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

Abstract

The present work highlights the effect of urea on solvation dynamics and the rotational relaxation of Coumarin 480 (C-480) in the Stern layer of aqueous micelles of cationic gemini surfactants, 12-4(OH)n-12 (n = 0, 1, 2). UV–visible absorption, steady-state fluorescence and fluorescence anisotropy, time-resolved fluorescence and fluorescence anisotropy, and dynamic light scattering measurements have been carried out for this study. The formation of micelles becomes disfavored in the presence of urea at high concentration. Solvation dynamics is bimodal in nature with fast solvation as a major component. The average solvation time increases, reaches a maximum, and then decreases with increasing concentration of urea because the degree of counterion dissociation also follows the same order with the addition of urea in the micellar solution. With increased degree of counterion dissociation, the extent of clustering of water molecules is increased, resulting in slower solvation process. The −OH group present in the spacer group of gemini surfactant controls the rate of solvation by shielding the water molecules from the probe molecules forming hydrogen bond. The microviscosity of micelles is decreased with increasing concentration of urea, as a result of which the rotational relaxation process becomes faster. In the presence of the −OH group in the spacer group, the microviscosity of micelles is enhanced, resulting in longer rotational relaxation time. Rotational relaxation process is bimodal in nature with the major contribution from the fast component to the fluorescence depolarization. Slow rotational relaxation is mainly due to the lateral diffusion of C-480 molecules along the surface of the micelle. The tumbling motion of the micelle as a whole is much slower than the lateral diffusion of C-480. Wobbling motion of C-480 becomes faster with increasing concentration of urea as a result of decreased microviscosity of micelles. The alignment of C-480 molecules in micelles might change with changing microviscosity.

The Effect of Electrolytes and Urea on the Ethyl Lauroyl Arginate and Cellulose Nanocrystals Foam Stability

“…As it is known from the literature, urea increases critical micelle concentration of surfactants [34], increases counterion dissociation [35], displaces the water from the surface of ionic surfactants, helps solvate the hydrophobic micelle cores by localizing at their surfaces, and changes the micelle shape and the number of surfactants associating in the micelle [36]. Recent data show urea orients at the interface within the hydrogen-bonded water network.…”

Role of Dual Nature of Ionic Liquid in Solvation Dynamics and Rotational Diffusion in Mixed Micelles: A Time‐Resolved Fluorescence and Fluorescence Anisotropy Study

“…Fast decays at a shorter wavelength are due to fluorescence from the unsolvated dipoles created in the excited state [74] . Of course, there could be a contribution from some solvated dipoles as well, which could not be detected due to the limitation of our instrument [60,75,76] . However, the growth observed at a longer wavelength is a manifestation of the solvation of the dipoles created in the excited state.…”

“…[74] Of course, there could be a contribution from some solvated dipoles as well, which could not be detected due to the limitation of our instrument. [60,75,76] However, the growth observed at a longer wavelength is a manifestation of the solvation of the dipoles created in the excited state. The excited solvated dipoles get relaxed and emit fluorescence at a longer wavelength and are thus delayed by the relaxation time.…”

Fluorescence Resonance Energy Transfer, Small-Angle Neutron Scattering, and Dynamic Light Scattering Study on Interactions of Gemini Surfactants Having Different Spacer Groups with Protein at Various Regions of Binding Isotherms

“…The concentration range chosen for each surfactant has started from a concentration much below the critical micelle concentration (cmc) and goes up to a concentration much above the cmc, that is, 0–20 mM. The cmc values of 12-4-12, 12-4­(OH)-12, and 12-8-12 reported earlier are 1.17, 0.96, and 0.72 mM, respectively. , Figure a demonstrates the changes in TICT fluorescence intensity ratios ( F / F o ) of DMASBT at 475 nm as the concentration of each of the three gemini surfactants varies. With increase in the concentration of a surfactant, fluorescence intensity initially increases and then decreases.…”

“…The cmc values of 12-4-12, 12-4(OH)-12, and 12-8-12 reported earlier are 1.17, 0.96, and 0.72 mM, respectively. 46,47 Figure 3a demonstrates the changes in TICT fluorescence intensity ratios ( F / F o ) of DMASBT at 475 nm as the concentration of each of the three gemini surfactants varies. With increase in the concentration of a surfactant, fluorescence intensity initially increases and then decreases.…”