Codeposition Modification of Cation Exchange Membranes with Dopamine and Crown Ether To Achieve High K+ Electrodialysis Selectivity.

Surface modification has been proven to be an effective approach for ion exchange membranes to achieve separation of counterions with different valences by altering interfacial construction of membranes to improve ion transfer performance. In this work, we have fabricated a series of novel cation exchange membranes (CEMs) by modifying sulfonated polysulfone (SPSF) membranes via codeposition of mussel-inspired dopamine (DA) and 4'-aminobenzo-15-crown-5 (ACE), followed by glutaraldehyde cross-linking, aiming at achieving selective separation of specific cations. The as-prepared membranes before and after modification were systematically characterized in terms of their structural, physicochemical, electrochemical, and electrodialytic properties. In the electrodialysis process, the modified membranes exhibit distinct perm selectivity to K+ ions in binary (K+/Li+, K+/Na+, K+/Mg2+) and ternary (K+/Li+/Mg2+) systems. In particular, at a constant current density of 5.0 mA·cm-2, modified membrane M-co-0.50 shows significantly prominent perm selectivity [Formula: see text] in the K+/Mg2+ system and M-co-0.75 exhibits remarkable performance in the K+/Li+ system [Formula: see text], superior to commercial monovalent-selective CEM (CIMS, [Formula: see text], [Formula: see text]). Besides, in the K+/Li+/Mg2+ ternary system, K+ flux reaches 30.8 nmol·cm-2·s-1 for M-co-0.50, while it reaches 25.8 nmol·cm-2·s-1 for CIMS. It possibly arises from the effects of pore-size sieving and the synergistic action of electric field driving and host-guest molecular recognition of ACE and K+ ions. This study can provide new insights into the separation of specific alkali metal ions, especially on reducing influence of coexisting cations K+ and Na+ on Li+ ion recovery from salt lake and seawater.

Sm(iii)[12-MCGa(III)shi-4] as a luminescent probe for G-quadruplex structures.

G-quadruplexes (GQs), spatial assemblies of guanine-rich DNA strands, play an important role in the regulation of gene expression and chromosome stabilization. These structures are recognized to be useful in cancer therapies as the presence of multiple G-quadruplexes in a telomeric strand stops cancer cell proliferation. Metallacrowns of the type 12-MC-4 form planar structures that have remarkable similarity to G-tetrads in terms of dimension, shape and the ability to bind alkali metal and lanthanide cations in a central cavity. The interaction between the Sm(iii)[12-MCGa(III)shi-4] (SmMC) metallacrown (MC) and human telomeric G-quadruplex structures was examined using several methods including CD titrations, CD melting temperatures, fluorescence titration of SmMC with GQ/Na+, fluorescence intercalator displacement (FID) assays and methods measuring the MC quenching effect on the Tb3+/GQ luminescence. It was proven that the studied metallacrown acted as a sensing probe and interacted with quadruplex DNA. The Stern-Volmer quenching constant (Kas) of Tb3+/GQ luminescence was calculated to be 3.9 × 105 M-1. The binding constant using the indirect FID method gave the result of 1.3 × 105 M-1. CD melting temperature experiments reveal the following pattern - the higher the concentration of the complex the lower the registered Tm for quadruplex DNA, which indicates a destabilizing effect of SmMC at higher GQ : MC ratios. These data implicate a shape and size selective interaction between MCs and GQs that may be exploited for telomere detection.

Thiacalix[4]crown based optical chemosensor for Fe3+, Li+ and cysteine: a Fe3+/Li+ ion synchronized allosteric regulation.

A heteroditopic chemosensor 2 based on a thiacalix[4]crown with a 1,3-alternate conformation has been synthesized and shows a selective fluorescence turn-off response with Fe(3+) ions in mixed aqueous media. Furthermore, the 2-Fe(3+) complex can be used as a chemosensing system for the detection of Li(+) and cysteine based on two different approaches. Moreover, the sequence addition of Fe(3+) and Li(+) triggers an Fe(3+)/Li(+) switchable on-off-on fluorescence chemosensor with negative allosteric regulations.

Molecular assembly of multi-wall carbon nanotubes with amino crown ether: synthesis and characterization.

Synthetic methodology and physicochemical characterization of multi-wall carbon nanotubes (MWCNTs) functionalized with a crown ether molecule is reported. The MWCNTs were synthesized by spray pyrolysis technique using toluene as carbon source and ferrocene as catalyst. The nanotubes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Oxidation of MWCNTs was carried out by 8 h of sonication in a mixture of sulfuric and nitric acid (3:1). The MWCNT-COOH was amidated with 4-aminobenzo-15-crown-5 under mild reaction conditions using N,N'-dicyclohexylcarbodiimide and dimethylaminopyridine as catalyst and dimethylformamide as solvent, at room temperature for 24 h. The amidation product was characterized by scanning electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and a mass spectrometry study to determine the fragmentation pattern being m/z 309, 177 and 149 the most important ions.

