Fine size control of platinum on carbon nanotubes: from single atoms to clusters.
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Nanotubes, Carbon↗
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Fibrous red phosphorus.
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Crystallization↗
Transition-metal doped zinc oxide nanowires.
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Nanostructures↗
Structure and lithium dynamics of Li2AuSn2--a ternary stannide with condensed AuSn4/2 tetrahedra.
The new stannide Li(2)AuSn(2) was prepared by reaction of the elements in a sealed tantalum tube in a resistance furnace at 970 K followed by annealing at 720 K for five days. Li(2)AuSn(2) was investigated by X-ray diffraction on powders and single crystals and the structure was refined from single-crystal data: Z=4, I4(1)/amd, a=455.60(7), c=1957.4(4) pm, wR2=0.0681, 278 F(2) values, 10 parameters. The gold atoms display a slightly distorted tetrahedral tin coordination with Au-Sn distances of 273 pm. These tetrahedra are condensed through common corners leading to the formation of two-dimensional AuSn(4/2) layers. The latter are connected in the third dimension through Sn-Sn bonds (296 pm). The lithium atoms fill distorted hexagonal channels formed by the three-dimensional [AuSn(2)] network. Modestly small (7)Li Knight shifts are measured by solid-state NMR spectroscopy that are consistent with a nearly complete state of lithium ionization. The noncubic local symmetry at the tin site is reflected by a nuclear electric quadrupolar splitting in the (119)Sn Mössbauer spectra and a small chemical shift anisotropy evident from (119)Sn solid-state NMR spectroscopy. Variable-temperature static (7)Li solid-state NMR spectra reveal motional narrowing effects at temperatures above 200 K, revealing lithium atomic mobility on the kHz time scale. Detailed lineshape as well as temperature-dependent spin lattice relaxation time measurements indicate an activation energy of lithium motion of 27 kJ mol(-1).
Alloys↗
High charge-carrier mobility in pi-deficient discotic mesogens: design and structure-property relationship.
Hexaazatrinaphthylene (HATNA) derivatives with six alkylsulfanyl chains of different length (hexyl, octyl, decyl and dodecyl) have been designed to obtain new potential electron-carrier materials. The electron-deficient nature of these compounds has been demonstrated by cyclic voltammetry. Their thermotropic behaviour has been studied by means of differential scanning calorimetry and polarised optical microscopy. The supramolecular organisation of these discotic molecules has been explored by temperature-dependent X-ray diffraction on powders and oriented samples. In addition to various liquid crystalline columnar phases (Col(hd), Col(rd)), an anisotropic plastic crystal phase is demonstrated to exist. The charge-carrier mobilities have been measured with the pulse-radiolysis time-resolved microwave-conductivity technique. They are found to be higher in the crystalline than in the liquid crystalline phases, with maximum values of approximately 0.9 and 0.3 cm(2) V(-1) s(-1), respectively, for the decylsulfanyl derivative. Mobilities strongly depend on the nature of the side chains.
Journal Article↗
Unusual high-temperature structural behaviour in ferroelectric Bi2WO6.
The crystal structure of Aurivillius phase ferroelectric Bi2WO6 has been studied in detail as a function of temperature by using high-resolution powder neutron diffraction. In agreement with an earlier study, a transition from space group P2(1)ab to B2cb occurs at about 660 degrees C. This transition corresponds to the loss of one octahedral tilt mode within the perovskite-like WO4 layer of the structure. A second, reconstructive, phase transition occurs around 960 degrees C, corresponding to the ferroelectric Curie point; in contrast to previous suggestions, the structure of this high-temperature phase contains layers of stoichiometry WO4, with WO6 octahedra sharing edges and corners, and with the fluorite-like Bi2O2 layers remaining essentially unchanged. This structure is closely related to that of the ambient temperature phase of lanthanide-doped derivatives, for example, Bi0.7Yb1.3WO6 recently reported. This phase-transition behaviour is in stark contrast to that of other members of the Aurivillius family, such as SrBi2Ta2O9 and Bi4Ti3O12, which retain the archetypal Aurivillius connectivity at all temperatures.
Journal Article↗
The influence of thermal and mechanical preparative techniques on the amorphous state of four poorly soluble compounds.
