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PubMed2006

Physicochemical properties of TTCP/DCPA system cement formed in physiological saline solution and its cytotoxicity.

In this paper, the physicochemical properties and cytotoxicity of calcium phosphate cement (CPC), prepared by mixing cement powders of tetracalcium phosphate (TTCP) and dicalcium phosphate (DCPA) with a cement liquid of physiological saline solution, were investigated. The microstructure evolution of various hardened cement bodies and their hydration crystals as a function of immersion time in similar physiological fluids, physiological saline solution (0.9% NaCl), or simulated body fluids (SBF), were also studied. Results show that the setting time of CPC is in the range of 12-15 min, which meets the clinical application demands. We also found that the mean compressive strength of the CPC samples immersed in SBF for 3 days is 104+/-10 MPa which reaches the transverse compressive strength, 106-133 MPa, of human long bone. The results obtained from both the X-ray powder diffraction analyses (XRD) and scanning electron microscopy (SEM) observations indicated that a reinforcing effect of some remaining TTCP particles in the early stages of immersion is mainly responsible for the increase in the initial strength. Although the CPC failed to keep this high level when immersed for a longer time, the initial reinforcing effect of the remaining TTCP particles provides advantages for clinical applications. This would be effective when the material is loaded at the very beginning of the implantation, especially for the material used as a fixation, which requires a certain initial strength in the early stages of the implantation. The cytotoxicity results showed that the relative growth rate (RGR%) of L929 cells on the CPC samples using physiological saline solution as a cement liquid was slightly superior to that of the samples using the 0.5 mol/L phosphate acid solution as the cement liquid. This was most likely caused by the pH difference between the two CPC samples immersed in a DMEM-BFS medium.

Animals↗

PubMed2007

Synthesis and characterization of biocompatible Fe3O4 nanoparticles.

In this study, magnetite (Fe3O4) nanoparticles with a size range of 8-20 nm were prepared by the modified controlled chemical coprecipitation method from the solution of ferrous/ferric mixed salt-solution in alkaline medium. In the process, two kinds of surfactant (sodium oleate and polyethylene glycol) were studied; then, sodium oleate was chosen as the apt surfactant to attain ultrafine, nearly spherical and well-dispersed (water-base) Fe3O4 nanoparticles, which had well magnetic properties. The size and size distribution of nanoparticles were determined by particle size analyzer. And the magnetite nanoparticles was characterized by X-ray powder diffraction (XRD) analysis, transmission electron microscopy (TEM), electron diffraction (ED) photography, Fourier transform infrared spectrometer (FT-IR), and vibrating-sample magnetometer (VSM). Also the effect of many parameters on the Fe3O4 nanoparticles was studied, such as reaction temperature, pH of the solution, stirring rate and concentration of sodium oleate. And the 5-dimethylthiazol-2-yl-2,5- diphenyltetrazolium bromide (MTT) assay was performed to evaluate the biocompatibility of magnetite nanoparticles. The results showed that the Fe3O4 nanoparticles coated by sodium oleate had a better biocompatibility, better magnetic properties, easier washing, lower cost, and better dispersion than the magnetite nanoparticles coated by PEG.

3T3 Cells↗

PubMed2006

On the efficient evaluation of Fourier patterns for nanoparticles and clusters.

Samples made of an isotropically oriented ensemble of atomic clusters or structures that are not large crystals (i.e. extended less than 10 periods in each direction) are at the frontier of today's material science and chemistry. Examples are nanoparticles, nanotubes, amorphous matter, polymers, and macromolecules in suspension. For such systems the computation of powder diffraction patterns (which may provide an efficient characterization) is to be performed the hard way, by summing contributions from each atom pair. This work deals with performing such computation in the most practical and efficient way. Three main points are developed: how to encode the enormous array of interatomic distances (which increase as the square or higher powers of the cluster diameter) to a much smaller array of equispaced values on a coarse grid (whose size increases linearly with the diameter); how to perform a fast computation of the diffraction pattern from this equispaced grid; how to optimize the grid step to obtain an arbitrarily small error on the computed diffraction pattern. Theory and examples are jointly developed and presented.

Journal Article↗

PubMed2002

Polymorphism of roxifiban.

