Insights into molecular recognition from the crystal structures of p-tert-butyl-calix[6]arene complexed with different solvents

The p-diethanolaminomethylcalix[4]arene-incorporated polyacrylonitrile-based facilitated-transport-nanofiber mat for O2/N2 separation

Separation of gases from air mixture is one of the most challenging and laborious separations due to the remarkably uniform molecular size of gas molecules. Therefore, the present study aimed to synthesize polyacrylonitrile-based nanofibers mat(NM) impregnated with p-diethanolaminomethylcalix[4]arene (PAN/p-DEAC4 NM) for the separation of two crucial gases O2 and N2. The affinity of the prepared PAN/p-DEAC4 NM for O2 was examined by optimizing the loading concentration of p-DEAC4 in the range from 5% to 20% (w/v). The results showed remarkable performance of the PAN/p-DEAC4 NM for O2/N2 separation with a superior O2/N2 selectivity of 12.75 and excellent permeance of 10.2 GPU for O2 and 0.8 GPU for N2 at 2 bar. The PAN/p-DEAC4 NM followed a facilitated transport mechanism for the separation of gases and it was revealed that the p-DEAC4 platform in the PAN NM is facilitating the transport of O2 due to its greater affinity towards O2. BET analysis revealed that the prepared NM possesses non-porous morphology with a surface area of 12.69 m2 g-1. SEM micrographs also confirmed the formation of defect-free NM. Thus, this study presents a unique perspective and direction for fabricating highly permeable nanofiber mats for O2/N2 separation.

Molecularly Mixed Composite Membranes for Gas Separation Based on Macrocycles Embedded in a Polyimide

Polyimides are a polymer class that has been extensively investigated as a membrane material for gas separation owing to its interesting permselective properties in a wide range of operation temperatures and pressures. In order to improve their properties, the addition of different filler types is currently studied. p-tert-Butylcalix[n]arene macrocycles (PTBCs) with different cavity sizes (PTBC4, PTBC6, PTBC8) were used as fillers in a commercial thermoplastic polyimide, with a concentration in the range 1-9 wt%, to develop nanocomposite membranes for gas separation. The selected macrocycles are attractive organic compounds owing to their porous structure and affinity with organic polymers. The nanocomposite membranes were prepared in the form of films in which the polymeric matrix is a continuous phase incorporating the dispersed additives. The preparation was carried out according to a pre-mixing approach in a mutual solvent, and the solution casting was followed by a controlled solvent evaporation. The films were characterized by investigating their miscibility, morphology, thermal and spectral properties. The gas transport through these films was examined as a function of the temperature and also time. The results evidenced that the incorporation of the chosen nanoporous fillers can be exploited to enhance molecular transport, offering additional pathways and promoting rearrangements of the polymeric chains.

Association Complexes of Calix[6]arenes with Amino Acids Explained by Energy-Partitioning Methods

Intermolecular complexes with calixarenes are intriguing because of multiple possibilities of noncovalent binding for both polar and nonpolar molecules, including docking in the calixarene cavity. In this contribution calix[6]arenes interacting with amino acids are studied with an additional aim to show that tools such as symmetry-adapted perturbation theory (SAPT), functional-group SAPT (F-SAPT), and systematic molecular fragmentation (SMF) methods may provide explanations for different numbers of noncovalent bonds and of their varying strength for various calixarene conformers and guest molecules. The partitioning of the interaction energy provides an easy way to identify hydrogen bonds, including those with unconventional hydrogen acceptors, as well as other noncovalent bonds, and to find repulsive destabilizing interactions between functional groups. Various other features can be explained by energy partitioning, such as the red shift of an IR stretching frequency for some hydroxy groups, which arises from their attraction to the phenyl ring of calixarene. Pairs of hydrogen bonds and other noncovalent bonds of similar magnitude found by F-SAPT explain an increase in the stability of both inclusion and outer complexes.