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  1. Abstract Fragmentation studies of cationized amino acids and small peptides as studied using guided ion beam tandem mass spectrometry (GIBMS) are reviewed. After a brief examination of the key attributes of the GIBMS approach, results for a variety of systems are examined, compared, and contrasted. Cationization of amino acids, diglycine, and triglycine with alkali cations generally leads to dissociations in which the intact biomolecule is lost. Exceptions include most lithiated species as well as a few examples for sodiated and one example for potassiated species. Like the lithiated species, cationization by protons leads to numerous dissociation channels. Results for protonated glycine, cysteine, asparagine, diglycine, and a series of tripeptides are reviewed, along with the thermodynamic consequences that can be gleaned. Finally, the important physiological process of the deamidation of asparagine (Asn) residues is explored by the comparison of five dipeptides in which the C‐terminal partner (AsnXxx) is altered. The GIBMS thermochemistry is shown to correlate well with kinetic results from solution phase studies. 
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    Free, publicly-accessible full text available May 1, 2024
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  3. Abstract This review encompasses guided ion beam tandem mass spectrometry studies of hydrated metal dication complexes. Metals include the Group 2 alkaline earths (Mg, Ca, Sr, and Ba), late first‐row transition metals (Mn, Fe, Co, Ni, Cu, and Zn), along with Cd. In all cases, threshold collision‐induced dissociation experiments are used to quantitatively determine the sequential hydration energies for M 2+ (H 2 O) x complexes ranging in size from one to 11 water molecules. Periodic trends in these bond dissociation energies are examined and discussed. Values are compared to other experimental results when available. In addition to dissociation by simple water ligand loss, complexes at a select size (which differs from metal to metal) are also observed to undergo charge separation to yield a hydrated metal hydroxide cation and a hydrated proton. This leads to the concept of a critical size, x crit , and the periodic trends in this value are also discussed. 
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  4. The gas-phase structures of cationized glycine (Gly), including complexes with Li + , Na + , K + , Rb + , and Cs + , are examined using infrared multiple-photon dissociation (IRMPD) spectroscopy utilizing light generated by a free electron laser, in conjunction with ab initio calculations. To identify the structures present in the experimental studies, measured IRMPD spectra are compared to spectra calculated at B3LYP/6-311+G(d,p) for the Li + , Na + , and K + complexes and at B3LYP/def2TZVP for the Rb + and Cs + complexes. Single-point energy calculations were carried out at the B3LYP, B3P86, and MP2(full) levels using the 6-311+G(2d,2p) basis set for Li + , Na + , K + and the def2TZVPP basis set for Rb + and Cs + . The Li + and Na + complexes are identified as metal cation coordination to the amino nitrogen and carbonyl oxygen, [N,CO]-tt, although Na + (Gly) may have contributions from additional structures. The heavier metal cations coordinate to either the carbonyl oxygen, [CO]-cc, or the carbonyl oxygen and hydroxy oxygen, [CO,OH]-cc, with the former apparently preferred for Rb + and Cs + and the latter for K + . These two structures reside in a double-well potential and different levels of theory predict very different relative stabilities. Some experimental evidence is provided that MP2(full) theory provides the most accurate relative energies. 
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  5. The kinetic energy dependences of the reactions of Pt + ( 2 D 5/2 ) with SO 2 were studied using a guided ion beam tandem mass spectrometer and theory. The observed cationic products are PtO + and PtSO + , with small amounts of PtS + , all formed in endothermic reactions. Modeling the kinetic energy dependent product cross sections allows determination of the product bond dissociation energies (BDEs): D 0 (Pt + –O) = 3.14 ± 0.11 eV, D 0 (Pt + –S) = 3.68 ± 0.31 eV, and D 0 (Pt + –SO) = 3.03 ± 0.12 eV. The oxide BDE agrees well with more precise literature values, whereas the latter two results are the first such measurements. Quantum mechanical calculations were performed for PtO + , PtS + , PtO 2 + , and PtSO + at the B3LYP and coupled-cluster with single, double, and perturbative triple [CCSD(T)] levels of theory using the def2-XZVPPD (X = T, Q) and aug-cc-pVXZ (X = T, Q, 5) basis sets and complete basis set extrapolations. These theoretical BDEs agree well with the experimental values. After including empirical spin–orbit corrections, the product ground states are determined as PtO + ( 4 Σ 3/2 ), PtS + ( 4 Σ 3/2 ), PtO 2 + ( 2 Σ g + ), and PtSO + ( 2 A′). Potential energy profiles including intermediates and transition states for each reaction were also calculated at the B3LYP/def2-TZVPPD level. Periodic trends in the thermochemistry of the group 9 metal chalcogenide cations are compared, and the formation of PtO + from the Pt + + SO 2 reaction is compared with those from the Pt + + O 2 , CO 2 , CO, and NO reactions. 
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