Supplementary Material: Water soluble amphiphilic gold nanoparticles with structured ligand shells Oktay Uzun, Ying Hu, Ayush Verma, Suelin Chen, Andrea Centrone, and Francesco Stellacci* Department of Material Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA; Tel: (+1) 617-452-3704; E-mail: frstella@mit.edu Experimental Section: All chemicals were purchased from Sigma-Aldrich unless otherwise noted (all solvents were reagent grade), and were used as received. 1 H-NMR spectra were acquired by using Varian Mercury-300. Unit mass determination was done by using a Bruker Omniflex MALDI-TOF spectrometer. IR spectra of the nanoparticles were obtained using Nicolet Nexus FTIR spectrometer.. Synthesis of sodium 11-mercaptoundecanesulfonate Scheme 1: Synthetic route for the synthesis sodium 11-mercaptoundecanesulfonate Synthesis of Sodium undec-10-enesulfonate 1 : 11-Bromoundecene (1.23 g, 5 mmol), sodium sulfite Na 2 SO 3 (1.26 g, 10 mmol), benzyltriethyl-ammonium bromide (13.6 mg), MeOH (8mL), and H 2 O (18mL) were refluxed for 15 h. The mixture was extracted with ether (2x20 ml). The white crystals, precipitated on cooling the aqueous solution to 0 0 C, were filtered and dried to give 0.9 g pure S1
white solid (80%). 1 H NMR (D 2 O): 5.76 (m, 1H), 4.78 (m, 2H), 2.69 (t, 2H), 1.85 (q, 2H), 1.53 (m, 2H), 1.11 (br s, 12H). Synthesis of sodium 11-acetylthio-undecanesulfonate: The terminal alkene group was converted into thiol functionality with a modified synthesis of Whitesides et. al. 2 Specifically, Sodium undec-10-enesulfonate (0.9 g, 10 mmol) and thioacetic acid (2 ml, 26 mmol), azobisisobutylonitrile (AIBN, catalytic amt, 10mg) in methanol (20 ml) were refluxed for 6 h. The volatiles were removed in vacuo, the residue was washed several times with ether, was filtered and dried to give 0.8 g pure white solid. 1 HNMR (D 2 O): 2.69 (m, 4H), 2.17 (s, 3H), 1.53 (m, 2H), 1.39 (m, 2H), 1.11 (br s, 14H). Synthesis of 11-mercaptoundecanesulfonate acid: Sodium 11-acetylthio undecanesulfonate was refluxed in 10% HCl (20 ml) for 2 h. After removal of the solvents in vacuo, the solid was crystallized from H 2 O, white solid (0.7 g, 79%). 1 HNMR (D 2 O): 2.69 (t, 2H), 2.34 (t, 2H), 1.53 (m, 2H), 1.39 (m, 2H), 1.11 (br s, 14H). (Mass spectrum (ESI) found: m/z = 291.1068 calcd:291.1059) 2) Synthesis of water soluble nanoparticles: 0.9 mmol of gold salt (HAuCl 4 ) were dissolved in ethanol and 0.9 mmol of the desired thiol mixture were added while stirring the reaction mixture, then a saturated ethanol solution of sodium borohydride (NaBH 4 ) was added dropwise for 2 h. The solution was stirred for 3 h and the reaction vessel was then placed in a refrigerator overnight, precipitated particles were collected via vacuum filtration with quantitative filter paper. NPs were washed with ethanol, methanol and acetone and dried under vacuum. To completely remove unbound ligands, particles were dialysed using 5 inch segments of cellulose ester dialysis membrane (Pierce, SnakeSkin, MWCO 3500) that were placed in 1 L beakers of MilliQ water and stirred slowly. The beakers were recharged with fresh water ca. every 8 h over the course of 72 h. The NP solutions were collected from the dialysis tubes, and the solvent was removed under vacuum at <45 C. S2
Nanoparticle decomposition was performed by using 50mg/mL iodine in methanol stock solution. 15mg of nanoparticle was dissolved in 0.2 ml of water. Then Iodine stock solution was added into nanoparticle solution until decomposing all the particles, this was further confirmed with the absence of plasmon peak with UV-Vis Spectroscopy. Then solvent was removed under vacuum and the NMR analysis was performed. Table 1. Chemical and physical properties of the particles used in this study Nanoparticle Core Size a (nm) Standard deviation (nm) Zeta potential in PBS (mv) Ratio of Ligands in the Reaction Ratio of Ligands found by 1 H NMR b All MUS 4.34 ± 1.26-45.3 ± 4.4 100% MUS 100% MUS MUS:OT(1:2) 4.93 ± 0.91-31 ± 3.8 33% MUS 32% MUS MUS:OT(2:1) 4.5 ± 1.00-33.3 ± 6.2 66% MUS 68% MUS a On average 250 particles were counted for the size distribution analysis b Calculated from 1 H NMR analysis after decomposition of the core, data are all ± 5%. S3
D2O Acetone EtOH EtOH Figure 3. NMR spectra of the MUS:OT (2:1) particles taken in D2O CD3OD H2O Figure 4. NMR spectra of the MUS:OT (2:1) particles after decomposition with iodine acquired in CD3OD S4
Zeta potential of the Nanoparticles: Zeta potentials (ζ), were measured by BHI, ZetaPALS instrument. For pure MUS NPs we measured 45.3±4.4 mv, MUS:OT 2:1 and 1:2 had a ζ of 33.3±6.2 mv and 31.0±3.4 mv respectively with 0.2mg/mL NP solution in PBS buffer (ph 7.4). 60 50 PBS buffer, ph 7.4 Zeta Potential (- mv) 40 30 20 10 0 All MUS MUS:OT (2:1) MUS:OT (1:2) Figure 5. Zeta potential of the nanoparticles in PBS buffer (ph 7.4) 1) Y. Segall, G. B. Quistad, J. E. Casida, Synthetic Commun. 2003, 33, 2151-2159. 2) J. Tien, A. Terfort, G.M. Whitesides, Langmuir 1997, 13, 5349-5355. S5