Coordination-driven self-assembly formation of Ru(II)-metallocycles based on 4-amino-1,8-naphthalimide Tröger's base supramolecular scaffold: Synthesis, characterization, and heparin-binding study

The synthesis, characterization, and heparin polyanion sensing properties of a series of [2 + 2] self-assembled Ru(II)-metallocycles based on a green emitting 4-amino-1,8-naphthalimide Tröger's base (TBNap) supramolecular scaffold are described here. TBNap was reacted in a 2:2 stoichiometric ratio with a series of half-sandwiched Ru₂(II)-acceptors (M₁ to M₄) to isolate four new tetranuclear Ru(II)-metallocycles, TB-MC-1 to TB-MC-4. All the metallocycles were characterized using NMR (¹H & ¹³C), FT-IR, and ESI-MS. A positive solvatochromism was observed for the metallocycles in different solvents with varying polarity. The strong-fluorescence emission of metallocycles was drastically quenched upon the addition of increasing concentration of heparin polyanions and the Stern-Volmer quenching constants (K_SV) were determined to be in the order of 10⁵ M⁻¹. All these results demonstrate the usefulness of metallocycles for sensing and quantifying the concentration of heparin polyanion.