Surface propensity of small organic biomolecules in vapor-water interface by XPS

Full text: Biochemical reaction in living systems takes place in aqueous solutions containing small organic molecules, known as osmolytes. These molecules affect the stability of different cellular structures. For example, denaturant osmolytes (e.g., urea and salts) favor the unfolded state of proteins whereas stabilizing osmolytes (e.g., TMAO and betaine) favor the folded state. Effects of the latter can be compared with the ions on the left side of the Hofmeister series, which help stabilize the native, folded structures of proteins. Regulation of osmolytes by living organisms allows them to survive extreme conditions that, otherwise, would account for unstable cellular structures. Accordingly, TMAO levels in muscles of deep-sea organisms were found to increase with the depth in which they are capture, possibly to counteract the destabilizing effect of pressure on molecular structures. Despite intensive studies, the atomic mechanisms of osmolytes are not well understood. In addition of providing basic knowledge of how life unfolds, unraveling these mechanisms will enable rational designs of new and more efficient osmolytes to control molecular structures. The aim of this study is to provide estimates of the relative concentration as well as orientation of different osmolytes and mixture of osmolytes at the vapour-water interface using X Ray Photoelectron Spectroscopy (XPS) technique in aqueous solutions. This will allow us to compare mechanisms of action of different protecting osmolytes; TMAO, betaine and glycine as well as denaturant osmolyte; urea. Based on recent measurements of the vapour-water surface tension, the stabilizing mechanism of TMAO may be different from the one of betaine and glycine. Moreover, our study will be useful to test computational models of osmolytes. (author)