Enhanced Coordination by Preorganization. Surface Chelate Effect and Signaling

ENHANCED COORDINATION BY PREORGANIZATION. SURFACE CHELATE EFFECT AND SIGNALING 

FIGURE 1. Surface-functionalized NPs. (a) NPs with a high density of binding units on its surface, (b) Multidentate coordination with NPs. 

This thermodynamic effect of the enhancement of classical recognition features is basically due to entropic factors related to the preorganization of the coordination sites on the surface that reduce the conformational flexibility of the receptors and increase their effective concentration at the surface. This results in a remarkable improvement of the recognition characteristics. From a molecular viewpoint, surface functionalization creates a multidentate coordination environment that displays a statistical advantage in relation to coordination when compared to the molecular receptor. This effect has also been called the surface chelate effect and is not a unique feature of surfaces functionalized with binding sites. It has also been reported for coordinating dendrimers that show a positive dendritic effect, which is related to 

FIGURE 2. Route for the preparation of a dual sorption and sensing material for Hg cation (first step) and indication and sorption reaction (second step). 

Most of the reported examples involve the use of MCM-41, MCM-48, hydrothermally stable mesoporous molecular sieves (SBA-15) or silica nanotube matrices in which certain selective probe molecules are covalently anchored to the pore walls. In addition, the very low detection limits observed for some of these systems suggest that the surface chelate effect also plays a role here. Following this approach, chemosensors for the signaling of Cy2+ 34 36 pg3+37 2+ 35,38 describcd. Optical pH sensors using 

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