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Crystal Forms (crystal + form)
Kinds of Crystal Forms Terms modified by Crystal Forms Selected AbstractsStructures of Four Crystal Forms of DecaplaninHELVETICA CHIMICA ACTA, Issue 5 2003Christopher Lehmann The glycopeptide antibiotic decaplanin (1; formerly known as MM 47761 and M86-1410) crystallizes in two P21 and two P6122 crystal forms, each with four monomers in the asymmetric unit, with solvent contents varying from 48 to 69%. Although with ca. 600 unique atoms, the structures are larger than typical small molecules, one was solved by direct methods. The other three were solved by typical macromolecular methods: single-wavelength anomalous diffraction (SAD) of the Cl-atoms present naturally in the structure, multiple-wavelength anomalous diffraction (MAD) at the Br absorption edge for a crystal soaked in NaBr solution, and molecular replacement. There is evidence of appreciable radiation damage with loss of 20,30% of the covalent and ionic halogens affecting the synchrotron datasets that may even have unintentionally facilitated the MAD structure solution. The structures contain the dimer units typical of antibiotics related to vancomycin, but, in addition, there are a variety of further intermolecular interactions responsible for the polymorphy leading to intertwined 61 -helices in two of the crystal forms. Except for the sugars and some sidechains, the conformations of the 16 independent monomers are very similar. [source] Crystal form and orientation of isotactic polypropylene samples prepared by vibration-injection moldingJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Jie Zhang Abstract A vibration,injection molding equipment was developed to prepare isotactic polypropylene injection samples to investigate their crystal form and orientation. Wide-angle X-ray scattering experiments (WAXD) were conducted in two modes: theta,theta mode and tube-fixed mode. Through vibration,injection molding, in additional to , form, , form, or , form can be obtained under different conditions. At high melt temperature (230), ,-PP can be induced and the core of the sample contains more ,-PP than the surface. At low melt temperature (190), ,-PP can be induced and the core and the surface of the sample contain approximate same proportion of ,-PP. Pole figures show that ,-PP of a static sample just orientates slightly along M direction, while that of vibration samples orientate much stronger. The orientation of the normal of (040), plane of the sample obtained at T = 230°C, f = 0.5 Hz, and Pv = 75MPa is preferred in M direction, and the orientation of the normal of (040), plane of the sample obtained at T = 190°C, f = 1.5 Hz, and Pv= 35 MPa is preferred in N direction. ,-PP and ,-PP do not show obvious orientation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Crystal structures of oxidized and reduced forms of human mitochondrial thioredoxin 2PROTEIN SCIENCE, Issue 10 2005Aude Smeets ASK1, apoptosis signal-regulating kinase 1; TXN, thioredoxin; hTXN1, human cytosolic/nuclear thioredoxin 1; hTXN2, human mitochondrial thioredoxin 2; hPRDX5, human peroxiredoxin 5. Gene symbols in this article follow standard nomenclature defined by the Human Genome Organization Nomenclature Committee (http://www.gene.ucl.ac.uk/nomenclature/). For this reason TXN is used instead of the commonly used Trx for designating thioredoxin in the literature. Abstract Mammalian thioredoxin 2 is a mitochondrial isoform of highly evolutionary conserved thioredoxins. Thioredoxins are small ubiquitous protein,disulfide oxidoreductases implicated in a large variety of biological functions. In mammals, thioredoxin 2 is encoded by a nuclear gene and is targeted to mitochondria by a N-terminal mitochondrial presequence. Recently, mitochondrial thioredoxin 2 was shown to interact with components of the mitochondrial respiratory chain and to play a role in the control of mitochondrial membrane potential, regulating mitochondrial apoptosis signaling pathway. Here we report the first crystal structures of a mammalian mitochondrial thioredoxin 2. Crystal forms of reduced and oxidized human thioredoxin 2 are described at 2.0 and 1.8 Å resolution. Though the folding is rather similar to that of human cytosolic/nuclear thioredoxin 1, important differences are observed during the transition between the oxidized and the reduced states of human thioredoxin 2, compared with human thioredoxin 1. In spite of the absence of the Cys residue implicated in dimer formation in human thioredoxin 1, dimerization still occurs in the crystal structure of human thioredoxin 2, mainly mediated by hydrophobic contacts, and the dimers are associated to form two-dimensional polymers. Interestingly, the structure of human thioredoxin 2 reveals possible interaction domains with human peroxiredoxin 5, a substrate protein of human thioredoxin 2 in mitochondria. [source] Crystallization Kinetics and X-ray Diffraction of Crystals Formed in Amorphous Lactose, Trehalose, and Lactose/Trehalose