TRYPTOPHAN-THYMINE ASSOCIATION AND BIOINSPIRED MEMBRANE SYSTEMS

A recent study demonstrated that the association tryptophan-thymine inhibits urothelial carcinogenesis and enhances the effectiveness of intravesical Bacillus Calmette-Guérin (BCG) therapy for bladder cancer. This work focused on the fluorescent properties of the amino acid tryptophan and the nitrogenous base thymine. To monitor the interaction between these two molecules, assays were conducted with each molecule separately and then together in the same system. The experiments were performed in media with varying pH values and in the presence of bioinspired membrane systems, like micelles and liposomes. A red shift was observed in the absorption spectra of thymine at alkaline pH. In the presence of negative SDS (Sodium Dodecyl Sulfate) micelles, a blue shift in thymine emission was observed with increasing SDS concentration, regardless of the pH of the medium. An increase in the concentration of SDS and CTAB (Cetyltrimethylammonium Bromide) resulted in an increase in the fluorescence intensity of thymine. These results indicate the interaction of thymine with ionic micelles, particularly in an alkaline environment, and in the presence of CTAB micelles. The static fluorescence anisotropy results for tryptophan, combined with spectral shift and emission intensity data, revealed a strong interaction of the protonated form of the tryptophan (in acidic pH media) with negative micelles, and of the deprotonated form (in basic pH media) with positive micelles. On the other hand, experiments involving the association of the two molecules have not demonstrated an effective interaction between them. With the molar concentration of tryptophan fixed, the concentration of thymine was increased, but no change in the fluorescent properties of both molecules was detected. For the assays in the presence of DMPC (Dimyristoylphosphatidylcholine) liposomes, we used the static anisotropy of two membrane probes: AHBA (2-amino-N-hexadecyl-benzamide) and DPH (1,6-Diphenyl-1,3,5-hexatriene). AHBA is located in the region of the polar heads of lipids, while DPH is located in the region of the fatty chains. The results showed that neither tryptophan nor thymine partitioned into the bilayer, even at high concentrations. The main conclusion of these studies is that both tryptophan and thymine are attracted to bioinspired membranes by electrostatic interactions rather than by the hydrophobic effect.