Abstract: There is a growing interest in application of mass spectrometry as a high throughput technique for quaternary structure studies of protein complexes. One way to study protein complexes by mass spectrometry is to specifically label peptides segments that carry critical structural information, and after protein digestion subsequently identify the labeled peptides using liquid chromatography - mass spectrometry. A chemical crosslinker forms covalent bonds at specific amino acid sidechains that are in proximity in the protein structure. This approach is used to probe the binding interface of LexA/RecA proteins in Escherichia coli (Chapter 3). In contrast, intact noncovalent protein complexes can be directly transferred into the gas phase, while retaining memory of their solution structures. Accurate molecular weight measurement by mass spectrometry can be used for stoichiometry determination of protein-protein and protein-ligand systems, as manifested by the two examples of stoichiometry determination of differently treated adiponectin oligomers (Chapter 4), and the silver binding properties of the N-terminal region of a bacterial protein CusB (Chapter 5).

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Over the last decade, scientific and engineering interests have been shifting from conventional ion mobility spectrometry (IMS) to field asymmetric waveform ion mobility spectrometry (FAIMS). Differential Ion Mobility Spectrometry: Nonlinear Ion Transport and Fundamentals of FAIMS explores this new analytical technology that separates and characterizes ions by the difference between their mobility in gases at high and low electric fields. It also covers the novel topics of higher-order differential IMS and IMS with alignment of dipole direction. The book relates the fundamentals of FAIMS and other nonlinear IMS methods to the physics of gas-phase ion transport. It begins with the basics of ion diffusion and mobility in gases, covering the main attributes of conventional IMS that are relevant to all IMS approaches. Building on this foundation, the author reviews diverse high-field transport phenomena that underlie differential IMS. He discusses the conceptual implementation and first-principles optimization of FAIMS as a filtering technique, emphasizing the dependence of FAIMS performance metrics on instrumental parameters and properties of ion species. He also explores ion reactions in FAIMS caused by field heating and the effects of inhomogeneous electric field in curved FAIMS gaps. Written by an accomplished scientist in the field, this state-of-the-art book supplies the foundation to understand the new technology of nonlinear IMS methods.

A 7-Tesla Fourier transform ion-cyclotron resonance (FTICR) mass spectrometer was modified to insert a surface inside the cell for ion-surface collisions leading to the dissociation of impacting ions. Modifications were made to the software/hardware to collide the ions brought into the cell and trap the resulting fragment and undissociated primary ions inside the cell. The trapping plates were also ramped to determine kinetic energy distributions of these ions. The surface-induced dissociation (SID) of benzene and chromium hexacarbonyl ions was first studied as test cases for the instrument. Then a systematic study of the SID of small protonated peptides formed by electrospray ionization was begun. A series of small alanine(A)-containing peptides, viz., AA, AAA, AAAA, AAAAA, and PAAAA were used in the study. In the absence of any direct comparisons of the SID processes with the commonly used technique of tandem mass spectrometry of collision-induced dissociations (CID) via collisions with a neutral gas, a comparative study of CID and SID using the same protonated peptides was made. Since multiple collisions are often used to enhance dissociation efficiency in CID, the CID was performed under single as well as multiple collisional activation conditions. Both on-resonance and sustained off-resonance irradiation excitation were used for CID experiments. Kinetic energy of the ions was varied by changing peak-to-peak voltage applied to the excitation plates. Results are shown in a series of graphs, and a simple theoretical model is presented. This direct comparison of the two activation techniques on the same instrument provided insights into the similarities and differences between these two. The results suggest that internal energy distributions of ions activated by ion-surface collision and multiple collision ion-gaseous neutral collisions are quite comparable. The results also suggest that, in ion-surface collisions, the ion collides with only a small fraction of th e self-assembled monolayer chain, making it effectively a process very similar to CID.