Selective extraction of sulfates in the form of alkali metal salts using charge-neutral molecular receptors is one of the holy grails of supramolecular chemistry. Herein we describe, for the first time, a squaramide-based ion pair receptor equipped with a crown ether site that is able to extract potassium sulfate from the aqueous to the organic phase (an analogous monotopic anion receptor lacking the crown ether unit lacks this ability). ¹H NMR, UV-vis, DOSY-NMR, DLS, and MS experiments and the solid-state single crystal structure provided evidence of the formation of a supramolecular core–shell like assembly upon interaction of the receptor with potassium sulfate. The presence of monovalent potassium salts, in contrast, promoted the formation of simple 1 : 1 complexes. Unlike the 4 : 1 assembly, the 1 : 1 complexes are poorly soluble in organic media. This feature was utilized to overcome the Hofmeister bias and allow for selective extraction of extremely hydrophilic sulfates over lipophilic nitrate anions, which was unambiguously proved by quantitative AES and ion chromatography measurements. A simple modification of the receptor structure led to a “naked eye” optical sensor able to selectively detect sulfates under both SLE and LLE conditions.

Environmentally sensitive, degradable microgels based on poly(N-isopropylacrylamide) (pNIPA) cross-linked with the diacryloyl derivative of cystine (BISS) were synthesized by applying surfactant-free emulsion polymerization. pNIPA contributed the sensitivity to temperature to the microgels and the cross-linker made them degradable and sensitive to pH. The morphology of the microgels was investigated by using scanning and transmission electron microscopies (SEM and TEM). The gels formed spherical particles with a narrow size distribution. The influence of temperature, pH and ionic strength on the swelling behavior and the stability of new microgels with various contents of BISS (0, 1 and 3%) were investigated by dynamic light scattering (DLS). It was found that microgels with 3% content of amino acid were highly stable over a wide range of investigated temperatures, pH values and ionic strengths, including the physiological conditions (pH = 7.4, IS = 0.15 M, and 37 °C). The reduction-induced degradation of these microgels by 0.01 M solution of dithiothreitol (DTT) or glutathione (GSH) was studied by means of SEM and TEM; the obtained micrographs showed the destruction of spherical microgel particles. The microgels containing 3% of BISS could be loaded with doxorubicin (DOX) by employing the electrostatic interactions between the DOX amine group and the ionized carboxyl group from BISS. A significant increase in the cumulative release of DOX was observed after changing pH from that characteristic to blood (∼7.4) to that existing in affected cells (∼5.0) and in the presence of GSH (C_GSH ∼ 10 mM). The cytotoxicity tests proved that the obtained microgels are interesting as useful carriers in directed drug delivery systems.

For the first time, by using precipitation polymerization in an aqueous solution, a cross-linked poly(acrylic acid)—(pAA) nanogel was synthesized. pAA was synthesized and cross-linked with N , N ′-methylenebisacrylamide (BIS) at 70°C in an acidified environment (pH 2) and containing 0.7 M NaCl using potassium persulfate as the initiator. Ionized pAA was soluble in water. The use of sodium chloride at low pH caused a decrease in the solubility of pAA and led to its precipitation and formation of cross-linked pAA nanogel. By using electron microscopies and light scattering techniques, the morphology, pH sensitivity and zeta potential of the obtained p(AA-BIS) nanogel were evaluated. The polymerization in an aqueous environment resulted in a very big swelling/shrinking coefficient (of approx. 4000) in response to pH and exhibited an unusually high negative zeta potential (of approx. −130 mV). These properties make the nanogel a very interesting sorbent and a construction material.