Supramolecular complexes offer a new and efficient way for the monitoring and removal of many substances emanating from technical processes, fertilization, plant and animal protection, or e.g. chemotherapy. Such pollutants range from toxic or radioactive metal ions and anions to chemical side products, herbicides, pesticides to drugs including steroids, and include degradation products from natural sources. The applications involve usually fast and reversible complex formation, due to prevailing non-covalent interactions. This is of importance for sensing as well as for separation techniques, where the often expensive host compounds can then be reused almost indefinitely. Immobilization of host compounds, e.g. on exchange resins or on membranes, and their implementation in smart new materials hold particular promise. The review illustrates how the design of suitable host compounds in combination with modern sensing and separation methods can contribute to solve some of the biggest problems facing chemistry, which arise from the everyday increasing pollution of the environment.

Supramolecular complexation for environmental control

The generation of liquid effluents containing organic and inorganic residues from industries present a potential hazardousness for environment and human health, being mandatory the elimination of these pollutants from the respective solutions containing them. In order to achieve this goal, several techniques are being used and among them, supported liquid membranes technologies are showing their potential for their application in the removal of metals contained in liquid effluents. Supported liquid membranes are a combination between conventional polymeric membranes and solvent extraction. Several configurations are used: flat-sheet supported liquid membranes, spiral wounds and hollow fiber modules. In order to improve their effectiveness, smart operations have been developed: non-dispersive solvent extraction, non-dispersive solvent extraction with strip phase dispersion and hollow fiber renewal liquid membrane. This paper overviewed some of these supported liquid membranes technologies and their applications to the treatment of metal-bearing liquid effluents.

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Supported liquid membranes technologies in metals removal from liquid effluents

The synthesis, complexation properties and catalytic activities under phase-transfer (PT) conditions of differently substituted cyclohexapeptoids are reported. Association constants, for small cationic alkali, and catalytic performances, in a model nucleophilic substitution, are comparable to those of representative crown ethers. Noteworthy, the N-[2-(2-methoxyethoxy)ethyl] side chain derivative presents a catalytic efficiency comparable to that of crypt-222, and higher than some commonly used quaternary ammonium salts and crown ethers. Moreover its association constant for Na+ complexation proved to be higher when compared with dicyclohexyl-18-crown-6. The synthesized cyclohexapeptoids represent the first example of these peptidomimetics in PT catalysis, anticipating interesting applications in biphasic PT methodology.

Cyclopeptoids: a novel class of phase-transfer catalysts

The effects of substituents and cavity size on catalytic efficiency of proline-rich cyclopeptoids under phase-transfer conditions were studied. High affinity constants (Ka) for the sodium and potassium cations, comparable to those reported for crown ethers, were observed for an alternated N-benzylglycine/l-proline hexameric cyclopeptoid. This compound was found to catalyze the alkylation of N-(diphenylmethylene)glycine cumyl ester in values of enantioselectivities comparable with those reported for the Cinchona alkaloid ammonium salts derivatives (83–96% ee), and with lower catalyst loading (1–2.5% mol), in the presence of a broad range of benzyl, allyl and alkyl halides.

Enantioselective Alkylation of Amino Acid Derivatives Promoted by Cyclic Peptoids under Phase-Transfer Conditions.

A Biomembrane Stencil for Crystal Growth and Soft Lithography of a Thermochromic Molecular Sensor.

Synthetic ionophores for the separation of Li+, Na+, K+, Ca2+, Mg2+ metal ions using liquid membrane technology

