Add time:07/22/2019         Source:sciencedirect.com

An investigation, based on the synergy between UV–Vis and FTIR-ATR spectroscopies and ElectroSpray Ionization Mass Spectrometry (ESI-MS), on the reactivity of 4-thiothymidine (S4-TdR) with H2O2, selected as a Reactive Oxygen Species (ROS) potentially related to Photo Dynamic Therapy (PDT), was performed. The nucleoside main absorption band in the UV–Vis range, centered at 337 nm, was monitored at several reaction times, confirming the S4-TdR reactivity with a process leading to thymidine (TdR), as the main reaction product, detected through its absorption at 270 nm. Actually, the generation of at least another by-product, absorbing at slightly higher wavelengths compared to S4-TdR, was inferred from UV–Vis spectra. FTIR-ATR and ESI-MS, MS/MS and MS3 measurements were then performed to unveil the nature of these reaction products, evidencing the presence of a hydroxylated S4-TdR as important intermediate reaction product. In particular, ESI-MS analyses suggested that the latter was generated as a couple of isomeric compounds, with the OH linked either to the SH group arising from C4=S tautomerization or to the methyl carbon (C7) of S4-TdR. Interestingly, the generation of a covalent dimer of S4-TdR, characterized by the presence of a disulfide (SS) bond, was also clearly inferred. The evolution of the cited products with reaction time was also be monitored using ESI-MS, confirming the role of hydroxylated S4-TdR as an intermediate towards the generation of the ultimate product, TdR. The described processes make S4-TdR a promising candidate as a molecular probe for the detection of H2O2 in PDT-related systems.

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