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Crystalline Form (crystalline + form)
Kinds of Crystalline Form Selected AbstractsHetero-Seeding and Solid Mixture to Obtain New Crystalline FormsCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2009Dario Braga Prof. Abstract Para -methyl benzyl alcohol (p -MeBA,II) and para -chloro benzyl alcohol (p -ClBA) are quasi-isostructural and share the same hydrogen-bond patterns, but their crystals are not isomorphous. No new polymorphs could be obtained by conventional polymorph screening based on different solvents and different crystallization conditions. Formation of a new polymorph of p -MeBA named p -MeBA,I, isomorphous with the crystal of p -ClBA, was induced by hetero-seeding with a small quantity of powdered p -ClBA added to a supersaturated solution of p -MeBA in hexane, while seeding of p -ClBA with p -MeBA,II failed to give a new phase of p -ClBA isomorphous with known crystalline p -MeBA,II. Mixed crystals of p -MeBA and p -ClBA were also prepared with different p -MeBA/p -ClBA ratios to understand the role of the different functional groups in the crystal structure. Crystal phases were characterized by combined use of single-crystal and powder X-ray diffraction, differential scanning calorimetry, and solid-state NMR spectroscopy. [source] High-precision measurement of internuclear distances using solid-state NMRCONCEPTS IN MAGNETIC RESONANCE, Issue 1 2008Jae-Seung Lee Abstract Today, nuclear magnetic resonance (NMR) is among the most efficient tools in structural studies. Measurement of interatomic distances is the most common way of determining high-resolution structures of molecules using NMR techniques. In this article, we describe NMR techniques for static powder samples, based on a two-dimensional single-echo scheme, enhanced with adiabatic cross-polarization. They can significantly increase the accuracy of measuring internuclear distances and turn NMR into a high-precision crystallographic technique, complementing the X-ray, and neutron-scattering methods. Experimental examples are presented for intramolecular CN and CC distances in ,-crystalline form of glycine. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 56,67, 2008. [source] Synthesis and Structural Characterisation of Copper(II) 15-Metallacrown-5 Complexes with PbII, HgII, AgI, NaI and YIII Central Metal IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2007Sabry Hamed Seda Abstract The new copper(II) 15-metallacrown-5 complexes with the central metal ions PbII, HgII, AgI, NaI and YIII, with the formula [MCu5L5]Xn {H2L is 2-picolinehydroxamic acid or (S)-phenylalaninehydroxamic acid and X, is NO3, or Cl,}, have been synthesised and characterised by NMR and UV/Vis spectroscopy, electrospray mass spectrometry and elemental analysis. The PbII - and HgII 15-metallacrown-5 complexes were obtained in the crystalline form as pyridine adducts [PbCu5(picha)5(py)6](NO3)2·3(py) and [HgCu5(picha)5(py)7](NO3)2·2(py) and their X-ray crystal structures were determined. In both complexes, each peripheral CuII ion of the metallacrown is coordinated by one pyridine molecule bonded in the axial position. In the case of the PbII derivative, one additional axial pyridine molecule is bound to the central metal ion, while in the case of the HgII derivative, two axial pyridine ligands are bound to the central HgII ion. The relative stability of the copper(II) 15-metallacrown-5 complexes with various central metal ions was determined on the basis of competition reactions. The relative preference of the 15-metallacrown-5 system for the central metal ion follows the series NaI, AgI < lanthanide(III), HgII < PbII.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] UV-vis-Induced Vitrification of a Molecular Crystal,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2007T. Naito Abstract A charge-transfer complex of 2,5-dimethyl- N,N,-dicyanoquinonediimine (DM) with silver (crystalline Ag(DM)2, defined as ,) is irreversibly transformed by UV-vis illumination. Depending on the illumination conditions, three new types of solids (defined as ,, ,, and ,) with different structural and physical properties are obtained and examined by a variety of analytical techniques, including solid-state, high-resolution, cross-polarization magic angle spinning (CP-MAS) 13C,NMR, elemental analysis (EA), mass spectrometry (MS), X-ray absorption fine structure (XAFS), and powder X-ray diffraction (XRD). The CP-MAS, EA, MS, and XAFS results indicate that compound , is a glass state of Ag(DM)2. The transformation from crystalline (,) to amorphous (,) solid Ag(DM)2 is an irreversible exothermic glass transition (glass-transition temperature 155.2,°C; ,H,=,,126.8,kJ,mol,1), which implies that the glass form is thermodynamically more stable than the crystalline form. Compound , (Ag(DM)1.5) consists of silver nanoparticles (diameter (7,±,2),nm ) dispersed in a glassy matrix of neutral DM molecules. The