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PubMed1997

Synthesis and structural characterization of mixed aluminum-gallium-offretites.

A new synthesis procedure is reported for the preparation of mixed Al,Ga-offretites over the entire solid solution range 0 < or = Ga/(Ga + Al) < or = 1. The resulting materials are characterized by X-ray powder diffraction, adsorption microcalorimetry and multinuclear solid state NMR. The 29Si MAS-NMR data are consistent with statistical occupancy of the T1 and T2 sites by aluminum and gallium, and also show no positive evidence for preferential siting effects between both framework metals. Isotropic chemical shifts and nuclear electric quadrupolar coupling constants for 27Al and 71Ga have been obtained from a field-dependent analysis of the center of gravity in the MAS-NMR spectra. H-Al,Ga-offretites produced by ammonium exchange and subsequent calcination reveal evidence of partial demetallation of the framework with formation of extra-lattice metal species.

Aluminum↗
PubMed1997

The crystallization kinetics of sodalites grown by the hydrothermal transformation of kaolinite studied by 29Si MAS NMR.

The hydrothermal transformation of kaolinite to basic sodalite Na8[AlSiO4]6 (OH.H2O)2 and hydroxoborate sodalite Na8[AlSiO4]6 [B(OH)4]2 has been investigated at different temperatures (353 and 473 K). In the early stage of the reactions, the crystallization kinetics was studied by X-ray powder diffraction, thermogravimetry, IR spectroscopy and 29Si MAS NMR spectroscopy. Besides the crystallization of the sodalites, no further intermediate phases were formed. MAS NMR of the 29Si nucleus has been found to be a versatile tool to follow the progress of reactions from the signal ratio of the initial material and the crystallization product because the differences in chemical shifts result in well-separated signals. From these measurements, the growth rates of the sodalites could be determined quantitatively even for the very early stages of crystallization. It was found that sodium carbonate impurities in the NaOH solution used for the synthesis has an important influence on the reaction kinetics.

Crystallization↗
PubMed2000

Physicochemical characterization of solid dispersions of the antiviral agent UC-781 with polyethylene glycol 6000 and Gelucire 44/14.

The purpose of this study was to prepare and characterize solid dispersions of the antiviral thiocarboxanilide UC-781 with PEG 6000 and Gelucire 44/14 with the intention of improving its dissolution properties. The solid dispersions were prepared by the fusion method. Evaluation of the properties of the dispersions was performed using dissolution studies, differential scanning calorimetry, Fourier-transform infrared spectroscopy and X-ray powder diffraction. To investigate the possible formation of solid solutions of the drug in the carriers, the lattice spacings [d] of PEG 6000 and Gelucire 44/14 were determined in different concentrations of UC-781. The results obtained showed that the rate of dissolution of UC-781 was considerably improved when formulated in solid dispersions with PEG 6000 and Gelucire 44/14 as compared to pure UC-781. From the phase diagrams of PEG 6000 and Gelucire 44/14 it could be noted that up to approximately 25% w/w of the drug was dissolved in the liquid phase in the case of PEG 6000 and Gelucire 44/14. The data from the X-ray diffraction showed that the drug was still detectable in the solid state below a concentration of 5% w/w in the presence of PEG 6000 and Gelucire 44/14, while no significant changes in the lattice spacings of PEG 6000 or Gelucire 44/14 were observed. Therefore, the possibility of UC-781 to form solid solutions with the carriers under investigation was ruled out. The results from infrared spectroscopy together with those from X-ray diffraction and differential scanning calorimetry showed the absence of well-defined drug-polymer interactions.

Anilides↗
PubMed2001

The influence of polyvinylpyrrolidone on naproxen complexation with hydroxypropyl-beta-cyclodextrin.

