Powder X-ray Diffraction Crystallography Research Articles

Dual organic-structure directing agents in the synthesis of high-silica MOR Zeolite: Cooperation or competition?

Constructing a high-silica framework of a given zeolite topology via a conventional hydrothermal synthetic strategy is still an open question. In this work, In this contribution, we report the high-silica MOR zeolite (Si/Al ratio: ∼30) was fabricated by a dual OSDA combination strategy at a fixed alkalinity (OH−/SiO2) ratio of around 0.4. Additionally, we found that bulky TEA+ cation and smaller neutral heterocycle molecules severed as the pore-filling agent and cooperatively squeeze the occupation of sodium cation resulting in the low sodium content of high-silica MOR zeolite. However, such cooperative behavior can be easily spoiled by the high alkalinity ratio above 0.5. With the increment of the alkalinity ratio, the sodium cations can retake the occupied sites and facilitate the MOR framework with a relatively low Si/Al ratio. As unveiled by the powder X-ray diffraction crystallography and combined spectroscopy strategies, the nature of different dual OSDA combinations occluded in the high-silica MOR zeolite with deduced aluminum enriched T sites provide the reference for the forthcoming target design of zeotype catalysts.

Synthesis, characterization and comprehensive study of a 3D Co(II) coordination polymer antibacterial activity

The current work reports the facile synthesis and complete characterization of a stable 3D Co(II)-based coordination polymer, namely Co(HCOO)2(4,4′-bpy) (1), (4,4′-bpy=4,4′-bipyridine), prepared via two different synthetic methods including solvothermal reaction and reflux method. The Co-coordination polymer was fully characterized by 1H NMR, FT-IR, FE-SEM, TGA, ICP, BET, single-crystal X-ray crystallography, powder X-ray diffraction crystallography, and VSM analysis. The cell treatment with Co-coordination polymer was evaluated, and the cytotoxicity study was done by MTT assays against the HEK-293 cell line. Furthermore, the antibacterial properties of Co-coordination polymer nanoparticles were investigated. The Co-coordination polymer showed significant antibacterial properties against the selected strains of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria.

Tailoring zeolite ERI aperture for efficient separation of CO2 from gas mixtures

Constructing the metal cation-mediated low-cost inorganic sorbent with high separation efficiency in CO2, N2, and CH4 remains a major challenge. Herein, we developed a series of alkali metal cations (Na+, K+, Rb+, Cs+)-exchanged ERI zeolites and adopted in the separation process of CO2 among the gas mixture. Among the ion-exchanged zeolites, the zeolite K-ERI showed a high adsorption volume of 70.84 cm3g−1 and an IAST selectivity of CO2/CH4: 6254, CO2/N2: 2872 at 298 K, respectively, far outweighed the reported metal cation exchanged zeolites. Combining powder X-ray diffraction crystallography and density functional theory calculations, we unequivocally unveiled that the metal cations located at s8r effectively tailored zeolite aperture, and metal cation-gas molecules interactions synergically restrained the pass-through capacity of CO2 in ion-exchanged ERI framework. Such a unique host–guest interaction governed by metal cations in aluminosilicate zeolite ERI affords a general strategy for gas separation.

Insights into the role of titanium sites in cyclohexanone ammoximation over titanium silicalite-1

The discovery of titanium silicalite-1(TS-1) is a milestone in the development of heterogeneous catalysts for the eco-benign and mild catalytic oxidation process. However, the interpretation of specific Ti location and its role in oxidation is severely hindered due to the limited crystal size of as-synthesized TS-1. Here, a high quality TS-1 (ca. 10 μm) was successfully fabricated by the pre-hydrolysis silica source strategy. As evidenced by powder X-ray diffraction crystallography, the preferred Ti locations were mainly found at T2, T4, and T11 in Ti-containing MFI framework. Combining multiple spectroscopy methods (i.e., FT-IR, UV–Vis, and UV Raman) and the reaction kinetics, the active center in TS-1 was demonstrated as an exposed site of hexa-coordinated titainum species. Furthermore, the powder X-ray crystallography also revealed that the ketone and oxime adsorbed in the zeolite host with intense host-guest interaction of framework oxygen atoms, and exhibiting an overwhelming spatial intimacy to the Ti species at the molecular scale. This unique phenomenon affords a plausible interpretation for the oxime reaction.

