The composition of biologic molecules isolated from biominerals suggests that control of mineral growth is linked to biochemical features. Here, we define a systematic relationship between the ability of biomolecules in solution to promote the growth of calcite (CaCO 3) and their net negative molecular charge and hydrophilicity. The degree of enhancement depends on peptide composition, but not on peptide sequence. Data analysis shows that this rate enhancement arises from an increase in the kinetic coefficient. We interpret the mechanism of growth enhancement to be a catalytic process whereby biomolecules reduce the magnitude of the diffusive barrier, E k, by perturbations that displace water molecules. The result is a decrease in the energy barrier for attachment of solutes to the solid phase. This previously unrecognized relationship also rationalizes recently reported data showing acceleration of calcite growth rates over rates measured in the pure system by nanomolar levels of abalone nacre proteins. These findings show that the growth-modifying properties of small model peptides may be scaled up to analyze mineralization processes that are mediated by more complex proteins. We suggest that enhancement of calcite growth may now be estimated a priori from the composition of peptide sequences and the calculated values of hydrophilicity and net molecular charge. This insight may contribute to an improved understanding of diverse systems of biomineralization and design of new synthetic growth modulators.biomineral ͉ calcite ͉ proteins

Polyaspartate domains are a prominent feature of proteins associated with biogenic carbonates and have been implicated in modifying crystal morphology through specific interactions with step edges. Here, we show that the morphology and growth kinetics of calcite are modified in a systematic way when a series of poly-L-aspartates, Asp 1-6 , are introduced into solution. In-situ measurements of step propagation rates by atomic force microscopy reveal these effects are strongly chain-length dependent and specific to the crystallographically distinct, obtuse and acute step types. Direct observations of differential roughening and rounding of the step edges demonstrate that, while Asp 1 and Asp 2 have stronger effects on acute step edges, a crossover occurs for the longer Asp 4,5,6 peptides that preferentially affect obtuse steps. Independent analysis of Asp n -step edge interactions by semiempirical quantum mechanical modeling gives estimates of aspartate-step edge binding energies and predicts that the crossover should occur at n ) 2. The switch occurs because, upon Asp n binding, the energy required to dehydrate acute steps is greater than that at the obtuse steps when n ) 3-6.Step velocity measurements show that the concentration of Asp n needed to stop growth scales exponentially and inversely with the calculated binding energies. A simple model of Asp n adsorption to the steps is derived from these results. These findings suggest a process by which small fluctuations in primary structure in proteins can control calcite shape.

The real (n) and imaginary (k) refractive indices of an immobilized monolayer of 27 nucleotide (nt) single stranded DNA (ssDNA) and the corresponding double stranded DNA (dsDNA) are measured in the 255-700 nm range. Multiple techniques are used to obtain consistent estimation. The coverage is approximately 6.5% with an average interchain distance of tethered ssDNA molecules of approximately 11.8 nm, which is significantly larger than the "footprint" of the chain on the surface. The measured increase in n by approximately 5% between the ssDNA and the dsDNA is 20% smaller than the expected change due to doubling of the molecular weight. The change in k is not significant, indicating that the electron delocalization effect expected in dsDNA due to base pair stacking is not important at optical frequencies.