The combined effect of hydroxypropyl-beta-cyclodextrin (HPbetaCD) and polyvinylpyrrolidone (PVP) on the solubility of naproxen (NAP) was studied. Phase-solubility analysis at different temperatures was used to investigate interactions in aqueous solution between NAP and the carriers, either alone or in combination. Equimolar NAP-HPbetaCD solid systems, in the presence or the absence of 15% (w/w) PVP, were prepared by cogrinding, kneading, coevaporation or freeze-drying, and characterized by differential scanning calorimetry, X-ray powder diffraction analysis, infrared spectroscopy and dissolution rates. The combined use of PVP and HPbetaCD resulted in a synergistic increasing effect of the aqueous solubility of NAP (120 times that of the pure drug). The phenomenon was interpreted in terms of the strongest complexation capacity of HPbetaCD towards NAP, which was reflected by an about 65% increase in the apparent stability constant of the NAP-HPbetaCD complex in the presence of only 0.1% (w/v) PVP. Variations in thermodynamic parameters accounted for a PVP role in the formation of a NAP-HPbetaCD-PVP ternary complex. The positive effect of PVP also reflected on NAP dissolution rates from solid preparations, because all ternary systems, with the exception of physical mixtures, dissolved faster than the corresponding NAP-HPbetaCD binary systems. The results of solid state studies accounted for the occurrence of mechanically- and/or thermally-induced stronger interactions in ternary than in binary systems, that in some cases led to a complete loss of NAP crystallinity.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed1999

Influence of polyethylene glycol 4000 on the polymorphic forms of diflunisal.

The present study was carried out to investigate the physico-chemical characteristics of diflunisal-PEG 4000 solid dispersions prepared by melting, solvent and melting-solvent methods. The solvents chosen were chloroform, methanol and ethanol-water due to the fact that the drug presents different polymorphic forms in these solvents. The characterization of solid dispersions was performed by X-ray powder diffraction because this technique has the advantage over other identification methods that it can detect both drug and ligand simultaneously. The X-ray diffraction patterns of the diflunisal-PEG systems suggested that the drug/polymer ratio and the solvent nature play an important role in the crystallization of the drug. In this regard, diflunisal crystallizes in form I at high concentrations of the drug (drug/polymer 2:1) in the solidified melt dispersions, however, polymorph III is mainly obtained as the polymer content increases (1:1 and 2:3). Likewise, in solid systems obtained by the solvent and melting solvent methods the drug solidifies in form III in ethanol/water and methanol while polymorph IV crystallizes in chloroform. Finally, DSC thermograms and hot-stage microscopy data of solid dispersions prepared by the melting method have allowed to draw the diflunisal-PEG 4000 solid-liquid phase diagram.

Calorimetry, Differential Scanning↗
PubMed1999

Solid state studies of drug-cyclodextrin inclusion complexes in PEG 6000 prepared by a new method.

The melting method was investigated as a possible method for producing drug-cyclodextrin (CD) inclusion compounds in a carrier. Various solid dispersions of alpha-, beta- and gamma-CD in polyethylene glycol (PEG) 6000 with and without the addition of 5% w/w indomethacin or griseofulvin were prepared using the original components. Characterisations of the samples included X-ray powder diffraction, modulated-temperature differential scanning calorimetry and dissolution tests by the paddle method according to USP XXI standard. Evidence of a complex between indomethacin and beta-CD in PEG 6000 was found. An indomethacin-gamma-CD complex formed a well defined phase in the PEG carrier, with tetragonal structure and unit cell parameters a=23.885(35) A and c=23.181(64) A. No complexation of indomethacin with alpha-CD, or with griseofulvin and beta-CD could be detected. It is suggested that competition between PEG and the drug for the binding to different CDs along with varying patterns of water loss from the CDs influence the inclusion reaction. The formation of complexes was accompanied by a decrease in the relative crystallinity of the dispersions. Dissolution tests showed that the CDs have a delaying effect on the release of indomethacin from PEG 6000 in the order alpha-CD<gamma-CD</=beta-CD.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2000

Physicochemical properties of amorphous precipitates of cimetidine-indomethacin binary system.

We have found that the binary system, consisting of a precipitate of cimetidine and naproxen, became amorphous due to intermolecular interaction. In order to clarify the interaction between cimetidine and other drugs, the physicochemical properties of binary systems consisting of cimetidine and drugs, phenacetin, salicylamide or indomethacin, were investigated. X-ray powder diffraction patterns and thermal analysis findings for the precipitates indicated that the cimetidine-indomethacin system has an amorphous structure, whereas the cimetidine-phenacetin and cimetidine-salicylamide systems do not. Fourier-transform infra-red (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy findings suggested that there is an intermolecular interaction between a proton in the imidazole ring of cimetidine and the C=O in the COOH of indomethacin. Since an interaction by the hydrogen bond between cimetidine and indomethacin would prevent three-dimensional arrangements of the molecules, the precipitate would be amorphous. In the cimetidine-indomethacin system, decarboxylation of indomethacin occurred below the melting temperature, indicating that the chemical stability decreased upon precipitation. Cimetidine was found to interact with drugs with a carboxyl group. The interaction would be applicable to make the amorphous system of the drugs and increase the solubility of the drugs.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

Complexation of phenytoin with some hydrophilic cyclodextrins: effect on aqueous solubility, dissolution rate, and anticonvulsant activity in mice.

