Cu(II) complex formation with xylitol in alkaline solutions Original Research Article

The formation of four Cu(II)–xylitol complexes was observed in aqueous alkaline solutions (11.0 ⩽ pH ⩽ 14.0, I=1.0, 20 °C) by means of direct current polarography and VIS spectrophotometry. Mononuclear hydroxy complexes, CuXyl(OH)− (logβ=17.7 ± 0.5), CuXyl(OH)22− (logβ=20.2 ± 0.3) and CuXyl2(OH)24− (logβ=22.4 ± 0.3), are formed at high ligand-to-metal ratios (L:M ⩾ 10), whereas dinuclear complex Cu2Xyl (logβ=29.2 ± 0.3) is the predominant species at low ligand-to-metal ratio (L:M=0.5). Diffusion coefficients and molar absorptivities of the complex species were determined. pH variable 13C NMR suggested that pKa values of xylitol are rather similar and equal to 13.8 ± 0.2, 13.9 ± 0.1 and 13.9 ± 0.2 for OH-groups adjacent to (C-1,C-5), (C-3) and (C-2,C-4) carbon atoms, respectively.