N,CN,Ag coordination bonds of the , form are not maintained in the , form. Decomposition of , by intense illumination results in a white solid (,), identified as being composed of silver nanoparticles (diameter (60,±,10),nm). Physical and spectroscopic (XAFS) measurements, together with XRD analysis, indicate that the silver nanoparticles in both , and , are crystalline with lattice parameters similar to bulk silver; however, the magnetic susceptibilities differ from bulk silver. [source] Evaluation of polymethacrylic ionomer as compatibilizers for MCPA6/clay compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Tongfei Wu Abstract The compatibilization effects provided by polymethacrylic ionomer (PMMA ionomer) on monomer-casting polyamide6 (MCPA6)/clay (pristine sodium montmorillonite) composites were studied in this work. The PMMA ionomer used in this study was sodium polymethacrylate ionomer (PMMA Na+ -ionomer), which is a copolymer of methyl methacrylate and sodium methacrylate, prepared using emulsion polymerization. MCPA6/clay/PMMA Na+ -ionomer composites were prepared by in situ anionic ring-opening polymerization (AROP) of ,-caprolactam (CLA). X-ray diffraction (XRD) and transmission electron microscopy (TEM) plus rheological measurement were used to characterize those composites. The results indicated that PMMA Na+ -ionomer is a good compatibilizer for this system. With increasing PMMA Na+ -ionomer content, a better dispersion of clay layers was successfully achieved in the MCPA6 matrix. Furthermore, differential scanning calorimetry (DSC) and XRD results indicated that well dispersed silicate layers limit the mobility of the MCPA6 molecule chains to crystallize, reduce the degree crystalline, and favor the formation of the ,-crystalline form of the MCPA6 matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Solid state characterization of mometasone furoate anhydrous and monohydrate formsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2005Xiaoming (Sean) Chen Abstract Mometasone furoate is a potent glucocorticoid anti-inflammatory agent. Its anhydrous Form 1 and monohydrate form were characterized by X-ray crystallography, X-ray powder diffraction at ambient and elevated temperature, thermal analysis, FT-IR, and dynamic moisture adsorption. In Form 1, mometasone furoate molecules pack tightly with molecules interlocked in a space group of P212121. The monohydrate form crystallizes in space group P1. The unit cell of the monohydrate contains one water molecule and one mometasone furoate molecule. The water molecules form channels along the a axis and mometasone furoate molecules pack in layers in the same direction. Dehydration was observed between 60 and 100°C by thermogravimetric analysis with a heating rate of 10°C/min. It corresponds to a broad endotherm over the same temperature range in the differential scanning calorimetry with the same heating rate. Variable temperature X-ray powder diffraction reveals that a new anhydrous form (Form 2) was fully produced above 90°C. This crystalline form was converted to Form 1 after being heated above 150°C; and was totally converted to the monohydrate after 1 day at 23°C, 45% RH. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2496-2509, 2005 [source] General pharmaceutics,The new physical pharmacyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2003E. F. "Gene" Fiese Abstract General Pharmaceutics is proposed as the broad study of the biopharmaceutical and physical chemical properties of each potential drug substance. When the first quality bulk lot is delivered, usually the first GMP bulk lot, an extensive profiling of the potential drug substance should commence. This profile should include solid-state characterization as well as thorough analyses of solubility, stability, and absorption properties of the drug substance that could affect the development of a viable medicine. As a result of these studies, a number of initial specifications could be developed: the preferred polymorphic or crystalline form identified, the preferred particle size to optimize absorption/development, and an initial biopharmaceutics classification with a dose limit to identify those cases in which the formulation can be expected to improve absorption and exposure. The broad topic of General Pharmaceutics is discussed in this Minireview including many advances in technology in this field as well as the rationale behind the proposed initial specifications. © 2003 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:1331,1342, 2003 [source] Variability in starch physicochemical and functional properties of yam (Dioscorea sp) cultivated in Ivory CoastJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2004N'Guessan Georges Amani Abstract An Erratum has been published for this article in Journal Of the Science of Food and Agriculture 85(5), 889 (2005). Native starches were extracted from 21 cultivars of four yam species