High-strength and -toughness calcite through hybridization with amino acids by sp2 to sp3 transformation

Biocalcite, which comprises organic and inorganic components, presents mechanical properties that exceed those of pure calcite. However, the mechanism by which incorporated organic components influence the structure and mechanical properties of calcite remains unclear. To investigate the structure-property relationship in biocalcite, we conducted modeling studies on the interaction between embedded amino acids and calcite. Our findings reveal the formation of C–C covalent bonds between two carboxyl groups when oxygen atoms interact with hydrogen bonds or O–H covalent bonds, suggesting a transformation in the hybrid orbital of carbon atoms from sp2 to sp3. Bader charge calculations on amino acids demonstrate that the strength of the newly formed C–C covalent bonds depends on the presence of a hydrogen atom attached to the carboxyl group. Stress-strain calculations illustrate that the overall bond order of the Ca–O ionic bonds plays a pivotal role in governing the mechanical properties of biocalcite.