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Macromolecular Ion-Solvent Interactions in Charged Droplets

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Charged droplets reveal their secrets

Charged liquid droplets can be found in aerosols, thunder clouds and electrospray. An EU-funded initiative investigated the processes involved in forming charged droplets to determine how they affect the accuracy of electrospray ionisation mass spectrometry (ESI-MS).

Climate Change and Environment
Fundamental Research

The ESI technique produces ions using an electrospray, where a high voltage is applied to a liquid to create an aerosol. This technique involves evaporation and fragmentation and droplets develop charge induced instabilities. Following the discovery of ESI around 50 years ago, a number of experimental techniques were developed that utilise aerosols composed of highly charged droplets, including ESI-MS. Charged liquid droplets are normally composed of solvent and charge carriers, such as simple ions or macroions like proteins or nucleic acids. The project MISICD (Macromolecular ion-solvent interactions in charged droplets) aimed to understand the complex chemical and physical properties of charged droplets. Several factors affect the charge state and stability of the macromolecule complex (such as a nucleic acid or protein). A poor understanding of the processes and principles that affect the stability of protein complexes hamper the development of ESI-MS as a high-throughput robust experimental method for the detection of protein-protein and protein-ligand interactions. The MISICD team laid down the theoretical basis for the processes affecting the accuracy of the ESI-MS technique. Researchers used molecular modelling to determine the role of factors such as evaporation rate and distinct droplet morphology in the stability of nucleic acids and proteins. They discovered that a weak protein complex changes structure and may dissociate in shrinking water droplets relative to its stability in bulk solution. The molecular computer model provided insights into the mechanisms underlying droplet desolvation, which involves the release of water electrostatically bound to a particle in a water-based solution. This model will lead to more efficient and better quality measurements, resulting in lower costs for drugs and improved monitoring of explosives at airports due to more efficient chemical analysis. An improved understanding of the physical chemistry of charged droplets will also help advance the field of atmospheric aerosols. The molecular physics of such aerosols plays a major role in determining climate and environmental conditions. Thus, computational studies of charged water droplets conducted by MISICD should help inform major political decisions regarding climate change.


Charged droplets, electrospray ionisation mass spectrometry, MISICD, macromolecule complex, desolvation

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