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PubMed2003

Polymorphism of ceramide 3. Part 1: an investigation focused on the head group of N-octadecanoylphytosphingosine.

The thermotropic phase behaviour of the ceramide N-octadecanoylphytosphingosine (CER3) was investigated using differential scanning calorimetry, X-ray powder diffraction and FT-IR spectroscopy. CER3 was shown to be a polymorphic substance depending on the crystallisation conditions. Three different solid states were found. The FT-IR results elucidate changes in the hydrogen bonding interactions of the ceramide head group. It was shown that the amide I and the amide II vibration bands are quite sensitive to the phase transitions of CER. There are clear shifts in the band positions of those bands passing the phase transitions. Furthermore, changes were observed in the NH- and OH- stretching region. The study shows that there are strong inter- and intramolecular hydrogen bonds between hydroxy groups in the ceramide head group. There are also strong hydrogen bonds to the amide oxygen as shown by the band positions of the amide vibrations. The H-bonding network and conformation of the head group of CER3 alters due to the phase transitions.

Amides↗

PubMed1999

Inclusion of ketoprofen with skimmed milk by freeze-drying.

Ketoprofen is a non-steroidal anti-inflammatory drug which is not soluble in water and creates gastrointestinal problems. In order to improve the solubility of the drug in water and enhance its dissolution rate, physical mixture (PM) and inclusion (IC) of ketoprofen with skimmed milk (SM) were prepared and investigated. Enhancement of solubility of ketoprofen was obtained by preparing its IC with SM which can be used because of its amino acid and surface active agents content and can also be used for treatment of gastric disturbance. Lyophilization technique was used to prepare the IC. Results obtained showed that the solubility of IC of ketoprofen with SM was almost four times greater than the solubility of the plain drug. Data from the dissolution rate determination have also indicated that IC of ketoprofen with SM significantly improved the dissolution rate of the drug compared with PM and the plain form. Differential scanning calorimetry (DSC), X-ray powder diffraction and scanning electron microscopic (SEM) analysis revealed the formation of IC of ketoprofen with SM.

Animals↗

PubMed2003

Water-vapor adsorption and surface area measurement of poorly crystalline boehmite.

Water-vapor adsorption on poorly crystalline boehmite (PCB) was studied using a gravimetric FTIR apparatus that measured FTIR spectra and water adsorption isotherms simultaneously. The intensity of the delta(HOH) band of adsorbed water changed linearly with water content and this linear relationship was used to determine the dry mass of the sample. Adsorption and desorption isotherms of PCB showed a Type IV isotherm. The BET(H2O) surface area of PCB was 514+/-36 m2/g. The mean crystallite dimensions of PCB were estimated to be 4.5 x 2.2 x 10.0 nm (dimensions along the a, b, and c axes, respectively) based on application of the Scherrer equation to powder diffraction data of PCB. A surface area value of 504+/-45 m2/g calculated using the mean crystallite dimensions was in good agreement with the BET(H2O) surface area. This work also demonstrated a method to determine surface areas for materials with minimal perturbation of their surface structure. In addition, the FTIR spectra of PCB were influenced by changes in water content. The delta(AlOH) band at 835 cm(-1) observed under dry conditions was assigned to the non-H-bonded surface OH groups. As the amount of adsorbed water increased, the intensity at 835 cm(-1) decreased and that at 890 and 965 cm(-1) increased. The 890- and 965-cm(-1) bands are assigned to surface OH groups H-bonded with adsorbed water.

Journal Article↗

PubMed2003

Crystallization behaviors of nanosized MgO particles from magnesium alkoxides.

