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Binding of Divalent Cations to Aqueous Acetate: Molecular Simulations Guided by Raman Spectroscopy

preprint
revised on 29.09.2020 and posted on 29.09.2020 by Denilson Mendes de Oliveira, Samual R. Zukowski, Vladimir Palivec, Jérôme Hénin, Hector Martinez-Seara, Dor Ben-Amotz, Pavel Jungwirth, Elise Duboué-Dijon

In spite of the biological importance of the binding of Zn2+, Ca2+, and Mg2+ to the carboxylate group, cation-acetate binding affinities and binding modes remain actively debated. Here, we report the first use of Raman multivariate curve resolution (Raman-MCR) vibrational spectroscopy to obtain self-consistent free and bound metal acetate spectra and one-to-one binding constants, without the need to invoke any a priori assumptions regarding the shapes of the corresponding vibrational bands. The experimental results, combined with classical molecular dynamics simulations with a force field effectively accounting for electronic polarization via charge scaling and ab initio simulations, indicate that the measured binding constants pertain to direct (as opposed to water separated) ion pairing. The resulting binding constants do not scale with cation size, as

the binding constant to Zn2+ is significantly larger than that to either Mg2+ or Ca2+, although Zn2+ and Mg2+ have similar radii that are about 25% smaller than Ca2+. Remaining uncertainties in the metal acetate binding free energies are linked to fundamental ambiguities associated with identifying the range of structures pertaining to non-covalently bound species.

Funding

DBA, DMdO, and SKZ were supported in part by the US National Science Foundation (CHE- 1763581). PJ thanks the Czech Science Foundation for support via an EXPRO grant no. 19- 26854X. EDD acknowledges support from the EMBO and Marie Curie Actions (fellowship ALTF 952-2015), and EDD and JH were supported in part by the "Initiative d’Excellence" program from the French State (Grants "DYNAMO", ANR-11-LABX-0011, and "CACSICE", ANR-11-EQPX- 0008). HMS and VP acknowledge support from the Czech Science Foundation (19-19561S). This work was performed with computer time allocated by the national supercomputing center IT4innovations in Ostrava (project OPEN-8-35), the European Regional Development Fund OP RDE (project ChemBioDrug no. CZ.02.1.01/0.0/0.0/16_019/0000729) computational resources, and the MetaCentrum data storage facilities.

History

Email Address of Submitting Author

duboue-dijon@ibpc.fr

Institution

CNRS, Laboratoire de Biochimie Théorique

Country

France

ORCID For Submitting Author

0000-0003-0871-5177

Declaration of Conflict of Interest

none

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