Determination of pKa values of some hydroxylated benzoic acids in methanol–water binary mixtures by LC methodology and potentiometry

Erdemgil, F. Z.; Şanlı, Senem; Şanlı, Nurullah; Özkan, Güleren; Barbosa, J.; Guiteras, J.; Beltrán, José Luís

doi:10.1016/j.talanta.2006.11.007

Cited by 175 publications

(107 citation statements)

References 26 publications

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“…However, in this study, we found that SA is more active than CA. The results are fully consistent with the HAT reaction mechanism, which is preferred in aprotic solvents, well characterised by the O-H bond-dissociation enthalpy (BDE) of ArOH (Ray et al 1996;Erdemgil et al 2007). However, in a non-polar aprotic solvent n-heptane (ε =1.92), the antioxidant activity trend may be CA > SA (Ray et al 1996;Erdemgil et al 2007).…”

Section: Gosupporting

confidence: 83%

Details of the antioxidant mechanism of hydroxycinnamic acids

Shang¹,

Liu²,

Min³

2015

Czech J. Food Sci.

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Antioxidant activities and free radical-mediated DNA strand breakages of five hydroxycinnamic acids were examined. Kinetic analysis of a stable galvinoxy (GO • )-scavenging reaction of hydroxycinnamic acids demonstrated that the molecular structure and the reaction medium were two important factors affecting the antioxidant mechanism and activity. In methanol, the kinetic process of the compounds, which have electron-donating groups (-OH, -OCH 3 ) in the ortho-or para-position of 4-OH, was primarily governed by the sequential proton loss electron transfer (SPLET mechanism). While, in ethyl acetate, the reaction mechanism is predominantly direct hydrogen atom transfer (HAT mechanism). But for the compounds having only one hydroxyl, both in ethyl acetate and methanol, the reaction mechanism is only HAT. At the same time, the compound bearing o-diphenoxyl is not the most active one in our tested environment.

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Section: Gosupporting

confidence: 83%

Details of the antioxidant mechanism of hydroxycinnamic acids

Shang¹,

Liu²,

Min³

2015

Czech J. Food Sci.

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“…[29][30][31][32][33][34] It has been found that pK a values of a given compounds show a linear relationship with the mole fraction of methanol-water (up to 50% methanol) organic binary mixtures. The plot of experimental pK a values of studied auxines against the mole fraction of methanol are given in Figure 5.…”

Section: Resultsmentioning

confidence: 99%

Determination of pKa values of some auxins in methanol-water mixtures by reversed phase liquid chromatography and potentiometric methods

