Surface Selectivity of Calcite on Self-Assembled Monolayers

Abstract

A series of molecular dynamics simulations has been performed to analyze in detail the structure of 16-mercaptohexadecanoic acid (even) and 15-mercaptopentadecanoic acid (odd) self-assembled monolayers (SAMs) and their interface with calcium carbonate prior to crystallization. Small structural differences are noted between the odd and even SAMs that cause the headgroup arrangement of the odd SAM to change its local coordination from six nearest neighbors to a 5 + 1 arrangement. It is observed that the disordered calcium carbonate forms layers of cations and anions at the charged interface with the SAM, and this layering predisposes the structure toward the (012) calcite surface and away from the (001) calcite surface. Calculated interfacial energies of the SAM–calcium carbonate interface demonstrate that the even SAM has a far stronger interaction with the calcium carbonate than the odd due to the better alignment of the headgroups and is therefore able to stabilize the growing calcite nucleus, leading to selective growth. Both the predicted orientational order and interfacial energies are in reasonable agreement with experimental observations.

Crystallisation rates of calcite from an amorphous precursor in confinement

“…The carbonate ions in the (01.2) surface have a fairly large φ angle of 63 • , compared with φ = 0 • for the (00.1) surface. Consequently, as noted in [29], the φ-distribution in ACC has a much closer resemblance to that in (01.2). This can be seen to be the case in Figures 5b and 5c where the φ-distribution of the second carbonate layer is plotted for both (01.2) and (00.1) at the three stages labelled in Figure 5a: A) pre-crystallisation, B) midway through, and C) post-crystallisation.…”

Octacalcium phosphate – a metastable mineral phase controls the evolution of scaffold forming proteins

“…Recently, an indirect example of such strategy has been provided for template controlled nucleation of calcite on self-assembled monolayers (SAMs) by Hamm et al 65 By an appropriate choice of the functional group chemistry (COOH, PO 4 , SH or OH) of the head groups of the SAMs and the conformation of their molecules (length of alkanethiol chains) the stereochemical matching has been changed. As shown by atomistic simulation, 66 the structural motifs of the growing calcite nuclei cause a distinctive change in the arrangement of the head groups of the SAM. The selforganized structure selection of the macromolecular template results in different shapes of calcite crystals grown on the SAMs.…”

Reconciling disparate views of template-directed nucleation through measurement of calcite nucleation kinetics and binding energies

“…Monolayers with a constant chain length show chemistry-specific effects with lower values of γ for surfaces of (i) C16-COOH compared with C16-SH and (ii) C11-SH compared with C11-PO 4 . Differences in chain length, likely through a combination of head group spacing and conformation (16,20,(33)(34)(35), also affect γ as evidenced by the significantly lower value for C16-SH compared with C11-SH. The very low number of crystallites that formed on C11-OH surfaces prevented reliable estimation of nucleation rates, and these data were not further analyzed.…”

“…SAM structure and packing, which are strongly influenced by chain length (39,40), have a strong control on calcite nucleation. A recent molecular dynamics analysis suggests these effects may be related to the degree of symmetry in interactions between SAM monomers and its impact on SAM order, highlighting once again the importance of cooperativity in both SAM-crystal-binding and templatedirected nucleation (35).…”