The effects of the size of the alkoxy group on the thermal decomposition behavior of magnesium alkoxides (magnesium methoxide and ethoxide) and the crystallization behavior of MgO was investigated using thermogravimetry, Fourier-transformed infrared spectroscopy, X-ray powder diffraction, and transmission electron microscopy. As the size of the alkyl group increased, the decomposition temperature decreased and resultant MgO crystallization of the alkoxide precursor was enhanced. In an inert N(2) atmosphere, the decomposition temperature of magnesium ethoxide was about 260 degrees C, which was lower than that of magnesium methoxide by approximately 70 degrees C. The degree of the crystallization of MgO particles from the ethoxide was also significantly higher than that of the methoxide. This result is explained in terms of the O-R bonding strength of the alkoxide. With use of the Kissinger method, the activation energy for the thermal decomposition of magnesium alkoxide was found to be dependent on the size of the alkyl group. The activation energies were 161+/-23 and 130+/-24 kJ/mol for the magnesium methoxide and the magnesium ethoxide, respectively.

Journal Article↗

PubMed1989

Morphology of mineral deposits on encrusted urinary catheters investigated by scanning electron microscopy.

Struvite and hydroxyapatite were precipitated from artificial urine onto the surfaces of catheter materials by the controlled addition of urease. They were precipitated both together and separately (by omitting components of the artificial urine), and with and without the inclusion of albumin (which was intended to mimic the proteinaceous debris found in infected urine). Precipitates were identified by X-ray powder diffraction and the artificially encrusted surfaces examined by scanning electron microscopy. In the presence of protein, hydroxyapatite was precipitated as a poorly crystalline form which aggregated to form a crust. Struvite crystals could be easily identified under the scanning electron microscope by their relatively large size and characteristic appearance. Fifteen encrusted catheters from patients were also examined by scanning electron microscopy, and a further six using X-ray microanalysis. Their appearance was very similar to that of the materials encrusted in vitro. Encrustation involves the formation of hydroxyapatite and the growth of struvite crystals, intimately associated with bacteria.

Durapatite↗

PubMed1989

Urinary tract stone disease in the United States veteran population. II. Geographical analysis of variations in composition.

The geographical distribution of crystalline components observed in urinary tract stones in the continental United States has been studied in the United States veteran population. Since the veteran population is at risk for urolithiasis the National Veterans Administration Crystal Identification Center was established in 1983 for the characterization of all crystal-containing veteran patient samples using high resolution x-ray powder diffraction. The geographical distribution of whewellite, weddelite, apatite, brushite, struvite, uric acid and uric acid dihydrate is presented. The percentage occurrence of the crystalline components, percentage occurrence of admixed stones and geographical distribution of the number of components in admixed stones also are presented. The data highlight that although the southeastern United States has the highest patient discharge rate for stones, this high discharge rate appears to be correlated specifically with a high discharge rate for calcium oxalate stones and not with a high discharge rate for any of the other common stone components.

Female↗

PubMed1983

Study of passed stones by means of X-rays, infrared and thermal analyses.

X-ray powder diffraction, infrared spectroscopy and thermal analysis were used to study 108 stones that had been passed spontaneously from the upper urinary tract. The presence of apatite in pure calcium oxalate stones classified by x-ray diffraction was confirmed by infrared analysis of the ignited product. Consequently, 102 of 108 stones were found to be composed of weddellite and/or whewellite, and apatite. Besides the contents of weddellite, whewellite and apatite, the content of organic matrix also was estimated by thermal analysis in 102 stones, ranging from 1.1 to 17.2 per cent. The stones then were divided into 3 groups according to the principal constituent: 1) weddellite, 2) whewellite and 3) apatite. Weddellite stones were significantly heavier and significantly higher in apatite content than whewellite stones. It is suggested that weddellite calculi tend to become larger than whewellite stones. The apatite content was correlated with the ratio of weddellite to weddellite plus whewellite ( r equals 0.528), and the content of organic matrix was correlated with the whewellite content (r equals 0.708). Thus, it is considered that the weddellite-apatite and whewellite-organic matrix associations have important roles in the development and growth of weddellite and whewellite calculi, respectively.

Apatites↗

PubMed2002

Chemical precipitation of heavy metals from acid mine drainage.

