Silicon surface biofunctionalization with dopaminergic tetrahydroisoquinoline derivatives

Abstract In this work we grafted vinyl- and azido-terminated tetrahydroisoquinolines (compounds 1 and 2 , respectively) onto H Si(1 1 1) silicon wafers obtaining highly stable modified surfaces. A double bond was incorporated into the tetrahydroisoquinoline structure of 1 to be immobilized by a light induced hydrosilylation reaction on hydrogen-terminated Si(1 1 1). The best results were obtained employing a polar solvent (DMSO), rather than a non-polar solvent (toluene). The azide derivative 2 was grafted onto alkenyl-terminated silicon substrates with copper-catalyzed azide-alkyne cycloaddition (CuAAC). Atomic force microscopy (AFM), contact angle goniometry (CA) and X-ray photoemission spectroscopy (XPS) were used to demonstrate the incorporation of 1 and 2 into the surfaces, study the morphology of the modified surfaces and to calculate the yield of grafting and surface coverage. CA measurements showed the increase in the surface hydrophobicity when 1 or 2 were incorporated into the surface. Moreover, compounds 1 and 2 were prepared starting from 1-( p -nitrophenyl)tetrahydroisoquinoline 3 under smooth conditions and in good yields. The structures of 1 and 2 were designed with a reduced A-ring, two substituents at positions C-6 and C-7, an N -methyl group and a phenyl moiety at C-1 in order to provide a high affinity against dopaminergic receptors. Moreover, O -demethylation of 1 was carried out once it was adsorbed onto the surface by treatment with BBr 3 . The method presented constitutes a simple, easily reproducible and high yielding approach for grafting complex organic biomolecules with dopaminergic properties onto silicon surfaces.