Interactions of Surface Active Agents with Congo Red

概要

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The spectral changes of Congo Red solution with the addition of Tween 80 and cetyl pyridinium chloride were measured at various pH.<BR>The wavelength of the absorption peak of the interaction product between Congo Red and Tween 80 is 510 mμ in the acidic medium as well as those in the neutral and the basic ones, from which it is considered that they produce a molecular compound of a definite constitution irrespective of the medium pH. However, since the amount of Tween 80 required to show the same effect in spectra increases with lowering pH, it is considered that only a base form of Congo Red is probably active and binds with Tween 80 at the amino groups.<BR>The solutions of Congo Red containing sufficient cetyl pyridinium chloride have an absorption peak at 460 mμ. The product is completely precipitated as the ratio of Congo Red to cetyl pyridinium chloride is 1/2 and dispersed in both sides of this ratio, which depends little on the medium pH. This is considered to show that cetyl pyridinium chloride binds with Congo Red at the sulfonate groups, the product becomes most hydrophobic as two sulfonates in a molecule are blocked and hydrophilic with an excess of the detergent.
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