Eosin, solubilization

The experiments prove this assumption in practice. In Figure 7a, the solubilization of Eosin in the monomeric aqueous surfactant solution indicates the CMC at 1.55.10 mol/1 while the corresponding polysiloxane (r=95) (Figure 7b) solubilizes Eosin without an indication of a CMC (24). For this polymer r... 

Dilute Matrigel in cold distilled water to 50 /xg in 50-100 /xl. Apply 25-50 /xg Matrigel to the filters, dry under hood, and reconstitute with serum-free medium. Place a solution of chemoattractant in the lower compartment of the Boyden chamber (in the absence of chemoattractant, very little cell migration occurs over a 6-h period). Place the coated filters in Boyden chambers, and close the chamber. Add to the upper chamber 2 to 3 x 10 cells in appropriate medium containing 0.1% BSA. Incubate at 37°C in 5% CO2 for 4-6 h. Remove the cells from the upper surface of the filter by wiping with a cotton swab or by passing them on tissue paper. Fix the filter (methanol or ethanol) and stain (haematoxylin-eosin or toluidine blue). Count the cells from various areas of the lower filter surface. Alternatively, migrated cells can be solubilized... 

Homogeneous photosensitization. Rose Bengal and Eosin-Y, anionic dyes used for generation of singlet oxygen, are not soluble in aprotic solvents. They can be solubilized in CS2 and CH2CI2 by complexation with 18-crown-6 or with Aliquat 336. 

UV - Vis spectroscopy or colorimetry give the amount of solubilization. The solubility of the dye remains almost constant until the concentration of surface-active agent attains the CMC, and then increases rapidly and almost linearly. The CMC value thus determined by solubilization is lower than those obtained from other measurements for the reasons discussed in the next section. This method is applicable to both aqueous and non-aqueous solutions. The latter requires the use of a water-soluble dye. Common oil-soluble dyes for this measurement are Orange OT, Sudan III and IV, Yellow OB and Aniline Blue, while common water-soluble dyes include Eosin, Merocyanin 540 and Methylene Blue. 

As discussed earlier, the use of an indicator to determine the CMC can be applied to aqueous as well as non-aqueous systems. Rhodamine B, for example, can be added to detect reversed micelles at very low surfactant concentrations. The transition from monomers to micelles can then be followed by the depolarization of the fluorescence. Another method involving the use of a dye is dye solubilization. For non-aqueous systems, a water-soluble dye should be used, for example, Eosin Y or Merocyanin 540. As soon as the first aggregates form, the solubilized dye can be measured by its UV-Vis absorbance. This method yields satisfactory results for some surfactants. However, sometimes the solubilization of such a dye is so high that the micellar structure is affected by the dye. If the solubilization is weaker, the dye taken up by the micelles is often insufficient to produce a reasonable signal. Especially when the CMC is very low, the pseudo-phase volume fraction of the micellar phase at concentrations just above the CMC is far too low to solubilize a significant amount of dye. This makes it difficult to define a clear CMC and requires the evaluation of different water-soluble dyes. It should be mentioned that as with aqueous... 

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