Charged supramolecular assemblies of surfactant molecules in gas phase

Abstract

The aim of this review is to critically analyze recent literature on charged supramolecular assemblies formed by surfactant molecules in gas phase. Apart our specific interest on this research area, the stimuli to undertake the task arise from the widespread theoretical and applicative benefits emerging from a comprehensive view of this topic. In fact, the study of the formation, stability, and physicochemical peculiarities of non-covalent assemblies of surfactant molecules in gas phase allows to unveil interesting aspects such as the role of attractive, repulsive, and steric intermolecular interactions as driving force of supramolecular organization in absence of interactions with surrounding medium and the size and charge state dependence of aggregate structural and dynamical properties. Other interesting aspects worth to be investigated are joined to the ability of these assemblies to incorporate selected solubilizates molecules as well as to give rise to chemical reactions within a single organized structure. In particular, the incorporation of large molecules such as proteins has been of recent interest with the objective to protect their structure and functionality during the transition from solution to gas phase. Exciting fall-out of the study of gas phase surfactant aggregates includes mass and energy transport in the atmosphere, origin of life and simulation of supramolecular aggregation in the interstellar space. Moreover, supramolecular assemblies of amphiphilic molecules in gas phase could find remarkable applications as atmospheric cleaning agents, nanosolvents and nanoreactors for specialized chemical processes in confined space. Mass spectrometry techniques have proven to be particularly suitable to generate these assemblies and to furnish useful information on their size, size polydispersity, stability, and structural organization. On the other hand molecular dynamics simulations have been very useful to rationalize many experimental findings and to furnish a vivid picture of the structural and dynamic features of these aggregates. Thus, in this review, we will focus on the most important achievements gained in recent years by both these investigative tools.

Electrospray ion mobility mass spectrometry of positively and negatively charged (1R,2S)‐dodecyl(2‐hydroxy‐1‐methyl‐2‐phenylethyl)dimethylammonium bromide aggregates

“…Mild ionization techniques as Fast‐Atom Bombardment (FAB), Matrix‐Assisted Laser Desorption/Ionization (MALDI) and mainly Electrospray Ionization (ESI) were preferred in our and several other studies …”

“…[5,6] Mild ionization techniques as Fast-Atom Bombardment (FAB), Matrix-Assisted Laser Desorption/Ionization (MALDI) and mainly Electrospray Ionization (ESI) were preferred in our and several other studies. [7][8][9][10] The study of surfactant self-assembly in the gas phase as charged aggregates constitutes a developing research field of interest since it allows information to be gained on their structural organization in the absence of surrounding interactions with the solvents as well as to exploit their use as gas-phase cleaning agents, vehicles of pulmonary drugs, specialized reactors for the synthesis of nanostructures and particularly for the chemical protection of biomolecules in mass spectrometric studies. [11,12] The majority of studies concerning the structural organization of these charged aggregates in the gas phase suggest that surfactant molecules are organized as reverse micelle-like assemblies, independently of the aggregate charge state and ESI solvent used.…”

Determination of the Structures of Uranyl–Tri‐n‐butyl‐Phosphate Aggregates by Coupling Experimental Results with Molecular Dynamic Simulations

“…reported that the structural organization of the surfactant in the gas phase depended on the nature and composition of the starting solution . The structure formed in the gas phase and detected by mass spectrometry results from a concurrence of the relative rates of evaporation of the dilution solvent, spontaneous transfer of surfactant molecules at the droplet surface, and aggregate structural rearrangements . In nonpolar media, such as alkanes, TBP is organized in small reverse aggregates,,,, whereas in methanol/water media it is likely that only molecular complexes are present in solution.…”

Micelles of the chiral biocompatible surfactant (1R,2S)‐dodecyl(2‐hydroxy‐1‐methyl‐2‐phenylethyl)dimethylammonium bromide (DMEB): molecular dynamics and fragmentation patterns in the gas phase

“…Also MD calculations are consistent with the occurrence of OH‐‐‐Br hydrogen bonding in large positively and negatively charged aggregates. On the other hand, the MD models that give CCS values in good agreement with experimental ones evidenced a less strict reverse micelle‐like structure and a more spread bromine anion distribution with respect to other supramolecular surfactant aggregates reported elsewhere …”

“…The study of charged aggregates of surfactant molecules in the gas phase is of growing interest both for theoretical and technological reasons . The main fallout of these investigations is the knowledge of the structural organization of the aggregates and of the mechanism through which amphiphilic molecules self‐assemble during the strongly out of equilibrium conditions characterizing the electrospray ionization process.…”