A computational study of the protonation of simple amines in water clusters

Abstract

The microsolvation study of a group of amines with a variable number of water molecules was performed by conducting a theoretical analysis of the properties of the clusters formed by the amines with up to seven molecules of water. We describe the microsolvation of several amines focusing on the dissociation of a water molecule that transfers a proton to the amine and forms a hydroxide ion. Ab initio calculations were performed on these clusters employing the DFT/B3LYP and MP2 methods with the 6-311++G(2d,p) basis set. Several stationary points for each cluster were thus located and characterized as minima from frequency calculations. Intermolecular BSSE corrected interaction energies were obtained. The protonation mechanism of the amines was examined in terms of some parameters that include the lengths of the bonds involved in the process of proton transfer and the frequencies associated with certain O-H and N-H stretching modes. On the basis of the calculations, all studied amines present similar behavior but trimethylamine, whose limitations to be integrated in the water hydrogen bond network cause the instability of some of their complexes. The cyclic configurations are the most stable structures up to five water molecules due to the presence of cooperative effects associated with the hydrogen bonds of water molecules. However, when the number of water molecules increases the spatial forms become the most stable configurations. The dissociated forms were not found to have the most stable configuration in any of the studied systems but energetic differences between the dissociated and non-dissociated forms decrease with the number of water molecules.

Ultrafast Vibrational Spectroscopy of Aqueous Solution of Methylamine from First Principles MD Simulations

“…But, as per an MD simulation, the amine group can form 1.77 hydrogen bonds with water molecules, while the reference interaction site model(RISM) predicted 2.4 hydrogen bonds per the same moiety. Marta et al . studied the structures of the hydrated clusters of methylamine by applying density functional theory (DFT).…”

A Modular and Diastereoselective 5+1 Cyclization Approach to N-(Hetero)Aryl Piperidines

“…It is known, however, that implicit continuum solvation models do not satisfactorily treat specific solvent-solute interactions, which are important for accurate description of the solvation of amines in protic solvents. 16 Indeed, when one or two explicit water (or MeOH) molecules were included to account for hydrogen bonding with solvent, the lowest-energy conformers of 8 and 9 (Scheme 2a, b), would now lead to the experimentally observed diastereomers 5a and 6a upon protonation from the exo faces. This computational model predicts diastereomeric ratios that are in good agreement with the experimental values.…”

“…13 C NMR (151 MHz, CD3CN) δ 175 16,. 137.28, 127.97, 118.26, 114.02, 59.16, 54.43, 46.19, 42.73, 35.23, 32.18, 27.77, 26.43, 23.21, 23.20, 21.63, 19.85.…”

Structural-topological preferences and protonation sequence of aliphatic polyamines: a theoretical case study of tetramine trien

“…They concluded that both forms, HL p and HL s , are formed in the first protonation step but HL p is predominant with a %-fraction of 86%. Clearly, even in some cases, where the same experimental technique was used, such as 13 C NMR, polyamines [25,26]. General shortcomings as well as advantages of each levels of theory tested here are well-known.…”