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

Abstract

Guanine quadruplexes (GQs) are four‐stranded DNA/RNA structures exhibiting an important polymorphism. During the past two decades, their study by time‐resolved spectroscopy, from femtoseconds to milliseconds, associated to computational methods, shed light on the primary processes occurring when they absorb UV radiation. Quite recently, their utilization in label‐free and dye‐free biosensors was explored by a few groups. In view of such developments, this review discusses the outcomes of the fundamental studies that could contribute to the design of future optoelectronic biosensors using fluorescence or charge carriers stemming directly from GQs, without mediation of other molecules, as it is the currently the case. It explains how the excited state relaxation influences both the fluorescence intensity and the efficiency of low‐energy photoionization, occurring via a complex mechanism. The corresponding quantum yields, determined with excitation at 266/267 nm, fall in the range of (3.0–9.5) × 10−4 and (3.2–9.2) × 10−3, respectively. These values, significantly higher than the corresponding values found for duplexes, depend strongly on certain structural factors (molecularity, metal cations, peripheral bases, number of tetrads …) which intervene in the relaxation process. Accordingly, these features can be tuned to optimize the desired signal.

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

“…The ranges of the Φ fl values determined for monomers and multimers ,,− containing solely major nucleobases are depicted as histograms in Figure . Notably, the emission of G-quadruplexes may be up to 1 order of magnitude more intense compared to their constitutive monomeric chromophores …”

“…Notably, the emission of G-quadruplexes may be up to 1 order of magnitude more intense compared to their constitutive monomeric chromophores. 43 When the excitation wavelength moves toward longer wavelengths, dramatic changes are observed in the fluorescence. In this respect, we note that both genomic and synthetic DNA exhibit a long absorption tail extending over the UVA spectral domain.…”

“…Going form monomeric to multimeric nucleic acids, the fluorescence behavior becomes much more complex, strongly depending on the secondary structure. The ranges of the Φ fl values determined for monomers and multimers ,,− containing solely major nucleobases are depicted as histograms in Figure . Notably, the emission of G-quadruplexes may be up to 1 order of magnitude more intense compared to their constitutive monomeric chromophores …”

Special issue on nucleic acid photophysics

“…This finding highlights the possibility that methylated purine nucleobases could be hotspots for DNA photoionization damage, underscoring the need for further investigation of the UV-induced processes of these epigenetic nucleobases in DNA and RNA. Markovitsi 30 presents a review article that discusses the effects of direct absorption of UV radiation on guanine quadruplexes (GQs). The review aims to provide comprehensive insights into the fundamental processes occurring in GQs upon absorption of UV radiation, shedding light on the potential applications of GQs in optoelectronic biosensors, and highlighting key factors influencing fluorescence emission and charge carrier generation in GQs.…”

The Rise of Bacterial G-Quadruplexes in Current Antimicrobial Discovery

“…Additional qualitative information can be obtained using fluorescence-based approaches disclosing accurate information on conformational rearrangements, loop fluctuations, topology, and ligand-binding properties. These can be achieved by exploiting the intrinsic fluorescence of G4s, which can also be used to discriminate G4s from other DNA folding structures, ,− as well as by incorporating fluorescent probes into strategic G4 sequence positions. , Effective fluorescent purine probes for studying nucleic acids have been developed . These include (i) 2-aminopurine (2AP), which has been employed to monitor the G4 conformational switch; − (ii) 8-vinylguanine (8vG), which can adopt both syn and anti conformations, becoming highly useful in monitoring different G4 topologies; and (iii) thienoguanosine ( th G) and isothiazolguanosine ( tz G).…”