Benchmarking Cationic Monolayer Protected Nanoparticles and Micelles for Phosphate-Mediated and Nucleotide-Selective Proton Transfer Catalysis

Both micelles and self-assembled monolayer (SAM)-protected nanoparticles are capable of efficiently hosting water-immiscible substrates to carry out organic reactions in aqueous media. Herein, we have analyzed the different catalytic effect of SAM-protected cationic nanoparticles and cationic surfactants of varying chain length towards base-catalyzed proton transfer mediated ring-opening reaction of 5-nitrobenzisoxazole (NBI) (also known as Kemp Elimination (KE) reaction). We use inorganic phosphate ion or different nucleotide (phosphate-ligated different nucleoside) as base to promote the reaction on micellar or nanoparticle interface. We find almost 2-3 orders of magnitude higher concentration of surfactants of comparable hydrophobicity required to reach the similar activity which attained by low cationic head group concentration bound on nanoparticle. Additionally, at low concentration of nanoparticle-bound surfactant or with high surfactant in micellar form, nucleotide-selectivity has been observed in activating KE reaction unlike free surfactant at low concentration. Finally, we showed enzyme-mediated nucleotide hydrolysis to generate phosphate ion which in situ upregulate the KE activity much more in GNP-based system compared to CTAB. Notably, we show a reasonable superiority of SAM-protected nanoparticles in activating chemical reaction in micromolar concentration of headgroup which certainly boost up application of SAM-based nanoparticles not only for selective recognition but also as eco-friendly catalyst. A systematic study has been reported to compare the pros and cons of both micellar and surfactant immobilized as self-assembled monolayer (SAM) on a nanoparticle system towards proton transfer catalysis. We showed the superiority of SAM compared to micelle at much lower concentration of headgroup compared to similar concentration of surfactants of even higher hydrophobicity.image

Automated summary

This study compares the catalytic effects of self-assembled monolayer (SAM)-protected cationic nanoparticles and cationic surfactants in an organic reaction. The results show that the nanoparticles exhibit higher activity at lower cationic head group concentrations compared to surfactants of similar hydrophobicity. The study also demonstrates the selectivity of nucleotides in the reaction and the enhancement of catalysis through enzyme-mediated nucleotide hydrolysis. These findings highlight the superiority of SAM-protected nanoparticles as catalysts and their potential applications in selective recognition and eco-friendly catalysis.