A number of studies in the literature have reported on the use of different preparative techniques to convert crystalline pharmaceutical compounds into the amorphous form. However, very few direct comparisons of different preparative techniques using the same drugs are available. The purpose of this study was to determine the influence of two techniques: quench cooling and ball milling on four structurally diverse pharmaceutical drugs. Dipyridamole, carbamazepine, glibenclamide, and indomethacin were converted to the amorphous form by (a) quench cooling of the drug melt and (b) ball milling. The chemical purity and physical form of the products was determined using diffractometric, spectroscopic, and thermal analytical techniques. Products were analysed immediately post preparation and after storage under different stability conditions. Quench cooling of the melt resulted in amorphous conversion of all four compounds. However with glibenclamide, quench cooling resulted in unacceptable chemical degradation whereas ball milling of glibenclamide resulted in a change in the keto-enol tautomerism at the aryl amide moiety of this drug. Ball milling resulted in predominantly amorphous products for all compounds except carbamazepine. Ball milling of carbamazepine resulted in a polymorphic transition of the starting material to form III. Physical stability studies showed that irrespective of preparative technique and storage conditions all samples showed at least partial reversion to the crystalline state after storage. Quench cooling of drug melts may be of use as a preparative technique however it can result in chemical degradation. Ball milling may also be of use as a preparative technique however its effectiveness is dependent on the unit cell structure of the compound.
Carbamazepine↗
Multiple-scattering extended X-ray absorption fine structure analysis of nanostructured iron(III) oxide in the pore system of mesoporous carbon CMK-1.
This work is devoted to the EXAFS analysis of nanostructured iron(III) oxide synthesized inside the pore system of mesoporous carbon CMK-1. A detailed study of the recording, preparation and evaluation of data recorded in fluorescence mode at the iron K-edge with and without multiple scattering is shown. The results obtained show that the local structure of Fe3+ inside nanostructured iron(III) oxide is different to that of the bulk material. Due to the small particle size, data analysis is much more difficult and data preparation more complex. Incorporating multiple scattering paths in the Fourier transforms and back-transforms during data evaluation gives structural insights that cannot be obtained using other spectroscopic methods, and this technique was used to draw conclusions about the first four coordination spheres of the nanostructured iron(III) oxide.
Carbon↗
Synthesis and characterization of aspartic acid complexes of antimony and bismuth triiodide.
New bioinorganic complexes of the aspartic acid with the antimony or bismuth triiodide were synthesized by a direct solid-solid reaction at room temperature. The formula of the complex is MI(3)[OOCCH(2)CH(NH(2))CO](2.5) x 2.5H(2)O (M = Sb, Bi). The complex may be a dimer with bridge structure. The crystal structure of the complexes belongs to a triclinic system. The lattice parameters are a = 0.9883 nm, b = 1.4284 nm, c = 2.0114 nm, alpha = 94.46 degrees , beta = 99.76 degrees and gamma = 100.1 degrees for the complex of antimony and a = 0.9756 nm, b = 1.4560 nm, c = 1.9875 nm, alpha = 94.18 degrees , beta = 97.25 degrees and gamma = 101.16 degrees for the complex of bismuth. The infrared spectra and thermal analyses can demonstrate the complex formation between the aspartic acid and the antimony or bismuth ion.
Antimony↗
High-throughput crystallization: polymorphs, salts, co-crystals and solvates of pharmaceutical solids.
The concepts of high-throughput (HT) screening and combinatorial synthesis have been integrated into the pharmaceutical discovery process, but are not yet commonplace in the pharmaceutical development arena. Emerging strategies to speed pharmaceutical development and capture solid form diversity of pharmaceutical substances have resulted in the emergence of HT crystallization technologies. The primary type of diversity often refers to polymorphs, which are different crystal forms of the same chemical composition. However, diverse salt forms, co-crystals, hydrates and solvates are also amenable to study in HT crystallization systems. The impact of form diversity encompasses issues of stability and bioavailability, as well as development considerations such as process definition, formulation design, patent protection and regulatory control. This review highlights the opportunities and challenges of HT crystallization technologies as they apply to pharmaceutical research and development.
Chemistry, Pharmaceutical↗
Solid-state phase behaviour of dodecylglycosides.
