Photophysical Studies of Novel Ruthenium Metal-Ligand Complexes Incorporated in Model Lipid-Membrane Bilayers

Abstract

We have designed and synthesized ruthenium metal-ligand complexes (MLCs) with amine- or acyl-reactive functional groups. The MLCs have potential as luminescent probes to investigate bio-macromolecular dynamics on the sub-microsecond-to-microsecond timescale. This timescale is of interest, for example, for analysis of the motions associated with macro-molecular assemblies and interactions of membrane-bound proteins. Here we report the photophysical and structural properties of MLCs (1) [HRu(CO)(4,4′-dicarboxy-bipyridyl)(PPh3)2]+ [PF6]- conjugated to dipalmitoyl-phosphatidyl-ethanolamine (DPPE), (2) [HRu(CO)(bpy) (PPh2C2H4COOH)2]+ [PF6]- conjugated to dimyristoyl-phosphatidyl-ethanolamine (DMPE) and (3) [(CF3CO2)Ru(CO) (5-aminophen)(Ph2PC2H2PPh2)]+ [PF6]- conjugated to DPPE and cholesterol. These conjugates were incorporated in 100nm-diameter-unilamellar lipid-membrane vesicles to investigate the photophysical properties of the probes in a model membrane environment and to evaluate the utility of these probes for investigating the physical properties of lipid membranes. We are also investigating the photophysical behavior of MLCs in Nanodiscs, which are ∼10nm-diameter phospholipid bilayers surrounded by a recombinant scaffold protein. We are using Nanodiscs as a platform for investigating the dynamics of transporter proteins, and we are using the MLCs as tools to characterize the physical properties of the Nanodisc-transporter assembly.