Water soluble polymers .75. Responsive Microdomains in Labeled N-octylamide-substituted poly(sodium maleate-alt-ethyl vinyl ether): Transient Fluorescence and Time-Resolved Fluorescence Anisotropy Studies

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Polymers and High Performance Materials


Dansyl fluorescent labels with two different spacer lengths (D2 and D8) were pendently attached to unmodified and 30 mol % n-octyl-modified copoly(sodium maleate-alt-ethyl vinyl ether). The time-resolved fluorescence anisotropy (TRFA) measurements of these labels were obtained in aqueous media as a function of pH and analyzed using impulse reconvolution analysis (IRA). At pH values below 6.7, the hydrophobically modified copolymers exist as compact globules, as evidenced by the long fluorescence emission Lifetimes of the labels. At these pH values, two rotational correlation times (RCTs) corresponding to two distinct molecular motions within associating hydrophobic microdomains are seen: one associated with the motion of the chromophore coupled to the copolymer backbone and the other associated with the rotational motion of the chromophore. Above pH 6.7, the copolymer is progressively extended with increasing pH, as indicated by the short emission lifetime of the labels and the observation of only one rotational correlation time corresponding to the rotational motion of the labels in an aqueous environment. Local rotational diffusion coefficients and local viscosities for the dansyl labels have also been estimated as a function of pH. The observed fluorescence data are consistent with the classic model proposed for pH-induced transition from a polysoap to an extended polyelectrolyte in dilute aqueous solution.

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