1,721,059 research outputs found
Oriented crystallization of octacalcium phosphate into beta-chitin scaffold
No full textComposites of β-chitin with octacalcium phosphate (OCP) or hydroxylapatite (HAP) were prepared by precipitation of the mineral into a chitin scaffold by means of a double diffusion system. The β-chitin was obtained from the pen of the Loligo sp. squid. Only oriented precipitation of OCP was observed. The OCP crystals with the usual form of (001) blades grow inside chitin layers preferentially oriented with the {100} faces parallel to the surface of the squid pen and were more stable to the hydrolysis to HAP with respect to that precipitated in solution. Reasons are given why mechanical factors are thought to be the predominant cause for the orientation of the OCP crystals with the a-axis almost normal to the chitin fibers. We conclude that in these in vitro experiments the compartmentalized space in the chitin governs the orientation of the crystals, even if epitaxial factors may play a role in the nucleation processes. © 2001 Elsevier Science B.V. All rights reserved
Crystallization of calcium carbonate salts into beta-chitin scaffold
No full textComposites of β-chitin with calcium carbonate polymorphs were prepared by precipitation of the mineral into a chitin scaffold by means of a double diffusion system. The β-chitin was obtained from the pen of the Loligo sp. squid. The three main polymorphs of calcium carbonate: aragonite, calcite and vaterite, were observed. Their location within the matrix is a function of the polymorph. The supersaturation inside the compartmentalized space in the chitin governs the location and polymorphism of the crystals. © 2002 Elsevier Science Inc. All rights reserved
Protein crystallization on polymeric film surfaces
No full textPolymeric films containing ionizable groups, such as sulfonated polystyrene, cross-linked gelatin films with adsorbed poly-L-lysine or entrapped poly-L-aspartate and silk fibroin with entrapped poly-L-lysine or poly-L-aspartate, have been tested as heterogeneous nucleant surfaces for proteins. Concanavalin A from jack bean and chicken egg-white lysozyme were used as models. It was found that the crystallization of concanavalin A by the vapor diffusion technique, is strongly influenced by the presence of ionizable groups on the film surface. Both the induction time and protein concentration necessary for the crystal nucleation decrease whereas the nucleation density increases on going from the reference siliconized cover slip to the uncharged polymeric surfaces and even more to the charged ones. Non-specific attractive and local interactions between the protein and the film surface might promote molecular collisions and the clustering with the due symmetry for the formation of the crystal nuclei. The results suggest that the studied polymeric film surfaces could be particularly useful for the crystallization of proteins from solutions at low starting concentration, thus using small quantities of protein, and for proteins with very long crystallization time. (C) 2001 Elsevier Science B.V. All rights reserved
Structure and morphology of synthetic magnesium calcite
No full textThe X-ray crystal structure refinements of two synthetic calcite single crystals containing 3.1 and 5.7 mol% magnesium were carried out. The structure of the second crystal was also refined at -80°C. No significant structural difference from biogenic magnesium calcite was found. Magnesium within the crystals of calcite forms a solid solution over the compositional range investigated. The principal axes of vibration ellipsoids at -80°C resemble very closely those of calcite suggesting that the large thermal parameters in magnesium calcite reflect increased thermal vibrations more than positional disorder. The crystals of magnesium calcite express new rhombohedral faces due to the interaction of magnesium with growing crystals. The role of magnesium in the morphology of single crystal and globular aggregates of magnesium calcite is discussed in view of its possible relevance in both biomineralization and crystal growth
Biomimetic crystallization of calcium carbonate polymorphs by means of collagenous matrices
No full textCrosslinked gelatin films with entrapped poly-L-aspartate were used to induce the crystallization of calcite and aragonite polymorphs. Calcite with high degrees of isomorphous substitution (up to 12 mol% magnesium) has been obtained. The morphology and layered organization of magnesium calibre crystals grown inside the crosslinked gelatin films with entrapped poly-L-aspartate resemble some structural features of radial calcitic colds. The concentration of entrapped poly-L-aspartate and the uniaxial deformation of the films control the growth of aragonite aggregates inside the films. Such aggregates grown inside uniaxially deformed films consist of parallel rods with an architectural assembly similar to that found in some marine organisms. The crystals' aggregation and the control of calcium carbonate polymorphism are related to the modelling of the nucleation sites by poly-L-aspartate structure and concentration, local supersaturation and microenvironment shape. The results indicate that the collagenous matrices with entrapped polyelectrolytes are versatile systems which can contribute to the elucidation of strategies for biomimetic materials chemistry
Polymorphism and architectural crystal assembly of calcium carbonate in biologically inspired polymeric matrices f
No full textThe control of the polymorphism and architectural crystal assembly of calcium carbonate minerals in gels formed by means of collagenous matrices with entrapped polypeptides is reported. It has been observed that the calcium carbonate polymorphic selectivity is related to the local supersaturation within the microenvironment where nucleation and growth occur. This crucial parameter is controlled in terms of the entrapped additive concentration and of the tailoring of the biopolymeric scaffold by mechanical deformation. Specific orientation effects and crystal aggregation of the mineral phases can be controlled either by the charged polypeptide with a beta structure or by the structural organization of the triple helical stretches in the collagenous matrix. This results in the growth and assembly of crystals into desired shapes and sizes by molecular recognition at a definite crystal face or by the control of the organic macromolecular microenvironment fit in the emerging area of biologically inspired approach to structured inorganic materials with appropriate physical and chemical properties. © The Royal Society of Chemistry 2000
Protein crystallisation on chemically modified mica surfaces
No full textChemically modified mica sheets have been tested as heterogeneous nucleant surfaces for lysozyme, concanavalin A and thaumatin. Smooth mica surfaces with reduced hydrophilic properties and different density of ionisable groups have been prepared by a silanisation reaction using mixtures of n-propyltriethoxysilane and 3-aminopropyltriethoxysilane in different percentages starting from 0 to 100% of aminosilane. The crystallisation experiments were carried out with the hanging drop vapour diffusion technique. The results suggest that these mica surfaces act as heterogeneous nucleant agents, whose effectiveness is due to non-specific attractive and local interactions between charged residues of the protein and the ionisable groups on the mica surfaces
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