Luminescence excitation spectra reveal low-lying excited states in stacked adenine bases.
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 approximately 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 approximately 0.9 eV as compared to the main form with the 260 nm/400 nm absorption/emission bands. The low-lying excited states suggest the stronger electronic coupling of the bases in a certain stacked form. It is proposed that such clusters of the stacked bases could provide the wire-like conductivity in the short segments of DNA.
Kononov
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Institute of Physics, Department of Molecular Biophysics, St. Petersburg State University, Ulyanovskaya 1198904 Petergoff, Russia. alexei.kononov@ens.fr
Bukina
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D000225:Adenine / Q000737:chemistry* / Q000528:radiation effects*; D000249:Adenosine Monophosphate / Q000737:chemistry; D005454:Fluorescence Polarization; D006863:Hydrogen-Ion Concentration; D049449:Luminescence; D008956:Models, Chemical; D009690:Nucleic Acid Conformation / Q000528:radiation effects; D010777:Photochemistry; D011061:Poly A / Q000737:chemistry; D012996:Solutions; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
D012996:Solutions; D014867:Water; D011061:Poly A; D000249:Adenosine Monophosphate; D000225:Adenine