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Colodrero R.M.P.,University of Malaga | Papathanasiou K.E.,University of Crete | Stavgianoudaki N.,University of Crete | Olivera-Pastor P.,University of Malaga | And 11 more authors.
Chemistry of Materials | Year: 2012

The chemistry of metal phosphonates has been progressing fast with the addition of new materials that possess novel structural features and new properties, occasionally in a cooperative manner. In this paper, we report a new family of functional lanthanide-carboxyphosphonate materials. Specifically, the lanthanide is La, Ce, Pr, Sm, Eu, Gd, Tb, or Dy and the carboxyphosphonate ligand is 2-hydroxyphosphonoacetic acid (H 3HPA). All reported LnHPA compounds, Ln 3(H 0.75O 3PCHOHCOO) 4·xH 2O (x = 15-16), crystallize in the orthorhombic system. Two types of structures were isolated: series I and II polymorphs. For both series, the three-dimensional (3D) open frameworks result from the linkage of similar organo-inorganic layers, in the ac-plane, by central lanthanide cations, which yield trimeric units also found in other metal-HPA hybrids. Large oval-shaped 1D channels are formed by the spatial separation of the layers along the b-axis and filled with lattice water molecules. LnHPA materials undergo remarkable crystalline-to-amorphous-to crystalline transformations upon dehydration and rehydration cycles, as confirmed by thermodiffraction and NMR spectroscopy. The highest proton conductivity was observed for GdHPA (series II), 3.2 × 10 -4 S cm -1 at 98% RH and T = 21 °C. The dehydration-rehydration chemistry was also followed by photoluminescence spectroscopy. It was shown that loss and reuptake of water molecules are accompanied by clear changes in the photoluminescence spectra and lifetimes of the Eu analog (series II). Our present results reveal a wide family of well-characterized, multifunctional lanthanide-based phosphonate 3D-structured metal-organic frameworks (MOFs) that show reversible crystalline-to-amorphous- to-crystalline transformations and, at the same time, exhibit high proton conductivity. © 2012 American Chemical Society.

Montalvo G.,University of Alcalá | Montalvo G.,Instituto Universitario en Ciencias Policiales | Pons R.,CSIC - Institute of Advanced Chemistry of Catalonia | Zhang G.,Leiden Institute of Chemistry | And 3 more authors.
Langmuir | Year: 2013

PEG stearates are extensively used as emulsifiers in many lipid-based formulations. However, the scheme of the principles of the lipid-surfactant polymer interactions are still poorly understood and need more studies. A new phase diagram of a lecithin/PEG 40 monostearate/water system at 30 C is reported. First, we have characterized the binary PEG 40 monostearate/water system by the determination of the critical micelle concentration value and the viscous properties. Then, the ternary phase behavior and the influence of phase structure on their macroscopic properties are studied by a combination of different techniques, namely, optical microscopy, small-angle X-ray scattering, differential scanning calorimetry, and rheology. The phase behavior is complex, and some samples evolve even at long times. The single monophasic regions correspond to micellar, swollen lamellar, and lamellar gel phases. The existence of extended areas of phase coexistence (hexagonal, cubic, and lamellar liquid crystalline phases) may be a consequence of the low miscibility of S40P in the lecithin bilayer as well as of the segregation of the phospholipid polydisperse hydrophobic chains. The presence of the PEG 40 monostearate has less effect in the transformation to the cubic phase for lecithin than that found in other systems with simple glycerol-based lipids. © 2013 American Chemical Society.

Colacio E.,University of Granada | Maria A. Palacios,University of Granada | Antonio Rodriguez-Dieguez,University of Granada | Antonio J. Mota,University of Granada | And 3 more authors.
Inorganic Chemistry | Year: 2010

A series of one-dimensional Ni2Ln cationic complexes have been prepared by assembling the in situ generated dinuclear mesocate [Ni 2(mbpb)3]2-building block [H2mbpb is the ligand 1, 3-bis(pyridine-2-carboxamide)benzene] with Ln3+ metal ions (Ln3+ = Gd, Tb, Dy). The crystal-field potentials for the two types of site symmetries found for these 3d-3d-4f complexes (LnO7 and LnO8) are quite different, which has a direct influence on the depopulation of the Stark sublevels, the magnetic anisotropy, and the magnetic properties. © 2010 American Chemical Society.

