Theoretical Equilibrium Shape of Calcite. 2. [4̅41] Zone and Its Role in Biomineralization

• Published in: Crystal growth & design 2011-09, Vol.11 (9), p.3985-3993
• Main Authors: Aquilano, Dino, Bruno, Marco, Massaro, Francesco Roberto, Rubbo, Marco
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Exact sciences and technology; Inorganic compounds; Materials science; Methods of crystal growth; physics of crystal growth; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg2005584

The Hartman–Perdok analysis on the ⟨4̅41⟩ zone of calcite was carried out, and the calculation of the surface and attachment athermal energies was performed on both unrelaxed and relaxed surfaces by using the interatomic Rohl potential and the GULP simulation code. The flat (F) character of the {101̅4} and {112̅0} forms and the stepped (S) character of the {011̅8} and {213̅4} forms contradict the observed occurrence frequency of natural crystals: {213̅4} > {011̅8} > {101̅4} > {112̅0}. A minor reduction of the relaxed surface energy values of both {011̅8} and {213̅4} forms could be sufficient to make the theoretical equilibrium shape of the crystal composed by the {101̅4}, {011̅2}, {101̅0}, {0001}, {011̅8}, and {213̅4} forms, which can explain the richness of the growth morphology of calcite, even if water adsorption is not considered. The theoretical analysis is focused on the {213̅4} scalenohedron to understand the adsorption of the enantiomers of some amino acids. Epitaxy models are described: (i) between the D and L {213̅4} surfaces and the adsorbed 2D layers of polar {010} and {01̅0} l-Asp; (ii) between the {101̅4} surfaces and the adsorbed 1D rows and 2D Asp layers; (iii) between the D and L {213̅4} surfaces and the adsorbed 2D layers of the {011} form of the alanine crystal. Hence, the enantiospecificity of the adsorption is better explained through a “cooperative molecular” approach, instead of searching for the best interaction of a single molecule on specific surface sites.