Zwitterions Layer at but Do Not Screen Electrified Interfaces

Muhammad Ghifari Ridwan, Buddha Ratna Shrestha, Nischal Maharjan, Himanshu Mishra*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

The role of ionic electrostatics in colloidal processes is well-understood in natural and applied contexts; however, the electrostatic contribution of zwitterions, known to be present in copious amounts in extremophiles, has not been extensively explored. In response, we studied the effects of glycine as a surrogate zwitterion, ion, and osmolyte on the electrostatic forces between negatively charged mica-mica and silica-silica interfaces. Our results reveal that while zwitterions layer at electrified interfaces and contribute to solutions' osmolality, they do not affect at all the surface potentials, the electrostatic surface forces (magnitude and range), and solutions' ionic conductivity across 0.3-30 mM glycine concentration. We infer that the zwitterionic structure imposes an inseparability among positive and negative charges and that this inseparability prevents the buildup of a counter-charge at interfaces. These elemental experimental results pinpoint how zwitterions enable extremophiles to cope with the osmotic stress without affecting finely tuned electrostatic force balance.

Original languageEnglish (US)
Pages (from-to)1852-1860
Number of pages9
JournalJournal of Physical Chemistry B
Volume126
Issue number8
DOIs
StatePublished - Mar 3 2022

Bibliographical note

Funding Information:
H.M. thanks Changzi Wang, a student from his course on Aquatic Chemistry (EnSE 202) at KAUST, for bringing this problem to his attention. The authors are indebted to Masha Belyi (Research Scientist, Amazon’s Team Alexa) for creating a Python script for analyzing hundreds of AFM force–distance curves generated in this work to pinpoint the trends in Debye lengths and surface potentials. M.G.R. thanks Mohammad Abbas (KAUST) for discussions on cell physiology; B.R.S. thanks Dr. Bruno Torres (KAUST) for providing colloidal probes for AFM experiments. The co-authors thank Ana Rouseva (KAUST) and Paulus Buijs (KAUST) for assisting with osmotic pressure measurements presented in C; Dr. Farizal Hakiki (KAUST) and Prof. Carlos Santamarina (KAUST) for characterizing dielectric responses of solutions presented in D; and Heno Hwang, KAUST Illustrator, for preparing and and TOC. H.M. acknowledges KAUST for funding (grant no. BAS/1/1070-01-01).

Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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