The main objective of this study was to evaluate the influence of hydroxypropylated beta- and gamma-cyclodextrins and Me-beta-cyclodextrin (HP-beta-CD, HP-gamma-CD, and Me-beta-CD, respectively) on the dissolution rate and bioavailability of the antiepileptic agent, phenytoin (DPH). The corresponding solid complexes were prepared by a freeze-drying method and characterized by infrared spectroscopy, X-ray powder diffraction, and differential scanning calorimetry studies. Evidence of inclusion complex formation in the case of HP-beta-CD was obtained by (1)H- and (13)C-nuclear magnetic resonance spectroscopy. Drug solubility and dissolution rate in 0.05 M potassium phosphate buffer (pH 6) were notably improved by employing the beta-CDs. Thus a 45% w/v HP-beta-CD or Me-beta-CD solution gave rise to an increase of dissolved drug of 420- and 578-fold, respectively. The Q(10) (i.e. percentage of dissolved DPH at 10 min) was 5.2% for the pure drug and 93, 98, and 96% for DPH/HP-beta-CD, DPH/HP-gamma-CD, and DPH/Me-beta-CD complexes, respectively. Moreover, it was found that in the maximal electroshock seizure test in mice the DPH/Me-beta-CD complex exhibited anticonvulsant activity similar to DPH sodium salt (NaDPH).

Animals↗
PubMed2002

Preparation of extruded carbamazepine and PEG 4000 as a potential rapid release dosage form.

The aim of this research was to use a ram extruder to prepare directly a fast release dosage form with uniform shape and density, containing carbamazepine (C) as a water-insoluble drug and polyethylene glycol 4000 (PEG) as a low melting binder. The potential inclusion of lactose (L) as a hydrophilic filler was also considered. The temperature suitable to ensure a successful extrusion process of several formulations containing PEG in different percentages was found to be below the melting point of the PEG. The influence of composition on the extrusion process of different ram speeds was checked by measuring the pressure at the steady state, the apparent shear rate and the apparent shear stress of a range of mixtures of drug, lactose and PEG. The physical-mechanical properties of extrudates, including tensile strength and Young's modulus, prepared with different ram velocities were also determined. The solid-state physical structure by differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) was established. The dissolution of the extrudates and their corresponding physical mixtures were compared. The mixtures were found to be shear thinning when extruded; the tensile strength of extrudates was dependent on the composition but not the extrusion rate, while the value of Young's modulus was strongly influenced by the rate of extrusion, but less affected by the composition of the extrudates. The results of DSC and XRD indicated that the solid structure of the extrudates corresponded to that of a physical mixture of the components, hence there had been no change in the physical form of the drug induced by extrusion. In terms of dissolution, the rate of the extrusion process did not influence the performance of the products, whereas the composition did. The extruded mixtures of an equivalent composition exhibited a more rapid release than a simple physical mixture. The addition of lactose reduced the dissolution rate.

Anticonvulsants↗
PubMed2003

Study of the solid state of carbamazepine after processing with gas anti-solvent technique.

The purpose of this study was to investigate the influence of supercritical CO2 processing on the physico-chemical properties of carbamazepine, a poorly soluble drug. The gas anti-solvent (GAS) technique was used to precipitate the drug from three different solvents (acetone, ethylacetate and dichloromethane) to study how they would affect the final product. The samples were analysed before and after treatment by scanning electron microscopy analysis and laser granulometry for possible changes in the habitus of the crystals. In addition, the solid state of the samples was studied by means of X-ray powder diffraction, differential scanning calorimetry, diffuse reflectance Fourier-transform infrared spectroscopy and hot stage microscopy. Finally, the in vitro dissolution tests were carried out. The solid state analysis of both samples untreated and treated with CO2, showed that the applied method caused a transition from the starting form III to the form I as well as determined a dramatic change of crystal morphology, resulting in needle-shaped crystals, regardless of the chosen solvent. In order to identify which process was responsible for the above results, carbamazepine was further precipitated from the same three solvents by traditional evaporation method (RV-samples). On the basis of this cross-testing, the solvents were found to be responsible for the reorganisation into a different polymorphic form, and the potential of the GAS process to produce micronic needle shaped particles, with an enhanced dissolution rate compared to the RV-carbamazepine, was ascertained.

