Plasmon-driven substitution of 4 mercaptophenylboronic acid to 4-nitrothiophenol monitored by surface-enhanced Raman spectroscopy

TL;DR

This study investigates plasmon-driven chemical reactions on silver nanoparticles using surface-enhanced Raman spectroscopy, revealing how reaction conditions influence deboronation and substitution processes, including a novel -B(OH)2 to -NO2 substitution.

Contribution

It demonstrates how laser wavelength, power, and nanoparticle morphology affect plasmon-driven reactions and uncovers a new substitution pathway monitored by SERS.

Findings

Deboronation depends on morphology and laser parameters.

Detection of unexpected NTP formation via oxidation of hydroxylamine.

Identification of a new plasmon-driven -B(OH)2 to -NO2 substitution.

Abstract

Plasmon-driven reactions on plasmonic nanoparticles (NPs) occur under significantly different conditions from those of classical organic synthesis and provide a promising pathway for enhancing the efficiency of various chemical processes. However, these reactions can also have undesirable effects, such as 4-mercaptophenylboronic acid (MPBA) deboronation. MPBA chemisorbs well to Ag NPs through its thiol group and can subsequently bind to diols, enabling the detection of various biological structures by surface-enhanced Raman scattering (SERS), but not upon its deboronation. To avoid this reaction, we investigated the experimental conditions of MPBA deboronation on Ag NPs by SERS. Our results showed that the level of deboronation strongly depends on both the morphology of the system and the excitation laser wavelength and power. In addition, we detected not only the expected products, namely thiophenol and biphenyl-4,4-dithiol, but also 4-nitrothiophenol (NTP). The crucial reagent for NTP formation was an oxidation product of hydroxylamine hydrochloride, the reduction agent used in Ag NP synthesis. Ultimately, this reaction was replicated by adding NaNO2 to the system, and its progress was monitored as a function of the laser power, thereby identifying a new reaction of plasmon-driven -B(OH)2 substitution for -NO2.