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The advancement of hybrid mass spectrometric tools as an indirect probe of molecular structure and dynamics relies heavily upon a clear understanding between gas-phase ion reactivity and ion structural characteristics. This work provides new insights into ion-neutral reactions of the model peptides (i.e., angiotensin II and bradykinin) on a per-residue basis by integrating hydrogen/deuterium exchange, ion mobility, tandem mass spectrometry, selective vapor binding, and molecular dynamics simulations. By comparing fragmentation patterns with simulated probabilities of vapor uptake, a clear link between gas-phase hydrogen/deuterium exchange and the probabilities of localized vapor association is established. The observed molecular dynamics trends related to the sites and duration of vapor binding track closely with experimental observation. Additionally, the influence of additional charges and structural characteristics on exchange kinetics and ion-neutral cluster formation is examined. These data provide a foundation for the analysis of solvation dynamics of larger, native-like conformations of proteins in the gas phase. 

The rates and mechanisms of chemical reactions that occur at a phase boundary often differ considerably from chemical behavior in bulk solution, but remain difficult to quantify. Ion–neutral interactions are one such class of chemical reactions whose behavior during the nascent stages of solvation differs from bulk solution while occupying critical roles in aerosol formation, atmospheric chemistry, and gas-phase ion separations. Through a gas-phase ion separation technique utilizing a counter-current flow of deuterated vapor, we quantify the degree of hydrogen–deuterium exchange (HDX) and ion–neutral clustering on a series of model chemical systems ( i.e. amino acids). By simultaneously quantifying the degree of vapor association and HDX, the effects of cluster formation on reaction kinetics are realized. These results imply that cluster formation cannot be ignored when modeling complex nucleation processes and biopolymer structural dynamics. 

Silica nanomaterials have been studied based on their potential applications in a variety of fields, including biomedicine and agriculture. A number of different molecules have been condensed onto silica nanoparticles’ surfaces to present the surface chemistry needed for a given application. Among those molecules, (3-aminopropyl)triethoxysilane (APS) is one of the most commonly applied silanes used for nanoparticle surface functionalization to achieve charge reversal as well as to enable cargo loading. However, the colloidal stability of APS-functionalized silica nanoparticles has not been thoroughly studied, which can be problematic when the high reactivity of amine groups is considered. In this study, four different types of silica nanoparticles with varied location of added APS have been prepared via a reverse micro emulsion process, and their colloidal stability and dissolution behavior have been investigated. Systematic characterization has been accomplished using transmission electron microscopy (TEM), silicomolybdic acid (SMA) spectrophotometric assay, nitrogen adsorption–desorption surface area measurement, and aerosol ion mobility-mass spectrometry to track the nanoparticles’ physical and chemical changes during dissolution. We find that when APS is on the interior of the silica nanoparticle, it facilitates dissolution, but when APS is condensed both on the interior and exterior, only the exterior siloxane bonds experience catalytic hydrolysis, and the interior dissolution is dramatically suppressed. The observation and analyses that silica nanoparticles show different hydrolysis behaviors dependent on the location of the functional group will be important in future design of silica nanoparticles for specific biomedical and agricultural applications.