Structure and Dynamic Properties of a Ti-Binding Peptide Bound to TiO2 Nanoparticles As Accessed by (1)H NMR...

Saturation transfer difference (STD) NMR spectroscopy is a powerful method for detecting and characterizing ligand-receptor interactions. In this study, the STD method was used to characterize the interactions of a Ti-binding peptide (TBP:RKLPDA) with TiO2 nanoparticles. The water peak in the NMR spectrum was selectively saturated, and the STD amplitudes for TBP were observed in the presence of TiO2, demonstrating that the side chains of the N-terminal residues Arg1 and Lys2 exhibit the strongest saturation transfer effect from water molecules; i.e., the two N-terminal residues are in contact with the TiO2 surface. The relaxation rate in the rotating frame, R1ρ, was observed to be high at the N-terminal residues; R1ρ decelerated toward the C-terminus, indicating that the N-terminal residues serve as anchors on the TiO2 surface and that the TBP motion bound to TiO2 particles is modeled as a wobble-in-cone with a fairly flexible C-terminus. The dissociation constant Kd of the TBP-TiO2 nanoparticle complex was 4.9 ± 1.8 mM, as estimated from the STD experiments and R1ρ measurements. The combination of these results and the negative zeta potential of the TiO2 surface validate that both the positively charged guanidyl group of Arg1 and amino group of Lys2 play key roles in interaction with the TiO2 surface by electrostatic force.