Covalent Organic Framework Based on Azacalix[4]arene for the Efficient Capture of Dialysis Waste Products

Abstract

Azacalix[n]arenes (ACAs) are lesser-known cousins of calix [n]arenes that contain nitrogen bridges instead of methylene bridges, so they generally have higher flexibility due to enlarged cavities. Herein, we report a highly substituted cationic azacalix[4]arene-based covalent organic framework (ACA-COF) synthesized by the Zincke reaction under microwave irradiation. The current work is a rare example of a synthetic strategy that utilizes the chemical functionalization of an organic macrocycle to constrain its conformational flexibility and thereby produce an ordered material. Considering the ACA cavity dimensions, and the density and diversity of the polar groups in ACA-COF, we used it for adsorption of uric acid and creatinine, two major waste products generated during hemodialysis treatment in patients with renal failure. This type of application, which has the potential to save ~400 liters of water per patient per week, has only been recognized in the last decade, but could effectively address the problem of water scarcity in arid areas of the world. Rapid adsorption rates (up to k = 2191 g mg -1 min -1 ) were observed in our COF, exceeding reported values by several orders of magnitude.

Macrocycle‐Based Covalent Organic Frameworks

“…Azacalix [4]arene, an analog of calix[n]arenes, is conformationally flexible in solution due to its enlarged cavities. Skorjanc et al [92] constructed COFs from azacalix [4]arene and Zincke salt, which showed 2D topology composed of highly substituted 3D building blocks (Figure 13d). The terminal amino groups connected with the bipyridium units determines framework extension, which shows wavelike square structure caused by the macrocyclic nature of the azacalix [4]arene (Figure 13e).…”

“…d) Schematic of azacalix [4]arene COFs. [92] e) structural models of the azacalix [4]arene COFs. f) Pseudo-second-order fitting and adsorption isotherm of uric acid and creatinine by the azacalix [4]arene COFs.…”

“…Reproduced with permission. [21,92] Copyright 2021, American Chemical Society; Copyright 2022, The Authors. Published by American Chemical Society, respectively.…”

“…c) UV-vis absorption spectra of cationic dyes including methylene blue and rhodamine B for the CX4-BD-1. d) Schematic of azacalix[4]arene COFs [92]. e) structural models of the azacalix[4]arene COFs.…”

Novel Microwave-Assisted Synthesis of COFs: 2020–2022

“…The capture of dialysis waste products is another use. The material combines a bispyridinium salt (BDB) with an azacalix [ 4 ] arene (ACA) following the Zincke reaction under irradiation of microwave materials at 90 °C for 3 h to generate the cationic ACA-COF [ 57 ]. Another ACA-COF was synthesized in solvothermal conditions, and the crystallinity observed was higher using microwave irradiation.…”