Formation of Complexes between the Conjugated Polyelectrolyte Poly{[9,9-bis(6′-N,N,N-trimethylammonium)hexyl]fluorene-phenylene) Bromide (HTMA-PFP) and Human Serum Albumin

The interaction between the conjugated polyelectrolyte poly{[9,9-bis(6'-N,N,N-trimethylammonium)hexyl]fluorenephenylene) bromide (HTMA-PFP) and human scrum albumin (HSA) has been investigated from changes observed in both the spectroscopic properties of HTMA-PFP and the intrinsic fluorescence of HSA. Absorption and fluorescence spectra of HTMA-PFP suggest that HTMA-PFP and HSA form polymer protein complexes due to electrostatic interactions between the cationic side chains of HTMA-PFP and the negatively charged surface of the protein. Interaction between both macromolecules induces an increase in the fluorescence signal of HTMA-PFP, which suggests that hydrophobic forces also contribute to the polymer protein complex stabilization. In addition, this interaction causes a decrease in the HSA fluorescence, partially due to static quenching and energy transfer between both macromolecules. Effects of HTMA-PFP on the thermal stability and protein conformation were explored from CD experiments. Results indicate that as polymer is added it binds to HSA and initiates unfolding. This unfolding process induces HTMA-PFP chains to become more extended, disrupting backbone interactions and increasing polymer fluorescence intensity.