The electronic structure of Pb1-xLaxTiO3 (PLT) compounds for x ranging from 0 to 30 at. % of La i... more The electronic structure of Pb1-xLaxTiO3 (PLT) compounds for x ranging from 0 to 30 at. % of La is investigated by means of soft x-ray absorption near edge structure (XANES) at the Ti L3,2 and O K edges. The greatest modification in the structure of the Ti 2p XANES spectra of the PLT compounds is observed in the region of the high energy peak of the L3 edge (eg states), which exhibits a splitting in the undoped sample. As the amount of lanthanum increases, this splitting becomes less pronounced. This modification is interpreted as a decrease in the degree of disorder of titanium atoms, which is correlated to the substitution of Pb by La atoms. The structural changes observed at the low energy peaks of the O K-edge XANES spectra of the PLT compounds may be interpreted in terms of hybridization between O 2p, Ti 3d, and Pb 6p orbitals. A decrease in the degree of hybridization observed as Pb atoms are replaced by La atoms may be related to the differences in the ferroelectric properties observed between x=0.0 and x=0.30 compounds.
ABSTRACT O K and Ti L2,3 x-ray absorption near-edge spectra (XANES) of Pb1−xBaxZr0.65Ti0.35O3 (PB... more ABSTRACT O K and Ti L2,3 x-ray absorption near-edge spectra (XANES) of Pb1−xBaxZr0.65Ti0.35O3 (PBZT) ferroelectric ceramic compounds with x varying from 0.0 to 0.40 were obtained. The XANES spectra at the O K edge were compared with ab initio calculations based on the structures obtained by x-ray diffraction, using the FEFF 8.2 code. The different features observed in the XANES spectra of PBZT samples were quite well reproduced with the calculations, especially for x≤0.20. However, for x>0.20 the ab initio calculations do not match the experimental spectra, indicating that for these Ba concentrations, the structural model deduced from powder x-ray diffraction does not reflect the actual local structure around oxygen atoms. Based on calculations of the local partial electron density of states (DOS), the main features of the O K-edge experimental spectra were assigned primarily to the hybridization between O 2p–Ti 3d, Pb 6p and Ba 5d orbitals. The differences in the ferroelectric character of the end-member x = 0.0 and 0.40 sample compositions has been interpreted as due to the decrease of the hybridization between Pb 6p and O 2p orbitals caused by the substitution of Pb2+ by Ba2+ atoms.
Mebendazole (MBZ) is a common benzimidazole anthelmintic that exists in three different polymorph... more Mebendazole (MBZ) is a common benzimidazole anthelmintic that exists in three different polymorphic forms, A, B, and C. Polymorph C is the pharmaceutically preferred form due to its adequated aqueous solubility. No single crystal structure determinations depicting the nature of the crystal packing and molecular conformation and geometry have been performed on this compound. The crystal structure of mebendazole form C is resolved for the first time. Mebendazole form C crystallizes in the triclinic centrosymmetric space group and this drug is practically planar, since the leastsquares methyl benzimidazolylcarbamate plane is much fitted on the forming atoms. However, the benzoyl group is twisted by 31(1)8 from the benzimidazole ring, likewise the torsional angle between the benzene and carbonyl moieties is 27(1)8. The formerly described bends and other interesting intramolecular geometry features were viewed as consequence of the intermolecular contacts occurring within mebendazole C structure. Among these features, a conjugation decreasing through the imine nitrogen atom of the benzimidazole core and a further resonance path crossing the carbamate one were described. At last, the X-ray powder diffractogram of a form C rich mebendazole mixture was overlaid to the calculated one with the mebendazole crystal structure. ß
Acta Crystallographica Section B Structural Science, 2007
The structure of Pb(1-x)Ba(x)Zr(0.65)Ti(0.35)O(3) (PBZT) ceramic materials with 0.00 &amp... more The structure of Pb(1-x)Ba(x)Zr(0.65)Ti(0.35)O(3) (PBZT) ceramic materials with 0.00 < or = x < or = 0.40 was studied using synchrotron X-ray powder diffraction data. According to the Rietveld refinements, the structure of PBZT ceramics with x = 0.00, 0.10 and 0.20 at room temperature was rhombohedral R3c. A phase transition from rhombohedral to cubic was observed at 543 and 463 K for x = 0.10 and 0.20, respectively. The refinement for the compositions x = 0.30 and x = 0.40 showed a cubic structure from 10 to 450 K, in good agreement with the dielectric properties of these samples.
