The interplay of peptide sequence and local structure in TiO₂ biomineralization

Using cyclic constrained TiO₂ binding peptides STB1 (CHKKPSKSC), RSTB1 (CHRRPSRSC) and linear peptide LSTB1 (AHKKPSKSA), it was shown that while affinity of the peptide to TiO₂ is essential to enable TiO ₂ biomineralization, other factors such as biomineralization kinetics and peptide local structure need to be considered to predict biomineralization efficacy. Cyclic and linear TiO₂ binding peptides show significantly different biomineralization activities. Cyclic STB1 and RSTB1 could induce TiO₂ precipitation in the presence of titanium(IV)-bis-ammonium- lactato-dihydroxide (TiBALDH) precursor in water or tris buffer at pH 8. In contrast, linear LSTB1 was unable to mineralize TiO₂ under the same experimental conditions despite its high affinity to TiO₂ comparable with STB1 and/or RSTB1. LSTB1 being a flexible molecule could not render the stable condensation of TiBALDH precursor to form TiO₂ particles. However, in the presence of phosphate buffer ions, the structure of LSTB1 is stabilized, leading to efficient condensation of TiBALDH and TiO₂ particle formation. This study demonstrates that peptide-mediated TiO ₂ mineralization is governed by a complicated interplay of peptide sequence, local structure, kinetics and the presence of mineralizing aider such as phosphate ions.