Chirally functionalized metal nanoparticles

Abstract

Chiral ligands-protected metal nanoparticles were synthesized and characterized using transmission electron microscopy, electron diffraction, X-ray diffraction, ultraviolet-visible spectroscopy, infrared spectroscopy, thermogravimetric analysis, mass spectrometry, nuclear magnetic resonance spectroscopy and elemental analysis. Cysteine-Au nanoparticles and 2,2'-bis(diphenylphosphino)-1,1'-binaphthalene (BINAP)-capped Au/Pd nanoparticles were synthesized using a single-phase method. While the cysteine molecule binds to Au via its thiol and carboxylate groups, the BINAP molecule caps the metal core via two P atoms. Their metallic cores exhibit face-centered cubic structures. 1,1'-bi(2-naphthol) and 1,1'-binaphthalene-2,2'-diamine which are weak nucleophiles were introduced onto 11-mercapto-undecanoic acid-Au NPs using ester/amide coupling reactions. The vibrational circular dichroism (VCD) computation shows that chiral ligands-protected metal nanoparticles exhibit chirality. The ν_asCOO^- band of L-cysteine reverses its sign of Δε after capping which suggests the conformational change and the interaction between COO^- and Au. The rotation of phenyl and the reduction of the binaphthalene-angle of the adsorbed BINAP have minor influence on the VCD spectra.