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Yañez S; Jatomea O; Velázquez E; Santacruz H; Navarro R; Inoue M (2015)

ION-PAIRING OF ANIONIC DTPA-BASED CYCLOPHANES WITH DIAMINOALKANES AND METHYLATED AMINO ACIDS, LYSINE AND ARGININE, IN THEIR DICATIONIC FORM

J INCL PHENOM MACRO 80(3-4):295-302
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© Springer Science+Business Media Dordrecht 2014. Complex formation of three anionic cyclophanes with the dications of diaminoalkanes and basic amino acid esters was studied by 1 H NMR titrations in aqueous media. Every cyclophane bearing six CH 2 CO 2 - arms consists of two diethylenetriaminepentaacetic (DTPA) units linked by two aromatic diamine units through amide bonds; the interlinking amine is p-xylen-ediamine (abbreviated as px), 4,4′-methylenedianiline (ma) or 4,4′-diaminobibenzyl (dab). The cyclophanes that exist in the anionic form cyH 2 4- (with two acidic protons) have multi-point electrostatic interaction with diaminoalkane dications + H 3 N(CH 2 ) n NH 3 + , so as to construct ion pairs stabilized by hydrogen-bonding between CH 2 CO 2 - and NH 3 + . The formation constants vary from 31 to 2,477 M -1 depending on the cation-anion combinations; the highest stability is found for the complex of the px-derived cyclophane, cy(px)H 2 4- , with diaminobutane, and the lowest for diaminobutane-cy(dab)H 2 4- pair. The stability is correlated with the chain length of the diaminoalkanes as well as the size of the cyclophanes. These geometrical factors are also crucial for ion-pairing with the dications of methylated lysine and arginine; the formation constant is 2,884 M -1 for (lys)H 2 2+ -cy(px)H 2 4- , and 1,688 M -1 for (arg)H 2 2+ -cy(px)H 2 4- , while the constants of the cy(ma)H 2 4- and cy(dab)H 2 4- complexes are in a much smaller range of 39-230 M -1 .