Roxifiban was found to exist in two polymorphic forms. The polymorphs were detected by X-ray powder diffraction and solid-state carbon nuclear magnetic resonance. A slight difference between the two polymorphs was also detected by isothermal microcalorimetry. However, no differences were observed by differential scanning calorimetry, infrared, or Raman spectroscopy. Solubility studies as a function of temperature in a discriminating solvent system permitted characterization of the thermodynamics of the polymorphs. The enthalpy of solution at 25 degrees C was 8.1 kcal/mol and 8.9 kcal/mol for Form I and Form II, respectively, and the thermodynamic transition point was 132 degrees C. The data confirm that the polymorphs are enantiotropic. Form II is the thermodynamically stable crystal form over the practical range of drug substance storage and handling and dosage form processing and storage. However, Form I has been kinetically stable after storage for more than 36 months at 25 degrees C/60% relative humidity with no conversion to Form II occurring.

Amidines↗

PubMed2002

Solid phases of tenoxicam.

In this report we describe the preparation and characterization of four polymorphic forms of tenoxicam; they are, three 1:1 stoichiometric solvates with acetonitrile, dioxane, and N,N-dimethylformamide, and an amorphous phase obtained by recrystallization in various solvents. Polymorph IV and solvates with dioxane and N,N-dimethylformamide are reported for the first time in this paper. In addition, three solvates were crystallized in acetone, ethyl acetate, and isopropyl alcohol. These solid forms were characterized by X-ray powder diffraction, differential scanning calorimetry, infrared spectroscopy, thermogravimetry, optical microscopy, and elemental analysis. Solid-state properties, intrinsic dissolution rate, and dissolution kinetics from formulated tablets are also provided.

1-Butanol↗

PubMed2002

Solid state characterization of E2101, a novel antispastic drug.

E2101, a novel antispastic drug, was found to exist in at least two polymorphs that were confirmed by X-ray powder diffraction (XRD). These two species are designated forms I and II. The physicochemical and thermodynamic properties of these polymorphs were characterized by variable temperature XRD, thermal analysis, hygroscopicity measurements, and dissolution studies. The transition temperature was also estimated from the solubilities determined at various temperatures. The E2101 polymorphs were anhydrous and adsorbed little moisture under high humidity conditions. The melting onsets and heats of fusion for form I were 148.1 +/- 0.2 degrees C and 38.2 +/- 1.0 kJ/mol, respectively, and for form II were 139.8 +/- 0.4 degrees C and 35.2 +/- 0.5 kJ/mol, respectively. The intrinsic dissolution rate of form II in JP 2 medium was 1.5-fold faster than that of form I, corresponding to the rank order of the aqueous solubility and the enthalpy of fusion. Accordingly, form I was thought to be thermodynamically more stable than form II and thus suitable for further development. According to the thermal analysis and variable temperature XRD results, the recrystallization of form I occurred at approximately 145 degrees C after form II melted, however, no crystal transition behavior was observed below the lower melting point. The DSC thermograms at various heating rates and van't Hoff plots from the solubility studies indicated that the polymorphic pair would be monotropic.

Acetamides↗

PubMed2001

Time-resolved X-ray scattering using synchrotron radiation applied to the study of a polymorphic transition in carbamazepine.

The thermodynamic status of alpha-carbamazepine has been clarified using equilibrium solubility measurements, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), heated X-ray powder diffraction (XRPD), and temperature-controlled X-ray scattering techniques. alpha-Carbamazepine is the least stable of the three well-characterized anhydrous polymorphs of carbamazepine at 25 degrees C. In addition, it was confirmed that alpha-carbamazepine undergoes an exothermic transition to gamma-carbamazepine at 130 degrees C. The novel technique of time-resolved simultaneous small- and wide-angle X-ray scattering has been successfully applied to monitor this transition in situ. It was concluded that alpha-carbamazepine has a monotropic relationship with gamma-carbamazepine.

Anticonvulsants↗

PubMed2001

Characterization of frozen solutions of glycine.

