Fluorescence polarization measurements interfaces

The laboratory coordinate system chosen for TIR fluorescence anisotropy measurements is illustrated in Figure 12.2. SRIOI molecules located at a water/oil interface (in the x-y plane) are excited by an s-polarized laser beam along the x -axis. The TIR fluorescence is then detected along the z-axis and its polarization is selected by a polarizer. The fluorescence decay profile observed under such a configuration is analysed for two limiting cases, depending on the structure of a water/oil interface two-dimensional or three-dimensional. 

In order to obtain a clearer picture on the interfacial polarity, we conducted picosecond TIR fluorescence spectroscopy by using sulforhodamine B (SRB) as a polarity probe molecule [5]. On the basis of fluorescence dynamic measurements of SRB adsorbed on a water/oil interface, we studied a relationship between thickness/roughness and the polarity at the interface. 

For quite some time, there have been indications for a phase-separation in the shell of polyelectrolyte block copolymer micelles. Electrophoretic mobility measurements on PS-PMAc [50] indicated that a part of the shell exhibits a considerable higher ionic strength than the surrounding medium. This had been corroborated by fluorescence studies on PS-PMAc [51-53] and PS-P2VP-heteroarm star polymers [54]. According to the steady-state fluorescence and anisotropy decays of fluorophores attached to the ends of the PMAc-blocks, a certain fraction of the fluorophores (probably those on the blocks that were folded back to the core/shell interface) monitored a lower polarity of the environment. Their mobility was substantially restricted. It thus seemed as if the polyelectrolyte corona was phase separated into a dense interior part and a dilute outer part. Further experimental evidence for the existence of a dense interior corona domain has been found in an NMR/SANS-study on poly(methylmethacrylate-fr-acrylic acid) (PMMA-PAAc) micelles [55]. 

In the case of a water/DCE interface [(c) and (d)], on the other hand, a fitting of the data by a single-exponential function cannot be attained by setting an emission polarizer at 45°, as confirmed by deviations of Re and Cr from the optimum values (c). When the fluorescence decay profile is measured by setting an emission polarizer at 54.7° (d), fluorescence anisotropy can be reasonably fitted by a single-exponential function including the time response in the initial stage of excitation (see also and... 

Although the structural differences between the water/CClq and water/DCE interfaces are not so large, the chemical and/or physical nature of the organic phase itself reflects on the photophysical properties of a probe molecule, indicating the novelty of the present experimental approaches. Systematic investigations are important to reveal factors governing structural and physical characteristics of water/oil interfaces. Therefore, we introduced fluorescence dynamic anisotropy and excitation energy transfer measurements to other water/oil interfacial systems the data are summarized in Table 12.3. The results are discussed in terms of the relationship between the interfacial stracture and the polarity at the water/oil interfaces (Section 12.6). 

Some essential discoveries concerning the organization of the adsorbed layer derive from the various spectroscopic measurements [38-46]. Here considerable experimental evidence is consistent with the postulate that ionic surfactants form localized aggregates on the solid surface. Microscopic properties like polarity and viscosity as well as aggregation number of such adsorbate microstructures for different regions in the adsorption isotherm of the sodium dedecyl sulfate/water/alumina system were determined by fluorescence decay (FDS) and electron spin resonance (ESR) spectroscopic methods. Two types of molecular probes incorporated in the solid-liquid interface under in situ equilibrium conditions... 

Kakiuchi and coworkers studied the transfer kinetics of ionic fluorescence probes via monitoring the fluorescence signal under TIR illumination [11-14]. A conventional arrangement for this type of measurement is exemplified in Fig. 4.2 [15]. The experiments were performed at the polarized water/DCE interface, with the anionic probe Eosin B (EB) transferring from the aqueous to the organic electrolytes. In this configuration, the most important contributions to... 

First, we studied the solvent relaxation in solutions of diblock copolymer micelles. A commercially available polarity-sensitive probe, patman (Fig. 10, structure I), frequently used in phospolipid bilayer studies [123], was added to aqueous solutions of PS-PEO micelles. The probe binds strongly to micelles because its hydrophobic aliphatic chain has a strong affinity to the nonpolar PS core. The positively charged fluorescent headgroup is supposed to be located in the PEO shell close to the core-shell interface. The assumed localization has been supported by time-resolved anisotropy measurements. 

Pyrene and dinaphthylpropane (DNP) fluorescence and nitroxide ESR probes have been successfully used to investigate the structure of the adsorbed layer of sodium dodecyl sulfate at the alumina-water interface [11,12], The fluorescence fine structure of pyrene yielded information on the polarity of the microenvironment in the adsorbed layer. Intramolecular excimer formation of DNP was used to measure the microfiuidity of this environment. The results indicate the presence of highly organized surfactant aggregates at the solid-liquid interface, formed by the association of hydrocarbon chains. 

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