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Singh A, Zamader A, Khakpour R, Laasonen K, Busch M, Robert M. Molecular Electrochemical Catalysis of CO-to-Formaldehyde Conversion with a Cobalt Complex. J Am Chem Soc 2024; 146:22129-22133. [PMID: 39083037 DOI: 10.1021/jacs.4c06878] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/15/2024]
Abstract
Formox, a highly energy-intensive process, currently serves as the primary source of formaldehyde (HCHO), for which there is a crucial and steadily growing chemical demand. The alternative electrochemical production of HCHO from C1 carbon sources such as CO2 and CO is still in its early stages, with even the few identified cases lacking mechanistic rationalization. In this study, we demonstrate that cobalt phthalocyanine (CoPc) immobilized on multiwalled carbon nanotubes (MW-CNTs) constitutes an excellent electrocatalytic system for producing HCHO with productivity through the direct reduction of CO, the two-electron reduction product of CO2. By carefully adjusting both the pH and the applied potential, we identified conditions that enable the production of HCHO with a partial current density of 0.64 mA cm-2 (17.5% Faradaic efficiency, FE) and a total FE of 61.2% for the liquid products (formaldehyde and methanol). A reduction mechanism is proposed.
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Affiliation(s)
- Ajeet Singh
- Université Paris Cité, CNRS, Laboratoire d'Electrochimie Moléculaire (LEM), F-75013 Paris, France
| | - Afridi Zamader
- Université Paris Cité, CNRS, Laboratoire d'Electrochimie Moléculaire (LEM), F-75013 Paris, France
| | - Reza Khakpour
- Department of Chemistry and Material Science, School of Chemical Engineering, Aalto University, 02150 Espoo, Finland
| | - Kari Laasonen
- Department of Chemistry and Material Science, School of Chemical Engineering, Aalto University, 02150 Espoo, Finland
| | - Michael Busch
- Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, 971 87 Luleå, Sweden
- Wallenberg Initiative Materials Science for Sustainability (WISE), Luleå University of Technology, 971 87 Luleå, Sweden
| | - Marc Robert
- Université Paris Cité, CNRS, Laboratoire d'Electrochimie Moléculaire (LEM), F-75013 Paris, France
- Institut Universitaire de France (IUF), F-75005 Paris, France
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2
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Nechaev AA, Gonzalez G, Verma P, Peshkov VA, Bannykh A, Hashemi A, Hannonen J, Hamza A, Pápai I, Laasonen K, Peljo P, Pihko PM. Exploration of Vitamin B 6-Based Redox-Active Pyridinium Salts Towards the Application in Aqueous Organic Flow Batteries. Chemistry 2024; 30:e202400828. [PMID: 38640462 DOI: 10.1002/chem.202400828] [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: 02/28/2024] [Revised: 04/15/2024] [Accepted: 04/16/2024] [Indexed: 04/21/2024]
Abstract
Pyridoxal hydrochloride, a vitamin B6 vitamer, was synthetically converted to a series of diverse redox-active benzoyl pyridinium salts. Cyclic voltammetry studies demonstrated redox reversibility under basic conditions, and two of the most promising salts were subjected to laboratory-scale flow battery tests involving galvanostatic cycling at 10 mM in 0.1 M NaOH. In these tests, the battery was charged completely, corresponding to the transfer of two electrons to the electrolyte, but no discharge was observed. Both CV analysis and electrochemical simulations confirmed that the redox wave observed in the experimental voltammograms corresponds to a two-electron process. To explain the irreversibility in the battery tests, we conducted bulk electrolysis with the benzoyl pyridinium salts, affording the corresponding benzylic secondary alcohols. Computational studies suggest that the reduction proceeds in three consecutive steps: first electron transfer (ET), then proton-coupled electron transfer (PCET) and finally proton transfer (PT) to give the secondary alcohol. 1H NMR deuterium exchange studies indicated that the last PT step is not reversible in 0.1 M NaOH, rendering the entire redox process irreversible. The apparent reversibility observed in CV at the basic media likely arises from the slow rate of the PT step at the timescale of the measurement.
