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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.

Montalvo G.,University of Alcala | 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.

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.

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.

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