Ion Mobility Studies of Electronically Excited States of Atomic Transition Metal Cations: Development of an Ion Mobility Source for Guided Ion Beam Experiments

The design of an ion mobility source developed to couple to a guided ion beam tandem mass spectrometer is presented. In these exploratory studies, metal ions are created continuously by electron ionization of the volatile hexacarbonyls of the three group 6 transition metals. These ions are focused into a linear hexapole ion trap, which collects the ions and then creates high intensity pulses of ions, avoiding excessive ion losses resulting from the low duty cycle of pulsed operation. The ion pulses are injected into a six-ring drift cell filled with helium where ions having different electronic configurations can separate because they have different ion mobilities. Such separation is observed for chromium ions and compares favorably with the pioneering work of Kemper and Bowers (J. Phys. Chem. 1991, 95, 5134). The results are then extended to Mo+ and W+, which also show efficient configuration separation. The source conditions needed for high intensities and good configuration separation are discussed in detail and suggestions for further improvements are also provided

Entropy measurements and the kinetic method: a statistically meaningful approach

AbstractIn the literature, data obtained using the kinetic method have been analyzed to provide both ion affinities and relative entropies for the competitive dissociations involved. In this work, the procedure used to extract this information is shown to be statistically flawed. Using more rigorous statistical procedures, we outline alternative methods of acquiring the same information, including straightforward means of analyzing the uncertainties in the thermodynamic quantities obtained. Fortunately, it is expected that the central values reported in previous work need not be changed, but the uncertainties are much larger than has been previously detailed. The validity of the assumptions involved in the extraction of entropy effects is discussed in some detail

Communication: Theoretical exploration of AuH2, D2, and HD reactive collisions

A quasi-classical study of the endoergic Au(1S) H 2(X1g+) → AuH (2) H(2S) reaction, and isotopic variants, is performed to compare with recent experimental results [F. Li, C. S. Hinton, M. Citir, F. Liu, and P. B. Armentrout, J. Chem. Phys. 134, 024310 (2011)].10.1063/1.3514899 For this purpose, a new global potential energy surface has been developed based on multi-reference configuration interaction ab initio calculations. The quasi-classical trajectory results show a very good agreement with the experiments, showing the same trends for the different isotopic variants of the hydrogen molecule. It is also found that the total dissociation into three fragments, AuHH, is the dominant reaction channel for energies above the H 2 dissociation energy. This results from a well in the entrance channel of the potential energy surface, which enhances the probability of H-Au-H insertion. © 2011 American Institute of Physics.This work is supported by Comunidad Autónoma de Madrid, Grant No. S-2009/MAT/1467, and by Ministerio de Ciencia e Innovación, Grant Nos. CSD2009-00038 and FIS2010-18132.Peer Reviewe

Deamidation of Protonated Asparagine-Valine Investigated by a Combined Spectroscopic, Guided Ion Beam, and Theoretical Study

Contains fulltext : 190029.pdf (publisher's version ) (Open Access

Zn2+ and Cd2+ cationized serine complexes: infrared multiple photon dissociation spectroscopy and density functional theory investigations

Contains fulltext : 161542correctie.pdf (publisher's version ) (Open Access) Contains fulltext : 161542.pdf (publisher's version ) (Closed access

IR spectroscopy of cationized aliphatic amino acids: Stability of charge-solvated structure increases with metal cation size

Gas-phase structures of alkali metal cationized (Li+, Na+, K+, Rb+, and Cs+) proline (Pro) and N-methyl alanine have been investigated using infrared multiple photon dissociation (IRMPD) spectroscopy utilizing light generated by a free electron laser and computational modeling. Measured IRMPD spectra are compared to spectra calculated at the B3LYP/6-311++G(2d,2p) level of theory to identify individual conformers. Calculations indicate that the stability of the salt bridge (SB; zwitterionic) conformer relative to the most stable canonical structure with a single formal charge site (charge solvation; CS) of aliphatic amino acids (e.g., Pro, N-methyl alanine, N-methyl glycine, and glycine) does not increase with size and polarizability of the alkali metal cations, in contrast to the trend commonly found for functionalized amino acids. In fact, the relative stability of SB over CS conformers reaches a maximum at [amino acid + Na]+. A uniform SB structure and two characteristic CS conformers are identified by theory to be relevant for alkali metalized Pro, N-methyl alanine, and N-methyl glycine. For CS structures, the alkali metal cation is either coordinated to the nitrogen and the carbonyl oxygen of the acid functionality (Li+, Na+) or is solely interacting with the carboxylic acid oxygens (K+, Rb+, and Cs+). The IRMPD spectra exhibit clearly distinguishable bands for the CO stretching modes of the carboxylic acid moiety in CS structures and for the carboxylate moiety in SB structures, allowing reliable structure assignments for all complexes investigated. The IRMPD spectra clearly exhibit the presence of mixed populations of SB and CS structures with the contribution of CS increasing toward the larger metal cations, in good agreement with the predictions from computational modeling. The special trend regarding formation and stability of individual gas-phase ion structures of aliphatic amino acids, lacking functionalized α-side chains, can be rationalized with the concept of hard and soft Lewis acids and bases. Furthermore, calculations show that the trends with metal cation size found for aliphatic amino acids with secondary amines are similar for ordinary aliphatic amino acids (Gly, Ala)

IRMPD Spectroscopic and Theoretical Structural Investigations of Zinc and Cadmium Dications Bound to Histidine Dimers

Contains fulltext : 229032.pdf (Publisher’s version ) (Open Access