Polymorphism of D-mannitol: Crystal structure and the crystal growth mechanism

The polymorphism of D-Mannitol(mannitol) is reviewed in this paper. It was found that the structure of the stable form is consistent in most literatures, but different authors have given different information about the two metastable forms. Therefore the commonly used nomenclature of mannitol was summarized based on the crystal unit cell parameters with the help of X-ray powder diffraction. Moreover, the crystal growth mechanism of mannitol polymorphs was summarized. Considering the lack of kinetic data for the metastable form especially, a reported method was attempted to apply to δ mannitol in an aqueous cooling crystallization process based on the induction time previously measured, and it was identified that the growth of the δ form follows the two-dimensional(2D) nucleationmediated mechanism. The results also indicate that the method based on induction time and supersaturation should have the potential to be expanded to the metastable polymorphs for the growth property study in a bulk system.     

Crystal structure of the high-alkaline serine protease PB92 from Bacillus alcalophilus

The crystal structure of a serine protease from the alkalophilicstrain Bacillus alcalophilus PB92 has been determined by X-raydiffraction at 1.75 Â resolution. The structure has beensolved by molecular replacement using the atomic model of subtilisinCarlsberg. The model of the PB92 protease has been refined toan R-factor of 14.0% and contains 1882 protein atoms, two calciumions and 188 water molecules. The overall folding of the polypeptide chain closely resembles that of the subtilisins. Furthermore,almost all of the secondary structure elements found in subtilisinCarlsberg are also present in the PB92 protease. The major differencesbetween the two structures are located around the deletion regions(residues 37 and 158–161 in subtilisin Carlsberg) andin two loops which are known to be the most variable parts ofsubtilisin structures. Flexibility of one of these loops (residues126–130 in the PB92 protease) is believed to account forthe inducedfit mechanism of substrate binding.     

X射线在晶体衍射分析中的应用

本文介绍了X射线晶体衍射分析的原理和方法,对X射线在晶体衍射分析中的应用进行了阐述。     

Escherichia coli aspartate carbamoyltransferase: the probing of crystal structure analysis via site-specific mutagenesis

Crystal structures are known for aspartate carbamoyltransferase(ATCase) in the T and R states, with and without the allostericactivator adenosine triphosphate (ATP) or inhibitor cytidinetriphosphate (CTP). Visual inspection of X-ray crystal structuresdoes not provide all of the information necessary for the determinationof structure-function relationships in protein molecules. Thisproblem is compounded because the crystalline states of themolecule may introduce effects due to crystal packing, restrictedflexibility and less than optimum enzymatic conditions. Therefore,alternative techniques are required to test mechanisms conjecturedfrom three-dimensional crystal structures of proteins. The techniqueof site-specific mutagenesis allows the researcher to test structure- function models based on threedimensional structures and toobtain further insight into characteristics of the enzyme. Site-specificmutagenesis has been used to probe residues believed to be criticalin the structure and function of ATCase. Selection of residuesto be mutated has depended extensively on three-dimensionalcrystal structures of the enzyme. To date, 48 site-specificmutations at 37 different amino acid sites have been published.Although a total of 118 mutants at 58 different sites has beencommunicated to our laboratory, only published mutants willbe considered in this review. In this paper, we compile forthe first time, review, and analyze the site-specific mutantsof ATCase. Site-specific mutagenesis of proteins has becomea powerful technique in modern-day molecular biology, especiallyin studying a molecule as large as aspartate carbamoyltransferase.In this review, the role of site-specific mutagenesis of ATCaseis discussed and improvements in the analysis are suggested.     

Appraisal of microwave-assisted ion-exchange in mordenite by crystal structure analysis

Transition metal-containing mordenite have been prepared by solid state ion exchange with microwave irradiation of mechanical mixtures of CoCl₂·6H₂O, NiCl₂·6H₂O and CuCl₂·2H₂O with mordenite at 750?W microwave power and for 10?C20?min treatment time. The prepared transition metal-mordenite were characterized by X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FT-IR), simultaneous TG and DTA thermal analyses (TG/DTA), surface area measurement (BET), and diffuse reflectance spectroscopy (DRS). The results show that Co²⁺, Ni²⁺, and Cu²⁺ metal ions are actually incorporated into mordenite pores. The extra-framework locations of metal cations were determined Rietveld refinement of XRD data, performed in the Cmcm space group for all three samples. Three metal sites were located: the first site is in an almost perfect boat-shaped coordination with framework oxygen??s, the second site is poorly coordinated while the third metal cation site was found at the center of mordenite cage in six-fold coordination to water molecules.     

