Behavior of cellobiose in iron-containing solutions: towards a better understanding of the dominant mechanism of degradation of cellulosic paper by iron gall inks

Cellobiose, a dimer of glucose wearing a glycosidic bond as in cellulose, was used as model molecule to understand the chemical degradation pathways taking place in iron gall inks impregnated papers. Experiments were carried out in liquid phase at 80 °C to study the effects of pH and of the presence of iron and oxygen on the cleavage of the glycosidic bond. Capillary electrophoresis was used to quantitatively follow the cellobiose degradation and the formation of glucose. Attenuated total reflectance infrared spectroscopy of freeze-dried samples was done to identify the presence of secondary products of reaction. UV–Visible spectroscopy allowed monitoring the iron(II) and iron(III) contents as a function of time and pH. The data reveal that the simultaneous presence of iron and oxygen enhances the degradation of cellobiose. Nevertheless, even if some oxidation of the sugar molecules occurs, the predominant pathway of cellobiose decomposition is found to be acid-catalyzed hydrolysis due to the high acidity of the medium generated from the oxidation and precipitation of iron.