MixturesJOURNAL OF FOOD SCIENCE, Issue 5 2005Song Miao ABSTRACT: Effects of storage time and relative humidity on crystallization kinetics and crystal forms produced from freeze-dried amorphous lactose, trehalose, and a lactose/trehalose mixture were compared. Samples were exposed to 4 different relative water vapor pressure (RVP) (44.1%, 54.5%, 65.6%, 76.1%) environments at room temperature. Crystallization was observed from time-dependent loss of sorbed water and increasing intensities of peaks in X-ray diffraction patterns. The rate of crystallization increased with increasing storage humidity. Lactose crystallized as ,-lactose monohydrate, ,-anhydrous, and anhydrous forms of ,- and ,-lactose in molar ratios of 5:3 and 4:1 in lactose and lactose/trehalose systems. Trehalose seemed to crystallize as a mixture of trehalose dihydrate and anhydrate in trehalose and lactose/trehalose systems. The crystal forms in a mixture of lactose and trehalose did not seem to be affected by the component sugars, but crystallization of the component sugars was delayed. Time-dependent crystallization of lactose and trehalose in the lactose-trehalose mixture could be modeled using the Avrami equation. The results indicated that crystallization data are important in modeling of crystallization phenomena and predicting stability of lactose and trehalose-containing food and pharmaceutical materials. Keywords: crystallization, lactose, trehalose, crystal form, X-ray diffraction [source] Crystallization behaviors of carbon fiber reinforced BN-Si3N4 matrix compositeCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2007Bin Li Abstract The crystallization behaviors of a new carbon fiber reinforced composite with a hybrid matrix comprising BN and Si3N4 prepared by precursor infiltration and pyrolysis were investigated by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The results show that the as-received composite is almost amorphous, and its main composition is BN and Si3N4. When heat treated at 1600°C, the composite is crystallized and shows a much better crystal form. When heat treated at 2100°C, Si3N4 in the matrix is decomposed, and BN exhibits a relatively complete crystallization. The existence of B4C and SiC is detected, which indicates the interfacial chemical reactions between nitride matrices and carbon fibers. The surface morphology of carbon fibers in the composite changed significantly when heated from 1600 to 2100°C, which also proved the occurrence of interfacial chemical reactions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preferred Phosphorus Ylide Formation Upon Alkylation of Lithiobis(diphenylphosphanyl)acetonitrile,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2007Leonie Braun Abstract Deprotonation of the readily available chelate phosphane bis(diphenylphosphanyl)acetonitrile (6) leads to stabilized carbanion system 7. Lithiobis(diphenylphosphanyl)acetonitrile (7) features a unique thf-stabilized monomeric structure in the crystal form with a short cyanonitrogen,Li contact. Alkylation of 7 with n -alkyl bromides (R,Br, R = ethyl, n -propyl, n -butyl, n -hexyl) takes place selectively at one phosphorus atom to yield stabilized ylides 8a,d (two examples characterized by X-ray diffraction). Treatment of 7 with the more reactive alkylation agents methyl iodide or benzyl bromide results in alkylation at both phosphorus atoms to give delocalized bis(phosphonium)ylides 9a,b (both characterized by X-ray diffraction). Similarly, the reaction of 7 with 1,3-dibromopropane or 1,4-dibromobutane yields six- and seven-membered heterocyclic bis(phosphonium)ylides 10a,b, respectively. The spectroscopic characterization and X-ray crystal structure analysis again indicate the presence of delocalized Ph2RP,C(CN),PRPh2 substructures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Storage stability study of margarines produced from enzymatically interesterified fats compared to margarines produced by conventional methods.EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 7-8 2005Physical properties Abstract In this study, margarine hardstocks were produced from two enzymatically interesterified fats at conversion degrees of 80 and 100%, a chemically randomized fat and a physically mixed fat, respectively. These four hardstocks blended with 50% of sunflower oil were mainly used for the production of table margarines in a pilot plant. Storage stability studies were carried out at storage temperatures of 5 and 25,°C during 12,wk. Margarines from the enzymatically interesterified fats were compared to the margarines produced by conventional methods and to selected commercial products. The changes in the physical properties of margarines, including hardness, dropping point, crystal form, and sensory evaluation, were examined during storage. It was observed that margarine storage stability increased with increasing conversion degree. The color of margarines made from the enzymatically interesterified fats was more similar to that of the physically mixed fat than