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At least 811 records · Page 45Linked to original sources
PubMed2003

Structure and composition of silicon-stabilized tricalcium phosphate.

Silicon stabilized tricalcium phosphate [Si-TCP] is formed within the calcium hydroxyapatite (HA)-tricalcium phosphate (TCP) system when a stoichiometric precipitate of hydroxyapatite is fired at 1,000 degrees in the presence of SiO(2). This paper proposes a composition range and crystallographic structure for Si-TCP. Reitveld XRD powder diffraction, transmission electron microscopy, infrared and proton nuclear magnetic resonance measurements show that crystalline Si-TCP is associated with the displacement of OH from an initial hydroxyapatite structure. The resulting calcium phosphate is modified by the incorporation of silicon into its structure with excess silica contributing to an amorphous component. Si-TCP has a monoclinic structure with a space group P2(1)/a akin to alpha-TCP with estimated lattice constants of a=12.863+/-0.004 A, b=9.119 +/-0.003 A, c=15.232+/-0.004 A, beta=126.3+/-0.1 degrees. It is proposed that Si(4+) substitutes for P(5+)in the TCP lattice with the average chemical composition of Si-TCP set primarily by the mechanisms available for charge compensation. While the formation of OH vacancies in HA initiates the transformation to Si-TCP, two mechanisms of charge compensation in the Si-TCP structure are plausible. If O(2-) vacancies provide charge compensation, the composition of Si-TCP is Ca(3)(P(0.9)Si(0.1)O(3.95))(2) derived for the addition of 0.33 mol SiO(2):mol HA. If excess Ca(2+) compensates, the composition is Ca(3.08)(P(0.92)Si(0.08)O(4))(2) derived for the addition of 0.25 mol SiO(2):mol HA. The reaction occurs most effectively when SiO(2) is added as a colloidal suspension rather than by the in-situ thermal decomposition of a silicon metallorganic compound. The material is a bioceramic of major biological interest because of its osteoconductivity and unique influence on skeletal tissue repair and remodeling.

Absorption↗
PubMed2004

Bioactive glass as a drug delivery system of tetracycline and tetracycline associated with beta-cyclodextrin.

The aim of this study was to evaluate the physical-chemical properties, in vivo biocompatibility and antimicrobial activity of bioactive glasses (BG) used as a controlled release device for tetracycline hydrochloride and an inclusion complex formed by tetracycline and beta-cyclodextrin at 1:1 molar ratio. The BG as well as their compounds loaded with tetracycline (BT) and tetracycline:beta-cyclodextrin (BTC) were characterized by FTIR spectroscopy, X-ray powder diffraction, differential scanning calorimetry and by scanning electron microscopy and energy dispersive spectroscopy. The in vivo test was carried out with female mice split into three groups treated with bioactive glass either without drugs, or associated with tetracycline, or with tetracycline:beta-cyclodextrin by subcutaneous implantation. The histological examination of tissue at the site of implantation showed moderate inflammatory reactions in all groups after 72 h. The bacterial effect was tested on A. actinomycetemcomitans suspended in BHI broth, with or without bioactive particles. A considerable bacteriostatic activity was found with BT and BTC glasses, as compared to plain glass. The presence of cyclodextrin was important to slow down the release of tetracycline for a long period of time and it was verified that the presence of tetracycline or its inclusion complex, tetracycline:beta-cyclodextrin, did not affect the bioactivity of the glass.

Animals↗
PubMed2004

Phosphate glasses for tissue engineering: Part 1. Processing and characterisation of a ternary-based P2O5-CaO-Na2O glass system.