The broad objective of this research was to better understand the physical chemistry of freeze drying of the system glycine/water, with emphasis on the role of polymorphism of glycine on freezing and freeze-drying behavior. Frozen solutions of glycine were characterized by differential scanning calorimetry (DSC) and by freeze-dry microscopy. Cooling rates ranged from 0.1 degrees C/min to quench-cooling by immersing samples in liquid nitrogen. During slow cooling, only a beta-glycine/ice eutectic mixture is formed, melting at -3.60 degrees C. For quench-frozen solutions, the low-temperature thermal behavior is more complex. A complex glass transition region is observed on the DSC thermogram, with midpoint temperatures at about -73 degrees C and -60 degrees C, as well as two separate crystallization exotherms. Use of very low heating rates in the DSC experiment allows resolution of four separate endotherms in the temperature range just below the melting of ice. The experimental data support the conclusion that these endotherms arise from melting of the beta-glycine/ice eutectic mixture at -3.6 degrees C, dissolution of crystals of alpha-glycine at -2.85 degrees C, and melting of the gamma-glycine/ice eutectic mixture at -2.70 degrees C. One of the endotherms could not be characterized because of inadequate resolution from the beta-glycine/ice eutectic melting endotherm. Freeze-dried solids were characterized by X-ray powder diffraction after annealing under conditions established by the DSC and freeze-dry microscopy experiments. Annealing at controlled temperatures in the melting region prior to recooling the system was useful not only in interpreting the complex DSC thermogram, but also in controlling the glycine polymorph resulting from freeze drying.

Freeze Drying↗

PubMed2004

Solid-state solubility influences encapsulation and release of hydrophobic drugs from PLGA/PLA nanoparticles.

Biodegradable nanoparticles formulated from poly(D,L-lactide-co-glycolide) (PLGA) and polylactide (PLA) polymers are being extensively investigated for various drug delivery applications. In this study, we hypothesize that the solid-state solubility of hydrophobic drugs in polymers could influence their encapsulation and release from nanoparticles. Dexamethasone and flutamide were used as model hydrophobic drugs. A simple, semiquantitative method based on drug-polymer phase separation was developed to determine the solid-state drug-polymer solubility. Nanoparticles using PLGA/PLA polymers were formulated using an emulsion-solvent evaporation technique, and were characterized for size, drug loading, and in vitro release. X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) were used to determine the physical state of the encapsulated drug. Results demonstrated that the solid-state drug-polymer solubility depends on the polymer composition, molecular weight, and end-functional groups (ester or carboxyl) in polymer chains. Higher solid-state drug-polymer solubility resulted in higher drug encapsulation in nanoparticles, but followed an inverse correlation with the percent cumulative drug released. The XRD and DSC analyses demonstrated that the drug encapsulated in nanoparticles was present in the form of a molecular dispersion (dissolved state) in the polymer, whereas in microparticles, the drug was present in both molecular dispersion and crystalline forms. In conclusion, the solid-state drug-polymer solubility affects the nanoparticle characteristics, and thus could be used as an important preformulation parameter.

Drug Compounding↗

PubMed2004

Structural characterization of prazosin hydrochloride and prazosin free base.

The three-dimensional solid-state structures of prazosin hydrochloride, C19H22N5O4+.Cl- (A), and prazosin free base, C19H21N5O4 (B), have been determined by synchrotron X-ray powder diffraction. A and B crystallize in triclinic P-1 and monoclinic Cc space groups, respectively, with one structural unit per asymmetric part. In A and B, the prazosin molecule adopts different conformations, which do not correspond to those obtained by DFT optimizations of protonated and free prazosin.

Hydrogen Bonding↗

PubMed2004

Structural characterization and enantioseparation of the chiral compound praziquantel.

In this study, we aimed to characterize the chiral compound type of a leading antischistosomal drug, praziquantel. The optically pure praziquantel enantiomers were recovered from the racemic mixture by enantiomeric separation, which was performed on preparative scale chromatography by using a novel beta-cyclodextrin type chiral column. The thermodynamic properties of praziquantel were determined from differential scanning calorimetry and the physical properties were studied by examining Fourier transform infrared spectroscopy and X-ray powder diffraction. Based on the differential scanning calorimetry data, a melting point binary phase diagram was constructed. A ternary solubility phase diagram of praziquantel in methanol was also determined at the temperature of 0 degrees C. All the experimental results support the conclusion that praziquantel is a racemic compound. The characterization of physical properties of praziquantel and the phase diagram are crucial for understanding the rationality for the successful resolution of praziquantel and also provide the basis for designing the strategy of separation and recovery of pure enantiomer.