Chlortalidone (HIGROTON) is a diuretic drug widely used in antihypertensive therapy. Thus far, on... more Chlortalidone (HIGROTON) is a diuretic drug widely used in antihypertensive therapy. Thus far, only two solidstate polymorphs of chlortalidone have been reported. We elucidated the structure of chlortalidone form I and a new polymorph. This new phase, namely, chlortalidone form III, was also entirely characterized. It was possible to conclude that it is a conformer with a different orientation of the chlorobenzenesulfonamide moiety. Compared to form I, it has a rotation of about 90°on the axis of the C-C bond bridging the substituted phenyl and isoindolinyl rings. This conformational feature is related to the crystal packing patterns of the chlortalidone forms. Furthermore, certain intermolecular hydrogen bonds are present in both polymorphs, giving rise to ribbons with chlortalidone enantiomers alternately placed into them. The chlortalidone form I and form III crystallize in the triclinic space group P1 j as racemic mixtures. Additional conformational details also differentiate the chlortalidone conformers. Slight twists on the isoindolinyl and sulfamyl groups exist. Considering all structural relationships, the fingerprint plots derived from the Hirshfeld surfaces exhibited the characteristics of the chlortalidone form I and form III crystal structures.
Estudo das formas cristalinas de insumos farmacêuticos por meio da técnica de difração de raios X... more Estudo das formas cristalinas de insumos farmacêuticos por meio da técnica de difração de raios X por pó e análises térmica: fluconazol, nifedipino, propanolol e mebendazol.
Estudo das formas cristalinas de insumos farmacêuticos por meio da técnica de difração de raios X... more Estudo das formas cristalinas de insumos farmacêuticos por meio da técnica de difração de raios X por pó e análises térmica: fluconazol, nifedipino, propanolol e mebendazol.
Doxycycline (DOX) is a tetracycline class drug that is used worldwide as a broad-spectrum antibio... more Doxycycline (DOX) is a tetracycline class drug that is used worldwide as a broad-spectrum antibiotic. Although its clinical importance and use have been known since the 1960s, only four crystal forms have been reported until now. These are doxycycline hyclate (DOX.HYC), which is a hydrochloride salt hemiethanolate-hemihydrate; its isomorphous hydrobromide, hydrochloride salt dihydrate (DOX·HCl·2H 2 O); and doxycycline monohydrate (DOX·H 2 O). Here we report the preparation of two new multicomponent molecular crystal forms of doxycycline and their crystal structure determination along with their melting temperature, aqueous solubility, and time-dependent dissolution profile. These crystal forms are a hydronitrate salt hemihydrate (DOX·HNO 3 ·0.5H 2 O) and an acetic acid solvate dihydrate (DOX·HAc·2H 2 O). The two new doxycycline crystal forms were compared with known forms, including DOX·HCl·2H 2 O, the structure of which was redetermined in this work. The structural variability of the protonation patterns, tautomerism of the keto−enolate moieties, and conformation of the amide groups was observed for these compounds. While intramolecular rings assembled through resonance-assisted hydrogen bond (RAHB) were observed in both fused keto−enol moieties of all structures, DOX·HCl·2H 2 O and DOX·HNO 3 ·0.5H 2 O have another RAHB encompassing the protonated amide carbonyl oxygen and the enolate oxygen. These two crystal forms have a net positive charge on their drug molecule as DOX·HYC. They crystallize with the N,N-dimethylamine and amide carbonyl groups protonated and the neighboring hydroxyl group deprotonated. DOX, by contrast, crystallizes as a zwitterion in DOX·HAc·2H 2 O similarly to DOX·H 2 O. Their amide carbonyl oxygens are not protonated, which differs from the salt forms. DOX·HNO 3 ·0.5H 2 O presents as two tautomers that are similar to those of DOX· HYC, namely, T1, in which the enolate oxygen is next to the protonated amine group, and T2, with the carbonyl oxygen close to the protonated amine group. These tautomers also differ in their amide conformations due to a rotation of ca. 180°on the C−C bond axis of the amide group, which directs the protonated carbonyl oxygen toward the enolate oxygen. DOX·HCl·2H 2 O has only one T1-like tautomer and therefore only one amide conformation similar to that of T1. A T1-like keto−enolate tautomer is present in DOX·HAc·2H 2 O, which exhibits an amide conformation similar to that of T2. Thermal (DSC and TG) and infrared analysis and equilibrium solubility, dissolution profiles, and forced degradation studies were performed to both new and known DOX forms. The results were correlated with their structural features. DOX·HNO 3 ·0.5H 2 O was the most soluble form. This new form was also more stable than the commercial DOX·HYC in the oxidation test and more stable than commercial DOX·H 2 O against acid and basic hydrolysis and in the photostability study. DOX·HNO 3 ·0.5H 2 O and DOX·HYC (commercial form) were observed to have similar drug release behaviors from capsules (F2 > 50) and therefore they could be interchangeable.
