1H NMR Study of the Adsorption Mechanism for Ti-Binding Peptide on TiO2 Nanoparticles

Abstract

The interaction mechanism of Ti-binding peptide (TBP:RKLPDA) and TiO2 nanoparticles was studied at the atomic level by NMR. Saturation transfer difference (STD) experiments were performed to identify the interaction sites of TBP with TiO2 surface. Water molecules on TiO2 nanoparticle surface were selectively saturated as a function of time. The initial slopes of STD amplitude build-up curve against saturation time were calculated for TBP proton peaks and the relative values of initial slopes were compared to be R Hδ 100% as a standard, K Hε 91%, L Hδ 16%, P Hβ 26%, D Hβ 22% and A Hβ 9%, showing that residues R and K have the strongest effect of saturation transfer from the bound water molecules. This result suggests 1st residue R and 2nd K directly contact to TiO2 surface. The zeta potential of TiO2 nanoparticles was measured to be −23 mV in average, indicating that the TiO2 surface is negatively charged. Thus, both positively charged guanidine group of R and amino group of K must play a key role in interaction with the TiO2 surface by electrostatic force. NOESY experiment for TBP/TiO2 mixture and ROESY experiment for TBP alone in aqueous solution were performed. The averaged backbone RMSD of ten best matched structures were 0.76±0.19Å for TiO2 bound TBP and 1.37±0.34Å for free TBP. The calculated structures of TiO2-bound TBP were more converged than those of free TBP, indicated that conformations of TBP are restricted to much more extend when it is adsorbed to the TiO2 surface.