representative of the yam population of Ivory Coast. They were first characterized for their proximate composition, starch physico-chemical properties (amylose content, particle size distribution, crystallinity, thermal properties and intrinsic viscosity). Some functional properties (swelling, solubility and pasting behaviour and paste clarity) were then determined. Analysis of variance and principal component analysis showed that three homogenous groups could be distinguished, mainly based on starch physico-chemical properties. The first group contained all yam starches of the D alata and the D cayenensis-rotundata complex species. It was characterized by a large diameter grain (approximately 25 µm), a high amylose content (around 25% db), a high intrinsic viscosity (mean of 190 cm3 g,1), and a high apparent viscosity and clarity of the paste. The second group contained the D esculenta varieties, characterized by a small granule size (diameter 6 µm), a low intrinsic viscosity (121 cm3 g,1), a high gelatinization enthalpy change (19 J g,1) and a low paste viscosity. The D dumetorum sample differed from the D esculenta group by having a pure A-type crystalline form and an opaque paste. A multiple regression showed that the volume fraction of the dispersed phase and native granule size (or amylose content) could account for close to 80% of the variability of paste apparent viscosity. Gel clarity appeared mainly linked to granule size, small granules from D dumetorum and D esculenta giving the most opaque gels. Copyright © 2004 Society of Chemical Industry [source] Unique Orientation Textures Induced by Confined Crystal Growth of Poly(vinylidene fluoride) in Oriented Blends with Polyamide 6MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 5 2007Akira Kaito Abstract Unique orientation textures have been induced by the confined crystal growth of PVDF in drawn films of PVDF/PA6 blends. Oriented films of PVDF/PA6 blends were prepared by uniaxially drawing melt-mixed blends. The drawn films with fixed lengths were heat-treated at 180,°C for 3 minutes to melt the PVDF component, followed by non-isothermal crystallization of PVDF at a cooling rate of 0.5,°C,·,min,1. The crystal orientation was studied by WAXD. When PVDF was melted and recrystallized in the drawn films of the PVDF/PA6,=,50/50 blend at a slow cooling rate, the crystal b- axis of the , -crystalline form of PVDF was oriented in the drawing direction, forming orthogonal orientation textures. SEM showed that stretched domains of PVDF with diameters of 0.2,0.5 µm were dispersed in the PA6 phase in the drawn films of the PVDF/PA6,=,50/50 blend. Spatial confinement of the crystal growth resulted in the alignment of the crystal b- axis along the long axis of the domains, because PVDF is crystallized in thin cylindrical domains. The orientation behavior is different from the oriented crystallization of PVDF/PA11 (Y. Li, A. Kaito, Macromol. Rapid Commun. 2003, 24, 255), in which transcrystallization from the interface causes the a- axis orientation to be in the drawing direction. It is thought that the domain size influenced the mechanism of oriented crystallization and the resultant crystal orientation. [source] DGEBA monomer as a solvent for syndiotactic polystyreneMACROMOLECULAR SYMPOSIA, Issue 1 2003Jaap Schut Abstract Syndiotactic polystyrene (sPS) has to be processed at high temperatures (i.e. >290°C due to its melting point of 270°C), which approaches its degradation temperature. We aim to facilitate the processing of sPS by lowering its melt temperature and viscosity with a curable epoxy/amine model system as reactive solvent, which will result in a thermoplastic-thermoset polymer blend. As a first step we therefore investigated the melting behaviour of sPS in epoxy monomer, established its phase diagram, and investigated the crystalline form of sPS in these mixtures. DGEBA epoxy monomer is found to be a solvent for syndiotactic polystyrene at temperatures above 220°C. The DGEBA-sPS phase diagram was established by means of DSC, on the basis of crystallization and melting peaks. The form of the curve in the phase diagram indicates that DGEBA is a poor solvent for sPS. In WAXS studies of blends only the , crystalline form was detected, not the , form, thus no sPS-DGEBA polymer-solvent compounds (clathrates) were detected. However, DGEBA can still serve as a monomer for improved processing as it depresses the crystallization temperature by 20 to 60 K upon addition of 20 to 90 wt% DGEBA respectively, while a 16 to 45 K melting peak depression can be observed by adding 20 to 90 wt% DGEBA. [source] Structure determination of new steroids from Abutilon pakistanicum by NMR techniquesMAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2008Munawar Hussain Abstract Two new steroids provisionally named as pakisteroid-A (1) and pakisteroid-B (2) have been isolated in crystalline form from Abutilon pakistanicum. Their structures have been