Antileukemic activity and cellular effects of rhodium(III) crown thiaether complexes.

The cytostatic properties of novel rhodium(III) thiacrown ether complexes [RhCl(LL)([9]aneS(3))](n+) with either aromatic κ(2)N ligands (n = 2) or anionic chelate ligands (n = 1) have been investigated for the human cancer cell lines HT-29 and MCF-7 and for immortalized HEK-293 cells. Taken together with literature IC(50) values for analogous complexes with polypyridyl ligands or 1,4-dithiane, the in vitro assays indicate that dicationic complexes with soft κ(2)N (imino) or κ(2)S (thiaether) ligands exhibit significantly higher antiproliferative effects than those with hard κ(2)N (amino) ligands. Dicationic complexes are more active than monocationic complexes with similar ligands. Pronounced apoptosis-inducing properties towards Jurkat cells were established for complexes with LL = bpm, dpq, and 1,4-dithiane. The order of activity (bpm > 1,4-dithiane > dpq > bpy) contrasts to that observed for adhesive cancer cells (bpm > bpy, 1,4-dithiane > dpq). Necrosis is insignificant in all cases. The percentage of Jurkat cells exhibiting apoptosis after 24 or 48 h incubation periods is directly correlated to the percentage of cells exhibiting high levels of reactive oxygen species. As established by online monitoring with a sensor chip system, treatment of MCF-7 cells with the bpm and 1,4-dithiane complexes leads to a significant and permanent concentration-dependent decrease in oxygen consumption and cellular adhesion.

Fluorescence sensors for lithium ions and small peptides.

Simple but powerful chemosensors were developed by taking advantage of self-assembly processes. First, we will describe a turn-on fluorescent sensor for the pharmacologically important lithium ion. The sensor can be used in purely aqueous solution, and it displays a very high selectivity for lithium over sodium and magnesium ions. It is based on a metallacrown receptor unit, which can be assembled in situ from simple building blocks. Furthermore, we will describe a cross-reactive sensor array for the detection of small peptides. The individual sensors of the array are formed by mixing metal complexes with fluorescent dyes.

Cell-selective, apoptosis-inducing rhodium(III) crown thiaether complexes.

Half-sandwich rhodium(III) polypyridyl (pp) complexes with the metal atom capped by the facial crown thiaether 1,4,7-trithiacyclononane [9]aneS(3) represent a promising class of apoptosis-inducing potent cytostatic agents. The necrotic damage caused by the complexes is negligible. In vitro cytotoxicity assays with the human cancer cell lines MCF-7 and HT-29 and immortalized HEK-293 cells indicate that the dicationic kappa(2)N(imino) complexes [([9]aneS(3))RhCl(pp)](2+) are much more active than monocationic complexes [([9]aneS(3))RhCl(2)(L)](+) (L=imidazole, CH(3)CN). Whereas the kappa(2)N(amino) complex [([9]aneS(3))RhCl(piperazine)](2+) is inactive, replacing piperazine with the structurally analogous kappa(2)S (thiaether) ligand 1,4-dithiane restores cytotoxicity as evidenced by IC(50) values in the range 8.1-11.6 microM. Spectroscopic (CD, UV/Vis, NOESY) and viscosity measurements indicate that the active dppz complex 8 (IC(50) values: 4.7-8.9 microM) exhibits strong intercalative binding towards DNA whereas the even more potent bipyrimidine complex 9 (IC(50) values: 0.6-1.9 microM) causes no alteration of the duplex B conformation. Weaker intercalative binding is observed for the dpq complex 7. A comparative annexin V-propidium iodide binding assay with lymphoma (BJAB) cells and healthy leukocytes demonstrates that the cytotoxic activity of complex 8 and particularly complex 9 is highly selective towards the malignant cells.

Supramolecular approach for solid state Brownian rotators.

Artificial molecular rotators were designed in an attempt to achieve unidirectional molecular rotation. Supramolecular assemblies of cations and crown ethers in the solid state were shown to form rotator structures, diverse in their rotational symmetry and frequency. The counter cation of [Ni(dmit)2]- anion, bearing one S=1/2 spin, was used to couple molecular rotation to magnetic properties. Random rotation of [18]crown-6 molecules was first observed in the Cs(+)2([18]crown-6)(3) supramolecule, where the rotational freedom of [18]crown-6 rotators was evidently coupled to the magnetic properties of [Ni(dmit)2]-pi-dimer. In other cases, dual rotary motions of anilinium([18]crown-6) and rotator-stator assemblies of (adamantylammonium)(dibenzo[18]crown-6) were investigated as a means to control rotational symmetries and frequencies in the solid state. The supramolecular approach for construction of molecular rotator-stator assemblies in the solid state is a convenient approach to the design of molecular rotary functionality in [Ni(dmit)2]- salts.

