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Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →In a 2017 mass-spectrometry study, researchers reported that highly charged ions of two proteins—cytochrome c and myoglobin—were among the most acidic organic species ever isolated and detected. The result concerns proton transfer by individual protein ions in the gas phase, not an acid that can be bottled or ranked by its pH in water.
What did the researchers make?
The “protein cations” were highly protonated, positively charged ions of cytochrome c and myoglobin. They were produced by electrospray ionization and studied inside a mass spectrometer. These are isolated gas-phase ions, not protein dissolved in water and not a practical chemical product. The authors described their subject as highly charged protein ions.
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How did the study establish their acidity?
The team used tandem mass spectrometry and ion–molecule reactions, changing the ions’ charge states and exposing them to other molecules and gases. They observed proton transfer to non-polar molecules and to gases including argon, oxygen, and nitrogen. In the gas phase, a species that readily donates a proton is acidic; these reactions showed that the highly charged protein ions could donate protons even to unusually weak proton acceptors.
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For cytochrome c, the researchers generated ions from a solution containing acetic acid and 1,2-butylene carbonate, used as a supercharging agent, then exposed them to gases in a modified ion trap. The ions lost protons in argon under the reported conditions, while a helium control showed essentially no reaction. The contrast helped test whether the observed proton loss depended on the gas involved.
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What does “strongest organic acid” mean here?
The headline needs a measurement attached to it. The study compared gas-phase acidity, assessed through proton-transfer behavior and basicity—not acidity in water. The authors reported that their most highly charged protein ions were more than 130 kJ mol⁻¹ less basic than the least basic known neutral organic molecules, including tetrafluoromethane and methane. Lower basicity in this comparison corresponds to a greater tendency to donate a proton.
The authors’ own carefully bounded conclusion was that highly charged cytochrome c and myoglobin ions were “the most acidic organic species to be isolated and detected.” That qualification matters: it describes organic species isolated and detected in the study’s gas-phase experiments, rather than proving an unrestricted record across every substance and every definition of acidity.
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Why this is not an aqueous pKa record
Acidity depends on the environment and the measurement. Aqueous pKa values describe proton donation in water; gas-phase basicity and proton-transfer experiments describe ions and molecules without bulk solvent. A protein ion carrying many positive charges can behave very differently from a neutral molecule dissolved in water. Consequently, this result cannot be inserted directly into a ranking of familiar liquid acids by aqueous pKa.
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallHow highly charged were the protein ions?
Zenaidee and colleagues reported an average of about one proton per four amino-acid residues for the highly charged protein ions they formed. Their calculations predicted that ions at a still greater charge density—one proton per three residues—should spontaneously lose a proton into vacuum. That one-per-three figure was a theoretical prediction, not the average experimentally achieved in the study.
What did the result suggest about electrospray ionization?
The authors interpreted their findings as more consistent with the chain-ejection model than with the charge-residue model for forming highly charged protein ions under the conditions they studied. This is the paper’s interpretation of those experiments, not a universal resolution of how electrospray produces ions in every system.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Who reported the finding, and when?
Muhammad A. Zenaidee, Michael G. Leeming, Fangtong Zhang, Toby T. Funston, and William A. Donald published “Highly Charged Protein Ions: The Strongest Organic Acids to Date” in Angewandte Chemie International Edition, volume 56, issue 29, pages 8522–8526 (2017). PubMed lists electronic publication on May 4, 2017, and an issue date of July 10, 2017. The result is therefore best described as the authors’ 2017 claim under their experimental scope; the cited record alone does not establish whether later studies have superseded it.
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