assigned as 3- O -,- D -glucopyranosyl-stigmasta-5,11(12)-diene (1) and 24,-ethylcholesta-5, 9(11), 22E-trien-3,-benzoate (2), respectively through extensive NMR studies. Copyright © 2008 John Wiley & Sons, Ltd. [source] Stability and electronic properties of magnetic peapodsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008S. Tóth Abstract We report on the temperature stability of N@C60 peapods using electron spin resonance. The atomic nitrogen escapes at higher temperatures in the peapod than in the crystalline form. We also report on the synthesis of novel magnetic fullerene peapod, a fullerene with an attached pyridine-nitroxide spin-label. This molecule can be the ultimate inner spin label for the SWCNTs as it is available in microscopic amounts and is not air sensitive. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Properties of recycled material containing poly(vinyl chloride), polypropylene, and calcium carbonate nanofillerPOLYMER ENGINEERING & SCIENCE, Issue 3 2008Branka Andri Even at low content, polypropylene significantly worsens mechanical properties of the recycled PVC composite, i.e. tensile strength at break and elongation at break. But, if small quantities of surface modified nanofiller calcium carbonate is added, an applicable composite that contains 10,30% of waste material can be made. It was determined that nanosized calcium carbonate lowers melting point of polypropylene, perhaps by changing its crystalline form and has no influence on thermooxidative degradation of poly(vinyl chloride). Addition of nanofiller slightly lowers the surface free energy of the composites what is more prone when the low content of polypropylene is present. The recovery of tensile strength and elongation at break occurs and those properties reach the highest value at about 6% of CaCO3. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Polymorphic behavior of nylon 6/saponite and nylon 6/montmorillonite nanocompositesPOLYMER ENGINEERING & SCIENCE, Issue 6 2002Tzong-Ming Wu X-ray diffraction methods and DSC thermal analysis have been used to investigate the structural change of nylon 6/clay nanocomposites. Nylon 6/clay has prepared by the intercalation of ,-caprolactam and then exfoliaton of the layered saponite or montmorillonite by subsequent polymerization. Both X-ray diffraction data and DSC results indicate the presence of polymorphism in nylon 6 and in nylon 6/clay nanocomposites. This polymorphic behavior is dependent on the cooling rate of nylon 6/clay nanocomposites from melt and the content of saponite or montmorillonite in nylon 6/clay nanocomposites. The quenching from the melt induces the crystallization into the , crystalline form. The addition of clay increases the crystallization rate of the , crystalline form at lower saponite content and promotes the heterophase nucleation of , crystalline form at higher saponite or montmorillonite content. The effect of thermal treatment on the crystalline structure of nylon 6/clay nanocomposites in the range between Tg and Tm is also discussed. [source] Ab initio structure determination of phase II of racemic ibuprofen by X-ray powder diffractionACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2010Patrick Derollez Annealing of the quenched ibuprofen at 258,K yielded a new crystalline form, called phase II. Powder X-ray diffraction patterns of this phase II were recorded with a laboratory diffractometer equipped with an INEL G3000 goniometer and a curved position-sensitive detector CPS120. The starting structural model was found by a Monte-Carlo simulated annealing method. The final structure was obtained through Rietveld refinements with rigid-body constraints for the phenyl group and soft restraints on the other interatomic bond lengths and bond angles. The cell volume is 5% larger than that of the conventional phase I at 258,K. It is also shown that the orientation of the propanoic acid group is drastically changed with respect to phase I, leading to strong modifications of the orientation of the O,H...O hydrogen bonds with respect to the chains of dimers. These structural considerations could explain the metastable character of this phase II. [source] Polymorphs of DABCO monohydrate as structural analogues of NaClACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2010Barbara Wicher A new crystalline form of 1,4-diazabicyclo[2.2.2]octane (DABCO) monohydrate, C6H12N2·H2O, crystallizing in the space group P31, has been identified during screening for cocrystals. There are three DABCO and three water molecules in the asymmetric unit, with two DABCO molecules exhibiting disorder over two positions related by rotation around the N...N axis. As in the monoclinic C2/c (Z, = 2) polymorph, the molecular components are connected via O,H...N hydrogen bonds into a polymeric structure that consists of linear O,H...N(CH2CH2)3N...H,O segments, which are approximately mutually perpendicular. The two polymorphic forms of