Publication Details (including relevant citation information):
Sen, Sudeshna, Pal, Uttam, Maiti, Nakul Chandra -
Abstract: Determination of pKa of OH groups present in D-ribose is crucial in order to elucidate the origin and mechanism of many catalytic processes that involve the ribose unit. However, there is hardly any report about the experimental pKa of the OH group due to lack of appropriate method. In this study we have investigated the protonation state of OH groups in D-ribose by introducing C-D labeling and measuring the changes in the isolated C-D frequency in several isotopologues of the compound with pH. The large shift in the ?C D of D ribose C1 D in ionized condition compared to other deuterium substituted D-riboses (e.g. D-ribose-C2-D, D-ribose-C3-D etc.) confirmed that C1 OH group preferred ionization and the ionization pKa was 11.8. Both the ionized and unionized structures of D-ribose preferred pyranose conformation, which was supported by 13C NMR experiments. Electronic redistribution via resonance and intra-molecular hydrogen bond formation were proposed to account for the stabilization of the ionized structure.
Address (URL): http://dx.doi.org/10.1021/jp4092392