Molecular Recognition on a Cavitand-Functionalized Silicon Surface

Abstract

A Si(100) surface featuring molecular recognition properties was obtained by covalent functionalization with a tetraphosphonate cavitand (Tiiii), able to complex positively charged species. Tiiii cavitand was grafted onto the Si by photochemical hydrosilylation together with 1-octene as a spatial spectator. The recognition properties of the Si-Tiiii surface were demonstrated through two independent analytical techniques, namely XPS and fluorescence spectroscopy, during the course of reversible complexation-guest exchange-decomplexation cycles with specifically designed ammonium and pyridinium salts. Control experiments employing a Si(100) surface functionalized with a structurally similar, but complexation inactive, tetrathiophosphonate cavitand (TSiiii) demonstrated no recognition events. This provides evidence for the complexation properties of the Si-Tiiii surface, ruling out the possibility of nonspecific interactions between the substrate and the guests. The residual Si-O(-) terminations on the surface replace the guests' original counterions, thus stabilizing the complex ion pairs. These results represent a further step toward the control of self-assembly of complex supramolecular architectures on surfaces.

Exclusive recognition of sarcosine in water and urine by a cavitand-functionalized silicon surface

“…Silicon wafers grafted respectively with Tiiii½C 10 H 19 ;CH 3 ;Ph and its complexation-inactive but structurally related thiophosphonate analogue TSiiii½C 10 H 19 ;H;Ph (Fig. 1) were prepared via photochemical hydrosilylation of the double bonds on H-terminated Si(100) surfaces (14). The reaction leads to the formation of strong, hydrolytically stable Si-C bonds, capable to withstand the exposure to water and biological fluids in a wide range of pH.…”

“…The complexation properties of tetraphosphonate cavitands anchored on silicon surface toward N-methyl pyridinium and N-methyl ammonium salts in organic solvents have been recently investigated (14). Tetraphosphonate cavitand ability to distinguish between amino acids and their N-methylated analogues remains to be explored, as well as the possibility to transfer their complexation properties to aqueous and biological environments.…”

Hydrogen bonding in phosphonate cavitands: Investigation of host-guest complexes with ammonium salts

“…(2) To clarify the gas-phase properties of complexes formed by phosphonate cavitands, [9] since one of their applications is gas sensing [10]. The earlier reported results have shown that the phosphonate cavitands are capable of selectively forming complexes with alcohols [11][12][13][14] and ammonium ions [7,15,16], which has just recently led to application of phosphonate cavitands in supramolecular polymers [17], molecular recognition on silicon surfaces [18], and product protection in amine methylation reactions [19]. Number and positioning of the P ϭ O groups at the upper rim and their relative orientation with respect to the cavity are the key host parameters in defining the multiple H-bonding interactions involved in the recognition process [16].…”

Physical Vapour Deposition Techniques for Producing Advanced Organic Chemical Sensors

“…Among them phosphonate cavitands represent a third-generation emerging class of synthetic receptors whose molecular recognition properties toward alcohols and water were thoroughly demonstrated at the molecular scale by several analytical techniques such as ESI-MS and X-ray crystallography . The compounds described in this section are two novel phosphonate cavitands devoted to the detection of short chain alcohols synthetized by Dalcanale and co-workers (Biavardi et al, 2009): tetraphosphonate (Tiiii) and tetrathiophosphonate (TSiiii). Figure 17 shows the structures of the two compounds: they present an open, conformationally rigid cavity, delimited by four inward oriented P=O/P=S bridging groups at the upper rim.…”