that of the margarine from the chemically randomized fat, which had less color. Crystal transformation was accelerated at high storage temperature. Crystal size was not only related to the types of crystals, but also to the driving force of temperature difference. A larger crystal size was observed at 5,°C than at 25,°C for the margarine made from the blend. Margarines produced from interesterified fats had better physical properties than the blend. Overall, the margarine produced from the enzymatically fully converted fat had physical properties similar to the margarine produced from the chemically interesterified fat. [source] Crystal form and orientation of isotactic polypropylene samples prepared by vibration-injection moldingJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Jie Zhang Abstract A vibration,injection molding equipment was developed to prepare isotactic polypropylene injection samples to investigate their crystal form and orientation. Wide-angle X-ray scattering experiments (WAXD) were conducted in two modes: theta,theta mode and tube-fixed mode. Through vibration,injection molding, in additional to , form, , form, or , form can be obtained under different conditions. At high melt temperature (230), ,-PP can be induced and the core of the sample contains more ,-PP than the surface. At low melt temperature (190), ,-PP can be induced and the core and the surface of the sample contain approximate same proportion of ,-PP. Pole figures show that ,-PP of a static sample just orientates slightly along M direction, while that of vibration samples orientate much stronger. The orientation of the normal of (040), plane of the sample obtained at T = 230°C, f = 0.5 Hz, and Pv = 75MPa is preferred in M direction, and the orientation of the normal of (040), plane of the sample obtained at T = 190°C, f = 1.5 Hz, and Pv= 35 MPa is preferred in N direction. ,-PP and ,-PP do not show obvious orientation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Crystallization Kinetics and X-ray Diffraction of Crystals Formed in Amorphous Lactose, Trehalose, and Lactose/Trehalose MixturesJOURNAL OF FOOD SCIENCE, Issue 5 2005Song Miao ABSTRACT: Effects of storage time and relative humidity on crystallization kinetics and crystal forms produced from freeze-dried amorphous lactose, trehalose, and a lactose/trehalose mixture were compared. Samples were exposed to 4 different relative water vapor pressure (RVP) (44.1%, 54.5%, 65.6%, 76.1%) environments at room temperature. Crystallization was observed from time-dependent loss of sorbed water and increasing intensities of peaks in X-ray diffraction patterns. The rate of crystallization increased with increasing storage humidity. Lactose crystallized as ,-lactose monohydrate, ,-anhydrous, and anhydrous forms of ,- and ,-lactose in molar ratios of 5:3 and 4:1 in lactose and lactose/trehalose systems. Trehalose seemed to crystallize as a mixture of trehalose dihydrate and anhydrate in trehalose and lactose/trehalose systems. The crystal forms in a mixture of lactose and trehalose did not seem to be affected by the component sugars, but crystallization of the component sugars was delayed. Time-dependent crystallization of lactose and trehalose in the lactose-trehalose mixture could be modeled using the Avrami equation. The results indicated that crystallization data are important in modeling of crystallization phenomena and predicting stability of lactose and trehalose-containing food and pharmaceutical materials. Keywords: crystallization, lactose, trehalose, crystal form, X-ray diffraction [source] High-order simulation of polymorphic crystallization using weighted essentially nonoscillatory methodsAICHE JOURNAL, Issue 1 2009Martin Wijaya Hermanto Abstract Most pharmaceutical manufacturing processes include a series of crystallization processes to increase purity with the last crystallization used to produce crystals of desired size, shape, and crystal form. The fact that different crystal forms (known as polymorphs) can have vastly different characteristics has motivated efforts to understand, simulate, and control polymorphic crystallization processes. This article proposes the use of weighted essentially nonoscillatory (WENO) methods for the numerical simulation of population balance models (PBMs) for crystallization processes, which provide much higher order accuracy than previously considered methods for simulating PBMs, and also excellent accuracy for sharp or discontinuous distributions. Three different WENO methods are shown to provide substantial reductions in numerical diffusion or dispersion compared with the other finite difference and finite volume methods described in the literature for solving PBMs, in an application to the polymorphic crystallization of L -glutamic acid. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Triboelectrification of Spray-dried Lactose Prepared from Different Feedstock ConcentrationsJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 1 2000ORLA E. CASSIDY Powder systems may acquire electrostatic charge during various pharmaceutical processing operations and may give rise to difficulties in handling and powder flow, mainly due to adhesion/cohesion effects. We have investigated the electrostatic charging of spray-dried lactose prepared from different feedstock concentrations using a laboratory spray-dryer. Triboelectrification of the spray-dried lactose samples was effected through contact with the stainless steel surface of either a mixing vessel or a cyclone separator. Results from both techniques showed differences in charge accumulation and particle-steel adhesion between the spray-dried lactose samples. As the feedstock concentration used to produce the spray-dried lactose was increased in the range 10,50% w/v, the mean charge on the lactose decreased from ,20.8 to ,1.3 nC g,1 and ,54.9 to ,4.1 nC g,1 for the mixing vessel and cyclone separator, respectively, with a corresponding decrease in adhesion. In addition, as the feedstock concentration was increased from 10 to 50% w/v, decreases were obtained in surface area values (1.06 to 0.56 m2 g,1), pore diameter (198.7 to 83.5 ,m) and pore volume (1.09 to 0.75 cm3 g,1), and together with differences in crystal form correlated with the charge and adhesion results. The results suggested that the feedstock concentration could have a considerable influence on the charging and adhesional properties of spray-dried lactose. This may have relevance during pharmaceutical processing and manufacturing operations. [source] Polymorphism incidence in commercial tablets of mebendazole: a vibrational spectroscopy investigationJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2008A. P. Ayala Abstract Mebendazole is a broad spectrum anthelminthic drug, which is widely used in large scale deworming programmes. This active pharmaceutical ingredient exhibits three crystal forms, namely, polymorphs A, B, and C. Therapeutic trials suggested that the most stable form, polymorph A, is inactive. However, the dissolution test normally used as a quality control tool is not able to discriminate among the polymorphs of mebendazole. In this work, the ability of the vibrational spectroscopic techniques (mid and nearinfrared absorption and Raman scattering) for the identification of the crystal form of this compound is evaluated. On the basis of these observations, this methodology is applied to determine the polymorphs of MBZ used in the formulation of the commercial tablets available in the Brazilian and German markets. Copyright © 2008 John Wiley & Sons, Ltd. [source] Production of trans -free margarine stock by enzymatic interesterification of rice bran oil, palm stearin and coconut oilJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 4 2010Prakash Adhikari Abstract BACKGROUND:Trans -free interesterified fat was produced for possible usage as a spreadable margarine stock. Rice bran oil, palm stearin and coconut oil were used as substrates for lipase-catalyzed reaction. RESULTS: After interesterification, 137,150 g kg,1 medium-chain fatty acid was incorporated into the triacylglycerol (TAG) of the interesterified fats. Solid fat contents at 25 °C were 15.5,34.2%, and slip melting point ranged from 27.5 to 34.3 °C. POP and PPP (,-tending TAG) in palm stearin decreased after interesterification. X-ray diffraction analysis demonstrated that the interesterified fats contained mostly ,, polymorphic forms, which is a desirable property for margarines. CONCLUSIONS: The interesterified fats showed desirable physical properties and suitable crystal form (,, polymorph) for possible use as a spreadable margarine stock. Therefore, our result suggested that the interesterified fat without trans fatty acid could be used as an alternative to partially hydrogenated fat. Copyright © 2010 Society of Chemical Industry [source] Complex oxide scintillators: Material defects and scintillation performancePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2008M. Nikl Abstract An overview of recognized structural defects, impurities and related trapping levels and their role in the scintillation mechanism is provided and discussed in single crystal materials belonging to tungstate, Ce- or Pr-doped aluminum perovskite, garnet and finally to Ce-doped silicate scintillators. New achievements and open problems in deeper understanding of electron and hole self-trapping phenomena and of the nature of defects in the crystal structure and their ability to localize migrating charge carriers are indicated. Fast optical ceramics and nanocomposite materials are pointed out as possible future advanced scintillators. Such novel technologies can in principle explore materials which are not available in the bulk single crystal form, but their figure-of-merit is dramatically dependent on the surface-interface defect states and related trapping and nonradiative recombination phenomena. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ferromagnetism in diluted magnetic semiconductors Ti1,xMxO2 (M = V, Cr, Mn and Ni)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006N. Shimizu Abstract Diluted magnetic semiconductors Ti1,xMxO2 (M = V, Cr, Mn, Fe, Ni and Cu) with x = 0.005 have been studied in a single crystal form. We have succeeded in growing Ti0.995M0.005O2 single crystals for M = V, Cr, Mn and Ni with the Rutile crystal structure by floating zone method, while it was not successful for M = Fe and Cu. It is found that the physical properties of these single crystals are greatly influenced by growth atmospheres. Among these crystals grown in a low oxygen partial pressure, Ti0.995M0.005O2 with M = Ni exhibited a typical ferromagnetic behavior even at room temperature. Crystallographic properties as well as magnetism have been studied. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The application of eigensymmetries of face forms to anomalous scattering and twinning by merohedry in X-ray diffractionACTA CRYSTALLOGRAPHICA SECTION A, Issue 3 2010H. Klapper The face form (crystal form) {hkl} which corresponds to an X-ray reflection hkl is considered. The eigensymmetry (inherent symmetry) of such a face form can be used to derive general results on the intensities of the corresponding X-ray reflections. Two cases are treated. (i) Non-centrosymmetric crystals exhibiting anomalous scattering: determination of reflections hkl for which Friedel's rule is strictly valid, i.e.I(hkl) = I() (Friedel pair, centric reflection), or violated, i.e.I(hkl) , I() (Bijvoet pair, acentric reflection). It is shown that those reflections hkl strictly obey Friedel's rule, for which the corresponding face form {hkl} is centrosymmetric. If the face form {hkl} is non-centrosymmetric, Friedel's rule is violated due to anomalous scattering. (ii) Crystals twinned by merohedry: determination of reflections hkl, the intensities of which are affected (or not affected) by the twinning. It is shown that the intensity is affected if the twin element is not a symmetry element of the eigensymmetry of the corresponding face form {hkl}. The intensity is not affected if the twin element belongs to the eigensymmetry of {hkl} (`affected' means that the intensities of the twin-related reflections are different for different twin domain states owing to differences either in geometric structure factors or in anomalous scattering or in both). A simple procedure is presented for the determination of these types of reflections from Tables 10.1.2.2 and 10.1.2.3 of International Tables for Crystallography, Vol. A [Hahn & Klapper (2002). International Tables for Crystallography, Vol. A, Part 10, edited by Th. Hahn, 5th ed. Dordrecht: Kluwer]. The application to crystal-structure determination of crystals twinned by merohedry (reciprocal space) and to X-ray diffraction topographic mapping of twin domains (direct space) is discussed. Relevant data and twinning relations for the 63 possible twin laws by merohedry in the 26 merohedral point groups are presented in Appendices A to D. [source] Effects of malonic acid treatment on crystal structure, melting behavior, morphology, and mechanical properties of isotactic poly(propylene)/wollastonite compositesPOLYMER COMPOSITES, Issue 6 2010Lin Li Wollastonite is treated with a new surface modifier (malonic acid). The influence of malonic acid treatment on the crystallization and mechanical properties of polypropylene (PP)/wollastonite composites has been studied. The results of differential scanning calorimetry, wide angle X-ray diffractometry, and polarized light microscopy prove that malonic acid-treated wollastonite increases the relative content of ,-crystal form of PP. The scanning electron microscopy shows that malonic acid-treated wollastonite has better compatibility with PP matrix than the untreated wollastonite. Higher ,-phase contents, smaller spherulite sizes, and better compatibility with PP matrix of the composites containing malonic acid-treated wollastonite result in improved impact strength and tensile strength, but lower flexural modulus. The results of Fourier transform infrared spectroscopy show that malonic acid reacts with the Ca2+ of wollastonite to form the calcium malonate, which acts as an effective ,-nucleating agent. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source] Melt processing of PA-66/clay, HDPE/clay and HDPE/PA-66/clay nanocompositesPOLYMER ENGINEERING & SCIENCE, Issue 6 2004Mahmood Mehrabzadeh Polyamide 66/clay, high-density polyethylene (HDPE)/clay and HDPE/PA66/clay nanocomposites were prepared, using a twin-screw extruder. The nanocomposites were characterized by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), optical microscopy and tensile testing. Effects of processing conditions and clay modifier were evaluated. The results show that exfoliation in the twin-screw extruder is enhanced by the incorporation of mixing and shearing elements and high residence times. Compatibility of the clay modifier with the polymer matrix plays an important role in exfoliation. Clay does not influence the crystal form, melting temperature or crystallinity of PA-66 and