pK Measurements Research Articles

Measurement of pK a values for phosphonium salts via the kinetics of proton transfer to an electrogenerated base

pKa values have for the first time been measured for common phosphonium ions, including butyl-, allyl-, prop-2-ynyl- and benzyl-triphenylphosphonium, by comparison through a linear Bronsted plot of their rates of proton transfer to an electrogenerated base with those involving carbon acids of known acidity.

ChemInform Abstract: Carbon Acidity. Part 76. The Remarkably Low Second pKa of 1‐Naphthylacetic Acid. Lithium Ion Pair Acidity in Tetrahydrofuran.

AbstractThe pK measurements show a variation with the concentration of the salts.

The pK ∗ of TRISH + in Na-K-Mg-Ca-Cl-SO 4 brines—pH scales

The stoichiometric dissociation constant, pK ∗ of TRISH + has been determined in NaCl, KCl, MgCl 2 and CaCl 2 solutions to an ionic strength of 6 molal. The results have been used to derive Pitzer coefficients for the interactions of TRIS with Na +, K +, Mg 2+ and Ca 2+ ions. These results can be used to determine the pK ∗ of TRISH + in mixed brines which can be used to calibrate pH electrodes. Measurements of pK ∗ of TRISH + in mixtures of NaCl-MgCl 2, NaCl-CaCl 2, NaCl-Na 2SO 4, KCl-MgCl 2 and KCl-CaCl 2, artificial seawater and Dead Sea waters were made to determine the reliability of the Pitzer coefficients. The estimated values were found to be in good agreement with the measured values provided corrections were made for the interactions of H + with SO 2− 4. It now is possible to use dilute solutions of TRIS and TRISH + to make buffers that can be used to make reproducible pH measurements in brines.

Serum pyruvate kinase in different neuromuscular diseases and in carriers of muscular dystrophy.

Serum pyruvate kinase and creatine kinase activities were measured in a group of patients with various neuromuscular diseases and in carriers of muscular dystrophy. Elevated values of PK were usually but not invariably associated with elevated levels of CK. THe data showed that PK activity was elevated in all patients with DMD, high values generally correlating inversely with age or disease duration. In definite carriers, the level of PK was raised simultaneously with CK, while in potential carriers, classified by their relationship with MD patients in mothers, sisters and other relatives, the PK levels were elevated in 23%, 44% and 10% respectively, indicating especially for sisters, an increased genetic probability of being a definite carrier. In this way, we have confirmed that the serum PK assay is more sensitive in younger subjects and that combined CK and PK measurement will be of value in detecting a higher proportion of potential carriers.

SYNTHESIS AND CHARACTERIZATION OF 2-MERCAPTO-2-THIONO-1,3,2-DIOXAPHOSPHOLANES AND DIOXAPHOSPHORINANES

Abstract 2-Mercapto-2-thiono-1,3,2-dioxaphospholanes and dioxaphosphorinanes, have been synthesized by the reactions of phosphorus pentasulphide with some 1,2-diols (viz., butane-2,3-diol and 2,3-dimethylbutane-2,3-diol) and 1,3-diols (viz., 2-methylpentane-2,4-diol, 2,2-dimethylpropane-1,3-diol and 2,2-diethylpropane-1,3-diol) in 1:2 molar ratio in dry benzene. These volatile compounds have been purified by distillation under reduced pressure. The 2-methylpentane-2,4-diol derivative, however, decomposed during attempted distillations. These new compounds have been characterized by elemental analysis, molecular weight determinations, measurement of pK a values and IR as well as NMR spectroscopic studies. The ammonium and sodium salts of some of these acids have also been characterized.

