Collision-induced dissociation of vanadium monoxide ion

2002

Self Cite

172

180

Guided ion beam tandem mass spectrometry has proved to be a robust tool for the measurement of thermodynamic information. Over the past twenty years, we have elucidated a number of factors necessary to make such thermochemistry accurate. Careful attention must be paid to the reduction of the raw data, ion intensities versus laboratory ion energies, to a more useful form, reaction cross sections versus relative kinetic energy. Analysis of the kinetic energy dependence of cross sections for endothermic reactions can then reveal thermodynamic data for both bimolecular and collision-induced dissociation (CID) processes. Such analyses need to include consideration of the explicit kinetic and internal energy distributions of the reactants, the effects of multiple collisions, the identity of the collision partner in CID processes, the kinetics of the reaction being studied, and competition between parallel reactions. This work provides examples illustrating the need to consider this multitude of effects along with details of the procedures developed in our group for handling each of them. ( W hen does a mass spectrometer become an ion beam instrument? Is this defined by the instrument, by whether the operator is an analytical or physical chemist, or by the experiments done? All mass spectrometers utilize ion beams, but the unspoken definition of an ion beam instrument is an apparatus that can be used to make quantitative physical measurements. In this regard, the capabilities of the instrumentation and the intent and training of the operator are all important factors. Whereas a mass spectrometer is often used as an identification tool through the use of mass spectral patterns, by taking advantage of the ability to easily change the kinetic energy of ions, it can also be a powerful instrument for the determination of thermodynamic data.In this article, I lay down some of the founding principles behind our use of tandem mass spectrometry, and in particular, so-called guided ion beam mass spectrometry to elucidate thermochemical information. This is achieved primarily by examining the kinetic energy dependence of endothermic ion-molecule reactions and determining their energy thresholds.Although many types of instruments have been used to perform such measurements, the link between such studies and guided ion beam techniques is a strong one. Indeed, the NIST Webbook [1] states in its section on Determinations of Reaction Endothermicity that "more commonly a so-called guided-beam apparatus is utilized for such determinations." Considering that there are only about a dozen such laboratories worldwide, this is a testament to the ability of this particular kind of apparatus to provide a plethora of high quality information. However, such information requires attention to myriad details, which are outlined in this article.Two fundamental types of reactions can be used to acquire thermodynamic information: Bimolecular exchange reactions, process 1, and collision-induced dissociation (CID), process 2.Reactions 1 can be either ex...

Section: Collision Partner In Collision-induced Dissociationmentioning

confidence: 77%

Mass spectrometry—Not just a structural tool: The use of guided ion beam tandem mass spectrometry to determine thermochemistry

2002

Self Cite

172

180

“…The ion guide minimizes losses of the reactant and any product ions resulting from scattering. The octopole passes through a static gas cell containing xenon, which is used as the collision gas for reasons described elsewhere [23,24]. After collision, the reactant and product ions drift to the end of the octopole where they are extracted and focused into a quadrupole mass filter for mass analysis.…”

Section: General Experimental Proceduresmentioning

confidence: 99%

Thermodynamics and Mechanisms of Protonated Diglycine Decomposition: A Guided Ion Beam Study

Heaton

2011

Self Cite

We present a full molecular description of fragmentation reactions of protonated diglycine (H + GG) by studying their collision-induced dissociation (CID) with Xe using a guided ion beam tandem mass spectrometer (GIBMS). Analysis of the kinetic energy-dependent CID cross sections provides the 0 K barriers for the sequential H 2 O+CO and CO+NH 3 losses from H + GG as well as for the reactions involved in y 1 and a 1 ion formation, after accounting for unimolecular decay rates, internal energy of reactant ions, and multiple ionmolecule collisions. Here, seven energetic barriers are measured for the fragmentation processes of H + GG, including the loss of H 2 O and of CO at~140 and~156 kJ/mol, the combined loss of (H 2 O+CO) and of (CO+NH 3 ) at~233 and~185 kJ/mol, and formation of y 1 and a 1 ions at~191 and~212 kJ/mol, respectively, with a second channel for a 1 formation opening at~326 kJ/mol. Theoretical energies from the preceding paper are compared with our experimental energies and found to be in good agreement. This validates the mechanisms explored computationally, including unambiguous identification of the b 2 ion as protonated 2-aminomethyl-5-oxazolone, thereby allowing a complete characterization of the elementary steps of H + GG decomposition. These results also demonstrate that all reactive species are available from the ground state conformation, as opposed to involving an initial broad distribution of protonated conformers. This result verifies the utility of the "mobile proton" model for understanding the fragmentation of protonated proteins.

“…The ion guide minimizes losses of the reactant and any product ions resulting from scattering. The octopole passes through a static gas cell containing xenon, which is used as the collision gas for reasons described elsewhere [33,34]. After collision, the reactant and product ions drift to the end of the octopole where they are extracted and focused into a quadrupole mass filter for mass analysis.…”

Section: General Experimental Proceduresmentioning

confidence: 99%

Thermodynamics and mechanism of protonated asparagine decomposition

Heaton

2009

Deamidation of the amino acid asparagine (Asn) is a primary route for spontaneous posttranslational protein modification biologically and is a pH dependent process. Here we present a full molecular description of the deamidation and (H 2 O ϩ CO) loss reactions of protonated asparagine, H ϩ (Asn), by studying its collision-induced dissociation (CID) with Xe using a guided ion beam (GIB) tandem mass spectrometer. Analysis of the kinetic energy-dependent CID cross sections provides the 0 K barriers for the deamidation and (H 2 O ϩ CO) loss reactions after accounting for unimolecular decay rates, internal energy of reactant ions, multiple ion-molecule collisions, and competition among the decay channels. Relaxed potential energy surface scans performed at the B3LYP/6-31G(d) level identify the transition-state (TS) and intermediate reaction species for these processes, structures that are further optimized at the B3LYP/6-311ϩG(d,p) level. Intrinsic reaction coordinate (IRC) calculations are also performed at this level on the rate-limiting reaction TSs to validate the molecular details and energy dependence of these species. Single point energies of the key optimized TSs and intermediates are calculated at B3LYP, B3P86, and MP2(full) levels using a 6-311ϩG(2d,2p) basis set. A number of alternative high-energy mechanisms for (H 2 O ϩ CO) loss from H ϩ (Asn) are also investigated. Combining both experimental work and quantum chemical calculations allows for a complete characterization of the elementary steps of these reactions as well as a comprehensive evaluation of the complex behavior of the deamidation reaction. (J Am Soc Mass Spectrom 2009, 20, 852-866)