The time resolved decay of
The time-resolved decay of the fluorescence anisotropy provides significant insights about the rotational relaxation of the fluorophore in organized assemblies . Therefore, with a view to delve into the microenvironment formed by the SDS micelle, time resolved fluorescence anisotropy decay of QS at different AG 1879 values has been recorded. In bulk water the anisotropy decay at pH 2, pH 7 and pH 12 is monoexponential and the observed time constants are 0.3 ns, 0.6 ns and 2.0 ns, respectively. All the data related to anisotropy decay measurements are summarized in Table 4. Fig. 9 shows the temporal anisotropy decay of QS in water and in SDS micellar solution at different pH. The anisotropy decay of QS bound to SDS micelle is found to be slower for all the three pH values studied compared to that in bulk water. The anisotropy decay of QS in micelles is double exponential at pH 2 and pH 12, whereas, single exponential at pH 7. The larger rotational time at pH 12 in bulk solution compared to pH 2 and pH 7 may be simply due to the increase in viscosity of the solution. Aggregation of QS molecules at pH 12 can be an additional factor for the observed increase in time constant. The observed longer time constants in micellar solutions compared to that in bulk water may be ascribed to the larger volume of rotating species (probe molecule along with the micelle). The time-resolved anisotropy results reveal that the motional restriction of the QS molecules increase with the increase in pH of the solution. These observations are in agreement with the results obtained using steady state anisotropy measurements.