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Macrocyclic Receptors for Sensing the Environmentally Important Gaseous Molecules
Published in Satish Kumar, Priya Ranjan Sahoo, Violet Rajeshwari Macwan, Jaspreet Kaur, Mukesh, Rachana Sahney, Macrocyclic Receptors for Environmental and Biosensing Applications, 2022
Satish Kumar, Priya Ranjan Sahoo, Violet Rajeshwari Macwan, Jaspreet Kaur, Mukesh, Rachana Sahney
The word cavitand is usually used for container-shaped molecules possessing a cavity, which allows them to engage in host-guest chemistry with guest molecules of a complementary shape and size. Due to their outstanding molecular recognition properties, they are perfectly suitable for supramolecular sensing. The rational design of these synthetic receptors is achieved based on the analyte gas to be detected through proper functionalization of a host such as resorcinarenes, quinoxaline arenes, controlling weak host-guest interactions. Bridging groups often play an important role in the design of cavitands for the detection of different gases.
Supramolecular Materials
Published in Ghenadii Korotcenkov, Handbook of Humidity Measurement, 2020
In addition, we have to recognize that despite all attempts, a fully specific supramolecular sensor, in which nonspecific interactions and competitive binding by undesired analytes have been eliminated, has not been yet obtained. Contrary to expectations, the mere presence of a cavity in the molecules, which forms the sensitive layer, does not guarantee sensing selectivity. This fact has been clearly demonstrated by Grate et al. (1996) some years ago by comparing the selectivity patterns of polymers with those of cavitands, cyclodextrins, and cyclophanes toward a set of analytes. It was found that selectivity response patterns of cavitands to small molecules can be similar to common amorphous and crystalline polymers (Grate et al. 1996), indicating that cavitand sensors can respond not only to molecules with an ideal fit in the cavity but also to sorbed molecules occupying both intracavity and intercavity sites (Dickert and Schuster 1995; Grate 2000; Pirondini and Dalcanale 2007; Schneider 2009; Kumar et al. 2017). This means that cavitand-based sensors are not selective. In particular, it was found that calixarene-based sensors are sensitive to ammonia gas, volatile amines, aromatic nitrogenous molecules, acidic gases (HCl, NOx, CO2), organic vapors, gaseous aromatic compounds, toxic gases, H2, etc. (Kumar et al. 2017). Hromadka et al. (2017) also reported that calixarene-based sensors cannot discriminate between individual VOCs. Grate et al. (1996) have shown that the binding and selectivity in the examples cited are governed primarily by general dispersion interactions and not by specific oriented interactions, which could lead to a molecular recognition. 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 (Grate 2000). Moreover, Pirondini and Dalcanale (2007) believe that a truly specific receptor for a given molecule can be designed and prepared. According to Pirondini and Dalcanale (2007), two different strategies can be envisioned to avoid nonspecific interactions. From the receptor side, the challenge is to design a host incorporating a suitable transduction group (i.e., a chromophore), which can be activated exclusively by the molecular recognition event. Alternatively, the collective behavior of self-organizing materials can be tapped to amplify the molecular recognition phenomena at the macroscopic level.
Syntheses and structures of thiophosphorylatocavitands and their reactivity towards first-row transition metal halides
Published in Inorganic and Nano-Metal Chemistry, 2020
Xiao-Li Liu, Jing-Long Liu, Nian-Nian Wang, Ai-Quan Jia, Qian-Feng Zhang
The cavitand structure is obtained by the bridging of a resorcarene molecule with various moieties, including alkyl groups (e.g., methylene), aromatic pacers, or phosphorus and silicon moieties.[1–9] Peculiarly, the studies of phosphorus-containing derivatives of resorcinarenes demonstrated their wide applicability for the complexation and separation of metal ions.[10–12] Phosphorus-containing groups play an important role in host–guest chemistry and the properties of the phosphoryl (P = O) and thiophosphoryl (P = S) groups have been proved to be particularly good donors for metal ions.[13–16] It has been reported that the phosphoryl group binds alkali or alkaline earth metal ions through its oxygen atom, whereas the sulfur atom of the P = S thiophosphoryl group has more affinity for soft cations. Previously, Dutasta reported that the tetra-thiophosphonatocavitand with long-chain alkyl substituents in its iiii configuration exhibits excellent extraction properties for soft metal ions, with a better affinity for Ag+ (91%), than for Tl+ (38%) and Hg2+ (16%). The extraction of other picrate salts (Cu2+, Ni2+, Co2+, Zn2+, Cd2+, Pb2+) was not detected.[12,17] The P = S thiophosphoryl group was attached to the resorcin[4]arene skeleton to produce the thiophosphorylated cavitand by using a two-step synthesis in this article.[17] It was thus interesting to explore the possibilities of thiophosphorylated cavitands with different substituents to complex with first-row transition metal species, such as MnCl2, CoCl2, CuCl2, ZnCl2, CuCl, and CuI, by UV/vis absorption.[18] We report herein that thiophosphorylated cavitands have better extraction properties towards Cu(I) specie by the comparison of Mn(II), Co(II), Cu(II), and Zn(II) species.