Excited‐State Dynamics of a Photoacid: A Potential Probe for Recognizing Transition from Lamellar to Nonlamellar Inverted Structures of Liposome based Nanocarriers

Abstract

AbstractLiposomes of a cationic lipid dioctadecyldimethylammonium bromide (DODAB) are efficient nanocarriers of nucleic acids. Incorporation of a neutral lipid monoolein (MO) in excess (xMO>0.5) changes the lamellar organization of DODAB liposomes into non‐lamellar inverted structures of DODAB/MO liposomes facilitating nucleic acid delivery to cells. Photoexcitation of 8‐hydroxypyrene‐1,3,6‐trisulfonic acid (HPTS), a photoacid, initiates an excited state proton transfer (ESPT) reaction in its protonated form (ROH*) generating the deprotonated anionic form (RO−*). The fluorescence intensity ratio (IROH*/IRO−*) of these two forms is governed by the ESPT dynamics, and increases with increasing MO content (xMO) in the cationic liposomes of DODAB. Transition from lamellar organization of DODAB liposomes into non‐lamellar inverted structures of DODAB/MO liposomes, due to incorporation of MO (xMO~0.7), is manifested by a significant increase of ESPT time (τPT) and the time constant of wobbling motion (τW) of HPTS. Thus, the lamellar organizations of DODAB or DODAB‐rich (xMO 0.2) liposomes and the non‐lamellar organizations of MO‐rich (xMO~0.7) liposomes are recognized by significantly different excited state dynamics of the photoacid.