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At least 1,513 records · Page 84Linked to original sources
PubMed2005

Development of fast-dissolving tablets of flurbiprofen-cyclodextrin complexes.

The present study was aimed at developing a tablet formulation based on an effective flurbiprofen-cyclodextrin system, able to allow a rapid and complete dissolution of this practically insoluble drug. Three different cyclodextrins were evaluated: the parent beta-cyclodextrin (previously found to be the best partner for the drug among the natural cyclodextrins), and two amorphous, highly soluble beta-cyclodextrin derivatives, i.e., methyl-beta-cyclodextrin and hydroxyethyl-beta-cyclodextrin. Equimolar drug-cyclodextrin binary systems prepared according to five different techniques (physical mixing, kneading, sealed-heating, coevaporation, and colyophilization) were characterized by Differential Scanning Calorimetry, x-ray powder diffractometry, infrared spectroscopy, and optical microscopy and evaluated for solubility and dissolution rate properties. The drug solubility improvement obtained by the different binary systems varied from a minimum of 2.5 times up to a maximum of 120 times, depending on both the cyclodextrin type and the system preparation method. Selected binary systems were used for preparation of direct compression tablets with reduced drug dosage (50 mg). Chitosan and spray-dried lactose, alone or in mixture, were used as excipients. All formulations containing drug-cyclodextrin systems gave a higher drug dissolved amount than the corresponding ones with drug alone (also at a dose of 100 mg); however, the drug dissolution behavior was strongly influenced by formulation factors. For example, for the same drug-cyclodextrin product the time to dissolve 50% drug varied from less than 5 minutes to more than 60 minutes, depending on the excipient used for tableting. In particular, only tablets containing the drug kneaded with methyl-beta-cyclodextrin or colyophilized with beta-cyclodextrin and spray-dried lactose as the only excipient satisfied the requirements of the Food and Drug Administration (FDA) for rapid dissolving tablets, allowing more than 85% drug to be dissolved within 30 minutes. Finally, it can be reasonably expected that the obtained drug dissolution rate improvement will result in an increase of its bioavailability, with the possibility of reducing drug dosage and side effects.

Analgesics↗
PubMed2004

The reliability of thermocouples in microwave ceramics processing.

It is not rare to hear arguments against the use of thermocouples for taking temperatures in processes that are taking place under microwave fields. However, the simplicity of this device makes it attractive to consider its use. One question that arises when thermocouples are employed is whether the electric field perturbs the measurement, and if the thermocouple affects the processing. The process that was chosen for conducting this test was the synthesis of spinel (MgAl2O4) using microwaves as a power supply and hematite (Fe2O3) as an additive for both spinel formation promotion and susceptor. The alumina-based systems are very important to study because this is one of the most common ingredients in refractory materials. There are many discussions about the improvement of the process when microwaves are used, but a kinetic comparison cannot be performed if the temperature is unknown, and that is the reason for emphasizing the measurement techniques. The analysis of the obtained samples was carried out by X-ray diffraction of powders. The results of this work show that there is no difference between the products obtained when the thermocouple was inserted in the system, compared to processing without it; hence the thermocouple is appropriate for this application.

Artifacts↗
PubMed2004

In-vitro intra- and inter-inhaler flow rate-dependent dosage emission from a combination of budesonide and eformoterol in a dry powder inhaler.

Some dry powder inhalers have profound inhalation flow rate-dependent dosage emission, and it has been suggested that there are links between the in vitro emitted dose, total lung deposition, and subsequent clinical response. We have measured the in vitro dosage delivery for a combination of budesonide and eformoterol in a new version of the Turbuhaler. At inhalation flow rates of 30, 60, and 90 Lmin(-1), the total dose emission for 10 separate inhalations from each of six inhalers was determined. The aerodynamic characteristics of the emitted dose using inhalation flow rates of 28.3 and 60 Lmin(-1) were measured using the Andersen Cascade Impactor. The mean (SD) emitted dose for budesonide, at 30, 60, and 90 Lmin(-1), was 37.5%(18.2%), 64.4%(16.6%), and 107.4%(36.0%) (of the nominal emitted dose), respectively, and for eformoterol were 38.0%(20.3%), 65.0%(16.8%), and 104.9%(36.2%) (of the nominal emitted dose), respectively. Variability of dose emission characteristics from each inhaler and between inhalers at each flow rate was found. The aerodynamic particle size characterization of the emitted dose at flow rates of 28.3 and 60 Lmin(-1) revealed a mean fine particle dose for budesonide of 11.9% and 28.6% of the nominal emitted dose, respectively, and similarly 10.0% and 26.3% for eformoterol. At 28.3 Lmin(-1), the majority of the emitted dose (54.8% for budesonide and 64.5% for eformoterol) was deposited in the throat and preseparator of the Andersen Cascade Impactor. The mass median aerodynamic diameters for budesonide and eformoterol at 28.3 Lmin(-1) were 3.2 and 3.6 microm, respectively, and similarly at 60 Lmin(-1) were 2.4 and 2.5 microm. The modified Turbuhaler containing a budesonide and eformoterol combined formulation shows intra- and inter-inhaler flow-dependent dosage emission. The clinical significance of the in vitro dose-dependent properties should be investigated.