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Affiliation(s)
- Anton A Nechaev
- Department of Chemistry, University of Jyväskylä, P.O. Box 35, Jyväskylä, 40014, Finland
| | - Gabriel Gonzalez
- Research Group of Battery Materials and Technologies, Department of Mechanical and Materials Engineering, Faculty of Technology, University of Turku, Turku, 20014, Finland
| | - Prachi Verma
- Department of Chemistry, University of Jyväskylä, P.O. Box 35, Jyväskylä, 40014, Finland
| | - Vsevolod A Peshkov
- Department of Chemistry, University of Jyväskylä, P.O. Box 35, Jyväskylä, 40014, Finland
| | - Anton Bannykh
- Department of Chemistry, University of Jyväskylä, P.O. Box 35, Jyväskylä, 40014, Finland
| | - Arsalan Hashemi
- Department of Chemistry and Material Science, School of Chemical Engineering, Aalto University, Espoo, 02150, Finland
| | - Jenna Hannonen
- Research Group of Battery Materials and Technologies, Department of Mechanical and Materials Engineering, Faculty of Technology, University of Turku, Turku, 20014, Finland
| | - Andrea Hamza
- Institute of Organic Chemistry, HUN-REN Research Centre for Natural Sciences, Magyar tudósok körutja 2, Budapest, 1117, Hungary
| | - Imre Pápai
- Institute of Organic Chemistry, HUN-REN Research Centre for Natural Sciences, Magyar tudósok körutja 2, Budapest, 1117, Hungary
| | - Kari Laasonen
- Department of Chemistry and Material Science, School of Chemical Engineering, Aalto University, Espoo, 02150, Finland
| | - Pekka Peljo
- Research Group of Battery Materials and Technologies, Department of Mechanical and Materials Engineering, Faculty of Technology, University of Turku, Turku, 20014, Finland
| | - Petri M Pihko
- Department of Chemistry, University of Jyväskylä, P.O. Box 35, Jyväskylä, 40014, Finland
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Chaves OA, Loureiro RJS, Serpa C, Cruz PF, Ferreira ABB, Netto-Ferreira JC. Increasing the polarity of β-lapachone does not affect its binding capacity with bovine plasma protein. Int J Biol Macromol 2024; 263:130279. [PMID: 38401585 DOI: 10.1016/j.ijbiomac.2024.130279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2023] [Revised: 02/15/2024] [Accepted: 02/16/2024] [Indexed: 02/26/2024]
Abstract
Despite ortho-quinones showing several biological and pharmacological activities, there is still a lack of biophysical characterization of their interaction with albumin - the main carrier of different endogenous and exogenous compounds in the bloodstream. Thus, the interactive profile between bovine serum albumin (BSA) with β-lapachone (1) and its corresponding synthetic 3-sulfonic acid (2, under physiological pH in the sulphonate form) was performed. There is one main binding site of albumin for both β-lapachones (n ≈ 1) and a static fluorescence quenching mechanism was proposed. The Stern-Volmer constant (KSV) values are 104 M-1, indicating a moderate binding affinity. The enthalpy (-3.41 ± 0.45 and - 8.47 ± 0.37 kJ mol-1, for BSA:1 and BSA:2, respectively) and the corresponding entropy (0.0707 ± 0.0015 and 0.0542 ± 0.0012 kJ mol-1 K-1) values indicate an enthalpically and entropically binding driven. Hydrophobic interactions and hydrogen bonding are the main binding forces. The differences in the polarity of 1 and 2 did not change significantly the affinity to albumin. In addition, the 1,2-naphthoquinones showed a similar binding trend compared with 1,4-naphthoquinones.
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Affiliation(s)
- Otávio A Chaves
- CQC-IMS, Department of Chemistry, University of Coimbra, Rua Larga, 3004-535 Coimbra, Portugal; Laboratory of Immunopharmacology, Centro de Pesquisa, Inovação e Vigilância em COVID-19 e Emergências Sanitárias (CPIV), Oswaldo Cruz Institute (IOC), Oswaldo Cruz Foundation (Fiocruz), 21040-361 Rio de Janeiro, RJ, Brazil.
| | - Rui J S Loureiro
- CQC-IMS, Department of Chemistry, University of Coimbra, Rua Larga, 3004-535 Coimbra, Portugal
| | - Carlos Serpa
- CQC-IMS, Department of Chemistry, University of Coimbra, Rua Larga, 3004-535 Coimbra, Portugal
| | - Pedro F Cruz
- CQC-IMS, Department of Chemistry, University of Coimbra, Rua Larga, 3004-535 Coimbra, Portugal
| | - Aurélio B B Ferreira
- Institute of Chemistry, Department of Organic Chemistry, Federal Rural University of Rio de Janeiro, Rodovia BR-465, Km 7, 23.890-000 Seropédica, RJ, Brazil
| | - José Carlos Netto-Ferreira
- Institute of Chemistry, Department of Organic Chemistry, Federal Rural University of Rio de Janeiro, Rodovia BR-465, Km 7, 23.890-000 Seropédica, RJ, Brazil.
