Figure 1. Polymerization of silicic acid.

Figure 2. An example of organo-silicate: ribose (bottom left), serine (bottom right), and threonine (top right), make Si-O-C bonds with silicic acid within the silica gel.

of silicic acid to silica gel. Silica gel is characterized by the presence of the Si-O-Si bonds and Si-OH groups. Organic materials can interact with silicic acid or silica gel by forming covalent Si-O-C bonds, to give an organo-silicate. Several authors have proposed that hydroxyl-containing bio-organic materials can react to form organo-silicates, which will help stabilize and preserve those organics (Sullivan, 1986; Williams, 1986; Zubay, 2000; Perry and Kolb, 2004). This is shown in Fig. 2, using the examples of threonine, serine and ribose.

The preservation of organic material within silicates can come about by two different mechanisms (Perry and Kolb, 2004). The first mechanism is entombment, in which organic material is entrapped in a silica gel, during the polymerization. In the second mechanism, organic compounds covalently bond with the OH groups of the silicates, to form Si-O-C bonds. This mode could be feasible for the

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