How Does Ammonium Interact with Aromatic Groups? A Density Functional Theory (DFT/B3LYP) Investigation

Abstract

DFT/B3LYP calculations were carried out on complexes formed by NH 4 + with aromatics, viz. benzene, phenol, pyrrole, imidazole, pyridine, indole, furane, and thiophene, to characterize the forces involved in such interactions and to gain further insight into the nature and diversity of cation-aromatic interactions. Such calculations may provide valuable information for understanding molecular recognition in biological systems and for force-field development. B3LYP/6-31G** optimization on 35 initial structures resulted in 11 different finally optimized geometries, which could be divided into three types: NH 4 + -π complexes, protonated heterocyclic-NH 3 hydrogen bond complexes, and heterocyclic-NH 4 + hydrogen bond complexes. For NH 4 + -π complexes, NH 4 + always tilts toward the carbon-carbon bond rather than toward the heteroatom or the carbonheteroatom bond. The calculated CHelpG charges suggest that the charge distribution of a free heterocyclic may be used to predict the geometry of its complex. Charge population and electrostatic interaction estimations show that the NH 4 + -π interaction has the largest nonelectrostatic interaction fraction (∼47%) of the total binding energy, while the NH 4 + -aromatic hydrogen bond interaction has the largest electrostatic fraction (∼90%). A good correlation between binding energy and electrostatic interaction in the NH 4 + -π complexes is found, which shows that nonelectrostatic interaction is important for cation-π binding. The results calculated with basis sets from 6-31G to 6-311++G(2df, 2dp) show that ∆E corr and ∆H corr do not require a basis-set superposition error (BSSE) correction, in view of experimental error, if a larger basis set is used in the calculation. The calculated ∆H corr values for the NH 4 + -C 6 H 6 complex with different basis sets suggest that the experimental ∆H may be overestimated.

Selective Complexation of N‐Alkylpyridinium Salts: Binding of NAD+ in Water

“…The residue was redissolved in methanol and subsequently membrane-filtered and again evaporated to dryness. If the NMR analysis of this crude product indicated a small excess of tetra-n-butylammonium hydroxide, the product was again dissolved in methanol, and the phosphonic acid starting material (10 The hydroquinone precursor (100 mg, 228 mmol) was dissolved in anhydrous THF (10 mL) and cooled to 0 8C. Then triethylamine (95 mL, 69.4 mg, 686 mmol, 3.0 equiv) and phenylhydrazine (55 mL) were added and stirred for 15 min, after which phenylphosphonic acid dichloride (100 mL, 140 mg, 718 mmol, 3.1 equiv) was added dropwise.…”

“…In recent years the p-cation interaction [9][10][11][12] has been shown to be a major noncovalent force used in numerous proteins. [13][14][15][16][17][18][19] Consequently, theoretical investigations have detailed the electrostatic, hydrophobic and dispersive contributions to this attraction, which works so well in aqueous solution.…”

Major mutations in calf-1 and calf-2 domains of glycoprotein IIb in patients with Glanzmann thrombasthenia enable GPIIb/IIIa complex formation, but impair its transport from the endoplasmic reticulum to the Golgi apparatus

“…Moreover, major mutations in the calf-2 domain of GPIIb, for example, skipping of exon 28,20,21 Ser870Stop, 22 and deletion of the whole GPIIb light chain, 23 were also shown to enable GPIIb/IIIa complex formation but impaired carbohydrate processing and surface expression of the complex. Finally, even a mutation associated with a deletion of both calf-1 and calf-2 domains (Arg597Stop) was recently found to enable formation of an unstable and rapidly degradable GPIIb/IIIa complex.…”

“…9 In our analyses of the model, which are purely theoretical and unsupported by experimental data, the respective contacts were partially disrupted in mutant GPIIbalt.25 and del.20. In GPIIb-alt.25 there was abolishment of the contact between amino group of Arg783 in ␣ v or of His787 in ␣IIb and the aromatic ring of Tyr594 in ␤3, which is a known stabilizing structure, 27,28 and in GPIIb-del.20 there was a deletion of 3 amino acids that are in the contact area with ␤3 (Figure 8). Notwithstanding these significant disruptions, intracellular GPIIb/IIIa complex formation was formed and was stable.…”

The Basicity of Unsaturated Hydrocarbons as Probed by Hydrogen‐Bond‐Acceptor Ability: Bifurcated NH+⋅⋅⋅π Hydrogen Bonding

“…[8] The addition of this electrostatic effect increases the binding enthalpy of the complex by several kcal.mol −1 such that ΔH for the gas phase NH 4 + ⋯C 6 H 6 complex is 19.3 kcal.mole −1 . [9] Calculations indicate that the energetics are dominated by the charge/quadrupole interaction [10] and do not significantly distort the π electron distribution.…”