Fluorescence properties of pyrylretinol

A fluorescent analog of retinol, 3,7-dimethyl-9-(1-pyryl)-2E,4E,6E,8E-nonat etraene-1-ol (referred to as pyrylretinol, or 1) has been synthesized. The fluorescence properties (e,g. quantum yield, Lifetime, steady-state anisotr opy, and excitation/enlission spectra) of this compound in various organic solvents and in dimyristoylphosphatidylcholine (DMPC) liposomes have been s tudied, and the results are compared with those obtained from 3-methyl-5-(1 -pyryl) -2E,4E-pentadiene-1-ol (2), which has the same fused aromatic ring system but a much shorter acyclic chain. 1 and 2 form excimer in aqueous me dia and fluorescence anisotropies of both 1 and 2 in DMPC liposomes exhibit an abrupt decrease at similar to 21-23 degrees C, which coincides with the main phase transition temperature of DMPC liposomes, indicating that both compounds may be a useful membrane probe, In addition, the binding and quen ching capability of pyrylretinol (1) to bovine serum albumin has been inves tigated, Pyrylretinol (1) binds with BSA with a binding constant of 3.6 x 1 0(4) M-1 although the value is somewhat lower than that obtained for retino l (3.06 x 10(5) M-1). Pyrylretinol(1) also quenches the BSA intrinsic fluor escence with the quenching rate constant of 1.67 x 10(13) M-1 s(-1) and the value is lower than that obtained for retinol (4.06 x 10(13) M-1 s(-1)). T he binding and quenching studies suggest that pyrylretinol (1) may serve as a useful fluorescence probe for structure/function studies of different re tinoid binding proteins.