Synthesis, Spectral Characterization and Potential Fluorescent Properties of Three Lanthanide(III) Ions Complexes with Nalidixic Acid.

Three new solid lanthanide complexes with nalidixic acid (HNal) with the stoichiometry [Ln(Nal)3]·5·.5H2O (Ln = Tb, Dy and Ho) were synthesized applying the green synthesis method from the aqueous solutions without the organic solvent addition and fully characterized by the elemental analysis, XRF, complexometric titration, gravimetric analysis, molar conductivity and solubility measurements, powder X-Ray diffraction, UV-Vis and infrared (FT-IR) spectroscopies. Moreover, the luminescent properties of the Tb(III), Dy(III), and Ho(III) complexes in the solid state and in the solutions were investigated. On the basis of the detailed spectral analysis, it was concluded that the nalidixate ligands bind to the lanthanide ions by the bidentate carboxylate and carbonyl groups while water molecules belong to the outer coordination sphere. At the excitation of UV light, the complexes exhibited characteristic emission of central lanthanide ions, the intensity of which depends significantly on the excitation wavelength and/or the solvent. Thus, the application of nalidixic acid (apart from biological activity) for the synthesis of luminescent lanthanide complexes was confirmed which can find potential applications in the field of photonic devices and/or bioimaging agents.

Analysis of adsorption energy distribution in selected hydrophilic-interaction chromatography systems with amide, amine, and zwitterionic stationary phases.

Adsorption mechanisms of caffeine, quercetin, and phenol as test substances in various chromatographic systems have been analyzed. The investigations were conducted using three different chromatographic columns packed with polar bonded stationary phases, that is, amide, amine, and zwitterionic. Methanol-water and acetonitrile-water systems with different organic solvent contents have been used as mobile phases. On the basis of adsorption isotherms obtained for the tested systems, Scatchard plots and adsorption energy distributions have been determined. The most likely retention mechanisms have been discussed. The results of investigations indicate that (i) the surfaces of tested adsorbents are energetically heterogeneous, and (ii) the main role in sorption mechanism is played by low-energy sites.

Tautomeric and Microscopic Protonation Equilibria of Anthranilic Acid and Its Derivatives.

The acid-base chemistry of three zwitterionic compounds, namely anthranilic (2-aminobenzoic acid), N-methylanthranilic and N-phenylanthranilic acid has been characterized in terms of the macroconstants Ka1, Ka2, the isoelectric point pHI, the tautomerization constant Kz and microconstants k11, k12, k21, k22. The potentiometric titration method was used to determine the macrodissociation constants. Due to the very poor water solubility of N-phenylanthranilic acid the dissociation constants pKa1 and pKa2 were determined in MDM-water mixtures [MDM is a co-solvent mixture, consisting of equal volumes of methanol (MeOH), dioxane and acetonitrile (MeCN)]. The Yasuda-Shedlovsky extrapolation procedure has been used to obtain the values of pKa1 and pKa2 in aqueous solutions. The pKa1 and pKa2 values obtained by this method are 2.86 ± 0.01 and 4.69 ± 0.03, respectively. The tautomerization constant Kz describing the equilibrium between unionized form ⇌ zwitterionic form was evaluated by the Kz method based on UV-VIS spectrometry. The method uses spectral differences between the zwitterionic form (found at isoelectric pH in aqueous solution) and the unionized form (formed in an organic solvent of low dielectric constant). The highest value of the Kz constant has been observed in the case of N-methylantranilic acid (log10Kz = 1.31 ± 0.04). The values of log10Kz for anthranilic and N-phenylanthranilic acids are similar and have values of 0.93 ± 0.03 and 0.90 ± 0.05, respectively. The results indicate that the tested compounds, in aqueous solution around the isoelectric point pHI, occur mainly in the zwitterionic form. Moreover, the influence of the type of substituent and pH of the aqueous phase on the equilibrium were analyzed with regard to the formation and the coexistence of different forms of the acids in the examined systems.

Studies on equilibrium of anthranilic acid in aqueous solutions and in two-phase systems: aromatic solvent-water.

The acid-base equilibria of anthranilic acid have been characterized in terms of macro- and microdissociation constants (dissociation constants K(a1), K(a2) and tautomeric constant K(z)). On the basis of spectrophotometric investigations the values of the distribution ratio D of anthranilic acid in the two-phase systems: aromatic solvent (benzene, ethylbenzene, toluene, chlorobenzene, bromobenzene)-aqueous solution were obtained. Employing the results of potentiometric titration in the two-phase systems: aromatic solvent-aqueous solution the distribution constant K(D) and dimerization constant K(dim) values were calculated. The influence of organic solvent polarity and pH of the aqueous phase on the contents of the particular forms of the acid in the two-phase systems were analyzed.

Studies on the distribution of N-phenylanthranilic acid in two-phase system: Aromatic solvent-water.

The detailed description of equilibria of N-phenylanthranilic acid in the aqueous solutions and in the two-phase systems: aromatic solvent-aqueous solution were obtained. The isoelectric point, pH(I), the dissociation constants of the protonated form, K(a1), and the neutral form, K(a2), in the aqueous solutions were determined from the apparent ionization constant in methanol-water solutions of various proportions by extrapolation to zero co-solvent using Yasuda-Shedlovsky procedure. On the basis of the spectrophotometric investigations, the values of the distribution ratio, D, of N-phenylanthranilic acid in the two-phase systems: aromatic solvent (benzene, ethylbenzene, toluene, chlorobenzene, bromobenzene)-aqueous solution were obtained. Employing the results of the potentiometric titration in the two-phase systems: aromatic solvent-aqueous solution, and using models of singular and multistep equilibria the values of the distribution constants, K(D), dimerization constants, K(dim), were calculated. The significant influence of the polarity of the applied aromatic solvents and pH of the aqueous phase on the percentage of the particular forms of N-phenylanthranilic acid in the two-phase systems was proved.