Supramolecular perspective on conformational changes in urea and sulfamide derivates induced by anions

Abstract

Compounds containing urea, thiourea and sulfonamide fragments are widely employed as anion carriers, being applied in phase transfer processes, pharmaceutical chemistry and agrochemistry. In the present work, the conformational behavior of urea, thiourea and sulfamide was theoretically and spectroscopically (NMR) analyzed upon the presence of fluoride. The influence of chloride, acetate and dihydrogenphosphate anions was evaluated on the conformations of sulfamide. N,N'-diindolyl compounds containing urea and sulfamide moieties were computationally studied and showed conformational changes induced by anions. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis confirmed the existence of hydrogen bonds in the urea-F, thiourea-F and diindolylurea-F complexes. The fluoride effect on the conformation of N,N'-diindolylurea was clear, since the free ligand exhibits the anti-anti conformer as the most stable, due to intramolecular hydrogen bonds between the carbonyl group and the H-N hydrogens of the indolyl groups. Nevertheless, in the presence of anions, the most stable conformation is sinsin, due to strong intermolecular hydrogen bonds between the fluoride and the receptor. Similarly, the complexation of sulfamide and diindolylsulfamide with anions (F -, Cl -, CH3COO and H 2PO4 -) through hydrogen bonds was confirmed by the above-mentioned theoretical techniques. The complex with fluoride was the most stable, followed by the oxoanions and then chloride.