Potentiometric and polarimetric studies of the reaction of boric acid and tetrahydroxyborate ion with polyhydroxy compounds

Values of the association constant, Kn, for the reaction of boric acid with sorbitol, mannitol, D-glucose, glycerol and ethylene glycol have been evaluated from a modified Antikainen equation using values of the dissociation constant, K*, obtained by the half-neutralisation method. This procedure gives values of Kn which are easily compared with each other, and which have trends which are compatible with other previously determined values. Measurements of pK* at various temperatures for the complexes of sorbitol and mannitol with boric acid allow estimates to be made of ΔH* and ΔS* for complexation. Polarimetric studies of the sorbitol and mannitol complexes in solution indicate that the tetrahydroxyborate ion, B(OH)–4, is more effectively complexed than boric acid and do not suggest any major differences in complexing ability between sorbitol and mannitol.

ChemInform Abstract: SULFONATION OF STRYCHNINE AND SOME RELATED COMPOUNDS BY SULFUR DIOXIDE‐MANGANESE DIOXIDE (THE LEUCHS REACTION)

AbstractManganese Dioxide (the Leuchs Reaction).

Investigation on oligo‐ and polygalacturonic acids by potentiometry and circular dichroism

AbstractThe potentiometric data concerning the dependence of the apparent pK with the degree of neutralization and the nature of counterions (Na or Ca) of galacturonic oligomers and polymers are discussed. They are characterized by an apparent charge density λapp which predicts their electrostatic behavior. The calculated osmotic coefficients from Katchalsky and Manning's theories are in good agreement with the experimental data obtained by potentiometry. The dependence of the osmotic coefficient (ϕCa) as a function of the polymer concentration is established by potentiometry and interpreted in terms of a multichain aggregation. In addition, it is proven that no Ca2+ is ever fixed in excess of stoichiometry. The dependence of CD spectra obtained under the same conditions as the pK measurements shows analogies between the two sets of results. The CD data, in agreement with 13C‐nmr measurements, suggest that in dilute solutions the polymer adopts two conformations: one (acidic form) which may be represented by threefold screw symmetry and a second (Na or Ca form) which can be related to a twofold screw symmetry. The twofold screw symmetry is known to allow the formation of cooperative “egg‐box” fixation of Ca without conformation change.

Sulfonation of strychnine and some related compounds by sulfur dioxide – manganese dioxide (the Leuchs reaction)

On the basis of pK measurements, 13C nmr, and chemical arguments, the zwitterionic structures 3 and 4 have been assigned to the two minor products obtained by sulfonating strychnine or brucine in water with a mixture of sulfur dioxide and manganese dioxide. The same reagent sulfonates the quaternary salts of strychnine and brucine to give betaines, but fails to sulfonate many other strychnine derivatives as well as a number of other alkaloids examined.

Measurement of pK for weak bases with the aid of sodium ion-selective electrodes

A method for obtaining pK a of weak bases from emf measurements of cells with glass pH electrodes and sodium ion-selective electrodes is described. The Harned-Ehlers method [1] uses hydrogen and Ag/AgCl electrodes; it yields accurate results but requires special apparatus and techniques and numerous data. The present method produces somewhat less accurate data; it retains the advantages of a cell with liquid junction, however, and is both simple and rapid. It is particularly suited to the study of bases where the solubility of AgCl is often of concern. To determine the equilibrium constant K a for the process BH + ⇌ B + H +, one measures the emf (E) of cells ▪ The emf of this cell is given by ▪ where k is the Nernst slope, 2.3026 RT/F. With weak bases (K b < 10 −4) and fixed small molality of Na + ( e.g. 0.01 m), the last term remains constant when the buffer is diluted with NaCl solution. More important, the activity coefficient term is small and varies linearly with ionic strength (I). Thus E is a linear function of I, with a small slope. This is not the case with the Harned method, where this term is log (γ BH+γ Cl-/γ B). The value of pK a can be derived from the intercept (E′) at I = O. Similar measurements of E′ for a reference base of known pK a ( e.g. tris(hydroxymethyl)aminomethane [2]) provide the value of E°. Id the buffer ratio and sodium molality are the same for the reference buffer and the unknown buffer, ΔpK a = ΔE′/k. Results are given for several weak bases in water and in 50% methanol/water at temperatures from 15 to 35°C. The responses of the electrodes were in accord with the Nernst slope. Two or three measurement were sufficient to yield values of pK a. The results agreed well with accepted constants from the literature.

