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.

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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.

The effect of sodium salicylate (Na-sal) and sodium cholate (Na-cholate) on the solvation dynamics in the water pool of aerosol-OT (AOT, sodium dioctylsulfosuccinate) microemulsion in n-heptane is reported. In the absence of any additive, the solvation dynamics of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) in AOT microemulsions is found to be biexponential with an average solvation time (〈τs〉) of 710 ps. In the water pool, 〈τs〉 decreases to 330 ps on addition of 1 mM Na-sal and increases to 3050 ps in the presence of 100 mM Na-cholate. The spectral width (Γ) of the time-resolved emission spectra of DCM in the water pool is found to be time dependent. This is ascribed to diffusion of the probe (DCM). The Na-sal-induced acceleration of the solvation dynamics is ascribed to the increase in the size of the water pool. In bulk water, in the presence of 100 mM Na-cholate (a bile salt), 〈τs〉 is ∼830 ps. This is 4 times shorter than 〈τs〉 in the presence of Na-cholate in the water pool. This is ascribed to extreme crowding in the water pool because of the presence of Na-cholate aggregates. In bulk water, the emission spectral width displays a very small time dependence in the presence of Na-cholate aggregates. This suggests that in this case self-diffusion is unimportant and the slow solvation arises entirely from the dynamic exchange.

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Solvation dynamics of 2,6-p-toluidinonaphthalene sulfonate (TNS) is studied in a large water pool (w 0 = 56) of aerosol sodium dioctylsulfosuccinate (AOT) microemulsion in n-heptane in the absence and the presence of a hydrophilic polymer, poly(vinylpyrrolidone) (PVP). The solvation dynamics of TNS in AOT microemulsions without polymer is found to be biexponential with a major component of 300 ± 30 ps (75%) and a slow component of 500 ± 50 ps (25%) with an average solvation time of 350 ps. In the presence of a polymer (0.75 wt % PVP) in the water pool, the solvation dynamics of TNS is found to be faster with components 70 ± 10 ps (75%) and 250 ± 25 ps (25%) and having an average solvation time of 115 ps. The very fast solvation dynamics in the presence of 0.75 wt % PVP in the water pool is similar to that in bulk water and is ascribed to strong binding of TNS to PVP. When the concentration of the polymer is increased to 2.5 wt % PVP, the solvation dynamics of TNS in polymer encapsulated microemulsions is found to be markedly slower. In the presence of 2.5 wt % PVP, the solvation dynamics in the water pool exhibits components of 100 ± 10 ps (33%), 600 ± 50 ps (47%) and 11 ± 1 ns (20%), with an average solvation time 2500 ps. This clearly indicates that, at high concentration of the polymer, dynamics of the water molecules inside the water pool of microemulsion is severely constrained.