Labeling of adenovirus particles with PARACEST agents.

Recombinant adenovirus type 5 particles (AdCMVLuc) were labeled with two different bifunctional ligands capable of forming stable complexes with paramagnetic lanthanide ions. The number of covalently attached ligands varied between 630 and 1960 per adenovirus particle depending upon the chemical reactivity of the bifunctional ligand (NHS ester versus isothiocyanide), the amount of excess ligand added, and the reaction time. The bioactivity of each labeled adenovirus derivative, as measured by the ability of the virus to infect cells and express luciferase, was shown to be highly dependent upon the number of covalently attached ligands. This indicates that certain amino groups, likely on the surface of the adenovirus fiber protein where cell binding is known to occur, are critical for viral attachment and infection. Addition of (177)Lu3+ to chemically modified versus control viruses demonstrated a significant amount of nonspecific binding of (177)Lu3+ to the virus particles that could not be sequestered by addition of excess DTPA. Thus, it became necessary to implement a prelabeling strategy for conjugation of preformed lanthanide ligand chelates to adenovirus particles. Using preformed Tm3+- L2, a large number of chelates having chemical exchange saturation transfer (CEST) properties were attached to the surface residues of AdCMVLuc without nonspecific binding of metal ions elsewhere on the virus particle. The potential of such conjugates to act as PARACEST imaging agents was tested using an on-resonance WALTZ sequence for CEST activation. A 12% decrease in bulk water signal intensity was observed relative to controls. This demonstrates that viral particles labeled with PARACEST-type imaging agents can potentially serve as targeted agents for molecular imaging.

Selective removal of 226Ra2+ from gas-field-produced waters.

The 226Ra2+ selectivity of both the self-assembled (iso)-guanosine-based systems and ionizable thiacalix[4]crown dicarboxylic acids was determined in gas-field-produced water and a metal ion-containing model solution (simulant). Seven gas-field-produced water samples have been analyzed. From a sample (K5D) with average metal ion concentrations ([metal(tot)] = 0.14 M), thiacalix[4]crown-5 dicarboxylic acid (10(-4) M) extracts 60% of the 226Ra2+ content. Extractions performed with the model solution ((M)K5D) indicate that in K5D there is significant competition in 226Ra2+ extraction due to the organic constituents of K5D, in particular with self-assembled extractants guanosine and isoguanosine. Nevertheless, all four extractants extract 226Ra2+ both from the produced water K5D and the model solution (M)K5D, even with a 100-fold excess of [metal(tot)] to [extractant]. The extracted 226Ra2+ cations could effectively be stripped from the extractants bywashing with pH 2 water. The results obtained with the extractants used, especially thiacalix[4]crown-5 dicarboxylic acid 3, clearly demonstrate the way to selectively remove Ra2+ from gas-field-produced waters.

Enantioselective capillary electrophoretic separation of tryptophane- and tyrosine-methylesters in a dual system with a tetra-oxadiaza-crown-ether derivative and a cyclodextrin.

Different dual selector systems containing a cyclodextrin derivative (methyl-beta-cyclodextrin and dimethyl-beta-cyclodextrin) and a new diaza-crown-ether derivative (N-[2-(1,4,10,13-tetraoxa-7,16-diazacyclooctadecan-7-yl)propanoyl]glycine) were studied in the enantioselective separation of tryptophan-methylester and tyrosine-methylester enantiomers. This paper deals with the systematic study of the effects of changing the composition of the background electrolyte on the resolution of the d- and l- forms using an experimental design approach. It was found that the dual systems allowed a better chiral separation of the amino acid derivatives. The experimental design approach also allowed improving the separation compared to the starting conditions (center point of the design), which were adopted from a previous study.

AT2-selective angiotensin II analogues containing tyrosine-functionalized 5,5-bicyclic thiazabicycloalkane dipeptide mimetics.

This paper reports the synthesis of two angiotensin II analogues with tyrosine-functionalized 5,5-bicyclic thiazabicycloalkane dipeptide mimetics replacing the Tyr(4)-Ile(5) residues. The preparation of these analogues relies on the synthesis and incorporation of an alpha,alpha-disubstituted chimeric amino acid derivative and on-resin bicyclization to a cysteine residue. The synthesized analogues both displayed high angiotensin AT(2)/AT(1) receptor binding preferences and had AT(2) receptor affinities in the same low nanomolar range as angiotensin II itself. Conformational analysis, using experimental constraints derived from NMR studies, indicated that the Tyr(4) and His(6) residues in one of the angiotensin II analogues were in close proximity to each other.