Solvation dynamics and rotational relaxation of coumarin 153 in mixed micelles of Triton X-100 and cationic gemini surfactants: effect of composition and spacer chain length of gemini surfactants

Abstract

Solvation dynamics and rotational relaxation of coumarin 153 (C-153) in mixed micelles of non-ionic surfactant, Triton X-100 and a series of cationic gemini surfactants, 12-s-12, 2Br with varying polymethylene spacer chain length (s = 3, 6, 8, 12) at different bulk mole fractions of a surfactant were studied. Studies were carried out by means of UV-Vis absorption, steady-state fluorescence and fluorescence anisotropy, time-resolved fluorescence and fluorescence anisotropy, and dynamic light scattering measurements. While micropolarity of the environment around C-153 in mixed micelles increased, the microviscosity decreased with increasing amount of a gemini surfactant. This is because the thickness of the Stern layer of micelles increases as a result of greater extent of penetration of water molecules. Solvation dynamics and rotational relaxation of C-153 become faster with increasing mole fraction of a gemini surfactant in the mixed micelles. Increasing the thickness of the Stern layer leads to an increase in the number of water molecules hydrogen bonded among themselves, resulting in an increase in polarity and microfluidity of the environment. At a given bulk mole fraction of a surfactant, the microviscosity of micelles decreases with increasing the spacer chain length of the gemini surfactant resulting in an increase in the rate of the rotational relaxation process. However, at a given bulk mole fraction of a surfactant, solvation dynamics becomes slower with increasing spacer chain length from s = 3 to 8 because of the increasing degree of counter ion dissociation. The slow rotational relaxation process is mainly due to the lateral diffusion of C-153 along the surface of the micelles. Rotationalmotion of the micelle as a whole is much slower than the lateral diffusion of C-153.

Effect of Urea on Solvation Dynamics and Rotational Relaxation of Coumarin 480 in Aqueous Micelles of Cationic Gemini Surfactants with Different Spacer Groups

“…It depicts that C-480 is present neither at the core of the micelles nor in the bulk water, but somewhere in between these two. According to literature reports, the micropolarity of the Stern layer is similar to methanol, 50 , 51 , 53 , 69 , 70 on the basis of which we state that C-480 molecules are mostly residing in the Stern layer. It is pertinent to note that C-480 being present in the Stern layer of micelles, microenvironment remains more or less same with the addition of urea in micellar systems.…”

“…It depicts that C-480 is present neither at the core of the micelles nor in the bulk water, but somewhere in between these two. According to literature reports, the micropolarity of the Stern layer is similar to methanol, 50,51,53,69,70 on the basis of which we state that C-480 molecules are mostly residing in the Stern layer.…”

What Does Time-Dependent Fluorescence Shift (TDFS) in Biomembranes (and Proteins) Report on?

“…Coumarin-153 is one of the best examples of fluorescent dyes appropriate for TDFS studies, especially for the neat solvents (Horng et al, 1995) and micellar systems (Sonu and Saha, 2016). It shows large Stokes shift and linear solvatochromic behavior.…”

Effect of Bile Salt Aggregates on the Prototropic Equilibria of Harmine, a Fluorescent β‐Carboline Alkaloid

“…Confined environment plays a very crucial role on the photophysics of the fluorophore/drug molecule which has been well explored in the literature . Similarly, various photophysical studies of harmine have been reported in different confined systems like micelles, microemulsions and cyclodextrins ,.…”