Self-assembly of reverse poloxamine induced by saccharide excipients: Insights from fluorescence

Abstract

Reverse poloxamines, a class of polyethylene oxide (PEO)/polypropylene oxide (PPO)-based amphiphiles with PPO segments placed at the periphery of their unique star-shaped molecular structure, are important building blocks for supramolecular assemblies. The reversed sequence of PEO/PPO blocks in these copolymers compared to regular poloxamines enhances chemical versatility, but limits their tendency to self-aggregate. Micellization of reverse poloxamines driven by saccharide excipients offers an interesting strategy to assemble these materials into useful, biocompatible microstructures for prospective applications. With this perspective, self-assembly of the reverse poloxamine, T90R4 has been investigated at various temperature/pH conditions in the presence of glucose and sucrose as model excipients, by spectrofluorometric techniques. Steady-state and time-resolved studies were performed using two versatile coumarin dyes as fluorescent probes to determine micelle parameters and obtain detailed insights on micropolarity, microviscosity and hydration in saccharide induced T90R4 micelles. It is found that while both glucose and sucrose induce micellization of T90R4, sucrose has a more favourable effect. The critical micelle temperatures are quite low (<10 °C), which is especially relevant considering the importance of saccharides as cryoprotectants. Furthermore, micelles can be converted from nonionic to cationic by varying the pH conditions, thus opening new opportunities for controlled assembly and clustering of the reverse poloxamines.