Exploring the catalytic and anticancer activity of gold(i) complexes bearing 1,3,5-triaza-7-phosphaadamantane (PTA) and related ligands

A series of water-soluble gold(i) complexes bearing phosphine ligands, [AuCl(L)] {where L = 1,3,5-triaza-7-phosphaadamantane, PTA (1); 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane, DAPTA (2); or 1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane-3,7-diylbisphenylmethanone, DBPTA (3)} and [AuCl(L)]X {where L is either PTA-CH2-C6H4-p-COOH and X = Br (4) or PTA-CH2-C6H3-p-OH-m-CHO and X = Cl (5)}, were synthesized under mild conditions and characterized with multinuclear (1H, 13C and 31P) nuclear magnetic resonance (NMR) spectroscopy, attenuated total reflection - Fourier transform infrared (ATR-FTIR) spectroscopy, matrix-assisted laser desorption/ionization - mass spectrometry (MALDI-MS) and elemental analysis. The catalytic activity of the complexes was evaluated in the peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone. Homogeneous reactions were conducted in aqueous media, while heterogeneous reactions were performed after immobilizing the complexes on porous carbon supports, including activated carbon (AC), carbon nanotubes (CNT) and their oxidized derivatives (AC-ox, AC-ox-Na, CNT-ox and CNT-ox-Na). The results demonstrated a better catalytic performance, in terms of yields and selectivity, under heterogeneous conditions depending on the nature of the carbon support. Finally, complexes 1-5 showed remarkable cytotoxicity against a selection of ovarian, lung and colon cancer cell lines, with IC50 values comparable to (or even better than) those of cisplatin. Interestingly, the most promising complexes exhibited good to excellent cytotoxicity against cancer cells while demonstrating substantial inactivity against normal ones.