A new class of redox-switched anthraquinone derived lariat ethers 1-(1-anthraquinonyloxy) 3, 6, 9 trioxaundecane 11-ol (M1), 1-(1-anthraquinonyloxy) 3, 6 dioxaoctane 9-ol (M2), 1-(1-anthraquinonyloxy) 3 oxapentane 5-ol (M3), 1-(1-anthraquinonyloxy) 3 oxapentane 5-butane (M4), 1-(1-anthraquinonyloxy) 3, 6 dioxaoctane 9-methane (M5) and 1-(1-anthraquinonyloxy) 3 oxapentane 5-methane (M6) have been synthesized and characterized by spectral analysis. These ionophores were used in liquid membrane carrier facilitated transport of main group metal cations across supported liquid membrane (SLM). Cellulose nitrate membrane was used as membrane support. Effect of various parameters such as variation in concentration of metal as well as ionophore, effect of chain length and end group of ionophore have been studied. The sequence of metal ions transported by ionophore M1 is Na

https://downloads.hindawi.com/journals/bca/2006/097141.pdf

Design and Synthesis of Redox-Switched Lariat Ethers and Their Application for Transport of Alkali and Alkaline-Earth Metal Cations Across Supported Liquid Membrane

The interest in understanding the interactions in living systems has made supra-molecular chemistry one of the fastest-growing and most active fields of chemistry. Supra-molecular chemistry has evolved from efforts to mimic the weak noncovalent interactions and the phenomenon of molecular recognition in biological systems. A series of redox-switched anthraquinone derived lariat ethers, l-(l-anthraquinonyloxy) 3, 6, 9 trioxaundecane ll-ol (MO, l-(l-anthraquinonyloxy) 3, 6 dioxaoctane 9-ol (M2), l-(l-anthraquinonyloxy) 3 oxapentane5-ol (M3), l-(l-anthraquinonyloxy) 3 oxapentane 5-butane (M4) have been synthesized and characterized by spectral analysis. These redox-switched ionophores were used as carrier in liquid membrane extraction and transport studies of alkali and alkaline earth metal ions. Effect of various parameters such as variation in concentration of metal as well as ionophore, effect of chain length and end group of ionophore have been studied. All ionophores show higher extraction with Li in reduced state of the carrier because Li has large binding efficiency for most of the redox polyethers. Ionophore Mh having a tetraethylene glycol + side chain with anthraquinone, shows maximum extraction for Κ ion in both oxidized and reduced state. Altering the structure of ionophores can be correlated to quantitative structure property relationship (QSPR), which helps in fabrication of ion selective electrode, redox switchable devices and sensors.

Redox Chemical Switching of Cation Transport in Liquid Membrane System

Stoichiometric Complexes of Some Main Group Metal Ions (Li+, Na+, K+, Ca++) with Redox -switched Lariat Ethers

Synthesis of redox switched ionophores 1-[1-anthraquinonyloxy] 3, 6 dioxaoctane-8-methane (A 1 ) and 1-[1-anthraquinonyloxy] 3 oxapentane-5-methane (A 2 ) has been reported. These ionophores have been used as carriers in liquid membrane transport and extraction studies of alkali and alkaline earth metal ions. The sequence of metal ions extracted and transported in oxidised and reduced state by ionophore A 1 is: Ca 2+ >K + >Li + >Mg 2+ and Li + >K + >Ca 2+ >Mg 2+ respectively. The order of extraction and transport of metal ions with respect to ionophore A 2 is Li + >K + >Ca + and Ca 2+ >K + >Li + respectively. Ionophore A 1 is selective for Ca 2+ while ionophore A 2 is selective for Li + ions. This selectivity may be used in ion selective electrode and redox switchable devices.

http://nopr.niscair.res.in/bitstream/123456789/19991/1/IJCA%2045A%285%29%201170-1172.pdf

Anubhuti Awasthy

Papers

Synthetic ionophores for the separation of Li+, Na+, K+, Ca2+, Mg2+ metal ions using liquid membrane technology

Design and Synthesis of Redox-Switched Lariat Ethers and Their Application for Transport of Alkali and Alkaline-Earth Metal Cations Across Supported Liquid Membrane

Redox Chemical Switching of Cation Transport in Liquid Membrane System

Stoichiometric Complexes of Some Main Group Metal Ions (Li+, Na+, K+, Ca++) with Redox -switched Lariat Ethers

Effect of side arm chain length of redox ionophores on uptake of some metal ions