Beiträge zur Chemie der Pyrrolpigmente, XVII / On the Chemistry of Pyrrole Pigments, XVII

The (Z,Z)-configuration of the bilivioline chromophoric system was established investigating an appropriate model compound by means of pK measurement, 1H NMR spectroscopy Lanthanide ion induced shift technique, electron absorption spectroscopy and PPP calculations. Moreover a syn-syn conformation which is twisted at the a-methine single bond and planar within the pyrromethene unit (based on the concept of partial structures of bile pigments) of the molecule was deduced.

Excited singlet state acidity constants for hydroxy and amino substituted anthraquinones and related compounds. Comparison of excited-state pK measurement procedures

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTExcited singlet state acidity constants for hydroxy and amino substituted anthraquinones and related compounds. Comparison of excited-state pK measurement proceduresH. H. Richtol and B. R. FitchCite this: Anal. Chem. 1974, 46, 12, 1749–1754Publication Date (Print):October 1, 1974Publication History Published online1 May 2002Published inissue 1 October 1974https://doi.org/10.1021/ac60348a065RIGHTS & PERMISSIONSArticle Views139Altmetric-Citations21LEARN 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 InReddit PDF (705 KB) Get e-Alerts Get e-Alerts

The evaluation of Δ C° p for acid-base equilibria from pK measurement

The use of the temperature variation of the dissociation constant for evaluating changes in Δ C° p is reviewed with a view to establishing the degree of reliability of such values. Δ C° p values obtained from dissociation constant measurements are compared, where possible, with the calorimetrically determined values. Significant differences are apparent, suggesting serious shortcomings in the indirect methods of evaluation used so far. The related question of the appropriate form of the pK( T) equation is also discussed. When the “most appropriate” form of pK( t), viz a five-constants equation is used with the accurate data of Ives for the dissociation of cyano-acetic acid, according to the method of Clarke and Glew, the results still retain large uncertainties on Δ C° p . Model exact pK data can be calculated from known assumed Δ G°, Δ H°, Δ C° p , first and second temperature derivatives of Δ C° p at a chosen reference temperature. By introducing variations of various magnitudes and signs on these model values, very accurate “experimental-like” pK values can be generated. When these accurate pK values are analysed on the computer, using the method of Clarke and Glew, and the results are compared, it becomes apparent that over the normal experimental range (O°−50°C or 60°C) even very small errors ( ca 0·00025 pK units) can lead to very large uncertainties on Δ C° p (especially at the two extremes of the temperature range) exceeding in some cases 20 cal. The identification of the true Δ C° p ( T) becomes impossible. It is concluded that the dissociation constant method is not capable as yet of furnishing reliable Δ C° p values; the extension of the temperature range to the neighborhood of 100°C and an increase in the degrees of freedom ( eg by measurements at 5° intervals) could combine to furnish fairly reliable Δ C° p values.

Studies of tubocurarine labelled with iodine or tritium

D-tubocurarine was reacted first with ICl and then with tritium by catalytic hydrogenolysis of the iodo derivative in the presence of tritium gaz. The specific radioactivity of the tritiated product reached 12 Ci/mmole and its biological activity was identical to that of the original material. From the iodinated material (0.8 atom per mole) pure monoiodo-d-tubocurarine was obtained by selective adsorption on a Biogel column. Localization of the halogen was characterized by pK's measurements of the two phenolic functions of the iodo and of the original d-tubocurarine. Circular dichroism spectra and toxicity measurements of the iodinated compound have shown that iodine does not, or very slightly only, modify the structural and biological properties of d-tubocurarine. Le chlorure de d-tubocurarine a été marqué successivement à l'iode et au tritium. La radioactivité spécifique du composé tritié est de 12 Ci/mmole et son activité biologique est identique à celle du produit de départ. La d-tubocurarine monoiodée a été obtenue par adsorption selective sur colonne de Biogel à partir d'un dérivé iodé à 0.8 atome par molécule. La mesure des pK des deux noyaux phénoliques du composé iodé a permis de préciser la position de l'halogène. Les spectres de dichroisme circulaire et les mesures de toxicité de la d-tubocurarine iodée ont montrés que l'halogène ne modifie pas sensiblement les propriétés structurales et biologiques de la molécule.

