Interconversion Among Different Forms of Lumichrome in Aqueous Pluronic P84 Solutions: Effects of Glucose, Urea, and Guanidine Hydrochloride

This work represents a detailed photophysical investigation of Lumichrome (LuC) in a hydrophobic triblock copolymer, Pluronic P84, as a function of the kosmotropic osmolyte, glucose, and the chaotropic osmolytes, urea and guanidine hydrochloride (GH). The spectral characteristics of LuC demonstrate that, addition of glucose lowers the critical micelle temperature (CMT) of P84, suggesting that dehydration of poly (propylene oxide) (PPO) blocks of P84 through the "sugaring-out" phenomena promotes micellization. In contrast, urea and GH increase the CMT of P84, indicating enhanced polymer hydration and weakened hydrophobic interactions that hinder micellization. Fluorescence spectra of LuC illustrate that osmolytes and temperature modulate the microenvironment of LuC. This was confirmed by finding different forms of LuC in P84 micelles with help of steady state and time resolved fluorescence emission studies. The emission spectrum shows a blueshift as temperature increases. The addition of glucose produced no significant shift in the dominant ~460 nm emission band, while additional emission features/shoulders appeared around ~530 and ~436 nm. Fluorescence lifetime data suggest that, along with 7,8-dimethylalloxazine (DMAL) form, A10, A3 and 7,8-dimethylisoalloxazine (DMIS) species of LuC may also exist within the P84 micelle. Fluorescence anisotropy measurements revealed distinct osmolyte-dependent rotational dynamics, indicating changes in the microenvironment surrounding LuC.