Bronchodilator Agents↗
PubMed2003

Unconventional magnetic correlations in DyB2C and HoB2C.

Layered borocarbides RB2C (R=Dy, Ho, and Er) have been studied by powder neutron diffraction at 2-30 K. ErB2C has two-sublattice antiferromagnetic order below T(N)=16.3 K, but DyB2C and HoB2C show a coexistence of a conventional canted k=(000) ferromagnetic structure and unconventional magnetic correlations. The k=(000) phase orders at T(c)=8.5 K (DyB2C) and 7.1 K (HoB2C), but low-Q diffraction peaks from the unconventional correlations appear above T(c) with different critical temperatures for different peaks: at 8, 10.5, and 15.7 K for HoB2C. This scattering is fitted as diffraction from a Warren-type random magnetic layer lattice and may result from quadrupolar interactions between R3+ spins.

Journal Article↗
PubMed2004

Direct determination of the magnetic ground state in the square lattice S = 1/2 antiferromagnet Li2VOSiO4.

Powder neutron diffraction and resonant x-ray scattering measurements from a single crystal have been performed to study the low-temperature state of the 2D frustrated, quantum-Heisenberg system Li2VOSiO4. Both techniques indicate a collinear antiferromagnetic ground state, with propagation vector k=(1 / 2 1 / 2 0), and magnetic moments in the a-b plane. Contrary to previous reports, the ordered moment at 1.44 K, m=0.63(3)micro(B), is very close to the value expected for the square lattice Heisenberg model ( approximately 0.6micro(B)). The magnetic order is three dimensional, with antiferromagnetic a-b layers stacked ferromagnetically along the c axis. Neither x-ray nor neutron diffraction shows evidence for a structural distortion between 1.6 and 10 K.

Journal Article↗
PubMed2006

Theoretical determination of the structures of CaSiO3 perovskites.

Density functional theory is used to determine the possible crystal structure of the CaSiO3 perovskites and their evolution under pressure. The ideal cubic perovskite is considered as a starting point for studying several possible lower-symmetry distorted structures. The theoretical lattice parameters and the atomic coordinates for all the structures are determined, and the results are discussed with respect to experimental data.

Calcium Compounds↗
PubMed2005

Crystal lattice as biological phenotype for insect viruses.

Many insect viruses survive for long periods by occlusion within robust crystalline polyhedra composed primarily of a single polyhedrin protein. We show that two different virus families form polyhedra which, despite lack of sequence similarity in the virally encoded polyhedrin protein, have identical cell constants and a body-centered cubic lattice. It is almost inconceivable that this could have arisen by chance, suggesting that the crystal lattice has been preserved because it is particularly well-suited to its function of packaging and protecting viruses.

Animals↗
PubMed2006

The preparation and structures of hydrogen ordered phases of ice.

Two hydrogen ordered phases of ice were prepared by cooling the hydrogen disordered ices V and XII under pressure. Previous attempts to unlock the geometrical frustration in hydrogen-bonded structures have focused on doping with potassium hydroxide and have had success in partially increasing the hydrogen ordering in hexagonal ice I (ice Ih). By doping ices V and XII with hydrochloric acid, we have prepared ice XIII and ice XIV, and we analyzed their structures by powder neutron diffraction. The use of hydrogen chloride to release geometrical frustration opens up the possibility of completing the phase diagram of ice.

Journal Article↗
PubMed2004

In-situ fabrication of nanostructured cobalt oxide powders by spray pyrolysis technique.

Nano-crystalline Co3O4 and CoO powders have been prepared by a spray pyrolysis approach. The effects of the reaction temperature and initial salts on the crystallinity and phase composition have been studied. Based on the TEM and XRD results, the crystal sizes were in the range of 1-10 nm. SEM and TEM observations also reveal that the nano-powders easily create micron-scale spherical agglomerates. The Co3O4 powders obtained by spraying nitrate solution at 500 degrees C show high specific surface area, which according to the BET method is 82.37 m2/g. The time/temperature phase diagram of cobalt oxides developed from XRD and DTA/TGA analyses shows the existence of a CoO phase at low and high temperature ranges when some specific preparation conditions are applied.

