Alcohols

The low molecular weight alcohols, such as methanol and ethanol, have been identified in interstellar clouds (Cronin and Chang, 1993). Alcohols through C-4 were found in aqueous extracts from meteorites such as Murchison and Murray meteorites (Cronin and Chang, 1993; Cronin, 1998). In addition, branched-chain isomers have been found to be more abundant than the straight-chain isomers. In general, on meteorites, there is a predominance of branched carbon chains over the straight ones, suggesting a process in which radical or ion stability of the intermediates may have been influential in the synthetic processes (Cronin, 1998). We were thus very interested in studying alcohols.

We have found that of all the compounds investigated in our lab, the alcohols were perhaps the most interesting and puzzling. The interaction with silicates had been hinted at in the literature (Azrak and Angell, 1973; Sweryda-Krawiec et al., 1999) but research investigating the interactions of alcohols with sodium silicate is rare in the literature. In cases where the interactions between alcohols and sodium silicate had been studied, work had been done entirely in the aqueous state, and no gels had been isolated (Samadi-Maybodi et al., 2001). We have investigated nearly a dozen different alcohols of varying structures, and have found that smaller alcohols with more branched or compact structures are more effective in causing silica polymerization. This may have been a factor in the possible alcohol-silicate processes on meteorites. The alcohol silicates revealed unique physical and spectral properties (Liesch and Kolb, 2007a).

Upon the addition of a small amount of an alcohol to the sodium silicate solution, the two substances appear to be fully miscible. However, with a greater volume of alcohol, the mixture begins to separate into two distinct layers. The lower whitish layer consists of partially polymerized silicate, which is fluid in nature and has a low viscosity. By adding additional alcohol, the lower layer eventually solidifies into a white, soft, rubbery gel. We have described this volume-dependent trend in further detail in the literature (Liesch and Kolb, 2007a). Curiously, the alcohol gels were the only ones from our laboratory where we could feasibly control the viscosity and extent of polymerization by changing the volume of the alcohols added.

Processing and drying these gels presented quite a challenge. The water-soluble nature of the gels and the dramatic gel-sol transformations observed while processing these gels suggests that sol-gel-sol transformations could play a major role with the preservation and transport of alcohols.

Interestingly, even the dried gels behaved unlike any other gels studied in our lab. These dried gels were opaque and rubbery, yet were not entirely solid. Within days, chunks of gel would go from having crisp, distinct edges to having rounded edges. Ultimately, this gradual loss of integrity led to the fusion of chunks into a single large mass (Liesch and Kolb, 2007a). Analysis of these unique gels indicated no organics, within the detection limit of our IR instrument. It appears that alcohols do catalyze the polymerization of sodium silicate. It may be possible that water-soluble organo-silicates are formed in the process (Samadi-Maybodi et al., 2001; Lambert et al., 2004), but are largely removed by washing gels with water. This possibility has yet to be fully investigated.

In addition to the volume-dependent trends and water-solubility, the gels from alcohols were unique in terms of their IR spectra. As summarized later in Table 2, the Si-O-Si band can be typically found just under 1,100 cm-1. In gels formed from the alcohols, this band had been dramatically shifted by over 50 cm-1, in some cases towards lower wavenumbers (Liesch and Kolb, 2007a). Dramatic shifts in the location of the Si-O-Si IR band were seen only in the gels of alcohols and, to a lesser extent, in the gels of the amino alcohols and the Maillard-metal complexes. The nature of these shifts has not been elucidated, but the shifts can be used as an empirical tool for the cataloguing and characterizing these gels.

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