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Formic and acetic acid pK(a) values increase under nanoconfinement

Organic acids are prevalent in the environment and their acidity and the corresponding dissociation constants can change under varying environmental conditions. The impact of nanoconfinement (when acids are confined within nanometer-scale domains) on physicochemical properties of chemical species is...

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Autores principales: Sit, Izaac, Fashina, Bidemi T., Baldo, Anthony P., Leung, Kevin, Grassian, Vicki H., Ilgen, Anastasia G.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The Royal Society of Chemistry 2023
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10390803/
https://www.ncbi.nlm.nih.gov/pubmed/37533784
http://dx.doi.org/10.1039/d2ra07944e
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author Sit, Izaac
Fashina, Bidemi T.
Baldo, Anthony P.
Leung, Kevin
Grassian, Vicki H.
Ilgen, Anastasia G.
author_facet Sit, Izaac
Fashina, Bidemi T.
Baldo, Anthony P.
Leung, Kevin
Grassian, Vicki H.
Ilgen, Anastasia G.
author_sort Sit, Izaac
collection PubMed
description Organic acids are prevalent in the environment and their acidity and the corresponding dissociation constants can change under varying environmental conditions. The impact of nanoconfinement (when acids are confined within nanometer-scale domains) on physicochemical properties of chemical species is poorly understood and is an emerging field of study. By combining infrared and Raman spectroscopies with molecular dynamics (MD) simulations, we quantified the effect of nanoconfinement in silica nanopores on one of the fundamental chemical reactions—the dissociation of organic acids. The pK(a) of formic and acetic acids confined within cylindrical silica nanopores with 4 nm diameters were measured. MD models were constructed to calculate the shifts in the pK(a) values of acetic acid nanoconfined within 1, 2, 3, and 4 nm silica slit pores. Both experiments and MD models indicate a decrease in the apparent acid dissociation constants (i.e., increase in the pK(a) values) when organic acids are nanoconfined. Therefore, nanoconfinement stabilizes the protonated species. We attribute this observation to (1) a decrease in the average dielectric response of nanoconfined aqueous solutions where charge screening may be decreased; or (2) an increase in proton concentration inside nanopores, which would shift the equilibrium towards the protonated form. Overall, the results of this study provide the first quantification of the pK(a) values for nanoconfined formic and acetic acids and pave the way for a unifying theory predicting the impact of nanoconfinement on acid–base chemistry.
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spelling pubmed-103908032023-08-02 Formic and acetic acid pK(a) values increase under nanoconfinement Sit, Izaac Fashina, Bidemi T. Baldo, Anthony P. Leung, Kevin Grassian, Vicki H. Ilgen, Anastasia G. RSC Adv Chemistry Organic acids are prevalent in the environment and their acidity and the corresponding dissociation constants can change under varying environmental conditions. The impact of nanoconfinement (when acids are confined within nanometer-scale domains) on physicochemical properties of chemical species is poorly understood and is an emerging field of study. By combining infrared and Raman spectroscopies with molecular dynamics (MD) simulations, we quantified the effect of nanoconfinement in silica nanopores on one of the fundamental chemical reactions—the dissociation of organic acids. The pK(a) of formic and acetic acids confined within cylindrical silica nanopores with 4 nm diameters were measured. MD models were constructed to calculate the shifts in the pK(a) values of acetic acid nanoconfined within 1, 2, 3, and 4 nm silica slit pores. Both experiments and MD models indicate a decrease in the apparent acid dissociation constants (i.e., increase in the pK(a) values) when organic acids are nanoconfined. Therefore, nanoconfinement stabilizes the protonated species. We attribute this observation to (1) a decrease in the average dielectric response of nanoconfined aqueous solutions where charge screening may be decreased; or (2) an increase in proton concentration inside nanopores, which would shift the equilibrium towards the protonated form. Overall, the results of this study provide the first quantification of the pK(a) values for nanoconfined formic and acetic acids and pave the way for a unifying theory predicting the impact of nanoconfinement on acid–base chemistry. The Royal Society of Chemistry 2023-08-01 /pmc/articles/PMC10390803/ /pubmed/37533784 http://dx.doi.org/10.1039/d2ra07944e Text en This journal is © The Royal Society of Chemistry https://creativecommons.org/licenses/by-nc/3.0/
spellingShingle Chemistry
Sit, Izaac
Fashina, Bidemi T.
Baldo, Anthony P.
Leung, Kevin
Grassian, Vicki H.
Ilgen, Anastasia G.
Formic and acetic acid pK(a) values increase under nanoconfinement
title Formic and acetic acid pK(a) values increase under nanoconfinement
title_full Formic and acetic acid pK(a) values increase under nanoconfinement
title_fullStr Formic and acetic acid pK(a) values increase under nanoconfinement
title_full_unstemmed Formic and acetic acid pK(a) values increase under nanoconfinement
title_short Formic and acetic acid pK(a) values increase under nanoconfinement
title_sort formic and acetic acid pk(a) values increase under nanoconfinement
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10390803/
https://www.ncbi.nlm.nih.gov/pubmed/37533784
http://dx.doi.org/10.1039/d2ra07944e
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