| Abstract |
The molecular recognition of five targeted amino acids differing in the nature of the side (R)- group and in the size of the aliphatic chain, glycine (Hgly), phenylalanine (Hphe), glutamic acid (Hglu(-)), 4-aminobutyric acid (Hgaba), and 6-aminohexanoic acid (Heahx), has been studied with a new heteroditopic receptor based in two distinct macrocycles, a cyclen and a crown ether moiety. The bismacrocycle L was synthesized via the bis-aminal route allowing to obtain the designed compound in gram scale and in good yield. Protonation constants of L and its binding constants with amino acids were determined by potentiometry in H2O/MeOH (1:1 v/v) solutions at 298.2 K and I=0.10 mol dm(-3) in NMe4NO3. Stronger binding ability of the HnLn+ receptor for a.-amino acids, Hgly and Hphen, than for the other studied substrates were found. Structural data derived from NMR studies showed that the binding of alpha-amino acids result from the cooperative participation of hydrogen bonds between the carboxylate group of amino acids and the polyammonium sites of cyclen, and the ion-dipole interactions between the ammonium group of the amino acids and the oxygen atoms of the crown ether. (C) 2012 Elsevier Ltd. All rights reserved. |