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Pereira RW, Ramabhadran RO. Accurate Computation of Aqueous p Kas of Biologically Relevant Organic Acids: Overcoming the Challenges Posed by Multiple Conformers, Tautomeric Equilibria, and Disparate Functional Groups with the Fully Black-Box p K-Yay Method. J Phys Chem A 2023; 127:9121-9138. [PMID: 37862610 DOI: 10.1021/acs.jpca.3c02977] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2023]
Abstract
The use of static electronic structure calculations to compute solution-phase pKas offers a great advantage in that a macroscopic bulk property could be computed via microscopic computations involving very few molecules. There are various sources of errors in the quantum chemical calculations though. Overcoming these errors to accurately compute pKas of a plethora of acids is an active area of research in physical chemistry pursued by both computational as well as experimental chemists. We recently developed the pK-Yay method in our attempt to accurately compute aqueous pKas of strong and weak acids. The method is fully black-box, computationally inexpensive, and is very easy for even a nonexpert to use. However, the method was thus far tested on very few molecules (only 16 in all). Herein, in order to assess the future applicability of pK-Yay, we study the effect of multiple conformers, the presence of tautomers under equilibrium, and the impact of a wide variety of functional groups (derivatives of acetic acid with substituents at various positions, dicarboxylic acids, aromatic carboxylic acids, amines and amides, phenols and thiols, and fluorine bearing organic acids). Starting with more than 1000 conformers and tautomers, this study establishes that overall errors of ∼ 1.0 pKa units are routinely obtained for a majority of the molecules. Larger errors are noted in cases where multiple charges, intramolecular hydrogen bonding, and several ionizable functional groups are simultaneously present. An important conclusion to emerge from this work is that, the computed pKas are insensitive (difference <0.5) to whether we consider multiple conformers/tautomers or only choose the most stable conformer/tautomer. Further, pK-Yay captures the stereoelectronic effects arising due to differing axial vs equatorial pattern, and is useful to predict the dominant acid-base equilibrium in a system featuring several equilibria. Overall, pK-Yay may be employed in several chemical applications featuring organic molecules and biomonomers.
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Affiliation(s)
- Roshni W Pereira
- Department of Chemistry, Indian Institute of Science Education and Research (IISER) Tirupati, Andhra Pradesh 517507, India
- Centre for Atomic Molecular Optical Sciences and Technology (CAMOST), Tirupati, Andhra Pradesh 517507, India
| | - Raghunath O Ramabhadran
- Department of Chemistry, Indian Institute of Science Education and Research (IISER) Tirupati, Andhra Pradesh 517507, India
- Centre for Atomic Molecular Optical Sciences and Technology (CAMOST), Tirupati, Andhra Pradesh 517507, India
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5
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Wallace M, Abiama N, Chipembere M. Measurement of the p Ka Values of Organic Molecules in Aqueous-Organic Solvent Mixtures by 1H NMR without External Calibrants. Anal Chem 2023; 95:15628-15635. [PMID: 37830153 PMCID: PMC10603606 DOI: 10.1021/acs.analchem.3c02771] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2023] [Accepted: 09/18/2023] [Indexed: 10/14/2023]
Abstract
Aqueous-organic solvent mixtures are commonly used for reactions or analyses, where the components of a system are insoluble in pure water. The acid dissociation constant is an important property to measure in these media as it determines the charge state, solubility, and reactivity of a molecule. While NMR spectroscopy is an established tool for the measurement of pKa in water, its use in aqueous-organic solvents is greatly hindered by the requirement for external calibrants on which a working pH scale is set. Such calibrants include buffer solutions, "anchor" molecules with known pKa values, and pH electrodes that have undergone lengthy calibration procedures in the solvent mixture of interest. However, such calibrations are often inconvenient to perform, while literature pKa data covering the required range may not be available at the solvent composition or the temperature of interest. Here, we present a method to determine pKa in aqueous-organic solvents directly by NMR. We first determine pKa of an organic acid such as 2,6-dihydroxybenzoic acid (2,6-DHB) by measuring its 1H chemical shift as a function of concentration along a concentration gradient using chemical shift imaging (CSI). Using 2,6-DHB as a reference, we then determine pKa of less acidic molecules in single CSI experiments via the variation of their 1H chemical shifts along pH gradients. As proof of concept, we determine the pKa values of organic acids and bases up to pKa 10 in 50% (v/v) 1-propanol/water, 50% (v/v) dimethyl sulfoxide/water, and 30% (v/v) acetonitrile/water and obtain good agreement with the literature values.