DABCO monohydrate can be considered as structural analogues of NaCl, with the nearly globular DABCO molecules showing distorted cubic closest packing and all octahedral interstices occupied by water molecules. [source] Crystallographic characterization of the first reported crystalline form of the potent hallucinogen (R)-2-amino-1-(8-bromobenzo[1,2- b;5,4- b,]difuran-4-yl)propane or `bromodragonfly': the 1:1 anhydrous proton-transfer compound with 3,5-dinitrosalicylic acidACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2010Graham Smith The 1:1 proton-transfer compound of the potent substituted amphetamine hallucinogen (R)-2-amino-1-(8-bromobenzo[1,2- b;5,4- b,]difuran-4-yl)propane (common trivial name `bromodragonfly') with 3,5-dinitrosalicylic acid, namely 1-(8-bromobenzo[1,2- b;5,4- b,]difuran-4-yl)propan-2-aminium 2-carboxy-4,6-dinitrophenolate, C13H13BrNO2+·C7H3N2O7,, forms hydrogen-bonded cation,anion chain substructures comprising undulating head-to-tail anion chains formed through C(8) carboxyl,nitro O,H...O associations and incorporating the aminium groups of the cations. The intrachain cation,anion hydrogen-bonding associations feature proximal cyclic R33(8) interactions involving both an N+,H...Ophenolate and the carboxyl,nitro O,H...O associations and aromatic ,,, ring interactions [minimum ring centroid separation = 3.566,(2),Å]. A lateral hydrogen-bonding interaction between the third aminium H atom and a carboxyl O-atom acceptor links the chain substructures, giving a two-dimensional sheet structure. This determination represents the first of any form of this compound and is in the (R) absolute configuration. The atypical crystal stability is attributed both to the hydrogen-bonded chain substructures provided by the anions, which accommodate the aminium proton-donor groups of the cations and give crosslinking, and to the presence of the cation,anion aromatic ring ,,, interactions. [source] A new polymorph of benzene-1,2-diamine: isomorphism with 2-aminophenol and two-dimensional isostructurality of polymorphsACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010Agnieszka Czapik A new crystalline form of benzene-1,2-diamine, C6H8N2, crystallizing in the space group Pbca, has been identified during screening for cocrystals. The crystals are constructed from molecular bilayers parallel to (001) that have the polar amino groups directed to the inside and the aromatic groups, showing a herringbone arrangement, directed to the outside. The known monoclinic form and the new orthorhombic polymorph exhibit two-dimensional isostructurality as the crystals consist of nearly identical bilayers. In the monoclinic form, neighbouring bilayers are generated by a unit translation along the a axis, whereas in the orthorhombic form they are generated by a c -glide. Moreover, the new form of benzene-1,2-diamine is essentially isomorphous with the only known form of 2-aminophenol. [source] The protein content in crystals and packing coefficients in different space groupsACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2000Klas M. Andersson A precise way of estimating the packing coefficient, i.e. the ratio between the protein and unit-cell volume, or solvent content in protein crystals is given. At present, the solvent content is not given for most proteins in the Protein Data Bank and in many cases where it is given the values are dubious. The mean density of proteins in the crystalline form is around 1.22,g,cm,3, not 1.35,g,cm,3 as usually stated. This is equivalent to 19.5,Å3 per non-H atom. A statistical investigation of the average protein content and packing coefficient in different space groups is presented. The packing coefficients are generally higher in the most frequently occurring space groups than in the uncommon space groups. There is also a remarkable difference in frequency distribution for enantiomorphous pairs of space groups. [source] Structure of the SARS coronavirus main proteinase as an active C2 crystallographic dimerACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 11 2005Ting Xu The 34,kDa main proteinase (Mpro) from the severe acute respiratory syndrome coronavirus (SARS-CoV) plays an important role in the virus life cycle through the specific processing of viral polyproteins. As such, SARS-CoV Mpro is a key target for the identification of specific inhibitors directed against the SARS virus. With a view to facilitating the development of such compounds, crystals were obtained of the enzyme at pH 6.5 in the orthorhombic space group P21212 that diffract to a resolution of 1.9,Å. These crystals contain one monomer per asymmetric unit and the biologically active dimer is generated via the crystallographic twofold axis. The conformation of the catalytic site indicates that the enzyme is active in the crystalline form and thus suitable for structure-based inhibition studies. [source] Induction and Inhibition of Preferential Enrichment by Controlling