Calixarene and Resorcarene Based Receptors: From Structural and Thermodynamic Studies to the Synthesis of a New Mercury(II) Selective Material

Abstract

Materials used in current technological approaches for the removal of mercury lack selectivity. Given that this is one of the main features of supramolecular chemistry, receptors based on calix[4]arene and calix[4]resorcarene containing functional groups able to interact selectively with polluting ions while discriminating against biologically essential ones were designed. Thus two receptors, a partially functionalized calix[4]arene derivative, namely, 5,11,17,23-tetra-tert-butyl [25-27-bis(diethyl thiophosphate amino)dihydroxy] calix[4]arene (1) and a fully functionalized calix[4]resorcarene, 4,6,10,12,16,18,22,24-diethyl thiophosphate calix[4]resorcarene (2) are introduced. Mercury(II) was the identified target due to the environmental and health problems associated with its presence in water Thus following the synthesis and characterization of 1 and 2 in solution ((1)HNMR) and in the solid state (X-ray crystallography) the sequence of experimental events leading to cation complexation studies in acetonitrile and methanol ((1)H NMR, conductance, potentiometric, and calorimetric measurements) with the aim of assessing their behavior as mercury selective receptors are described. The cation selectivity pattern observed in acetonitrile follows the sequence Hg(II) > Cu(II) > Ag(I). In methanol 1 is also selective for Hg(II) relative to Ag(I) but no interaction takes place between this receptor and Cu(II) in this solvent. Based on previous results and experimental facts shown in this paper, it is concluded that the complexation observed with Cu(II) in acetonitrile occurs through the acetonitrile-receptor adduct rather than through the free ligand. Receptor 2 has an enhanced capacity for uptaking Hg(II) but forms metalate complexes with Cu(II). These studies in solution guided the inmobilization of receptor 1 into a silica support to produce a new and recyclable material for the removal of Hg(II) from water. An assessment on its capacity to extract this cation from water relative to Cu(II) and Ag (I) shows that the cation selectivity pattern of the inmobilized receptor is the same as that observed for the free receptor in methanol. These findings demonstrate that fundamental studies play a critical role in the selection of the receptor to be attached to silicates as well as in the reaction medium used for the synthesis of the new decontaminating agent.

Turning the volume down on heavy metals using tuned diatomite. A review of diatomite and modified diatomite for the extraction of heavy metals from water

“…Depending on the nature of the receptor, these are known Table 2 Summary of data on the removal of polluting ions from water by raw and modified diatomite. to complex and discriminate very effectively between anions or cations [93][94][95][96][97][98][99][100][101][102][103]. There is abundant evidence in the literature that these receptors can be tailored in order to interact with heavy metals without removing biologically essential ions.…”

Green Synthesis of Oligomer Calixarenes

“…Calixarenes have been broadly used, among others, as liquid crystal materials [10][11][12], sensors [13,14], catalysts [15,16], the stationary phase of chromatography [17], host molecules [18][19][20][21][22][23][24][25], or even semiconductors [26]. As a role in the guest-host system molecule, calix [4] arene and 4-tert-butylcalix [6]arene can be the host molecules for compounds such as trifluoromethyl-benzene contained in pesticides [24].…”

“…This finding makes calixarenes as a promising candidate as a host molecule to be used in chemical sensors to measure neutral organic molecules. In addition to being the host molecules for neutral compounds, calixarene and its derivatives were also proven to be a host for the molecular ion compounds such as heavy metal ions [19,20]. It is no wonder that calix[n]arenes have been greatly synthesized and yielded various oligomers with n = 4-20 according to their purposes.…”

“…Various modifications of functional clusters have also been developed in order to yield the desired molecular structures, for example, the modification of the aryl group [27] or the aldehyde. The modification can be in the form of the addition of a functional cluster such as alkyl cluster and hydroxyl cluster or the elimination of a functional cluster in the starting materials used or further modification of the calixarene molecules formed [19]. Some of the modifications make the calixarene structure more rigid, thereby forming the expected conformations [28].…”

Enthalpies of solution of C-alkylresorcin[4]arenes in alcohols at T= 298.15 K

“…The versatility of these compounds has been widely documented and they are quite important in supramolecular chemistry [1][2][3][4][5][6][7][8]. Studies related to the synthesis, conformational properties and applications in (host + guest) systems of C-alkylresorcin [4]arenes and their derivatives have been reported in the literature [1,[3][4][5][6][7][8][9][10][11][12][13][14]. Although abundant information on these topics is available, the physicochemical behavior of these macrocycles in solution is still not well understood and only a few works have been published [3,11,[15][16][17][18].…”