Supporting Information. Biomimetic Dopamine Derivative for Selective Polymer Modification of Halloysite Nanotube Lumen

Transcription

1 Supporting Information Biomimetic Dopamine Derivative for Selective Polymer Modification of Halloysite Nanotube Lumen Weng n Yah, Hang Xu, Hiroe Soejima, Wei Ma, Yuri Lvov and Atsushi Takahara* Experimental section Materials Halloysite was obtained from Applied Minerals Inc. Aluminium oxide (80 nm, Wako Pure Chemicals), silica microsphere (500 nm, Polysciences Inc.), copper(i) bromide (CuBr, Wako Pure Chemicals, 99.9%), 2-bromoisobutyryl bromide (Sigma-Aldrich, 98%), 2,2 -Bipyridyl (bpy, Wako Pure Chemicals, 99.5%), 2,2,2-trifluoroethanol (TFE, Acros, 99.9%), dopamine hydrochloride (Sigma-Aldrich co.), imidazole (Wako Pure Chemicals, 98%), and chlorotriethylsilane (TESCl, Tokyo Chemical Industry, co. Ltd., >97.0%) were used as received. Methyl methacrylate (Wako Pure Chemicals, 98.0%) was distilled under vacuum before polymerization. Silicon wafer and alumina plate were cut into 1 cm x 1 cm pieces, cleaned by ultrasonication using acetone, 2-propanol, and subsequently exposed to vacuum ultraviolet-rays for 10 min under 30 Pa. Scheme S1. Synthesis of Dopa Synthesis of 2-bromo-N-[2-(3,4-dihydroxyphenyl)ethyl]-isobutyryl amide (Dopa) The synthesis of the dopamine based ATRP initiator Dopa was performed using similar method as described elsewhere. 1-5 Triethylsilyl chloride (TESCl, 50.0 mmol) was added dropwise via dropping funnel into a solution consisting of dopamine hydrochloride (42.0 mmol) and imidazole (50.0 mmol) in 150 ml dry purified CH 2 Cl 2, after stirred for 4 h at room temperature. The resulting solution was cooled in an ice bath and 2-bromoisobutyryl bromide (46.0 mmol diluted with CH 2 Cl 2 ) was added into the S1

2 reaction mixture at 0 ºC using a dropping funnel. The ph of the solution was maintained at 6-7 with addition imidazole (128.0 mmol). The reaction mixture was stirred for 12 h at room temperature under anhydrous conditions. The solvent was evaporated under reduced pressure to give yellowish liquid. The crude product was further purified by silica gel column chromatography (6 % ethyl acetate in hexane) to give colorless liquid of Pro-Dopa. The protected initiator (16.7 g, 31.5 mmol, yield 74.7 %) was determined by 1 H NMR (400 MHz, CDCl 3 ): δ (aromatic, 3H), 3.50 (q, 2H), 2.75 (t, 2H), 1.94 (s, 6H), 0.95(t, 18H), 0.53 (q, 12H). The TES protected initiator was further deprotected by acid condition using HCl (2N) in THF to give white solid of Dopa. 1 H NMR (400 MHz, CDCl 3 ): δ (aromatic, 3H), 3.50 (q, 2H), 2.75 (t, 2H), 1.94 (s, 6H). NH H Br Al rich surface NH H Br Br SI-ATRP n NH Si rich surface Halloysite Halloysite-Dopa Halloysite-Dopa-PMMA Scheme S2. Anchoring of Dopa initiator and Subsequent SI-ATRP. Surface Modification of Halloysite with Dopa Flask containing Dopa and halloysite suspension (Dopa/halloysite = 0.5/1, w/w) in THF:H 2 (4:1) was mixed under magnetic stirring at room temperature for 48 hours. The solution was stirred and evacuated using a vacuum pump. The slight fizzing of the suspension indicated that air was being removed from the lumen of the halloysite tubules and replaced with Dopa solution. The final product was washed with THF:H 2 (4:1), collected by five sonication-centrifugation cycles and dried under reduced pressure. Modifications of aluminium oxide and silica substrate/nanoparticle were performed in similar manner. Surface initiated-atrp (SI-ATRP) of MMA from Halloysite Surface A typical protocol for the SI-ATRP was as follows: 1g of halloysite-dopa, 2 g of MMA monomer and 4g of TFE solution were charged in a well-dried glass tube with a stopcock and degassed by the freeze-thaw process three times. CuBr (0.03 mmol) and bpy (0.06 mmol) were introduced into another glass tube, which was degassed by five S2