This paper presents the results of a study of the thermal properties, X-ray powder diffraction (XRPD), NMR and solubility of a range of phosphate-based glasses. Ion release and pH measurements were also obtained. The compositions were limited by fixing the P2O5 mol% content at 45, 50 and 55 mol%, and varying the CaO mol% at 30, 35 and 40 mol%. Initial data collected from thermal analysis showed an increase in the Tg values, with increasing CaO mol%, as expected. An increase in crystallisation temperatures with increasing CaO mol% was also observed, with sharp peaks indicating the presence of single and/or double phases. Initial XRPD data revealed that the 45 mol% P2O5 precipitated a calcium bridged trimetaphosphate (Na4Ca[PO3]6) at the sodium oxide contents of 25 and 20 mol%, but at the 15 mol% level two phases formed, NaCa[PO3]3 and Ca2P2O7. The 50 mol% P2O5 compositions showed two sodium phosphate-rich phases [NaCa(PO3)3 and NaPO3] for the lower calcium containing compositions, and a calcium phosphate phase [CaP2O6] for compositions with higher CaO mol%. The 55 mol% P2O5 compositions, exhibited similar phases for the lower calcium containing compositions, and a single calcium phosphate phase (CaP2O6) was identified for the higher calcium containing composition. NMR analysis revealed the presence of Q1 and Q2 species in the 45 mol% P2O5 compositions, and Q2 species present in the 50 and 55 mol% P2O5 compositions. The non-linear data obtained from the thermal and solubility analyses conducted were attributed to the packing density of the 45 mol% P2O5 compositions. The solubility was seen to decrease with increasing CaO mol%, for all the glasses investigated, and all the compositions showed a gradual decrease in pH with time, and this was accounted for by the release of Na+ and Ca2+ ions into solution.

Biocompatible Materials↗
PubMed1997

Rietveld analysis and Fourier maps of hydroxyapatite.

Rietveld analysis was applied to the X-ray powder diffraction data of well-crystallized hydroxyapatites synthesized at 80 degrees C and pH 7.4. The least-squares refinement program adopted for Rietveld analysis showed good pattern fitting with the calculated profile. The a- and c-axis dimensions, a-0.943046 + 0.000126 nm and c-0.687485 +/- 0.000104 nm, were obtained and compared with the data estimated from a single peak. The lattice dimensions obtained by Rietveld analysis were much closer to the values of a single crystal, a = 0.9432 nm and c-0.6881nm. Fourier analysis was also performed. The maps of electron densities expressed the existing possibility of each atom composing hydroxyapatite in the crystal structure. In particular, columnar calcium and screw-axis calcium were clearly revealed. These data agreed well with the computer graphics model of hydroxyapatite reported previously.

Computer Simulation↗
PubMed1999

Zirconia-fluorapatite materials produced by HIP.

Composites of tetragonal zirconia and fluorapatite were sealed in steel tubes and hot isostatically pressed at 1200 degrees C. The phases formed in the samples were evaluated by X-ray powder diffraction. When the composites contained larger amounts of fluorapatite, the tetragonal zirconia changed gradually into the cubic phase with decreasing zirconia content. These phase changes occurred due to a transfer of calcium from fluorapatite, which acted as an additional dopant in zirconia. Small amounts of monoclinic zirconia were also present in all samples. The cell dimension in fluorapatite was changed with the composition of the composite. However, decomposition of the fluorapatite was not possible to detect. Vickers hardness and fracture toughness were measured and ranged from 5.1 to 10.8 GPa and 0.9-5.5 MPam1/2, respectively. Microstructures in the composites were studied with scanning electron microscopy.

Apatites↗
PubMed2002

Synthesis and photophysical study of highly luminescent coordination compounds of rare earth ions with thenoyltrifluoroacetonate and AZT.

This work presents the study of the interaction between zidovudine (AZT) and rare earth (RE) ions with thenoyltrifluoroacetonate (TTA). The complexes [RE(TTA)(3) x (AZT)(2)] (where RE(III)=Eu and Gd) were prepared by reaction between the [RE(TTA)(3) x (H(2)O)(2)] precursors and AZT dissolved in acetone in the molar ratio 1:2. The obtained luminescent materials were characterized by microanalyses (C, H, N), complexometric titration, IR spectroscopy, X-ray powder diffraction and thermal analysis (DSC and TG/DTG). The luminescence data indicate that the substitution of the two water molecules by AZT in the europium complex causes an intensification of luminescence corresponding to the (5)D(0) -->(7)F(J) (J=0-4) transitions associated with one of the site symmetries. Based on the luminescence spectrum of the Eu(III)-compound the Omega(lambda) experimental intensity parameters (lambda=2 and 4) were calculated for the electronic transitions (5)D(0)-->(7)F(2, 4). The Omega(2) intensity parameter for this new compound is higher than for the precursor compound, suggesting an effective interaction between the AZT and the chemical environment of the Eu(III) ion. Luminescence data confirm that the AZT complex and precursor compound have a comparable emission quantum efficiency.

