2,2′-((Thiobis(ethane-2,1-diyl))bis(azanediyl))bis(N-(naphthalen-1-yl)acetamide) (L): A solution of 20 % NaOH (3.4 g, 0.085 mol) was added to a stirred solution of 1-naphthylamine (9.34 g, 0.051 mol) in CH2Cl2 (30 mL). The mixture was cooled to 0 °C and chloroacetyl chloride (9.29 g, 0.083 mol) was added dropwise for 45 min. After stirring at 0 °C for 100 min, the mixture was allowed to warm to RT. The aqueous layer was separated and extracted with CH2Cl2 (2×25 mL). The combined organic phases were washed with HCl (5 % v/v), NaHCO3 (5 % v/v) and H2O, dried over MgSO4 and filtered to obtain a white solid. The crude product was purified by silica column chromatography and characterized as 2-chloro-N-(1-naphthyl)acetamide (74 %).
A solution of 2-chloro-N-(1-naphthyl)acetamide (439.34 mg, 2 mmol) in tetrahydrofuran (THF; 25 mL) was added dropwise to a solution of 2,2′-thiobis(ethylamine) (120 mg, 1 mmol) and triethylamine (202.24 mg, 2 mmol) dissolved in THF (50 mL) over 1 h in an ice bath. After the addition was completed, the reaction mixture was kept at reflux for 4 h. The solvent was removed in vacuo, and the residue was washed with H2O/CHCl3 (1:3 v/v; 4×20 mL). The resulting organic phase was dried in vacuo to give L as a pink powder (407.05 mg, 84 %): 1H NMR (500 MHz, CDCl3): δ=2.81 (t, 4 H), 3.12 (t, 4 H), 3.72 (m, 4 H), 5.84 (s, 2 H), 7.41–7.59 (m, 2 H), 7.72 (m, 2 H), 7.80 (m, 2 H), 7.92 (m, 4 H), 8.10 (m, 4 H), 10.35 ppm (s, 2 H); 13C NMR (500 MHz, CDCl3) δ=30.32, 54.85, 58.37, 120.69, 124.80, 125.73, 125.90, 127.20, 128.05, 128.19, 133.03, 133.56, 169.83 ppm; IR (KBr):
=1436 ((CC)ar), 1676 (CO), 3262 cm−1 (NH); MALDI-TOF MS: m/z 487.21 [M+H]+; Anal. calcd for C28H30N4O2S: C 69.1, N 11.5, S 6.6, H 6.2, found: C 69.3, N 11.2, 6.4, H 6.6.
Preparation of AgNPs: Citrate-stabilized AgNPs of different shapes (spherical and triangular) were synthesized in aqueous solution following the Frank methodology.48 For the synthesis of AgNPs with spherical shape, sodium citrate (2.0 mL, 1.25×10−2 m), AgNO3 (5.0 mL, 3.75×10−4 m), and H2O2 (5.0 mL, 5.0×10−2 m) were. After that, freshly prepared NaBH4 (2.5 mL, 5.0×10−3 m) was added. To obtain AgNPs with triangular shape, before the addition of NaBH4, KBr (40 μL, 1.0×10−3 m) was added to the solution. Once all reagents were combined, the resulting solutions were carefully swirled to fully mix the reactants. Almost immediately, the progression of the reaction becomes evident through the visual changes consistent with the growth of silver nanoprisms. Yellow and blue colors were observed for the spherical and triangular AgNPs, respectively (see Figure 1S, Supporting Information). Using Equations 2 and 3, N=30.70D3, and the resulting spherical AgNPs solution had a concentration of CAgNP=7.8×10−10 M with AgNPs of (25±3) nm size.
Preparation of AuNPs: Preparation of AuNPs was performed following the Turkevish method49 through reduction of tetrachloroaurate ions (AuCl4−) by boiling in aq sodium citrate solution. HAuCl4⋅3 H2O (49.5 mg, 0.125 mmol) dissolved in nanopure H2O (125 mL; 18.2 MΩ cm) was added to a preheated solution of sodium citrate (12.5 mL, 1 wt %). The resulting solution was heated to 100 °C for 60 min and turned colorless before changing to violet and finally to ruby red. AuNPs obtained using this method appear as almost monodispersed globular structures with a size of (20±5) nm, which are stabilized by weakly bound citrate anions. Using Equations 2 and 3, N=30.896D3 for AuNPs and the resulting AuNPs solution was found to have a of CAuNPs=3.7×10−9 M.