Modifying the properties of organic molecules by conjugation with metal complexes : the case of peptide nucleic acids and of the intrinsically chiral thiahelicenes

Modification of the properties of organic molecules by means of conjugation with transition metals to obtain organometallic systems with improved reactivity, spectroscopic, and chemico-physical properties, is a long-standing strategy. This approach has yielded excellent results in many research fields due to its versatility, with infinite possible combinations of transition metals and organic systems. This review focuses on the most innovative results of the authors’ research in the field of organometallic conjugates of peptide nucleic acids (PNAs) and 7-thiahelicenes. In both cases, the presence of the metal gives the organic molecule with specific chemico-physical properties, which can be useful for applications in catalysis, imaging, electrochemical and, spectroscopic analysis. In particular, the conjugation of PNA, with transition metal complexes involving chromium and iron makes it possible to achieve significant IR and electrochemical detection at a very low concentration without affecting the specificity and efficiency of PNA/DNA binding. Dinuclear Re-PNA conjugates were rapidly internalised in DU145 and PC3 prostate cancer cells. This confirmed the fundamental role of the metal in increasing the cell uptake of PNA, and favoured the down-regulation of the expression of the miR-21. The complexation of 7-thiahelicenes with different metals was first performed to obtain systems with improved nonlinear optical properties. Enantiomerically pure gold complexes of phosphorus-containing 7-thiahelicenes gave high enantiomeric excess in a number of asymmetric reactions.