Biocompatible Materials↗
PubMed2004

High-resolution and analytical TEM investigation of metastable-tetragonal phase stabilization in undoped nanocrystalline zirconia.

Submicron and nano-sized nanocrystalline pure zirconia (ZrO2) powders having metastable tetragonal and tetragonal-plus-monoclinic crystal structures, respectively, were synthesized using the sol-gel technique. The as-precipitated and the calcinated ZrO2 powders were analyzed for their morphology, nanocrystallite size and structures, aggregation tendency, local electronic properties, and elemental compositions by conventional and high-resolution transmission electron microscopy and field-emission analytical electron microscopy, including energy-dispersive X-ray and electron energy-loss spectroscopies. The results from this study indicate that a combination of nanocrystallite size, strain-induced grain-growth confinement, and the simultaneous presence of the monoclinic phase can lead to stabilization of the metastable tetragonal-phase in undoped ZrO2. As a result, the tetragonal phase is stabilized within ZrO2 nanocrystallites up to 100 nm in size, which is 16 times larger than the previously reported critical size of 6 nm.

Crystallization↗
PubMed2004

A simple route towards CuO nanowires and nanorods.

CuO nanowires and nanorods were synthesized through a novel controllable solution-phase hydrothermal method using a nonionic surfactant polyethylene glycol (PEG) as the structure-directing template. The lengths of obtained 1D CuO nanostructures could be successfully controlled through choosing different molecular weights of PEG. The phase structures and morphologies were investigated by XRD, TEM, HRTEM and SAED. The formation mechanisms of the nanorods and nanowires were investigated and discussed on the basis of the experimental results.

Bromides↗
PubMed2006

Quantitative measurement of indomethacin crystallinity in indomethacin-silica gel binary system using differential scanning calorimetry and X-ray powder diffractometry.

Differential scanning calorimetry (DSC) and X-ray powder diffractometry (XRPD) methods were developed for the quantitative analysis of the crystallinity of indomethacin (IMC) in IMC and silica gel (SG) binary system. The DSC calibration curve exhibited better linearity than that of XRPD. No phase transformation occurred in the IMC-SG mixtures during DSC measurement. The major sources of error in DSC measurements were inhomogeneous mixing and sampling. Analyzing the amount of IMC in the mixtures using high-performance liquid chromatography (HPLC) could reduce the sampling error. DSC demonstrated greater sensitivity and had less variation in measurement than XRPD in quantifying crystalline IMC in the IMC-SG binary system.

Calibration↗
PubMed2002

Characterization and quantitation of clarithromycin polymorphs by powder X-ray diffractometry and solid-state NMR spectroscopy.

Characterization of clarithromycin polymorph was performed by solid-state cross polarization and magic angle spinning (CP/MAS) 13C-NMR spectroscopy. Two polymorphs, form II and form I, of clarithromycins indicated characteristic resonances of C1 carbonyl carbon at 176.2 and 175.2 ppm, respectively. Since each peak of C1 carbon was well separated in the spectrum of the two polymorphs, we performed quantitative analysis of the polymorphic fraction from the peak area of these peaks. The peak area of form I was found to linearly increase with an increase of its content, with a correlation coefficient of above 0.99. Solid-state NMR was found to be a useful technique to determine the characteristics of the polymorphic forms.

Clarithromycin↗
PubMed2006

Specific inclusion mode of guest compounds in the amylose complex analyzed by solid state NMR spectroscopy.

The inclusion compound formation between linear amylose of molecular weight 102500 (AS100) and p-aminobenzoic acid (PA) during the sealed-heating process was investigated by powder X-ray diffractometry, infrared spectroscopy and solid state NMR spectroscopy. Sealed-heating of AS100 and PA at 100 degrees C for 6 h provided an inclusion compound with 6(1)-helix structure, while a 7(1)-helix structure was found when sealed-heating was carried out at 150 degrees C for 1 h. The formation of an inclusion compound was not observed when sealed-heating was performed at 50 degrees C for 6 h. The 7(1)-helix inclusion compound maintained its structure even during storage at high temperature while the 6(1)-helix inclusion compound decomposed and returned to the original V(a)-amylose upon heating to 180 degrees C. Quantitative determination revealed that one PA molecule could be included per one helical turn of AS100 for both 6(1)-helix and 7(1)-helix inclusion compounds. Solid state NMR spectroscopy suggested that PA molecules were included in the amylose helix core in the 7(1)-helix inclusion compound, while in the case of 6(1)-helix inclusion compound, PA molecules were accommodated in the interstices between amylose helices. Moreover, the inclusion compound formation by sealed-heating of AS100 was also observed when using PA analogues as guest compounds. The binding ratio of AS100 and PA analogues varied depending on the size of guest molecules.