Hydrogenated bulk Zn 1Àx Co x O samples were synthesized via standard solid-state reaction route ... more Hydrogenated bulk Zn 1Àx Co x O samples were synthesized via standard solid-state reaction route with Co molar concentrations up to 15 at.%. Magnetic characterization demonstrates a room temperature ferromagnetic behavior associated to a paramagnetic Curie-Weiss component. Detailed microstructural analysis was carried out to exclude the presence of extrinsic sources of ferromagnetism. The magnetization increases linearly as a function of Co concentration. Hall measurements reveal an insulating character for the whole set of samples. In this context, the defect mediated magnetic coupling between the Co atoms under the scope of the bound magnetic polarons model is used to interpret the observed room temperature ferromagnetism.
For the first time combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) exper... more For the first time combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) experiments were carried out to probe the short-and long-range order in lanthanum-modified PbTiO3 ceramic materials (Pb1-x La x TiO3) for x ranging from 0 to 30 atom% of ...
The understanding of the structural origin of relaxor ferroelectrics has been doubtlessly a long-... more The understanding of the structural origin of relaxor ferroelectrics has been doubtlessly a long-standing puzzle in the field of ferroelectricity. Thus, motivated by the interest in improving the comprehension of this important issue, it a framework is proposed for explaining the origin of the relaxor state in ordinary ferroelectrics induced via the isovalent-ion substitution. Based on the martensitic transformation concepts, it is proposed that the continuous addition of isovalent ions in a so-called normal ferroelectric decreases considerably the elastic strain energy. This results in a gradual transformation of ferroelectric domain patterns from a micrometer polydomain structure ͑twins͒, through single domains, to nanometer-polar-"tweed" structures with glasslike behavior, that are, in turn, strongly driven by point defects and surface effects. The electrical interaction between these weakly coupled polar-tweed structures leads to a wide spectrum of relaxation times, thus resulting in a dielectric relaxation process, the signature of relaxor ferroelectrics.
A modified polymeric precursor method based on the Pechini process was used to synthesize β-BaB 2... more A modified polymeric precursor method based on the Pechini process was used to synthesize β-BaB 2 O 4 (β-BBO) crystalline phase. D-sorbitol (C 6 H 14 O 6 ) was used as a polymerizing agent to avoid the loss of boron during the samples' calcination and crystallization. The β-BBO stoichiometric crystalline phase was only obtained when sorbitol was added to the solution. The results of Raman spectroscopy show that the amorphous phase is only completely eliminated when the samples are heat-treated at 750 • C for 20 h. Thin films of β-BBO phase displaying a preferred orientation were obtained when crystallized at 750 • C for 2 h and deposited on sapphire substrate.
