Iveta Pilařová

Spectroscopic study of protonation of oligonucleotides containing adenine and cytosine

Acidobasic properties of purine and pyrimidine bases (adenine, cytosine) and relevant nucleosides (adenosine, cytidine) were studied by means of glass-electrode potentiometry and the respective dissociation constants were determined under given experimental conditions (I = 0.1 M (NaCl), t = (25.0 ± 0.1) °C): adenine (pKHL = 9.65 ± 0.04, pKH2L = 4.18 ± 0.04), adenosine (pKH2L = 3.59 ± 0.05), cytosine (pKH2L = 4.56 ± 0.01), cytidine (pKH2L = 4.16 ± 0.02). In addition, thermodynamic parameters for bases: adenine (ΔH0 = (−17 ± 4) kJ mol−1, ΔS0 = (23 ± 13) J K−1 mol−1), cytosine (ΔH0 = (−22 ± 1) kJ mol−1, ΔS0 = (13 ± 5) J K−1 mol−1) were calculated. Acidobasic behavior of oligonucleotides (5′CAC-CAC-CAC3′ = (CAC)3, 5′AAA-CCC-CCC3′ = A3C6, 5′CCC-AAA-CCC3′ = C3A3C3) was studied under the same experimental conditions by molecular absorption spectroscopy. pH-dependent spectral datasets were analyzed by means of advanced chemometric techniques (EFA, MCR-ALS) and the presence of hemiprotonated species concerning (C+-C) a non-canonical pair (i-motif) in titled oligonucleotides was proposed in order to explain experimental data obtained according to literature.