Oxidizing Ru(II) Complexes as Irreversible and Specific Photo-Cross-Linking Agents of Oligonucleotide Duplexes

Abstract

Oxidizing polyazaaromatic Ru(II) complexes containing two TAP ligands (TAP = 1,4,5,8-tetraazaphenanthrene) are able under illumination to cross-link irreversibly the two strands of an oligonucleotide (ODN) duplex by covalent bond formation. The cross-linking proceeds by two successive absorptions of a photon. An adduct of the metallic complex on a guanine (G) base of one ODN strand is first photoproduced, followed by a second photoaddition of the same Ru species to a G base of the complementary strand, provided that the two G moieties are separated by 0 or 1 base pair. These two processes lead to the cross-linking of the two strands. Such a photo-cross-linking is easily detected with [Ru(TAP)(2)(phen)](2+) (1; phen = 1,10-phenanthroline) and [Ru(HAT)(2)(phen)](2+) (2; HAT = 1,4,5,8,9,12-hexaazatriphenylene), whereas it is not observed with [Ru(TAP)(2)TPAC](2+) (3; TPAC = tetrapyridoacridine) at the same level of loading of the duplex by 3. With a concentration of 3 similar to that of 1 and 2, when the loading of the duplex by 3 is much more important than with 1 and 2, the photo-cross-linking with 3 can thus also be observed. As 3 intercalates its TPAC ligand into the base pairs stack, its mobility is restricted in the duplex. In contrast, 1 and 2 can adopt different geometries of interaction, which probably facilitate the photo-cross-linking.

A Rigid Dinuclear Ruthenium(II) Complex as an Efficient Photoactive Agent for Bridging Two Guanine Bases of a Duplex or Quadruplex Oligonucleotide

“…This suggests that the two metallic centres behave independently in spite of the conjugated TPAC bridging ligand. Secondly, complex 1 has an oxidizing power in its 3 MLCT (metal-to-ligand charge transfer) excited state [4] similar to that of the mononuclear bis-TAP complexes mentioned above. Under illumination, 1 should thus also be able to extract one electron from a guanine base and give rise to an adduct of the metallic species to the G moiety as observed, for example, with [Ru-A C H T U N G T R E N N U N G (tap) 2 …”

“…These two steps give rise to the bridging of the two ODN strands. [3] With the aim of exploring novel targets for these photocrosslinkings and also improving these photoinduced double anchoring processes, we studied an a priori more appropriate Ru complex, namely the dinuclear [(tap) 2 RuA C H T U N G T R E N N U N G (tpac)Ru-A C H T U N G T R E N N U N G (tap) 2 ] 4 + complex (1, TPAC= tetrapyridoacridine). The photophysical and electrochemical properties of this compound suggest that it should act as an efficient photocrosslinking agent for the following reasons.…”

“…[3,5] Moreover, due to the presence of the two Ru metallic centres and the four TAP ligands in 1, the probability of obtaining more than one photoadduct on the same complex 1 should increase and improve the photocrosslinking.…”

Ru–TAP complexes and DNA: from photo-induced electron transfer to gene photo-silencing in living cells

“…Viscosity measurements with CT-DNA indicate that [Ru(HAT) 2 phen] 2+ induces an increase in viscosity that is slightly lower than that with ethidium bromide [34], and its retention of emission polarization anisotropy in the presence of DNA is significantly lower than that for a classical metallo-intercalator [35]. presence of 100 mM NaCl and 100 mM KCl), which is mainly attributed to important electrostatic interactions between the negatively charged phosphate backbone and the 4+ charge of the complex.…”

“…In order to demonstrate unambiguously the formation of a bi-adduct via the occurrence of photo-cross-linking between two G-containing oligonucleotides, three types of photo-oxidizing Ru complexes have been tested [35] [32] indicates that it interacts less efficiently with DNA than complexes containing a classical intercalating ligand such as dppz or PHEHAT. Viscosity measurements with CT-DNA indicate that [Ru(HAT) 2 phen] 2+ induces an increase in viscosity that is slightly lower than that with ethidium bromide [34], and its retention of emission polarization anisotropy in the presence of DNA is significantly lower than that for a classical metallo-intercalator [35].…”