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Murke S, Chen W, Pezzotti S, Havenith M. Tuning Acid-Base Chemistry at an Electrified Gold/Water Interface. J Am Chem Soc 2024; 146:12423-12430. [PMID: 38599583 PMCID: PMC11082902 DOI: 10.1021/jacs.3c13633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2023] [Revised: 03/11/2024] [Accepted: 03/13/2024] [Indexed: 04/12/2024]
Abstract
Acid-base reactions are ubiquitous in solution chemistry, as well as in electrochemistry. However, macroscopic concepts derived in solutions, such as pKa and pH, differ significantly at electrified metal-aqueous interfaces due to specific solvation and applied voltage. Here, we measure the pKa values of an amino acid, glycine, at a gold/water interface under a varying applied voltage by means of spectroscopic titration. With the help of simulations, we propose a general model to understand potential-dependent shifts in pKa values in terms of local hydrophobicity and electric fields. These parameters can be tuned by adjusting the metal surface and applied voltage, respectively, offering promising, but still unexplored, paths to regulate reactivity. Our results change the focus with respect to common interpretations based on, for example, apparent local pH effects and open interesting perspectives for electrochemical reaction steering.
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Affiliation(s)
| | | | | | - Martina Havenith
- Department of Physical Chemistry
II, Ruhr University Bochum, D-44801 Bochum, Germany
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2
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Litman Y, Chiang KY, Seki T, Nagata Y, Bonn M. Surface stratification determines the interfacial water structure of simple electrolyte solutions. Nat Chem 2024; 16:644-650. [PMID: 38225269 PMCID: PMC10997511 DOI: 10.1038/s41557-023-01416-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Accepted: 12/07/2023] [Indexed: 01/17/2024]
Abstract
The distribution of ions at the air/water interface plays a decisive role in many natural processes. Several studies have reported that larger ions tend to be surface-active, implying ions are located on top of the water surface, thereby inducing electric fields that determine the interfacial water structure. Here we challenge this view by combining surface-specific heterodyne-detected vibrational sum-frequency generation with neural network-assisted ab initio molecular dynamics simulations. Our results show that ions in typical electrolyte solutions are, in fact, located in a subsurface region, leading to a stratification of such interfaces into two distinctive water layers. The outermost surface is ion-depleted, and the subsurface layer is ion-enriched. This surface stratification is a key element in explaining the ion-induced water reorganization at the outermost air/water interface.
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Affiliation(s)
- Yair Litman
- Max Planck Institute for Polymer Research, Mainz, Germany.
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK.
| | | | - Takakazu Seki
- Max Planck Institute for Polymer Research, Mainz, Germany
| | - Yuki Nagata
- Max Planck Institute for Polymer Research, Mainz, Germany
| | - Mischa Bonn
- Max Planck Institute for Polymer Research, Mainz, Germany.
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3
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Musegades LJ, Curtin OP, Cyran JD. Determining the Surface p Ka of Perfluorooctanoic Acid. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2024; 128:1946-1951. [PMID: 38352857 PMCID: PMC10860129 DOI: 10.1021/acs.jpcc.3c07235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Revised: 01/12/2024] [Accepted: 01/15/2024] [Indexed: 02/16/2024]
Abstract
Perfluorooctanoic acid (PFOA) is an environmentally prevalent and persistent organic pollutant with toxic and bioaccumulative properties. Despite the known importance of perfluorinated pollutants in the global environment, molecular-level details of the physicochemical behavior of PFOA on aqueous interfaces remain poorly understood. Here, we utilized two surface-specific techniques, vibrational sum frequency generation spectroscopy (SFG) and surface tensiometry, to investigate the pH-induced structural changes of PFOA and octanoic acid (OA) and determined the apparent pKa at the air-water surface. The SFG spectra and surface activity model were investigated over a wide range of pHs. With the surface tension measurements, the surface pKa values for OA and PFOA are determined to be 3.8 ± 0.1 and 2.2 ± 0.2, respectively. These results could provide insights into improved remediation of PFOAs and may impact climate modeling of perfluorinated alkyl chain molecules.
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Affiliation(s)
| | - Owen P. Curtin
- Boise
State University, Boise, Idaho 83725, United States of America
| | - Jenée D. Cyran
- Boise
State University, Boise, Idaho 83725, United States of America
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4
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Mandalaparthy V, Tripathy M, van der Vegt NFA. Anions and Cations Affect Amino Acid Dissociation Equilibria via Distinct Mechanisms. J Phys Chem Lett 2023; 14:9250-9256. [PMID: 37812174 DOI: 10.1021/acs.jpclett.3c02062] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/10/2023]
Abstract
Salts reduce the pKa of weak acids by a mechanism sensitive to ion identity and concentration via charge screening of the deprotonated state. In this study, we utilize constant pH molecular dynamics simulations to understand the molecular mechanism behind the salt-dependent dissociation of aspartic acid (Asp). We calculate the pKa of Asp in the presence of a monovalent salt and investigate Hofmeister ion effects by systematically varying the ionic radii. We observe that increasing the anion size leads to a monotonic decrease in Asp pKa. Conversely, the cation size affects the pKa nonmonotonically, interpretable in the context of the law of matching water affinity. The net effect of salt on Asp acidity is governed by an interplay of solvation and competing ion interactions. The proposed mechanism is rather general and can be applicable to several problems in Hofmeister ion chemistry, such as pH effects on protein stability and soft matter interfaces.