Anti-HIV Agents↗
PubMed2003

Interfacial molecular recognition between polysaccharides and calcium carbonate during crystallization.

Based on the basic principles of biomineralization, using beta-cyclodextrin, hepatin and soluble starch as organic matrices, employing the biomimetic method, the crystallization of CaCO(3) was studied by Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction analysis (XRD), scanning electronic microscopy (SEM), thermal gravity-differential thermal analysis and conductivity analysis. The results show that polysaccharides have an effect on the crystallization of CaCO(3). CaCO(3) crystals also have an effect on polysaccharides. The possible mechanism of this interaction is discussed.

Biomimetics↗
PubMedDate not supplied

Characterisation of synthetic beta-haematin and effects of the antimalarial drugs quinidine, halofantrine, desbutylhalofantrine and mefloquine on its formation.

Infrared spectroscopy, elemental analysis and X-ray powder diffraction show that the product of 30 min of reaction of haematin in 4.5 M acetate, pH 4.5 at 60 degrees C is identical to beta-haematin prepared in 4.5 M acetic acid at 70 degrees C overnight (pH 2.6). There is no evidence for formation of haem-acetate complex, which could not be isolated, even from 11.4 M acetate solution. The antimalarial drugs quinidine, halofantrine, desbutylhalofantrine and mefloquine were found to inhibit formation of beta-haematin, while 5-, 6- and 8-aminoquinoline and quinoline were found to have no effect. Quinidine was shown to form a complex with ferriprotoporphyrin IX in 40% DMSO with log K = 5.02 +/- 0.03. Log K values for halofantrine and desbutylhalofantrine are 5.29 +/- 0.02 and 5.15 +/- 0.02 respectively (solutions containing 30% acetonitrile in addition to DMSO to solubilise these drugs), which are both stronger than chloroquine under the same conditions (log K = 4.56 +/- 0.02).

Antimalarials↗
PubMed1998

Crystalline properties of carbamazepine in sustained release hydrophilic matrix tablets based on hydroxypropyl methylcellulose.

The influence of hydroxypropyl methylcellulose (HPMC) on the crystal habit properties of carbamazepine in sustained release matrix tablets and in aqueous solutions was investigated using differential scanning calorimetry (DSC), X-ray powder diffraction and scanning electron microscopy (SEM). The results suggest that HPMC inhibits the transformation of carbamazepine to carbamazepine dihydrate in the gel layer of hydrated tablets and in aqueous solutions (depending on HPMC concentration), participates in its crystallization process and induces amorphism of carbamazepine crystals. The mechanism which explains these effects envisages the polymer serving as a template or microsubstrate for nucleation in the crystallization process. We assume that the interaction between the drug and polymer occurs by hydrogen bonding. The hydroxyl groups of the polymer may attach to the drug at the site of water binding, and thus its transformation to the dihydrate form, is inhibited. A more specific interaction involves structural matching (similar bond spacing distances) between inter-atomic distances in the crystal lattice of carbamazepine dimer and intra-atomic distances along the polymer chain.

Calorimetry, Differential Scanning↗
PubMed2000

The effect of egg albumin on the crystalline properties of carbamazepine in sustained release hydrophilic matrix tablets and in aqueous solutions.

The influence of egg albumin (EA) on the crystal habit properties of carbamazepine (CBZ) in aqueous solutions, solid-state, and in sustained release matrix tablets was investigated using differential scanning calorimetry (DSC), hot-stage microscopy (HSM), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and contact angle goniometer (CAG). The results suggest that in solid-state mixtures, EA affected the polymorphic transitions of CBZ from the beta to the alpha form. In hydrated matrix tablets and aqueous solutions, EA influenced the conversion rate of CBZ to the dihydrate form depending on EA concentration. It was found that increasing EA concentration enhanced CBZ dihydrate aggregation, an effect that leads to the formation of crystals with high mechanical strength and decrease of CBZ solubility. Possible mechanisms, which explain crystal growth and aggregation, as well as alteration of CBZ polymorphic transitions in the solid-state, gel layer, and in aqueous solution were suggested. In the gel layer of hydrated tablets the kinetics of CBZ transformation to the dihydrate form, crystal growth and aggregation were influenced by various processes: matrix hydration, erosion mechanism and the formation of metastable conditions, which favor aggregation and growth. The release kinetics of CBZ from the matrix highly correlated with the crystalline and morphological changes occurring in the matrix.

