Macroscopic and Microscopic Protonation Equilibria of Some α-Amino Acids in Dimethyl Sulfoxide–Water Mixtures

Doğan, Alev; Aslan, Nazife; Erden, Pınar Esra; Canel, Esin; Kılıç, Esma

doi:10.1007/s10953-015-0363-8

Cited by 2 publications

(2 citation statements)

References 57 publications

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“…Nevertheless, an estimate of p K a1 is obtained (Table ). The p K a1 of valine compares with the value of 3.00 reported by Dogăn et al in 40% (v/v) DMSO/H 2 O. For phthalic acid, complete titration curves are recorded, allowing both p K a values to be fitted (Figure ).…”

Section: Resultssupporting

confidence: 61%

“…The electrochemical measurement of pH requires careful calibration of electrodes either using solutions of known pH in the solvent mixture of interest – or by applying a specific correction to the pH reported by an electrode that has been calibrated using conventional aqueous buffers. , Alternatively, pH may be determined from the NMR chemical shifts or UV/vis spectra of compounds with known p K a values. , However, electrode corrections and p K a data are only available in a small number of aqueous–organic mixtures. , Finally, p K a values can be measured without knowledge of pH using conductometric methods . However, such approaches require high-purity materials, and only one compound may be analyzed per titration.…”

Section: Introductionmentioning

confidence: 99%

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Measurement of the pK_a Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by ¹H NMR without External Calibrants

Wallace,

Abiama,

Chipembere

2023

Anal. Chem.

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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 pK a 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 pK a 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 pK a 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 pK a in aqueous–organic solvents directly by NMR. We first determine pK a 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 pK a 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 pK a values of organic acids and bases up to pK a 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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Section: Resultssupporting

confidence: 61%

Section: Introductionmentioning

confidence: 99%

Measurement of the pK_a Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by ¹H NMR without External Calibrants

Wallace,

Abiama,

Chipembere

2023

Anal. Chem.

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The Microscopic and Tautomeric Protonation Constants of Some α-Amino Acids in Dioxane–Water Mixtures

Tanalp

Doğan

2021

J Solution Chem

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Macroscopic and Microscopic Protonation Equilibria of Some α-Amino Acids in Dimethyl Sulfoxide–Water Mixtures

Cited by 2 publications

References 57 publications

Measurement of the pK_a Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by ¹H NMR without External Calibrants

Measurement of the pK_a Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by ¹H NMR without External Calibrants

The Microscopic and Tautomeric Protonation Constants of Some α-Amino Acids in Dioxane–Water Mixtures

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Macroscopic and Microscopic Protonation Equilibria of Some α-Amino Acids in Dimethyl Sulfoxide–Water Mixtures

Cited by 2 publications

References 57 publications

Measurement of the pKa Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by 1H NMR without External Calibrants

Measurement of the pKa Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by 1H NMR without External Calibrants

The Microscopic and Tautomeric Protonation Constants of Some α-Amino Acids in Dioxane–Water Mixtures

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Measurement of the pK_a Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by ¹H NMR without External Calibrants

Measurement of the pK_a Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by ¹H NMR without External Calibrants