Calixarenes. 20. The interaction of calixarenes and amines

Abstract

The interaction of calixarenes and amines in CH3CN solution is postulated to involve a two-step process, viz., proton transfer from the calixarene to the amine to form the amine cation and the calixarene anion followed by association of the ions to form a complex. The overall association complex for p-allylcalix[4]arene and ZerZ-butylamine, as a typical example, is about 106, the larger part of this arising from the proton transfer, as measured from UV spectral observations, and the smaller part arising from the association of the ions, as measured from *H NMR observations. A 2D NOE spectrum of this complex indicates that the methyl groups of the amine and the allyl groups of the calixarene are proximate, in agreement with an emfo-calix structure for the complex.

Interaction of Calix[4]arene and Aliphatic Amines: A Combined NMR, Spectrophotometric and Conductimetric Investigation

“…3 calixOH + NR 3 Kp calixO -+ HNR 3 + Thus, the equilibrium constant, Kp, is defined by Equation 1. The Lambert-Beer law allows to relate the above equation to the measured absorbances at 310 nm.…”

“…1 In acetonitrile, calixarenes react with amines via proton transfer forming salts, that, as proposed by Gutsche, would exist as an equilibrium between exo and endo-calix complexes, in the same manner that calixarenes interact with soft metal cations and fullerenes, 2 even at low concentrations, such as that used in spectrophotometric titrations. 3,4 In solid state, 5 the exo-calix structure of the salt formed by calix [4]arene and piperidine does not show interactions between ammonium ion and the calixarene cavity, and the interaction between ions occurs only through one hydrogen bond between N + -H and O -of calix [4]arene. Coulombic interactions have a major role for structures of ammoniumcalixarene salts carrying acid groups.…”

Recuperação de Eu(III) e U(VI) de efluentes aquosos utilizando a técnica de membranas líquidas suportadas (MLS) e macrocíclicos como agentes extratores

“…Esta transferência é causada por uma diferença de solubilidade dos constituintes dentro das duas fases imiscíveis. A extração é feita durante a mistura de duas fases por agitação mecânica ou hidrodinâmica [16][17][18][19].…”

“…Ainda mais, cátions metálicos podem se coordenar com moléculas do solvente e serem extraídos. Este sistema é caracterizado pelo deslocamento da água coordenada das espécies metálicas, por solventes contendo oxigênio na molécula, tais como éteres, cetonas e ésteres [16][17][18][19].…”

“…Uma propriedade das mais importantes dos agentes quelantes é o caráter ácido-base fraco. Pelo ajuste do pH da fase aquosa, é possível controlar a reação de quelação com diferentes íons metálicos, dando origem à uma extração seletiva [16][17].…”