Interactions of Water with Mono- and Diamino Derivatives ofN,N‘-Dimethyluracil

Abstract

Molecular structures of mono- and diamino derivatives of N,N‘-dimethyluracil and their complexes with water are investigated by ab initio quantum chemical methods at the MP2/6-31G(d,p) level of theory. The results of the calculations demonstrate that the formation of the N···H−O hydrogen bonds with participation of the nitrogen atom of the amino group in the N,N‘-dimethyl-5,6-diaminouracil complex with water is caused by the intrinsic properties of this substituent. An analysis of the geometries and water−amine interaction energies for different monohydrates of mono- and diamino derivatives of N,N‘-dimethyluracil indicates that the formation of this H bond requires the presence of the neighboring proton donor group. The energy of the N···H−O hydrogen bonds depends on a degree of conjugation between the lone pair of the nitrogen atom and the π system of the rest of the molecule. In the case of amino derivatives of uracil, the weakest conjugation is observed for the substituent at the C(5) atom. Therefore, the N···H−O hydrogen bond is formed by this amino group. A comparison of the amine−water interaction energies and the relative stability of isomeric monohydrates allows for the conclusion that the formation of such nonstandard hydrogen bonds is the most favorable way for interactions of 1,2-diamines with water and other proton donors.

Intra- and Intermolecular Interactions in the Crystals of 3,4-Diamino-1,2,4-triazole and Its 5-Methyl Derivative. Experimental and Theoretical Investigations of Charge Density Distribution

“…In the case of aliphatic amines, the ability of amino groups to serve as a proton withdrawal site in hydrogen bonds is well-known. , However, in the case of the conjugated amino group, this phenomenon is rarer but is also observed. , The most interesting situation was found for compounds where two vicinal amino groups are bonded to a conjugated ring. Investigation of the molecular structure of monohydrate of N , N ′-dimethyl-5,6-diaminouracil indicated that the strength of the n−π conjugation for two amino groups was considerably different. Both substituents may serve as proton acceptors in hydrogen bonding but this property strongly depends on involvement of the lone pair of nitrogen atom in conjugation.…”

“…55,56 The most interesting situation was found for compounds where two vicinal amino groups are bonded to a conjugated ring. Investigation of the molecular structure of monohydrate of N,N 0 -dimethyl-5,6diaminouracil 57 indicated that the strength of the nÀπ conjugation for two amino groups was considerably different. Both substituents may serve as proton acceptors in hydrogen bonding but this property strongly depends on involvement of the lone pair of nitrogen atom in conjugation.…”

Molecular Structure and Hydrogen Bonding in Polyhydrated Complexes of Adenine: A DFT Study

“…Recently, the same conclusion was made for the amino group in rare tautomers of guanine 52 and amino derivatives of uracil. 53 Therefore, we performed additional calculations for adenine monohydrate to locate the complex containing the N(10)‚‚‚H-O hydrogen bond. However, it was found that such a complex does not correspond to local minimum on the potential energy surface.…”

Effects of Hydrogen Bonding on the Acidity of Uracil

“…Perhaps the most well studied water−nucleobase interactions involve uracil. − Uracil contains many consecutive hydrogen-bond-donor and -acceptor groups, which makes it ideal for studying hydrogen-bond interactions. Indeed, modified uracil−water complexes (such as those involving uracil hydroxy tautomers, 5-substituted uracil derivatives, thiouracils, or amino derivatives of N , N ‘-dimethyluracil) and the anions of uracil−water complexes , have also been investigated.…”