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Guanidinium Group Remains Protonated in a Strongly Basic Arginine Solution
Author(s) -
Xu Bo,
Jacobs Michael I.,
Kostko Oleg,
Ahmed Musahid
Publication year - 2017
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201700197
Subject(s) - protonation , arginine , chemistry , group (periodic table) , guanidine , guanidinium chloride , computational chemistry , stereochemistry , crystallography , combinatorial chemistry , organic chemistry , biochemistry , amino acid , ion , enzyme
Knowledge of the acid dissociation constant of an amino acid has very important ramifications in the biochemistry of proteins and lipid bilayers in aqueous environments because charge and proton transfer depend on its value. The acid dissociation constant for the guanidinium group in arginine has historically been posited as 12.5, but there is substantial variation in published values over the years. Recent experiments suggest that the dissociation constant for arginine is much higher than 12.5, which explains why the arginine guanidinium group retains its positive charge under all physiological conditions. In this work, we use X‐ray photoelectron spectroscopy to study unsupported, aqueous arginine nanoparticles. By varying the pH of the constituent solution, we provide evidence that the guanidinium group is protonated even in a very basic solution. By analyzing the energy shifts in the C and N X‐ray photoelectron spectra, we establish a molecular level picture of how charge and proton transport in aqueous solutions of arginine occur.