Threshold Collision-Induced Dissociation Determination and Molecular Orbital Calculations of the Binding Energies of Sodium and Silver Ions to Small Nitrogen-Containing Ligands

Abstract

The binding energies at 0 K of sodium and silver ions to ammonia, methylamine, ethylamine, acetonitrile, and benzonitrile were determined using threshold collision-induced dissociation (CID) and molecular orbital calculations at the ab initio and density functional theory levels. There is good agreement between experimental and calculated binding energies. For the five ligands, threshold CID/CCSD(t)(fu)/6-311++G(2df,p)//MP2(fu)/6-311++G(d,p) Na+ binding energies are the following: ammonia, 25.6 ± 2.8/24.8; methylamine, 27.0 ± 1.4/25.9; ethylamine, 27.7 ± 2.3/27.1; acetonitrile, 30.0 ± 2.3/30.3; and benzonitrile, 32.7 ± 1.4/35.0 (B3LYP/6-311++G(d,p)//B3LYP/6-311++G(d,p)) kcal/mol. Threshold CID and B3LYP/DZVP Ag+ binding energies are the following: ammonia, 40.6 ± 3.0/38.9; methylamine, 41.5 ± 2.3/41.1; ethylamine, 42.9 ± 1.4/43.2; acetonitrile, 40.8 ± 2.0/39.3; and benzonitrile, 41.5 ± 2.8/43.1 kcal/mol. Wherever comparisons with literature data are possible, the Na+ binding energies determined in this study are in good agreement with established data. For Ag+ binding energies, agreement with the few published theoretical values is not as good. A comparison of Na+ and Ag+ binding energies for the five N-containing ligands in this study and those for water, methanol, and ethanol published earlier (El Aribi, H.; Shoeib, T.; Ling, Y.; Rodriquez, C. F.; Hopkinson, A. C.; Siu, K. W. M. J. Phys. Chem. A 2002, 106, 2908−2914) shows that for every ligand the Ag+ binding energy is higher than the Na+ binding energy. As a group, the amines exhibit the largest differences between Ag+ and Na+ binding energies, followed by the nitriles; the alcohols exhibit the smallest differences. These results are in line with previous observations that Ag+ prefers binding with nitrogen to binding with oxygen.

Dissociation of the N-Cα bond and competitive formation of the [zn−H]•+ and [cn+2H]+ product ions in radical peptide ions containing tyrosine and tryptophan: The influence of proton affinities on product formation

“…Similar observations have also been made in the dissociation of protonated tripeptides where the heteroresidue is in the central position [40]. In addition, the discrepancy in our case could also have been a result of limited computational accuracy; typical computational errors in DFT calculations at our level of theory relative to the best experimental data are within 2-3 kcal mol Ϫ1 [43,44]. Addition of a glycine residue to the indolyl radical increases the PA; the magnitude of this effect can be estimated from the difference in PAs (5.4 kcal mol Ϫ1 ) between the phenoxy radicals II and I.…”

Gas-phase fragmentation of the Ag+—phenylalanine complex: Cation—π interactions and radical cation formation

“…All critical points were characterized by harmonic frequency calculations and were shown to be at minima, unless otherwise stated. The B3LYP/ DZVP level of theory was previously used to calculate enthalpies and free energies for association reactions of Ag ϩ and a variety of ligands containing nitrogen [16,31] and oxygen [32] donor atoms to within 2 kcal mol Ϫ1 of the experimental values. This level of theory was also successfully used to obtain silver ion affinities and basicities of all naturally-occurring amino acids [18].…”

Binding sites, rotational conformers, and electronic states of Sc–C6H5X (X=F, CH3, OH, and CN) probed by pulsed-field-ionization electron spectroscopy

“…Rodgers and co-worker 9 investigated binding energies and ligand substitution effects of alkali metal ions with toluene, fluorobenzene, 10 phenol, 11 anisole, 12 aniline, 13 and methylanilines 14 and copper ions with toluene, halobenzenes, phenol, anisole, naphthalene, aniline, and methylanilines. 15 Aribi et al 16 obtained binding energies of sodium and silver ions with benzonitrile and other nitrogencontaining ligands. Both groups applied threshold collisioninduced dissociation in their measurements.…”