Observation of Magic Number Clusters from Thermal Dissociation Molecular Dynamics Simulations of Lithium Formate Ionic Clusters

Abstract

Molecular dynamics (MD) simulations are well positioned to elucidate the aspects of electrospray ionization (ESI) and high-energy collision dissociation (HCD), as well as give insight into processes that involve neutral species that cannot be observed experimentally in ESI, HCD, and collisioninduced dissociation (CID). Here, we utilize temperature dissociation molecular dynamics (TDMD) to model the HCD/CID of lithium formate clusters carrying a single positive charge. These simulations successfully reproduce the experimental ESI HCD spectra of lithium formate solutions and also support the existence of magic number clusters (MNCs) that have been observed. The simulations also provide strong evidence that the main fragmentation channel of such clusters involves neutral (LiHCOO) 2 dimers.

Mobile Protons Limit the Stability of Salt Bridges in the Gas Phase: Implications for the Structures of Electrosprayed Protein Ions

“…This method overcomes a key limitation of traditional MD simulations, where protonation patterns remain static throughout the entire run. 24,26,28,29,31,33,34 We find that, despite the fleeting nature of charge−charge contacts, salt bridges promote the preservation of compact structures during CIU. However, this stabilization is less pronounced than might be expected from zwitterionic models that neglect the mobile nature of H + .…”

“…100,101 Moreover, it is unclear how to map experimental ion temperatures to a specific MD temperature. 33 (2) The extent of experimental CIU is limited by the fact that excess heating destroys the ions via CID (see protein fragments at CE = 80 V, Figure 3C). This is in contrast to MD simulations where proteins remain covalently intact at any temperature.…”

“…[M + z H] z + protein ions produced by “native” ESI can maintain solution-like conformations. − This structural robustness has been attributed to kinetic trapping, that is, the presence of large activation barriers that preclude transitions to thermodynamically stable gas-phase structures. ,− Many aspects of gaseous proteins remain poorly understood, ,, largely because mass spectrometry (MS) and ion mobility spectrometry (IMS) experiments only provide low-resolution structural insights. Molecular dynamics (MD) simulations have therefore become an important tool in this area. ,,− …”

Density functional theory computational study of [M∙Pro‐H]+ (M = Pb, Ba, or Pt) complexes in the gas phase

“…Comparing the calculated band positions to spectroscopic data over the IR region will clarify whether their dominant structures are A‐ or H‐type, or other isomer types that have not been explored in the current work. An alternative approach, one that is not discussed in this work, is to simulate dissociation reactions using a molecular dynamics method, such as that described in a computational study of [Li·HCOO] n ·Li + clusters [37]. The study shows that thermal decay simulations for energy‐minimized structures of the clusters yielded fragmentation results that are consistent with collision‐induced dissociation tandem mass spectra of the clusters prepared using the electrospray ionization method.…”

Sulfolane-Induced Supercharging of Electrosprayed Salt Clusters: An Experimental/Computational Perspective

“…The current work aims to contribute to a better understanding of supercharging by examining a completely different type of analyte, i.e., alkali metal halide clusters. Our interest in these clusters reflects the fact that these species have played a central role for earlier mechanistic studies of the ESI process. ,,− As a typical example, [Na n Cl m ] ( n − m )+ clusters are formed when electrospraying aqueous NaCl solutions. Practitioners are familiar with such clusters because of their use as mass calibrants, , as well as a source of chemical noise for improperly desalted samples .…”