Fluorescence properties of DNA nucleosides and nucleotides: A refined steady-state and femtosecond investigation

The room-temperature fluorescence properties of DNA nucleoside and nucleotide aqueous solutions are studied by steady-state and time-resolved spectroscopy. The steady-state fluorescence spectra, although peaking in the near-UV region, are very broad, extending over the whole visible domain. Quantum yields are found to be mostly higher and the fluorescence decays faster than those reported in the literature. The fluorescence spectra of the 2'-deoxynucleosides are identical to those of the 2'-deoxynucleotides, with the exception of 2'-deoxyadenosine, for which a, difference in the spectral width is observed. The steady-state absorption and fluorescence spectra do not show any concentration dependence in the range 5 X 10(-6) to 2 x 10(-3) M. All fluorescence decays are complex and cannot be described by monoexponential functions. From the zero-time fluorescence anisotropies recorded at 330 run, it is deduced that after excitation at 267 mn the largest modification in the electronic structure is exhibited by 2'-deoxyguanosine. In the case of purities, the fluorescence decays and quantum yields are the same for 2'-deoxynucleosides and 2'-deoxynucleotides. In contrast, for pyrimidines, the fluorescence quantum yields of nucleotides are higher and the fluorescence decays slower as compared to those of the corresponding nucleosides showing that the phosphate moiety affects the excited-state relaxation.