Journal of Pharmaceutical and Biomedical Analysis, 2011
A robust, direct, rapid and non-destructive X-ray diffraction crystallography method to detect th... more A robust, direct, rapid and non-destructive X-ray diffraction crystallography method to detect the polyprenylated benzophenones 7-epi-clusianone (1) and guttiferone A (2) in extracts from Garcinia brasiliensis is presented. Powder samples of benzophenones 1 and 2, dried hexane extracts from G. brasiliensis seeds and fruit's pericarp, and the dried ethanolic extract from G. brasiliensis seeds were unambiguously characterized by powder X-ray diffractometry. The calculated X-ray diffraction peaks from crystal structures of analytes 1 and 2, previously determined by single-crystal X-ray diffraction technique, were overlaid to those of the experimental powder diffractograms, providing a practical identification of these compounds in the analyzed material and confirming the pure contents of the powder samples. Using the X-ray diffraction crystallography method, the studied polyprenylated benzophenones were selectively and simultaneously detected in the extracts which were mounted directly on sample holder. In addition, reference materials of the analytes were not required for analyses since the crystal structures of the compounds are known. High performance liquid chromatography analyses also were comparatively carried out to quantify the analytes in the same plant extracts showing to be in agreement with X-ray diffraction crystallography method. .br (A.C. Doriguetto).
Ti K-edge x-ray absorption near-edge spectroscopy ͑XANES͒ and Raman scattering were used to study... more Ti K-edge x-ray absorption near-edge spectroscopy ͑XANES͒ and Raman scattering were used to study the solid solution effects on the structural and vibrational properties of Pb 1−x Ba x Zr 0.65 Ti 0.35 O 3 with 0.0Ͻ x Ͻ 0.40. Compared with x-ray diffraction techniques, which indicates that the average crystal symmetry changes with the substitution of Pb by Ba ions or with temperature variations for samples with x = 0.00, 0.10, and 0.20, local structural probes such as XANES and Raman scattering results demonstrate that at local level, the symmetry changes are much less prominent. Theoretical XANES spectra calculation corroborate with the interpretation of the XANES experimental data.
In this work, we investigated the temperature dependence of short and long-range ferroelectric or... more In this work, we investigated the temperature dependence of short and long-range ferroelectric ordering in Pb0.55La0.30TiO3 relaxor composition. High-resolution x-ray powder diffraction measurements revealed a clear spontaneous macroscopic cubic-to-tetragonal phase transition in the PLT relaxor sample at ~60 K below the maximum of the dielectric constant peak (Tm). Indeed, the x-ray diffraction (XRD) data showed that at 300 K (above
The active pharmaceutical ingredient (API) doxycycline (DOX) is a broad-spectrum antibiotic mainl... more The active pharmaceutical ingredient (API) doxycycline (DOX) is a broad-spectrum antibiotic mainly used in the treatment of respiratory and urinary tract infections and, like many drugs, its efficacy may be affected by the crystal form. Up to now, only the crystal structure of doxycycline hyclate (DOX$HYC) (generic name of brand names such as DORYXÒ, PERIOSTATÒ, ATRIDOXÒ, and VIBRAMYCINÒ) has been reported. This study presents the single-crystal X-ray diffractometry structural characterisation of another crystal form, doxycycline monohydrate (DOX$H 2 O) (generic name of brand names such as MONODOXÒ and ORACEAÒ). The DOX$H 2 O structure was compared with the known DOX$HYC one in terms of intra-and intermolecular geometries, and their melting temperature, water solubility and dissolution rate were measured. These data allowed us to establish relationships between solid state properties related to the pharmaceutical performance of the two DOX crystal variants and their supramolecular structures for the first time. Both hyclate and monohydrate forms crystallise the DOX molecules as zwitterions in which their dimethylamine groups are protonated and one of their hydroxyl groups is deprotonated. Whereas two conformers were observed in the DOX$HYC (i.e., the amine group is next to the enolate in one of them (T1) and beside the carbonyl in the other one (T2)), only one (T2) was found in DOX$H 2 O. Additionally, in the hyclate form, the presence of ethanol in the crystal lattice could be related to a rotation around the C-C bond of the amide group, directing the oxygen toward the amine group in one (T1) of the two conformers present in this solid state phase. Meanwhile, in the other crystallographically independent molecule (T2), the amide nitrogen is on the same side as the amine. However, only the conformer similar to T1 in DOX$HYC was observed in DOX$H 2 O. The crystal packing of DOX$H 2 O was stabilised by several intermolecular hydrogen bonds, with each drug entity interacting with another two DOX and three water molecules in such a way that a compact supramolecular network was formed. This structure was saturated in terms of hydrogen bonding, which could be related to its lower solubility and dissolution rate relative to DOX$HYC.