Kellermeier M.,University of Regensburg | Melero-Garcia E.,Laboratorio Of Estudios Crystalograficos | Glaab F.,University of Regensburg | Klein R.,University of Regensburg | And 4 more authors.
Journal of the American Chemical Society | Year: 2010

In biomineralization, living organisms carefully control the crystallization of calcium carbonate to create functional materials and thereby often take advantage of polymorphism by stabilizing a specific phase that is most suitable for a given demand. In particular, the lifetime of usually transient amorphous calcium carbonate (ACC) seems to be thoroughly regulated by the organic matrix, so as to use it either as an intermediate storage depot or directly as a structural element in a permanently stable state. In the present study, we show that the temporal stability of ACC can be influenced in a deliberate manner also in much simpler purely abiotic systems. To illustrate this, we have monitored the progress of calcium carbonate precipitation at high pH from solutions containing different amounts of sodium silicate. It was found that growing ACC particles provoke spontaneous polymerization of silica in their vicinity, which is proposed to result from a local decrease of pH nearby the surface. This leads to the deposition of hydrated amorphous silica layers on the ACC grains, which arrest growth and alter the size of the particles. Depending on the silica concentration, these skins have different thicknesses and exhibit distinct degrees of porosity, therefore impeding to varying extents the dissolution of ACC and energetically favored transformation to calcite. Under the given conditions, crystallization of calcium carbonate was slowed down over tunable periods or completely prevented on time scales of years, even when ACC coexisted side by side with calcite in solution. © 2010 American Chemical Society.

Kellermeier M.,University of Regensburg | Kellermeier M.,University of Konstanz | Eiblmeier J.,University of Regensburg | Melero-Garcia E.,Laboratorio Of Estudios Crystalograficos | And 3 more authors.
Crystal Growth and Design | Year: 2012

Crystal architectures delimited by sinuous boundaries and exhibiting complex hierarchical structures are a common product of natural biomineralization. However, related forms can also be generated in purely inorganic environments, as exemplified by the existence of so-called "silica-carbonate biomorphs". These peculiar objects form upon coprecipitation of barium carbonate with silica and self-assemble into aggregates of highly oriented, uniform nanocrystals, displaying intricate noncrystallographic morphologies such as flat sheets and helicoidal filaments. While the driving force steering ordered mineralization on the nanoscale has recently been identified, the factors governing the development of curved forms on global scales are still inadequately understood. In the present work, we have investigated the circumstances that lead to the expression of smooth curvature in these systems and propose a scenario that may explain the observed morphologies. Detailed studies of the growth behavior show that morphogenesis takes crucial advantage of reduced nucleation barriers at both extrinsic and intrinsic surfaces. That is, sheets grow in a quasi-two-dimensional fashion because they spread across interfaces such as walls or the solution surface. In turn, twisted forms emerge when there is no foreign surface to grow on, such that the evolving aggregates curve back on themselves in order to use their own as a substrate. These hypotheses are corroborated by experiments with micropatterned surfaces, which show that the morphological selection intimately depends on the topology of the offered substrate. Finally, we demonstrate that, with the aid of suitable template patterns, it is possible to directly mold the shape (and size) of silica biomorphs and thus gain polycrystalline materials with predefined morphologies and complex structures. © 2012 American Chemical Society.