Anticonvulsants↗
PubMed2000

Structural relationship and desolvation behavior of cromolyn, cefazolin and fenoprofen sodium hydrates.

The hydrated crystal structures of cromolyn, cefazolin, and fenoprofen sodium salts are reported. The former two compounds are non-stoichiometric hydrates, whereas the fenoprofen lattice maintains its stoichiometry over a broad range of relative humidity. The relationship between composition, lattice parameters, and relative humidity is studied using a combination of moisture sorption isotherms and variable humidity X-ray powder diffraction. The dehydration properties of the sodium salts are related to the ion coordination and hydrogen bonding of the water molecules in the structures. Anisotropic lattice contraction is observed during dehydration of the cromolyn and cefazolin sodium and is related to the closeness of intermolecular contacts in the hydrated structures.

Cefazolin↗
PubMed2000

The formulation of Halofantrine as either non-solubilizing PEG 6000 or solubilizing lipid based solid dispersions: physical stability and absolute bioavailability assessment.

A non-solubilizing solid dispersion formulation (polyethylene glycol 6000) and two solubilizing solid dispersions (Vitamin E TPGS and a Gelucire 44/14/Vitamin E TPGS blend) containing the antimalarial, Halofantrine (Hf), were formulated for bioavailability assessment in fasted beagles to determine if the oral absorption of Hf can be enhanced by these delivery systems. Solid dispersions comprising varying proportions of drug to carrier were prepared by the fusion method. Whilst the non-solubilizing formulation was assessed according to its dispersion characteristics, the solubilizing solid dispersions were assessed by their ability to form microemulsions upon dispersion. Studies in fasted beagles showed that the solid dispersions afforded a five- to seven-fold improvement in absolute oral bioavailability when compared with the commercially available tablet formulation. The delivery of Hf in either a solubilizing or non-solubilizing solid dispersion did not result in significant differences in oral bioavailability. The physical stability of the solid dispersions was studied using differential scanning calorimetry and X-ray powder diffraction.

Antimalarials↗
PubMed2000

Effect of solvent on the preparation of surfactant-free poly(DL-lactide-co-glycolide) nanoparticles and norfloxacin release characteristics.

The surfactant-free nanoparticles of poly(DL-lactide-co-glycolide) (PLGA) were prepared by dialysis method without surfactant and physicochemical properties such as particle size and drug contents were investigated against used initial solvent. The size of PLGA nanoparticles and drug contents were significantly changed by used initial solvent. The size of PLGA nanoparticles prepared from dimethylacetamide (DMAc), dimethylformamide (DMF), and dimethylsulfoxide (DMSO) as a initial used solvent was smaller than that of acetone. Selected initial solvent used to dissolve the copolymer significantly affects the size of nanoparticles and drug contents. It was shown that PLGA nanoparticles have spherical shapes from the results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. It was thought that surfactant-free nanoparticles of PLGA entrapping norfloxacin (NFX) has nice drug loading capacity without free-drug on the surface of nanoparticles through the analysis of X-ray powder diffraction. From these results, it was showed the potential that the PLGA nanoparticles could be formed successively by dialysis method without surfactant. Release kinetics of NFX used as a model drug was governed by not only drug contents but also particle size parameter. The higher the drug contents and the larger the particle size resulted in slower the drug release.

Anti-Infective Agents↗
PubMed2000

Highly compressible paracetamol: I: crystallization and characterization.

It was found that polyvinylpyrrolidone (PVP) is an effective additive during crystallization of paracetamol and significantly influenced the crystallization and crystal habit of paracetamol. These effects were attributed to adsorption of PVP onto the surfaces of growing crystals. It was found that the higher molecular weights of PVP (PVP 10000 and PVP 50000) were more effective additives than lower molecular weight PVP (PVP 2000). Paracetamol particles obtained in the presence of 0.5% w/v of PVP 10000 or PVP 50000 had near spherical structure and consisted of numerous rod-shaped microcrystals which had agglomerated together. Particles obtained in the presence of PVP 2000 consisted of fewer microcrystals. Differential scanning calorimetry (DSC) and X-ray powder diffraction (XPD) experiments showed that paracetamol particles, crystallized in the presence of PVP, did not undergo structural modifications. By increasing the molecular weight and/or the concentration of PVP in the crystallization medium the amount of PVP incorporated into the paracetamol particles increased. The maximum amount of PVP in the particles was 4.32% w/w.