HDPE. However, it acts as a nucleation agent, increases marginally the crystallization temperatures, and reduces the crystallite size. Clay in the blend nanocomposites acts as a compatibilizer and changes the morphology of the blend. TEM micrographs suggest the presence of an exfoliated structure in PA-66 and an intercalated structure in HDPE. Polym. Eng. Sci. 44:1152,1161, 2004. © 2004 Society of Plastics Engineers. [source] Crystal packing of a bacteriophage MS2 coat protein mutant corresponds to octahedral particlesPROTEIN SCIENCE, Issue 10 2008Pavel Plevka Abstract A covalent dimer of the bacteriophage MS2 coat protein was created by performing genetic fusion of two copies of the gene while removing the stop codon of the first gene. The dimer was crystallized in the cubic F432 space group. The organization of the asymmetric unit together with the F432 symmetry results in an arrangement of subunits that corresponds to T = 3 octahedral particles. The octahedral particles are probably artifacts created by the particular crystal packing. When it is not crystallized in the F cubic crystal form, the coat protein dimer appears to assemble into T = 3 icosahedral particles indistinguishable from the wild-type particles. To form an octahedral particle with closed surface, the dimer subunits interact at sharper angles than in the icosahedral arrangement. The fold of the covalent dimer is almost identical to the wild-type dimer with differences located in loops and in the covalent linker region. The main differences in the subunit packing between the octahedral and icosahedral arrangements are located close to the fourfold and fivefold symmetry axes where different sets of loops mediate the contacts. The volume of the wild-type virions is 7 times bigger than that of the octahedral particles. [source] A new polymorph of 2-methyl-6-nitroanilineACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Samantha K. Callear A new crystal form of 2-methyl-6-nitroaniline, C7H8N2O2, crystallizing with Z, = 2 in the space group P21/c, has been identified during screening for salts and cocrystals. The different N,H...O hydrogen-bonding synthons result in linear V-shaped chains in the new polymorph, rather than the helical chain arrangement seen in the known form where Z, = 1. The presence of a second component during crystallization appears to have determined the resultant crystal form of 2-methyl-6-nitroaniline. [source] Water molecules in the crystal structure of tricyclic acyclovirACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2001Kinga Suwi The biologically important molecule tricyclic acyclovir, presented here as 3-[(2-hydroxyethoxy)methyl]-6-methyl-3H -imidazolo[1,2- a]purin-9(5H)-one dihydrate, C11H13N5O3·2H2O, shows conformational flexibility, which is observed in the solid state as two symmetrically independent molecules with different side-chain conformations. Additionally, one of these molecules exhibits side-chain disorder, such that there are three different conformations in the crystal. Water molecules found in the crystal form (H2O)8 clusters which are located between molecules of tricyclic acyclovir. The complex hydrogen-bond network formed between water and tricyclic acyclovir in the solid state may be related to the solvation of the molecules in solution. [source] Promoting crystallization of antibody,antigen complexes via microseed matrix screeningACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2010Galina Obmolova The application of microseed matrix screening to the crystallization of antibody,antigen complexes is described for a set of antibodies that include mouse anti-IL-13 antibody C836, its humanized version H2L6 and an affinity-matured variant of H2L6, M1295. The Fab fragments of these antibodies were crystallized in complex with the antigen human IL-13. The initial crystallization screening for each of the three complexes included 192 conditions. Only one hit was observed for H2L6 and none were observed for the other two complexes. Matrix self-microseeding using these microcrystals yielded multiple hits under various conditions that were further optimized to grow diffraction-quality H2L6 crystals. The same H2L6 seeds were also successfully used to promote crystallization of the other two complexes. The M1295 crystals appeared to be isomorphous to those of H2L6, whereas the C836 crystals were in a different crystal form. These results are consistent with the concept that the conditions that are best for crystal growth may be different from those that favor nucleation. Microseed matrix screening using either a self-seeding or cross-seeding approach proved to be a fast, robust and reliable method not only for the refinement of crystallization conditions but also to promote crystal nucleation and increase the hit rate. [source] Structure determination of the minimal complex between Tfb5 and Tfb2, two subunits of the yeast transcription/DNA-repair factor TFIIH: a retrospective studyACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2010Denis E. Kainov