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The Ion Mobility / Ion Chromatography Method

Structural Information of the Gas Phase Conformation of Molecules or Non-Covalent Clusters

! Determining the Peptide Configuration of (gly-ala)7X+

Predicted from Ramachandrin plot :

X+

% !-helicity

H Na K+ Rb +

+

+

23% 59% 77% 90%

Calculations predict that for X+= Cs+ that the !" helical structure is 10 kcal•mol-1 more stable than the globular configuration

Ion mobility experiments show that for X+= H+, Li+, Cs+ the a cross sections are all within 211- 216 Å2 at 300K which charaterizes these as globular compact zwitterionic structures.

Witt & Bowers: JACS 2000,122, 3458.

Thermochemistry by Threshold Collision-Induced Dissociations

Determination of Accurate Gas-Phase Binding Energies and Reaction Barriers

! Threshold Collision-Induced Dissociation

Threshold collision-induced dissociation (CID), which is an intrinsically endothermic reaction, is used to determine the energy threshold of the dissociation of the molecular ion AB+.

AB+

  • +

    Xe

A+

+B

  • +

    Xe

(1)

The threshold measured for the reaction in eq. (1), E0, corresponds to the highest energy along the reaction coordinate for dissociation, i.e., the activation barrier, which occurs at the transition state for the reaction.

! Bond Dissociation Energies of Cr(CO)6

The measured threshold corresponds to the bond dissociation energy (BDE) of CO from Cr(CO)n.

D 0 ( A + B )

=

E0

(2)

Total cross section clearly varies smoothly with energy and that CO losses are clearly sequential.

Ervin & Armentrout: J. Phys. Chem. 2001,115, 1213.

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