Single crystal X-ray structure analysis for two thiazolylazo indole dyes

To determine the tautomeric form of the hetarylazo indole dye 3-(5-methylthiazol-2-yldiazenyl)-2-phenyl-1H-indole (1), 1-methyl-3-(thiazol-2-yldiazenyl)-2-phenyl-1H-indole (2) was synthesized as a model compound and both molecules were characterized by single crystal X-ray diffraction. (1) crystallized in the monoclinic system, space group C2/c, a = 31.064(2), b = 7.4051(5), c = 27.7138(18) Å, β = 97.617(1)°, V = 6318.9(7) Å³, Z = 8, while dye 2 crystallized in the monoclinic system, space group P2₁/n, a = 11.4660(11), b = 9.8223(9), c = 14.2049(14) Å, β = 97.418(2)°, V = 1586.4(3) Å³, Z = 4. The asymmetric unit of 1 contains two crystallographically independent molecules, in which geometries and conformations differ slightly, while there is only one molecule in the asymmetric unit for 2. The intermolecular N–H?N hydrogen bonds in (1) link the molecules, via parallel, infinite sheets, along the a axis and stabilize the crystal structure; in 2, there is no classical intermolecular hydrogen bond.     

High-resolution solid-state NMR structure of an anticancer agent

We demonstrate that solid-state NMR methods can be used to rapidly determine the high-resolution 3D structure of Epothilone B in the polycrystalline state. The solid-state NMR structures exhibit an average heavy atom RMSD to the mean structure of 0.14 A. The 3D-structural analysis leads to stereospecific assignments and provides insight into the influence of intermolecular interactions upon ssNMR chemical-shift parameters. Our results pave the way to the study of ligand-microtubule interactions in a noncrystalline and insoluble environment at atomic level.     

High-resolution FTIR analysis of coal gas

Coal gas samples collected from a laboratory scale gasifier have been analysed using high-resolution (0.125 cm^?1) Fourier transform infrared spectrometry (FTIR). The gas samples were introduced into an evacuated 8.76 m path-length gas cell and backfilled with nitrogen to 1 atm. Carbonyl sulphide and ammonia were quantified in samples with concentrations ranging from trace to 370 ppm, and non-detectable to 25 ppm, respectively. Other compounds identified in the coal gas samples include: methane, ethane, ethylene, ?C₃ hydrocarbons, acetylene, carbon monoxide, carbon dioxide, ethylene oxide, methane thiol, hydrogen cyanide, formaldehyde, cyanogen (?), ethane thiol (?), methanol, and nitric acid (?). Several compounds were sought but were not present in detectable quantities (less than ≈ 1 ppm). These include: nickel carbonyl, arsine, benzene, methyl chloride, methylamine, HCI, nitrogen oxides, and phosgene. Selected compounds, e.g. ammonia, were quantified by calibration with a standard gas. High resolution FTIR, a nearly universal detector, is especially useful for determining presence or absence of specific pollutants or interest which are not easily determined by routine gas chromatographie methods.     

Synthesis and X-ray single crystal structure analysis of an inorganic nucleoside analog

The inorganic nucleoside analog [Boc-aeg{Cu(pda)py-Ac}-OMe] (3) is prepared and fully characterized. The X-ray single crystal analysis reveals that 3 assembles by apical Cu–O bonds into a coordination polymer, with short Cu–Cu distances of 5.32 and 5.78 Å. The solid state structure of 3 is in accordance with an isotactic structural model for charge neutral inorganic nucleic acids analogs. Aeg = (2-aminoethyl)glycine, py-Ac = 4-acetyl pyridine, pda = pyridine-2,6-dicarboxylic acid.     

Molecular and crystal structure of cellulose triacetate I: A parallel chain structure

The crystal structure of cellulose triacetate I (CTA I), obtained by heterogeneous acetylation of ramie cellulose I, has been determined by a combined X-ray diffraction and stereochemical model analysis. The structure packs in a two chain, orthogonal unit cell with dimensions $\text{a = 23.63}\text{A}\text{?}$, $\text{b = 6.27}\text{A}\text{?}$, $\text{c (}\text{fibre repeat}\text{) = 10.43}\text{A}\text{?}$, but with P2₁ symmetry. The two chains pack with parallel polarity and the two-fold screw axes coincide with the chain axes. In these respects, the structure of CTA I is similar to that of cellulose I. The conformations of the chain and of the glucose residue are similar to the conformation of the crystalline cellotriose undecaacetate, in that the ф, ψ angles, the 0(6) rotational positions, acetate positions and bond and conformation angles are comparable in both structures. The reliability of the structure determination of CTA I is indicated by the crystallographic R = 0.242.     

