A study of the adhesion of organosulfur compounds at the surface of silica is proposed. This work defines a previously unknown mode of binding hydrocarbon to the surface of silica. Chemical reactions of molecules grafted on surfaces are of growing interest in surface science; these systems, characterized by IR transmission and solid state NMR, have direct relevance to bioadhesion--the physical and chemical interactions of bacteria adhering to membrane, or white blood cells adhering to bioimplants. There are four major targets: 1. New surface reactions on Silica (100012). We will react organosulfur compounds with the surface of silica heated to 1000C in high vacuum. For example, a thiol gives a thiosiloxane film containing the S-Si bond. 2.Surface Grafting of Bifunctional Molecules on Silica (1000). Bifunctional molecules, containing the organosulfur head group to react with the silica (1000) and a terminal functional group exposed at the surface will be grafted. The second functionality must either not react with the silica (1000) or be chemically protected from such reaction. For example, in a bifunctional molecule such as a halogenated alkanethiol, Cl-(CH2)nSH, both the S and the Cl could potentially interact with surface siloxanes. Trifunctional cysteine could be absorbed exclusive through its SH group by protecting the carboxylate through esterification and the amine through alkylation. 3. In-situ reactions. The goal is to prepare surface functionalities which could not be prepared directly from absorption of bifunctional molecules. Dealkylation and hydrolysis of protected groups referred to in 2 above will be the first experiments. Another examine would be preparation of an aldehyde terminated thiosiloxane film; the adsorbate precursor C=O (CH2)nSH is synthetically inaccessible. This firm may weakly coordinate /adhere metals. 4. Adsorbate-Interactions with the Modified Surfaces. Studies of the molecular environment at the interface reveal the fundamental factors affecting surface-adsorbate interactions. We will vary systematically the alkyl chain length and the chain terminus to effect steric and chemical control of the surface's absorption properties. These effects will be probed with spectroscopic studies of controlled atmosphere environments such as e.g. reversible pyridine coordination.
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