Novel N-heterocyclic carbene silver(I) complexes: Synthesis, structural characterization, and anticancer activity

In this study, we synthesized four novel unsymmetrically substituted NHC ligands (la-d) and their Ag(I) complexes (2a-d). All new compounds were characterized using elemental analysis, FT-IR, H-1 NMR, and C-13 NMR spectroscopy and X-ray crystallography. The molecular structure of complex 2d was elucidated through single crystal X-ray diffraction analyses. Single crystal structural studies for complex 2d show that the benzene rings (C9-C14) and the central benzimidazole ring system make dihedral angles of 85.65(11)degrees. The Ag-Cl and Ag-C single bond lengths are 2.3553(7) and 2.096(2)angstrom, respectively. The C-Ag-C/ bond angle is 168.27(7)degrees. Both salts and complexes were tested for their anti-cancer potential against three human cancer cell lines (DU-145, MCF-7, and MDA-MB-231) and non-cancer cells adipose from mouse (L-929) for 24 h, 48 h and 72 h using the MTT assays. However, the Ag(I)-NHC complexes (2a-d) showed a dose and time-dependent cytotoxic activity against all cell lines. MDA-MB-231 human breast carcinoma cells were the most sensitive to the Ag(I)-NHC complex displaying IC50 lower than 1 mu M all time points. Further, the IC(50)s for Ag(I)-NHC were higher in non-cancer cells, suggesting that complexes possessed noteworthy selectivity for human cancer cells.