Faculty Interaction

Scott Mcluckey

Department of Chemistry
Purdue University

Brief Project Description:

Our research initiative is to develop new and improved methodologies for manipulating and interrogating macro-molecular ions with strong emphasis on large polypeptide and oligonucleotides species. With our experimental apparatus which is composed of mainly home-modified mass spectrometers, reactions between ions of opposite polarities can be carried out in the gas phase. A variety of observations have been made, depending on the properties of the reactant ions and experimental conditions. The two major reaction pathways involve the formation of complexes and charge transfer via either proton transfer or electron transfer. Such observations have demonstrated useful applications in gas phase ion synthesis and charge manipulations. It is in our interest to advance the understanding of the fundamentals of such reactions from a thermodynamic perspective, which should also help us to perform these reactions in a more controlled fashion. Simulation of the gas phase reactions using theoretical calculations, mainly with Gaussian software, may shed some light on it. For example, we are interested in charge inversion reactions whereby the polarity of an analyte ion of interest is inverted by virtue of reaction with a reagent ion of greater absolute charge. We have been conducting both experiments and ab initio calculations on model systems to determine the combinations of chemical functionalities associated with the charge sites that either maximize or minimize the observation of positive ion/negative ion complexes. This type of reactions has been applied to manipulate the ion polarity and charge states. Figure 1 demonstrates the use of sequential charge inversion reactions between peptides ions and dendrimer ions to increase ion charge states in the gas phase with relatively high efficiency. ab initio calculations with model systems indicated that the carboxylic groups on the negatively charged polyamidoamine (PAMAM) dendrimers and the primary amine groups on the positively charged diamino (DAB) dendrimers are suitable for proton transfer reactions while minimizing the possible formation of a complex.