Eiblmeier J.,University of Regensburg | Kellermeier M.,University of Konstanz | Deng M.,University of Kiel | Kienle L.,University of Kiel | And 2 more authors.
Chemistry of Materials | Year: 2013

Mineralization of alkaline-earth carbonates in silica-rich media at high pH leads to fascinating crystal morphologies that strongly resemble products from biomineralization, despite the absence of any organic matter. Recent work has demonstrated that elaborate CaCO3 structures can be grown in such systems even at high supersaturation, as nanoparticles of amorphous calcium carbonate (ACC) were spontaneously coated by skins of silica and thus served as temporary storage depots continuously supplying growth units for the formation of crystalline calcite. In the present study, we have precipitated barium carbonate under similar conditions and found surprisingly different behavior. At low silica concentrations, there was no evidence for an amorphous carbonate precursor phase and crystallization occurred immediately, resulting in elongated crystals that showed progressive self-similar branching due to the poisoning influence of silicate oligomers on the growth process. Above a certain threshold in the silica content, rapid crystallization was in turn prevented and amorphous nanoparticles were stabilized in solution. However, in contrast to previous observations made for CaCO3, the particles were found to be hybrids consisting of a silica core that was surrounded by a layer of amorphous barium carbonate, which was then again covered by a an outer shell of silica. These self-assembled core-shell-shell nanoparticles were characterized by different techniques, including high-resolution transmission electron microscopy and elemental analyses at the nanoscale. Time-dependent studies further evidence that the carbonate component in the particles can either be permanently trapped in an amorphous state (high silica concentrations, leading to impervious outer silica skins), or be released gradually from the interstitial layers into the surrounding medium (intermediate concentrations, giving porous external shells). In the latter case, enhanced particle aggregation induces segregation of silica hydrogel with embedded amorphous BaCO3 precursors, which later crystallize in the matrix to yield complex ultrastructures consisting of uniform silica-coated nanorods. The spontaneous formation of core-shell-shell nanoparticles and their subsequent development in the system is discussed on the basis of local pH gradients and inverse pH-dependent trends in the solubility of carbonate and silica, which link their chemistry in solution and provoke coupled mineralization events. Our findings depict a promising strategy for the production of multilayered nanostructures via a facile one-pot route, which is based on self-organization of simple components and may be exploited for the design of novel advanced materials. © 2013 American Chemical Society.

Rodriguez-Ruiz I.,Laboratorio Of Estudios Crystalograficos | Delgado-Lopez J.M.,Laboratorio Of Estudios Crystalograficos | Duran-Olivencia M.A.,Laboratorio Of Estudios Crystalograficos | Iafisco M.,CNR Institute of Science and Technology for Ceramics | And 4 more authors.
Langmuir | Year: 2013

In this work, the efficiency of bioinspired citrate-functionalized nanocrystalline apatites as nanocarriers for delivery of doxorubicin (DOXO) has been assessed. The nanoparticles were synthesized by thermal decomplexing of metastable calcium/citrate/phosphate solutions both in the absence (Ap) and in the presence (cAp) of carbonate ions. The presence of citrate and carbonate ions in the solution allowed us to tailor the size, shape, carbonate content, and surface chemistry of the nanoparticles. The drug-loading efficiency of the two types of apatite was evaluated by means of the adsorption isotherms, which were found to fit a Langmuir-Freundlich behavior. A model describing the interaction between apatite surface and DOXO is proposed from adsorption isotherms and ζ-potential measurements. DOXO is adsorbed as a dimer by means of a positively charged amino group that electrostatically interacts with negatively charged surface groups of nanoparticles. The drug-release profiles were explored at pHs 7.4 and 5.0, mimicking the physiological pH in the blood circulation and the more acidic pH in the endosome-lysosome intracellular compartment, respectively. After 7 days at pH 7.4, cAp-DOXO released around 42% less drug than Ap-DOXO. However, at acidic pH, both nanoassemblies released similar amounts of DOXO. In vitro assays analyzed by confocal microscopy showed that both drug-loaded apatites were internalized within GTL-16 human carcinoma cells and could release DOXO, which accumulated in the nucleus in short times and exerted cytotoxic activity with the same efficiency. cAp are thus expected to be a more promising nanocarrier for experiments in vivo, in situations where intravenous injection of nanoparticles are required to reach the targeted tumor, after circulating in the bloodstream. © 2013 American Chemical Society.

