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PubMed2007

Quantitative and molecular analysis of buspirone hydrochloride polymorphs.

Quantitative and molecular analysis have been performed on two main polymorphs of buspirone hydrochloride (BUS-HCl). Quantitative analysis of solid-state composition of pharmaceutical powders is necessary to ensure safety and efficacy of drug substance and to validate the production processes. In this study, X-ray powder diffraction and differential scanning calorimetry have been used for the quantitative analysis of two polymorphic forms of BUS-HCl. In addition, single crystal X-ray study of Form 1 revealed its crystal structure, however, a similar study on Form 2 was not possible due to the difficulties encountered in producing it. Molecular analysis including partial charge analysis has been performed by using Gaussian simulation package to find the electro-negativity pattern in molecule. 1H and 13C solid-state NMR spectra of polymorphs were recorded and also regression equations and QM theory were developed to predict the 1H and 13C NMR spectra through the use of atomic environmental descriptors. The NMR differences between the two polymorphs were discussed by using prediction and experimental results and description of each NMR shift for carbon and hydrogen atoms.

Buspirone↗
PubMed1978

Ambiguities in IR and X-ray characterization of amphotericin B.

Two distinct IR spectra of amphotericin B have been reported. These differences can be obtained from the same sample by surprisingly small changes in the method of sample preparation. Type I spectra (hand-ground samples) are characterized by a sharp C = O stretching band at 1692 cm-1, and Type II spectra (vibrator-ground samples) are characterized by a broad C = O stretching band near 1710 cm-1. X-ray powder diffraction demonstrates that vibrator grinding promotes a transition from a crystalline to an amorphous phase. The two phases are not bioequivalent. Differential thermal analysis reveals a transition near 157 degrees and samples heated to 158 degrees give only Type II IR spectra. However, a marked color change accompanies such heating (i.e., structural changes affecting the chromophore have been thermally induced), while X-ray spectra show an increase of only about 30% in amorphous content. Furthermore, hand-ground samples heated to 120 degrees still display only Type I IR spectra. Thus, the vibrator-induced transition is not solely a static thermal effect. Many observed spectral lines can be assigned to specific functional groups.

Amphotericin B↗
PubMed1984

Mechanism of freeze-thaw instability of aluminum hydroxycarbonate and magnesium hydroxide gels.

The effect of freeze-thaw cycles on the physical stability of aluminum hydroxycarbonate and magnesium hydroxide gels was studied. Coagulation following a freeze-thaw cycle, leading to the formation of visible aggregates, affected the content uniformity of both gels. The freeze-thaw cycles did not affect the crystal form or surface characteristics of the gels as determined by X-ray powder diffraction and point of zero charge, but caused a slight reduction in the rate of acid neutralization and a large increase in the rate of sedimentation. The greatest effect was observed after the first freeze-thaw cycle. While the duration of freezing was not a factor, the rate of freezing was important and was inversely related to the aggregate size. The aggregates which formed following a freeze-thaw cycle were not redispersed by shaking, but were reversed by ultrasonic treatment or homogenization. The adsorption of polymers or surface-active agents prior to freezing reduced and, in some cases, prevented the formation of aggregates. The physical instability produced by a freeze-thaw cycle was explained by the modified DLVO theory. The force exerted on the particles by the growing ice crystals forced the particles into the primary minimum, producing strong interparticle attraction. On thawing, simple agitation did not provide enough force to overcome the attractive force of the primary minimum. Adsorption of polymers or surface-active agents increased the steric repulsive force and prevented the particles from reaching the primary minimum.

Aluminum Hydroxide↗
PubMed1984

Polymorphism of butyrophenones related to haloperidol.

A comparison of X-ray powder diffraction patterns, IR spectra, and crystal structures of structurally related compounds belonging to the butyrophenone family has been undertaken to obtain information about the elements of chemical structure which predispose a substance to exhibit polymorphism. Five butyrophenones, differing by the nature of only one substituent, were selected. After crystallization from 15 solvents, it appears that two compounds of the group exhibit more than one crystalline form. An explanation of the absence of polymorphism in the other compounds of the group is proposed and discussed.

Butyrophenones↗
PubMed1988

Physical characterization of the hydrates of urapidil.

Three hydrates of urapidil were prepared and characterized by means of differential scanning calorimetry, thermogravimetric analysis, infrared spectroscopy, X-ray powder diffraction, intrinsic dissolution rates, and solution calorimetry. The stoichiometry of the urapidil hydrates was found to be 1:5, 1:3, and 1:1 (urapidil:water). The crystal and molecular structures of urapidil pentahydrate were determined from three-dimensional X-ray data. The stability of the pentahydrate and monohydrate under different storage conditions was also determined.