Acetaminophen↗
PubMed2001

Dissolution properties and anticonvulsant activity of phenytoin-polyethylene glycol 6000 and -polyvinylpyrrolidone K-30 solid dispersions.

Solid dispersions of phenytoin in polyethylene glycol 6000 and polyvinylpyrrolidone K-30 with different drug-to-carrier ratios were prepared by the solvent method with the aim of increasing dissolution rate and bioavailability of the drug. These new formulations were characterized in the solid state by FT-IR spectroscopy, X-ray powder diffraction, and differential scanning calorimetry. Drug solubility and dissolution rate are improved by these formulations, particularly with SDPEG 1/20 and SDPVP 1/20 systems. Storage was found to influence the stability of the solid dispersions. By maximal electroshock test, it was found that the intraperitoneal administration in mice of the SDPEG 1/20 and SDPVP 1/20 systems exhibited anticonvulsant activity similar to diphenylhydantoin sodium salt.

Animals↗
PubMed2002

Polymorphism of the CNS active drug Org 13011: the application of high temperature analysis to detect new polymorphs.

The polymorphism of the CNS active compound Org 13011 was studied using different crystallisation methods (i.e. different solvents and cooling rates). The samples were analysed by Raman, solid state NMR, X-ray powder diffraction (XRPD) and thermal analysis. This led to the characterisation of two crystalline forms A and B. Further high temperature analysis using Raman, XRPD, solid state NMR and DSC revealed another two (high temperature) crystalline forms C and D. The transitions to the high temperature crystalline forms occur at temperatures of about 60 degrees C. This study shows that the application of high temperature experiments is useful and can lead to the discovery of new crystalline forms.

Central Nervous System Agents↗
PubMed2002

Polymorphic behavior of an NK1 receptor antagonist.

Four anhydrous polymorphic forms (I, II, III and IV) of an NK1 receptor antagonist, Compound A, have been discovered. The pure compound can exist as either Forms I or II at room temperature and Forms III or IV at elevated temperatures. The four polymorphs were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis, X-ray powder diffraction (XRPD) and solid-state NMR spectroscopy (SSNMR). Polymorphic transformations in the solid phase were studied using DSC, hot stage XRPD, temperature-modulated SSNMR and hot stage optical microscopy. The solubilities of Forms I and II in tert-butyl acetate at different temperatures were measured and the relative stability of the two forms was established. The thermodynamic transformation temperatures between Forms I and III, as well as Forms II and IV, were estimated by DSC. Transformation from Form III to IV, which is undetectable in a normal calorimetric run, was revealed through careful thermal programming. An interesting conversion route from Form I, a more stable form at room temperature, to Form II, a less stable form at room temperature was discovered.

Calorimetry, Differential Scanning↗
PubMed2002

Factors affecting incorporation of drug into solid solution with HPMCP during solvent change co-precipitation.

Drug-hydroxypropyl methylcellulose phthalate (HPMCP) mixtures were completely dissolved in acetone, and the resulting solution was added drop-wise into HCl(aq). Resulting co-precipitates were filtered, and then dried under vacuum at 45 degrees C, -800 mbar for 24 h. Modulated differential scanning calorimetry, thermogravimetric analysis, X-ray powder diffraction and HPLC were used to detect and quantify different phases present in co-precipitates. A 1/8 factorial study followed by a circumscribed central composite (CCC) study of significant factors, were used to detect and quantify respectively, the effects that processing factors had on the percentage of drug present in co-precipitates which was incorporated into solid solution (the response). Robustness of the model obtained from the CCC study was tested. Statistically significant factors were found to be the percentage of drug added into solvent, stirrer speed, and antisolvent pH. The statistically significant mathematical model obtained from the CCC study predicted that the dominant factor influencing the response is the percentage of drug added into solvent. The effect of stirrer speed on the response includes a local maximum at stirrer speed approximately 700 rpm. Both stirrer speed and antisolvent pH showed interactions with the percentage of drug added into solvent. The model obtained from this study indicated the possibility of two opposing phenomena influencing the response: crystallization inhibition by HPMCP, and solvent-antisolvent plasticization. Testing of this model using eight experimentally determined points showed reasonable robustness, with six out of eight points lying inside 95% prediction intervals.

Acetone↗