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-β-Dthioglucose (1), (ii) 1-β-D-thioglucose tetraacetate (2), and (iii) 2-mercaptoethyl R-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 sulfursgold bond. With the mannose derivative, in which the carbohydrate moiety was separated from the gold surface by the spacer unit sOCH2CH2SH, 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.

Novel phthalocyanine (Pc) molecules have been designed and synthesized to incorporate a thiol moiety for the formation of monolayer films onto gold-coated optical waveguides via the technique of self-assembly. The thiol moiety is connected to the Pc macrocycle by either a (CH2)11 or (CH2)3 hydrocarbon chain. Both Pc SAMs have been characterized on the metal surface using reflection absorption infrared (RAIR) spectroscopy. The RAIR spectra suggest that the two Pc molecules lie in a different orientation with respect to the gold surface. This behavior can be rationalized with consideration of the different structures (the different alkyl connecting chain lengths and different macrocyclic peripheral side chains) of the two Pc molecules. The fluorescence emission spectrum of each of the Pc SAMs has been obtained by exciting each monolayer along the longitudinal axis of the optical waveguide via laser-induced evanescent wave stimulation. The use of the longer mercaptoalkyl connecting chain appears to inhibit quenching of the electronically excited state through energy transfer to the metal layer. It is thought that the presence of peripheral alkyl side chains (six hexyl or seven decyl chains, respectively) minimizes self-quenching in the single-component SAM film. It has also been shown that the fluorescence signal of the (CH2)11 mercaptoalkyl Pc SAM can be reversibly quenched by exposure to gaseous nitrogen dioxide (NO2). The decrease in fluorescence intensity has been related to increasing NO2 concentration by a Stern−Volmer relationship. The Pc SAM can detect concentrations of NO2 down to 10 ppmv with no interferent effect seen from other environmentally relevant gases:  carbon monoxide and carbon dioxide. These results suggest that SAMs of specifically designed materials, such as Pc's, may be used as sensitive receptor molecules to form the basis of a novel technology for the development of optical chemical sensors for gaseous species.

A series of three Phthalocyanine (Pc) derivatives have been designed, synthesised and formulated as selfassembled monolayers (SAMs) on gold-coated optical waveguides. The alkyl chain tethering the Pc macrocycles to the gold surface via a thiol moiety varied in length viz. (CH 2 ) 11 , (CH 2 ) 8 and (CH 2 ) 3 . The three Pc SAMs have been characterised using re¯ection absorption infrared spectroscopy and ¯uorescence spectroscopy excited via the evanescent wave. The infrared data have shown that the length of the alkyl tether has a profound effect on the orientation and packing density of the Pc macrocycle on the gold surface. Similarly, the intensity of ¯uorescence observed from the Pc monolayers was related to the length of the alkyl tether. A further investigation of the C 11 Pc derivative SAM has shown that the monolayer ®lm was stable, exhibiting no oxidation and only minor orientation changes on the gold surface over a period of 24 months as determined by infrared and ¯uorescence spectroscopy. The longevity of the Pc SAM is thought to be due to the macrocyclic ring possibly preventing oxidation of the thiolate root. As simple alkanethiols are known to oxidise at gold surfaces, the stability results obtained for the Pc derivative would suggest that macrocyclic SAMs may have properties that are more suitable for long term applications.

We show how a simple reparameterization can reduce the number of parameters that need to be estimated by numerical maximum likelihood in site occupancy models. Three examples are provided.