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 Release Mechanisms of Poly(ethylene glycol) Macroion from Aqueous Charged Nanodroplets. MedLine Citation: PMID:  22530680     Owner:  NLM     Status:  Publisher Abstract/OtherAbstract: Ion-release processes in nanodroplets that contain excess charge are of central importance in atmospheric aerosols as well as in determining the charge state distributions of macroions that are detected in electrospray mass spectrometry (ESMS) experiments. We performed molecular simulations of systems of a poly(ethylene glycol) (PEG) associated with various ions ($\rm Na^+$, $\rm Li^+$, $\rm Ca^{2+}$) in aqueous charged nanodroplets in order to investigate the manner that the macroion emerges from an aqueous nanodroplet as well as its final charge state. In the study we focused on a specific region of the parameter space with respect to charge and size of droplets that is close to the Rayleigh limit. We found that for sizes of droplets with linear dimensions of several nanometers and length of PEG up to 100 monomers, the PEG macroion emerges from the droplet following a three-step process: i) phase separation; ii) gradual extension of the macroion out of the droplet and iii) drying-out of the solvent or spontaneous detachment of the macroion from the droplet. The third step is determined by the ratio of charge on the macroion to the ions in the water portion of the droplet. When the charge is carried by macroions the charge induced instability manifests by following one of the expected scenarios of Rayleigh instability, however the assumptions of the Rayleigh model break-down. We also examined the release of the macroion below the Rayleigh limit and we found that the macroion emerges from the droplet by drying-out of the solvent. On balance of phenomenological evidence we concluded that ion-evaporation mechanism (IEM) in its most common meaning is not the followed mechanism for the parameter space of the systems that we studied. The final charge state of the macroion is in excellent agreement with experimental data of Fenn and co-workers. Authors: Jun Kyung Chung; Styliani Consta Publication Detail: Type:  JOURNAL ARTICLE     Date:  2012-4-24 Journal Detail: Title:  The journal of physical chemistry. B     Volume:  -     ISSN:  1520-5207     ISO Abbreviation:  -     Publication Date:  2012 Apr Date Detail: Created Date:  2012-4-25     Completed Date:  -     Revised Date:  - Medline Journal Info: Nlm Unique ID:  101157530     Medline TA:  J Phys Chem B     Country:  - Other Details: Languages:  ENG     Pagination:  -     Citation Subset:  - Export Citation: APA/MLA Format     Download EndNote     Download BibTex MeSH Terms Descriptor/Qualifier:

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