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Affiliation(s)
- Matthew Wallace
- School of Pharmacy, University
of East Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
| | - Nduchi Abiama
- School of Pharmacy, University
of East Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
| | - Miranda Chipembere
- School of Pharmacy, University
of East Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
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6
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Hashemi A, Khakpour R, Mahdian A, Busch M, Peljo P, Laasonen K. Density functional theory and machine learning for electrochemical square-scheme prediction: an application to quinone-type molecules relevant to redox flow batteries. DIGITAL DISCOVERY 2023; 2:1565-1576. [PMID: 38013904 PMCID: PMC10561546 DOI: 10.1039/d3dd00091e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/20/2023] [Accepted: 09/11/2023] [Indexed: 11/29/2023]
Abstract
Proton-electron transfer (PET) reactions are rather common in chemistry and crucial in energy storage applications. How electrons and protons are involved or which mechanism dominates is strongly molecule and pH dependent. Quantum chemical methods can be used to assess redox potential (Ered.) and acidity constant (pKa) values but the computations are rather time consuming. In this work, supervised machine learning (ML) models are used to predict PET reactions and analyze molecular space. The data for ML have been created by density functional theory (DFT) calculations. Random forest regression models are trained and tested on a dataset that we created. The dataset contains more than 8200 quinone-type organic molecules that each underwent two proton and two electron transfer reactions. Both structural and chemical descriptors are used. The HOMO of the reactant and LUMO of the product participating in the oxidation reaction appeared to be strongly associated with Ered.. Trained models using a SMILES-based structural descriptor can efficiently predict the pKa and Ered. with a mean absolute error of less than 1 and 66 mV, respectively. Good prediction accuracy of R2 > 0.76 and >0.90 was also obtained on the external test set for Ered. and pKa, respectively. This hybrid DFT-ML study can be applied to speed up the screening of quinone-type molecules for energy storage and other applications.
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Affiliation(s)
- Arsalan Hashemi
- Department of Chemistry and Material Science, School of Chemical Engineering, Aalto University 02150 Espoo Finland
| | - Reza Khakpour
- Department of Chemistry and Material Science, School of Chemical Engineering, Aalto University 02150 Espoo Finland
| | - Amir Mahdian
- Department of Chemistry and Material Science, School of Chemical Engineering, Aalto University 02150 Espoo Finland
| | - Michael Busch
- Institute of Theoretical Chemistry, Ulm University Albert-Einstein Allee 11 89069 Ulm Germany
| | - 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
- Department of Chemistry and Material Science, School of Chemical Engineering, Aalto University 02150 Espoo Finland
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Walton-Raaby M, Floen T, García-Díez G, Mora-Diez N. Calculating the Aqueous pK a of Phenols: Predictions for Antioxidants and Cannabinoids. Antioxidants (Basel) 2023; 12:1420. [PMID: 37507958 PMCID: PMC10376140 DOI: 10.3390/antiox12071420] [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: 05/30/2023] [Revised: 06/30/2023] [Accepted: 07/10/2023] [Indexed: 07/30/2023] Open
Abstract
We aim to develop a theoretical methodology for the accurate aqueous pKa prediction of structurally complex phenolic antioxidants and cannabinoids. In this study, five functionals (M06-2X, B3LYP, BHandHLYP, PBE0, and TPSS) and two solvent models (SMD and PCM) were combined with the 6-311++G(d,p) basis set to predict pKa values for twenty structurally simple phenols. None of the direct calculations produced good results. However, the correlations between the calculated Gibbs energy difference of each acid and its conjugate base, ΔGaq(BA)°=ΔGaqA-°-ΔGaq(HA)°, and the experimental aqueous pKa values had superior predictive accuracy, which was also tested relative to an independent set of ten molecules of which six were structurally complex phenols. New correlations were built with twenty-seven phenols (including the phenols with experimental pKa values from the test set), which were used to make predictions. The best correlation equations used the PCM method and produced mean absolute errors of 0.26-0.27 pKa units and R2 values of 0.957-0.960. The average range of predictions for the potential antioxidants (cannabinoids) was 0.15 (0.25) pKa units, which indicates good agreement between our methodologies. The new correlation equations could be used to make pKa predictions for other phenols in water and potentially in other solvents where they might be more soluble.
