Jan Romanski

Selective Ammonium Nitrate Recognition by a Heteroditopic Macrotricyclic Ion-Pair Receptor

The heteroditopic macrotricyclic molecular receptor 1, which bears a tripodal anion binding domain and 4,10,16-triaza-18-crown-6 cation recognition domain, proves to be an effective ion-pair receptor. In the absence of the cobound cation (TBA(+) salts) receptor 1 preferably binds nitrate and nitrite over other anions, including basic anions such as acetate or dihydrogenphosphate. Ammonium cation binding by the 4,10,16-triaza-18-crown-6 subunit significantly enhances the strength of the nitrate and nitrite complexation at the triamide recognition site of the receptor. In the presence of ammonium cations, the association constants of nitrate binding reach an impressive value of 1050 M(-1) in highly polar DMSO-d6. Interestingly, the binding of other anions such as chloride and bromide is not enhanced in the presence of a cobound NH4(+) cation. The increased affinity of [1·NH4(+)]PF6(-) for anionic species is attributed to a strong cooperative effect that arises from the properly positioned binding sites in the receptor 1 cavity, thus allowing for the formation of the ion pair. Under liquid/liquid conditions, receptor 1 is able to extract NH4NO3 from an aqueous to an organic phase, as inferred from (1)H NMR spectroscopic and nitrite/nitrate colorimetric analyses.

Tuning the binding properties of a new heteroditopic salt receptor through embedding in a polymeric system

In this communication, we describe a polymerizable, heteroditopic salt receptor, based on an amino acid scaffold, which is able to bind sodium salts of chloride, acetate and nitrate. A poly(butyl methacrylate) derivative containing receptor was then prepared. In contrast to receptor copolymer is capable of extracting sodium nitrate from aqueous media.

Influence of polymer network-metal ion complexation on the swelling behaviour of new gels with incorporated α-amino acid groups

New gels based on N-isopropylacrylamide and amino acid L-ornithine were prepared by free radical polymerization in aqueous solutions. To make the amino acid attachable to the polymer chain the acrylic group was added to the δ-amino group of ornithine, to obtain N-δ-acrylic ornithine. After the polymerization process the α-amino acid groups were unbound. The relative content of amino acid incorporated into the polymeric network of the gels was estimated from 1HNMR spectra, then compared with the molar fraction used for the polymerization process. The presence of free α-amino acid groups attached to the polymeric network of the gels enabled the complexation of some di- and trivalent metal cations. Copper ions, which can form two complexes of different stoichiometry (1 : 1 and 1 : 2) with amino acids, were used to investigate the influence of the complexation process on the swelling behavior of the gels. The influence of amino acid content, temperature and copper ion concentration on the swelling process was also examined. The gels were found to be most sensitive to concentrations of copper ions in the range 10−6–10−5 M. As the amount of amino acid in the polymer network increases the gels gradually lose their temperature-sensitivity and become more sensitive to copper ion concentration. The volume-phase-transition temperature decreases significantly after the addition of copper ions. Analysis of the UV-Vis spectra and the swelling behavior indicates that both 1 : 1 and 1 : 2 complexes are present in the swollen state of the gels, whereas the latter complex is more dominant in the shrunken state.

Selective NaNO2 recognition by a simple heteroditopic salt receptor based on L-ornithine molecular scaffold

This paper describes the development of a simple heteroditopic salt receptor consisting of aza-18-crown-6 (a cation binding domain), nitrophenylurea (an anion binding domain) and an additional metacrylamide group appended to the carboxylic, α-amine and δ-amino groups of L-ornithine. Detailed binding studies showed that this receptor is capable of effectively and selectively binding NaNO2 salt.

Stable and degradable microgels linked with cystine for storing and environmentally triggered release of drugs

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 (CGSH∼ 10 mM). The cytotoxicity tests proved that the obtained microgels are interesting as useful carriers in directed drug delivery systems.

Cooperative ion pair recognition by multitopic L-ornithine based salt receptors

The L-ornithine scaffold was used to develop molecular receptors with improved efficacy in ion pair binding. With two appropriately oriented strong anion binding domains (urea and (thio)urea groups) and one cation binding group (crown ether moiety), these receptors exhibit effective association with the sodium salts of selected anions. We show that the simultaneous action of the two anion binding domains, reinforced by cation coordination, is responsible for the binding strength of receptors 1 and 2. The binding constants for the anions and sodium salt complexes of these receptors were determined using spectrophotometric and 1H NMR titration measurements. Besides carboxylate ions, in the presence of sodium cations all the selected anions associate with receptors 1 and 2 in a positive cooperative manner. The strongest cooperative binding was observed for the association of sodium chloride with receptor 2, supported by urea and thiourea anion binding domains (Ka = 85 500 M−1). Lacking two strong anion binding domains, receptors 4 and 5 can only interact with sodium chloride much more weakly (Ka = 5100 and 8900 M−1, respectively).

