The fluorescence depolarization dynamics of organic fluorescent dye probes (nile red, cresyl violet, DODCI, rhodamine B, and rhodamine DPPE) were studied in cationic, anionic, and neutral micelles by picosecond time-resolved single-photon-counting technique. The fluorescence anisotropy decay of the dye intercalated inside the micelle is a two-exponential function. The anisotropy decay was interpreted by using a model of rotational (wobbling) and translational diffusion of the dye in the micelle coupled with the rotational motion of the micelle as a whole. The rotational and translational diffusion coefficients of the dye, the order parameter, and the semicone angle for the wobbling diffusion in the micelle were determined. The concept of “microviscosity” in the micelle was critically discussed in the light of the rotational and translational diffusion coefficients and their temperature dependence.

A model-free method is described for constructing time-resolved area-normalized emission spectra (TRANES) using luminescence decays at all emission wavelengths. An isoemissive point in TRANES indicates that the observed emission from the sample is due to two species only, irrespective of the origin of the two species or the excited-state kinetics. Proof for the existence of an isoemissive point in TRANES is given for various cases involving two emissive species. The isoemissive point in TRANES is qualitatively similar to the isosbestic point in time-resolved absorption spectra (TRAS) in kinetic spectrophotometry involving two species.

The mitogen-activated protein kinase (MAPK) pathways are known to be involved in various processes of growth, differentiation and cell death. In spite of their ubiquitous presence and seemingly enormous cross-talk with each other, their action is very specific. This review deals with various aspects of the three different MAPK pathways (ERK, p38 and JNK) and how their specificity is brought about.

Nile red is a widely used hydrophobic dye for probing the structure, dynamics, and environment in many biological and microheterogeneous systems. This paper reports emission-wavelength-dependent fluorescence intensity decay of Nile red in membranes and micelles. Global analysis of these multiple fluorescence decays reveals a double-exponential decay with negative amplitudes for the short-lifetime component at longer emission wavelengths. This indicates an excited-state kinetics leading to the formation of a new species in the excited state from the initially excited state. In both the cases, the short lifetime corresponds to that of the initially excited species. This excited-state kinetics is also observed in the case of viscous organic solvents such as 1-octanol and glycerol and is attributed to that of an excited-state solvent relaxation.

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.