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![Figure. Mass spectrum of 2e. The molecular ion peak at m/z 1322 corresponds to [M+H] + for molecular formula C 84 H 120 O 12 .](profile/Birendra-Adhikari-4/publication/265137269/figure/fig2/AS:614394434183188@1523494456654/Figure-Mass-spectrum-of-2e-The-molecular-ion-peak-at-m-z-1322-corresponds-to-M-H.png)
Figure. Mass spectrum of 2e. The molecular ion peak at m/z 1322 corresponds to [M+H] + for molecular formula C 84 H 120 O 12 .
Source publication
p-tert-Butylcalixarene hexacarboxylic acid initially binds with low symmetry, to later adopt a highly symmetric up-down alternating conformation in the presence of Pb, Sr or Ba. The conformational dynamics for the three ions are distinct, from 15 hours, to 20 days, to 38 days, respectively.
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Citations
... While pursuing this, we found complementary use for the calix [6]arene hexacarboxylic acid towards binding of Pb, Sr and Ba with a new calix [6]arene octahedral geometry occurring. [28][29][30] Recently we reported that calixarenes are promising receptors for liquid membrane transport of choline-fluorophore conjugates. 15 Our results indicated that the presence of ionizable, pre-organized functional groups such as those on a calixarene scaffold provide effective transport of choline-fluorophore conjugates. ...
Upper rim phosphonic acid functionalized calix[4]arene affects selective transport of multiple molecular payloads through a liquid membrane. The secret is in the attachment of a receptor-complementary handle to the payload. We find that the trimethylammonium ethylene group present in choline is one of several general handles for the transport of drug and drug-like species. Herein we compare the effect of handle variation against the transport of serotonin and dopamine. We find that several ionizable amine termini handles are sufficient for transport and identify two ideal candidates. Their performance is significantly enhanced in HEPES buffered solutions. This inquiry completes a series of 3 studies aimed at optimization of this strategy. In completion a new approach towards synthetic receptor mediated selective small molecule transport has emerged; future work in vesicular and cellular systems will follow.
... Very recently, we reported on the complexation of Pb (II), Sr(II) and Ba(II) with p-tert-butylcalix [6]arene hexacarboxylic acid 1 ( Figure 1) (16,17). In these reports, we found that calixarene hexacarboxylic acid binds rapidly with all three metals and form low-symmetry 'lozenge' shaped complexes (18). ...
Calix[6]arene hexacarboxylic acid binds instantly and with low symmetry to Pb, Sr and Ba. Later a highly symmetric up-down alternating conformation emerges. The solution structures are identical to their p-tert-butylcalix[6]arene hexacarboxylic acid counterparts. With either receptor, an octahedral cage is formed around the metal. The transformation from low to high symmetry however proceeds at significantly faster rates for the de-t-butylated host.
In this paper, extraction behaviors of different carboxylic acid modified calixarenes towards Eu(III) and Nd(III) were performed. These extractants were extensively evaluated for the extraction abilities for extraction of Eu(III) and Nd(III) under different conditions, including pH, concentration of extractants and temperature. Carboxylic acid modified calix[6]arene (extractant-2) showed remarkably high extraction ability for Eu(III) and Nd(III). The thermodynamic parameters (enthalpy, entropy and Gibbs free energy) were determined. The extraction of Eu(III) with extractant-2 occurred with a cation exchange reaction and this extraction reaction is an exothermic process. Kinetic studies of reactive extraction of Eu(III) with extractant-2 were performed in a stirred cell. The value of mass-transfer coefficient of Eu(III) in chloroform was evaluated to be 3.35 × 10⁻⁶ m s⁻¹. The Hatta number was calculated and observed to vary in the range of 3.80 × 10⁻⁴–9.10 × 10⁻⁴. The effects of stirring speed, the phase volume ratio and species concentration on the initial extraction rate and Hatta number, demonstrate that the reaction is a very slow chemical reaction process occurring at the bulk of the organic phase. The rate constants of forward and backward reactions were determined to be 3.05 × 10⁻² (kmol m⁻³)−0.64 s⁻¹ and 1.55 × 10⁻³ (kmol m⁻³)−2.64 s⁻¹, respectively.
A novel calixarene derivative, amidoxime group modified calix[8]arene (C8A-AO), was synthesized from the nitrile group modified calix[8]arene (C8A-CN), and then the nitrile group was changed into an amidoxime group by treating with hydroxylamine under alkaline solution. The products were characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, field-emitting scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), elemental analysis and thermogravimetric analysis (TGA). The prepared C8A-AO was applied to adsorb U(vi) in low concentration uranium solutions, less than 1 mg L⁻¹. The effects of pH, contact time, initial concentration, and temperature on the sorption of U(vi) on C8A-AO were investigated. The adsorption efficiency of U(vi) on C8A-AO reached more than 95% in neutral solution. The results showed the adsorbent C8A-AO had an excellent distribution coefficient (Kd) when the initial uranium concentration was less than 1 mg L⁻¹. Additionally, the adsorption results revealed that the kinetics of U(vi) adsorption followed a pseudo-second-order model and the adsorption isotherm fitted well with the Langmuir model. The results of thermodynamic parameters showed that the adsorption process of U(vi) was spontaneous, feasible and endothermic. Furthermore, the excellent selective adsorption capability of U(vi) in simulated seawater suggested that C8A-AO was a potential adsorbent for recovery of U(vi) from seawater.