Sleutel M.,Vrije Universiteit Brussel | Van Driessche A.E.S.,Laboratorio Of Estudios Crystalograficos | Pan W.,University of Houston | Reichel E.K.,U-Systems | And 2 more authors.
Journal of Physical Chemistry Letters | Year: 2012

Viscosity effects on the kinetics of complex solution processes have proven hard to predict. To test the viscosity effects on protein aggregation, we use the crystallization of the protein glucose isomerase (gluci) as a model and employ scanning confocal and atomic force microscopies at molecular resolution, dynamic and static light scattering, and rheometry. We add glycerol to vary solvent viscosity and demonstrate that glycerol effects on the activation barrier for attachment of molecules to the crystal growth sites are minimal. We separate the effects of glycerol on crystallization thermodynamics from those on the rate constant for molecular attachment. We establish that the rate constant is proportional to the reciprocal viscosity and to the protein diffusivity. This finding refutes the prevailing crystal growth paradigm and illustrates the application of fundamental kinetics laws to solution crystallization. © 2012 American Chemical Society.

Van Driessche A.E.S.,Laboratorio Of Estudios Crystalograficos | Garcia-Ruiz J.M.,Laboratorio Of Estudios Crystalograficos | Delgado-Lopez J.M.,Laboratorio Of Estudios Crystalograficos | Sazaki G.,Laboratorio Of Estudios Crystalograficos
Crystal Growth and Design | Year: 2010

In this work we studied the kinetics of gypsum crystals growing from aqueous solutions as a function of temperature and supersaturation. Laser confocal differential interference contrast microscopy (LCM-DIM) and atomic force microscopy (AFM) were used to observe in situ the step advancement and the evolution of the surface morphology of the {010} face. We found that, for the experimental conditions used in this study, 2D nucleation is the main step generation mechanism, even at low supersaturations, and only a few spiral hillocks were observed. Due to the elongated morphology of 2D islands along the c-axis and the frequent nucleation of multilayer 2D islands, {010} faces growing from a supersatured solution developed a "hill and valley" topography. This type of surface topography is observed at all temperatures. The step kinetic coefficient, βst, was determined in the temperature range 20-80 °C, and a steep increment in the kinetic coefficient is found with increasing temperature. From these data, the activation barrier for incorporation of building units in the {010} face was determined to be 70.7 ± 5.0 kJ/mol. Analysis of the kinetic data shows that at low temperatures (≤40 °C) growth of the {010} face is dominated by a mixed regime and at higher temperatures (>40 °C) growth is controlled solely by diffusion. © 2010 American Chemical Society.

Sleutel M.,Vrije Universiteit Brussel | Sazaki G.,Hokkaido University | Van Driessche A.E.S.,Laboratorio Of Estudios Crystalograficos
Crystal Growth and Design | Year: 2012

The morphology and step kinetics of 2D islands and spiral hillocks of lysozyme crystals growing from purified and contaminated solutions were determined and compared. It was found that the morphology and step dynamics of spiral hillocks of lysozyme crystals are less affected by the presence of impurities in the growth solution as compared to steps generated by 2D nucleation. These observations could be satisfactorily explained considering the terrace exposure time of spiral hillocks (τ sp) and 2D islands (τ 2D) and the characteristic impurity adsorption time (τ i). For lysozyme, overlapping time scales of terrace exposure and impurity adsorption exist and τ i ≈ τ sp < τ 2D. Hence, when crystal growth is dominated by spiral hillocks, less impurities are adsorbed onto the crystal surface and a more pure crystal lattice is formed. Although spiral hillocks reduce the effect of impurities, they do play a significant role in the mechanism of step bunching. © 2012 American Chemical Society.

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