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Issue 7, 2008
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New branched macrocyclic ligand and its side-arm, two urea-based receptors for anions: synthesis, binding studies and crystal structure

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Abstract

The synthesis and characterization of the two new hosting molecules for anions 4(N),10(N)-bis-[2-(4-nitrophenylureido)acetamido]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L1) and 1-((diethylcarbamoyl)methyl)-3-(4-nitrophenyl)urea (L2) are reported. L1 is a branched tetraazamacrocycle bearing two p-nitrophenylureido groups as side-arms, whereas L2 has the same linear chain and binding moiety of L1 side-arm. The best synthetic routes for use in obtaining L1 were explored, affording the synthesis of the new intermediate 4, a versatile building block for further functionalized branched macrocyclic hosts. The binding properties of both ligands towards the halides series and acetate anions (G) were investigated by NMR and UV-Vis spectroscopy in a dimethyl sulfoxide–0.5% water solution. Both ligands interact with F, Cl and AcO while Br and I did not. The NMR experiments proved that the binding occurs via H-bond to the ureido fragments. Fluoride anion is basic enough to deprotonate the ureido group of both ligands, thus preventing the determination of the addition constants to both ligands; this was instead possible for Cl and AcO. L1 forms G–L species of 1 : 1 ([GL1]) and 2 : 1 ([G2L1]) stoichiometry while L2 forms only the 1 : 1 [GL2] species. The higher value of the formation constant of the [AcOL1]vs. the [AcOL2] species (log K = 5.5 vs. 2.8 for the reaction AcO + L = AcOL) suggested that both side-arms of L1 cooperate in binding acetate; this does not occur with Cl. The results confirmed that this tetraaza-macrocyclic base acts as a preorganizing scaffold for side-arms when they are linked to it via an amide function. The crystal structure of L2·H2O is also reported.

Graphical abstract: New branched macrocyclic ligand and its side-arm, two urea-based receptors for anions: synthesis, binding studies and crystal structure

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Publication details

The article was received on 14 Dec 2007, accepted on 06 Feb 2008 and first published on 26 Feb 2008


Article type: Paper
DOI: 10.1039/B719342D
Citation: New J. Chem., 2008,32, 1204-1214
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    New branched macrocyclic ligand and its side-arm, two urea-based receptors for anions: synthesis, binding studies and crystal structure

    M. Formica, V. Fusi, E. Macedi, P. Paoli, G. Piersanti, P. Rossi, G. Zappia and P. Orlando, New J. Chem., 2008, 32, 1204
    DOI: 10.1039/B719342D

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