Electron Spin Resonance and Differential Scanning Calorimetry as Combined Tools for the Study of Liposomes in the Presence of Long Chain Nitroxides

Abstract

Macroscopic and molecular techniques such as differential scanning calorimetry (DSC) and electron spin resonance (ESR), respectively, were used to characterize both structure and dynamics of liposomes built up with dioleoyltrimethylammonium propane (DOTAP) and dioleoylphosphatidylethanolamine (DOPE) lipids. These liposomes are good candidates to act as molecular carriers in cancer therapy, such as, for instance, boron neutron capture therapy (BNCT). DSC revealed that neither Tm nor ΔHm of the gel-liquid crystal phase transition depended on the presence of relatively concentrated exogenous molecules as they are the n-DSA and n-DPC spin probes used in this work. The results suggested that the structure and the internal dynamics of the liposomes did no change after small loading of the paramagnetic probes. This was proved at a molecular level by the computer analysis of the ESR spectra of the above probes, which revealed discontinuities of the motional parameters (correlation times, τ⊥ and τ∥, and order para...