Chem. Pharm. Bull. 54(5) 761—763 (2006)

Many studies have described the determination of luminescence, radiotherapeutic applications, and development of chelators for lanthanide ions (Ln ) in the past several years. In the application of lanthanide ions for photometry, fluorometry and bioassay, the development of selective chelators and probes for lanthanide ions is important. The electronic configurations of lanthanide ions have 4f electrons, for instance Eu and Lu have 7 and 14 4f electrons, respectively, except for Y (4f 0) and La (4f 0). However, information about the development of the chelators which selectively form the complexes with Y , La , Eu , and Lu ions is lacking since lanthanide ions have extremely similar chemical properties. Here, we used La (4f 0), Eu (4f 7), and Lu (4f 14) to study in order to show clearly whether the ability of complexation changes with the number of 4f electrons. Although 18-crown-6 ether (1), ethylenediaminetetraacetic acid (EDTA) (2), and calix[6]arene (3) have often been used as chelators for the complexation of lanthanide ions, these chelators form the complexes with La , Eu and Lu ions and have no selectivity for selective complexation of their ions. Our aims in this study are the molecular design and synthesis of novel chelators for the highly selective recognition of Y , La , Eu and Lu corresponding to the number of 4f electrons, 0, 0, 7, and 14, respectively. To achieve the molecular design and the synthesis of functional chelators which selectively bind with Y , La , Eu or Lu ions, we synthesized target double-stranded amino acid-Cat(OH) (8) and double-stranded peptide-Cat(OH) (9) by conjugation with two 2,3-dihydroxybenzoic acid (Cat, 5) at N-terminus of the double-stranded peptide (or amino acid) conjugated with two -Ile-Pheor -Pheresidues to a spacer. In designing the functional chelators we have designed them using absolute hardness (h) and absolute electronegativity (c) based on the hardness concept. The values of c and h were calculated by Eqs. 1 and 2. c m (∂E /∂N )u (r) (Ip Ea) / 2 (1)