The disintegration energy of 113Sn why have PL/ PK measurements yielded incorrect values?

The P L/ P K method of determining the ϵ-capture decay energy fails badly in the case of 113Sn. We suggest that the discrepancies in the measured values may be due to variable amounts of 250 d 119Sn m present in the 115 d 113Sn samples.

Acid‐base equilibria of dipyridylethylenes studied by absorption and fluorescence spectrometry

AbstractIn connection with photochemical and fluorimetric studies and with previous pK measurements on styrylpyridines, the acid‐base equilibria of the trans‐1,2‐dipyridylethylenes have been studied by absorption and fluorescence spectrometry. The results obtained by the two methods are compared and the pK's of first and second protonation discussed in dependence with the nitrogen positional isomerism.The measurements of the dissociation constant of the trans‐3‐styrylpyridinium ion is also reported as a particularly convenient application of fluorescence spectrometry.

Nitroimidazoles II. synthesis and reactions of iodonitroimidazoles

AbstractThe synthesis and some chemical reactions of various iodonitroimidazoles and methods of distinguishing between the 4‐ and 5‐ nitro derivatives by UV and pK measurements are described.

The Relation of Kinetics of Coupling of Developer Soluble Colour Couplers to Structure and Photographic Activity

AbstractThe ratio of Coupling Rate Constant: Deamination Rale Constant (k2, k1) for a considerable number of magenta, yellow and cyan developer soluble colour couplers has been determined by competition between deamination and coupling. The determinations were made in a medium approximating to the colour developer using 5-diethylamino-2-aminotoluene as the developing agent. pK measurements showed that all the colour couplers were fully ionised in this medium. The photographic data have been shown to fit the empirical equation, γ = A log t + B where γ = Contrast, t = Time of Development in minutes, A = Activity Constant and B = Inducticn Constant, k2, k1 and A values have been shown to be related by the equations, A=3.55 e–5.05×102(K1/K2) for oxidation by K3Fe(CN)6 A=3.55 e–5.05×102(K1/K2) for oxidation by AgCl.These equations show that the photographic activity of a colour coupler is related to its rate of coupling with oxidised developer and increases with increase in k2/k1. Further they also show that t...

Studies on uncaria alkaloid. XX. Structure of rhynchophylline. 5. Structure of rhynchophylline and isorhynchophylline.

Reduction of rhynchophylline with lithium aluminum hydride afforded an indoline derivative, which indicated the 3-position of the oxindole ring in its molecule is a spiro type, and the formula (III) was forwarded for rhynchophylline in analogy with uncarine. Rhynchophylline and isorhynchophylline are considered to be 4-epimers, similar to uncarine-A and -B, because their compositions are the same, their ultraviolet and infrared spectra are in close similarity, and the two easily undergo isomerization. From the measurement of pK, the formula (V) for rhynchophylline and (IV) for isorhynchophylline are proposed.

蛔虫駆除薬の研究 (第2報)

By the application of amines, alcohols, and water to N-acylkainic anhydrides (III, IV) and N-acyldihydrokainic anhydrides (VI, VII), obtained from α-kainic acid (I) and α-dihydrokainic acid (II), the corresponding monoamides, monoesters, and N-acylkainic acids (VIII to XXXIII) were prepared. These mono-substituted compounds were proved to be α-substituted derivatives from the measurement of pK′ of N-acetyl-glycine- and N-acylkainic derivatives. Further, (V) and (VIII) were derived to (XXXIV) and (XXXV) through N-acylkainic dichlorides.