Sugars And Sugar Alcohols

Like amino acids, sugars play an important role in life as we know it. As any student of introductory biology or biochemistry can explain, sugars are an excellent energy source, make up part of our genetic material, and play key roles in a plethora of metabolic pathways (Lehninger et al., 2004). Sugars also play key roles in cellular recognition and provide structural support (Lodish et al., 2004). While structurally similar to sugars, sugar alcohols differ due to the reduction of their carbonyl groups to hydroxyl groups. In addition to their biological relevance, sugar-like compounds have been identified on meteorites (Cooper et al., 2001), thus establishing their astrobiological relevance. Some aspects of sugar-silicate interactions have already been studied (Kubicki and Heaney, 2002; Lambert et al., 2004).

Unlike the other classes of organic compounds already discussed, the sugars and sugar alcohols interact with sodium silicate gradually to form gels over a matter of days. These gels are typically soft, and some sol-gel-sol transformations have been observed. In the cases involving sugar alcohols, the sol-gel-sol transformations could be quite dramatic as these gels were water soluble. Often, a darkening can be observed in the solutions and gels resulting from sugars or sugar alcohols. Any traces of color seemed to be eliminated during the washing process, as the dried gels consist of small whitish chunks.

Taken as a whole, it appears that sugars and sugar alcohols merely catalyze the polymerization of sodium silicate solution. Entombment of organics seems unlikely as no organics have been observed in our IR spectra to date. While we observed no organics in the IR spectra, previous studies actually suggest a mechanism of cova-lent bond formation—not in the solid state, but as aqueous hypercoordinate chemical species (Kubicki and Heaney, 2002; Lambert et al., 2004). Thus, while the focus of our research has been on the mechanisms of silicification in the solid-state gels, it is possible that in addition to catalysis or entombment the mechanism of covalent bond formation is also occurring to produce water-soluble organo-silicates.

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