Anion effect on the conformational equilibrium of sulfamide and its N,N'-diindolyl derivative: insights on anion transportation

Abstract

The relatively high acidity of the sulfamide hydrogens suggests a potential for the development of sulfamide derivatives as novel anion receptors. The interactions of sulfamide with F−, Cl−, CH3COO−, and H2PO4− anions were spectroscopically (1H and 19F NMR) and theoretically (density functional theory) analyzed, and the complexation through hydrogen bonds was confirmed by changes in the NMR signals and theoretical calculations. The replacement of 2 sulfamide hydrogens with indolyl groups yields the N,N′‐diindolylsulfamide (DIS, N‐1H‐indol‐4‐yl‐N′‐1H‐indol‐7‐ylsulfuric diamide), whose bond rotations allow the interaction of 4 H(N) atoms with anions. The conformational preferences of DIS change upon the presence of anions, but they are practically insensitive to the anion type. According to the quantum theory of atoms in molecules, natural bond orbital analysis, and NMR chemical shifts, as well as to a thermodynamic cycle, the complex with fluoride is the most stable, followed by the oxoanion‐derived models.