Ultrafast excited state dynamics and light-switching of [Ru(phen)2(dppz)]2+ in G-quadruplex DNA

Chunfan Yang,Chun-Hua Huang,Zeqing Jiao,Qian Zhou,Ben-Zhan Zhu,Hongmei Su,Hongmei Zhao

doi:10.1038/s42004-021-00507-0

Abstract

The triplet metal to ligand charge transfer (3MLCT) luminescence of ruthenium (II) polypyridyl complexes offers attractive imaging properties, specifically towards the development of sensitive and structure-specific DNA probes. However, rapidly-deactivating dark state formation may compete with 3MLCT luminescence depending on different DNA structures. In this work, by combining femtosecond and nanosecond pump-probe spectroscopy, the 3MLCT relaxation dynamics of [Ru(phen)2(dppz)]2+ (phen = 1,10-phenanthroline, dppz = dipyridophenazine) in two iconic G-quadruplexes has been scrutinized. The binding modes of stacking of dppz ligand on the terminal G-quartet fully and partially are clearly identified based on the biexponential decay dynamics of the 3MLCT luminescence at 620 nm. Interestingly, the inhibited dark state channel in ds-DNA is open in G-quadruplex, featuring an ultrafast picosecond depopulation process from 3MLCT to a dark state. The dark state formation rates are found to be sensitive to the content of water molecules in local G-quadruplex structures, indicating different patterns of bound water. The unique excited state dynamics of [Ru(phen)2(dppz)]2+ in G-quadruplex is deciphered, providing mechanistic basis for the rational design of photoactive ruthenium metal complexes in biological applications.

Highlights

The triplet metal to ligand charge transfer (3MLCT) luminescence of ruthenium (II) polypyridyl complexes offers attractive imaging properties, towards the development of sensitive and structure-specific DNA probes
It is found that the inhibited dark state channel in double-stranded DNA (ds-DNA) is open in G-quadruplex, and the ultrafast dark state formation dynamics of [Ru2dppz]2+ is sensitive to the content of water molecules in local DNA structures
The dark state formation rate of [Ru2dppz]2+ is ~10.5 ps when bound to the bilateral TTA loops of HT and is ~15.6 ps when bound to the diagonal thymine–thymine–thymine–thymine (TTTT) loops of Oxyticha nova, indicating different patterns of bound water molecules contained in different structural loops

Summary

Introduction

The triplet metal to ligand charge transfer (3MLCT) luminescence of ruthenium (II) polypyridyl complexes offers attractive imaging properties, towards the development of sensitive and structure-specific DNA probes. The replacement of T base (mismatch) tends to weaken the π–π stacking of G-quartets[33] and such changes should be helpful for the ruthenium complexes approaching G-quadruplex core, which will offer better protection from the water, it is expected that the emission lifetime of [Ru(phen)2dppz]2+ should be increased if the mismatch point is the binding site.

Results

Conclusion