The solid-state phase behaviour of lyophilised n-dodecyl-beta-D-glucoside (beta-C(12)G(1)), n-dodecyl-beta-D-maltoside (beta-C(12)G(2)) and n-dodecyl-beta-D-maltotrioside (beta-C(12)G(3)) has been investigated by differential scanning calorimetry (DSC) and X-ray techniques. For beta-C(12)G(1), lyophilisation results in a formation of a crystalline anhydrate. The lamellar spacing (37 Angstroms) is consistent with an alkyl chain packing in which the chains are not interdigitated. At 80 degrees C, the material melts into a lamellar liquid crystal with a lamellar spacing of 32 Angstroms, which suggests that the non-interdigitated chain packing of the crystalline state is retained in the liquid crystal. In contrast, lyophilisation of beta-C(12)G(2) and beta-C(12)G(3) results in the formation of a glassy state, best described as a frozen version of the lamellar liquid crystal. For beta-C(12)G(2), the lamellar spacing in the glass and liquid crystal suggests interdigitation of the alkyl chains. The glass transition temperature was found to be 65 degrees C for beta-C(12)G(2) and 100 degrees C for beta-C(12)G(3), which compares favourably with the glass transition of the parent carbohydrates. A second crystalline modification of beta-C(12)G(1) was prepared by precipitation from an aqueous solution at temperatures below the Krafft point (38 degrees C). For this modification, the lamellar distance (24 Angstroms) is consistent with interdigitated alkyl chains. At 50 degrees C, the crystalline material melts into a liquid crystalline phase. The material also readily loses water and rapidly re-crystallises to the anhydrate. The amount of water lost upon drying is consistent with the idea that the material is a monohydrate of beta-C(12)G(1). The drying and re-crystallisation processes give rise to 'pre-transitions' in the DSC thermograms and illustrate the importance of careful control of water in any analysis of the phase behaviour of alkylglycosides.
Butanols↗
Physical solid-state properties and dissolution of sustained-release matrices of polyvinylacetate.
Solid-state compatibility and in vitro dissolution of direct-compressed sustained-release matrices of polyvinylacetate (PVAc) and polyvinylpyrrolidone (PVP) containing ibuprofen as a model drug were studied. Polyvinylalcohol (PVA) was used as an alternative water-soluble polymer to PVP. Differential scanning calorimetry (DSC) and powder X-ray diffractometry (PXRD) were used for characterizing solid-state polymer-polymer and drug-polymer interactions. The mechanical treatment for preparing physical mixtures of polyvinyl polymers and the drug (i.e. simple blending or stressed cogrinding) was shown not to affect the physical state of the drug and the polymers. With the drug-polymer mixtures the endothermic effect due to drug melting was always evident, but a considerable modification of the melting point of the drug in physical binary mixtures (drug:PVP) was observed, suggesting some interaction between the two. On the other hand, the lack of a significant shift of the melting endothermic peak of the drug in physical tertiary drug-polymer mixtures revealed no evidence of solid-state interaction between the drug and the present polymers. Sustained-release dissolution profiles were achieved from the direct-compressed matrices made from powder mixtures of the drug and PVAc combined with PVP, and the proportion of PVAc in the mixture clearly altered the drug release profiles in vitro. The drug release from the present matrix systems is controlled by both diffusion of the drug through the hydrate matrix and the erosion of the matrix itself.
Calorimetry, Differential Scanning↗
Preparation and evaluation of glibenclamide-polyglycolized glycerides solid dispersions with silicon dioxide by spray drying technique.
Solid dispersions (SDs) of glibenclamide (GBM); a poorly water-soluble drug and polyglycolized glycerides (Gelucire with the aid of silicon dioxide (Aerosil 200); as an adsorbent, were prepared by spray drying technique. SDs and spray dried GBM in comparison with pure GBM and corresponding physical mixtures (PMs) were initially characterized and then subjected to ageing study up to 3 months. Initial characterization of SDs and spray dried GBM by DSC and XRPD showed that GBM was present in its amorphous form (AGBM). Improvement in the solubility and dissolution rate was observed for all samples. DRIFT spectroscopy revealed presence of hydrogen bonding in SDs. During ageing study, almost no decrease of in vitro drug dissolution was observed, over the period of 3 months as compare with freshly prepared SDs. Slight crystallinity in SDs was observed in the DSC and XRPD studies during ageing. Moreover in vivo study in Swiss Albino mice also justified the improvement in the therapeutic efficacy of amorphous GBM in SDs over pure GBM. Thus, present study demonstrated the high potential of spray drying technique for obtaining stable free flowing SDs of poorly water-soluble drugs using polyglycolized glycerides carriers with the aid of silicon dioxide as an adsorbent.
Animals↗
Micro-mechanical properties of drying material bridges of pharmaceutical excipients.