The 1,3-benzenediamidoethanethiol dianion (BDET, known commercially as MetX) has been developed to selectively and irreversibly bind soft heavy metals from aqueous solution. In the present study BDET was found to remove > 90% of several toxic or problematic metals from AMD samples taken from an abandoned mine in Pikeville, Kentucky. The concentrations of metals such as iron, may be reduced at pH 4.5 from 194 ppm to below 0.009 ppm. The formation of stoichiomietric BDET-metal precipitates in this process was confirmed using X-ray powder diffraction (XRD), proton nuclear magnetic resonance (1H NMR), and infrared spectroscopy (IR).

Chemical Precipitation↗

PubMed1999

The highly ordered double-stranded RNA genome of bluetongue virus revealed by crystallography.

The concentration of double-stranded RNA within the bluetongue virus core renders the genome segments liquid crystalline. Powder diffraction rings confirm this local ordering with a 30 A separation between strands. Determination of the structure of the bluetongue virus core serotype 10 and comparison with that of serotype 1 reveals most of the genomic double-stranded RNA, packaged as well-ordered layers surrounding putative transcription complexes at the apices of the particle. The outer layer of RNA is sufficiently well ordered by interaction with the capsid that a model can be built and extended to the less-ordered inner layers, providing a structural framework for understanding the mechanism of this complex transcriptional machine. We show that the genome segments maintain local order during transcription.

Animals↗

PubMed2000

Relationship of crystal structure to interionic interactions in the lithium-manganese spinel oxides

Lithium manganese oxides in the form of cubic spinel phases (space group Fd3m) are formed in a LixMn3-xO4 system for rather limited values of x. Structural investigations by X-ray powder diffraction, applied to the Li-Mn-O compounds, indicate the formation of a second crystalline phase, Li2MnO3 (space group C2/m), with the increasing lithium content. Total Li+ content per unit cell and the cation distribution over a spinel lattice in LixMn3-xO4 have been studied by measurements of integrated intensities of X-ray reflections, and by structure refinement using Rietveld profile analysis. In an attempt to understand the factors affecting cation distribution in the spinel lattice, we applied the computer modelling techniques and investigated the Li+, Mn3+ and Mn4+ ion distribution by calculating the lattice energy, combined with energy minimisation procedures, using the General Utility Lattice Program (GULP), a program designed for simulation of ionic and semi-ionic solids, based on interatomic potential models.

Journal Article↗

PubMed1993

Effects of calcium phosphate solutions on dentin permeability.

Calcium phosphate solutions at various concentrations and pH levels were used to obstruct the dentinal tubules. The effects were evaluated by measurements of permeability through dentin discs and by scanning electron microscopy. Precipitation kinetics were followed by pH changes in the solutions and products were determined by X-ray powder diffraction. The solutions were applied in two ways: (a) calcium and phosphate solutions were mixed before application and (b) one solution (calcium or phosphate) was applied first followed by the other solution. Three kinds of human dentin discs were used; one with smear layer and the other two with tubules exposed by sonication or etched by acid. The high concentration calcium phosphate solutions at pH = 9.5 rapidly precipitated amorphous calcium phosphates that obstructed the dentinal tubules and decreased dentin permeability by 85% or more. At pH = 5.6, the calcium phosphate solutions precipitated large crystals of dicalcium phosphate dihydrate. In this case, the effectiveness in obstructing dentinal tubules was found to be procedure sensitive.

Acid Etching, Dental↗

PubMed2000

Water-enhanced crystallization of leucite in dental porcelain.

