Environmental Gas Sensing with Cavitands

Abstract

Environmental gas sensing needs stringent sensor requirements in terms of sensitivity, selectivity and ruggedness. One of the major issues to be addressed is combining in a single device the conflicting requirements of molecular-level selectivity and low-ppb sensitivity. The exploitation of synthetic molecular receptors as sensing materials is particularly attractive to address the selectivity issue, to single out the desired analytes in the presence of overwhelming amounts of interferents. This minireview summarizes the strategies in environmental gas and vapor sensing using molecular receptors as selective hosts for specific analytes, with the main focus on cavitands. In particular, we highlight the use of these macrocycles as selective preconcentrator units to be integrated into portable devices for environmental monitoring. Depending on the class of analytes to be detected, the molecular recognition properties of cavitands can be manipulated through the proper choice of the bridging groups at the upper rim, and their transducer integration can be implemented through the manifold functionalization options at the lower rim.

A new, deep quinoxaline-based cavitand receptor for the complexation of benzene

“…Indeed, the demand for fast and reliable detection of biological and chemical hazards is rising continuously and optimal sensors for environmental, security and biomedical applications must be sufficiently responsive to allow detection of the target analyte at low concentrations, and selective enough to respond primarily to a single chemical species in the presence of interferents. In this respect, quinoxaline-based cavitands, exploiting the -basicity and hydrophobicity of their cavity are ideal hosts to interact with aromatic compounds (Pinalli et al, 2018). Following this line of ISSN 2056-9890 research, we have synthesized a new member of the quinoxaline family, DeepQxCav, in which the cavity has been made deeper by the addition of four 1,4 dioxane rings on the quinoxaline walls.…”

Crystal structure of a host–guest complex between mephedrone hydrochloride and a tetraphosphonate cavitand

“…This method takes advantage of the ability shown by tetraphosphonate cavitands to selectively recognize the + NH 2 -CH 3 group ( + NHR-CH 3 in the case of cocaine) common to all the above-mentioned drug salts through the concomitant formation of CH 3 Á Á Á interactions and hydrogen bonding. Indeed, resorcinarene-based cavitands (Cram, 1983;Cram & Cram, 1994) decorated at the upper rim with phosphonate groups or quinoxaline moieties have long been exploited for their molecular recognition properties towards charged and neutral molecules (Dutasta, 2004;Vachon et al, 2011;Melegari et al, 2013;Pinalli et al, 2016;Tudisco et al, 2016;Trzciń ski et al, 2017;Pinalli et al, 2018;Wu et al, 2012;Clé ment et al, 2015). In order to further assess the recognition properties of tetraphosphonate cavitands towards quaternary ammonium salts of social interest, the supramolecular complex between Tiiii[C 3 H 7 , CH 3 , C 6 H 5 ] and mephedrone hydrochloride is herein reported and analysed, both in the solid state through the detailed analysis of its crystal and molecular structure, and in solution via NMR studies.…”

Host–guest supramolecular interactions between a resorcinarene-based cavitand bearing a –COOH moiety and acetic acid

“…In the past, the QCM approach has also been used in combination with resorcinarene-based cavitands for the molecular recognition of short-chain linear alcohols (Melegari et al, 2008), and for the detection of aromatic hydrocarbons in water (Giannetto et al, 2018). Cavitands, bowl-shaped synthetic macrocycles (Cram, 1983), have been successfully employed as sensors at the solid-gas interface (Pinalli et al, 2018;Tudisco et al, 2016), and also as building blocks for crystal engineering . In order to endow the preorganized cavity with hydrogen-bonding acceptor and donor properties, a tetramethyleneresorcin[4]arene functionalized at the upper rim with a carboxylic acid group, CavCOOH-in, was synthesized as receptor for the recognition of acetic acid.…”