Monitoring Supramolecular Self-Assembly using Time-Resolved Fluorescence Spectroscopy

Time-resolved fluorescence spectroscopy is used to observe subtleties in supramolecular structure during the self-assembly of polymers in solution. Lifetime distribution analysis of the fluorescence decay kinetics of the solvent-sensitive fluorescent probe 1-anilino-8-naphthalene sulfonic acid associated with the di-block copolymer poly(2-vinylpyridine)41–poly(ethylene oxide)204 (P2VP-PEO) as it self-assembles enabled identification of three microdomains, distinguishable on the basis of micropolarity. These microdomains can be assigned to different supramolecular substructures: the micelle corona (high polarity), the micelle core and the P2VP globule (both low polarity), and the core–corona interface and the globule–PEO junction (both intermediate polarity). Changes in the relative population distributions of these sub-structures as a function of P2VP-PEO pinpoint the onset of micellization corresponding to the critical micelle concentration (CMC) of the copolymer, but indicate significant variation in supramolecular structure, including micelle formation, well below the CMC. This suggests that supramolecular self-assembly in polymeric systems has characteristics of a second order phase transition.

Room temperature phosphorescence of 6-bromo-2-naphthol in micelles of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers and in their mixed aggregates with sodium dodecyl sulfate

Room temperature phosphorescence (RTP) of 6-bromo-2-naphthol has been investigated in aqueous micellar solutions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers as well as in their mixed aggregates with sodium dodecyl sulfate. RTP of the phosphorophor was enhanced to some extent in the micelles of the block copolymers. However, marked enhancement of RTP was observed in the mixed aggregates. The enhancement of RTP is attributed to effective incorporation of the phosphorophor into the micelles and the aggregates, resulting in suppression of nonradiative deactivation of the phosphorescent state.

Identification of nucleotides with identical fluorescent labels based on fluorescence polarization in surfactant solutions

A solution-phase steady-state polarization-based method for discriminating among the four DNA nucleotides labeled identically with tetramethylrhodamine is described and demonstrated. Labeled nucleotides were dissolved in buffered surfactant solutions. In room temperature 4.5 mM Triton X-100 solutions at neutral pH, the measured steady-state polarizations of tetramethylrhodamine-labeled dATP, dCTP, dGTP and dUTP were 0.261 +/- 0.003, 0.112 +/- 0.003, 0.288 +/- 0.003, and 0.147 +/- 0.003, respectively. A blind test of 40 samples showed no errors in classification based on polarization. The reproducibility obtained during this study demonstrates that the four dye-labeled nucleotides can be discriminated with more than 99.8% confidence.