Molecular Structure↗

PubMed2006

Polymorphism on leflunomide: stability and crystal structures.

Two polymorphs of Leflunomide were found and studied (form I and II). Both of them were characterized by X-ray powder diffraction and thermal analysis. Single crystals were obtained and both structures were solved. Forms I and II crystallize in the space group P2(1)/c with two and one independent molecules per asymmetric unit, respectively. Thermodynamic stability of the two forms is assessed by differential scanning calorimetry. The cohesion in the crystal of form I (the more stable) is provided by both by H bonding as well as pi...pi interactions, while in form II it is given only by the former. The independent molecules in form I adopt different conformations thus allowing for a larger number of intermolecular interactions.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2005

Pharmaceutical liquid crystals: the relevance of partially ordered systems.

Pharmaceutical solids have generally been characterized as either three-dimensional crystals or amorphous solids based on X-ray powder diffraction and modulated temperature differential scanning calorimetry. In contrast, fewer examples of thermotropic and lyotropic liquid crystals, or mesophases, appear in the pharmaceutical literature, and that literature teaches that the aforementioned analytical techniques should be complemented with polarized light microscopy and small-angle X-ray scattering in order to effectively identify potential liquid crystalline states. Lyotropic liquid crystals are induced by the presence of solvent, and have been extensively described elsewhere in the context of emulsion technology; however, other pharmaceutical examples are emerging. Thermotropic liquid crystals are induced by a change in temperature and are essentially free of solvent, where more pharmaceutical applications appear in the literature. In the present review the general structural characteristics that favor the formation of liquid crystalline mesophases are categorized by therapeutic target and molecular size, and the analytical means of their identification are presented.

Amyloid↗

PubMed2006

Investigating the hydrate conversion propensity of different etoricoxib lots.

The physical stability of bulk active pharmaceutical ingredients (API) is of significant scientific and regulatory concern. Carrying out physical stability testing on lots with varying rates of hydrate conversion can potentially lead to erroneous conclusions if these rate differences remain unknown and unstudied. The lot dependency of etoricoxib's rate of hemihydrate conversion was investigated and a quick discriminatory technique was developed to qualitatively assess relatively slow to rapidly converting lots. This novel technique was also used to screen potential parameters affecting the hydrate conversion rate such as particle size/surface area, amorphous content, and initial hemihydrate content. Based on qualitative X-ray powder diffraction (XRPD) and quantitative Raman data, significant effects on the rate of hydration were observed with the addition of small amounts of amorphous etoricoxib. Furthermore, it was found that the presence of hemihydrate also increased the rate of conversion by seeding anhydrous etoricoxib. This suggests that the initial presence of the hydrate form can cooperatively accelerate conversion. A better understanding of the factors affecting hydrate conversion rates resulted in the appropriate selection of storage conditions for both the bulk API and the formulated product.

Calorimetry, Differential Scanning↗

PubMed2006

Polymorphism and pseudopolymorphism of salicaine and salicaine hydrochloride crystal polymorphism of local anaesthetic drugs, part V.

The local anaesthetic drug salicaine hydrochloride (hydroxytetracaine hydrochloride, 4-butylamino-2-hydroxybenzoic acid 2-dimethylaminoethyl ester hydrochloride, SLCHC) and the free-base salicaine (SLC) were characterized by thermal analysis, vibrational and solid-state NMR-spectroscopy, X-ray powder diffraction, X-ray single crystal structure analysis, and water vapor sorption analysis. Additionally, the crystal structures of the anhydrate mod. II degrees (monoclinic, space group P2(1)/n), the hydrated mod. I (triclinic, space group P(bar)1), and of the free base (SLC) in the form of the hemihydrate (triclinic, space group P(bar)1 are discussed. Mod. II degrees of the polymorphic SLCHC is the thermodynamically stable form at room temperature and is present in commercial products mostly contaminated with a hydrated form that is isomorphic with mod. I. Mod. II degrees crystallizes from most organic solvents and from the melt below 110 degrees C. Mod. I crystallizes from the melt at temperatures above 110 degrees C, and additionally appears on dehydration of the hydrated mod. I. A third polymorph monotropically related to mod. II degrees was found by freeze-drying. The free-base SLC was found to crystallize from ethanol/water as a triclinic hemihydrate.

