Abstract
AbstractAcidobasic 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 (pK HL = 9.65 ± 0.04, pK H2L = 4.18 ± 0.04), adenosine (pK H2L = 3.59 ± 0.05), cytosine (pK H2L = 4.56 ± 0.01), cytidine (pK H2L = 4.16 ± 0.02). In addition, thermodynamic parameters for bases: adenine (ΔH 0 = (−17 ± 4) kJ mol−1, ΔS 0 = (23 ± 13) J K−1 mol−1), cytosine (ΔH 0 = (−22 ± 1) kJ mol−1, ΔS 0 = (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.
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