Synthesis of gold(III) ← gold(i)-NHC through disproportionation: The role of gold(i)-NHC in the induction of apoptosis in HepG2 cells

Starting from the proligand 2-[(6-methylpyridin-2-yl)]imidazo[1,5-a]pyridin-4-ylium hexafluorophosphate(1·PF6), three new complexes, viz. [Au(1)2] [PF6] (2), [1/2AuCl2, 1/2AuCl4]- [(1H)]+ (3), and [Au(1)Cl3] (4), have been synthesized and characterized employing different spectroscopic methods. [Au(1)Cl3] (4) has been synthesized by the disproportionation process. During the transformation of 2 to 4, the annelated proligand stabilizes both Au(i) and Au(iii), and the isolation of the intermediate (3) confirms the conversion of Au(i) → Au(iii) through the disproportionation pathway. The solid state structures of 2, 3 and 4 have been determined. Linear geometry was observed in 2, whereas complex 4 adopted square-planar geometry. Gold complexes 2 and 4 have been subjected to growth inhibitory studies. Complex 2 induced apoptosis in HepG2 cells along with increased expression of proteins involved in the mitochondrial death pathway, suggesting that apoptosis may occur via the mitochondrial death pathway.