The fluorescence anisotropy decay of two dyes merocyanine 540 and oxazine 1 has been studied in a polymer−surfactant aggregate containing poly(vinylpyrrolidone) (PVP) and sodium dodecyl sulfate (SDS). The results are analyzed in terms of the necklace model of the polymer−surfactant aggregate. The rotational motion of the probe is assumed to involve “wobbling-in-cone” along with translational motion along the micellar surface. It is observed that the presence of the polymer chains around the spherical SDS micelles causes significant retardation of both the wobbling motion as well as the translational motion of the two dyes. As a result, the wobbling and translational diffusion of the dyes in the PVP−SDS aggregate are slower than those in SDS micelle.

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Solvation dynamics of 2,6-p-toluidinonaphthalene sulfonate (TNS) is studied using picosecond time-resolved emission spectroscopy in an aqueous solution of poly(vinylpyrrolidone) (PVP) and in a polymer-surfactant aggregate consisting of PVP and sodium dodecyl sulfate (SDS). On addition of PVP to an aqueous solution of TNS, the emission quantum yield (φ f ) of TNS increases about 210 times in 0.75 wt % aqueous solution of PVP. The solvation dynamics of TNS in 0.75 wt % aqueous solution of PVP is found to be biexponential with a major component (85%) of 60 ps and a slower one of 800 ps (15%). The retardation of the solvation dynamics in the dilute polymer solution compared to that in the bulk water is attributed to the restricted movement of water molecules in the vicinity of the polymer chains. The solvation dynamics of TNS in the PVP-SDS aggregate is described by two components, 300 ( 20 ps (55%) and 2500 ( 100 ps (45%). The slower solvation dynamics in PVP-SDS aggregate compared to PVP alone or SDS alone indicates serious restrictions on the mobility of the water molecule squeezed between polymer chains and micellar (SDS) surface.

Solvation dynamics in the molten globule state of a protein, glutaminyl-tRNA synthetase (GlnRS), has been studied using both a noncovalent probe (bis-ANS) and a covalent probe 4-(N-thioacetylamino)-phthalimide. In the native state of GlnRS, bis-ANS exhibits an average solvation time (〈τ S 〉) of 1400 ps, which is 12 times longer than that for the covalent probe (120 ps). The difference in the solvation times for the two probes in the native state of the protein is ascribed to different locations of the probes. The covalent probe resides close to the protein surface and experiences fast relaxation of the water molecules. The noncovalent probe penetrates deeper inside the protein and displays slower relaxation in the buried region. In the molten globule state, 〈τ S 〉 is 400 ps for the noncovalent probe and 250 ps for the covalent probe. Evidently, in the molten globule state, 〈τ S 〉 is much longer than that the longest component of the solvation dynamics (∼1 ps) in bulk water. This shows that, in the compact molten globule state, the protein retains considerable residual structure.