Tfb5 interacts with the Tfb2 subunit of the general transcription factor TFIIH to ensure efficient nucleotide-excision repair in eukaryotes. The crystal structure of the complex between Tfb5 and the C-terminal region of Tfb2 (Tfb2C) from Saccharomyces cerevisiae has recently been reported. Here, the structure-determination process is described as a case study. Although crystals were obtained readily, it was not possible to determine experimental phases from a first crystal form (Tfb2412,513,Tfb52,72) that diffracted to 2.6,Å resolution. Shortening of the Tfb2C from its N-terminus was decisive and modified the crystal packing, leading to a second crystal form (Tfb2435,513,Tfb52,72). These crystals diffracted to 1.7,Å resolution with excellent mosaicity and allowed structure determination by conventional approaches using heavy atoms. The refined structure from the second crystal form was used to solve the structure of the first crystal form by molecular replacement. Comparison of the two structures revealed that the N-terminal region of Tfb2C and (to a lesser extent) the C-terminal region of Tfb5 contributed to the crystal packing. A detailed analysis illustrates how variation in domain boundaries influences crystal packing and quality. [source] A dipicolinate lanthanide complex for solving protein structures using anomalous diffractionACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2010Guillaume Pompidor Tris-dipicolinate lanthanide complexes were used to prepare derivative crystals of six proteins: hen egg-white lysozyme, turkey egg-white lysozyme, thaumatin from Thaumatococcus daniellii, urate oxidase from Aspergillus flavus, porcine pancreatic elastase and xylanase from Trichoderma reesei. Diffraction data were collected using either synchrotron radiation or X-rays from a laboratory source. In all cases, the complex turned out to be bound to the protein and the phases determined using the anomalous scattering of the lanthanide led to high-quality electron-density maps. The binding mode of the complex was characterized from the refined structures. The lanthanide tris-dipicolinate was found to bind through interactions between carboxylate groups of the dipicolinate ligands and hydrogen-bond donor groups of the protein. In each binding site, one enantiomeric form of the complex is selected from the racemic solution according to the specific site topology. For hen egg-white lysozyme and xylanase, derivative crystals obtained by cocrystallization belonged to a new monoclinic C2 crystal form that diffracted to high resolution. [source] Analysis of multiple crystal forms of Bacillus subtilis BacB suggests a role for a metal ion as a nucleant for crystallizationACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2010M. Rajavel Bacillus subtilis BacB is an oxidase that is involved in the production of the antibiotic bacilysin. This protein contains two double-stranded ,-helix (cupin) domains fused in a compact arrangement. BacB crystallizes in three crystal forms under similar crystallization conditions. An interesting observation was that a slight perturbation of the crystallization droplet resulted in the nucleation of a different crystal form. An X-ray absorption scan of BacB suggested the presence of cobalt and iron in the crystal. Here, a comparative analysis of the different crystal forms of BacB is presented in an effort to identify the basis for the different lattices. It is noted that metal ions mediating interactions across the asymmetric unit dominate the different packing arrangements. Furthermore, a normalized B -factor analysis of all the crystal structures suggests that the solvent-exposed metal ions decrease the flexibility of a loop segment, perhaps influencing the choice of crystal form. The residues coordinating the surface metal ion are similar in the triclinic and monoclinic crystal forms. The coordinating ligands for the corresponding metal ion in the tetragonal crystal form are different, leading to a tighter packing arrangement. Although BacB is a monomer in solution, a dimer of BacB serves as a template on which higher order symmetrical arrangements are formed. The different crystal forms of BacB thus provide experimental evidence for metal-ion-mediated lattice formation and crystal packing. [source] Pseudo-merohedral twinning and noncrystallographic symmetry in orthorhombic crystals of SIVmac239 Nef core domain bound to different-length TCR, fragmentsACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2010Walter M. Kim HIV/SIV Nef mediates many cellular processes through interactions with various cytoplasmic and membrane-associated host proteins, including the signalling , subunit of the T-cell receptor (TCR,). Here, the crystallization strategy, methods and refinement procedures used to solve the structures of the core domain of the SIVmac239 isolate of Nef (Nefcore) in complex with two different TCR, fragments are described. The structure of SIVmac239 Nefcore bound to the longer TCR, polypeptide (Leu51,Asp93) was determined to 3.7,Å