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Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·L−1 KNO3 for the interaction of Eu–Glycylhistidine (Glyhis) with five biologically important zwitterionic buffers (Z) (HEPES, EPPS, PIPES, POPSO and HEPPSO). The formation constants for the binary Eu(III) + Glyhis or Eu(III) + Z systems and ternary Eu(III) + Glyhis + Z systems have been evaluated, and the lowest value for formation constant is assigned to the system Eu(III) + Glyhis + PIPES. The electrochemical behavior of the Eu–Glyhis complex with selected zwitterionic buffers was studied on the surface of a glassy carbon electrode using cyclic, differential pulse and square wave voltammetric techniques. The values of the standard heterogeneous rate constant (K s), diffusion coefficients of the reduction (D red) and oxidation (D ox) processes were calculated for all the studied systems. The data reveal that PIPES is the most suitable of these zwitterionic buffers for study of the biological behavior of Glycylhistidine in its europium complexes.

The formation of binary and ternary model complexes of Eu(III) with the nucleobases 5-aminouracil (5-amino 2,4-dioxy pyrimidine), dihydrouracil (5,6-dihydro-2,4-dioxy pyrimidine), thymine (2,4-dihydroxy 5-methyl pyrimidine), adenine (6-aminopurine), uracil (2,4-dioxy pyrimidine), and PIPES (piperazine 1,4-bis(2-ethane sulfonic acid) dissodium salt) has been studied potentiometrically at (25.0 ± 0.1) °C and at an ionic strength of I = 0.1 mol·dm−3 (KNO3). The formation of the 1:1, 2:1 binary, and 1:1:1 and 2:1:1 ternary complexes is inferred from the corresponding titration curves. Initial estimates of the formation constants of the resulting species and the protonation constants of the different ligands used have been refined with the SUPERQUAD computer program. The experimental conditions were selected such that self-association of the nucleobases and their complexes was negligibly small; that is, the monomeric and protonated complexes were studied. Recognition of nucleobases and CT-DNA by the luminescen...

The interaction of Eu(9-ANCA)3 (9-ANCA = anthracene-9-carboxylic acid) with DNA has been investigated by a fluorescence method. Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·dm−3 KNO3 for the interaction of Eu(III) and 9-ANCA with adenosine 5′-diphosphate (ADP), adenosine 5′-triphosphate (ATP), N-acetyl glutamic acid (Nc-Glu), N-acetyl leucine (Nc-Leu), and N-acetyl lysine (Nc-Lys) in a 1:1:1 ratio. The formation of various mixed ligand complexes was inferred from the potentiometric titration curves. The formation constants of the binary and ternary complexes have been refined with the SUPERQUAD computer program. The interaction of Eu(III)-(9-ANCA) with Nc-Glu, Nc-Leu, and Nc-Lys has been investigated by electroanalytical methods including cyclic voltammetry (CV), differential pulse polarography (DPP), and square wave voltammetry (SWV) on a glassy carbon (GC) electrode.

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·dm−3 KNO3 for the interaction of the biologically important ligands N-acetylhistidine, N-acetyl l-leucine, N-acetylglutamic acid, N-acetylhistamine, N-acetylaspartic acid, and La(III), Gd(III), Sm(III), Tb(III), Eu(III), and Dy(III) with the nucleotides guanosine 5′-monophosphate (5′-GMP), cytedine 5′-monophosphate (5′-CMP), inosine 5′-monophosphate (5′-IMP), adenosine 5′-monophosphate (5′-AMP), adenosine 5′-diphosphate (5′-ADP), adenosine 5′-triphosphate (5′-ATP), and cytedine 5′-triphosphate (5′-CTP) in 1:1:1 and 1:2:1 ratios. The formation constants of various mixed ligand complexes were inferred from the potentiometric titration curves. Initial estimates of the formation constants of the resulting species and the formation constants of the different N-acetyl amino acid (NAA) and nucleotide (NU) complexes in metal ligand ratios 1:1 and 2:1 have been refined with the SUPERQUAD computer program. ...