4-Aminobenzoic Acid↗
PubMed2006

Preparation, characterization and in vitro dissolution studies of solid systems of valdecoxib with chitosan.

In the present study, the solubilizing and amorphizing properties of Valdecoxib (a poorly water soluble anti inflammatory drug) with low molecular weight chitosan (a polymer), have been investigated. Binary systems of varying drug/polymer ratios were prepared using different techniques (physical mixing, co-grinding, kneading) and were tested for dissolution. Drug carrier interactions were investigated in both the liquid and solid state, by phase solubility analysis, differential scanning calorimetry, powder X-ray diffractrometry, FT-IR spectroscopy and scanning electron microscopy. The solubility of the drug increased with increasing polymer concentration showing A(N) type phase solubility diagram. Differential scanning calorimetry, powder X-ray diffractrometry and scanning electron microscopic studies of binary systems suggested generation of amorphous form of drug (in kneading and co ground mixtures). IR spectroscopy revealed the presence of hydrogen bonding in kneading and co ground mixtures. Drug dissolution was improved with increasing the polymer concentration in the mixture (Kneaded>co ground>physical mixture), which was attributed to the amorphonization and/or decreased drug crystallinity, size and polymer wetting effect. Enhanced dissolution combined with its direct compression feasibility and anti ulcerogenic action results in low molecular weight chitosan for developing fast release oral solid dosage forms of valdecoxib.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2006

Correlation between inertial impaction and laser diffraction sizing data for aerosolized carrier-based dry powder formulations.

PURPOSE: The purpose of the study was to determine whether the drug fine particle fraction (FPF) from different dry powder aerosol formulations measured by laser diffraction at a range of flow rates correlated with that measured by inertial impaction. MATERIALS AND METHODS: Ten binary formulations were prepared containing 1.5% w/w salbutamol base or sulphate, blended with the sieved (63-90 microm) fraction of different sugars (regular lactose, spray-dried lactose, sorbitol, dextrose or maltose). A further six ternary formulations were prepared containing 1.5% w/w salbutamol sulphate, 97% coarse lactose (63-90 microm) and 1.5% micronised or intermediate-sized lactose (1-50 microm). The FPF particles (< 5 microm) of these formulations were measured by laser diffraction and inertial impaction at flow rates between 28.3 and 100 l min(-1). RESULTS: When only the particles with diameter < 60 microm obtained by laser diffraction were considered the FPF (< 5 microm) could be determined and this enabled the aerosolisation of all 16 blends to be feasibly compared at flow rates ranging from 28.3 to 100 l min(-1). A significant linear correlation was found between the fine fractions measured by laser diffraction and the salbutamol fine fractions determined by inertial impaction (r2 = 0.934). Such correlation was also confirmed for formulations containing added fine lactose. CONCLUSION: Particle size measured by laser diffraction under the employed conditions reflected the aerodynamic properties of the drug. Laser diffraction can be used as on-, in- and/or at-line measurements and controls for dry powder aerosol formulations.

Adrenergic beta-Agonists↗
PubMed2003

Properties and stability of a liquid crystal form of cyclosporine-the first reported naturally occurring peptide that exists as a thermotropic liquid crystal.

A new solid-state form of cyclosporine produced by spray-drying exhibited characteristics consistent with a liquid crystal. No sharp diffraction peaks were observed by powder X-ray diffraction; however, analysis by both small-angle X-ray diffraction (SAXR) and microscopic under polarized light (PLM) confirmed the existence of two-dimensional ordered liquid crystal. Hot stage microscopy revealed a solid-to-liquid transition, in the range of 118 to 125 degrees C. Moreover, the solid-to-liquid transition showed frequency dependence by dielectric analysis (DEA), and was coincidental with a stepwise heat capacity change measured by differential scanning Calorimetry (DSC). The two-dimensional order was maintained above the solid-to-liquid transition temperature indicated by low-angle diffraction by SAXR and birefringence by PLM. However, birefringence was lost at temperatures above 170 degrees C, indicating the conversion of the liquid crystal into an isotropic liquid. In situ annealing experiments, by DSC, revealed the presence of an endotherm, unexplained by either a phase transition or solvent loss, and it is believed to be the result of a structural rearrangement that has no impact on the macroscopic properties of the material. Spray-dried cyclosporine at room temperature is therefore a frozen thermotropic liquid crystal due to the presence of two-dimensional order and the lack of substantial residual solvent. This is, to our knowledge, the first report of the existence of a thermotropic liquid crystal of a naturally occurring peptide.

Calorimetry, Differential Scanning↗