OBJECTIVE: The purpose of this study was to determine whether long-term exposure of dental porcelain to saliva during temporary cementation of a porcelain-fused-to-metal (PFM) restoration could enhance leucite crystallization if the restoration is refired. Such water-enhanced leucite crystallization in dental porcelains could lead to porcelain-metal thermal incompatibility problems. METHODS: Six commercial dental body porcelains and the Component No. 1 (leucite-containing) frit of the Weinstein et al. [13] patent were studied. For each porcelain, 30 coupon specimens were randomly assigned to a treatment group. Ten specimens were placed in artificial saliva, 10 in distilled water, and 10 in a desiccator and were stored for six months. At the end of the six months, an additional 10 coupons of each porcelain were prepared to serve as a control. All 40 specimens of each porcelain were randomized and subjected to one additional firing. Leucite weight fraction was determined by quantitative X-ray powder diffraction analysis via an internal standard technique. RESULTS: Comparisons among the treatments via the least-squares-means test-adjusting for porcelain showed that the saliva group mean leucite weight fraction was significantly higher than that of the other groups. The change in porcelain thermal expansion that would be associated with a leucite change in this range would be between 0.2 x 10(-6) K-1 and 0.3 x 10(-6) K-1. SIGNIFICANCE: The results of this work constitute the first demonstration that moisture absorbed by a porcelain can act as a glass modifier and enhance the crystallization of the glass during subsequent firing. The effect was sufficiently large to generate thermal expansion changes that would exceed the maximum safe mismatch between porcelain and metal.

Absorption↗

PubMed1996

Potential interference of leucite crystallization during porcelain thermal expansion measurement.

OBJECTIVES: The elevated temperatures and slow heating and cooling rates associated with a thermal expansion run provide a thermal treatment comparable to those previously shown to produce leucite crystallization in dental PFM porcelains. The purpose of this study was to determine whether the exposure of dental porcelains to the time-temperature profile of a thermal expansion run could result in leucite crystallization, a potential interference with the accurate determination of the thermal expansion coefficient. METHODS: A total of 112 thermal expansion specimens were prepared, 16 each of six commercially available body porcelains, as well as the "Component No. 1" (leucite-containing) frit of the Weinstein et al. (1962) patent. In a randomized design, the leucite contents of specimens subjected to a 3 degrees C/min thermal expansion run were compared to those of untreated controls. The leucite content of each specimen was determined via quantitative X-ray powder diffraction using an Al2O3 internal standard. One-tailed t-tests were applied to determine whether the dilatometer thermal treatment produced a statistically significant increase in leucite content. RESULTS: The heat treatment afforded by a 3 degrees C/min dilatometer run was not sufficient to induce measurable leucite crystallization in any of the porcelains examined in this study. SIGNIFICANCE: The crystallization of leucite during a dilatometer heating run can be ruled out as a possible interference with the determination of the coefficient of thermal expansion of dental porcelain.

Aluminum Silicates↗

PubMed1992

Plasticization of poly(hydroxybutyrate) in vivo.

The influence of a variety of treatments on the mobility and crystallinity of poly(hydroxybutyrate) (PHB) in whole cells and native granules has been proved using 13C-n.m.r. spectroscopy and X-ray powder diffraction, and correlated with the known biological effects of these treatments. It was concluded that at least water is responsible for PHB plasticization in vivo, and that only native mobile PHB is susceptible to depolymerases. Another, probably hydrophobic, component appears to be involved either as plasticizer or nucleation inhibitor. Three states of the granule are identified in addition to the native, biologically-competent state: freeze-drying of whole cells leads to a partially-immobilized amorphous state which can be restored virtually to native mobility by rehydration; extended centrifugation of native granules in aqueous suspension, or treatment with hydrophobic detergents under certain conditions, leads to a crystalline state that is less susceptible to exogenous depolymerase; and heating to 95 degrees C or refrigeration has no detectable effect on mobility but leads to inactivation of the granule, presumably via damage to superficial membrane or protein.

Alcaligenes↗

PubMed2000

Synthesis of carbonated calcium phosphate ceramics using microwave irradiation.

Carbonated hydroxyapatites (CHA) were synthesized by the substitution of calcium carbonate for calcium hydroxide during the reaction with diammonium phosphate under microwave irradiation. The X-ray powder diffraction analysis indicates the decrease of alpha-axis up to 20 mol% of carbonate substitution confirming the formation of the B-type CHA. Further increase of carbonate content shows the presence of tricalcium phosphate (TCP) in addition to CHA. Reaction of substituted magnesium carbonate instead of calcium carbonate in the above process results in the formation of biphasic calcium phosphate (BCP) ceramics consisting of both CHA and TCP phases. Fourier transform infrared spectroscopic study also confirmed the carbonate substitution in HA and BCP formation. The in vitro solubility study in phosphate buffer of pH 7.2 at 37 degrees C showed the resorbable nature of the BCP samples. The present study thus indicates the feasibility of in situ formation of BCP ceramics using microwave irradiation.

