Abstract
Although metal cations are prevalent in biological media, the species of multi-metal cationized biomolecules have received little attention so far. Studying these complexes in isolated state is important, since it provides intrinsic information about the interaction among them on the molecular level. Our investigation here demonstrates the unexpected structural diversity of such species generated by a matrix-assisted laser desorption ionization (MALDI) source in the gas phase. The photodissociation spectroscopic and theoretical study reflects that the co-existing isomers of [Arg+Rb+K−H]+ can have energies ≥95 kJ/mol higher than that of the most stable one. While the result can be rationalized by the great isomerization energy barrier due to the coordination, it strongly reminds us to pay more attention to their structural diversities for multi-metalized fundamental biological molecules, especially for the ones with the ubiquitous alkali metal ions.
Highlights
Metal ions are essential for living processes by regulating structures and functions of various biological molecules, including amino acids, peptides, proteins, and nucleic acids [1,2,3,4,5]
Previous results about singly alkali metal cationized amino acids show that the arginine changes from its nonzwitterionic to zwitterionic form between lithium and sodium, indicating the metal ion size can highly affect their structures [19]
For the hetero di-metal cationized species, each stable isomer was found to be accompanied by a twin isomer, characterized by exchanging the positions of the two different metal ions
Summary
Metal ions are essential for living processes by regulating structures and functions of various biological molecules, including amino acids, peptides, proteins, and nucleic acids [1,2,3,4,5]. The interaction of metal ions with amino acids and peptides have been extensively studied and the internal rules relative to their structural preference have been gradually revealed in the past 20 years [17,18,19,20,21,22,23,24,25]. Most of these studies only focus on the singly metalized complexes, and we still know little about such complexes with multiple metal ions. The results can further introduce the study of micro solvation of such bimetallic ions on the single molecule level, which bridges the structure and property study for such molecules in the gas and condensed phases
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