Chemical Phenomena↗
PubMed1989

Physical characterization of the methanol solvate of urapidil.

The methanol solvate of urapidil was prepared and characterized by means of differential scanning calorimetry, thermogravimetric analysis, infrared spectroscopy, X-ray powder diffraction, intrinsic dissolution rate, and solution calorimetry. The stoichiometry of the urapidil:methanol solvate was found to be 1:1. The crystal and molecular structures were determined from three-dimensional X-ray data. The stability of the solvate under different storage conditions was also determined.

Calorimetry, Differential Scanning↗
PubMed1989

Polymorphism of estramustine.

As the solubility in water of the cytotoxic drug estramustine is less than 1 mg/L, polymorphism can have an impact on the bioavailability of orally administered drug. Therefore, the solid state characteristics of estramustine samples, crystallized from different solvents, were investigated by means of X-ray crystallography, thermal analysis, and IR spectroscopy. The DSC data indicated the existence of several phases. Four forms--A, B, C, and D--were confirmed. Phase A was obtained when crystallizing from solvents with a moderate or low dieletric constant (less than approximately 24). This form was an anhydrate and found to be the stable one. When crystallizing from methanol, metastable solvates, with approximately 0.5 mol for phase B or approximately 1 mol for form C, were precipitated. Both types were transformed to phase A during storage. This desolvation was accelerated by heating. Crystallizing from a mixture of acetone and water resulted in a monohydrate, form D, which was converted to the anhydrous type A upon heating. As forms B, C, and D were solvates which transformed to another crystal form upon desolvation, they were polymorphic solvates of the anhydrate, type A. Symmetry and unit cell dimensions of the stable form of estramustine (phase A) were determined by means of a single-crystal X-ray technique (orthorhombic, a = 23.90, b = 20.69, c = 8.76, space group P212121). In addition, the crystallographic parameters of form D were deduced from calculations based on powder diffraction data.

Chemical Phenomena↗
PubMed1993

Degradation and release properties of pellets fabricated from three commercial poly(D,L-lactide-co-glycolide) biodegradable polymers.

Poly(D,L-lactide-co-glycolide, 50:50) samples of similar molecular weight were obtained from three commercial sources and were characterized by gel permeation chromatography, differential scanning calorimetry, X-ray powder diffraction, viscometry, and proton nuclear magnetic resonance spectroscopy. Pellets were prepared by melt-pressing spray-dried polymer with a 4-mm standard concave punch and die set and a thermostated holder of original design. Amaranth (5% w/w) was incorporated in pellets used for release studies. Degradation and release studies were conducted at 37 degrees C in pH 7.2 phosphate buffered saline. The molecular weights of all polymers were found to decrease continuously after exposure to phosphate buffered saline. All polymers showed two distinct regions of molecular weight decrease. Mass loss experiments for all polymers resulted in sigmoidal curves typical of polymers undergoing bulk hydrolysis. The onset of mass loss (defined as 10% mass loss) was found to differ by as much as 6 days among the three polymers studied. The release studies showed an initial burst of release followed by a period of 15-25 days during which little or no dye was released. A second phase of release followed, lasting approximately 10 days, until all dye was released. The time at which release began slightly preceded the onset of mass loss.

Buffers↗
PubMed1994

X-ray structural studies and physicochemical characterization of the 1-butanol, 1-pentanol, and 1,4-dioxane solvates of succinylsulfathiazole.

The crystal structures and thermal decomposition of three solvated forms of the antibacterial drug succinylsulfathiazole (SST) have been studied. The solvates, with 1:1 host-guest stoichiometry, are SST x 1-butanol (1) SST x 1-pentanol (2), and SST x 1,4-dioxane (3). Solvates 1 and 2 crystallize in the triclinic system, space group P1, with two formula units per cell, and are nearly isostructural. The OH groups of the guest molecules in both solvates engage in hydrogen bonding to the host SST and occupy cavities in the crystals. Solvate 3 is triclinic, space group P1, with two formula units per cell, but the two independent solvent molecules are located in crystallographically distinct channels. In one channel, solvent molecules are hydrogen bonded to the host while, in the other, they are held by van der Waals interactions only. The structural results are in accord with thermogravimetric and differential scanning calorimetric data which indicate one-step desolvation for 1 and 2 but two-step desolvation for 3. X-ray powder diffraction was used to attempt identification of the polymorphic forms of SST resulting from desolvation of 1-3. Desolvation of 1 and 3 appears to yield pure polymorphs of SST while 2 yields a mixture of polymorphs. The activation energies for the desolvation of the nearly isomorphous solvates 1 and 2 were found by dynamic thermogravimetry to be 155 and 149 kJ mol(-1), respectively.

