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The design of a new ion mobility mass spectrometer is presented. The design features an electrospray ion source; an ion funnel to transmit ions efficiently from the source to the mobility cell and to accumulate ions in the pulsed ion mode; a mobility cell, and a quadrupole mass analyzer. Each part of the instrument is described in detail. Preliminary results obtained with the new instrument are presented to demonstrate its capabilities. Equilibrium experiments showed that the ΔG°(300 K) values for the addition of the first water molecule to the doubly protonated peptides bradykinin, angiotensin II, and LHRH are in the range from −3.5 to −2.5 kcal/mol. The corresponding values for the singly protonated ions are >−0.5 kcal/mol for angiotensin II and LHRH, but equal to −2.6 kcal/mol for bradykinin. The stronger bonding in bradykinin may be due to the presence of a salt bridge structure. Ion arrival time distributions showed that singly protonated peptides can form aggregates of the form (nM + nH)n+. The mobilities of these ions indicated that they are near spherical. Heating the drift cell to ∼450 K caused dissociation of the (2M + 2H)2+ion into two (M + H)+units on the 1 ms experimental time scale. A theoretical fit to the experimental data yielded rate constants and a barrier for dissociation of 30 ± 2 kcal/mol for bradykinin and 39 ± 3 kcal/mol for LHRH.

Measurements are reported for sequential clustering of CH4to Fe+and Ni+ions under equilibrium conditions. Detailed density functional theory calculations were performed to provide structural and electronic configuration information and to help analyse and interpret the experimental data. The calculations indicate that the first two CH4ligands add on opposite sides of the Fe+core ion in an η3configuration, in an η2configuration for Ni+, and induce significant s/dhybridization on both of the metal centers. This hybridization both reduces Pauli repulsion and fosters sigma donation from the ligands into the 4sorbital on M+. Another major covalent interaction is the donation from CH4into the singly occupied dorbital(s) on M+for both η2and η3configurations. For Fe+, the change of spin state, from 6D (3d64s1) to 4F (3d7), takes place during the clustering of the first methane ligand. The clustering of the third CH4to Fe+and Ni+, unlike Co+(CH4)3, is not impeded by the s/dhybridization present for n= 1 and 2. The interactions of all three CH4ligands with the Fe+and Ni+core are essentially the same. The m/z120 peak [nominally Fe+(CH4)4] and the m/z122 peak [nominally Ni+(CH4)4] were formed irreversible in the temperature range from 270 to 170 K, probably due to the persistent impurity we reported earlier for the Co+system. The n= 5 and 6 ligands are very weakly bound and begin a second solvation shell. Calculations suggest the n= 6 cluster forms a pseudo octahedral complex.