(673c) Adsorption Characterization of Biomolecular Growth Modifiers of Calcium Oxalate Monohydrate Crystals

Controlling crystallization processes can facilitate the tailoring of materials properties by modulating growth, composition, and structure. Crystal growth modifiers range from small organic molecules to macromolecules such as polymers and proteins. In nature, ensembles of biomolecular modifiers are known to mediate biomineralization, the assembly of organic-inorganic materials (e.g. bones, teeth, exoskeletons). Adsorption of biomolecules at crystal interfaces can either hinder or promote the addition of growth units and subsequently produce unique crystal habits through enhanced anisotropic growth. Understanding the fundamental principles underlying such interactions can inform the design and control of crystal habits, and forms the central objective of this work. We exemplify the study of such systems using bovine serum albumin (BSA) and its constitutive peptides along with calcium oxalate monohydrate (COM) crystals as a model system. In our previous work we have demonstrated BSA to be an effective growth modifier of COM crystals. Here we extend that work to further investigate the thermodynamic and molecular aspects of BSA-COM interactions using COM particles for adsorption isotherm experiments. Using isothermal titration calorimetry (ITC), we extract enthalpic and entropic contributions to equilibrium free energy of BSA adsorption on COM. To understand the specific and putative contributions from fragments of solvated BSA interfaces, as well as buried hydrophobic fragments, we study short peptides derived from a BSA-Trypsin digest. COM binders are identified from the digest library and their efficacies as modifiers are evaluated at the bulk scale by quantifying their effects on crystal habit. The binding thermodynamics and affinities of the lead peptides are compared to the results obtained from the native BSA protein. A key outcome of this work will be to establish rational principles for designing peptides as crystal growth modifiers from known proteins that can be applied to other proteins and crystallization processes. This has implications in understanding the fundamentals of modifier-crystal interactions, as well as in tuning structure and property of both biogenic and synthetic materials for various applications.