RESUMEN
Ordered mesoporous glasses based on the 80% SiO(2)-15% CaO-5% P(2)O(5) system including up to 3.5% Ce(2)O(3), 3.5% Ga(2)O(3) or 7.0% ZnO (in mol.%) were synthesized by the evaporation-induced self-assembly process using Pluronic® 123 as a surfactant. An ordered hexagonal mesophase was observed in both the unsubstituted glass (denoted in this paper as B: blank) and glasses containing <0.4% of substituent by X-ray diffraction, transmission electron microscopy and electron diffraction. The increase in the amount of substituent led to a decrease in the mesopore order. B glass exhibited good textural properties: S(BET)=515m(2)g(-1), D(P)=4.7nm and V(P)=0.58cm(3)g(-1). With the inclusion of cerium, gallium and zinc oxides the textural properties decreased, but remained in amounts useful for clinical applications. Zinc-containing samples showed the highest decrement in the textural properties. Substituted glasses exhibited a quick in vitro bioactive response except when the ZnO content was over 0.4%. Taking into account the ordered mesoporosity, the quick in vitro bioactive response and the added values of the substituents, this new family of glasses are promising candidates for applications in bone tissue engineering.
Asunto(s)
Materiales Biocompatibles/química , Cerio/química , Galio/química , Vidrio/química , Zinc/química , Ensayo de Materiales , Microscopía Electrónica de Rastreo , Microscopía Electrónica de Transmisión , Propiedades de Superficie , Ingeniería de Tejidos , Difracción de Rayos XRESUMEN
In this work, the glass transition temperature and chemical durability of bioactive phospho-silicate glasses were experimentally determined and correlated to the structural descriptor Fnet derived from classical molecular dynamics simulations. The replacement of CaF2 for Na2O in the parent glass 45S5 enhances both chemical durability and density, while the replacement of CaF2 for CaO lowers chemical durability. The proposed descriptor, Fnet, provides satisfactorily correlations with glass transition temperature and chemical durability over a wide range of compositions.
Asunto(s)
Flúor/química , Vidrio/química , Fósforo/química , Relación Estructura-Actividad Cuantitativa , Silicatos/química , Compuestos de Calcio/química , Fluoruro de Calcio/química , Óxidos/química , Transición de Fase , Compuestos de Sodio/química , Temperatura de Transición , Agua/químicaRESUMEN
The issue of the contribution of the addition of F to glass bioactivity is not well resolved. This work reports on the surface reactivity in different solutions (DMEM and Tris) for some potentially bioactive glasses based on the composition of 45S5 glass, in which CaF(2) is substituted alternately for (part of) CaO and Na(2)O. The reactivity of F-containing glasses has been compared with that of the reference 45S5 system. The aim of this study is to explain in detail the mechanism of formation of an apatitic crystalline phase at the interface between the inorganic material and simulated biological media. A multi-technique investigation approach proposes a set of reactions involving Ca-carbonate formation, which are somewhat different from that formerly proposed by Hench for 45S5 bioactive glass, and which occur when a F-containing glass surface is in contact with a SBF. The usefulness of IR spectroscopy in recognizing the starting step of apatite (and/or FA) formation with respect to XRD technique is well established here.
Asunto(s)
Líquidos Corporales , Fluoruros/química , Vidrio/química , Materiales Biocompatibles/química , Materiales Biocompatibles/metabolismo , Líquidos Corporales/química , Líquidos Corporales/metabolismo , Calcio/química , Cerámica , Concentración de Iones de Hidrógeno , Ensayo de Materiales , Microscopía Electrónica de Rastreo , Sodio/química , Espectroscopía Infrarroja por Transformada de Fourier , Propiedades de Superficie , Difracción de Rayos XRESUMEN
Glasses belonging to the Na(2)O-CaO-P(2)O(5)-SiO(2) system and modified by CaF(2) substitution for CaO and Na(2)O alternatively, were synthesized and characterized experimentally and computationally. The results of molecular dynamics simulations show that fluorine is almost exclusively bonded to modifier cations (Ca and Na) with coordination number close to 4. A similar mean coordination number value is found in the crystal phases obtained by means of thermal treatment at fixed temperature. Addition of fluorine increases the polymerization of silicate tetrahedra by removing modifiers from the siliceous matrix. No appreciable amount of Si-F bonds are detected.
Asunto(s)
Flúor/química , Vidrio , Simulación por Computador , Compuestos de Flúor/química , Iones/química , Modelos Moleculares , Conformación Molecular , Temperatura , Difracción de Rayos XRESUMEN
Two series of glasses of general formula (2-p) SiO2.1.1Na2O.CaO.pP2O5.xZnO (p=0.10, 0.20; x=0.0, 0.16, 0.35, and 0.78) have been analyzed for physico-chemical surface features before and after contact with simulated body fluid, morphological characteristics, and osteoblast-like cells behavior when cultured on them. The resulted good cell adhesion and growth, along with nonsignificant changes of the focal contacts, allow the authors to indicate HZ5 and HP5Z5 glasses as the ones having optimal ratio of Zn/P to maintain acceptable cell behavior, comparable to the bioactive glass (Bioglass) used as a control; results are also rationalized by means of three-dimensional models derived by molecular dynamic simulations, with decomposition and conversion rates optimized with respect to the parent Hench's Bioglass.