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Affiliation(s)
- Varun Mandalaparthy
- Department of Chemistry, Technical University of Darmstadt, 64287 Darmstadt, Germany
| | - Madhusmita Tripathy
- Department of Chemistry, Technical University of Darmstadt, 64287 Darmstadt, Germany
| | - Nico F A van der Vegt
- Department of Chemistry, Technical University of Darmstadt, 64287 Darmstadt, Germany
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5
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Pollet R, Chin W. In silico Investigation of the Thermochemistry and Photoactivity of Pyruvic Acid in an Aqueous Solution of NaCl. Chemistry 2023; 29:e202302225. [PMID: 37539648 DOI: 10.1002/chem.202302225] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Revised: 08/03/2023] [Accepted: 08/04/2023] [Indexed: 08/05/2023]
Abstract
The photochemistry of oxocarboxylic acids contributes significantly to the complex chemistry occurring in the atmosphere. In this regard, pyruvic acid undergoes photoreactions that lead to many diverse products. The presence of sodium cation near pyruvic acid in an aqueous solution, or its conjugate base in non-acidic conditions, influences the hydration equilibrium and the photosensitivity to UV-visible light of the oxocarboxylic acid. We performed an ab initio metadynamics simulation which serves two purposes: first, it unveils the mechanisms of the reversible hydration reaction between the keto and the diol forms, with a free-energy difference of only 2 kJ/mol at 300 K, which shows the influence of sodium on the keto/diol ratio; second, it provides solvent-shared ion pairing (SSIP) and contact ion pairing (CIP) structures, including Na+ coordinated to carbonyl, for the calculations of the electronic transition energies to an antibonding π* orbital, which sheds light on the photoactivity of these two forms in the actinic region.
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Affiliation(s)
- Rodolphe Pollet
- Université Paris-Saclay, CEA, CNRS, NIMBE, 91191, Gif-sur-Yvette, France
| | - Wutharath Chin
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, 91405, Orsay, France
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6
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Sit I, Fashina BT, Baldo AP, Leung K, Grassian VH, Ilgen AG. Formic and acetic acid p Ka values increase under nanoconfinement. RSC Adv 2023; 13:23147-23157. [PMID: 37533784 PMCID: PMC10390803 DOI: 10.1039/d2ra07944e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2022] [Accepted: 06/22/2023] [Indexed: 08/04/2023] Open
Abstract
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 pKa 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 pKa 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 pKa 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 pKa 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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Affiliation(s)
- Izaac Sit
- Department of Nanoengineering, University of California San Diego La Jolla CA 92093 USA
| | - Bidemi T Fashina
- Geochemistry Department, Sandia National Laboratories Albuquerque NM 87123 USA
| | - Anthony P Baldo
- Geochemistry Department, Sandia National Laboratories Albuquerque NM 87123 USA
| | - Kevin Leung
- Geochemistry Department, Sandia National Laboratories Albuquerque NM 87123 USA
| | - Vicki H Grassian
- Department of Chemistry & Biochemistry, University of California San Diego La Jolla CA 92093 USA
| | - Anastasia G Ilgen
- Geochemistry Department, Sandia National Laboratories Albuquerque NM 87123 USA
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7
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Deal A, Smith AE, Oyala KM, Campolo GH, Rugeley BE, Mose TA, Talley DL, Cooley CB, Rapf RJ. Infrared Reflection-Absorption Spectroscopy of α-Keto Acids at the Air-Water Interface: Effects of Chain Length and Headgroup on Environmentally Relevant Surfactant Films. J Phys Chem A 2023; 127:4137-4151. [PMID: 37103984 PMCID: PMC10184673 DOI: 10.1021/acs.jpca.3c01266] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2023] [Revised: 04/12/2023] [Indexed: 04/28/2023]
Abstract
A variety of organic surfactants are found at air-water interfaces in natural environments, including on the surfaces of aqueous aerosols. The structure and morphology of these organic films can have profound impacts on material transfer between the gas and condensed phases, the optical properties of atmospheric aerosol, and chemical processing at air-water interfaces. Combined, these effects can have significant impacts on climate via radiative forcing, but our understanding of organic films at air-water interfaces is incomplete. Here, we examine the impact of the polar headgroup and alkyl tail length on the structure and morphology of organic monolayers at the air-water interfaces. First, we focus on the substituted carboxylic acids, α-keto acids, using Langmuir isotherms and infrared reflection absorption spectroscopy (IR-RAS) to elucidate key structures and phase behaviors of α-keto acids with a range of surface activities. We show that the structure of α-keto acids, both soluble and insoluble, at water surfaces is a compromise between van der Waals interactions of the hydrocarbon tail and hydrogen bonding interactions involving the polar headgroup. Then, we use this new data set regarding α-keto acid films at water surfaces to examine the role of the polar headgroup on organic films using a similar substituted carboxylic acid (α-hydroxystearic acid), an unsubstituted carboxylic acid (stearic acid), and an alcohol (stearyl alcohol). We show that the polar headgroup and its hydrogen bonding interactions can significantly affect the orientation of amphiphiles at air-water interfaces. Here, we provide side-by-side comparisons of Langmuir isotherms and IR-RA spectra for a set of environmentally relevant organic amphiphiles with a range of alkyl tail lengths and polar headgroup structures.
