Cu(II) complex formation with xylitol in alkaline solutions

Area of Science:

• Coordination Chemistry
• Solution Chemistry
• Spectroscopic Analysis

Background:

• Copper(II) ions are essential trace elements with diverse biological roles.
• Xylitol, a sugar alcohol, can act as a ligand in coordination complexes.
• Understanding metal-ligand interactions is crucial for various applications, including medicine and materials science.

Purpose of the Study:

• To investigate the formation and characterization of copper(II)-xylitol complexes in aqueous alkaline solutions.
• To determine the speciation of copper(II) as a function of xylitol concentration and pH.
• To elucidate the structural and chemical properties of the formed complexes.

Main Methods:

• Direct current polarography and VIS spectrophotometry were employed to study complex formation.
• pH-dependent 13C Nuclear Magnetic Resonance (NMR) spectroscopy was used to determine xylitol's pKa values.
• Analysis of complex stability constants (log beta) and diffusion coefficients.

Main Results:

• Four distinct copper(II)-xylitol complexes were identified: mononuclear CuXyl(OH)-, CuXyl(OH)2(2-), CuXyl2(OH)2(4-), and dinuclear Cu2Xyl.
• Mononuclear species predominate at high ligand-to-metal ratios (L:M ≥ 10).
• The dinuclear complex Cu2Xyl is the primary species at low L:M ratio (0.5).
• Xylitol exhibits pKa values around 13.8-13.9, indicating its deprotonation in alkaline conditions.

Conclusions:

• The speciation of copper(II) in alkaline solutions is highly dependent on the xylitol-to-copper ratio.
• The determined stability constants and physical properties provide insights into copper-xylitol interactions.
• This research contributes to understanding metal-polyol complexation in biologically relevant pH ranges.