Anion Binding Inside a Bambus[6]uril Macrocycle in Chloroform

Abstract

Bambus[6]urils are a class of neutral anion receptors with outstanding binding properties in various solvents. The host–guest associations of bambusurils in aqueous environments have been investigated in detail, but their behavior in nonpolar solvents has not yet been reported. This paper presents isothermal calorimetry and 1H NMR data on the binding of dodecabenzylbambus[6]uril (Bn12BU[6]) to seventeen anions in chloroform. Under these conditions, anion inclusion in the macrocycle appears to be enthalpy‐driven, yielding complexes with stability constants of up to 1010 m−1. Perchlorate was optimally sized for inclusion in Bn12BU[6], while larger anions exhibited significantly lower affinity for the macrocycle. In addition, complexes of bambusuril and anions can be differentiated by NMR analysis based on the unique chemical shifts of characteristic peaks in their spectra. This finding was used to perform quantitative and qualitative analysis of multiple anion mixtures.

Size-matched recognition of large anions by cyanostar macrocycles is saved when solvent-bias is avoided

“…These uses include ion-pair catalysis, 6 lithium ion batteries with PF 6 À electrolyte, 7 and perchlorate, ClO 4 À , in rocket fuel that infiltrates waterways impacting human health. This belief abruptly changed with the creation of size-matched receptors, the cyanostar, 1,12 bambusuril, 3,4,13 and tricarb 2 macrocycles that showed large affinities for larger anions. This belief abruptly changed with the creation of size-matched receptors, the cyanostar, 1,12 bambusuril, 3,4,13 and tricarb 2 macrocycles that showed large affinities for larger anions.…”

“…1 While this behaviour leads to potent cooperativity and interesting selfassemblies (Fig. Bambus [6]urils 3,4,13 are an example of such 1 : 1 systems. Receptors that form 1 : 1 complexes would better allow direct causal connections to be made between the molecular structure, the solvents used, and the observed anion affinities.…”

“…5c). 4,13 The solvents used to test the size selectivity in all cases (iPrCS in CD 2 Cl 2 :CD 3 OD, bambu [6]suril in H 2 O and CHCl 3 ) have reasonable acceptor numbers (AN). Higher AN values may lead to biased solvation of those anions with more available lone pairs.…”

A Família Das Bambus[n]urilas

“…Desde a descoberta da MeBU [6], diversos derivados foram reportados contendo resíduos alifáticos e substituintes aromáticos. [33][34][35][36][37] De maneira geral, as glicolurilas dissubstituídas reagem com formaldeído em meio ácido, em condições específicas, produzindo as respectivas BU[n] funcionalizadas (Figura 5). As benzil-bambus [4]urila (BnBU [4]), benzil-bambus [6]urila (BnBU [6]) e propil-bambus [6] urila (PrBU [6]) 34 foram obtidas a partir das 2,4-dibenzilglicolurila ou 2,4-dipropilglicolurila, respectivamente, em solventes apolares, e não em meio aquoso como na síntese da MeBU [6].…”

“…As benzil-bambus [4]urila (BnBU [4]), benzil-bambus [6]urila (BnBU [6]) e propil-bambus [6] urila (PrBU [6]) 34 foram obtidas a partir das 2,4-dibenzilglicolurila ou 2,4-dipropilglicolurila, respectivamente, em solventes apolares, e não em meio aquoso como na síntese da MeBU [6]. A BnBU[6] obtida era capaz de formar complexos com elevada constante de formação com diversos ânions em clorofórmio, 35 As metil-semitio-bambus [4]urila (MeBUS [4]) e metil-semitio--bambus [6] …”