A theoretical study of red-shifting and blue-shifting hydrogen bonds occurring between imidazolidine derivatives and PEG/PVP polymers

A theoretical study is presented with the aim to investigate the molecular properties of intermolecular complexes formed by the monomeric units of polyvinylpyrrolidone (PVP) or polyethyleneglycol (PEG) polymers and a set of four imidazolidine (hydantoine) derivatives. The substitution of the carbonyl groups for thiocarbonyl in the hydantoin scaffold was taken into account when analyzing the effect of the hydrogen bonds on imidazolidine derivatives. B3LYP/6-31G(d,p) calculations and topological integrations derived from the quantum theory of atoms in molecules (QTAIM) were applied with the purpose of examining the N-Ha <-O hydrogen bond strengths formed between the amide group of the hydantoine ring and the oxygen atoms of PVP and PEG polymers. The effects caused by the N-Ha <-O interaction fit the typical evidence for hydrogen bonds, which includes a variation in the stretch frequencies of the N-H bonds. These frequencies were identified as being vibrational red-shifts because their values decreased. Although the values of such calculated interaction energies are between 12 and 33 kJ mol(-1), secondary intermolecular interactions were also identified. One of these secondary interactions is formed through the interaction of the benzyl hydrogen atoms with the oxygen atoms of the PVP and PEG structures. As such, we have analyzed the stretch frequencies on the C-H bonds of the benzyl groups, and blue-shifts were identified on these bonds. In this sense, the intermolecular systems formed by hydantoine derivatives and PVP/PEG monomers were characterized as a mix of red-shifting and blue-shifting hydrogen-bonded complexes.