DNA/RNA: Building Blocks of Life Under UV Irradiation

Abstract

International audienceDuring the last 10 years, intense experimental and theoretical work has proven the existence of ultrafast nonradiative decay routes for UV-excited monomeric nucleic acid bases, accounting for their high photostability. This mechanism has been explained by the occurrence of easily accessible conical intersections connecting the first excited ππ* state with the ground state. However, recent studies of substituent and solvent effects indicate that the situation is more complicated than what was initially thought, notably by the presence of dark excited states. Moreover, the actual shape of the excited-state potential energy surface may induce nonexponential dynamics. Further efforts are needed in order to clarify how various environmental factors affect the structural and dynamical aspects of the nucleic acid base excited states

Photoprotection: extending lessons learned from studying natural sunscreens to the design of artificial sunscreen constituents

“…DNA/RNA nucleobases are known to undergo intrinsic ring-centred oop deformations following UV photoexcitation that mediate ultrafast IC and efficient reformation of the ground state parent molecule. 85,[160][161][162][163] Such oop deformation-based IC routes are also intrinsic to the DNA/RNA base pairs and isolated nucleosides, but these can also undergo IC along PCET reaction paths -which are proposed to account for the much shorter excited state lifetimes of nucleosides compared to the isolated nucleobases. 85,135,164 Within the cellular medium, strands of RNA, ADP or ATP, that contain analogous molecular moieties to that of DNA nucleobases and nucleosides, are also expected to show some degree of photostability -protecting their molecular integrity and the local environment by absorbing (and thus reducing) the incident UV flux.…”

Assessment of the Potential Energy Hypersurfaces in Thymine within Multiconfigurational Theory: CASSCF vs. CASPT2

“…Over the last decade, a great deal of work has been done and yet plenty of controversy still surrounds the characterization of the main intrinsic photochemical mechanisms governing the photoinduced processes occurring in the DNA nucleobases [1][2][3][4][5][6][7][8][9][10][11]. Insight into their photochemical pathways provides unique information to ascertain the effect of light irradiation on the cellular system and is tightly related to the ability possessed by the genetic material to dissipate the excess of energy gained upon absorption in a harmless manner.…”

The Excited‐State Decay of 1‐Methyl‐2(1H)‐pyrimidinone is an Activated Process

“…[1,2] These short lifetimes are attributed to very effective internal conversions (ICs) mediated by conical intersections (see, for example, refs. [3][4][5][6][7]).…”

“…Via these intersections electronic ground states and dark excited states, presumably of singlet np* character, are accessible (for a recent summary, see ref. [2]). The ultrafast IC to the ground state is considered to be instrumental in protecting DNA bases from UV damage since it renders (competing) photochemical transformations improbable.…”

“…The ultrafast IC to the ground state is considered to be instrumental in protecting DNA bases from UV damage since it renders (competing) photochemical transformations improbable. [1,2] Despite this rapid IC, UV-induced photodamage of DNA bases occurs in yields which turn repair mechanisms indispensable for life on earth. [8] One of the damages is the (6-4) lesion formed between thymine bases adjacent on the DNA strand ( Figure 1).…”