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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