X‐ray crystal structure analysis for CI Disperse Orange 61

The synthesis, crystal structure analysis and characterisation of a monoazo dye, CI Disperse Orange 61, are reported. The dye crystallised in the triclinic system, space group P‐1 with a = 8.859(2), b = 9.899(2), c = 11.417(3)Å, α = 78.51(4)°, β = 70.37(3)°, γ = 80.46(4)°, V = 918.8(4)ų and Z = 2. There is only one molecule in the asymmetric unit. The two phenyl rings are oriented at a dihedral angle of 57.87(20)°. In the crystal structure, intermolecular C–H…N hydrogen bonds link the molecules into centrosymmetric dimers, forming R₂²(30) ring motifs, in which they may be effective in the stabilisation of the structure. The π…π stacking (interactions) between the phenyl rings may further stabilise the structure, with a centroid–centroid distance of 3.741(4)Å.     

Easy adaptation of protein structure to sequence

An investigation into the conservation of coarse, medium andfine grain structural properties has been performed over a dataset of 175 protein tertiary structures in 34 different families,each characterized by a common core fold and a library of conservedsites formed for each family. It is shown that, while the conservationof coarse and medium grain properties correlates to the structuraldeviation between the proteins, fine grain properties are poorlyconserved except in functional sites. This flexibility in finegrain properties suggests that folding can be viewed as an optimizationprocess whereby side chains have freedom to position themselvesas best as possible given environmental conformationa] constraintsand that given a basic framework, the local structure is ableto adapt easily to sequence variation. The conserved cores ofthe 34 families are used to estimate a minimal core size of35% of the fold, consistent with buried residue considerations.Finally, conservation in side chain l torsion angles is combinedwith structural deviation, sequence deviation and resolutionto suggest a set of example structure pairs suitable for testingautomatic homology modelling programs     

SHS-produced boron carbide: Some special features of crystal structure

Boron carbides with carbon contents (??) of 7?C24 at. % were prepared by SHS method and their lattice parameters were determined by high-precision XRD analysis. An unusually wide spread in the literature data on lattice parameters of boron carbide as a function of ?? was associated with the process of crystal ordering caused by gradual replacement of boron by carbon atoms. For SHS-produced boron carbide, the above spread turned out minimal. Lattice parameter c was found to attain the unusually high values of 12.20?C12.31 s was observed at ?? = 13.2%. The widths of diffraction lines from boron carbide were found to depend on ?? and attain their maximum values at ?? = 13.2% when the lattice is most disordered. Our results can make a basis for elaborating the means for regulating the structure/properties of boron carbide.     

Effect of processing on crystal structure

The performance of fats in many of their uses in food products is directly dependent on their crystal structure. Fats exist in several crystal modifications, each of which exhibits physical properties that influence the behavior of the fat differently in various applications. The crystal forms in which fats exist and their rates of transformation from one modification to another are dependent upon their molecular composition and configuration. Processing procedures such as blending, hydrogenation, interesterification, fractionation, etc., markedly alter the molecular composition and configuration. Other processing, such as votating and tempering practices, directly affect the crystal structure of the products. Thus, through judicious choice of processing procedures, the crystal characteristics of products can be governed to obtain the desired performance in specific applications. Presented at the AOCS Short Course, East Lansing, Mich., Aug. 29-Sept. 1, 1966.     

二羟基乙二肟的合成与晶体结构

以盐酸羟胺和草酸二乙酯为原料,在乙醇-水溶液中反应,得到二羟基乙二肟(DHG),培养出该化合物的单晶。并利用元素分析、红外光谱、X射线单晶衍射等方法对该化合物进行了表征。结果表明,该晶体属于单斜晶系,空间群为Pn,晶胞参数a=0.522 19(15)nm,b=0.387 37(11)nm,c=1.075 0(3)nm,β=115.396(5)°,V=0.216(11)nm3,Dc=1.873 g/cm3,Z=2,F(000)=128,R1=0.029 8,wR2=0.079 0。     

Effect of pressure on the crystal structure of ettringite

X-ray diffraction and infrared data have been collected from a sample of ettringite from ambient pressure to 6.4 GPa. The sample was found to reversibly transform to an amorphous phase at 3 GPa. The isothermal bulk modulus of ettringite was found to be 27(7) GPa and the incompressibilities of the lattice parameters were found to be 71(30) GPa along a and 108(36) GPa along c.     

Computer molecular-dynamics simulation of the structure of crystal nanomaterials

The molecular-dynamics simulation of crystal system of silicon carbide at various temperatures has been performed using methods and programs of computer molecular design. Graphs of radial-distribution functions have been obtained for Si-C pairs of atoms, as well as the configurations of atoms in crystal systems at various temperatures. The dependence of the melting point of the SiC crystal system vs. the characteristics of the initial crystal structure to the approximation of the given Tersoff potential and molecular assembly has been studied at the constant number of particles, pressure, and temperature.