Study on the Surface Interactions of Co(II) with Phospholipids from the Marine Environment

Abstract

Natural phospholipid (PL)n extract from cultured green algae Dunaliela tertiolecta was used as the main component of cell membranes for studies on the interaction with trace metal Co(II). The phospholipids of the membranes were extracted from other biological components using TiO2-µSPE cartridges selective for the phosphate group according to a completely new protocol. The interaction of Co(II) with natural and standard phospholipids, phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylglycerol (PG) are registered only in the presence of the additional chelating ligand 1,10-Phenathroline (Phen). 1,10-Phenathroline, as a model of humic substances in the marine environment, formed a neutral complex with Co(II) by the substitution of water molecules of central metal ions. The interaction of hydrophobic mixed-ligand complexes with phospholipids was enabled by the substitution of the remaining water molecules in the coordination shell of Co(II), which was registered by voltammetric measurements. The Co(II)-Phen-PL complex is reduced from the adsorbed state at −1.65 V by the transfer of two electrons, followed by its irreversible dissociation and desorption, indicating an EC mechanism. The interaction between the mixed-ligand complexes Co(II)-Phen-lipids was confirmed by atomic force microscopy (AFM). AFM images of PL, PL with Phen mixture and PL, Phen with Co(II) showed different 3D structures on the mica surface, indicating changes caused by the interaction between cobalt(II), 1,10-Phenanthroline and phospholipids.