Carbamazepine↗
PubMed2003

Evaluation of beta-lactose, PVP K12 and PVP K90 as excipients to prepare piroxicam granules using two wet granulation techniques.

The present investigation aimed at evaluating the use of different excipients, beta-lactose and polyvinylpyrrolidone of two molecular weights (PVP K12 and PVP K90), in the production of improved release piroxicam granules, by wet granulation using both water and steam as granulation liquid. The formulations examined were: piroxicam (Px)/beta-lactose; Px/PVP K12 and Px/PVP K90, each one at a 1:9 weight ratio. The most significant difference between beta-lactose and PVP is that, using the first excipient, both steam and water granules were produced while, when PVP were employed, only steam granules were obtained. Image analysis revealed that beta-lactose steam granules had a larger surface area with respect to water granules, whereas lower values of this parameter were observed in PVP-s granules, confirming the Scanning Electron Microscopy micrographs and the fractal analysis results. As regards the enhancement of the dissolution profiles, the best result was obtained using beta-lactose steam granules followed by PVP K12 ones, even if the reactive dimension values indicated that during the dissolution process PVP K12 granules modified the surface more than beta-lactose granules. As regards PVP K90, this excipient was the one less influencing the granule morphology and the dissolution behaviour. Differential Scanning Calorimetry analysis suggested the partial amorphisation of the drug in the granules containing the three excipients. This result was then confirmed by X-ray powder diffraction analysis. Therefore, beta-lactose and PVP K12 could be proposed as useful excipients to enhance the dissolution rate of Px from granules prepared using the steam granulation technique.

Drug Evaluation, Preclinical↗
PubMed2002

Use of municipal incinerator bottom ash as sintering promoter in industrial ceramics.

The use of glassy frits obtained from municipal incinerator bottom ash and glass cullet, as sintering promoters in the production process of porcelainized stoneware, was investigated. The emphasis was on studying the similarities and differences with respect to the standard body. The characterization involved the application of several techniques: chemical analysis, X-ray powder diffraction, linear shrinkage during firing, water absorption, bending strength and spot resistance test. The results show that, the addition of these glassy frits in the body improve the characteristics of water absorption and spot resistance which is related to the absence of surface porosity originated by the glassy phase. Moreover, addition of glassy frits to the porcelanized stoneware body does not change significantly its bending strength. In the firing conditions used there is a slight worsening in the tiles planarity, while there is a significant modification of the color, which becomes darker with respect to the base body.

Ceramics↗
PubMed2003

Mineralogy of shells from two freshwater snails Belgrandiella fontinalis and B kuesteri.

X-ray powder diffraction (XRD) was used to study the mineral composition of shells of snails Belgrandiella fontinalis and Belgrandiella kuesteri collected from three freshwater springs in northeastern Slovenia. The fractions of aragonite, calcite, dolomite and quartz in particular shells were determined. The analysed shells consisted of two or more distinct inorganic layers. The outer shell layer for both species and all sampling localities contained aragonite. The outer layer of B. fontinalis collected at one locality, also contained a small fraction of calcite ( approximately 1 molar%) besides the dominant aragonite. Calcite was identified in the inner layer(s) of both species (2 to 3 molar%), while quartz was found only in B. kuesteri (5-7 molar%). However, both species sampled at one locality showed the presence of dolomite (approx. 20 molar%) in the inner layer(s). The presence of dolomite in the shells of adult gastropods and even molluscs is unusual. A possible formation mechanism and specific ecological factor that could influence the precipitation of dolomite in the shells of different Belgrandiella species is discussed.

Animals↗
PubMed2001

A novel method for the preparation of III-V semiconductors: sonochemical synthesis of InP nanocrystals.

A novel method for the preparation of III-V semiconductor has been provided in this paper. At room temperature, InP nanocrystals with diameter of approximately 9 nm were successfully obtained under high-intensity ultrasonic irradiation for 4 h from the reaction of InCl(3).4H2O, yellow phosphorus and KBH4 in the mixed solvents of ethanol and benzene. Changing some parameters can effectively control the size of the products and possible explanations were offered. The products were characterized by X-ray powder diffraction, transmission electron microscope and electron diffraction pattern. The ultrasonic irradiation and the solvents are both important in the formation of the product.