This work is part of a larger research effort to elucidate the properties and morphology of pharmaceutical granules produced by wet-granulation. In this work, we measure forces exerted by the drying interparticle bridges. The bridges were formed from aqueous solutions of common pharmaceutical excipients both non-polymeric (lactose, mannitol) and polymeric (hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC), polyvinylpyrrolidone (povidone) (PVP)). We also study the morphology, microstructure and crystalline structure of solidifying bridges. We find that the solidifying behavior and final properties of bridges differ dramatically, depending on the composition of the solution. Bridges containing only lactose or mannitol tend to expand upon solidification, pushing the ends of the bridge apart; in contrast, pure HPC, HPMC, or PVP bridges tend to contract. Bridges crystallized from solution of the pure non-polymeric excipients are polycrystalline, brittle, and have low strength; bridges from the polymeric excipients are amorphous, strong and tough. When the polymeric and non-polymeric excipients are used together, behavior closer to either one or the other extreme takes place. This depends on the relative amount of polymer in the bridge. It was also found that the different polymers impart different behavior on the bridge. The observed differences in solidification behavior have important implications for granule formation, drying and ultimate bridge and granule properties; these are discussed at some length in the paper.
Crystallization↗
Structural, spectral, linear and nonlinear optical properties of new nonlinear optical L-histidinium trichloroacetate crystals.
Single crystals of a new histidinium salt: L-histidinium trichloroacetate {abbreviated as LHTCA; [(C(3)N(2)H(4))CH(2)CH(NH(3))(CO(2))](+)CCl(3)COO(-)} were grown by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in a non-centrosymmetric space group P2(1) of monoclinic system with cell parameters a=5.4505(18) A, b=25.769(8) A, c=9.210(2) A and beta=99.98(2) degrees. The vibrational structure of the compound confirms the presence of various functional groups in the molecule. The UV-vis-NIR spectrum shows a good transparency in the whole of the region from ultraviolet to near IR. The Kurtz powder SHG measurement confirms the frequency doubling of the crystal. Thermal behaviour of the crystals has been investigated by DSC analysis. These preliminary results suggest that LHTCA crystal can act as a potential and promising candidate for frequency doubling applications even from the near UV region to the near IR.
Crystallization↗
Spectral and thermal study of the ternary complexes of nickel with sulfasalazine and some amino acids.
The ternary complexes of Ni(II) with sulfasalazine (H(3)SS) as a primary ligand and alanine (ala), aspartic acid (asp), histidene (hist), methionine (meth) and serine (ser) amino acids as secondary ligands have been synthesized. Characterization of the complexes was based on elemental analyses, IR, UV-vis, mass spectra, magnetic moment and thermal analysis (TG). The isolated complexes were found to have the general formula [M(HSS)(AA)]4H(2)O (AA=ala, asp, hist, meth, or ser amino acid) where nickel is tetra-coordinated. The thermal stability of the complexes was studied and the weight losses for the decomposition of the complexes were calculated and correlated with the mass fragmentation pattern. In most cases, the amino acid moiety is removed along with the Schiff base moiety leaving NiO as a metallic residue. The metallic residue was confirmed by powder XRD measurements.
Amino Acids↗
Controlled release of rhodium (II) carboxylates and their association complexes with cyclodextrins from hydroxyapatite matrix.
Preparation and characterization of a controlled release system of rhodium (II) citrate, acetate. propionate, butyrate and their inclusion or association compounds with cyclodextrin (CD) are described. The porous hydroxyapatite (HA) was characterized by X-ray powder pattern diffraction, FTIR and solid state 31P NMR. Scanning electron microscopy and gas adsorption analysis (BET) were also performed. Release profiles of rhodium (II) carboxylates and their inclusion or association compounds from HA matrix were obtained at different drug loadings (5% and 10%). These were reasonably consistent with a diffusion model. This analysis, mainly using rhodium (II) citrate and butyrate, showed that the strategy of using CDs with a HA matrix may offer a useful new method for the controlled release of these compounds, and hence an alternative strategy for the controlled release of chemotherapeutic agents containing toxic metals. This may be a valuable new technique for localized anti-tumour chemotherapy that minimizes the side effects of such agents.
Carboxylic Acids↗
Sonochemical synthesis of iron phosphide.
The sonochemical reaction of Fe(CO)5 and triethylphosphine has been found to produce solid amorphous iron phosphide of composition FeP. The resulting compound was characterized by elemental microanalysis, scanning electron microscopy, energy-dispersive X-ray analysis, and Debye-Scherrer powder X-ray diffraction. X-ray powder patterns were obtained after the amorphous material had been heated above 950 degrees C and then slowly cooled to induce crystallization. This reaction provides the first use of ultrasound to sonochemically synthesize amorphous phosphide semiconductor materials from organometallic precursors.
Journal Article↗