147 research outputs found
Polymorphism, Structure, and Nucleation of Cholesterol·H2O at Aqueous Interfaces and in Pathological Media: Revisited from a Computational Perspective
No full textWe revisit the important issues of polymorphism, structure, and nucleation of cholesterol center dot H2O using first-principles calculations based on dispersion-augmented density functional theory. For the lesser known monoclinic polymorph, we obtain a fully extended H-bonded network in a structure akin to that of hexagonal ice. We show that the energy of the monoclinic and triclinic polymorphs is similar, strongly suggesting that kinetic and environmental effects play a significant role in determining polymorph nucleation. Furthermore, we find evidence in support of various O-H center dot center dot center dot O bonding motifs in both polymorphs that may result in hydroxyl disorder. We have been able to explain, via computation, why a single cholesterol bilayer in hydrated membranes always crystallizes in the monoclinic polymorph. We rationalize what we believe is a single-crystal to single-crystal transformation of the monoclinic form on increased interlayer growth beyond that of a single cholesterol bilayer, interleaved by a water bilayer. We show that the ice-like structure is also relevant to the related cholestanol center dot 2H(2)O and stigmasterol center dot H2O crystals. The structure of stigmasterol hydrate both as a trilayer film at the air-water interface and as a macroscopic crystal further assists us in understanding the polymorphic and thermal behavior of cholesterol center dot H2O. Finally, we posit a possible role for one of the sterol esters in the crystallization of cholesterol center dot H2O in pathological environments, based on a composite of a crystalline bilayer of cholesteryl palmitate bound epirmrially as a nucleating agent to the monoclinic cholesterol center dot H2O form
Stereochemistry at the Interface between Crystals and Biology: Extended Abstract of the 1998 Prelog Lecture
No full textHandbook of Biomeralization. Edited by Edmund Bäuerlein, Peter Behrens, and Matthias Epple.
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Handbook of Biomineralization. Herausgegeben von Edmund Bäuerlein, Peter Behrens und Matthias Epple.
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Crystallization Pathways in Biomineralization
No full text A crystallization pathway describes the movement of ions from their source to the final product. Cells are intimately involved in biological crystallization pathways. In many pathways the cells utilize a unique strategy: They temporarily concentrate ions in intracellular membrane-bound vesicles in the form of a highly disordered solid phase. This phase is then transported to the final mineralization site, where it is destabilized and crystallizes. We present four case studies, each of which demonstrates specific aspects of biological crystallization pathways: seawater uptake by foraminifera, calcite spicule formation by sea urchin larvae, goethite formation in the teeth of limpets, and guanine crystal formation in fish skin and spider cuticles. Three representative crystallization pathways are described, and aspects of the different stages of crystallization are discussed. An in-depth understanding of these complex processes can lead to new ideas for synthetic crystallization processes of interest to materials science. </jats:p
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