent. A number of such calculated powder patterns from insulin and lysozyme have been included in the powder diffraction database and successfully used for search-match identification. However, the fit could be much improved if peak asymmetry and multiple bulk-solvent corrections were included. When including a large number of protein data sets in the database some problems can be foreseen due to the large number of overlapping peaks in the low-angle region, and small differences in unit cell parameters between pdb-data and powder data. It is suggested that protein entries are supplied with more searchable keywords as protein name, protein type, molecular weight, source organism etc. in order to limit possible hits.

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Born out of Fire and Ice: Polymorph Studies of the Antiviral Famciclovir

Crystals ◽

10.3390/cryst11020129 ◽

2021 ◽

Vol 11 (2) ◽

pp. 129

Author(s):

Liana Vella-Zarb ◽

Ulrich Baisch

Keyword(s):

Variable Temperature ◽

Chemical Properties ◽

Crystal Form ◽

X Ray Diffraction ◽

Crystal Forms ◽

X Ray ◽

Physical Chemical ◽

Diffraction Patterns ◽

Crystalline Forms

There is much interest and focus on solid forms of famciclovir. However, in spite of the abundance of reported differences in oral bioavailability, compressibility, and other physical–chemical properties of the various crystal forms of this drug, very little precise structural analysis is available in the literature to date. The form used in the commercial formulation is the anhydrous form I. Patents and patent applications report three different anhydrous crystalline forms on the basis of unindexed powder diffraction patterns. Single-crystal and variable-temperature X-ray diffraction experiments using the commercially available anhydrous form of famciclovir were carried out and led not only to the crystal structure determination of the anhydrous form I, but also to discovery of a new crystal form of anhydrous famciclovir from powder data.

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Vibrational spectroscopic and Hirshfeld surface analysis of carvedilol crystal forms

International Journal of Pharmaceutics ◽

10.1016/j.ijpharm.2018.10.051 ◽

2018 ◽

Vol 553 (1-2) ◽

pp. 261-271 ◽

Cited By ~ 1

Author(s):

Livia D. Prado ◽

Alexandre B.X. Santos ◽

Helvécio V.A. Rocha ◽

Glaucio B. Ferreira ◽

Jackson A.L.C. Resende

Keyword(s):

Surface Analysis ◽

Hirshfeld Surface ◽

Hirshfeld Surface Analysis ◽

Crystal Forms

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Tunable Nonlinear Optical Property of MnS Nanoparticles with Different Size and Crystal Form

Nanomaterials ◽

10.3390/nano10010034 ◽

2019 ◽

Vol 10 (1) ◽

pp. 34

Author(s):

Zhihao Zhang ◽

Pengchao Li ◽

Yuzong Gu

Keyword(s):

Optical Property ◽

Nonlinear Optical ◽

Nonlinear Optical Property ◽

Nonlinear Refraction ◽

Synthesis Method ◽

Crystal Form ◽

Optical Nonlinearity ◽

Photon Absorption ◽

Third Order ◽

Crystal Forms

It is significant to study the reason that semiconductor material has adjustable third-order optical nonlinearity through crystal form and dimensions are changed. αMnS nanoparticles with different crystal forms and sizes were successfully prepared by one-step hydrothermal synthesis method and their size-limited third-order nonlinear optical property was tested by Z-scan technique with 30 ps laser pulses at 532 nm wavelength. Nanoparticles of different crystal forms exhibited different NLO (nonlinear optical) responses. γMnS had stronger NLO response than αMnS because of higher fluorescence quantum yield. Two-photon absorption and the nonlinear refraction are enhanced as size of nanoparticlesreduced. The nanoparticles had maximum NLO susceptibility which was 3.09 × 10−12 esu. Susceptibility of αMnS increased about nine times than that of largest nanoparticles. However, it was reduced when size was further decreased. This trend was explained by the effects of light induced dipole moments. And defects in αMnS nanoparticles also had effect on this nonlinear process. MnS nanoparticles had potential application value in optical limiting and optical modulation.

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Crystal Structures of and Polarized Absorption-Spectroscopy in Racemic and Resolved [Ru(bpy)3] (ClO4)2 and [Zn(bpy)3] (ClO4)2Bpy=2,2'-Bipyridine

Australian Journal of Chemistry ◽

10.1071/ch9950929 ◽

1995 ◽

Vol 48 (5) ◽

pp. 929 ◽

Cited By ~ 35

Author(s):

E Krausz ◽

H Riesen ◽

AD Rae

Keyword(s):

Room Temperature ◽

Energy Difference ◽

Temperature Structure ◽

Asymmetric Unit ◽

Threefold Axis ◽

Crystal Forms ◽

The Third ◽

Racemic Form ◽

Ligand Charge Transfer ◽

Dominant Influence

[Zn( bpy )3] (ClO4)2 and [ Ru ( bpy )3] (ClO4)2 are isomorphous in both their racemic and resolved crystal forms. The resolved materials are monohydrates and have a C 2, Z = 8, structure with two independent formula units on general sites in the asymmetric unit. The cations have the same chirality. The inherent threefold axis of each cation lies approximately parallel to the c axis. The unrelated racemic form has a C2/c, Z = 4, structure which is a commensurate modulation of a P3c1, Z = 2, parent structure, typified by the room-temperature structure of [ Ru ( bpy )3] (PF6)2. A primary, secondary and tertiary axis of P3c1 become the c, b and a axes respectively of C2/c, retaining a third of the symmetry elements of P3c1. The crystals grow as multiply contacted twins. This structure bas just one spectroscopic site with the cation lying on a twofold axis that passes through the metal and one of the bidendate ligands and relates the other two ligands to each other. This feature is particularly useful in the study of the optical spectroscopy of the metal-to- ligand charge transfer excitations of [ Ru ( bpy )3]2+ and related systems. A comparison of structural and spectral data indicates that the positions of the anions have a dominant influence on the relative energies of the metal-to- ligand excitations. An energy difference between excitations involving the two (lower-energy) equivalent ligands and the third ligand of the order of 800 cm-1 is indicated in both singlet and triplet regions for the racemic perchlorate. The absorption spectra of [ Ru ( bpy )3]2+and [Os( bpy )3]2+ in a number of crystalline hosts are compared and discussed.

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