Asunto(s)
Materiales Biocompatibles/química , Vidrio/química , Zinc/química , Animales , Adhesión Celular , Línea Celular , Proliferación Celular , Adhesiones Focales , Ensayo de Materiales , Ratones , Osteoblastos/citología , Osteoblastos/fisiología , Propiedades de SuperficieRESUMEN
The crystal and molecular structure of Tirofiban [N-(n-butanesulfonyl)-O-(4-(4-piperidinyl)-butyl)-(S)-tyrosine] is here reported. In the solid state the carboxylic group is in the anionic form while the piperidine molecule appear in the protonated form. By H NMR spectroscopy and potentiometric study three pKa are found: pKa(COOH) = 3.1 (1), pKa(NHPIP) = 11.6(1) and pKa(NHSO2) = 13.8(1). The complexing ability of Tirofiban towards various metal ions (Cu(II), Ni(II), Co(II), Cd(II), Pb(II), Zn(II) and Ca(II)) is also determined by means of potentiometric studies. The prevailing species are [M(TirH)2]2+ where the ligand coordinates the metal ion through carboxylic group, while the piperidine nitrogen is still protonated. The great stability of these complexes may be due to the presence of hydrogen bond interactions, as well as the formation of stacking interactions involving the phenyl ring of the tyrosine residue.
Asunto(s)
Metales/metabolismo , Inhibidores de Agregación Plaquetaria/metabolismo , Tirosina/análogos & derivados , Tirosina/metabolismo , Enfermedad Coronaria/tratamiento farmacológico , Enlace de Hidrógeno , Concentración de Iones de Hidrógeno , Ligandos , Espectroscopía de Resonancia Magnética , Modelos Moleculares , Inhibidores de Agregación Plaquetaria/química , Inhibidores de Agregación Plaquetaria/farmacología , Potenciometría , Espectrofotometría Infrarroja , Tirofibán , Tirosina/química , Tirosina/farmacologíaRESUMEN
A solution study on the complex ability of galactaric acid (GalaH(2)) for complexation with Ca(2+), Mg(2+) and Zn(2+) ions is reported. The stability constants of the complex species are determined by means of potentiometric measurements. From the dependence of stability constants on temperature, the DeltaH degrees and DeltaS degrees values are also determined. The formation of the complex species is an endothermic process and DeltaH degrees and DeltaS degrees values suggest a chelate coordination mode of galactaric acid involving carboxylic oxygen and alpha-hydroxylic group. The prevailing species at acidic or neutral pH is [MGala] (M=Ca(2+), Mg(2+), Zn(2+)) which is also isolated in the solid state and characterised by means of IR spectroscopy. On increasing pH, the [MGalaH(-1)](-) species is also formed, where the coordinated OH group undergoes deprotonation.
Asunto(s)
Metales Pesados/química , Azúcares Ácidos/química , Calcio/química , Calcio/metabolismo , Cationes/química , Cationes/metabolismo , Estabilidad de Medicamentos , Concentración de Iones de Hidrógeno , Magnesio/química , Magnesio/metabolismo , Metales Pesados/metabolismo , Estructura Molecular , Compuestos Organometálicos/química , Espectrofotometría Infrarroja , Azúcares Ácidos/metabolismo , Termodinámica , Zinc/química , Zinc/metabolismoRESUMEN
The binary and ternary systems 2,2'-bipyridine (bpy)-M(II)-NO2psglyH2 (M(II) = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II); NO2psglyH2 = N-(2-nitrophenylsulfonyl)glycine) were investigated in aqueous solution by means of potentiometry and electron spectroscopy in order to identify the type, number and stability of the complex species as a function of pH and metal-to-ligand molar ratio. The aim is to evaluate the effect of a substituent on the phenyl ring of the N-sulfonyl amino acids on their coordination properties. The prevailing species in the binary systems is the [ML] (M = Co(II), Ni(II), Cu(II), Cd(II), Pb(II)) where the amino acid molecule is in the dianionic form and coordinates the metal ion through both carboxylic oxygen and deprotonated sulfonamidic nitrogen, while in the Mn(II)- and Zn(II)-containing binary system the only complex species found are those with the amino acid in the monoanionic form. In the ternary 2,2'-bipyridine-containing systems the chelating coordination mode of the dianionic amino acid is maintained with M(II) = Co(II), Ni(II), Cu(II), Cd(II), Pb(II) and the addition of the aromatic base also enables the Zn(II) ion to substitute for the sulfonamide nitrogen-bound hydrogen of NO2psglyH2.
Asunto(s)
2,2'-Dipiridil/metabolismo , Metales/metabolismo , Cadmio/metabolismo , Cobalto/metabolismo , Cobre/metabolismo , Electrones , Concentración de Iones de Hidrógeno , Iones , Cinética , Plomo/metabolismo , Manganeso/metabolismo , Níquel/metabolismo , Potenciometría , Análisis Espectral , Zinc/metabolismoRESUMEN
The metal binding properties of a 18-residue zinc finger peptide containing a CCHC box which reproduces one of the cysteine-rich domains of a putative nucleic acid binding protein encoded by the Fw transposable element from Drosophila melanogaster were investigated through electronic and 1H NMR spectroscopy. Dissociation constants of 2(+/- 1) x 10(-12) M and 4(+/- 1) x 10(-7) M were determined for the Zn2+ and Co2+ adduct, respectively. These values are similar to those for other CCHC-peptides investigated previously, although the length of the spacer between the second cysteine and the histidine apparently exerts some influence on the spectral properties and on the stability of the Co(2+)-peptide adduct. The 1H NMR spectrum of the present Co(2+)-derivative contains a number of well resolved hyperfine-shifted resonances between 350 and -50 ppm which arise from the metal binding residues and nearby groups. These peaks can in principle be profitably exploited to monitor protein-nucleic acid interactions.