Synthetic Protocols and Characterization

All reagents and solvents were of reagent grade from commercial suppliers (Sigma Aldrich and etc.). ¹H (400 MHz) NMR spectra were acquired on a Bruker-400 spectrometer. Fluorescence spectra were recorded on a Shimadzu RF-5301PC fluorometer. Absorption spectra were measured on Varian Cary 100 Bio UV-Visible spectrophotometer. A microplate reader (PerkinElmer Victor2, USA) was used for resazurin and CCK-8 assay. LC-MS data were collected on a Shimadzu LCMS-2010 system. GC-TCD studies were performed on an Agilent 7820A system. CO-RMs (CORM-2, CORM-3, CORM-A1 and CORM-401) and H₂S probe (AzMC) were purchased from Sigma-Aldrich and were used without purification. Pure CO gas was purchased from Airgas company. iCORM-2 and iCORM-3 were prepared according to the literature procedures.^{12 (link), 54 (link)} CO prodrugs (CO-103 and CO-111)^{27 , 55 (link)} and H₂S probe (DNS-Az)⁵⁶ were synthesized according to the literature procedures.