Search results for "polymorph"

Nuclear ribosomal DNA (nrDNA) concerted evolution in natural and artificial hybrids of Armeria (Plumbaginaceae)

1999

Nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) sequences from artificial hybrids and backcrosses between Armeria villosa ssp. longiaristata and A. colorata were studied to assess the possible effects of concerted evolution in natural hybrids. F1 artificial hybrids show the expected pattern of additive polymorphisms for five of the six variable sites as estimated from direct sequences. However, homogenization of polymorphism is already observed in the F2, and is biased towards A. colorata except for one site. In backcrosses, an expected tendency towards homogenization of polymorphic sites in the direction of the recurrent parent is observed for five sites, although this does…

A brief history of the formation of DNA databases in forensic science within Europe.

2001

The introduction of DNA analysis to forensic science brought with it a number of choices for analysis, not all of which were compatible. As laboratories throughout Europe were eager to use the new technology different systems became routine in different laboratories and consequently, there was no basis for the exchange of results. A period of co-operation then started in which a nucleus of forensic scientists agreed on an uniform system. This collaboration spread to incorporate most of the established forensic science laboratories in Europe and continued through two major changes in the technology. At each step agreement was reached on which systems to use. From the beginning it was realise…

Influence of CYP2D6 polymorphism on the cytotoxicity of the designer drug 4-methylthioamphetamine (4-MTA)

2007

Optimization of sample preparation conditions for detecting trace amounts of β-tegafur in α- and β-tegafur mixture.

2012

We report a semiquantitative method for determining trace amounts (<1%) of thermodynamically stable forms in polymorphic mixtures, focusing on sample preparation ef- fects on solid phase transitions. Tegafur (5-fluoro-1-(oxolan-2-yl)-1,2,3,4-tetrahydropyrimidine- 2,4-dione) was used as a model material in this study. The amounts of the thermodynamically stable $ tegafur were increased to levels detectable by powder X-ray diffractometry by grind- ing the samples in a ball mill in the presence of water. The limit of detection for this method was as low as 0.0005% of $ tegafur in " and $ tegafur mixtures. The amount of $ tegafur after sample preparation was found to be proportional to the init…

Granulocyte cytosolic calcium in type 2 diabetes

2005

Thermal, spectroscopic and crystallographic analysis of mannose-derived linear polyols

2018

The major diastereomer formed in the Barbier-type metal-mediated allylation of D-mannose has previously been shown to adopt a perfectly linear conformation, both in solid state and in solution, resulting in the formation of hydrogen-bonded networks and subsequent aggregation from aqueous solution upon stirring. Here, a comprehensive study of the solid state structure of both the allylated D-mannose and its racemic form has been conducted. The binary melting point diagram of the system was determined by differential scanning calorimetry analysis, and the obtained results, along with structure determination by single crystal X-ray diffraction, confirmed that allylated mannose forms a true rac…

New zeolite-like RUB-5 and its related hydrous layer silicate RUB-6 structurally characterized by electron microscopy.

2020

RUB-5 and its related hydrous layer silicate RUB-6 were synthesized in the 1990s, but so far their structures have remained unknown due to their low crystallinity and disorder. The combination of 3D electron diffraction, X-ray powder diffraction, high-resolution transmission electron microscopy, structural modelling and diffraction simulations has enabled a comprehensive description of these two nanomaterials, revealng a new framework topology and a unique silica polymorph.

Pressure-induced phase transformations in mineral chalcocite, Cu2S, under hydrostatic conditions

2014

Abstract High-pressure room-temperature angle-dispersive powder X-ray diffraction measurements on Cu2S chalcocite were performed up to 30 GPa using a diamond-anvil cell, He as pressure transmitting medium and synchrotron radiation. Two first-order phase transitions were found at 3.2 and 7.4 GPa. The indexation of the powder diffraction patterns suggests three different monoclinic cells for the low-pressure chalcocite and the two high-pressure phases. Subtle changes in the X-ray diffraction patterns suggest a third pressure-induced transition above 26 GPa. Structural parameters and compressibility are discussed and compared to those reported in a previous study on Cu2S nanowires.

1989

Some structurally disordered models for poly(tetrafluoroethylene) were elaborated and the corresponding calculated X-ray diffraction patterns compared with experimental patterns. This and differential scanning calorimetry results suggest some differences between the virgin powder and a sintered polycrystalline plate of poly(tetrafluoroethylene). These differences may be related to the crystal phase transitions that occur in a range of temperatures close to room temperature.

Polymorphism in Strontium Tungstate SrWO 4 under Quasi-Hydrostatic Compression

2016

The structural and vibrational properties of SrWO4 have been studied experimentally up to 27 and 46 GPa, respectively, by angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy measurements as well as using ab initio calculations. The existence of four polymorphs upon quasi-hydrostatic compression is reported. The three phase transitions were found at 11.5, 19.0, and 39.5 GPa. The ambient-pressure SrWO4 tetragonal scheelite-type structure (S.G. I41/a) undergoes a transition to a monoclinic fergusonite-type structure (S.G. I2/a) at 11.5 GPa with a 1.5% volume decrease. Subsequently, at 19.0 GPa, another structural transformation takes place. Our calculations indicate two possi…