The electronic structure of Pb1-xLaxTiO3 (PLT) compounds for x ranging from 0 to 30 at. % of La i... more The electronic structure of Pb1-xLaxTiO3 (PLT) compounds for x ranging from 0 to 30 at. % of La is investigated by means of soft x-ray absorption near edge structure (XANES) at the Ti L3,2 and O K edges. The greatest modification in the structure of the Ti 2p XANES spectra of the PLT compounds is observed in the region of the high energy peak of the L3 edge (eg states), which exhibits a splitting in the undoped sample. As the amount of lanthanum increases, this splitting becomes less pronounced. This modification is interpreted as a decrease in the degree of disorder of titanium atoms, which is correlated to the substitution of Pb by La atoms. The structural changes observed at the low energy peaks of the O K-edge XANES spectra of the PLT compounds may be interpreted in terms of hybridization between O 2p, Ti 3d, and Pb 6p orbitals. A decrease in the degree of hybridization observed as Pb atoms are replaced by La atoms may be related to the differences in the ferroelectric properties observed between x=0.0 and x=0.30 compounds.
ABSTRACT O K and Ti L2,3 x-ray absorption near-edge spectra (XANES) of Pb1−xBaxZr0.65Ti0.35O3 (PB... more ABSTRACT O K and Ti L2,3 x-ray absorption near-edge spectra (XANES) of Pb1−xBaxZr0.65Ti0.35O3 (PBZT) ferroelectric ceramic compounds with x varying from 0.0 to 0.40 were obtained. The XANES spectra at the O K edge were compared with ab initio calculations based on the structures obtained by x-ray diffraction, using the FEFF 8.2 code. The different features observed in the XANES spectra of PBZT samples were quite well reproduced with the calculations, especially for x≤0.20. However, for x>0.20 the ab initio calculations do not match the experimental spectra, indicating that for these Ba concentrations, the structural model deduced from powder x-ray diffraction does not reflect the actual local structure around oxygen atoms. Based on calculations of the local partial electron density of states (DOS), the main features of the O K-edge experimental spectra were assigned primarily to the hybridization between O 2p–Ti 3d, Pb 6p and Ba 5d orbitals. The differences in the ferroelectric character of the end-member x = 0.0 and 0.40 sample compositions has been interpreted as due to the decrease of the hybridization between Pb 6p and O 2p orbitals caused by the substitution of Pb2+ by Ba2+ atoms.
Mebendazole (MBZ) is a common benzimidazole anthelmintic that exists in three different polymorph... more Mebendazole (MBZ) is a common benzimidazole anthelmintic that exists in three different polymorphic forms, A, B, and C. Polymorph C is the pharmaceutically preferred form due to its adequated aqueous solubility. No single crystal structure determinations depicting the nature of the crystal packing and molecular conformation and geometry have been performed on this compound. The crystal structure of mebendazole form C is resolved for the first time. Mebendazole form C crystallizes in the triclinic centrosymmetric space group and this drug is practically planar, since the leastsquares methyl benzimidazolylcarbamate plane is much fitted on the forming atoms. However, the benzoyl group is twisted by 31(1)8 from the benzimidazole ring, likewise the torsional angle between the benzene and carbonyl moieties is 27(1)8. The formerly described bends and other interesting intramolecular geometry features were viewed as consequence of the intermolecular contacts occurring within mebendazole C structure. Among these features, a conjugation decreasing through the imine nitrogen atom of the benzimidazole core and a further resonance path crossing the carbamate one were described. At last, the X-ray powder diffractogram of a form C rich mebendazole mixture was overlaid to the calculated one with the mebendazole crystal structure. ß
Acta Crystallographica Section B Structural Science, 2007
The structure of Pb(1-x)Ba(x)Zr(0.65)Ti(0.35)O(3) (PBZT) ceramic materials with 0.00 &amp... more The structure of Pb(1-x)Ba(x)Zr(0.65)Ti(0.35)O(3) (PBZT) ceramic materials with 0.00 < or = x < or = 0.40 was studied using synchrotron X-ray powder diffraction data. According to the Rietveld refinements, the structure of PBZT ceramics with x = 0.00, 0.10 and 0.20 at room temperature was rhombohedral R3c. A phase transition from rhombohedral to cubic was observed at 543 and 463 K for x = 0.10 and 0.20, respectively. The refinement for the compositions x = 0.30 and x = 0.40 showed a cubic structure from 10 to 450 K, in good agreement with the dielectric properties of these samples.
