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MECHANISMS OF QUENCHING OF THE FLUORESCENCE OF A BENZO[a]PYRENE TETRAOL METABOLITE MODEL COMPOUND BY 2′‐DEOXYNUCLEOSIDES
Author(s) -
Geacintov Nicholas E.,
Zhao Rushen,
Kuzmin Vladimir A.,
Kim Seog K.,
Pecora Lorenzo J.
Publication year - 1993
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1993.tb09547.x
Subject(s) - chemistry , metabolite , pyrene , benzo(a)pyrene , quenching (fluorescence) , fluorescence , stereochemistry , photochemistry , environmental chemistry , organic chemistry , biochemistry , physics , quantum mechanics
Abstract— The hydrophobic interactions of bulky polycyclic aromatic hydrocarbons with nucleic acid bases and the formation of noncovalent complexes with DNA are important in the expressions of the mutagenic and carcinogenic potentials of this class of compounds. The fluorescence of the polycyclic aromatic residues can be employed as a probe of these interactions. In this work, the interactions of the (+) ‐trans stereoisomer of the tetraol 7,8,9,10‐tetrahydroxytetrahydrobenzo[a]pyrene (BPT), a hydrolysis product of a highly mutagenic and carcinogenic diol epoxide derivative of benzo[a]pyrene, were studied with 2′‐deoxynucleosides in aqueous solution by fluorescence and UV spectroscopic techniques. Ground‐state complexes between BPT and the purine derivatives 2′‐deoxyguanosine (dG), 2′‐deoxyadenosine (dA), and 2′‐deoxyinosine (dI) are formed with association constants in the range of ∼40–130 M −1 Complex formation with the pyrimidine derivatives 2′‐deoxythymidine (dT), 2′‐deoxycytidine (dC), and 2′‐deoxyuridine (dU) is significantly weaker. Whereas dG is a strong quencher of the fluorescence of BPT by both static and dynamic mechanisms (dynamic quenching rate constant k dyn = [2.5 ± 0.41 × 10 9 M 1 s 1 , which is close to the estimated diffusion‐controlled value of ∼ 5 × 10 9 M − 1 s −1 ), both dA and dI are weak quenchers and form fluorescenceemitting complexes with BPT. The pyrimidine derivatives dC, dU, and dT are efficient dynamic fluorescence quenchers ( K dyn ∼ [1.5–3.0] × 10 9 M −1 s −1 ), with a small static quenching component due to complex formation evident only in the case of dT. None of the four nucleosidcs dG, dA, dC and dT are dynamic quenchers of BPT in the triplet excited state; the observed lower yields of triplets are attributed to the quenching of single excited states of BPT by 2′‐deoxynucleosides without passing through the triplet manifold of BPT. Possible fluorescence quenching mechanisms involving photoinduced electron transfer are discussed. The strong quenching of the fluorescence of BPT by dG, dC and dT accounts for the low fluorescence yields of BPT‐native DNA and of pyrene‐DNA complexes.