Conformational analysis of peptides and their metal-complexed species using H/D exchange reactions and kinetic studies

The goal of this dissertation was four-fold: (1) To study the conformational variation of model peptides induced by metal complexation and/or sequential fragmentation. (2) To identify the existence of different sets of conformers for the b-type fragment ions of peptides. (3) To probe the peptide dependency of conformational changes that occur upon metal ion complexation as well as the peptide-dependency for the existence of different conformers of b ₅+ fragment ions. (4) To develop a novel method to measure the molecular weight of the complex species in solution.; Chapter 1 includes and overview of the this dissertation, the introduction about the significance of H/D exchange reactions and metal complexation of peptides, and the methodology utilized in this study.; In Chapter 2, we demonstrate that WHWLQL hexapeptide, its b-series fragment ions as well as the sodiated and potassiated-WHWLQL show different H/D exchange patterns in the gas phase. The results of fragmentation experiments indicate that K+ and Na+ are located at the Trp-His segment of the WHWLQL hexapeptide. The combined results of kinetic studies and SORI-CAD experiments suggest long-range intramolecular interactions between the adduct metal and various functional groups of the WHWLQL in the sodiated and potassiated-WHWLQL.; In Chapter 3, using the double SWIFT isolation and double H/D exchange reactions, we show that b-series fragment ions of the WHWLQL hexapeptide exist as two energetically different sets of conformers in the gas phase: the Fast-Exchanging Conformers (FEC) and the Slow-Exchanging Conformers (SEC).; Data in Chapter 4 indicates that how the side chain characteristic of a peptide affects the metal-induced conformational variations of peptides. To study peptide dependency of conformational variations, we selected the acidic side chain peptide DSIP (Delta-Sleep-Inducing Peptide) and the basic side chain peptide GHRP (Growth-Hormone-Releasing peptide). The H/D exchange studies indicate that the conformational variations (upon metal complexation) of these two peptide strongly depend on their side chain characteristics. In addition, in this chapter we show that the FEC and SEC can be formed for all three peptides (WHWLQL, DSIP, and GHRP) studied herein. However, the calculated rate constant for the first H/D exchange of the b₅+ fragment ion ions (FEC and FEC) of these peptides strongly depend on the side chain characteristics of the peptides.; In Chapter 5, we present a novel method called SDORP (Simultaneous Determination of Reaction Parameters) to determine the average molecular weight of the fulvic acid species.