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Affiliation(s)
- Alexandra
M. Deal
- Department
of Chemistry and Cooperative Institute for Research in Environmental
Sciences, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Abigail E. Smith
- Department
of Chemistry, Trinity University, San Antonio, Texas 78212, United States
| | - Krista M. Oyala
- Department
of Chemistry, Trinity University, San Antonio, Texas 78212, United States
| | - Giovanna H. Campolo
- Department
of Chemistry, Trinity University, San Antonio, Texas 78212, United States
| | - Burgess E. Rugeley
- Department
of Chemistry, Trinity University, San Antonio, Texas 78212, United States
| | - Tim A. Mose
- Department
of Chemistry, Trinity University, San Antonio, Texas 78212, United States
| | - Denver L. Talley
- Department
of Chemistry, Trinity University, San Antonio, Texas 78212, United States
| | - Christina B. Cooley
- Department
of Chemistry, Trinity University, San Antonio, Texas 78212, United States
| | - Rebecca J. Rapf
- Department
of Chemistry, Trinity University, San Antonio, Texas 78212, United States
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8
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Hashemi A, Peljo P, Laasonen K. Understanding Electron Transfer Reactions Using Constrained Density Functional Theory: Complications Due to Surface Interactions. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2023; 127:3398-3407. [PMID: 36865990 PMCID: PMC9969872 DOI: 10.1021/acs.jpcc.2c06537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Revised: 01/25/2023] [Indexed: 06/18/2023]
Abstract
The kinetic rates of electrochemical reactions depend on electrodes and molecules in question. In a flow battery, where the electrolyte molecules are charged and discharged on the electrodes, the efficiency of the electron transfer is of crucial importance for the performance of the device. The purpose of this work is to present a systematic atomic-level computational protocol for studying electron transfer between electrolyte and electrode. The computations are done by using constrained density functional theory (CDFT) to ensure that the electron is either on the electrode or in the electrolyte. The ab initio molecular dynamics (AIMD) is used to simulate the movement of the atoms. We use the Marcus theory to predict electron transfer rates and the combined CDFT-AIMD approach to compute the parameters for the Marcus theory where it is needed. We model the electrode with a single layer of graphene and methylviologen, 4,4'-dimethyldiquat, desalted basic red 5, 2-hydroxy-1,4-naphthaquinone, and 1,1-di(2-ethanol)-4,4-bipyridinium were selected for the electrolyte molecules. All of these molecules undergo consecutive electrochemical reactions with one electron being transferred at each stage. Because of significant electrode-molecule interactions, it is not possible to evaluate outer-sphere ET. This theoretical study contributes toward the development of a realistic-level prediction of electron transfer kinetics suitable for energy storage applications.
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Affiliation(s)
- Arsalan Hashemi
- Research
Group of Computational Chemistry, Department of Chemistry and Materials
Science, Aalto University, FI-00076 Aalto, Finland
| | - Pekka Peljo
- Research
Group of Battery Materials and Technologies, Department of Mechanical
and Materials Engineering, Faculty of Technology, University of Turku, 20014 Turun Yliopisto, Finland
| | - Kari Laasonen
- Research
Group of Computational Chemistry, Department of Chemistry and Materials
Science, Aalto University, FI-00076 Aalto, Finland
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9
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Deal AM, Vaida V. Infrared Reflection–Absorption Spectroscopy of α-Hydroxyacids at the Water–Air Interface. J Phys Chem A 2022; 126:8280-8294. [DOI: 10.1021/acs.jpca.2c04462] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Alexandra M. Deal
- Department of Chemistry and Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Veronica Vaida
- Department of Chemistry and Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado 80309, United States
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