Absorption↗

PubMed2006

Structure and physical stability of hydrates and thermotropic mesophase of calcium benzoate.

The aim of this study is to investigate the hydration and the dehydration processes of calcium benzoate hydrates (trihydrate and monohydrate), thermotropic mesophases (dehydrated mesophase and lyophilized mesophase) and amorphous state, and the influence of their molecular order on those processes. X-ray analysis revealed that trihydrate has a planar structure composed of two types of planes-one from benzoic acid, water, and calcium ion and another from benzoic acid and water-and that both planes are linked by three water molecules. It was found that calcium benzoate was able to exist as thermotropic mesophases by dehydration of trihydrate and lyophilization. These mesophases were characterized by polarizing-light microscopy (PLM), X-ray powder diffraction (XRPD), differential thermal analysis (DTA), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Both mesophases prepared by two procedures showed some similar physical properties, but lyophilized mesophase seemed to have molecular structure with higher order than dehydrated mesophase. The mesophases exhibited different hydration behavior. The dehydrated mesophase showed a stepwise rehydration process where it became monohydrate first and then trihydrate. The lyophilized mesophase became trihydrate without appearance of monohydrate. An amorphous form could also be prepared and it rehydrated first to the monohydrate and then trihydrate. The results suggest that the more disordered dehydrated mesophase and amorphous state change to monohydrate whereas the more ordered lyophilized mesophase cannot change to monohydrate but only to trihydrate.

Absorption↗

PubMed2006

Understanding processing-induced phase transformations in erythromycin-PEG 6000 solid dispersions.

Since the quality and performance of a pharmaceutical solid formulation depend on solid state of the drug and excipients, a thorough investigation of potential processing-induced transformations (PITs) of the ingredients is required. In this study, the physical phenomena taking place during formulation of erythromycin (EM) dihydrate solid dispersions with polyethylene glycol (PEG) 6000 by melting were investigated. PITs were monitored in situ using variable temperature X-ray powder diffraction (VT-XRPD), differential scanning calorimetry (DSC), and hot-stage microscopy (HSM). Possible intermolecular interactions between the drug and polymer in the solid state were further studied by Fourier transform infrared (FTIR) spectroscopy. While in the absence of PEG the dehydration was the only transformation observed, hot-melt processing with the polymer caused the drug to undergo multiple phase transformations (EM dihydrate --> EM dehydrate --> EM anhydrate). This alteration in phase behavior of EM was attributed to the ability of PEG in promoting nucleation and crystal growth of the EM anhydrate through a solvent-mediated route. In situ monitoring of solid dispersion formation, especially by VT-XRPD and HSM, enabled both early-stage detection of phase transformations during the hot-melt processing and better process understanding.

Chemistry, Pharmaceutical↗

PubMed2006

Study of retinoic acid polymorphism.

Some authors recently hypothesized the existence of a new retinoic acid (RA) phase in addition to the two already known polymorphs. We investigated RA polymorphism and our results exclude the presence of new modifications and refine the properties of the known forms. By comparison of simulated and acquired X-Ray Powder Diffraction (XRPD) it was possible to identify only the known monoclinic (I) and the triclinic (II) modifications; the same were also characterized by DSC, IR, and Raman spectroscopy. A solubility study associated to DSC allowed establishing an enantiotropic relationship between the two forms, with form II being less stable (DeltaGII/I=0.71 kJ/mol at 37 degrees C) below the transition temperature (136.6 degrees C; DeltaH=3.2 kJ/mol). The intrinsic dissolution rate (IDR) (I=61 microg/cm2xmin-1; II=125 microg/cm2xmin-1) confirmed this energetic relationship. The kinetics of solid transition I-->II was examined and its activation energy estimated (356 kJ/mol). The attempts to produce new phases allowed the development of methods to obtain the two polymorphs with high chemical and polymorphic purity. A validated DSC method is presented that enables detection of the presence of form I at a level of 1% (w/w) when in mixture with form II.

Calorimetry, Differential Scanning↗