Luminescence Excitation Spectra Reveal Low-lying Excited States in Stacked Adenine Bases.

摘要

Luminescence emission, polarization, and excitation spectra of polyadenylic acid (poly(A)) have been studied in room-temperature aqueous solution (pH 8). The temperature dependence of the luminescence of poly(A) at two different excitation wavelengths in the range 10-70 degrees C has also been studied and compared with that of adenosine 5'-monophosphate (AMP). It has been found that the luminescence excitation spectrum and the polarization curve of poly(A) solution reveal a low-intensity electronic transition at about 320 nm which is red-shifted by ~0.9 eV from the maximum of the absorption spectrum at 260 nm. A model of two luminescent stacked forms is suggested. The difference in the ground state levels of these two stacked forms obtained from the temperature dependencies of the emissions is insignificant ( approximately 1 kcal/mol). This means a lowering of the excited state of the stacked form with the 320 nm/420 nm absorption/emission bands by ~0.9 eV as compared to the main form with the 260