Bulk Nanostructure of Mixtures of Choline Arginate, Choline Lysinate, and Water

Lucas N Wong; Manuel Brunner; Silvia Imberti; Gregory G Warr; Rob Atkin

doi:10.1021/acs.jpcb.4c01482

Bulk Nanostructure of Mixtures of Choline Arginate, Choline Lysinate, and Water

J Phys Chem B. 2024 May 16;128(19):4853-4863. doi: 10.1021/acs.jpcb.4c01482. Epub 2024 May 1.

Authors

Lucas N Wong¹, Manuel Brunner¹, Silvia Imberti², Gregory G Warr³, Rob Atkin¹

Affiliations

¹ School of Molecular Sciences, The University of Western Australia, Crawley, WA 6009, Australia.
² UKRI, STFC, ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom.
³ School of Chemistry and University of Sydney Nano Institute, The University of Sydney, Sydney, NSW 2006, Australia.

PMID: 38691762
DOI: 10.1021/acs.jpcb.4c01482

Abstract

Neutron diffraction with empirical potential structure refinement was used to investigate the bulk liquid nanostructure of mixtures of choline arginate (Ch[Arg]), choline lysinate (Ch[Lys]), and water at mole ratios of 1Ch[Arg]:1Ch[Lys]:6H₂O (balanced), 1Ch[Arg]:1Ch[Lys]:20H₂O (balanced dilute), 3Ch[Arg]:1Ch[Lys]:12H₂O (Arg^- rich), and 1Ch[Arg]:3Ch[Lys]:12H₂O (Lys^- rich). The Arg^- and Lys^- anions tend not to associate due to electrostatic repulsion between charge groups and weak anion-anion attractions. This means that the local ion structures around the anions in these mixtures resemble the parent single-component systems. The bulk liquid nanostructure varies with the Arg^-:Lys^- ratio. In the Lys^--rich mixture (1Ch[Arg]:3Ch[Lys]:12H₂O), Lys^- side chains cluster into a continuous apolar domain separated from a charged domain of polar groups. In the balanced mixture (1Ch[Arg]:1Ch[Lys]:6H₂O), Lys^- side chains form discrete apolar aggregates within a continuous polar domain of Arg^-, Ch⁺, and water, and in the Arg^--rich mixture (3Ch[Arg]:1Ch[Lys]:12H₂O), the distribution of Lys^- and Arg^- is nearly homogeneous. Finally, in the balance dilute system (1Ch[Arg]:1Ch[Lys]:20H₂O), a percolating water domain forms.