Solubilization of 5-methoxy tryptamine molecular probes in CTAB and SDS micelles: a cmc and binding constant study

To understand the change in environmental conditions when a probe is incorporated in micelles, an absorption and fluorescence spectral study on the solubilization behaviour of 5-methoxy tryptamine (5-MT) and N,N-dimethyl-5-methoxy tryptamine (5-NMT) has been made in CTAB and SDS for their neutral and cationic forms. The blue shift in emission wavelength is accompanied by increase in intensity with increasing surfactant concentration for almost all the cases except for the cationic probe in CTAB surfactant. This exceptional behaviour can be attributed to the quenching of emission intensity caused by Br(-) ions. Spectral correlations with solvent polarity parameters indicate relatively less polar binding sites in CTAB and SDS as compared to water. The binding constant and cmc values have been determined for CTAB and SDS using both the neutral and the cationic probes, which are in good agreement with the literature values. Higher value of binding constant and lower polarity of the binding sites justify 5-NMT as a better binding probe as the two methyl groups make the molecule more hydrophobic and drag it to the interior of both the micelles.