Dynamic simulations of polypeptide templates to promote Ca-carbonate nuclei

Over the years, there have been a number of attempts to form synthetic organic templates that mimic dynamic processes at the interface between organic matter and mineral surfaces. One approach has been to isolate the templating matrix from mineralized tissues and examine the growth of calcium salts in the presence of this matrix. Other experiments have focused on synthetic (bio-)organic templates, such as polymers, macromolecular complexes, phospholipid vesicles, pleated polyamino acids entrapped in gelatin self-assembled monolayers on gold substrates, and Langmuir films. In the case of Langmuir monolayers, the amphiphilic molecules can be designed in such a way that they act as artificial two-dimensional nuclei for the promotion of crystal nucleation. Such films have been used as templates to direct the crystal nucleation and growth of calcium carbonate. For example, Buijnsters et al. (2001)1 used Langmuir films of amide-containing phospholipids in the presence of calcium ions to form well-defined two-dimensional domains at the air-water interface. This is the starting point of our molecular dynamics simulations. After deriving a pure-core potential set for fast molecular dynamics simulations, we have created different two-dimensional networks of amide-containing phospho¬lipids that serve as templates for Ca carbonate seed formation. We can vary the distance and structural arrangement of the functional groups to control adsorption and seed formation. The molecular dynamics runs in these calculations contain water with different concentrations of Ca2+ and CO32- ions. We have chosen a slightly different approach for polypeptide chains as template formers. Hybrids of two and three-dimensional networks of these chains with varying connectivities (chemically and structurally) were used to simulate interfaces for early seed formation. Charged (mostly negatively) functional groups on the networks allow polar carbonate surfaces to be exposed at the interface whereas in air or water (without a template), typically the non-polar surface such as (104) is the most stable one. The ultimate goal of this project is to provide systematic insight into template and, thus, seed formation control from a theoretical point of view. Ultimately, we want to understand which carbonate will form with which surface at the interface depending on the template provided.