Dual Sensing by Simple Heteroditopic Salt Receptors Containing an Anthraquinone Unit

We synthesized simple ion pair receptors consisting of a crown ether cation binding site and an anthraquinone-supported thiourea anion binding domain and studied their anion-, cation-, and salt-binding properties using spectroscopic, spectrophotometric, and electrochemical measurements in acetonitrile solution. Apart from carboxylate anions, which cause deprotonation, all the anions tested were found to associate with receptor 1 more strongly in the presence of sodium cations, whereas in the presence of potassium or ammonium cation the anion binding strength was greatly diminished. A homotopic anion receptor 3, lacking a crown ether unit, was unable to bind sodium salt more strongly than tetrabutylammonium salts. Solution and solid-state X-ray measurements revealed that strong sodium coordination with the cation-binding domain is responsible for the salt-binding enhancement. Electrochemical measurements showed that the addition of anions to the receptor 1 pretreated with sodium cations resulted in greater changes in reduction potentials compared to the addition of anions to receptor 1 in the absence of Na(+).

Oxidation of ferrocenemethanol grafted to a hydrogel network through cysteine for triggering volume phase transition

New gels based on N-isopropylacrylamide and cysteine were prepared by free radical polymerization in aqueous solutions. To attach the amino acid to the polymer chain, its α-amino group was modified with acryloyl chloride and N,N′-bisacryloylcystine was obtained. Next, the disulfide bridges were reduced to thiol groups and the attachment of ferrocenemethanol to the chains was performed. The influence of the amount of electroactive groups and their degree of oxidation on the temperature of volume phase transition was investigated. The gel formed from the polymerization solution containing 2% N,N′-bisacryloylcystine could undergo the volume phase transition triggered by changing the ferrocene state of oxidation. The temperature window of the gel sensitivity to the oxidation state of its ferrocene component was 35–40 °C. During the transition the volume of the gel could be changed even by more than an order of magnitude. Thin layers of the electroactive and thermoresponsive gel could be anchored on the surface of a glassy carbon electrode. This was achieved by electroformation of radicals at the electrode surface. The influence of the volume phase transition triggered by a temperature change on redox processes of ferrocene moieties bound to the network was examined voltammetrically.

Ion pair binding by an L-tyrosine-based polymerizable molecular receptor

Two new multitopic salt receptors based on the L-tyrosine scaffold were synthesized using a simple approach. Both receptors consisted of cation and anion binding domains, as well as a polymerizable function. The anion, cation and salt binding properties of these receptors were studied spectrophotometrically in acetonitrile solution. The collected data revealed the stronger association of receptors with ion pairs relative to single anions. The highest enhancement in salt binding was found for receptor 1, which was equipped with a urea-based anion binding site. Sodium coordination with the cation binding domain and carbonyl urea group of the receptor was found to be responsible for the salt binding enhancement. New functional polymers containing the receptor units were synthesized and characterized. A preliminary extraction study of these receptors and copolymers is also presented.

New ampholytic microgels based on N-isopropylacrylamide and α-amino acid: changes in swelling behavior as a function of temperature, pH and divalent cation concentration

Several new microgels based on N-isopropylacrylamide and the amino acid L-ornithine were synthesized by means of surfactant free emulsion polymerization. N-δ-Acryloyl ornithine was copolymerized with N-isopropylacrylamide and N,N′-methylenebisacrylamide, leading to the synthesis of a new ampholytic microgel. The swelling behavior of the obtained microgels with respect to the amount of amino acid incorporated in the polymer network, temperature, concentration of ions and pH was investigated. The pH dependence of the microgel size, measured at a constant temperature, was found to exhibit a minimum; the pH range where the minimum appeared corresponded well with the pH range where zwitterions dominated. The temperature dependence of the swelling process obtained for different pH values showed that for the pH region where zwitterions dominated, the polymer networks collapsed more efficiently. The presence of free α-amino acid groups attached to the polymeric network of the microgels also enabled the complexation of some metal cations. The influence of the presence of two metal ions (Cu2+ and Ca2+), which differ significantly in their ability to form complexes with the α-amino-acid, on the swelling behavior was investigated. It was found that the presence of copper ions that form stable complexes with the α-amino acid strongly influenced the swelling behavior of the investigated microgels.