Exploring the complex map of insulin polymorphism: a novel crystalline form in the presence of m-cresol.

In this study, the first crystal structure of a novel crystal form of human insulin bound to meta-cresol in an acidic environment is reported. The combination of single-crystal and powder X-ray diffraction crystallography led to the detection of a previously unknown monoclinic phase (P21). The structure was identified from the powder patterns and was solved using single-crystal diffraction data at 2.2 Å resolution. The unit-cell parameters at pH 6.1 are a = 47.66, b=70.36, c=84.75 Å, β = 105.21°. The structure consists of two insulin hexamers per asymmetric unit. The potential use of this insulin form in microcrystalline drugs is discussed.

Investigation of α-amino acid N-carboxyanhydrides by X-ray diffraction for controlled ring-opening polymerization

The need for a scalable synthesis of not sequence defined polypeptides as biomaterials is met by the ring-opening polymerization of α-amino acid N-carboxyanhydrides (NCAs). Even though this polymerization technique appears straight forward, it holds pitfalls in terms of reproducibility and overall control over the polymerization conditions, which depends, beside choice of solvent or initiator, significantly on reagent purity. In addition, the synthesis of monomers can lead to the formation of racemic amino acids. Thus, in this work, we describe the benefits of highly pure monomers in order to control nucleophilic ring-opening polymerization NCAs. Hereby, monomer purity is investigated by relating melting points of NCAs with single-crystal and powder X-ray diffraction crystallography data, which further proves retained stereo-information of NCAs.

Design and Fabrication of Polymer Layered Silicate Nanocomposites for Water Purification

ABSTRACTZeolite and cellulose-acetate nanocomposites were fabricated in this study using a combination of melt blending and solution mixing. The nanocomposites were optimized for heavy metal adsorption using spiked lead and cadmium solutions. Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy and Powder X-Ray diffraction crystallography were used for physical characterization. Fourier Transform Infrared spectra showed a reduction of the hydroxyl peak for cellulose acetate and that of the residual silanol group for zeolites symbolizing bonding during nanocomposite formation. Scanning Electron Microscope results showed an increase in voids with zeolite loading in the nanocomposites, a useful characteristic of good adsorbents. Powder X-ray diffraction crystallography results showed a reduction in 2 theta values for the nanocomposites due to penetration of the polymer into the silicate lattice e.g. zeolite 2 theta peak at 7.44°reduced to 7.09°in the nanocomposites signifying an increase in crystal lattice d- spacing from 1.188 nm to 1.247 nm. The nanocomposites adsorbed a maximum of 97.20% lead ions and 85.06% cadmium ions from solution.

Influence of synthetic conditions on the formation of thermally and hydrolytically stable Sc-based metal–organic frameworks

Three new coordination polymers ((CH3)2NH2)[Sc(H2O)2(fdc)2]·1,5CH3CN (1), ((CH3)2NH2)2[Sc(fdc)2(HCOO)] (2), [Sc2(H2O)2(fdc)3] (3) based on scandium cations and 2,5-furandicarboxylate ligand (fdc2−) have been synthesized and characterized by single crystal and powder X-ray diffraction crystallography, TG, elemental analyses and IR-spectroscopy. Compound 1 is formed from layers bind by hydrogen bonds. Calculated accessible for solvent volume is 41%. Compound 2 is a structure of negatively charged layers connected with interlayer dimethylammonium cations. Layered compound 3 appeared to be thermally stable (up to 300 °C) and retain its structure in wide range of pH from 1 to 13. Additionally, the solid-state luminescence properties of compounds 2 and 3 we investigated.