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·dm-3 (KNO3) for the interaction of guanine (2-amino-6-oxypurine), thymine (2,4-dihydroxy-5-methylpyrimidine), adenine (6-aminopurine), uracil (2,4-dioxypyrimidine), hypoxanthine (6-oxypurine), and Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Ca(II), and Mg(II) with the biologically important secondary ligands glycine (aminoethanoic acid), bicine [N,N-bis(2-hydroxyethyl)glycine], tricine [N,N,N-tris(hydroxymethyl)methylglycine], and ADA [N-(2-acetamido)-3-iminodiacetic acid] in a 1:1:1 ratio. The experimental conditions were selected such that self-association of the nucleobases and their complexes was negligibly small; that is, the monomeric normal and protonated complexes were studied. The formation of various 1:1:1 mixed ligand complexes was inferred from the potentiometric titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants of g...

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 KNO3 for the interaction of adenosine 5‘-monophosphate, guanosine 5‘-monophosphate, cytidine 5‘-monophosphate, and La(III), Ce(III), Pr(III), and Eu(III) with the biologically important secondary ligand zwitterionic buffers (3-[N-morpholinol])-2-hydroxypropanesulfonic acid, 2-(N-morpholino)ethanesulfonic acid, N-2-acetamido-2-aminoethanesulfonic acid, and N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid. Measurements were made in a 1:1:1 ratio. Formation constants for the monohydroxy, dihydroxy, and dimeric ligand complexes for the binary systems Ln(III) + adenosine 5‘-monophosphate, Ln(III) + guanosine 5‘-monophosphate, Ln(III) + cytidine 5‘-monophosphate, and Ln(III) + zwitterionic buffers have been evaluated. The formation of various 1:1:1 normal and protonated mixed ligand complex species was inferred from the potentiometric pH-titration curves. The experimental conditions were selected...

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 KNO3 for the interaction of the purine nucleotides adenosine 5‘-mono, 5‘-di, and 5‘-triphosphate and Cu(II), Co(II), Ni(II), Mn(II), Zn(II), Ca(II), and Mg(II) with the biologically important secondary ligand zwitterionic buffers 3-(N-morpholino)propanesulfonic acid, 3-[(1,1-dimethyl-2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid, N-(2-hydroxyethyl)piperazine-N‘-2-hydroxypropanesulfonic acid, piperazine-N,N‘-bis(2-ethanesulfonic acid), and piperazine-N,N‘-bis(2-hydroxypropanesulfonic acid) in a 1:1:1 ratio and the formation of various 1:1:1 normal and protonated mixed-ligand complex species was inferred from the potentiometric pH titration curves. The experimental conditions were selected such that self-association of the purine nucleotides and their complexes was negligibly small; i.e., the monomeric normal and protonated ternary complexes were studied. Initial estimates of the formatio...

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 (KNO3) for the interaction of guanosine 5‘-monophosphate, inosine 5‘-monophosphate...

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 KNO3 for the interaction of adenosine 5‘-mono-, 5‘-di-, and 5‘-triphosphate and Cu(II), Co(II), Ni(II), Mn(II), Zn(II), Ca(II), and Mg(II) with the biologically important secondary ligand zwitterionic buffers 3-[N-bis(hydroxyethyl)amino]-2-hydroxypropanesulfonic acid, 3-[N-tris(hydroxymethyl)methylamino]-2-hydroxypropanesulfonic acid, (3-[N-morpholinol)-2-hydroxy propanesulfonic acid, N-(2-acetamido)-2-aminoethanesulfonic acid, and 2-(cyclohexylamino)ethanesulfonic acid in a 1:1:1 ratio, and the formation of various 1:1:1 normal and protonated mixed ligand complex species was inferred from the potentiometric pH titration curves. The experimental conditions were selected such that self-association of the nucleotides and their complexes was negligibly small; i.e., the monomeric normal and protonated ternary complexes were studied. Initial estimates of the formation constants of the resulting sp...

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 (KNO3) for the interaction of glycine (aminoethanoic acid), serine (2-amino-3-hydroxypropanoic acid), methionine (2-amino-4-(methylthio)butanoic acid), aspartic acid (aminobutanedioic acid), glutamic acid (2-aminopropanedioic acid), and histidine (α-amino-1H-imidazole-4-propanoic acid) and Cu(II), Co(II), Ni(II), Mn(II), and Zn(II) with the biologically important secondary ligand zwitterionic buffers β-hydroxy-4-morpholinepropanesulfonic acid (MOPSO), 4-morpholinepropanesulfonic acid (MOPS), 3-[bis(2-hydroxyethyl)amino]-2-hydroxy-1-propanesulfonic acid (DIPSO), and 3-[N-tris(hydroxymethyl)methyl)amino]-2-hydroxypropanesulfonic acid (TAPSO) in 1:1:1 and 1:1:2 ratios, and the formation of various 1:1:1 ternary complexes and 1:1:2 quaternary complex species was inferred from the potentiometric pH titration curves. Initial estimates of the formation constants of the resulting species and the acid...

