Ectoine hydration, aggregation and influence on water structure

Abstract

Neutron diffraction with isotopic H/D substitution on water, augmented by Empirical Potential Structure Refinement has been applied to extract the hydration properties of the osmolyte zwitterionic ectoine at 1.5 M concentration. This has evidenced differences between the hydration of COO⁻ and NH groups, both in terms of number of water molecules involved in the hydration shell and of three-dimensional symmetry. Signatures of ectoine–ectoine contacts, due to hydrogen bonds, have been found, as possible precursors of ectoine aggregation at higher concentrations. The influence of ectoine on the water structure is ascribed to the dipolar electric field generated by the exposed charges of ectoine.

GRAPHICAL ABSTRACT

Keywords:

• Ectoine
• H-bond
• hydration
• neutron diffraction
• water structure

Acknowledgments

Beamtime awarded by ISIS under RB number 1710038 is gratefully acknowledged. The data that support the findings of this study are openly available (The release date is: Fri Oct 02 10:00:00 BST 2020) in ISIS Data Journal at http://doi.org/10.5286/ISIS.E.87768521, reference number RB1710038. The authors thank Prof. Alan Soper for the availability of the room temperature water data and acknowledge useful discussions with P. Corsi, L. Ruggiero and M. Sbroscia.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Michael Di Gioacchino http://orcid.org/0000-0001-7465-2456

Silvia Imberti http://orcid.org/0000-0001-7037-6829

Maria Antonietta Ricci http://orcid.org/0000-0002-6904-6686

Additional information

Funding

This work has been performed within the Agreement No. 0018318 (02/06/2014) between STFC and Consiglio Nazionale delle Ricerche (CNR), concerning collaboration in scientific research at the spallation neutron source ISIS and with partial financial support of CNR. The Grant of Excellence Departments, Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR) (Articolo 1, commi 314 337 Legge 232/2016) is greatly acknowledged.