Singlet Excited State Dynamics of Tetrakis(4-N-methylpyridyl)porphine Associated with DNA Nucleotides

Abstract

The singlet excited state behavior of tetrakis(4-N-methylpyridyl)porphine (T4MPyP) in the presence of the four mononucleotides of DNA in aqueous solution has been examined. Addition of the nucleotides of adenine, thymine, or cytosine to a solution containing T4MPyP results in an increase in the fluorescence intensity of the porphyrin, while addition of guanine substantially quenches the intensity. Optical absorption measurements demonstrate noncovalent interactions of the nucleotides with the porphyrin, resulting in bathochromic shifts in the Soret region. Binding constants for the base:porphyrin complexes were determined from steady-state absorption data to be 1743 ± 68, 385 ± 15, 2433 ± 150, and 198 ± 7 M-1 for dAMP, dTMP, dGMP, and dCMP, respectively. The T4MPyP singlet state lifetime increases from 5.29 to 11.3, 10.3, and 7.8 ns in the presence of dAMP, dTMP, and dCMP, respectively. In the case of dGMP, the lifetime data was best fit to a Lorentzian distribution centered at 0.69 ns and a discrete component at 3 ns. The quenching was modeled using an excited state reaction mechanism coupled with ground state complexation. The quenching is attributed to electron transfer between guanine (the most reducing of the bases) and T4MPyP (i.e., reductive quenching of the porphyrin singlet state).

Effects of environment on the photophysical characteristics of mesotetrakis methylpyridiniumyl porphyrin (TMPyP)

“…However, in our experimental results, we did not observe any significant dependence of st on f. The changes in the TMPyP absorption and fluorescence spectra due to variations of the solvent polarity could be associated with charge transfer (CT) between the porphyrin core and lateral groups, which contributes to the formation of their lowest absorption maximum [32][33][34]. However, when CT transitions do occur at the change of the environment polarity, the absorption and fluorescence spectra appear significantly shifted [35] while in our experiments we have observed just a weak effect of solvent polarity on the TMPyP spectra.…”

“…The larger Stokes shift in water, compared to that of organic solvents, can be associated to a higher f in water. It can also be associated to the solvent polarity effect on the CT transition, as proposed in the literature [32][33][34]. However, the increase of environment polarity generally induces a red shift of the CT absorption band [35].…”

Fluorescence-Quenching Phenomenon by Photoinduced Electron Transfer between a Fluorescent Dye and a Nucleotide Base

“…charge recombination between a dye and nucleobases. 9,20,[46][47][48] We here evaluated the reversibility of the fluorophore-DNA conjugates listed in Table 3 (Alexa 488, 5-FAM, BODIPY FL, Alexa 532, and 6-JOE) by repeating denature and hybridization steps using temperature control under continuously supplying blue LED with the maximum emission of 470 nm (0.1 mW) to all of the hybridization solution (the concentration of DNA probes and its complementary DNA were 40 and 160 nM, respectively). All of the DNA probes examined here were completely reversible after exposure to the above-mentioned conditions over a period of a few hours.…”

Interactions between meso-tetrakis(4-(N-methylpyridiumyl))porphyrin TMPyP4 and DNA G-quadruplex of telomeric repeated sequence TTAGGG

“…A and A f , respectively, represent the absorbance at 432 nm for the TMPyP4/DNA mixture and that for free TMPyP4. The inset of Figure 3 The charge transfer between the singlet excited-state of TMPyP4 and the ground-state of guanine base is thermodynamically possible [13,14] as shown in the following equation.…”