Dithiosulfindene Adsorption and Reaction on Gold Nanoparticles in Water

Dithiosulfindene (DTS) is a model molecule for dithiolethiones, a class of biomedically important sulfur-rich compounds with the general formula R-1-S-S-C(-S)-R-2. Reported herein is a combined experimental and computational study of DTS interactions with plasmonic gold nanoparticles (AuNPs) in water. DTS adsorptions and reactions on AuNPs were investigated using a combination of UV-vis, Raman, and surface-enhanced Raman spectroscopy (SERS) methods. The saturation packing density of DTS on AuNPs is 596 pmol/cm(2), and its structure and conformation on AuNP surfaces depend critically on its packing density. NaOH reacts with DTS both in water and on AuNPs, converting DTS into thiosalicylic acid (TSA). TSA produced by NaOH reaction with DTS preadsorbed onto AuNPs partitions between remaining on the AuNP surfaces and being released to the supernatant of the reaction solution. UV-vis measurements revealed that NaOH reaction with DTS in solution and on AuNPs both follow first-order kinetics with a rate constant of 0.71 and 2.94 h(-1), respectively. In contrast, SERS is highly effective in detecting the completeness of the reactions and informative for identifying the reaction products, but is unreliable for either in situ monitoring of the NaOH reaction with DTS adsorbed on aggregated AuNPs or ex situ detecting of solution composition change from NaOH reaction with DTS in solution. The insights derived from this study should be important for developing an in-depth understanding of dithiolethione adsorptions and reactivities on AuNPs. This work also highlights the advantages and limitations of SERS for both in situ and ex situ monitoring of chemical reactions in solutions.