Hofmeister anionic effects on hydration electric fields around water and peptide

Heejae Kim, Hochan Lee, Gayeon Lee, Haeyoung Kim, Minhaeng Cho

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24 Citations (Scopus)


Specific ion effects on water dynamics and local solvation structure around a peptide are important in understanding the Hofmeister series of ions and their effects on protein stability in aqueous solution. Water dynamics is essentially governed by local hydrogen-bonding interactions with surrounding water molecules producing hydration electric field on each water molecule. Here, we show that the hydration electric field on the OD bond of HOD molecule in water can be directly estimated by measuring its OD stretch infrared (IR) radiation frequency shift upon increasing ion concentration. For a variety of electrolyte solutions containing Hofmeister anions, we measured the OD stretch IR bands and estimated the hydration electric field on the OD bond to be about a hundred MVcm with standard deviation of tens of MVcm. As anion concentration increases from 1 to 6 M, the hydration electric field on the OD bond decreases by about 10, indicating that the local H-bond network is partially broken by dissolved ions. However, the measured hydration electric fields on the OD bond and its fluctuation amplitudes for varying anions are rather independent on whether the anion is a kosmotrope or a chaotrope. To further examine the Hofmeister effects on H-bond solvation structure around a peptide bond, we examined the amide I′ and II′ mode frequencies of N-methylacetamide in various electrolyte D 2O solutions. It is found that the two amide vibrational frequencies are not affected by ions, indicating that the H-bond solvation structure in the vicinity of a peptide remains the same irrespective of the concentration and character of ions. The present experimental results suggest that the Hofmeister anionic effects are not caused by direct electrostatic interactions of ions with peptide bond or water molecules in its first solvation shell. Furthermore, even though the H-bond network of water is affected by ions, thus induced change of local hydration electric field on the OD bond of HOD is not in good correlation with the well-known Hofmeister series. We anticipate that the present experimental results provide an important clue about the Hofmeister effect on protein structure and present a discussion on possible alternative mechanisms.

Original languageEnglish
Article number124501
JournalJournal of Chemical Physics
Issue number12
Publication statusPublished - 2012 Mar 28

Bibliographical note

Funding Information:
This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (MEST) (Grant Nos. 2009-0078897, 20110020033) to M.C. Also, we thank the financial supports from the Korea Basic Science Institute (T31401) grant to M.C. and NRF (2010-0020209) grant to H.L.

Copyright 2012 Elsevier B.V., All rights reserved.

ASJC Scopus subject areas

  • General Physics and Astronomy
  • Physical and Theoretical Chemistry


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