A fluorescent analog of retinol, 3,7-dimethyl-9-(1-pyryl)-2E,4E,6E,8E-nonatetraene-1-ol (referred to as pyrylretinol, or 1) has been synthesized. The fluorescence properties (e.g. quantum yield, lifetime, steady-state anisotropy, and excitation/emission spectra) of this compound in various organic solvents and in dimyristoylphosphatidylcholine (DMPC) liposomes have been studied, 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 media and fluorescence anisotropies of both 1 and 2 in DMPC liposomes exhibit an abrupt decrease at ∼21–23°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 quenching capability of pyrylretinol (1) to bovine serum albumin has been investigated. Pyrylretinol (1) binds with BSA with a binding constant of 3.6 × 104 M−1, although the value is somewhat lower than that obtained for retinol (3.06 × 105 M−1). Pyrylretinol (1) also quenches the BSA intrinsic fluorescence with the quenching rate constant of 1.67 × 1013 M−1 s−1 and the value is lower than that obtained for retinol (4.06 × 1013 M−1 s−1). The binding and quenching studies suggest that pyrylretinol (1) may serve as a useful fluorescence probe for structure/function studies of different retinoid binding proteins.
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Vol. 72 • No. 3