Interactions of a pyrene-labeled polyelectrolyte with oppositely charged rodlike micelles monitored by fluorescence quenching with thallium ions

摘要

Interactions between poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) labeled with 1 mol % pyrene (PyPAMPS) and rodlike micelles of dimethyloleylamineoxide (DMOAO) were studied by a fluorescence quenching technique using thallium cations (Tl+) as a quencher. The micelle surface charge density was varied by solubilizing n-hexadecyltrimethylammonium chloride (CTAC) in the DMOAO micelle in varying mole fractions or by varying the pH of DMOAO micelle solutions. Macroscopic phase separation was observed when the mole fraction of solubilized CTAC (Y) was increased to a critical level (Y-p) in the PyPAMPS-DMOAO/CTAC system or the pH was decreased to a critical value (pH(p)) in the PyPAMPSDMOAO system. All fluorescence experiments were performed at Y < Y-p or at pH > pH(p). When Y is sufficiently low or the pH is sufficiently high, the fluorescence of pyrene (Py) labels was efficiently quenched by Tl+ ions and there was no effect of the presence of the micelles on the quenching. As Y was increased or the pH was decreased to a certain critical level(Y, or pH,), the quenching was abruptly diminished, corresponding to the onset of soluble polymer-micelle complex formation. This is due to the protection of Py labels solubilized in the micelle upon polymer-micelle complex formation. The critical charge densities of the micelles calculated from Y-c and pH(c) were in good agreement. All the critical values of Y-c, pH(c), Y-p, and pH(p) depend on the ionic strength (mu) (e.g., Y-p = 0.04 and Y-c = 0.008 at mu = 0.10, while Y-p = 0.11 and Y-c = 0.021 at mu = 0.30). For comparison, interactions of PyPAMPS with spherical micelles of dimethyldodecylamineoxide were investigated by varying Y with CTAC. It was found that Y-c values for the rodlike and spherical micelles were virtually identical at a given ionic strength, although Y-p for the latter was approximately 1.5 times larger than that for the former. [References: 34]