| Self-assembly of monomolecular layers on solid surfaces has emerged as a simple yet powerful method for modification of interfacial properties. Recently, significant interest has focused on using self-assembled monolayers (SAMs) to study molecular recognition at surfaces as it is relevant in immunoassays, sensing, and other applications. SAMs formed from complex synthetic ‘host’ receptors contain molecular cavities for targeted recognition of specific ‘guest’ molecules. The challenge here has been to understand the role of molecular organization, structure, and forces in the recognition process, and thereby to improve selectivity in binding of guests such as metal ions, sugars, organic vapors, steroids, and apolar molecules. The research reported in this dissertation aims to address this challenge and establish principles that will be the basis for methods whereby the chemical selectivity of surfaces can be tailored.; To quantitatively explore the nature of targeted recognition a combination of near-surface sensitive spectroscopic tools such as surface plasmon resonance (SPR) and polarization modulation IR reflection absorption spectroscopy (PM-IRRAS) were implemented. Two modified calix[4]resorcinarene host receptors were synthesized such that they possess the same macrocyclic cavity for guest-host association but different sulfur containing alkyl chains for self-assembly on gold surfaces. It was found that the chemical structure of the host has profound effects on the monolayer structure and guest-host binding. Adsorption of small, neutral organic molecules was used to show that SAMs formed from calix[4]resorcinarene demonstrate strong and selective association with certain guest molecules from aqueous solutions and mixtures. The results highlight the interplay between steric size and forces such as hydrogen bonding and hydrophobic interactions. It is demonstrated for the first time that SAMs can discriminate between structural isomers. The results reported here also demonstrate for the first time the capability to ionize calix[4]resorcinarene monolayers, which opens up the use of electrostatic interactions to expand applications in sensing of ionic molecules and metallic ions, adsorption of heavy metals, and formation of selective sites that can act as catalytic centers. Ionic multilayer structures are demonstrated that make it possible to modify the size and upper rim functionality of the host cavity without the complications typically involved in covalent synthesis.*; *This dissertation is multimedia (contains text and other applications not available in printed format). |