Chlortalidone (HIGROTON) is a diuretic drug widely used in antihypertensive therapy. Thus far, on... more Chlortalidone (HIGROTON) is a diuretic drug widely used in antihypertensive therapy. Thus far, only two solidstate polymorphs of chlortalidone have been reported. We elucidated the structure of chlortalidone form I and a new polymorph. This new phase, namely, chlortalidone form III, was also entirely characterized. It was possible to conclude that it is a conformer with a different orientation of the chlorobenzenesulfonamide moiety. Compared to form I, it has a rotation of about 90°on the axis of the C-C bond bridging the substituted phenyl and isoindolinyl rings. This conformational feature is related to the crystal packing patterns of the chlortalidone forms. Furthermore, certain intermolecular hydrogen bonds are present in both polymorphs, giving rise to ribbons with chlortalidone enantiomers alternately placed into them. The chlortalidone form I and form III crystallize in the triclinic space group P1 j as racemic mixtures. Additional conformational details also differentiate the chlortalidone conformers. Slight twists on the isoindolinyl and sulfamyl groups exist. Considering all structural relationships, the fingerprint plots derived from the Hirshfeld surfaces exhibited the characteristics of the chlortalidone form I and form III crystal structures.
Estudo das formas cristalinas de insumos farmacêuticos por meio da técnica de difração de raios X... more Estudo das formas cristalinas de insumos farmacêuticos por meio da técnica de difração de raios X por pó e análises térmica: fluconazol, nifedipino, propanolol e mebendazol.
Estudo das formas cristalinas de insumos farmacêuticos por meio da técnica de difração de raios X... more Estudo das formas cristalinas de insumos farmacêuticos por meio da técnica de difração de raios X por pó e análises térmica: fluconazol, nifedipino, propanolol e mebendazol.
Doxycycline (DOX) is a tetracycline class drug that is used worldwide as a broad-spectrum antibio... more Doxycycline (DOX) is a tetracycline class drug that is used worldwide as a broad-spectrum antibiotic. Although its clinical importance and use have been known since the 1960s, only four crystal forms have been reported until now. These are doxycycline hyclate (DOX.HYC), which is a hydrochloride salt hemiethanolate-hemihydrate; its isomorphous hydrobromide, hydrochloride salt dihydrate (DOX·HCl·2H 2 O); and doxycycline monohydrate (DOX·H 2 O). Here we report the preparation of two new multicomponent molecular crystal forms of doxycycline and their crystal structure determination along with their melting temperature, aqueous solubility, and time-dependent dissolution profile. These crystal forms are a hydronitrate salt hemihydrate (DOX·HNO 3 ·0.5H 2 O) and an acetic acid solvate dihydrate (DOX·HAc·2H 2 O). The two new doxycycline crystal forms were compared with known forms, including DOX·HCl·2H 2 O, the structure of which was redetermined in this work. The structural variability of the protonation patterns, tautomerism of the keto−enolate moieties, and conformation of the amide groups was observed for these compounds. While intramolecular rings assembled through resonance-assisted hydrogen bond (RAHB) were observed in both fused keto−enol moieties of all structures, DOX·HCl·2H 2 O and DOX·HNO 3 ·0.5H 2 O have another RAHB encompassing the protonated amide carbonyl oxygen and the enolate oxygen. These two crystal forms have a net positive charge on their drug molecule as DOX·HYC. They crystallize with the N,N-dimethylamine and amide carbonyl groups protonated and the neighboring hydroxyl group deprotonated. DOX, by contrast, crystallizes as a zwitterion in DOX·HAc·2H 2 O similarly to DOX·H 2 O. Their amide carbonyl oxygens are not protonated, which differs from the salt forms. DOX·HNO 3 ·0.5H 2 O presents as two tautomers that are similar to those of DOX· HYC, namely, T1, in which the enolate oxygen is next to the protonated amine group, and T2, with the carbonyl oxygen close to the protonated amine group. These tautomers also differ in their amide conformations due to a rotation of ca. 180°on the C−C bond axis of the amide group, which directs the protonated carbonyl oxygen toward the enolate oxygen. DOX·HCl·2H 2 O has only one T1-like tautomer and therefore only one amide conformation similar to that of T1. A T1-like keto−enolate tautomer is present in DOX·HAc·2H 2 O, which exhibits an amide conformation similar to that of T2. Thermal (DSC and TG) and infrared analysis and equilibrium solubility, dissolution profiles, and forced degradation studies were performed to both new and known DOX forms. The results were correlated with their structural features. DOX·HNO 3 ·0.5H 2 O was the most soluble form. This new form was also more stable than the commercial DOX·HYC in the oxidation test and more stable than commercial DOX·H 2 O against acid and basic hydrolysis and in the photostability study. DOX·HNO 3 ·0.5H 2 O and DOX·HYC (commercial form) were observed to have similar drug release behaviors from capsules (F2 > 50) and therefore they could be interchangeable.
