Bound states spectral concentration

The applicability of this in situ method for the determination of surface areas depends not only on knowledge of the dye s molecular area in the adsorbed state but also on the assumption that the chosen spectral parameter measures the surface concentration of the dye. In order to test the relation between adsorption of dye to silver halide and its spectral characteristics in the bound state, the behavior of Pseudocyanine in a coarse silver halide suspension (Dispersion D) was studied. This particular dispersion was chosen because some of its relevant adsorption characteristics had already been examined (22, 23). Moreover, observations by Boyer and Cappelaere with Pseudocyanine adsorbed on AgBr powders (5) indicated that /-band intensity varied with the amount of adsorbed dye and was not sensitive to the concentration of Ag+ or Br" ions in the range pAg 3.3-8.7. 

Fc is the fluorescence of the dye in a lipid vesicle suspension with a lipid concentration of C F0 and Fx are the limiting dye fluorescence readings in the absence of lipid and at very high lipid concentrations, respectively. The fluorescence as a function of lipid concentration is fitted to this equation via nonlinear regression. The results of such measurements for a series of styryl dyes (10), as well as the spectral characteristics of the dyes in several solvents, are given in Table I. As expected, the membrane affinity of the dyes increases with the length of the chromophore or the number of carbons in the appended hydrocarbon chains. Also noteworthy is the striking increase in fluorescence quantum yield for the membrane-bound dyes this is probably due to the well-ordered immobile environment of the membrane, which inhibits nonradiative decay processes that require molecular motion in the excited state. 

In this system, the adsorption of the stabilizer was characterized throroughly employing various spectroscopic techniques. Especially, H and C liquid state NMR spectroscopy proved as a useful probe for the surface chemistry of nanoparticles in concentrated dispersions, as species adsorbed to the surface can be identified, however the functional groups directly adjacent to the surface are motionally hindered, which results in spectral broadening [85], It is hence possible to assess the amount of surface-bound species, determine the functional groups binding to the particle surface, and qualitatively investigate the chemistry of both particle surface and bulk solution. In the zirconia case, it was detected that indeed only partially the initially bound benzyl alcohol solvent is replaced by the stabilizer... 

The decay profiles gave no indication of displaced EB, provided the concentration of DAP " was kept below ca. 120 iM, although excitation and detection wavelengths were optimized in favor of preferentially observing intercalated dye. Furthermore, the fluorescence spectral records showed that added DAP was present exclusively in the intercalated form and that, under the experimental conditions, none was bound to the polynucleotide surface or free in solution. Gated fluorescence spectra, recorded at different times after the excitation pulse, were identical within experimental error and remained in excellent agreement with those recorded by steady-state methods. 

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