Translational diffusion of fluorescent probes on a sphere: Monte Carlo simulations, theory, and fluorescence anisotropy experiment

Abstract

Translational diffusion of fluorescent molecules on curved surfaces ͑micelles, vesicles, and proteins͒ depolarizes the fluorescence. A Monte Carlo simulation method was developed to obtain the fluorescence anisotropy decays for the general case of molecular dipoles tilted at an angle ␣ to the surface normal. The method is used to obtain fluorescence anisotropy decay due to diffusion of tilted dipoles on a spherical surface, which matched well with the exact solution for the sphere. The anisotropy decay is a single exponential for ␣ϭ0°, a double exponential for ␣ϭ90°, and three exponentials for intermediate angles. The slower decay component͑s͒ for ␣ 0 arise due to the geometric phase factor. Although the anisotropy decay equation contains three exponentials, there are only two parameters, namely ␣ and the rate constant, D tr /R 2 , where D tr is the translational diffusion coefficient and R is the radius of the sphere. It is therefore possible to determine the orientation angle and translational diffusion coefficient from the experimental fluorescence anisotropy data. This method was applied in interpreting the fluorescence anisotropy decay of Nile red in SDS micelles. It is necessary, however, to include two other independent mechanisms of fluorescence depolarization for molecules intercalated in micelles. These are the wobbling dynamics of the molecule about the molecular long axis, and the rotation of the spherical micelle as a whole. The fitting of the fluorescence anisotropy decay to the full equation gave the tilt angle of the molecular dipoles to be 1Ϯ2°and the translational diffusion coefficient to be 1.3Ϯ0.1ϫ10 Ϫ10 m 2 /s.

Photoinduced electron transfer from N,N-dimethylaniline to 7-amino Coumarins in protein-surfactant complex: Slowing down of electron transfer dynamics compared to micelles

“…We calculated several rotational parameters using two step and wobbling in cone model. [43][44][45][46] The two-step model describes the fact that the observed slow rotational relaxation is a convolution of the relaxation time corresponding to the overall rotation of the micelles ͑ m ͒ and lateral diffusion of the probe ͑ D ͒. The wobbling in a cone model describes the internal motion of the probe ͑ e ͒ in terms of the cone angle ͑ 0 ͒ and wobbling diffusion coefficient ͑D w ͒.…”

Increase of Fluorescence Anisotropy Upon Self‐Assembly in Headgroup‐Labeled Surfactants

“…Fluorescence lifetime can change if the fluorophore environment changes dramatically 11. Furthermore, RET can decrease r 0 and aggregation is expected to increase V 12. This work demonstrates that significant changes do occur upon self‐assembly in cases where r 0 is held constant.…”

“…Fluorescence lifetime can change if the fluorophore environment changes dramatically. [11] Furthermore, RET can decrease r 0 and aggregation is expected to increase V. [12] This work demonstrates that significant changes do occur upon self-assembly in cases where r 0 is held constant. That is to say that increases in V are not counterbalanced by decreases in t. Further discussion of these phenomena will be simplified by the use of a rotational correlation time, u ¼ (hV)/(RT).…”

Fluorescence Anisotropy to Study the Preferential Orientation of Fluorophores in Ordered Bi-Dimensional Systems: Rhodamine 6G/Laponite Layered Films

“…4-7 should include the instrumental response for the excitation and emission polarized light and an orientation factor that takes into account the possible reorientation of the transition dipole moment of the chromophores during the fluorescence lifetime. This orientation factor, which can be time-dependent, is responsible for the fluorescent depolarization of the excitation polarization in many nonrigid and randomly distributed molecular systems [87], and has been largely used to determine the rotational diffusion motion of fluorescent or labeled-fluorescent proteins and other biological systems [91][92][93]. Many processes can affect the reorientation factor.…”