Ultrafast FRET to Study Spontaneous Micelle‐to‐Vesicle Transitions in an Aqueous Mixed Surface‐Active Ionic‐Liquid System1. Issue 16 (5th September 2014)

• Record Type: Journal Article
• Authors: Mandal, Sarthak; Kuchlyan, Jagannath; Banik, Debasis; Ghosh, Surajit; Banerjee, Chiranjib; Khorwal, Vijaykant; Sarkar, Nilmoni
• Is Part Of: Chemphyschem. Volume 15:Issue 16(2014)
• Page Start: 3544
• Page End: 3553
• Publication Date: 2014-09-05
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.201402372
• Languages: English
• ISSNs: 1439-4235

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The spontaneous micelle‐to‐vesicle transition in an aqueous mixture of two surface‐active ionic liquids (SAILs), namely, 1‐butyl‐3‐methylimidazolium <italic>n</italic>‐octylsulfate ([C<sub>4</sub>mim][C<sub>8</sub>SO<sub>4</sub>]) and 1‐dodecyl‐3‐methylimidazoium chloride ([C<sub>12</sub>mim]Cl) is described. In addition to detailed structural characterization obtained by using dynamic light scattering, transmission electron microscopy (TEM), and cryogenic TEM techniques, ultrafast fluorescence resonance energy transfer (FRET) from coumarin 153 (C153) as a donor (D) to rhodamine 6G (R6G) as an acceptor (A) is also used to study micelle–vesicle transitions in the present system. Structural transitions of SAIL micelles ([C<sub>4</sub>mim][C<sub>8</sub>SO<sub>4</sub>] or [C<sub>12</sub>mim]Cl micelles) to mixed SAIL vesicles resulted in significantly increased <sc>D</sc>–A distances, and therefore, increased timescale of FRET. In [C<sub>4</sub>mim][C<sub>8</sub>SO<sub>4</sub>] micelles, FRET between C153 and R6G occurs on an ultrafast timescale of 3.3 ps, which corresponds to a <sc>D</sc>–A distance of about 15 Å. As [C<sub>4</sub>mim][C<sub>8</sub>SO<sub>4</sub>] micelles are transformed into mixed micelles upon the addition of a 0.25 molar fraction of [C<sub>12</sub>mim]Cl, the timescale of FRET increases to 300 ps, which suggests an increase in the <sc>D</sc>–A distance to 31 Å. At a 0.5 molar fraction of [C<sub>12</sub>mim]Cl, unilamellar vesicles are formed in which FRET occurs on multiple timescales of about 250 and 2100 ps, which correspond to <sc>D</sc>–A distances of 33 and 47 Å. Although in micelles and mixed micelles the obtained <sc>D</sc>–A distances are well correlated with their radius, in vesicles the obtained <sc>D</sc>–A distance is within the range of the bilayer thickness.</p> </abstract>