Rainer Ludwig

Solvent extraction of heavy metals with macrocyclic ligands based on calix[4]arenes

Ligand 1, a calix[4]arene-based compound with a crown-6 moiety, efficiently extracts the heavy metal ions Hg2+ and Pb2+ from weakly acidic solutions due to their compatible ion radius. The CO2H groups are essential for the metal extraction, as seen from a comparison with the corresponding ester compound 2. Ligand 3 as a crown-5 is also capable of extracting smaller cations such as Zn2+ and Cd2+ from weakly acidic solutions. Compound 5, bearing four CO2H groups, shows quantitative extraction for Hg2+ and Pb2+ at pH values above 2.5 and 2.8, respectively. Extraction takes place to some extent even if water-soluble organic complexing reagents are present in the aqueous phase, such as EDTA. Quantitative back-extraction is achieved by using 0.75 M HNO3.

A calixarene-based extractant with selectivity for AmIII over LnIII

Calix[6]arene-based extractant 4 shows high selectivity and extractability for AmIII from weakly acidic solutions due to the cooperativity of different ligating groups.

Counting of labelled tyrosine molecules in hydrophobic yoctolitre wells filled with water

Time-dependent radioactivity and solid-state 13C-NMR measurements of tyrosine entrapped in water-filled yoctolitre (10(-24) L) wells with hydrophobic walls are reported; the results indicate that such wells induce the formation of quasi solid tyrosine if they are brought in contact with 0.1 M solutions of this edge amphiphile.

Turning Ionophores into Chromo- and Fluoro-Ionophores

This chapter concerns the use of selective, calixarene-based ligands for optical signalling in chemical analysis [1]. Although chromophoric ligands of many types are wellknown, calixarenes provide a number of novel and useful examples. Exploitation via optical sensing of the recognition of both ions and neutral molecules by macrocycles in general is based on their ease of application in, for example, flow-cells or optical fibre tips [2-7]. Macrocyclic chromophores or fluorophores may be employed in devices of various levels of sophistication, nonetheless [7]. A simple system for cation detection, discussed in Section 2, uses an auxiliary chromophore or fluorophore mixed in the sensing membrane with a neutral ligand. A newer approach is to have the chromophoric group as part of the ligand, with guest binding causing either a bathochromic or hypsochromic shift of the absorption (Section 3). The high sensitivity of fluorescence detection is one of the reasons for the design of calixarenes bearing fluorophoric groups (Section 4), the binding response being an increase or decrease in the fluorescence emission, a change in the monomer/excimer emission ratio, or a change in the emission wavelength.