title: A femtosecond study of excitation-wavelength dependence of solvation dynamics in a vesicle.
abstract: The dependence of fluorescence and solvation dynamics of coumarin 480 (C480) in a dimyristoyl-phosphatidylcholine (DMPC) vesicle on excitation wavelength (lambda(ex)) was studied with femtosecond fluorescence upconversion. The study revealed an ultrafast 1.5-ps component of solvation that was not detected earlier. C480 exhibits pronounced red-edge excitation shift (REES) by 10 nm in a DMPC vesicle. This is due to the microheterogeneity of the lipid vesicle. In lipids, the probe is distributed in different locations with varying static and dynamic electrostatic responses. Solvent relaxation becomes faster and the amount of dynamic Stokes shift decreases with increasing lambda(ex). For excitation at the red end (lambda(ex) = 430 nm), the solvation time was found to be 1.5 ps. However, for excitation at the blue end, (lambda(ex) = 390 nm), there are two substantially slower components of 250 and 2000 ps. It seems that for lambda(ex) = 390 nm, the major contribution to total emission is due to the probe (C480) molecules in the hydrophobic and restricted locations inside the lipid bilayer. Excitation at 430 nm preferentially selects the probe molecules in a highly mobile environment (water pool of the lipid).
authors: Physical Chemistry Department, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India.
authors: Pratik
authors: P
authors: Sen
authors: Subhadip
authors: S
authors: Ghosh
authors: Sudip Kumar
authors: SK
authors: Mondal
authors: Kalyanasis
authors: K
authors: Sahu
authors: Durba
authors: D
authors: Roy
authors: Kankan
authors: K
authors: Bhattacharyya
authors: Keisuke
authors: K
authors: Tominaga
mesh_terms: D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D005453:Fluorescence; D008051:Lipid Bilayers; D009682:Magnetic Resonance Spectroscopy; D009502:Neutrons; D012542:Scattering, Radiation; D012997:Solvents / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D008051:Lipid Bilayers; D012997:Solvents; D004134:Dimyristoylphosphatidylcholine