Simplified spectrophotometric determination of acid dissociation constants

Frohliger, John O.; Dziedzic, Joseph E.; Steward, Omar W.

doi:10.1021/ac60293a006

Cited by 7 publications

(3 citation statements)

References 10 publications

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“…Eq‐7 is of limited use in mixed solvent systems because of the challenges associated with directly measuring pH at high concentrations of organic cosolvent using glass pH electrodes [82,83] . To circumvent this problem for o ‐HBA and p ‐HBA, we have modified the method of Frohlinger [84] for our system: i. e., added a small amount of fluoride ion to our buffer system which will act as an NMR pH probe; [85] Eq‐7 can then be re‐written as:

\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr log{{\left[{A}^{-}\right]}\over{\left[HA\right]}}=log{K}_{a}+log{{{\gamma }_{HA}}\over{{\gamma }_{{A}^{-}}}}-{\rm l}{\rm o}{\rm g}{K}_{HF}-{\rm l}{\rm o}{\rm g}{{{\gamma }_{HF}}\over{{\gamma }_{{F}^{-}}}}+{\rm l}{\rm o}{\rm g}{{\left[{F}^{-}\right]}\over{\left[HF\right]}}={\rm \ }\hfill\cr ({\rm p}{K}_{HF}^{apparent}-{\rm p}{K}_{HA}^{apparent})+{\rm l}{\rm o}{\rm g}{{\left[{F}^{-}\right]}\over{\left[HF\right]}}\hfill\cr}}

…”

Section: Resultsmentioning

confidence: 99%

“…Eq-7 is of limited use in mixed solvent systems because of the challenges associated with directly measuring pH at high concentrations of organic cosolvent using glass pH electrodes. [82,83] To circumvent this problem for o-HBA and p-HBA, we have modified the method of Frohlinger [84] for our system: i. e., added a small amount of fluoride ion to our buffer system which will act as an NMR pH probe; [85] Eq-7 can then be re-written as:…”

Section: Urea Addition Has No Significant Effect Upon the Intramolecu...mentioning

confidence: 99%

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Does Urea Preferentially Interact with Amide Moieties or Nonpolar Sidechains? A Question Answered Through a Judicious Selection of Model Systems

et al. 2022

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The transfer model suggests that urea unfolds proteins mainly by increasing the solubility of the amide backbone, probably through urea-induced increase in hydrogen bonding. Other studies suggest that urea addition increases the magnitude of solvent-solute van der Waals interactions, which increases the solubility of nonpolar sidechains. More recent analyses hypothesize that urea has a similar effect in increasing the solubility of backbone and sidechain groups. In this work, we compare the effects of urea addition on the solvation of amides and alkyl groups. At first, we study the effects of urea addition upon solvent hydrogen bonding acidity and basicity through the perturbation in the fluorescence spectrum of probes 1-AN and 1-DMAN. Our results demonstrate that the solvent's hydrogen bonding properties are minimally affected by urea addition. Subsequently, we show that urea addition does not perturb the intra-molecular hydrogen bonding in salicylic acid significantly. Finally, we investigate how urea preferentially interacts with amide and alkyl groups moieties in water by comparing the effects of urea addition upon the solubility of acetaminophen and 4-tertbutylphenol. We show that urea affects amide and tbutyl solubility (lowers the transfer free energy of both amide (backbone) and alkyl (sidechain) groups) in a similar fashion. In other words, preferential interaction of urea with both moieties contributes to protein denaturation.

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\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr log{{\left[{A}^{-}\right]}\over{\left[HA\right]}}=log{K}_{a}+log{{{\gamma }_{HA}}\over{{\gamma }_{{A}^{-}}}}-{\rm l}{\rm o}{\rm g}{K}_{HF}-{\rm l}{\rm o}{\rm g}{{{\gamma }_{HF}}\over{{\gamma }_{{F}^{-}}}}+{\rm l}{\rm o}{\rm g}{{\left[{F}^{-}\right]}\over{\left[HF\right]}}={\rm \ }\hfill\cr ({\rm p}{K}_{HF}^{apparent}-{\rm p}{K}_{HA}^{apparent})+{\rm l}{\rm o}{\rm g}{{\left[{F}^{-}\right]}\over{\left[HF\right]}}\hfill\cr}}

…”

Section: Resultsmentioning

confidence: 99%

Section: Urea Addition Has No Significant Effect Upon the Intramolecu...mentioning

confidence: 99%

Does Urea Preferentially Interact with Amide Moieties or Nonpolar Sidechains? A Question Answered Through a Judicious Selection of Model Systems

et al. 2022

View full text Add to dashboard Cite

show abstract

“…THEORY AND CALCULATIONS Among several publications on calculations involving spectrophotometric data are articles which describe a derivation of normal equations for the calculation of molar absorptivities and formation constants (221), a general method for the evaluation of equilibrium constants and their errors for multicomponent systems (188), a method for calculating the stability constants of complexes of low and moderate stability (62), a method for the determination of acid dissociation constants in which a known concentration of a weak acid with a known dissociation constant is used in equilibrium with the acid under investigation (125), and a discussion of the errors in the determination of equilibrium constants and extinction coefficients of charge transfer complexes (208). The absorbance ratio method has been applied to the analysis of binary mixtures using a reference spectrum (71).…”

Section: Reaction Mechanismsmentioning

confidence: 99%