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Affiliation(s)
- Max Walton-Raaby
- Department of Chemistry, Thompson Rivers University, Kamloops, BC V2C 0C8, Canada
- Department of Chemistry, University of Waterloo, Waterloo, ON N2L 3G1, Canada
| | - Tyler Floen
- Department of Chemistry, Thompson Rivers University, Kamloops, BC V2C 0C8, Canada
| | | | - Nelaine Mora-Diez
- Department of Chemistry, Thompson Rivers University, Kamloops, BC V2C 0C8, Canada
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Hossain MN, Khakpour R, Busch M, Suominen M, Laasonen K, Kallio T. Temperature-Controlled Syngas Production via Electrochemical CO 2 Reduction on a CoTPP/MWCNT Composite in a Flow Cell. ACS APPLIED ENERGY MATERIALS 2023; 6:267-277. [PMID: 36644114 PMCID: PMC9832436 DOI: 10.1021/acsaem.2c02873] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Accepted: 12/13/2022] [Indexed: 06/17/2023]
Abstract
The mixture of CO and H2, known as syngas, is a building block for many substantial chemicals and fuels. Electrochemical reduction of CO2 and H2O to syngas would be a promising alternative approach for its synthesis due to negative carbon emission footprint when using renewable energy to power the reaction. Herein, we present temperature-controlled syngas production by electrochemical CO2 and H2O reduction on a cobalt tetraphenylporphyrin/multiwalled carbon nanotube (CoTPP/MWCNT) composite in a flow cell in the temperature range of 20-50 °C. The experimental results show that for all the applied potentials the ratio of H2/CO increases with increasing temperature. Interestingly, at -0.6 V RHE and 40 °C, the H2/CO ratio reaches a value of 1.2 which is essential for the synthesis of oxo-alcohols. In addition, at -1.0 V RHE and 20 °C, the composite shows very high selectivity toward CO formation, reaching a Faradaic efficiency of ca. 98%. This high selectivity of CO formation is investigated by density functional theory modeling which underlines that the potential-induced oxidation states of the CoTPP catalyst play a vital role in the high selectivity of CO production. Furthermore, the stability of the formed intermediate species is evaluated in terms of the pKa value for further reactions. These experimental and theoretical findings would provide an alternative way for syngas production and help us to understand the mechanism of molecular catalysts in dynamic conditions.
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Benchmarking the Computed Proton Solvation Energy and Absolute Potential in Non-aqueous Solvents. Electrochim Acta 2023. [DOI: 10.1016/j.electacta.2022.141785] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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10
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Selectivity of CO2, carbonic acid and bicarbonate electroreduction over Iron-porphyrin catalyst: a DFT study. Electrochim Acta 2023. [DOI: 10.1016/j.electacta.2022.141784] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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11
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Aksenova I, Pomogaev V. Stability of Dibromo-Dipyrromethene Complexes Coordinated with B, Zn, and Cd in Solutions of Various Acidities. Molecules 2022; 27:molecules27248815. [PMID: 36557945 PMCID: PMC9784619 DOI: 10.3390/molecules27248815] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 12/08/2022] [Accepted: 12/08/2022] [Indexed: 12/15/2022] Open
Abstract
The spectral luminescent properties of dipyrromethenates halogenated with bromine on both ends of the long axis and coordinated using boron fluoride, zinc, or cadmium in neutral ethanol and acidified with hydrochloric acid solutions were studied. The constants of the acid-base equilibrium of the complexes in the proton-donor solvents in the ground and excited states was determined. The mechanisms of complex protonation were discussed, depending on the structure of the compounds. The electronic structures of the neutral and protonated compounds were modeled and analyzed based on the quantum-chemical method. The structures and spectral-luminescence properties were calculated using the SMD model of ethanol solvent using the TD-DFT theory with the B3LYP functional and the composite def2-SVP/def2-TZVP/def2-TZVPP_ECP basis sets, depending on the atomic number of the elements.
