Self-assembled carbohydrate monolayers: Formation and surface selective molecular recognition

The formation of self-assembled monolayers (SAMs) of representative thiocarbohydrate derivatives onto a gold surface has been investigated to build an artificial carbohydrate scaffold to mimic non-bonded molecular recognition phenomena. Three types of carbohydrate SAMs were formulated from (i) 1-beta-D-thioglucose (1), (ii) 1-beta-D-thioglucose tetraacetate (2), and (iii) 2-mercaptoethyl alpha-D-mannopyranoside (3). Subsequently, each SAM was spectroscopically characterized by reflection-absorption infrared spectroscopy (RAIRS). Deprotection of the acylated carbohydrate SAM was achieved in situ, indicating that chemical transformation may be performed without disruption of the sulfur-gold bond. With the mannose derivative, in which the carbohydrate moiety was separated from the gold surface by the spacer unit -OCH2CH2SH, it was possible to demonstrate that such a carbohydrate SAM was able to interact selectively with a specific carbohydrate binding protein, i.e., concanavalin A (Con A). Exposure of the mannose derived SAM to a solution of Con A led to a specific binding interaction as measured by RAIRS and surface plasmon resonance (SPR). In contrast, on exposure of the mannose SAM to the L-fucose-specific lectin tetragonolobus purpureas, no such binding was observed. These results suggest that highly ordered SAMs of specifically designed carbohydrate derivatives can be formulated to mimic natural cell surface structures and used to study selective molecular recognition interactions.