3 cycles of vacuum pumping and flushing with argon. The copper catalyst solution was degassed by repeated freeze-thaw cycles and then injected to the monomer solution. The resulting reaction mixture was again degassed by repeated freeze-thaw cycles to remove the oxygen and stirred in an oil bath at 60 C for 24 h generate a PMMA brush from halloysite lumen. The reaction was stopped by opening the glass vessel to air. The reaction mixture was poured into methanol to precipitate halloysite-dopa-pmma. The halloysite-dopa-pmma were washed with THF and centrifuged for five times to remove the weakly bound polymer adsorbed on halloysite surface, and were dried under reduced pressure. In a control experiment, ATRP of pure halloysite (without Dopa initiator) was carried out under same polymerization condition and denoted as halloysite-control. Instrumentation. Fourier transform infrared (FT-IR) measurements were carried out on a Spectrum ne (Perkin Elmer, Japan Co., Ltd) using KBr pellets. The thermal gravimetric analysis (TGA) was performed o a Seiko SII-EXSTAR 600 TG/DTA 6200 thermobalance with heating rate of 10 C min -1 under nitrogen. 1 H NMR spectra were recorded in chloroform-d at 25 C using a Bruker AV-400 spectrometer ( 1 H MHz). The chemical shifts in ppm were referenced to the tetramethylsilane (δ 0) internal standard. 13 C solid-state NMR spectra were obtained on a JEL ECA400 spectrometer at 400 MHz (spinning rate, 15 khz) using a cross-polarization sequence with a 5 ms contact time and a 3s relaxation delay; chemical shifts were measured relative to tetramethylsilane (TMS) using hexamethylbenzene (HMB) as a secondary reference (δ = ppm assigned to aromatic carbon and 16.9 ppm assigned to aliphatic carbon). TEM images were obtained with JEL JEM-2200FS electron microscope operating at an acceleration voltage of 200 kv, which was equipped with a Gatan USC4000 CCD camera. Samples for TEM observation were deposited from a suspension in ethanol for unmodified and modified halloysite onto carbon coated copper grid. XPS measurements were carried out on an XPS-APEX (Physical Electronics Co. Ltd.) at 1 x 10-6 Pa using a monochromatic Al-Kα X-ray source of 300 W. All of the XPS data were collected at a takeoff-angle of 45 and a low-energy (25 ev) electron flood gun was used to minimize sample charging. The survey spectra ( ev) and high-resolution spectra of the 1s, Al2p, Si2p, C1s, N1s, and Br3d regions were acquired at pass energies for the analyzer of and 25.0 ev, respectively. An X-ray beam was focused onto an area with a diameter of ca. 0.2 mm. S3

4 Absorbance (a.u.) Dopa Halloysite-Dopa Halloysite-Dopa-PMMA Wavenumber (cm -1 ) Figure S1. FTIR spectra of Dopa, halloysite-dopa and halloysite-dopa-pmma. Table S1. Surface analysis results of bare Al and Si substrate before and after Dopa treatment Atomic % 1s Al2p Si2p C1s N1s Br3d Bare Substrate Alumina <0.1 <0.1 Silica Rinsed+Sonication Alumina-Dopa Silica-Dopa S4

5 Intensity (a.u.) 1s Halloysite Halloysite-Dopa C 1s Si 2s Al 2s Si 2p Al 2p Halloysite-Dopa-PMMA Halloysite-control Binding Energy (ev) Figure S2. XPS survey spectra of halloysite, halloysite-dopa, halloysite-dopa-pmma, and halloysite-control. 0-5 TG (%) Halloysite Halloysite-Dopa Halloysite-Dopa-PMMA Temperature ( o C) Figure S3. TGA thermograms of halloysite, halloysite-dopa and halloysite-dopa-pmma. S5

6 References (1) Fan, X.; Lin, L.; Dalsin, J. L.; Messersmith, P. B. J. Am. Chem. Soc. 2005, 127, (2) Majewski, A. P.; Schallon, A.; Jerome, V.; Freitag, R.; Muller, A. H. E.; Schmalz, H. Biomacromolecules 2012, 13, (3) Fan, X.; Lin, L.; Messersmith, P. B. Biomacromolecules 2006, 7, (4) Fan, X.; Lin, L.; Messersmith, P. B. Compos. Sci. Technol. 2006, 66, (5) Neoh, K. G.; Kang, E. T. ACS Appl. Mater. Interfaces 2011, 3, S6