Styliani Consta, Lisa M. Wingen, Yiming Qin, Veronique Perraud, Barbara J. Finlayson-Pitts
{"title":"Molecular Modeling of the Late Stages of Ionization without an External Energy Source Coupled to Mass Spectrometry","authors":"Styliani Consta, Lisa M. Wingen, Yiming Qin, Veronique Perraud, Barbara J. Finlayson-Pitts","doi":"10.1039/d4cp03597f","DOIUrl":null,"url":null,"abstract":"Ionization via desorption of charged analytes from the surface of solid amorphous glutaric acid particles, without the assistance of an external energy source, has been shown to be a promising method that can be coupled to mass spectrometry. We conduct mechanistic studies of the later stages of this ionization process using atomistic molecular dynamics. Our analysis focuses on the hydrogen bonding, diffusion, and ion desorption from nano-aggregates of glutaric acid. These nano-aggregates exhibit an extended H-bonded network, often comprising H-bonded chains, linear dimeric assemblies, and occasionally cyclic trimeric assemblies. These local structures serve as centers for proton transfer reactions. The intermediate hydrocarbon chain between the proton-carrying oxygen sites prevents proton diffusion over a long distance unless there is significant translational or rotational movement of the proton-carrying diacid molecule. Our calculations show that diffusion on the surface is an order of magnitude faster than in the core of the nano-aggregate, which aids effective proton transfer on the particle's exterior. We find that ionic species desorb from the aggregate's surface through independent evaporation events of small clusters, where the ion is coordinated by only a few glutaric acid molecules. Near the nano-aggregate's Rayleigh limit, jets capable of releasing multiple ions were not observed. These observations suggest a more general ion-evaporation mechanism that applies to low-dielectric particles of various sizes, complementing the original ion-evaporation mechanism proposed for aqueous droplets with an approximate radius of 10–15 nm. The combined evidence from molecular modeling presented here and the thermodynamic properties of solid and supercooled liquid glutaric acid indicates that the stronger signals of glutaric acid observed in mass spectra, relative to other experimentally tested diacids, can be attributed to its significantly lower melting point and the reduced enthalpy of vaporization of its amorphous state compared to other tested diacids.","PeriodicalId":99,"journal":{"name":"Physical Chemistry Chemical Physics","volume":null,"pages":null},"PeriodicalIF":2.9000,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Physical Chemistry Chemical Physics","FirstCategoryId":"92","ListUrlMain":"https://doi.org/10.1039/d4cp03597f","RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
引用次数: 0
Abstract
Ionization via desorption of charged analytes from the surface of solid amorphous glutaric acid particles, without the assistance of an external energy source, has been shown to be a promising method that can be coupled to mass spectrometry. We conduct mechanistic studies of the later stages of this ionization process using atomistic molecular dynamics. Our analysis focuses on the hydrogen bonding, diffusion, and ion desorption from nano-aggregates of glutaric acid. These nano-aggregates exhibit an extended H-bonded network, often comprising H-bonded chains, linear dimeric assemblies, and occasionally cyclic trimeric assemblies. These local structures serve as centers for proton transfer reactions. The intermediate hydrocarbon chain between the proton-carrying oxygen sites prevents proton diffusion over a long distance unless there is significant translational or rotational movement of the proton-carrying diacid molecule. Our calculations show that diffusion on the surface is an order of magnitude faster than in the core of the nano-aggregate, which aids effective proton transfer on the particle's exterior. We find that ionic species desorb from the aggregate's surface through independent evaporation events of small clusters, where the ion is coordinated by only a few glutaric acid molecules. Near the nano-aggregate's Rayleigh limit, jets capable of releasing multiple ions were not observed. These observations suggest a more general ion-evaporation mechanism that applies to low-dielectric particles of various sizes, complementing the original ion-evaporation mechanism proposed for aqueous droplets with an approximate radius of 10–15 nm. The combined evidence from molecular modeling presented here and the thermodynamic properties of solid and supercooled liquid glutaric acid indicates that the stronger signals of glutaric acid observed in mass spectra, relative to other experimentally tested diacids, can be attributed to its significantly lower melting point and the reduced enthalpy of vaporization of its amorphous state compared to other tested diacids.
期刊介绍:
Physical Chemistry Chemical Physics (PCCP) is an international journal co-owned by 19 physical chemistry and physics societies from around the world. This journal publishes original, cutting-edge research in physical chemistry, chemical physics and biophysical chemistry. To be suitable for publication in PCCP, articles must include significant innovation and/or insight into physical chemistry; this is the most important criterion that reviewers and Editors will judge against when evaluating submissions.
The journal has a broad scope and welcomes contributions spanning experiment, theory, computation and data science. Topical coverage includes spectroscopy, dynamics, kinetics, statistical mechanics, thermodynamics, electrochemistry, catalysis, surface science, quantum mechanics, quantum computing and machine learning. Interdisciplinary research areas such as polymers and soft matter, materials, nanoscience, energy, surfaces/interfaces, and biophysical chemistry are welcomed if they demonstrate significant innovation and/or insight into physical chemistry. Joined experimental/theoretical studies are particularly appreciated when complementary and based on up-to-date approaches.