Kelen¹,

Şanlı²

2009

J. Braz. Chem. Soc.

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Os hormônios das plantas são de vital importância para o seu funcionamento normal. As auxinas são uma classe de fito-hormônios envolvidas em muitos aspectos do crescimento. Os ácidos indol-3-acético (IAA), indol-3-pirúvico (IPA) e indol-3-lático (ILA) são auxinas com funções biológicas estimulantes do processo de crescimento, tais como elongação e divisão. Neste estudo, os valores pK a de IAA, IPA e ILA em misturas de metanol-água a 30%, 40% e 50% (v/v) foram determinados usando potenciometria, cromatografia líquida (LC) e metodologia LC-DAD. Valores de pK a em água, preditos pelo método SPARC também foram investigados.Plant hormones are of vital importance for the normal functioning of plants. Auxins are a class of phytohormones involved in many aspects of plant growth. Indole-3-acetic acid, (IAA), indole-3-pyruvic acid (IPA) and indole-3-lactic acid (ILA) are auxins with biological functions stimulating growth processes such as cell elongation and division. In this study, the pK a values of IAA, IPA and ILA in 30%, 40% and 50% (v/v) methanol-water mixtures were determined using potentiometry, liquid chromatography (LC) and LC-DAD methodology. Also, the pK a values in water predicted by the SPARC on-line calculator have been investigated. Keywords: dissociation constants, LC, LC-DAD, methanol-water mixtures, plant hormones, potentiometry IntroductionDissociation constants are important physicochemical parameters of a substance, and the knowledge of these parameters is of fundamental importance in a wide range of applications and research areas. The chromatographic retention and electrophoretic behaviour of ionizable compounds strongly depend on the pK a of the compound and the mobile phase pH. Therefore, a satisfactory knowledge of the acid-base behaviour of substances in a hydro-organic media such as methanol (MeOH)/water is essential to predict the influence of pH on selectivity and retention in liquid chromatography (LC), and also to optimize analytical procedures for the separation of ionizable compounds by various techniques. [1][2][3] Methanol is one of the most utilized solvents due to its good solvating properties of organic compounds. In addition, due to its relatively high dielectric constant (ε = 32.63) dissolves ionic solutes and prevents ion-pair formation at very high solute concentrations. Among the organic solvents, methanol is the closest one to water in terms of its structure and properties and, therefore, acidic dissociation in methanol occurs in an analogous way to that in aqueous solution. However, methanol can solve a wide majority of organic acids more effectively than water and in many cases it is a more suitable solvent for the determination of the dissociation constants. 4 There are a large spectrum of pK a determination techniques including potentiometry, conductivity, calorimetry, UV-Vis and NMR spectrometry, mass spectrometry, liquid chromatography, capillary zone electrophoresis, and software computational predictions. Among these techniques, the potentiometric titration is most ec...

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“…The coformers selected for the present study were ferulic and syringic acids, belonging to the class of nutraceutic acids, whose pK a1 values are 4.27 (Erdemgil et al, 2007) and 3.86 (Chuysinuan et al, 2009), respectively. According to the socalled 'rule of three', when synthesizing a mixed crystal, a salt is expected if ÁpK a [pK a(base) -pK a(acid) ] is greater than 2 or 3 units, while the formation of a cocrystal is observed if ÁpK a is less than 0 (Childs et al, 2007;Bhogala et al, 2005).…”

Section: Electronic Reprintmentioning

confidence: 99%

New pharmaceutical salts containing pyridoxine

2017

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Two mixed crystals were obtained by crystallizing the active pharmaceutical ingredient pyridoxine [systematic name: 4,5-bis(hydroxymethyl)-2-methylpyridin-3-ol, PN] with (E)-3-(4-hydroxy-3-methoxyphenyl)prop-2-enoic acid (ferulic acid) and 4-hydroxy-3,5-dimethoxybenzoic acid (syringic acid). PN and the coformers crystallize in the form of pharmaceutical salts in a 1:1 stoichiometric ratio, namely 3-hydroxy-4,5-bis(hydroxymethyl)-2-methylpyridin-1-ium (E)-3-(4-hydroxy-3-methoxyphenyl)prop-2-enoate, C 8 H 12 NO 3 + ÁC 9 H 9 O 5 À , and 3-hydroxy-4,5-bis(hydroxymethyl)-2-methylpyridin-1-ium 4-hydroxy-3,5-dimethoxybenzoate monohydrate, C 8 H 12 NO 3 + ÁC 10 H 11 O 5 À ÁH 2 O, the proton exchange between PN and the acidic partner being supported by the differences of the pK a values of the two components and by the C-O bond lengths of the carboxylate groups. Besides complex hydrogen-bonding networks, -interactions between aromatic moieties have been found to be important for the packing architecture in both crystals. Hirshfeld surface analysis was used to explore the intermolecular interactions in detail and compare them with the interactions found in similar pyridoxine/carboxylic acid salts.

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Determination of pKa values of some hydroxylated benzoic acids in methanol–water binary mixtures by LC methodology and potentiometry

Cited by 175 publications

References 26 publications

Details of the antioxidant mechanism of hydroxycinnamic acids

Details of the antioxidant mechanism of hydroxycinnamic acids

Determination of pKa values of some auxins in methanol-water mixtures by reversed phase liquid chromatography and potentiometric methods

New pharmaceutical salts containing pyridoxine

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