Biocompatible Materials↗

PubMed2000

Synthesis of biomimetic Ca-hydroxyapatite powders at 37 degrees C in synthetic body fluids.

An important inorganic phase for synthetic bone applications, calcium hydroxyapatite (HA, Ca10(PO4)6(OH)2), was prepared as a nano-sized (approximately 50 nm), homogeneous and high-purity ceramic powder from calcium nitrate tetrahydrate and diammonium hydrogen phosphate salts dissolved in modified synthetic body fluid (SBF) solutions at 37 degrees C and pH of 7.4 using a novel chemical precipitation technique. The synthesized precursors were found to easily reach a phase purity >99% after 6 h of calcination in air atmosphere at 90 degrees C, following oven drying at 80 degrees C. There was observed, surprisingly, no decomposition of HA into the undesired beta-TCP phase even after heating at 1,600 degrees C in air for 6 h. This observation showed the superior high-temperature stability of such 'biomimetic' HA powders as compared to those reported in previous studies. The former powders were also found to contain trace amounts of Na and Mg ions, originating from the use of SBF solutions instead of pure water during their synthesis. Characterization and chemical analysis of the synthesized powders were performed by X-ray powder diffraction, energy-dispersive X-ray spectroscopy, Fourier-transform infra-red spectroscopy, scanning electron microscopy, and inductively coupled plasma atomic emission spectroscopy.

Body Fluids↗

PubMed2000

Characterization of co-polymers of lactic and glycolic acid for supercritical fluid processing.

Polymers of lactic and glycolic acid are often used for the production of injectible microparticles with controlled drug release. In the variety of processes used for the microparticle formulation, the Aerosol Solvent Extraction System (ASES) is rather special. Microparticle formation and drying take place in one step by precipitating a methylene chloride solution of the polymer in supercritical CO2. This process sets special requirements to the polymers in crystallinity, solubility, and thermal behavior that are best fulfilled by blocked copolymers. This study investigates a number of lactide-co-glycolide polymers with blocked distribution of the co-monomers by NMR spectroscopy and powder diffraction. The molar ratios are determined by 1H-NMR spectroscopy to verify the manufacturer's declarations of the purchased specimens. Additionally, the block length is determined by application of 13C-NMR. Therefore, a method reported in the literature was modified and evaluated in order to calculate the length of lactide and glycolide sequences in the polymer. Furthermore, this study looks at the impact of synthesis conditions on block length and crystallinity, and the impact of the blocking on both, crystallinity and solubility of the polymers.

Biocompatible Materials↗

PubMed2000

Effect of TiO2-Ag2O additives on the formation of calcium phosphate based functionally graded bioceramics.

The combined effect of titanium dioxide and silver oxide on the in situ formation of biphasic calcium phosphate ceramics was investigated. Titania (5-20 mol%) was mixed with pure hydroxyapatite (HA) or HA containing Ag2O (10-20 mol%) and was heated to 900 degrees C for 12 h. The sintered samples were found to contain tricalcium phosphate (beta-TCP) and other phases along with HA depending upon the amount as well as the type of the additives used as evidenced by X-ray powder diffraction (XRD) and fourier transform infrared (FT-IR) spectroscopic studies. Enhanced TCP formation with reduced impurity phases was observed with TiO2-Ag2O addition. In vitro solubility study in phosphate buffer at physiological conditions shows the resorbable nature of these materials. A functionally graded material (FGM) structure was formed by spreading TiO2-Ag2O mixture on the surface of the HA green compact and heating at 900 degrees C. The FGM shows gradient structure of TCP and HA from the surface to the interior of the pellet in addition to titania and silver phases.

Biocompatible Materials↗