A Direct Measurement of the Absolute Energies of Protonated Gly-Pro-Gly-Gly Conformations Using Ion Mobility Spectrometry and Guided Ion Beam Tandem Mass Spectrometry.

Threshold collision-induced dissociation of conformations selected by ion mobility spectrometry is described as a method to determine their absolute relative energies. Here, the method is demonstrated with the cis and trans conformers of the protonated tetrapeptide, Gly-Pro-Gly-Gly, which differ in the orientation of the peptide bond at the proline residue. The trans conformation was found to be more stable than the cis conformation by 4.

Bond Dissociation Energies for Diatomic Molecules Containing 3d Transition Metals: Benchmark Scalar-Relativistic Coupled-Cluster Calculations for 20 Molecules.

Benchmark scalar-relativistic coupled-cluster calculations for dissociation energies of the 20 diatomic molecules containing 3d transition metals in the 3dMLBE20 database ( J. Chem. Theory Comput.

Methane Activation by 5 d Transition Metals: Energetics, Mechanisms, and Periodic Trends.

Although it has been known for almost three decades that several 5d transition-metal cations will activate methane at room temperature, a more detailed examination of these reactions across the periodic table has only recently been completed. In this Minireview, we compare and contrast studies of the kinetic energy dependence of these reactions as studied using guided-ion-beam tandem mass spectrometry. Thermochemistry for the various products observed (MH , MH , MC , MCH , MCH , and MCH ) are collected and periodic trends evaluated and discussed.

Discriminating Properties of Alkali Metal Ions Towards the Constituents of Proteins and Nucleic Acids. Conclusions from Gas-Phase and Theoretical Studies.

Quantitative insight into the structures and thermodynamics of alkali metal cations interacting with biological molecules can be obtained from studies in the gas phase combined with theoretical work. In this chapter, the fundamentals of the experimental and theoretical techniques are first summarized and results for such work on complexes of alkali metal cations with amino acids, small peptides, and nucleobases are reviewed. Periodic trends in how these interactions vary as the alkali metal cations get heavier are highlighted.

Hydrated copper ion chemistry: guided ion beam and computational investigation of Cu2+(H2O)n (n = 7-10) complexes.

Cross sections for the threshold collision-induced dissociation of Cu(2+)(H(2)O)(n), where n = 8 - 10, are measured using a guided ion beam tandem mass spectrometer. The primary dissociation pathway is found to be loss of a single water molecule followed by the sequential loss of additional water molecules until n = 8, at which point charge separation to form CuOH(+)(H(2)O)(4) (+) H(+)(H(2)O)(3) is observed to occur at a slightly lower energy than loss of a water molecule. Competition from charge separation prohibits the formation of appreciable amounts of the n = 7 or smaller complexes as reactants in the source.

Quantum chemical study of the reactions between Pd+/Pt+ and H2O/H2S.

The study of the reactions of water and hydrogen sulfide with palladium and platinum cations has been completed in this work, in both low- and high-spin states. Our calculations predict that only the formation of platinum sulfide is exothermic (in both spin states), whereas for the remaining species the oxides and sulfides are found to be more reactive than their corresponding bare metal cations. An in-depth analysis of the reaction paths leading to metal oxide and sulfide species is given, including various minima, and several important transition states.

Threshold collision-induced dissociation of hydrated magnesium: experimental and theoretical investigation of the binding energies for Mg(2+)(H2O)x complexes (x=2-10).

The sequential bond energies of Mg(2+)(H2O)x complexes, in which x=2-10, are measured by threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer. From an electrospray ionization source that produces an initial distribution of Mg(2+)(H2O)x complexes in which x=7-10, complexes down to x=3 are formed by using an in-source fragmentation technique. Complexes smaller than Mg(2+)(H2O)3 cannot be formed in this source because charge separation into MgOH(+)(H2O) and H3O(+) is a lower-energy pathway than simple water loss from Mg(2+)(H2O)3.

Metal-cyclopentadienyl bond energies in metallocene cations measured using threshold collision-induced dissociation mass spectrometry.

Metal-cyclopentadienyl bond dissociation energies (BDEs) were measured for seven metallocene ions (Cp(2)M(+), Cp = η(5)-cyclopentadienyl = c-C(5)H(5), M = Ti, V, Cr, Mn, Fe, Co, Ni) using threshold collision-induced dissociation (TCID) performed in a guided ion beam tandem mass spectrometer. For all seven room temperature metallocene ions, the dominant dissociation pathway is simple Cp loss from the metal. Traces of other fragment ions were also detected, such as C(10)H(10)(+), C(10)H(8)(+), C(8)H(8)(+), C(3)H(3)(+), H(2)M(+), C(3)H(3)M(+), C(6)H(6)M(+), and C(7)H(6)M(+), depending on the metal center.

Thermodynamics and mechanism of protonated asparagine decomposition.

Deamidation of the amino acid asparagine (Asn) is a primary route for spontaneous post-translational protein modification biologically and is a pH dependent process. Here we present a full molecular description of the deamidation and (H(2)O + CO) loss reactions of protonated asparagine, H(+)(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 + CO) loss reactions after accounting for unimolecular decay rates, internal energy of reactant ions, multiple ion-molecule collisions, and competition among the decay channels.

Heats of formation of Co(CO)(2)NOPR(3), R = CH(3) and C(2)H(5), and its ionic fragments.

A joint threshold photoelectron photoion coincidence spectrometry (TPEPICO) and collision-induced dissociation (CID) study on the thermochemistry of Co(CO)(2)NOPR(3), R = CH(3) (Me) and C(2)H(5) (Et), complexes is presented. Adiabatic ionization energies of 7.36 +/- 0.