Determination of protolytic equilibria for methyl 3-azido-6-iodo-2,3,6-trideoxy-α-d-arabino-hexopyranoside by ab initio and spectrophotometric methods

UV absorption spectra of methyl 3-azido-6-iodo-2,3,6-trideoxy-α-d-arabino-hexopyranoside were recorded over a wide pH range. On this basis, a relationship between absorbance and pH was plotted, from which deprotonation equilibrium constants of this compound were determined. Further, quantum-mechanical calculations were performed at the ab initio level both in the gas phase by using the Restricted Hartree Fock (RHF), Møller–Plesset (MP2) methods and under consideration of solvation effects within the Polarizable Continuum Model (PCM), which enabled location of preferred protonation and deprotonation centers of this compound. The results provided the basis for discussion of the influence of substituents in the sugar ring on protolytic equilibria occurring in aqueous solutions of 3-azido-2,3-dideoxy sugars.