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This work reports on the synthesis and characterization of three tritopic receptors and their binding properties toward various anions, as their tetrabutylammonium salts, and three alkali metal–acetate salts by UV–vis, fluorescence, 1 H, 7 Li, 23 Na, and 39 K NMR in MeCN/dimethyl sulfoxide (DMSO) 9:1 (v/v). Molecular recognition studies showed that the receptors have good affinity for oxyanions. Furthermore, these compounds are capable of ion-pair recognition of the alkali metal–acetate salts studied through a cooperative mechanism. Additionally, molecular modeling at the density functional theory (DFT) level of some lithium and sodium acetate complexes illustrates the ion-pair binding capacity of receptors. The anion is recognized through strong hydrogen bonds of the NH– groups from the two urea sites, while the cation interacts with the oxygen atoms of the polyether spacer. This work demonstrates that these compounds are good receptors for anions and ion pairs.

With the objective of studying the conformational and macrocyclic effects of selected metal chelates on their peroxidase activities, Cu2+ and Fe3+ complexes were synthesized with a macrocyclic derivative of ethylenediaminetetraacetic acid and o-phenylenediamine (abbreviated as edtaodH2) and its new open-chain analogue (edtabzH2). The Fe3+ complex of edtaodH2 has a peroxidase-like activity, whereas the complex of edtabzH2 does not. The X-ray study of the former shows the formation of a dimeric molecule {[Fe(edtaod)]2O} in which each metal with an octahedral coordination is overposed over the macrocyclic cavity, as a result of rigid macrocyclic frame, to form an Fe–O–Fe bridge; the exposure of the central metal to the environment facilitates the capture of oxygen to drive the biomimetic activity. The peroxidase-inactive Fe3+ complex consists of a mononuclear complex ion [Fe(edtabz)(H2O)]+, the metal ion of which is suited in a distorted pentagonal bipyramid to be protected from environmental oxygen. The copper(II) complexes, which have mononuclear structures with high thermodynamic stability compared with the iron(III) complexes, show no peroxidase activity. The steric effects play a fundamental role in the biomimetic activity.

Thermosensitive polymers based on poly(N‐isopropylacrylamide) (pNIPAM) have been widely evaluated in a variety of biomedical applications due to their particular thermal behavior in aqueous solutions. Despite this, few works have focused on the complementary analysis of the thermal transitions of pNIPAM polymers in linear and crosslinked form. In this work, linear and crosslinked poly(N‐isopropylacrylamide‐co‐acrylic acid) p(NIPAM‐co‐AA) copolymers were synthesized at similar NIPAM/AA feed composition and their thermosensitive behavior was studied by turbidimetric methods, FTIR spectroscopy analysis, and temperature‐dependent swelling measurements. The intermolecular crosslinking hindered the hydrophobic aggregation of chain segments, leading to higher transition temperatures of synthesized polymers. AA units promoted the intersegment hydrogen bonds during heating and strengthened the hydrogen bond interactions water‐network. The effect of the thermosensitive behavior of p(NIPAM‐co‐AA) copolymer on curcumin (CUR) release kinetic was also studied. The low uptake level of p(NIPAM‐co‐AA) hydrogel, partially shrunken at 37°C, produced a CUR sustained delivery, reaching the release equilibrium state up to 18 h. Hydrogels of p(NIPAM‐co‐AA) with a suitable composition exhibited a promising performance for the CUR controlled delivery at physiological conditions.

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