Hydrogenated bulk Zn 1Àx Co x O samples were synthesized via standard solid-state reaction route ... more Hydrogenated bulk Zn 1Àx Co x O samples were synthesized via standard solid-state reaction route with Co molar concentrations up to 15 at.%. Magnetic characterization demonstrates a room temperature ferromagnetic behavior associated to a paramagnetic Curie-Weiss component. Detailed microstructural analysis was carried out to exclude the presence of extrinsic sources of ferromagnetism. The magnetization increases linearly as a function of Co concentration. Hall measurements reveal an insulating character for the whole set of samples. In this context, the defect mediated magnetic coupling between the Co atoms under the scope of the bound magnetic polarons model is used to interpret the observed room temperature ferromagnetism.
For the first time combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) exper... more For the first time combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) experiments were carried out to probe the short-and long-range order in lanthanum-modified PbTiO3 ceramic materials (Pb1-x La x TiO3) for x ranging from 0 to 30 atom% of ...
The understanding of the structural origin of relaxor ferroelectrics has been doubtlessly a long-... more The understanding of the structural origin of relaxor ferroelectrics has been doubtlessly a long-standing puzzle in the field of ferroelectricity. Thus, motivated by the interest in improving the comprehension of this important issue, it a framework is proposed for explaining the origin of the relaxor state in ordinary ferroelectrics induced via the isovalent-ion substitution. Based on the martensitic transformation concepts, it is proposed that the continuous addition of isovalent ions in a so-called normal ferroelectric decreases considerably the elastic strain energy. This results in a gradual transformation of ferroelectric domain patterns from a micrometer polydomain structure ͑twins͒, through single domains, to nanometer-polar-"tweed" structures with glasslike behavior, that are, in turn, strongly driven by point defects and surface effects. The electrical interaction between these weakly coupled polar-tweed structures leads to a wide spectrum of relaxation times, thus resulting in a dielectric relaxation process, the signature of relaxor ferroelectrics.
A modified polymeric precursor method based on the Pechini process was used to synthesize β-BaB 2... more A modified polymeric precursor method based on the Pechini process was used to synthesize β-BaB 2 O 4 (β-BBO) crystalline phase. D-sorbitol (C 6 H 14 O 6 ) was used as a polymerizing agent to avoid the loss of boron during the samples' calcination and crystallization. The β-BBO stoichiometric crystalline phase was only obtained when sorbitol was added to the solution. The results of Raman spectroscopy show that the amorphous phase is only completely eliminated when the samples are heat-treated at 750 • C for 20 h. Thin films of β-BBO phase displaying a preferred orientation were obtained when crystallized at 750 • C for 2 h and deposited on sapphire substrate.