resolution (Rwork = 28.7%) in the tetragonal space group P43212. The structure of SIVmac239 Nefcore in complex with the shorter TCR, polypeptide (Ala63,Arg80) was determined to 2.05,Å resolution (Rwork = 17.0%), but only after the detection of nearly perfect pseudo-merohedral crystal twinning and proper assignment of the orthorhombic space group P212121. The reduction in crystal space-group symmetry induced by the truncated TCR, polypeptide appears to be caused by the rearrangement of crystal-contact hydrogen-bonding networks and the substitution of crystallographic symmetry operations by similar noncrystallographic symmetry (NCS) operations. The combination of NCS rotations that were nearly parallel to the twin operation (k, h, ,l) and a and b unit-cell parameters that were nearly identical predisposed the P212121 crystal form to pseudo-merohedral twinning. [source] Structure analysis of endosialidase NF at 0.98,Å resolutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2010Eike C. Schulz Endosialidase NF (endoNF) is a bacteriophage-derived endosialidase that specifically degrades ,-2,8-linked polysialic acid. The structure of a new crystal form of endoNF in complex with sialic acid has been refined at 0.98,Å resolution. The 210,kDa homotrimeric multi-domain enzyme displays outstanding stability and resistance to SDS. Even at atomic resolution, only a minor fraction of side chains possess alternative conformations. However, multiple conformations of an active-site residue imply that it has an important catalytic function in the cleavage mechanism of polysialic acid. [source] The structure of dihydrodipicolinate reductase (DapB) from Mycobacterium tuberculosis in three crystal formsACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2010Robert Janowski Dihydrodipicolinate reductase (DHDPR, DapB) is an enzyme that belongs to the l -lysine biosynthetic pathway. DHDPR reduces the ,,,-unsaturated cyclic imine 2,3-dihydrodipicolinic acid to yield the compound 2,3,4,5-tetrahydrodipicolinic acid in a pyridine nucleotide-dependent reaction. The substrate of this reaction is the unstable product of the preceding enzyme dihydrodipicolinate synthase (DHDPS, DapA). Here, the structure of apo-DHDPR from Mycobacterium tuberculosis is reported in two orthorhombic crystal forms, as well as the structure of DHDPR from M. tuberculosis in complex with NADH in a monoclinic crystal form. A comparison of the results with previously solved structures of this enzyme shows that DHDPR undergoes a major conformational change upon binding of its cofactor. This conformational change can be interpreted as one of the low-frequency normal modes of the structure. [source] Structure of the X (ADRP) domain of nsp3 from feline coronavirusACTA CRYSTALLOGRAPHICA SECTION D, Issue 12 2009Justyna A. Wojdyla The structure of the X (or ADRP) domain of a pathogenic variant of feline coronavirus (FCoV) has been determined in tetragonal and cubic crystal forms to 3.1 and 2.2,Å resolution, respectively. In the tetragonal crystal form, glycerol-3-phosphate was observed in the ADP-ribose-binding site. Both crystal forms contained large solvent channels and had a solvent content of higher than 70%. Only very weak binding of this domain to ADP-ribose was detected in vitro. However, the structure with ADP-ribose bound was determined in the cubic crystal form at 3.9,Å resolution. The structure of the FCoV X domain had the expected macro-domain fold and is the first structure of this domain from a coronavirus belonging to subgroup 1a. [source] A new crystal form of human tear lipocalin reveals high flexibility in the loop region and induced fit in the ligand cavityACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2009Daniel A. Breustedt Tear lipocalin (TLC) with the bound artificial ligand 1,4-butanediol has been crystallized in space group P21 with four protein molecules in the asymmetric unit and its X-ray structure has been solved at 2.6,Å resolution. TLC is a member of the lipocalin family that binds ligands with diverse chemical structures, such as fatty acids, phospholipids and cholesterol as well as microbial siderophores and the antibiotic rifampin. Previous X-ray structural analysis of apo TLC crystallized in space group C2 revealed a rather large bifurcated ligand pocket and a partially disordered loop region at the entrace to the cavity. Analysis of the P21 crystal form uncovered major conformational changes (i) in ,-strands B, C and D, (ii) in loops 1, 2 and 4 at the open end of the ,-barrel and (iii) in the extended C-terminal segment, which is attached to the ,-barrel via a disulfide bridge. The structural comparison indicates high conformational plasticity of the loop region as well as of deeper parts of the ligand pocket, thus allowing adaptation to ligands that differ vastly in size and shape. This illustrates a mechanism for promiscuity in ligand recognition which may also be relevant for some other physiologically important members of the lipocalin protein family. [source] | ||||||||||||||||