Journal article
Gas phase stripping of alkali cations from biomolecules via reaction with crown ethers
International journal of mass spectrometry and ion processes, Vol.175(1), pp.179-186
05/01/1998
DOI: 10.1016/S0168-1176(98)00121-9
Abstract
Electrospray mass spectra of biomolecules produced from salty solutions can exhibit a large number of alkali adducts. Often the number of attached alkali metal atoms exceeds the net charge state of the ion. For example, the spectral intensity of the 2+ charge state of gramicidin S, cyclo[Val-Orn-Leu-
d-Phe-Pro]
2, (GS), withdrawn from a sodium-containing water:methanol solution, is distributed over (GS + 2H)
2+, (GS + H + Na)
2+, (GS + 2Na)
2+, (GS−H + 3Na)
2+, (GS−2H + 4Na)
2+, (GS−3H + 5Na)
2+, and (GS−4H + 6Na)
2+. Each additional metal cation displaces a proton without affecting the net charge of the biomolecule. Hence, in (GS−2H + 4Na)
2+, at least two of the alkali metal adducts must involve displacement of protons from non-traditional basic sites. The character of these coordination sites must be either “salt-like” or zwitterionic. Alkali adducts of trapped polypeptide ions may be removed via gas phase ion-molecule “stripping” reactions with crown ethers 12-crown-4, 15-crown-5, or 18-crown-6. Both products of the stripping reaction, the desalted biomolecule of reduced charge and the alkali-metal-attached crown, are observed in the FTICR mass spectra. For gas phase, “hyper-metallated” peptides, in which the number of adducted alkali metal ions exceeds the net charge, we suggest that some of the attached cations replace amide protons by coordinating as a salt or zwitterion to a tautomerized, deprotonated amide link in the backbone of the peptide. Alkali adduction to these non-traditional base sites leads to slightly higher stripping rates, probably by removing the secondary constraints of transannular NH···O C hydrogen bonds, which makes attached alkali cations more accessible to the stripping reagent. Stripping of K
+ is faster than stripping of Na
+, as may be expected for electrostatically bound cations.
Details
- Title: Subtitle
- Gas phase stripping of alkali cations from biomolecules via reaction with crown ethers
- Creators
- R.Marshall Pope - Brigham Young UniversityNanzhu Shen - Brigham Young UniversitySteven A. Hofstadler - Environmental Molecular Sciences LaboratoryDavid V. Dearden - Brigham Young University
- Resource Type
- Journal article
- Publication Details
- International journal of mass spectrometry and ion processes, Vol.175(1), pp.179-186
- Publisher
- Elsevier B.V
- DOI
- 10.1016/S0168-1176(98)00121-9
- ISSN
- 0168-1176
- eISSN
- 1873-2801
- Language
- English
- Date published
- 05/01/1998
- Academic Unit
- Medicine Administration
- Record Identifier
- 9984627217002771
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