Preparation of TiO2 particles with13C Silk-TBP on the surface.
The nanoparticles of TiO2 (Aeroxide TiO2P25), which were kindly provided by NIPPON AEROSIL co., JP, had an average particle size of 21 nm and a surface area of 50 ± 15 m2/g. The TiO2 nanoparticles were suspended in water and sonicated twice for 30 min with a 50% duty cycle. The suspension was then centrifuged at 10,000 rpm for 15 min, and the precipitated TiO2 nanoparticles were washed in distilled water. This process was repeated, and the particles were dried overnight. The dried particles were suspended in 20 mM phosphate buffer at pH = 7.0 and sonicated again for 10 min with a 50% duty cycle. The peptides (TBP, (AGSGAG)2, and Silk-TBP) were dissolved in 20 mM phosphate buffer and mixed with the suspended TiO2 nanoparticle solutions, respectively. The weight ratio of the peptide and suspended TiO2 nanoparticle was 1:1 for each case. Finally, the state of dispersion of the mixture after standing overnight was observed.
Solid-state 13C CP/MAS NMR Measurement .
The 13C Silk-TBP (20 mg) was dissolved in 20 mM phosphate buffer at pH = 7.0 (10 ml) and mixed with the TiO2 nanoparticles (50 mg). The solution was stirred for 4 h at 100 rpm to reach equilibrium. Then equilibrated. Then the suspension was centrifuged at 10,000 rpm for 10 min and excess peptide dissolved in the supernatant was removed. This process was repeated. Thus, TiO2 particles with 13C Silk-TBP adsorbed on the surface were obtained after drying. The13C CP/MAS NMR spectra of the 13C Silk-TBP and 13C Silk-TBP adsorbed on the surface of TiO2 nanoparticles were recorded on a Bruker Avance 400 NMR spectrometer with an operating frequency of 100.0 MHz for13C at a sample spinning rate of 8 kHz in a 4 mm diameter ZrO2 rotor. The numbers of scans were 1 K for13C Silk-TBP and 40 K for 13C Silk-TBP adsorbed on the TiO2 nanoparticles. The pulse delay was 5 s and contact time was 2 ms. The 13C chemical shifts were referenced to TMS using adamantane as a secondary standard (13CH peak at 28.8 ppm).