Hydroxyethyl Urea Crystal Hydrate: Experimental and Theoretical Study

Hydroxyethyl urea (HEU) is an important urea derivative that finds wide application in various fields from cosmetics to a component of low-freezing batteries. In all areas of its application, special attention is paid to noncovalent interactions with water. In this work, we investigated the noncovalent interactions of HEU with water and also obtained and studied the crystal hydrate of this substance. The obtained crystal hydrates were studied by experimental and theoretical methods. Thus, the incorporation of water molecules into the HEU crystal leads to a broadening of the characteristic peaks in FTIR, and on diffractograms, it affects the change of peak intensity. The calculation results indicate that the hydrogen (H) atoms bonded to the nitrogen atoms of HEU represent the nucleophilic region. The area around the oxygen (O) atoms of HEU represents the electrophilic region. The O–H[Formula: see text]O hydrogen bond lengths in HEU-n ⋅ W ([Formula: see text] 1–12) clusters range from 1.685 Å to 2.066 Å, with electron densities between 0.0178 and 0.0456 au and bond energies of 3.891–13.491 kcal/mol. N–H[Formula: see text]O hydrogen bonds exhibit lengths of 1.900–2.116 Å, electron densities of 0.0185–0.0287 au, and bond energies between 3.671 kcal/mol and 6.808 kcal/mol. Reduced Density Gradient (RDG) analysis confirmed that hydrogen bonding is the dominant interaction in the formation of HEU hydrates.

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