Potentiometric and conductimetric studies of chemical equilibria for pyridoxine hydrochloride in aqueous solutions: simple experimental determination of pKa values and analytical applications to pharmaceutical analysis

Santos, Thiago de Almeida Drumond dos; Costa, Diego Oliveira da; Pita, Samuel Silva da Rocha; Semaan, Felipe S.

doi:10.1590/s0100-46702010000400010

Cited by 27 publications

(13 citation statements)

References 13 publications

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“…This compares to p K a values of 5.1 ± 0.02 and 9.0 ± 0.03 for the aromatic nitrogen and phenol hydroxyl, respectively, measured by potentiometry. 50 However, other studies indicate pyridoxine in aqueous solution at neutral pH exists as a mixture of neutral and zwitterionic species. 51−53 While the identity of the titrating species is not clear, the pH dependence of μ 23 / RT is evident.…”

Section: Discussionmentioning

confidence: 99%

Aspects of Weak Interactions between Folate and Glycine Betaine

et al. 2016

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Folate, or vitamin B9, is an important compound in one-carbon metabolism. Previous studies have found weaker binding of dihydrofolate to dihydrofolate reductase in the presence of osmolytes. In other words, osmolytes are more difficult to remove from the dihydrofolate solvation shell than water; this shifts the equilibrium toward the free ligand and protein species. This study uses vapor-pressure osmometry to explore the interaction of folate with the model osmolyte, glycine betaine. This method yields a preferential interaction potential (μ23/RT value). This value is concentration-dependent as folate dimerizes. The μ23/RT value also tracks the deprotonation of folate’s N3–O4 keto–enol group, yielding a pKa of 8.1. To determine which folate atoms interact most strongly with betaine, the interaction of heterocyclic aromatic compounds (as well as other small molecules) with betaine was monitored. Using an accessible surface area approach coupled with osmometry measurements, deconvolution of the μ23/RT values into α values for atom types was achieved. This allows prediction of μ23/RT values for larger molecules such as folate. Molecular dynamics simulations of folate show a variety of structures from extended to L-shaped. These conformers possess μ23/RT values from −0.18 to 0.09 m–1, where a negative value indicates a preference for solvation by betaine and a positive value indicates a preference for water. This range of values is consistent with values observed in osmometry and solubility experiments. As the average predicted folate μ23/RT value is near zero, this indicates folate interacts almost equally well with betaine and water. Specifically, the glutamate tail prefers to interact with water, while the aromatic rings prefer betaine. In general, the more protonated species in our small molecule survey interact better with betaine as they provide a source of hydrogens (betaine is not a hydrogen bond donor). Upon deprotonation of the small molecule, the preference swings toward water interaction because of its hydrogen bond donating capacities.

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Section: Discussionmentioning

confidence: 99%

Aspects of Weak Interactions between Folate and Glycine Betaine

et al. 2016

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“…There is good agreement with the study of Richardson et al 35 35 . However, titration of 3-hydroxypyridine and its analogue, pyridoxine, follows the sequence indicated in equation (iv) 37,38 . Based on these studies, we propose the pKa assignments for PIH are as indicated in figure 2.…”

Section: Determination Of Pka Valuesmentioning

confidence: 99%

The interaction of pyridoxal isonicotinoyl hydrazone (PIH) and salicylaldehyde isonicotinoyl hydrazone (SIH) with iron

Chen

Kong

Xie

et al. 2018

Journal of Inorganic Biochemistry

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The interaction of pyridoxal isonicotinoyl hydrazone (PIH) and salicylaldehyde isonicotinoyl hydrazone (SIH), two important biologically active chelators, with iron has been investigated by spectrophotometric methods. High iron(III) affinity constants were determined for PIH, logβ=37.0 and SIH, logβ=37.6. The associated redox potentials of the iron complexes were determined using cyclic voltammetry at pH7.4 as +130mV (vs normal hydrogen electrode, NHE) for PIH and +136mV(vs NHE) for SIH. These redox potentials are much higher than those corresponding to iron chelators in clinical use, namely deferiprone, -620mV; desferasirox, -600mV and desferrioxamine, -468mV. Although the positive redox potentials of SIH and PIH are similar to that of EDTA, namely +120mV, the iron complexes of these two hydrazone chelators, unlike the iron complex of EDTA, do not redox cycle in the presence of vitamin C. These properties render PIH and SIH as excellent scavengers of iron, under biological conditions. Both SIH and PIH scavenge mononuclear iron(II) and iron(III) rapidly. These fast kinetic properties of the hydrazone-based chelators provide a ready explanation for the adoption of SIH in fluorescence-based methods for the quantification of cytosolic iron(II).

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“…It can be due to the relationships between the pK a values and those structures, which may help studies in drugs design and also explain the biopharmaceutical properties of substances (Duran, Aydemir, 2012;Barbosa et al, 2001). There are several experimental methods for determining the acidity constants in aqueous solutions for example, conductometry, spectrophotometric, capillary electrophoresis, calorimetric adsorption, potentiometric titration, HPLC, solubility, partition and distribution (Reijenga et al, 2013;Heinze, 1984;Thurlkill et al, 2005;Santos et al, 2010). In addition to experimental methods, theoretical prediction of the pKa values has received considerable attention and many studies have been carried out on this topic in recent years (Kelly, Cramer, Truhlar, 2006;Ho, Coote, 2010).…”

Section: Introductionmentioning

confidence: 99%

Theoretically nanoscale study on ionization of muscimol nano drug in aqueous solution

Kiani

Abbaszadeh

Pousti

et al. 2015

Braz. J. Pharm. Sci.

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In the present work, acid dissociation constant (pK a ) values of muscimol derivatives were calculated using the Density Functional Theory (DFT) method. In this regard, free energy values of neutral, protonated and deprotonated species of muscimol were calculated in water at the B3LYP/6-31G(d) basis sets. The hydrogen bond formation of all species had been analyzed using the Tomasi's method. It was revealed that the theoretically calculated pK a values were in a good agreement with the existing experimental pK a values, which were determined from capillary electrophoresis, potentiometric titration and UV-visible spectrophotometric measurements.Uniterms: Nanodrug. Muscimol. Acid/dissociation constants. Computational chemistry. Density Functional Theory.No presente trabalho, calculou-se a constante de dissociação do ácido (pK a ) dos derivados de muscimol, utilizando-se o método da teoria do funcional de densidade (DFT). Com esse objetivo, calcularam-se os valores das espécies neutra, protonada e desprotonada do muscimol em água em base B3LYP/6-31G(d). A formação da ligação de hidrogênio de todas as espécies foi analisada utilizando o método de Tomasi. Demonstrou-se que os valores de pKa calculados teoricamente estavam em boa concordância com os valores experimentais disponíveis, determinados por eletroforese capilar, titulação potenciométrica e medidas por espectrofotometria UV-visível.Unitermos: Nanofármaco. Muscimol. Ácido/constantes de dissociação. Química computacional. Teoria do funcional de densidade.

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Potentiometric and conductimetric studies of chemical equilibria for pyridoxine hydrochloride in aqueous solutions: simple experimental determination of pKa values and analytical applications to pharmaceutical analysis

Cited by 27 publications

References 13 publications

Aspects of Weak Interactions between Folate and Glycine Betaine

Aspects of Weak Interactions between Folate and Glycine Betaine

The interaction of pyridoxal isonicotinoyl hydrazone (PIH) and salicylaldehyde isonicotinoyl hydrazone (SIH) with iron

Theoretically nanoscale study on ionization of muscimol nano drug in aqueous solution

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