Search results for "Crystal structure analysis"
showing 7 items of 7 documents
Essential features of the polytypic charoite-96 structure compared to charoite-90
2011
AbstractCharoite, ideally (K,Sr,Ba,Mn)15–16(Ca,Na)32[(Si70(O,OH)180)](OH,F)4·nH20, is a rock-forming mineral from the Murun massif in Yakutia, Sakha Republic, Siberia, Russia, where it occurs in a unique alkaline intrusion. Charoite occurs as four different polytypes, which are commonly intergrown in nanocrystallme fibres. We report the structure of charoite-96(a =32.11(6),b =19.77(4),c =7.23(1) Å, β = 95.85(9)°,V =4565(24) Å3, space groupP21/m),which was solvedab initioby direct methods on the basis of 2676 unique electron diffraction reflections collected by automated diffraction tomography and refined toR1/wR2=0.34/0.37. The structure of charoite-96 is related to that of the charoite-90,…
The structure of charoite, (K,Sr,Ba,Mn)(15-16)(Ca,Na)(32)[(Si-70(O,OH)(180))](OH,F)(4.0)center dot nH(2)O, solved by conventional and automated elect…
2010
AbstractCharoite, ideally (K,Sr,Ba,Mn)15–16(Ca,Na)32[(Si70(O,OH)180)](OH,F)4.0·nH2O, a rare mineral from the Murun massif in Yakutiya, Russia, was studied using high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray spectroscopy, precession electron diffraction and the newly developed technique of automated electron-diffraction tomography. The structure of charoite (a= 31.96(6) Å,b= 19.64(4) Å,c= 7.09(1) Å, β = 90.0(1)°,V= 4450(24) Å3, space groupP21/m) was solvedab initioby direct methods from 2878 unique observed reflections and refined toR1/wR2= 0.17/0.21. The structure can be visualized as being composed of three different dreier silicate chains: a d…
Impact of the ΔPhe configuration on the Boc-Gly-ΔPhe-NHMe conformation: experiment and theory
2019
Conformational propensities of N-t-butoxycarbonyl-glycine-(E/Z)-dehydrophenylalanine N′-methylamides (Boc-Gly-(E/Z)-ΔPhe-NHMe) in chloroform were investigated by NMR and IR techniques. The low-temperature crystal structure of the E isomer was determined by single crystal X-ray diffraction and the experimental data were elaborated by theoretical calculations using DFT (B3LYP, M06-2X) and MP2 approaches. The β-turn tendencies for both isomers were determined in the gas phase and in the presence of solvent. The obtained results reveal that the configuration of ΔPhe residue significantly affects the conformations of the studied dehydropeptides. The tendency to adopt β-turn conformations is sign…
Molecular and crystal structure of Ac-(Z)-ΔAbu-NMe2 and Ac-DL-Abu-NMe2 as compared to those of related molecules
2004
Abstract The molecular and crystal structures of two homologous amino acid derivatives: N-acetyl-α,β-dehydro-butyrine N´,N´-dimethylamide (1) and N-acetyl-DL-butyrine N´,N´-dimethylamide (2), have been determined by X-ray crystallography. Similar solid-state association of both compounds is observed; despite different molecular conformation, they form centrosymmetric dimers linked by the intermolecular N–H…O hydrogen bonds. The conformation of two crystallographically independent molecules of 1 [with torsion angles ϕ, ψ, χ 1 ≈ (–47°, 130°, 3°), respectively] is also characteristic of other related diamides – ΔAla, ΔPhe and ΔLeu – previously studied in the solid state. To analyse whether thi…
Automated electron diffraction tomography – development and applications
2019
Electron diffraction tomography, a potential method for structure analysis of nanocrystals, and, in more detail, the strategies to use automated diffraction tomography (ADT) technique are described. Examples of ADT application are discussed according to the material class.
The conformation cis of N-acetyl-N-methyl-α,β-dehydroalanine N′-methylamide and saturated analogues
2007
A series of three homologous amino acids derivatives: N-acetyl-N-methyl-α,β–dehydroalanine N′-methylamide (1), N-acetyl-N-methyl-L-alanine N′-methylamide (2), and N-acetyl-N-methyl-DL-alanine N′-methylamide have been synthesised. The racemic species undergoes spontaneous separation into L and D-enantiomers. From these two chiral forms, the structure of L-enantiomer (3) was analysed. The molecules of 1 – 3 adopt the cis arrangement of the N-terminal amide bond. The molecular conformations are similar for 1 (φ, ψ = 94.6(1)°, −1.7(1)°) and 3 (φ, ψ = 111.5(1)°, −23.8(1)°), and also 2 (φ, ψ = −114.8(2)°, 29.5(2)°), if inversion through the chiral C2 carbon is considered. They are stabilised by i…
Combined Use of Structure Analysis, Studies of Molecular Association in Solution, and Molecular Modelling to Understand the Different Propensities of…
2021
The arrangement of hydroxyl groups in the benzene ring has a significant effect on the propensity of dihydroxybenzoic acids (diOHBAs) to form different solid phases when crystallized from solution. All six diOHBAs were categorized into distinctive groups according to the solid phases obtained when crystallized from selected solvents. A combined study using crystal structure and molecule electrostatic potential surface analysis, as well as an exploration of molecular association in solution using spectroscopic methods and molecular dynamics simulations were used to determine the possible mechanism of how the location of the phenolic hydroxyl groups affect the diversity of solid phases formed…