the Mode of the Polymorphic Transition with Seed CrystalsCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2006Rui Tamura Prof. Abstract Both induction and inhibition of "preferential enrichment", an unusual symmetry-breaking enantiomeric-resolution phenomenon observed upon simple recrystallization of a certain kind of racemic crystals from organic solvents, have been successfully achieved by controlling the mode of the polymorphic transition during crystallization with appropriate seed crystals. Such control of the polymorphic transition can be interpreted in terms of a novel phenomenon consisting of 1) the adsorption of prenucleation aggregates, 2) the heterogeneous nucleation and crystal growth of a metastable crystalline form, and 3) the subsequent polymorphic transition into the more stable form; these three processes occur on the same surface of a seed crystal. We refer to this phenomenon as an "epitaxial transition", which has been confirmed by means of in situ attenuated total reflection (ATR) FTIR spectroscopy in solution and the solid state, differential scanning calorimetry (DSC) measurements of the deposited crystals, and X-ray crystallographic analysis of the single crystals or the direct-space approach employing the Monte Carlo method with the Rietveld refinement for the structure solution from the powder X-ray diffraction data. [source] Comparison of Properties of Aib-Rich Peptides in Crystal and Solution: A Molecular Dynamics StudyCHEMPHYSCHEM, Issue 5 2004Haibo Yu Abstract In order to study the differences of the structural properties of Aib-rich peptides in solution and in the crystalline state, molecular dynamics (MD) simulations of the Aib-containing peptide II (pBrBz-(Aib)5 -Leu-(Aib)2 -OMe) were performed in the crystalline state, starting from two different conformers obtained experimentally by X-ray diffraction. The structural properties as derived from X-ray crystallography (e.g., torsional angles and hydrogen bonds) are well-reproduced in both constant-volume and constant-pressure simulations, although the force-field parameters used result in a too-high density of the crystals. Through comparison with the results from previous MD and nuclear magnetic resonance (NMR) studies of the very similar peptide I (Z-(Aib)5 -Leu-(Aib)2 -OMe) in dimethylsulfoxide (DMSO) solution, it is found that, in the crystal simulation, the conformational distribution of peptide II is much narrower than that in the solution simulation of peptide I. This leads to a significant difference in 3J(HN, HC,) coupling constant values, in agreement with experimental data, whereas the NOE intensities or proton,proton distance bounds appear insensitive to the difference in conformational distribution. For small peptides the differences between their conformational distribution in the crystalline form and in solution may be much larger than for proteins, a fact which should be kept in mind when interpretating molecular properties in the solution state by using X-ray crystallographic data. [source] Gel growth and characterization of , -DL-methionineCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2006E. Ramachandran Abstract DL-Methionine [C5H11NO2S] is one of the essential amino acids in humans. It has two crystalline forms, viz., ,- and ,- methionine. In the present study, , - form is crystallized in silica gel; under suitable pH conditions by single diffusion method. The grown crystals were characterized by density measurement and single crystal X-ray diffraction. Fourier transform infrared (FTIR) spectroscopic studies, thermal analysis and scanning electron microscopic (SEM) studies were also made as part of the structural studies. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Actin-binding domain of mouse plectinFEBS JOURNAL, Issue 10 2004Crystal structure, binding to vimentin Plectin, a large and widely expressed cytolinker protein, is composed of several subdomains that harbor binding sites for a variety of different interaction partners. A canonical actin-binding domain (ABD) comprising two calponin homology domains (CH1 and CH2) is located in proximity to its amino terminus. However, the ABD of plectin is unique among actin-binding proteins as it is expressed in the form of distinct, plectin isoform-specific versions. We have determined the three-dimensional structure of two distinct crystalline forms of one of its ABD versions (pleABD/2,) from mouse, to a resolution of 1.95 and 2.0 Å. Comparison of pleABD/2, with the ABDs of fimbrin and utrophin revealed structural similarity between plectin and fimbrin, although the proteins share only low sequence identity. In fact, pleABD/2, has been found to have the same compact fold as the human plectin ABD and the fimbrin ABD, differing from the open conformation described for the ABDs of utrophin and dystrophin. Plectin harbors a specific binding site for intermediate filaments of various types within its carboxy-terminal