Journal of Pharmaceutical and Biomedical Analysis, 2011
A robust, direct, rapid and non-destructive X-ray diffraction crystallography method to detect th... more A robust, direct, rapid and non-destructive X-ray diffraction crystallography method to detect the polyprenylated benzophenones 7-epi-clusianone (1) and guttiferone A (2) in extracts from Garcinia brasiliensis is presented. Powder samples of benzophenones 1 and 2, dried hexane extracts from G. brasiliensis seeds and fruit's pericarp, and the dried ethanolic extract from G. brasiliensis seeds were unambiguously characterized by powder X-ray diffractometry. The calculated X-ray diffraction peaks from crystal structures of analytes 1 and 2, previously determined by single-crystal X-ray diffraction technique, were overlaid to those of the experimental powder diffractograms, providing a practical identification of these compounds in the analyzed material and confirming the pure contents of the powder samples. Using the X-ray diffraction crystallography method, the studied polyprenylated benzophenones were selectively and simultaneously detected in the extracts which were mounted directly on sample holder. In addition, reference materials of the analytes were not required for analyses since the crystal structures of the compounds are known. High performance liquid chromatography analyses also were comparatively carried out to quantify the analytes in the same plant extracts showing to be in agreement with X-ray diffraction crystallography method. .br (A.C. Doriguetto).
Ti K-edge x-ray absorption near-edge spectroscopy ͑XANES͒ and Raman scattering were used to study... more Ti K-edge x-ray absorption near-edge spectroscopy ͑XANES͒ and Raman scattering were used to study the solid solution effects on the structural and vibrational properties of Pb 1−x Ba x Zr 0.65 Ti 0.35 O 3 with 0.0Ͻ x Ͻ 0.40. Compared with x-ray diffraction techniques, which indicates that the average crystal symmetry changes with the substitution of Pb by Ba ions or with temperature variations for samples with x = 0.00, 0.10, and 0.20, local structural probes such as XANES and Raman scattering results demonstrate that at local level, the symmetry changes are much less prominent. Theoretical XANES spectra calculation corroborate with the interpretation of the XANES experimental data.
In this work, we investigated the temperature dependence of short and long-range ferroelectric or... more In this work, we investigated the temperature dependence of short and long-range ferroelectric ordering in Pb0.55La0.30TiO3 relaxor composition. High-resolution x-ray powder diffraction measurements revealed a clear spontaneous macroscopic cubic-to-tetragonal phase transition in the PLT relaxor sample at ~60 K below the maximum of the dielectric constant peak (Tm). Indeed, the x-ray diffraction (XRD) data showed that at 300 K (above
The active pharmaceutical ingredient (API) doxycycline (DOX) is a broad-spectrum antibiotic mainl... more The active pharmaceutical ingredient (API) doxycycline (DOX) is a broad-spectrum antibiotic mainly used in the treatment of respiratory and urinary tract infections and, like many drugs, its efficacy may be affected by the crystal form. Up to now, only the crystal structure of doxycycline hyclate (DOX$HYC) (generic name of brand names such as DORYXÒ, PERIOSTATÒ, ATRIDOXÒ, and VIBRAMYCINÒ) has been reported. This study presents the single-crystal X-ray diffractometry structural characterisation of another crystal form, doxycycline monohydrate (DOX$H 2 O) (generic name of brand names such as MONODOXÒ and ORACEAÒ). The DOX$H 2 O structure was compared with the known DOX$HYC one in terms of intra-and intermolecular geometries, and their melting temperature, water solubility and dissolution rate were measured. These data allowed us to establish relationships between solid state properties related to the pharmaceutical performance of the two DOX crystal variants and their supramolecular structures for the first time. Both hyclate and monohydrate forms crystallise the DOX molecules as zwitterions in which their dimethylamine groups are protonated and one of their hydroxyl groups is deprotonated. Whereas two conformers were observed in the DOX$HYC (i.e., the amine group is next to the enolate in one of them (T1) and beside the carbonyl in the other one (T2)), only one (T2) was found in DOX$H 2 O. Additionally, in the hyclate form, the presence of ethanol in the crystal lattice could be related to a rotation around the C-C bond of the amide group, directing the oxygen toward the amine group in one (T1) of the two conformers present in this solid state phase. Meanwhile, in the other crystallographically independent molecule (T2), the amide nitrogen is on the same side as the amine. However, only the conformer similar to T1 in DOX$HYC was observed in DOX$H 2 O. The crystal packing of DOX$H 2 O was stabilised by several intermolecular hydrogen bonds, with each drug entity interacting with another two DOX and three water molecules in such a way that a compact supramolecular network was formed. This structure was saturated in terms of hydrogen bonding, which could be related to its lower solubility and dissolution rate relative to DOX$HYC.
Uploads
Papers by Person Neves