PHOTOPHYSICS OF 7-HYDROXYTETRAHYDROISOQUINOLINE-3-CARBOXYLIC ACID ANDITS DERIVATIVES

The following derivatives of 7-hydroxytetrahydroisoquinoline-3-carbox acid {Tic(OH) [I]}, a conformationally restricted analogue of tyrosine , were synthesized for the purpose of photophysical studies and in ord er to elucidate the nature of tyrosine fluorescence and its decay: Ac- Tic(OH) [II], Ac-Tic(OH)-NHMe [III], Tic(OH)-NHMe [IV], Ala-Tic(OH) [V ], Ac-Ala-Tic(OH) [VI], and Tic(OH)-Gly-NH2 [VII]. For the simple Tic( OH) derivatives I-IV, the N-methylamide was found to be a more effecti ve quencher than the acetyl group. For the peptidic derivatives V-VII the highest quenching of the fluorescence of the phenolic chromophore was observed in the case of Ala-Tic(OH). The simple Tic(OH) derivative s I-IV were also the subject of theoretical studies (MOPAC 93). The ob tained thermodynamic parameters (MOPAC calculations) and the fluoresce nce components were discussed on the basis of the rotamer theory in or der to explain the participation of an individual rotamer in the compl ex process of the fluorescence decay of tyrosine.