Metal Cation Dependence of Interactions with Amino Acids: Bond Energies of Rb⁺ and Cs⁺ to Met, Phe, Tyr, and Trp

Abstract

The interactions of rubidium and cesium cations with four amino acids (AA) including methionine (Met), phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp) are examined in detail. Experimentally, the bond dissociation energies (BDEs) are determined using threshold collision-induced dissociation of the Rb(+)(AA) and Cs(+)(AA) complexes with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy dependent cross sections include consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. 0 K BDEs of 121.0 ± 7.0 (102.8 ± 6.6), 123.8 ± 7.2 (112.9 ± 5.5), 125.8 ± 7.4 (115.6 ± 6.9), and 138.1 ± 7.5 (125.0 ± 6.8) kJ/mol are determined for complexes of Rb(+) (Cs(+)) with Met, Phe, Tyr, and Trp, respectively. Quantum chemical calculations are conducted at the B3LYP, MP2(full), and M06 levels of theory with geometries and zero point energies calculated at the B3LYP level using def2-TZVPPD basis sets. Results obtained using all three levels show good agreement with experiment, with B3LYP values being systematically low and MP2(full) and M06 values being systematically high. At 0 and 298 K, theory predicts the ground-state conformers for M(+)(Met) either have tridentate binding of the metal cation to the carbonyl, amino, and sulfur groups (MP2 and M06) or to both oxygens of a zwitterionic conformation (B3LYP). At 298 K, binding to the carboxylic acid group and the sulfur also becomes competitive. For the aromatic amino acids at 0 K, most levels of theory favor tridentate binding of the metal ions to the backbone carbonyl and amino groups along with the π-cloud of the ring, whereas for Rb(+)(Trp) and Cs(+)(AA), B3LYP theory favors binding to only the carbonyl and ring groups. At 298 K, B3LYP favors the latter binding mode for all three Rb(+)(aromatic AA) complexes. Comparison of these results to those for the smaller alkali cations provides insight into the trends in binding affinities and structures associated with metal cation variations.

Base-Pairing Energies of Proton-Bound Dimers and Proton Affinities of 1-Methyl-5-Halocytosines: Implications for the Effects of Halogenation on the Stability of the DNAi-Motif

“…The threshold regions of the measured CID cross-sections are modeled using procedures developed elsewhere [55][56][57][58][59][60][61][62] that have been found to reproduce CID cross-sections well [63][64][65][66][67]. Details regarding data handling and analysis procedures, which includes explicitly accounting for the internal and translational energy distributions of the reactant proton-bound dimers, the effects of multiple ion-neutral collisions, and the lifetime of the dissociating proton-bound dimers, are summarized in the Supplementary Information.…”

Selective encapsulation of cesium ions using the cyclic peptide moiety of surfactin: Highly efficient removal based on an aqueous giant micellar system

“…Among alkali metal ions, Cs + has received considerable attention in Japan because of the spread of radioactive 137 Cs from nuclear reactor accidents into the environment [6]. Cyclic peptides can be potentially used as novel sorbents since Cs + follows the same biological pathways and binds at the same ionophore or enzyme sites as K + [7][8][9]. Recently, several cyclic peptides used as sorbents for alkali metals have been reported to form unique self-assembled structures [10,11].…”

Self‐Assembled Multimetallic/Peptide Complexes: Structures and Unimolecular Reactions of [Mn(GlyGly−H)2n−1]+ and Mn+1(GlyGly−H2n]2+ Clusters in the Gas Phase

“…Collision-induced dissociation (CID) is aw idely used method for structure elucidationo fc omplexes of metal cations with biomolecules such as amino acids, [23][24][25][26][27][28][29] peptides, [30][31][32] and nucleic acid bases. [33,34] The effecto fm etal cations on the dissociation pattern and activation energy of amino acid complexes have been studied by CID.…”