Figure 1.

Preparation and functionalization of nanodiamonds (NDs) with lysine in the presence of a three-carbon-length linker: (A) synthesis of compound 1 [N′-(N^α,N^ε-bis-Boc-lysyl),N″-(Fmoc)-diaminopropane], reagents, and solvents – Fmoc-NH(CH₂)₃NH₂ · HCl, HATU [N,N,N′,N′-tetramethyl-O-(7-azabenzotriazol-1-yl) uronium hexafluorophosphate], diisopropylethylamine, and dimethylformamide (DMF); (B) Fmoc deprotection, reagents, and solvents – 50% (v/v) piperidine-DMF; (C) reoxidation of pristine carboxylated NDs, reagents – concentrated sulfuric acid and concentrated nitric acid, and preparation of acid chloride–functionalized NDs, reagents – thionyl chloride; (D) synthesis of Boc-protected lysine-functionalized NDs, solvent – DMF; (E) deprotection of Boc on lysine-functionalized NDs, reagents, and solvents – hydrochloric acid and dichloromethane.