DOI: https://doi.org/10.55373/mjchem.v27i5.131

Keywords: Amide; anion receptors; titration; hydrogen bonding; DFT studies

Abstract

Developing anion receptors has garnered significant attention and enthusiasm among researchers owing to the pivotal role of anions in various processes and applications. The development of receptors to remove harmful pollutants is crucial because anion abundance can harm ecosystems. Therefore, in this study five diamide compounds namely 1,2-bis[N,N'-6-(4-pyridylmethylamido) pyridyl-2-carboxyamido]ethane (L1), 1,2-bis[N,N'-6-(4-pyridylmethylamido)pyridyl-2-carboxy amido]propane (L2), 1,2-bis[N,N'-6-(4-pyridylmethylamido)pyridyl-2-carboxyamido]butane (L3), 1,2-bis[N,N'-6-(4-pyridylmethylamido)pyridyl-2-carboxyamido]pentane (L4) and 1,2-bis [N,N'-6-(4-pyridylmethylamido)pyridyl-2-carboxyamido]hexane (L5) were synthesized to explore the hydrogen bonding interactions with chloride, bromide, nitrate, phosphate and chromate anions. ¹H NMR spectroscopy and Density Functional Theory (DFT) calculations were employed to explore the binding affinities of the ligands. ¹H NMR titrations revealed distinctive shifts in the NH proton signals upon interaction with anions, particularly showing strong hydrogen bonding with chloride and phosphate anions. Titration with nitrate displayed upfield shifts, attributed to the presence of internal charge transfer. DFT calculations demonstrated that the combination of ligands and phosphate anions was the most stable, as indicated by the lowest binding energies. Both ¹H NMR and DFT results consistently showed that chloride and phosphate formed the most stable complexes with the ligands, demonstrating their high selectivity for these anions.