Inhibitory activity of the novel Zn[(OPPh2)(SePPh2)N]2 complex towards the Platelet Activating Factor (PAF) and thrombin: Comparison with its isomorphous Co(II) and Ni(II) analogues

The Zn(OPPh₂)(SePPh₂)N]₂ complex was prepared by a metathetical reaction between a Zn(II) salt and the deprotonated form of the dichalcogenoimidodiphosphinato ligand (OPPh₂)(SePPh₂)N]⁻. X-ray crystallography revealed a pseudo-tetrahedral MO₂Se₂ coordination sphere, owed to the asymmetric (O,Se) nature of the chelating ligand. A comparison between the structural features of the M(OPPh₂)(SePPh₂)N]₂ complexes, M = Co, Ni, Zn, shows that the three complexes are isomorphous. The IR and ³¹P NMR properties of Zn(OPPh₂)(SePPh₂)N]₂ are analyzed in the framework of its crystallographic structure, and are compared with data on similar systems. The above three complexes, along with the (OPPh₂)(SePPh₂)NH ligand and SeO₂, are investigated as inhibitors of the Platelet Activating Factor (PAF) and thrombin activities. The paramagnetic M(OPPh₂)(SePPh₂)N]₂ complexes, M = Co, Ni, exhibit an approximately 65-fold increased activity, compared to diamagnetic Zn(OPPh₂)(SePPh₂)N]₂, in both the PAF- and the thrombin-induced aggregation of washed rabbit platelets (WRP). The above three complexes show a comparable significant inhibitory activity in the PAF-induced aggregation of rabbit platelet rich plasma (RPR). Remarkably, SeO₂, a form of Se present in blood, exhibits a very strong and selective inhibitory activity towards the PAF-induced aggregation of WPR. Our studies extend the dataset of metal complexes investigated as inhibitors of PAF and thrombin.