1-Butanol↗
PubMed1995

Physicochemical characterization of a new respirable form of nedocromil.

Elongated, respirable particles of nedocromil were prepared by its crystallization from N-methyl-2-pyrrolidone (NMP) obtained from an aqueous solution of its sodium salt by precipitation with hydrochloric acid. Aerosols of these particles were recently generated and characterized for their aerodynamic properties (Chan, H.-K.; Gonda, I. J. Aerosol Med. 1993, 6, 241-249). This paper reports the physiochemical properties of the solid form of nedocromil as characterized by polarizing optical and scanning electron microscopies, thermal analysis (DSC, TGA), X-ray powder diffraction, water vapor adsorption isotherms, mass spectrometry, solid state Fourier transform IR and solution 1H-NMR spectroscopies.

Administration, Inhalation↗
PubMed1995

Structure and thermal stability of alprazolam and selected solvates.

Five forms of the drug alprazolam have been identified by thermal analysis and X-ray powder diffraction (XRD). The single crystal X-ray structures of two of these species, a polymorph 1 and a dihydrate 2, were determined. The dihydrate crystallized from a solution of alprazolam in methanol containing traces of water. Species 3 and 4 are nonstoichiometric solvates with ethanol and acetonitrile, respectively. The differential scanning calorimetric curves for the solvates 2-4 are similar, showing a desolvation endotherm, followed by an exotherm associated with recrystallization, and a final endotherm for the fusion of alprazolam. The solvates 3 and 4 were shown to be isomorphous by XRD. The products of desolvation of 2-4 were identified by their XRD traces. Solvates 2 and 3 yield polymorph 1 on desolvation, whereas solvate 4 yields a different polymorph.

Alprazolam↗
PubMed1993

Monocrystalline iron oxide nanocompounds (MION): physicochemical properties.

We have previously described a novel monocrystalline iron oxide nanocompound (MION), a stable colloid that enables target specific MR imaging. In this study, the physicochemical properties of MION are reported using a variety of analytical techniques. High resolution electron microscopy indicates that a MION consists of hexagonal shaped electron-dense cores of 4.6 +/- 1.2 nm in diameter. This iron oxide core has an inverse spinel crystal structure which was confirmed by x-ray powder diffraction. Chemical analysis showed that each core has 25 +/- 6 dextran molecules (10 kD) attached, resulting in a unimodal hydrodynamic radius of 20 nm by laser light scattering. Because of the flexibility of the dextran layer, the radius is only 8 nm in nonaqueous reverse micelles. At room temperature, MION exhibit superparamagnetic behavior with an induced magnetization of 68 emu/g Fe at 1.5 T. Mössbauer studies show that the saturation internal magnetic field is 505 KOe, and blocking temperature is at 100 K. The R1 relaxivity of MION is 16.5 (mM.sec)-1 and the R2 relaxivity is 34.8 (mM.sec)-1 in aqueous solution at 37 degrees C and 0.47 T. In vitro phantom studies show that the detectability of MION in liver tissue is less than 50 nmol Fe/g tissue using gradient echo imaging techniques.

Ferric Compounds↗
PubMed2005

Direct observation of the growth process of MgO nanoflowers by a simple chemical route.

Novel flowerlike nanostructures consisting of MgO nanofibers were successfully synthesized by a simple chemical route with H(2)O at 950 degrees C in an Ar atmosphere. Various durations of heating gave different growth stages that led to varied product morphologies. The synthesized products were systematically studied by X-ray powder diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray analysis. The results show that the nucleation and growth process of the nanoflowers seems to be a vapor-solid mechanism, and that the total heating time during the reaction process is a critical factor for the development of MgO nanoflowers. Initially, Mg particles formed on the Si substrate, followed by the formation of MgO clusters as nucleation centers on the magnesium melt surface and the nucleation of short MgO nanofibers, then growth of the MgO nanofibers occurred, and finally MgO nanoflowers were formed. Besides nanoflowers, novel hierarchical MgO nanostructures were also observed. These nanostructures may be used as three-dimensional composite materials and as supports for other materials.

