Supramolecular detection of solvent vapours with calixarenes: Mass-sensitive sensors, molecular mechanics and BET studies

Abstract

Abstract. Chemical sensors, based on highly mass sensitive QMB or SAW devices, coated with thin layers of calixarenes, enable the detection of organic solvent vapours, especially halogenated or aromatic hydrocarbons, down to a few ppm. Force field calculations allow the tailoring of these sensor materials seeing that the predicted interaction energies between the host molecules and a large variety of analytes are linearly correlated to the measured sensor effects. These correlations and also BET adsorption analysis prove the analyte recognition properties of these calixarene coatings to be mainly based on host/guest inclusion principles.Keywords: QMB-SAW-sensors, calixarenes, MM3 force field, BET.Functionalized calixarenes represent an important class of basic skeletons for the synthesis of lipophilic or polar host-systems for the inclusion of favored neutral molecules or ions in solid or liquid state systems [1,2]. The outstanding capacity of the calixarenes as receptors is mainly based on their variable chemical modification potential and their conformational pliability which enables a kind of induced fit on the shape of a suitable guest molecule [3]. Unlike the meanwhile immense number of examples for the detection of ions, there is still a lack of appropriate and powerful sensitive materials and optimized transducer devices for the development of chemical sensors for neutral compounds. The use of supramolecular principles by the application of macrocyclic, enzyme-like calixarenes as sensor coatings on the highly mass sensitive QMB or SAW [4] devices offer promising potentialities [5]. Calixarenes are easy to modify with respect to the shape and size of their cavity and afford a broad potential for development. Due to the fact that QMB and SAW devices are highly sensitive to mass changes of the sensor layer (in the range of 10-9 to 10-t4 g) the systems enable an universal applicability provided analyte molecules are incorporated into the calixarene coatings.

Materials and Transducers Toward Selective Wireless Gas Sensing

“…356,403 However, selectivity response patterns of cavitands to small molecules can be similar to common amorphous polymers 404 indicating that cavitand sensors can respond not solely only to molecules with an ideal fit in the cavity but also to sorbed molecules occupying both intracavity and intercavity sites. 96,405–407 Nevertheless, the presence of a preorganized cavity in cavitands does promise an advantage in sensitivity compared to amorphous polymers, especially if applied to the sensor in multilayers. 406 …”

Calixarenes in Thin Film Supramolecular Materials

“…The results indicated that the size of the attached alkyl chain did not influence the complexation properties but deep cavity cavitands selectively discriminated between xylene isomers based on their shape.52 In a further study that correlated both theoretical and experimental results, Dickert and Schuster showed that thin films of 61 gave a large response to toluene vapours. 54 This was thought to be due to CH -x interactions between the host and guest respective alkyl and aromatic sites. The results also showed that the selective recognition of analytes by the thin films was due mainly to host/guest inclusion interactions.54 In a later report Dickert et al reports the detection of solvent vapours at concentrations as low as 2 .…”

Biomimetic Molecular Recognition Elements for Chemical Sensing

“…This shape enables calixarenes to act as effective receptors as a result of their natural cavities. Favorable host cavities are essentially formed by cyclic intramolecular hydrogen bonding of the hydroxyl groups to create the cup or cone shape of the calixarene [97]. Researchers have found it possible to control the host selectivity to ion or small-molecule binding by functional modification of the upper and lower rims [96].…”

“…Using calixarenes with multiple different functional groups incorporated on the lower rim has shown that the photophysical properties of these systems can be easily influenced by different target binding modes. Aside from chromogenic sensors, these biomimetic receptor materials have shown successful incorporation into a variety of sensor platforms, including quartz crystal microbalance and surface acoustic wave oscillator base sensors, as the selective coatings [97]. The shape and chiral selective capabilities of calixarene-based coatings have shown to offer a solution to the selectivity problem of several sensing platforms.…”