Fluorescence of Thymine Tautomers at Room Temperature in Aqueous Solutions

Abstract

Fluorescence and absorption spectra of 10 -4 M thymine in aqueous solutions at different pH values are reported at room temperature. The shape of the fluorescence spectrum is found to change when the excitation wavelength is varied. The absorption spectra for the aqueous pH 4-8 thymine solutions in the range 240-300 nm are believed to include the diketo tautomer T1 and the enol-keto tautomer T2. Steady-state fluorescence spectra and ab initio calculations support the existence of these neutral species in their ground state. The lifetimes of the excited states of the T1 and T2 tautomers are 0.72 and 3.87 ns, respectively. Aqueous thymine solutions with pH values below pH 3 contain a protonated enol-keto form of T2 in addition to the major diketotautomer T1 in its neutral form. The lifetime of the protonated enol-keto form is 4.2 ns. On the other hand, thymine solutions with pH values above pH 8 contain mixtures of the neutral forms of T1 and T2 as well as their monoanioic forms. However, aqueous thymine solutions at pH values above pH 11 contain a 1:1 equilibrium mixture of the monoanionic forms 1-HTand 3-HT -. The lifetimes for these monoanionic forms are expected to be shorter than 0.05 ns.

Normal Vibrational Mode Analysis and Assignment of Benzimidazole by ab Initio and Density Functional Calculations and Polarized Infrared and Raman Spectroscopy

“…27,36 As expected, Figure 4B shows that most of the observed C-H bond lengths of BZI are shorter than the estimated values. Exceptions for this trend are observed in C4-H3 and N1-H5 bond lengths that are remarkably stretched out to approach the estimated values.…”

Thin‐Film Properties of DNA and RNA Bases: A Combined Experimental and Theoretical Study

“…At the HF/ 6-31G** level, 3 a is predicted to be the energetically lowestlying form of thymine, which is in line with previous studies. [21,43,44] All other isomers are found to be 48-130 kJ mol À1 higher in energy. Because of the structural similarity to uracil, we would expect-besides the analogous behavior of the energetics-a similar description of the ionization potentials.…”

Elementary Molecular Mechanisms of the Spontaneous Point Mutations in DNA: A Novel Quantum-Chemical Insight into the Classical Understanding

“…It is generally believed that Thy exists in the canonical diketo form in the gas phase as well as in the aqueous solution (Kwiatkowski & Pullman, 1975), but there is experimental evidence of small amounts of its rare tautomeric forms in the gas phase (Fujii et al, 1986;Tsuchiya et al, 1988) and in the solution (Hauswirth & Daniels, 1971;Katritzky & Waring, 1962;Morsy et al, 1999;Samijlenko et al, 2010;Suwaiyan et al, 1995). Also laser ablation in combination with MB-FTMW spectroscopy spectroscopy has been used to establish unambiguously the presence of the diketo form of thymine in the gas phase and to obtain its structure (López et al, 2007).…”