A Surface Plasmon Resonance Investigation of the Selective Interaction of Organic Vapors with Cavitands

A class of supramolecules, called cavitands, that have been shown to exhibit discotic phases depending on the structure, are shown to have potential for sensing applications. Certain cavitands (macrocyclic compounds based on resorcinarenes) display selectivity of interactions with organic vapors. We use Surface Plasmon Resonance (SPR) to demonstrate this principle. The two cavitands chosen for this study, had both a different size and shape of the preorganized cavity and were exposed to a variety of aromatic and chlorinated hydrocarbons. QxCav-1 (cavitand) was found to have a marked preference for the aromatic compounds; with the sequence of selectivity, determined by SPR to be nitrobenzene > toluene > benzene. MeCav-2 (cavitand) on the other hand, showed higher selectivity to dichloromethane with respect to aromatic vapors at room temperature. Cavitands therefore represent attractive sensing materials, with potential for application in devices using optical transduction schemes based on a refractive index change

Optical Sensing of the Selective Interaction of Aromatic Vapors with Cavitands

Cavitands represent an important class of synthetic molecular receptors with significant potential for chemical recognition. We use surface plasmon resonance (SPR) to demonstrate this fact using several organic vapors (aromatic and non-aromatic analytes) and three cavitands. The three cavitands (abbreviated QxCav-1, MeCav-2, and PzCav-3) chosen for this study, had a different size and shape of the pre-organized cavity. QxCav-1 was found to have a marked preference for the aromatic compounds while MeCav-2 showed an insignificant response towards these analytes and PzCav-3 showed intermediate preference for some of these analytes. The recognition pattern reveals the importance of the cavity size for interaction and confinement of the analytes. Based on the results, it is expected that cavitands will have great potential for application in chemical sensing devices using optical transduction schemes such as SPR

Influence of Cavity Depth on the Responses of SPR Sensors Coated with Self-Assembled Monolayers of Cavitands

Cavitands are synthetic organic compounds with enforced cavities of molecular dimensions. Cavitand Self-assembled Monolayers are shown to be highly responsive materials for SPR based chemical vapor sensing. The SAM approach permits an unambiguous comparison of the influence of cavity depth and synergistic interactions between cavitand and guest molecule. This eliminates the possibility of response biases arising from differences in sensing layer morphology. Consistent with earlier results on spin coated cavitands, aromatic vapors are selectively complexed within cavitand 3 (quinoxaline-bridged cavitand) and show lesser affinity for cavitand 2 (pyrazine-bridged cavitand) and cavitand 1 (methylene-bridged cavitand) owing to their smaller cavity depths. Cavitand 1, with its meniscus shaped pi basic cavity, selectively interacts only with small molecules with acidic methyl groups such as nitromethane and acetonitrile. Modeling results corroborate the experimental data and show that increased van der Waals interactions within cavitand 3 are responsible for the higher selectivity towards aromatic vapors

Electrochemical Experimental Study for the Characterization of Tetraferrocenyl-Cavitand, Synthetized in Click-Reaction

The electrochemical property of the new tetraferrocenyl-cavitand molecule was investigated in dimethyl formamide solvent using conventional and micro size platinum working electrodes. Quasi reversible redox character was found with one oxidation and one reduction wave of diffusion character. No electrode fouling could be observed. Different methods were used for determination of the diffusion coefficient of this species. In part of the measurements chronoamperometric measurements with microelectrode were carried out and evaluated according to the method introduced by Aoki and Osteryoung. Amperometric measurements with microelectrodes, as well as CV-s with conventional size electrode were also used in these studies