Medium effect on the second-stage dissociation constant of N-(2-acetamido)imino diacetic acid (H₂ADA)

Abstract

The second-stage dissociation constant values of N-(2-acetamido)imino diacetic acid (H2ADA) were determined at 25 ± 0.1 °C by potentiometric titration in different mixed-solvent mixtures (methanol, ethanol, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, and dioxane). It was observed that the pKa value is slightly influenced as the solvent is enriched in methanol and ethanol, and remains practically constant in the presence of different amounts of DMF and DMSO. A prounounced change in the pKa value was observed as the solvent is enriched in acetone or dioxane. These results are discussed in terms of various solvent characteristics. It is concluded that the electrostatic effect has only a relatively small influence on the dissociation equilibrium of the imino group [Formula: see text]. Other solvent effects such as solvent basicity, different stabilization of the free base of the conjugate acid by hydrogen bonding interactions in aquoorganic solvent media relative to pure aqueous media, as well as proton–solvent interaction play an important role in the acid dissociation equilibrium.

Thermodynamics of the second-stage dissociation of 2-[N-(2-hydroxyethyl)-N-methylaminomethyl]-propenoic acid (HEMPA) in water at different ionic strength and different solvent mixtures

“…Other investigators reported similar results for (CAPS and CAPSO) [6], (BES) [7], (ACES and CHES) [8], TRICINE [9], TES [10], ADA [11,12], (HEPPS and MOPSO) [13], (MOPS) [14], and (MOBS and HEPBS) [15]. These studies have provided precise knowledge about the thermodynamic quantities associated with the dissociation process as well as about the suitability of a biological buffer.…”

Medium Effect on the Apparent Dissociation Constants of Guanine, Thymine, Uracil, Hypoxanthine, and Cytosine in Various Hydroorganic Media

“…The literature is yet limited in terms of the acid base properties of guanine, hypoxanthine, cytosine, uracil, or thymine in hydroorganic media. This contribution reports the solvent effect on the acid dissociation constants of the previous nucleobases as a continuation of the authors' work on the dissociation constants of biologically important compounds. − …”

Potentiometric determination of the second-stage dissociation constants of some hydrogen ion buffers for biological research in various water + organic solvent mixtures

“…Zwitterionic buffers-comparable to amino acids-show significant advantages over conventional buffers: insignificant penetration through a biological membrane, maximum buffer capacity at the physiological pH range 6.0-8.50, and no enzyme substrate or enzyme inhibitor properties. Though studies on the dissociation constants of acids and bases in mixed and nonaqueous solvents have been extensively investigated, relatively little work has been done to determine the dissociation constants of the biologically important zwitterionic buffers (2)(3)(4)(5)(6)(7).…”