Journal Article↗
PubMed2002

Spectroscopic studies on polymeric cobalt(II) and nickel(II) complexes with bridging succinonitrile and succinonitrile isotopomer ligands.

A series of cobalt(II) and nickel(II) complexes were synthesized using succinonitrile and its [1,4-13C2], [15N2]-, [2,2,3,3-2H4]- and [1,4-13C,-2,2,3,3-2H4]- isotopomers as bridging ligands. Spectroscopic studies, as well as X-ray powder diffraction profiles, were used to identify the nature of the octahedral coordination sphere of the central metal ions and to assign the vibrational spectra in full detail. The succinonitrile ligands were found to be in trans configuration in all the complexes studied and to be coordinated via the lone pairs of their nitrile nitrogens. The rule of mutual exclusion was found to be fulfilled for the succinonitrile ligands under the Ci symmetry of the complexes and the vibrations of the succinonitrile ligands were found to appear in either the infrared or the Raman spectra. All succinonitrile isotopomers exhibited blue-shifts of 43-71 cm(-1) upon coordination, while most of the other vibrations remained unchanged or underwent small shifts of only a few wavenumbers. The mass differences of the succinonitrile isotopomers were found to shift mainly the vibrations of the respective affected part of the molecules in comparison with the normal succinonitrile. The exchange of the halides, which are coordinated to the central metal ion, was also found to influence the vibrations of the associated water molecules and we could identify vibrational bands arising due to the H-bond interaction between the halides and the water molecules. Finally, we showed that all complexes under consideration have, spectroscopically, the same symmetry.

Bromine↗
PubMed2003

The infrared and Raman spectra of ethylammonium hexafluorosilicate [C2H5NH3]2SiF6.

The X-rays powder diffraction pattern of [C2H5NH3]2SiF6 was obtained and indexed on the basis of a hexagonal unit cell. The vibrational spectra (IR and Raman) of this compound were recorded and discussed in relation to the above-mentioned crystal structure. The vibrational spectra of the cations indicate that they are disordered and hydrogen bonded to the anions. On the opposite, the Raman spectrum of the anions could be interpreted in terms of ordered groups. The combination bands observed in the 2300-1800 cm(-1) spectral region in the IR spectrum indicate that this compound may contain C-NH3 groups.

Anions↗
PubMed2003

Structure and vibrational study of the trimethylammonium hexafluorosilicate [(CH3)3NH]2SiF6 compound.

The X-ray powder diffraction pattern of [(CH(3))(3)NH](2)SiF(6) was obtained and indexed on the basis of a centred cubic unit cell with the P4(1)32 as the likely space group. The Infrared and Raman spectra of this compound have been recorded at room temperature and discussed in relation to the crystal structure. In this salt, the bands corresponding to the cation vibrational modes show that the symmetry of these cations is distorted from the free C(3v) one and that they are strongly hydrogen-bonded to the respective anions. However, the spectra of the anions can be interpreted in term of ordered groups as indicated by the splitting of the bands corresponding to some degenerate vibrational modes. The harmonic frequencies, corresponding to the (CH(3))(3)NH-SiF(6)-NH(CH(3))(3) optimised geometry, were calculated using the SCF semi-empirical MNDO-PM3 method.

Anions↗
PubMed2003

Fourier transform infrared spectra and molecular structure of 5-methoxytryptamine, N-acetyl-5-methoxytryptamine and N-phenylsulfonamide-5-methoxytryptamine.

5-Methoxytryptamine (5-MT) is a potent antioxidant and has radioprotective action. N-acetyl-5-methoxytryptamine (melatonin, NA-5-MT) is a free radical scavenger and antioxidant, which protects against oxidative damage due to a variety of toxicants. The infrared spectra of 5-MT, NA-5-MT and new synthesized N-phenylsulfonamide-5-methoxytryptamine (PS-5-MT) were investigated in the region between 4000 and 400 cm(-1). Vibrational assignments of the molecules have been made for fundamental modes on the basis of the group vibrational concept, infrared intensity and comparison with the assignments for related molecules. X-ray powder diffraction patterns of molecules were also recorded. In order to optimize the geometries of the molecules, molecular mechanic calculations (MM3) were performed. Conformational analysis of 5-MT, NA-5-MT and PS-5-MT was also established by the using PM3 method.

5-Methoxytryptamine↗