Experimental and computational study of the pH dependence of dithiopurine (DTP) interaction with gold nanoparticles (AuNPs)

Understanding molecular level ligand interfacial interaction with gold nanoparticles (AuNPs) is important for AuNP applications such as catalysts, drug delivery vehicles, and so forth. As an organothiol that can undergo multiple tautomerization, protonation and deprotonation reactions, 2,6-dithiopurine (DTP) can have many different structures in solution and on AuNP surfaces. The goal of this research is to determine the structure of DTP on AuNPs at different pHs using a combination of experimental investigation and computational modeling. The experimental DTP UV-vis spectra and the DTP adsorption on AuNPs are pH strongly dependent, indicating the structural complexity of DTP in solution. The DTP SERS spectra suggest that the DTP on the AuNPs adopted mainly two specific structure compositions, indicating that the DTP structures in solution and on AuNPs can be significantly different. More advanced theoretical modeling is needed in order to understand the structural complexity of DTP in solution and on AuNPs.