Uracil-water interaction revisited - in search of single H-bonded secondary minima

• Published in: Physical chemistry chemical physics : PCCP 2024-02, Vol.26 (6), p.5169-5182
• Main Authors: Buczek, Aneta, Rzepiela, Kacper, Kupka, Teobald, Broda, Ma gorzata A, Kar, Tapas
• Format: Article
• Language: English
• Subjects: Angles (geometry); Aqueous solutions; Bond energy; Bonding; Hydrogen bonds; Minima; Perturbation theory; Potential energy; Uracil; Vibration mode
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d3cp04057g

Monohydrated uracil (UW) complexes are stabilized by both O HO and NH O hydrogen bonds (H-bonds), simultaneously participating in forming three stable cyclic structures. The role and contribution of these individual H-bonds (O HO and NH O) to the stability of the three UW complexes are still not understood, because of the technical problems in obtaining their optimized structures by standard geometry optimization. The present study explores a non-standard approach to identify three single H-bonded local minima structures without imaginary frequency using DFT (M06-2X, B3LYP and B3LYP-D3), MP2 and CCSD(T) theories and Dunning's correlation-consistent aug-cc-pVTZ basis set, in both vacuum and aqueous media (CPCM method). The results reveal that these new structures are very shallow secondary minima between two deep wells or next to a deep well of primary minima (double H-bonded structures) in the potential energy surface. The H-bond energy of these single H-bonded complexes is found to be less sensitive to a wide range (about 15-20 degrees) of O HO and NH O angles, and the linearity is preferred in the stable three single H-bonded structures. The technical method used to locate such a shallow minimum is described in detail and may be useful for identifying local minima in other cases where consecutive multiple H-bonded structures are global minima. Energy decomposition (using symmetry adapted perturbation theory (SAPT)) of interaction energy, electron redistribution, and relevant vibrational modes are discussed. Monohydrated uracil structures. The lower three structures are double H-bonded structures, and upper four structures represent single H-bonded structures. Single H-bonded structures participating in a double H-bonded arrangement are shown by arrows.