ESCA in Selected Organic Systems

Why do we study such cell-silicate interactions Human exposure to certain mineral silicate dusts has been associated frequently with the development of pneumoconiosis and other similar lung diseases. This has led to alterations of practices, enactment of programs of removal and replacement, and the virtual creation of major US government agencies, for example, the EPA. In many in- 

Chemical modifications by derivitizing the surfaces of mineral fiber silicates have revealed alterations in reactivity in in vitro cell toxicity studies, suggesting a multifactorial character of particle/cell interactions [171]. In addition, the adsorption of bovine serum albumin onto asbestos fibers has been shown by infrared spectroscopy and NMR to be mediated by O—H—N hydrogen bonds [172]. In view of the various hypotheses put forward in the bulk biochemical studies and the apparent surface-oriented origins of these reactions, it is important to examine the features of the silicate/cell interfaces and surfaces. Herein we present a typical case of the interaction between a related alumino-silicate (i.e., cummingtonite) and bioorganic cell interaction. 

The relative amount of surface A1 wrt. Si increases very markedly when cum-mingtonite is treated with cells as compared to a firesh sample or one that is placed only in a medium. The Si/A1 ratio can decrease in two ways—either Al+ ions are released from the tetrahedral and octahedral lattices and drawn to the cell/silicate interface in the presence of cells, or the reverse happens to the silicon. On the other hand, no aluminum was detected either in the medium or in the cells after contact with the aluminosilicate. During cell/silicate interaction there is also a definite increase in the concentration of Fe on the surface and a slight increase in the level of Mg. 

Other related cell (rat tumor and lung cells)/silicate (Chrysotile-sheet silicate asbestos, silicon, silica, hornblende) interaction studies performed using ESCA have been reviewed in detail elsewhere by Seal and his coworkers [177-180]. The general feature inherent to all of these systems is that there seems to be a particular type of chemical interaction between the cells and the silicate involving direct coupling between the cell and the tetrahedral silicate subunit with a corresponding release of these components to the octahedral subunit (i.e., the Al, Mg, and particularly the Fe). The results also suggest that some of the Fe is inserted into the cell. 

Since the early 1970s, XPS has been the favored method for the surface chemical analysis of polymers [181, 182] but it is not without problems, not least of which is the small dynamic range of the chemical shift of the C Is photoelectron line and other peaks of interest (e.g., O Is, N Is, Si 2p, S 2p, etc.). There have 

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