New ligand bearing preorganized binding side-arms interacting with ammonium cations: Synthesis, conformational studies and crystal structureElectronic supplementary information (ESI) available: molecular modeling studies. See http://www.rsc.org/suppdata/nj/b3/b306778e/

Abstract

The synthesis and characterization of the new tetraazamacrocycle 4-(N),10-(N)-bis[2-(3-hydroxy-2-oxo-2Hpyridin-1-yl)acetamido]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L) is reported. L shows two 3-(hydroxy)-1-(carbonylmethylen)-2(1H)-pyridinone moieties as side-arms of a tetra-aza-macrocyclic base. The key coupling of side-arms was studied and the most significant results were obtained by activating the 3-(benzyloxy)-1-(carboxymethyl)-2(1H)-pyridinone as pentafluorophenol ester. The acid-base properties of L and its capability to interact with simple ammonium cations were investigated by potentiometric measurements in aqueous solution (298.1 AE 0.1 K, I ¼ 0.15 mol dm À3 ). Protonated species of L can bind NH 4 + or primary ammonium cations such as MeNH 3 + discriminating them from secondary or tertiary ammonium cations such as Me 2 NH 2 + or Me 3 NH + which are not bound in aqueous solution.1 H and 13 C NMR spectra showed the existence in solution of two conformers on the NMR time scale due to the rotational restriction of the two N-C=O groups. The activation parameters were determined by dynamic variable-temperature NMR analysis.Molecular dynamics calculations gave results in agreement with the experimental data for both conformation and ammonium-binding studies, underlining that the transformation of the two secondary amines of the macrocyclic base to amide functions, forces the side-arms to remain fixed in position, almost face to face and thus to be preorganized to interact with other species. The crystal structure of the [HL]ClÁ8H 2 O species shows the high number of preorganized hydrogen bond sites capable, in this case, of interacting directly with five H 2 O molecules.

Synthesis of novel Iron(III) chelators based on triaza macrocycle backbone and 1-hydroxy-2(H)-pyridin-2-one coordinating groups and their evaluation as antimicrobial agents

“…Very few polyaza macrocycles bearing HOPO coordinating groups have been described [48,[51][52][53][54]. Macrocycles offer the potential to fine tune the metal chelating properties by varying the cycle's size and fexibility.…”

Hydrogen Bonded Semi‐Rigidified Bispyridyl‐Incorporating Aryl Amide Oligomers: Efficient "C"‐Styled Receptors for Aliphatic Ammoniums, a Remarkable Protonation Effect and Chiral Induction

“…It has been reported that the carbonyl oxygen is good hydrogen bonding acceptor for alkyl ammonium protons. 28,29 Therefore, it was envisaged that both compounds might complex salts 3-5 ( Figure 2) in chloroform through intermolecular hydrogen bonding. Before the complexing behaviour was investigated, we first explored the possibility of strong acid-tuned conformational shifting.…”

A macrocyclic ligand able to bind gallium(iii) by preorganized pendant arms; coordination and kinetic studies

“…2). 19 The fluorescence emission spectra of the Ga(III)/L system, recorded under the experimental conditions used for the kinetic measurements, revealed greater modifications than those of the free ligand. In fact, exciting at 301 nm the fluorophore shows an enhancement of the fluorescence (CHEF) for the Ga(III)/L system together with a slight decrease in the k em , which is at 361 nm in the presence of Ga 3+ instead of 369 nm in the absence of the metal ion (see Fig.…”

“…The two HPO moieties have been driven to cooperate by the macrocyclic skeleton in binding guests. 19 The preorganization of the side-arms leads to the formation of an electron rich structure formed by the four converging oxygen atoms and thus suitable to bind hard metal cations.…”