Ultraviolet spectra and structure of zinc-cellulose complexes in zinc chloride solution

The spectral characteristics of aqueous zinc chloride solutions (67% w/w) containing cellulose, cellobiose, maltose, β-methyl glucoside, and glucose were compared. The results suggest that zinc ion forms loose complexes with the C2 or C3 hydroxyl groups of glucose or methyl glucopyranoside. The absorption of light in the 200–220 nm range indicates the formation of these types of complexes. In solutions containing cellobiose or cellulose, zinc ion forms complexes with the hemiacetal oxygen atom of the anhydroglucose at the nonreducing end and a hydroxyl group of an anhydroglucose unit at the reducing end. This type of complex absorbs at 290 nm. Light absorption of cellobiose solutions at 235 nm was also correlated with similar complexes involving the anomeric oxygen at the reducing end of cellobiose. The absorption at 290 nm was proportional to the zinc chloride concentration. The presence of calcium ion also enhances the absorption; however, ion alone cannot form a complex with cellulose.