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

The spectral characteristics of aqueous zinc chloride solutions (67% w/w) c ontaining cellulose, cellobiose, maltose, beta-methyl glucoside, and glucos e were compared. The results suggest that zinc ion forms loose complexes wi th the C2 or C3 hydroxyl groups of glucose or methyl glucopyranoside. The a bsorption 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 a t 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 i nvolving the anomeric oxygen at the reducing end of cellobiose. The absorpt ion at 290 nm was proportional to the zinc chloride concentration. The pres ence of calcium ion also enhances the absorption; however, ion alone cannot form a complex with cellulose. (C) 1999 John Wiley & Sons, Inc.