Chemistry↗
PubMed1997

Preparation of Silica-Based Mesoporous Materials From Fluorosilicon Compounds: Gelation of H2SiF6 in Ammonia Surfactant Solution

The silica-based mesoporous molecular sieves were synthesized from fluorosilicon compounds and Al, Ti with the hydrolysis reaction of H2SiF6 in an ammonia-surfactant mixed solution. Well-crystalline mesoporous molecular sieves were obtained after several hours at the atmospheric conditions. The solid products were characterized by X-ray powder diffraction, nitrogen adsorption/desorption, transmission electron microscopy and solid-state NMR spectroscopy. The solid products show high specific surface areas in the range of 627-1040 m2/g, depending on the amount of Al and Ti. Also, they exhibit narrow pore size distributions in the range of 31-35 A according to the addition of Al and Ti. 29Si MAS NMR indicate that all samples mainly contain Q4 types sites. Also, the peak intensity of Q3 sites decreases with increasing amount of aluminum. In 27Al MAS NMR spectra, all samples give intense lines from 4-coordinate aluminum. These results show that aluminum species are incorporated into the framework of Si-MMS. As the amount of Al increases, the intensity line from 6-coordinate aluminum increases. This result represents the increase of the fraction of amorphous aluminum species.

Journal Article↗
PubMed1999

gamma-Radiation Synthesis of the Nanocrystalline Semiconductors PbS and CuS.

The nanocrystalline semiconductors PbS and CuS were prepared by gamma-irradiation at room temperature in an ethanol system for the first time. Carbon disulfide was used as the sulfur source; lead acetate and copper chloride were used as metal ion sources. X-ray Powder Diffraction was used to characterize the products and Transmission Electron Microscopy to determine their morphology. The purity and compositions of the products were examined by X-ray photoelectron spectra. The photoluminescence property of as-prepared PbS was studied. A blue shift was observed in the PL spectra, indicating the quantum size effect on nanocrystalline PbS. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

3D Monolayers of 1,4-Benzenedimethanethiol on Au and Ag Clusters: Distinct Difference in Adsorption Geometry with the Corresponding 2D Monolayers.

Au and Ag clusters of 3-nm mean diameter were prepared with 1,4-benzenedimethanethiol (BDMT) as the capping molecule. In both the monolayer-capped clusters, BDMT adsorbs in the dithiolate form in contrast to in the 2D monolayers, where the dithiolate form exists only in the case of Ag. As a result, the molecule lies flat on the cluster surface in both Au and Ag, whereas the molecular plane is perpendicular to the surface in the 2D monolayer of Au. This difference in adsorbate structure is attributed to the evolution in the cluster surface as adsorption occurs. Transmission electron microscopy and X-ray powder diffraction suggest that no superlattice of the clusters exists. Mass spectrometry suggests the presence of the phase transfer reagent at the surface. X-ray photoelectron spectroscopy confirms the chemical similarity of the two surfaces and suggests that the thiolate at the surface is susceptible to X-ray beam induced damage. Copyright 1999 Academic Press.

Journal Article↗
PubMed2000

Covalent Grafting of Ethylene Glycol into the Zn-Al-CO(3) Layered Double Hydroxide.

Zn-Al-CO(3) layered double hydroxide was synthesized at room temperature using a procedure reported elsewhere. After characterization, 0.5 g of the Zn-Al-CO(3) layered compound was reacted under air with 15 cm(3) of ethylene glycol at 80 degrees C for a period of 5 days. After washing with acetone and drying at 50 degrees C, the resulting white powder was characterized by X-ray powder diffraction, thermal analysis (simultaneous TG/DSC), elemental analysis (C, H, N, Al, and Zn content), and FTIR spectroscopy. All of the experimental data were consistent with the bidentade grafting of ethylene glycol into the interlayer surface of the Al-Zn double hydroxide. The stoichiometry obtained [Zn(0.66)Al(0.34)(OCH(2)CH(2)O)](OH)(0.34).0.4H(2)O] showed that all of the surface hydroxide groups were replaced by ethylene glycol through Al-(Zn)-O-C bonds. Carbonate could not be detected by FTIR, proving that OH(-) was probably the actual intercalated counteranion. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Templated Synthesis of CdS/PAN Composite Nanowires under Ambient Conditions.

CdS/PAN (polyacrylonitrile) composite nanowires were prepared by templated synthesis under ambient conditions, using a 4 : 1 (v/v) distilled water-isopropyl alcohol solvent mixture and Na(2)S(2)O(3) as sulfur source. Transmission electron microscopy images showed typical CdS/PAN nanowires with diameters less than 6 nm and lengths from 200 nm to 1 µm. CdS/PAN nanowires were also characterized by FT-infrared spectra (FTIR), X-ray powder diffraction (XRD) patterns, and UV-vis spectra. It is found that the feed mole ratio of CdCl(2) to AN exerts a significant influence on the formation and morphology of CdS/PAN nanowires. In addition, possible mechanism of the reactive process was presented. Copyright 2000 Academic Press.

Journal Article↗