| Deoxyribonucleic acid（DNA）is composed of four natural bases-adenine（A）,thymine（T）,guanine（G）and cytosine（C）,which plays a crucial role in genetic information storage.However,the continuous exposure of DNA to endogenous genotoxic substances,including reactive oxygen species,ionizing radiation,and alkylating agents,could give rise to the formation of covalent DNA adducts.Such nucleobase alteration has been proven to induce serious cytotoxicity and genomic instability,which is a risk factor for cancer.Therefore,the effective detection of DNA adducts is important for in-depth understanding of the adduct formation mechanism and the corresponding biological processes involved in DNA damage at the molecular level.In recent years,the fluorescent labeling technology has been widely utilized to study the structural dynamics of nucleic acids owing to the easy accessibility,exquisite sensitivity and selectivity.However,the traditional large-conjugated fluorophores tend to disturb the native configurations of DNA and further interfere with relevant normal biological interactions.Accordingly,there is a crucial need to develop quasi-intrinsic optical probes to identify the covalent adduct in DNA with minimal disturbance to the native structure.Motivated by the preponderance of quasi-intrinsic optical probes,we computationally investigated the spectral properties of various fluorescent base analogues in solution,which can be employed as fluorescent probes to selectively identify the DNA adducts in real time.The primary innovations are related as follows:1.Fluorescent adenine analogues with ESPT characteristic utilized for real-time detecting DNA adductThe 8-oxoG is a DNA adduct caused by oxidative damage,which lacks effective intrinsic emission and tends to form stable base pair with natural adenine（A）.To recognize 8-oxoG efficiently,a variety of quasi-intrinsic optical probes are performed based on the adenine.Firstly,the calculations revealed that the modified A-analogues could bring enhanced photoluminescence arisen from theπ-conjugation.Secondly,it is found that,the fluorescence is insensitive to base pairing with thymine,while the excited state intermolecular proton transfer（ESPT）induced efficient fluorescence quenching is observed upon pairing with the 8-oxoG.The related mechanism of proton transfer reaction is demonstrated by constructing the relaxed potential energy surfaces（PECs）in both S0 and S1 states.2.Quasi-intrinsic fluorescent probes for detecting the DNA adduct(ABPd G)based on an excited-state intermolecular charge transfer mechanismThe ABPG is one of the most representative carcinogenic DNA adducts formed by human exposure to 4-aminobiphenyl（4-ABP）during dye production,rubber-manufacturing processes and cigarette smoke.Herein,a series of C-analogues are performed as fluorescent probes to detect the target adduct.All considered analogues can be classified into three groups according to their optical behavior:type I(t C,DMAC)possess bright emission after base pairing with both natural G and covalent ABPG;Meanwhile,the fluorescence of type II analogues（C1,5m C,d Cyd,5hm C）tends to be completely quenched after base pairing with G and ABPG;Finally,the photoluminescence of type III（t CO and PC）is insensitive to base pairing with G,while an“OFF–ON”signal is observed in the presence and absence of ABPG,respectively.Especially,the t CO possesses large Stokes shift and high fluorescence intensity,which is proposed as an example to unveil the mechanism of enhanced photoluminescence and the effect of base pairing.3.Theoretical study of fluorescent guanine analogues for real-time detection of 5f CThe 5f C is a kind of presentative covalent DNA adducts originated from gene epigenetic modification that plays an important role in life.Considering the cytosine adduct 5f C prefer to form stable WC base pair with guanine（G）,a set of fluorescent G-analogues are performed to identify the target adduct.The calculations revealed that the modified deoxyribonucleoside analogue（8vd G）possesses efficient fluorescence emission,which is in good agreement with the experimental value.It is also found that the enhanced photoluminescence of 8v G was insensitive to base pairing with native cytosine,while the fluorescence tends to be completely quenched upon pairing with 5f C.Obviously,the optical changes（“Turn-on”and“Turn-off”）in the absence and presence of 5f C can be utilized to identify the DNA adduct.Finally,we further examined the effects of binding to deoxyribose on the electronic spectra to evaluate the direct usefulness of highly selective G-analogues in biological environments. |