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12
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An Accurate Approach for Computational pKa Determination of Phenolic Compounds. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27238590. [PMID: 36500683 PMCID: PMC9736058 DOI: 10.3390/molecules27238590] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 11/30/2022] [Accepted: 12/01/2022] [Indexed: 12/12/2022]
Abstract
Computational chemistry is a valuable tool, as it allows for in silico prediction of key parameters of novel compounds, such as pKa. In the framework of computational pKa determination, the literature offers several approaches based on different level of theories, functionals and continuum solvation models. However, correction factors are often used to provide reliable models that adequately predict pKa. In this work, an accurate protocol based on a direct approach is proposed for computing phenols pKa. Importantly, this methodology does not require the use of correction factors or mathematical fitting, making it highly practical, easy to use and fast. Above all, DFT calculations performed in the presence two explicit water molecules using CAM-B3LYP functional with 6-311G+dp basis set and a solvation model based on density (SMD) led to accurate pKa values. In particular, calculations performed on a series of 13 differently substituted phenols provided reliable results, with a mean absolute error of 0.3. Furthermore, the model achieves accurate results with -CN and -NO2 substituents, which are usually excluded from computational pKa studies, enabling easy and reliable pKa determination in a wide range of phenols.
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13
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Busch M, Ahlberg E, Laasonen K. Universal Trends between Acid Dissociation Constants in Protic and Aprotic Solvents. Chemistry 2022; 28:e202201667. [PMID: 35791810 DOI: 10.1002/chem.202201667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Indexed: 01/07/2023]
Abstract
pKa values in non-aqueous solvents are of critical importance in many areas of chemistry. Our knowledge is, despite their relevance, still limited to the most fundamental properties and few pKa values in the most common solvents. Taking advantage of a recently introduced computationally efficient procedure we computed the pKa values of 182 compounds in 21 solvents. This data set is used to establish for the first time universal trends between all solvents. Our computations indicate, that the total charge of the molecule and the charge of the acidic group combined with the Kamlet-Taft solvatochromic parameters are sufficient to predict pKa values with at least semi- quantitative accuracy. We find, that neutral acids such as alcohols are strongly affected by the solvent properties. This is contrasted by cationic acids like ammonium ions whose pKa is often almost completely independent from the choice of solvent.
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Affiliation(s)
- Michael Busch
- Institute of theoretical chemistry, Ulm University, Albert-Einstein Allee 11, 89069, Ulm, Germany
- Department of chemistry and material science, School of chemical engineering, Aalto University, Kemistintie 1, 02150, Espoo, Finland
| | - Elisabet Ahlberg
- Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 41296, Gothenburg, Sweden
| | - Kari Laasonen
- Department of chemistry and material science, School of chemical engineering, Aalto University, Kemistintie 1, 02150, Espoo, Finland
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14
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Modeling pKa of the Brønsted Bases as an Approach to the Gibbs Energy of the Proton in Acetonitrile. Int J Mol Sci 2022; 23:ijms231810576. [PMID: 36142490 PMCID: PMC9502073 DOI: 10.3390/ijms231810576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2022] [Revised: 09/07/2022] [Accepted: 09/08/2022] [Indexed: 11/17/2022] Open
Abstract
A simple but efficient computational approach to calculate pKa in acetonitrile for a set of phosphorus, nitrogen, and carbon bases was established. A linear function that describes relations between the calculated ΔG’a.sol(BH+) and pKa values was determined for each group of bases. The best model was obtained through the variations in the basis set, in the level of theory (density functionals or MP2), and in the continuum solvation model (IPCM, CPCM, or SMD). The combination of the IPCM/B3LYP/6-311+G(d,p) solvation approach with MP2/6-311+G(2df,p)//B3LYP/6-31G(d) gas-phase energies provided very good results for all three groups of bases with R2 values close to or above 0.99. Interestingly, the slopes and the intercepts of the obtained linear functions showed significant deviations from the theoretical values. We made a linear plot utilizing all the conducted calculations and all the structural variations and employed methods to prove the systematic nature of the intercept/slope dependence. The interpolation of the intercept to the ideal slope value enabled us to determine the Gibbs energy of the proton in acetonitrile, which amounted to −258.8 kcal mol−1. The obtained value was in excellent agreement with previously published results.
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