SMARTER crystallography of the fluorinated inorganic–organic compound Zn3Al2F12·[HAmTAZ

We present in this paper the structure resolution of a fluorinated inorganic-organic compound--Zn(3)Al(2)F(12)·[HAmTAZ](6)--by SMARTER crystallography, i.e. by combining powder X-ray diffraction crystallography, NMR crystallography and chemical modelling of crystal (structure optimization and NMR parameter calculations). Such an approach is of particular interest for this class of fluorinated inorganic-organic compound materials since all the atoms have NMR accessible isotopes ((1)H, (13)C, (15)N, (19)F, (27)Al, (67)Zn). In Zn(3)Al(2)F(12)·[HAmTAZ](6), (27)Al and high-field (19)F and (67)Zn NMR give access to the inorganic framework while (1)H, (13)C and (15)N NMR yield insights into the organic linkers. From these NMR experiments, parts of the integrant unit are determined and used as input data for the search of a structural model from the powder diffraction data. The optimization of the atomic positions and the calculations of NMR parameters ((27)Al and (67)Zn quadrupolar parameters and (19)F, (1)H, (13)C and (15)N isotropic chemical shifts) are then performed using a density functional theory (DFT) based code. The good agreement between experimental and DFT-calculated NMR parameters validates the proposed optimized structure. The example of Zn(3)Al(2)F(12)·[HAmTAZ](6) shows that structural models can be obtained in fluorinated hybrids by SMARTER crystallography on a polycrystalline powder with an accuracy similar to those obtained from single-crystal X-ray diffraction data.

Structure of polymer electrolytes: the crystal structure of poly(ethylene oxide) 4:RbSCN

The crystal structure of the polymer electrolyte poly(ethylene oxide) 4:RbSCN has been elucidated by powder X-ray diffraction crystallography. The structure is important since it is the largest cation system to be established to date. The complex is isostructural with the previously characterised 4:1 complexes of the salts KSCN and NH 4SCN. It consists of the PEO chain in helical ttgttgttḡttḡ conformation enclosing the large Rb + cation in each turn of the helix. Rb + is coordinated by five ether oxygens and two SCN − ions. The thiocyanate anions in turn coordinate two neighbouring cations simultaneously along one PEO chain. As in all the previously determined 3:1 and 4:1 PEO-salt complexes, there are no direct interchain interactions. The general structural principles which may be determined from the crystal structures solved so far are discussed including the effect of cation size (ranging from Li + to Rb +) on the PEO conformation.

The hepatoprotective cytochrome P-450 enzyme inhibitor isolated from the Nigerian medicinal plant Cochlospermum planchonii is a zinc salt

Aqueous extracts of Cochlospermum planchonii Hook.f. (Cochlospermaceae) rhizomes are used by native medical practitioners in northern Nigeria to treat jaundice. An extract prepared by a laboratory adaptation of their method was hepatoprotective in carbon tetrachloride-treated rats (CCl 4), and it inhibited cytochrome P-450 enzymes, which constitutes a plausible hepatoprotective mechanism. A crystalline inhibitor (0.3% of dry weight of rhizomes) was isolated using inhibition of two rat cytochrome P-450 enzymes, aminopyrine- N-demethylase and aniline hydroxylase, as bioassays to guide fractionation by solvent partitioning, polyamide column chromatography, preparative thin layer chromatography and fractional crystallization. The inhibitor was identified as zinc formate by inductively coupled plasma atomic emission spectroscopy, nuclear magnetic resonance spectroscopy and comparison with synthetic material by powder X-ray diffraction crystallography. Synthetic and plant-derived zinc formate were equally effective as inhibitors of cytochrome P-450 enzymes and as hepatoprotective agents in carbon tetrachloride-treated rats. Cochlospermum planchonii rhizomes contain unusually high levels of manganese and zinc, although much higher levels have been observed in plants considered to be hyperaccumulators of these metals.