A femtosecond study of solvation dynamics and anisotropy decay in a catanionic vesicle: excitation-wavelength dependence

Dey, Shantanu ; Sasmal, Dibyendu Kumar ; Das, Dibyendu Kumar ; Bhattacharyya, Kankan (2008) A femtosecond study of solvation dynamics and anisotropy decay in a catanionic vesicle: excitation-wavelength dependence ChemPhysChem, 9 (18). pp. 2848-2855. ISSN 1439-4235

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Official URL: http://onlinelibrary.wiley.com/doi/10.1002/cphc.20...

Related URL: http://dx.doi.org/10.1002/cphc.200800658

Abstract

The structure and dynamics of a catanionic vesicle are studied by means of femtosecond up-conversion and dynamic light scattering (DLS). The catanionic vesicle is composed of dodecyl-trimethyl-ammonium bromide (DTAB) and sodium dodecyl sulphate (SDS). The DLS data suggest that 90 % of the vesicles have a diameter of about 400 nm, whereas the diameter of the other 10 % is about 50 nm. The dynamics in the catanionic vesicle are compared with those in pure SDS and DTAB micelles. We also study the dynamics in different regions of the micelle/vesicle by varying the excitation wavelength (λex) from 375 to 435 nm. The catanionic vesicle is found to be more heterogeneous than the SDS or DTAB micelles, and hence, the λex-dependent variation of the solvation dynamics is more prominent in the first case. The solvation dynamics in the vesicle and the micelles display an ultraslow component (2 and 300 ps, respectively), which arises from the quasibound, confined water inside the micelle, and an ultrafast component (<0.3 ps), which is due to quasifree water at the surface/exposed region. With an increase in λex, the solvation dynamics become faster. This is manifested in a decrease in the total dynamic solvent shift and an increase in the contribution of the ultrafast component (<0.3 ps). At a long λex (435 nm), the surface (exposed region) of a micelle/vesicle is probed, where the solvation dynamics of the water molecules are faster than those in a buried location of the vesicle and the micelles. The time constant of anisotropy decay becomes longer with increasing λex, in both the catanionic vesicle and the ordinary micelles (SDS and DTAB). The slow rotational dynamics (anisotropy decay) in the polar region (at long λex) may be due to the presence of ionic head groups and counter ions.

Item Type:Article
Source:Copyright of this article belongs to John Wiley and Sons.
Keywords:Anisotropy; Excitation Wavelength; Micelles; Solvation Dynamics; Vesicles
ID Code:77126
Deposited On:10 Jan 2012 05:55
Last Modified:10 Jan 2012 05:55

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