The Ubiquity of High-Energy Nanosecond Fluorescence in DNA Duplexes

Abstract

During the past few years, several studies reported that a significant part of the intrinsic fluorescence of DNA duplexes decays with surprisingly long lifetimes (1–3 ns) at wavelengths shorter than the ππ* emission of their monomeric constituents. This high-energy nanosecond emission (HENE), hardly discernible in the steady-state fluorescence spectra of most duplexes, was investigated by time-correlated single-photon counting. The ubiquity of HENE contrasts with the paradigm that the longest-lived excited states correspond to low-energy excimers/exciplexes. Interestingly, the latter were found to decay faster than the HENE. So far, the excited states responsible for HENE remain elusive. In order to foster future studies for their characterization, this Perspective presents a critical summary of the experimental observations and the first theoretical approaches. Moreover, some new directions for further work are outlined. Finally, the obvious need for computations of the fluorescence anisotropy considering the dynamic conformational landscape of duplexes is stressed.

On the Use of the Intrinsic DNA Fluorescence for Monitoring Its Damage: A Contribution from Fundamental Studies

“…58,59 The amplitude of this disorder depends on the duplex size 60,61 and the ionic strength of the solution, 62 both factors affecting the DNA photophysical properties. 23,42 Given the dependence of the electronic coupling on the conformational disorder, the absorption and fluorescence spectra of DNA multimers are the envelope of a multitude of electronic transitions. Emission stems from various types of electronic excited states, localized on individual nucleobases or collective, some of them being stronger emitters than others.…”

“…Measurements on the intrinsic fluorescence of undamaged DNA reported in the recent literature concern, in addition to steady-state spectra, the determination of fluorescence decays and fluorescence anisotropies from the femtosecond to the nanosecond time scales, as well as time-resolved spectra. − ,− The latter have largely contributed to comprehending the factors governing photon emission. The main outcomes of these studies are highlighted in ref .…”

“…In duplexes, the fingerprint of collective states with dominant exciton character appears mainly at short wavelengths of their emission spectrum; they can be differentiated from the localized ππ* states via their lifetime and their anisotropy. , A typical example is the duplex d(GC) n •d(GC) n , whose narrow fluorescence spectrum, peaking at ∼300 nm (Figure a), has been correlated with excitons extended over at least four nucleobases across both strands …”

“…66 For comparison, we mention that the fluorescence maxima of all mononucleosides and mononucleotides are located below 334 nm, 45 while those of equimolar mixtures corresponding to G•C and A•T pairs at 330 and 325 nm, respectively. 42 2.3. Strand Flexibility: A Key Player.…”

Processes triggered in guanine quadruplexes by direct absorption of UV radiation: From fundamental studies toward optoelectronic biosensors

“…The interaction among the guanines of the core and the loop nucleobases could be responsible for a peculiar fluorescence component appearing at the blue part of the spectrum and decaying on the ns timescale. Although such high‐energy long‐lived fluorescence, correlated with collective excited states, is ubiquitous in duplexes, 67 it was detected just for one four‐stranded structure, OXY/K + 36 . Further studies are needed to elucidate the geometrical and electronic features of these emitting states.…”