R5 repeat domain. Our experiments revealed an additional vimentin-binding site of plectin, residing within the CH1 subdomain of its ABD. We show that vimentin binds to this site via the amino-terminal part of its rod domain. This additional amino-terminal intermediate filament protein binding site of plectin may have a function in intermediate filament dynamics and assembly, rather than in linking and stabilizing intermediate filament networks. [source] Effect of long-term natural aging on the thermal, mechanical, and viscoelastic behavior of biomedical grade of ultra high molecular weight polyethyleneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010H. Fouad Abstract In the total joint prostheses, Ultra High Molecular Weight Polyethylene (UHMWPE) may undergo an oxidative degradation in the long term. The overall properties of UHMWPE are expected to be altered due to the oxidative degradation. The goal of this study is to investigate the effects of natural aging up to 6 years in air on the thermal, mechanical, and viscoelastic properties of UHMWPE that was used in total joint replacement. The changes in UHMWPE properties due to aging are determined using Differential Scanning Calorimetry (DSC), uniaxial tensile tests, and Dynamic Mechanical Analysis (DMA). The DSC results show that the lamellar thickness and degree of crystallinity of UHMWPE specimens increase by 38% and 12% due to aging. A small shoulder region in the DSC thermograms is remarked for aged specimens, which is an indication of formation of new crystalline forms within their amorphous region. The tensile properties of aged and nonaged UHMWPE specimens show a significant decrease in the elastic modulus, yield, fracture stresses, and strain at break due to aging. The DM testing results indicate that the storage modulus and creep resistance of UHMWPE specimens decrease significantly due to aging. Also, it is remarked that the , relaxation peak for aged UHMWPE specimens occurs at lower temperature compared to nonaged ones. The significant reduction in the strength and creep resistance of UHMWPE specimens due to aging would affect the long-term clinical performance of the total joint replacement and should be taken into consideration during artificial joint design. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Solid lipid microparticles produced by spray congealing: Influence of the atomizer on microparticle characteristics and mathematical modeling of the drug releaseJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2010Nadia Passerini Abstract The first aim of the work was to evaluate the effect of atomizer design on the properties of solid lipid microparticles produced by spray congealing. Two different air atomizers have been employed: a conventional air pressure nozzle (APN) and a recently developed atomizer (wide pneumatic nozzle, WPN). Milled theophylline and Compritol® 888ATO were used to produce microparticles at drug-to-carrier ratios of 10:90, 20:80, and 30:70 using the two atomizers. The results showed that the application of different nozzles had significant impacts on the morphology, encapsulation efficiency, and drug release behavior of the microparticles. In contrast, the characteristics of the atomizer did not influence the physicochemical properties of the microparticles as differential scanning calorimetry, Hot Stage microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy analysis demonstrated. The drug and the lipid carrier presented in their original crystalline forms in both WPN and APN systems. A second objective of this study was to develop a novel mathematical model for describing the dynamic process of drug release from the solid lipid microparticles. For WPN microparticles the model predicted the changes of the drug release behavior with particle size and drug loading, while for APN microparticles the model fitting was not as good as for the WPN systems, confirming the influence of the atomizer on the drug release behavior. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:916,931, 2010 [source] Process induced disorder in crystalline materials: Differentiating defective crystals from the amorphous form of griseofulvinJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2008Tao Feng Abstract This research investigates milling induced disorder in crystalline griseofulvin. Griseofulvin was subjected to cryogenic milling for various lengths of time. For comparison, the amorphous form of griseofulvin was also prepared by the quench melt method. Different analytical techniques were used to study the differences between the cryomilled, amorphous and crystalline forms of the drug. Cryogenic milling of griseofulvin progressively reduces the crystallinity of the drug by inducing crystal defects, rather than amorphous materials. Raman analysis provides evidence of structural differences between the two. The differences between the defective crystals produced by milling and the amorphous form are significant enough as to be measurable in their bulk thermal properties. Defective crystals show significant decrease in the heat of fusion as a function of milling time but do not exhibit a glass transition nor recrystallization from the amorphous form. Crystal defects undergo recrystallization upon heating at temperatures well below the glass transition temperature (Tg) in a process that is separate and completely independent from the crystallization of the amorphous griseofulvin, observed above Tg. Physical mixtures of defective crystals and amorphous drug demonstrate that the thermal events associated with each form persist in the mixtures, unaffected by the presence of the other form. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97: 3207,3221, 2008 [source] Quantitation of crystalline and amorphous forms of anhydrous neotame using 13C CPMAS NMR spectroscopyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2005Thomas J. Offerdahl Abstract Although most drugs are formulated in the crystalline state, amorphous or other crystalline forms are often generated during the formulation process. The presence of other forms can dramatically affect the physical and chemical stability of the drug. The identification and quantitation of different forms of a drug is a significant analytical challenge, especially in a formulated product. The ability of solid-state 13C NMR spectroscopy with cross polarization (CP) and magic-angle spinning (MAS) to quantify the amounts of three of the multiple crystalline and amorphous forms of the artificial sweetener neotame is described. It was possible to quantify, in a mixture of two anhydrous polymorphic forms of neotame, the amount of each polymorph within 1,2%. In mixtures of amorphous and crystalline forms of neotame, the amorphous content could be determined within 5%. It was found that the crystalline standards that were used to prepare the mixtures were not pure crystalline forms, but rather a mixture of crystalline and amorphous forms. The effect of amorphous content in the crystalline standards on the overall quantitation of the two crystalline polymorphic forms is discussed. The importance of differences in relaxation parameters and CP efficiencies on quantifying mixtures of different forms using solid-state NMR spectroscopy is also addressed. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2591,2605, 2005 [source] Solid-state solubility influences encapsulation and release of hydrophobic drugs from PLGA/PLA nanoparticlesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2004Jayanth Panyam Abstract Biodegradable nanoparticles formulated from poly(D,L -lactide- co -glycolide) (PLGA) and polylactide (PLA) polymers are being extensively investigated for various drug delivery applications. In this study, we hypothesize that the solid-state solubility of hydrophobic drugs in polymers could influence their encapsulation and release from nanoparticles. Dexamethasone and flutamide were used as model hydrophobic drugs. A simple, semiquantitative method based on drug,polymer phase separation was developed to determine the solid-state drug,polymer solubility. Nanoparticles using PLGA/PLA polymers were formulated using an emulsion,solvent evaporation technique, and were characterized for size, drug loading, and in vitro release. X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) were used to determine the physical state of the encapsulated drug. Results demonstrated that the solid-state drug,polymer solubility depends on the polymer composition, molecular weight, and end-functional groups (ester or carboxyl) in polymer chains. Higher solid-state drug,polymer solubility resulted in higher drug encapsulation in nanoparticles, but followed an inverse correlation with the percent cumulative drug released. The XRD and DSC analyses demonstrated that the drug encapsulated in nanoparticles was present in the form of a molecular dispersion (dissolved state) in the polymer, whereas in microparticles, the drug was present in both molecular dispersion and crystalline forms. In conclusion, the solid-state drug,polymer solubility affects the nanoparticle characteristics, and thus could be used as an important preformulation parameter. © 2004 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 93:1804,1814, 2004 [source] Applications of Raman spectroscopy to pharmacyJOURNAL OF RAMAN SPECTROSCOPY, Issue 5 2004Giancarlo Fini Abstract This paper gives a summary of this special issue on ,Pharmaceutical Applications of Raman Spectroscopy'. It summarizes the papers collected and introduces the possible applications of classical Raman spectroscopy (macro and micro) and surface-enhanced Raman spectroscopy to the identification of pharmacologically active substances, their qualitative and quantitative analysis, characterization of crystalline forms and structure determination. Copyright © 2004 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||