Deuterium Substitution and Charge Retention in Ions of Organic and Bioorganic Compounds. Part 1. Apamin

This work continues the development of a new method for detecting different structural forms of biomolecules or organic compounds by analyzing hydrogen/deuterium exchange mass spectra of multiply charged (z > 1) or singly charged (z = 1) ions. The method is based on the best approximation of experimental mass spectra obtained by electrospray ionization of electrolyte solutions using a linear combination of several H/D/z distributions, assuming independent substitution of exchangeable hydrogen atoms with deuterium and independent retention of a certain number of charge carriers. The method is tested using apamin, an 18-amino acid polypeptide with a molecular mass of about 2025.886 Da. The relation between the obtained mass spectral components and the structural forms of apamin formed during hydrogen/deuterium exchange is analyzed. The comparison is made for conditions with and without the addition of ND-containing gas.