The acid dissociation constant of the imidazolium ion
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Dissociation constants of the protonated form of imidazole base have been measured from 0 to 50° at 5° intervals. The use of different formulæ for the extrapolation of data to zero ionic strength is discussed, and the results are compared with the available literature values. The acid dissociation constant of the imidazolium ion is given by the equations pKa= 472·269/T+ 15·1061 – 0·0487442T+ 0·00005440T0, or pKa= 1906·884/T+ 0·6225 – 0·0000848T; the thermodynamic quantities derived from the first equation are discussed.Keywords:
Dissociation constant
Acid dissociation constant
Imidazole
The transformation of α-d-isosaccharinic acid into α-d-isosaccharino-1,4-lactone proceeds relatively slowly. Consequently, the transformation constant, KL, has been determined kinetically in 1.0 mol·dm−3 NaClO4 and at 23 °C. A previous determination in 0.1 mol·dm−3 NaClO4 and at 23 °C has been reinterpreted. The values obtained have been coupled with other data in the literature to demonstrate that the magnitude of the transformation constant is independent of ionic strength, and its value was determined to be log KL° = 0.80 ± 0.02. Data from the literature for the dissociation of α-d-isosaccharinic acid have been re-evaluated to determine both the "intrinsic" and "composite" dissociation constants at zero ionic strength, namely, log Ka° = −4.04 ± 0.06 and log Kc° = −4.90 ± 0.07, respectively. The present data permit a much more thorough understanding of the aqueous chemistry of α-d-isosaccharinic acid to be ascertained than has previously been possible.
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Abstract The effects of ionic strength and pH on adsorption of lysozyme to three strong cation exchangers have been studied. Adsorption equilibrium data obtained using the batch techniques corresponded well to the Langmuir isotherm. Ionic strength had a considerable influence on the isotherms. In all cases, the maximum binding capacity of the three exchangers decreased while the apparent dissociation constant increased with increasing ionic strength. The maximum binding capacity also decreased while the apparent dissociation constant was not significantly affected by an increase in pH. It was found that the three exchangers exhibited different levels of binding capacity under identical solution conditions. This was shown to be caused by variation in the arrangement and distribution of charged groups. However, the ion‐exchange matrix had little effect on the apparent dissociation constant.
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Abstract The dissociation constant for the carboxy proton is evaluated by means of two independent methods: potentiometric titration (3.05) and ‐ more reliable ‐ distribution between octanol and H 2 O (2.96).
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Micelles in the Physical/Analytical Chemistry Laboratory. Acid Dissociation of Neutral Red Indicator
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMicelles in the Physical/Analytical Chemistry Laboratory. Acid Dissociation of Neutral Red IndicatorKathryn R. Williams and Loretta H. Tennant View Author Information Department of Chemistry, University of Florida, Gainesville, FL 32611-7200Cite this: J. Chem. Educ. 2001, 78, 3, 349Publication Date (Web):March 1, 2001Publication History Received3 August 2009Published online1 March 2001Published inissue 1 March 2001https://pubs.acs.org/doi/10.1021/ed078p349https://doi.org/10.1021/ed078p349research-articleACS PublicationsRequest reuse permissionsArticle Views2230Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Dissociation,Micelles,Pharmacology,Sodium dodecyl sulfate,Surfactants Get e-Alerts
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Dissociation constants of the protonated form of imidazole base have been measured from 0 to 50° at 5° intervals. The use of different formulæ for the extrapolation of data to zero ionic strength is discussed, and the results are compared with the available literature values. The acid dissociation constant of the imidazolium ion is given by the equations pKa= 472·269/T+ 15·1061 – 0·0487442T+ 0·00005440T0, or pKa= 1906·884/T+ 0·6225 – 0·0000848T; the thermodynamic quantities derived from the first equation are discussed.
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Imidazole
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The dissociation constant for hirudin was determined by varying the concentration of hirudin in the presence of a fixed concentration of thrombin and tripeptidyl p-nitroanilide substrate. The estimate of the dissociation constant determined in this manner displayed a dependence on the concentration of substrate which suggested the existence of two binding sites at which the substrate was able to compete with hirudin. A high-affinity site could be correlated with the binding of the substrate at the active site, and the other site had an affinity for the substrate that was 2 orders of magnitude lower. Extrapolation to zero substrate concentration yielded a value of 20 fM for the dissociation constant of hirudin at an ionic strength of 0.125. The dissociation constant for hirudin was markedly dependent on the ionic strength of the assay; it increased 20-fold when the ionic strength was increased from 0.1 to 0.4. This increase in dissociation constant was accompanied by a decrease in the rate with which hirudin associated with thrombin. This rate could be measured with a conventional recording spectrophotometer at higher ionic strength and was found to be independent of the binding of substrate at the active site.
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