Effect of the Compartmentalization Into Liposome's Cavity on the Relaxation Times of F- and PF6 - Anions

: The entrapment of fluoride (F-) and hexafluorophosphate (PF6 -) anions within liposome inner cavities significantly alters their magnetic resonance properties, offering potential advancements in imaging technologies. This study addresses the need for improved MRI contrast agents, particularly those enabling precise monitoring of drug delivery systems. By leveraging the unique interaction between these anions and the liposomal membrane, we investigate their effects on nuclear magnetic relaxation. Specifically, we observe that both longitudinal (T1) and transverse (T2) relaxation times of the nuclei associated with the encapsulated anions are substantially shortened. This relaxation enhancement is dependent on vesicle size, being more pronounced for smaller liposomes, and varies with anion type and concentration. Notably, PF6 - induces a greater reduction in T1 and T2 relaxation times compared to F-. The observed effects are attributed to the dynamic interactions between the anions and the liposomal bilayer, which are modulated by the vesicle's physicochemical properties. The results reveal a striking two-order magnitude decrease in the 19F T1 of liposomes loaded with PF6 -, demonstrating their potential utility as sensitive MRI reporters. This work underscores the broader implications of tailoring liposome compositions for specific biomedical applications. The study not only advances the understanding of liposome-anion interactions but also establishes a pathway for the development of novel contrast agents with high sensitivity and specificity, bridging the gap between material science and clinical imaging innovations.