Solvent interconnectedness permits measurement of proximal as well as distant phase transitions in polymer mixtures by fluorescence

We monitored the fluorescence intensity and anisotropy of 1,6-diphenyl-1,3, 5-hexatriene (DPH) incorporated in bovine serum albumin (BSA) and dimyristo ylphosphatidylcholine (DMPC) vesicle membranes. which in turn were embedded in optically clear gelatin solutions, as a function of temperature DPH in BSA gave unanticipated large changes in fluorescence intensity and anisotro py at the instant of gelatin gel melting. Both steady state anisotropy and fluorescence intensity reported the gel-sol transition point in gelatin una mbiguously, which was independently confirmed as physical-pour point of the gel. In the case of DMPC vesicles, fluorescence intensity indicated the ge latin transition, while the anisotropy indicated DMPC phase transition. Thi s fluorescence methodology uniquely offered a common probe for two distinct transitions in two distinct domains interconnected by the solvent, water. (C) 2001 Elsevier Science B.V. All rights reserved.