Cu(II) complex formation with xylitol in alkaline solutions

The formation of four Cu(II)-xylitol complexes was observed in aqueous alkaline solutions (11.0 less than or equal to pH less than or equal to 14.0, I = 1.0, 20degreesC) by means of direct current polarography and VIS spectrophotometry. Mononuclear hydroxy complexes, CuXyl(OH)(-)(log beta = 17.7 +/- 0.5), CuXyl(OH)(2)(2-) (log beta = 20.2 +/- 0.3) and CUXYl(2)(OH)(2)(4-) (log beta = 22.4 +/- 0.3), are formed at high ligand-to-metal ratios (L:M greater than or equal to 10), whereas dinuclear complex CU(2)XYl (log beta = 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 C-13 NMR suggested that pK(a) 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. (C) 2003 Elsevier Ltd. All rights reserved.