Phospholipid-porphyrin conjugates: deciphering the driving forces behind their supramolecular assemblies

Phospholipid-porphyrin conjugates (Pl-Por) are nowadays considered as a unique class of building blocks that can self-assemble into supramolecular structures that possess multifunctional properties and enhanced optoelectronics characteristics compared to their monomeric counterparts. However, despite their versatile properties, little is known about the assembling mechanism of Pl-Por conjugates and their molecular organization inside these assemblies. To gain a better understanding on their assembling properties, we synthesized two new series of Pl-Por conjugates with different alkyl sn2-chain lengths linked via an amide bond to either pheophorbide-a (PhxLPC) or pyropheophorbide-a (PyrxLPC). By combining a variety of experimental techniques with molecular dynamics simulations, we investigated both the assembling and optical properties of the Pl-Por either self-assembled or when incorporated into lipid bilayers. We demonstrated that Pl-Por conjugates can form assemblies that mimic lipid bilayer structures. Moreover, our results highlight that the non-covalent interactions between porphyrin cores play a central role in controlling both the structure of the lipid bilayer membranes and their subsequent optical properties. The fluidity of the phospholipid bilayer in which the Pl-Por conjugates were incorporated, was shown to play an important role in driving their interaction within the lipid matrix. Altogether, this work could be used as guidelines for the design of new Pl-Por conjugates that self-assemble into bilayer-like supramolecular structures with tunable morphology and optical properties.