The apparent second stage dissociation constants of piperazine-N,N-bis[2-hydroxypropanesulfonicacid] (POPSO), N-[2-hydroxyethy1]piperazine-N‘-3-propane sulfonic acid (HEPPS), 2-[N-cyclohexylamino]ethanesulfonic acid (CHES) and mono[tris(hydroxymethyl)aminomethane] phosphate (Trizma) were determined at (25.0 ± 0.1) °C and I = 0.1 mol dm-3 (KNO3) by potentiometric pH titration in pure water and different hydroorganic solvent media. The organic solvents used were methanol and ethanol as amphiprotic hydrogen bond acceptor−donor (HBA-D) solvents, N,N-dimethylformamide (DMF), dimethy1 sulfoxide, acetone, and dioxane as hydrogen bond acceptor solvents, and acetonitrile as an HBA−HBD solvent. The ESAB2M computer program was used to refine the initial estimates of the apparent second-stage dissociation constants of the four zwitterionic buffers studied. pka2* values change with increasing organic content of the solvent mixture. The results obtained are discussed in terms of average macroscopic properties of the mi...

The apparent second-stage dissociation constants of 3-(N-morpholino)propanesulfonic acid, 3-[(1,1-dimethyl-2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid, and N-(2-hydroxyethyl)piperazine-N‘-(2-hydroxypropanesulfonic acid) were determined at (25.0 ± 0.1) °C and I = 0.1 mol dm-3 (KNO3) by potentiometric pH titration in pure water and different hydroorganic solvent media. The organic solvents used were methanol, ethanol as amphiprotic hydrogen bond acceptor−donor (HBA-D) solvents, N,N-dimethylformamide, dimethyl sulfoxide, acetone, dioxane as hydrogen bond acceptor solvents, and acetonitrile as (HBA-HBD) solvent. The ESAB2M computer program was used to refine the initial estimates of the apparent second-stage dissociation constants of the three zwitterionic buffers studied. pKa2* values change with increasing organic content of the solvent mixture. The results obtained are discussed in terms of average macroscopic properties of the mixed solvents. The implications of the results with regard to specific...

The apparent dissociation constants of 3-[N-(tris(hydroxy methyl)methyl)amino]-2-hydroxypropane sulfonic acid (TAPSO), 3-[N,N-bis(2-hydroxyethyl)amino]-2-hydroxypropane sulfonic acid (DIPSO), and 3...

The apparent dissociation constants of 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS) and 3-(cyclohexylamino)-2-hydroxy-1-propanesulfonic acid (CAPSO) were determined at (25.00 ± 0.10) °C and I = 0.1 mol dm-3 KNO3 by potentiometric pH titration in pure water and different hydroorganic solvent media. The organic solvents used were methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, acetone, and dioxane. Initial estimates of the apparent dissociation constant values of the two zwitterionic amino propanesulfonic acid buffers studied have been refined with the ESAB2M computer program. pKa2* values change with an increase in the concentration of organic solvent. The results obtained are discussed in terms of average macroscopic properties of the mixed solvents and the possible variation in microheterogenity of the solvation shells around the solute.

The apparent dissociation constants of malic acid (hydroxybutanedioic acid), tartaric acid (2,3-dihydroxybutanedioic acid), phthalic acid (1,2-benzenedicarboxylic acid), and succinic acid (butane-1,4-dioic acid) were determined at 25 °C and ionic strength I = 0.10 mol dm-3 KNO3 by potentiometric pH titration in pure water and water + methanol, water + ethanol, water + N,N-dimethylformamide, water + dimethyl sulfoxide, and water + acetonitrile. pKa values increase with an increase in the concentration of the organic solvents. These results are discussed in terms of solvent characteristics. Solvent basicity and stabilization of the conjugate acid free base by hydrogen-bonding interactions in hydroorganic solvent media relative to pure aqueous media as well as proton−solvent interaction play an important role in the acid dissociation equilibrium.

The dissociation constant of acetic acid, benzoic acid, 3-phenylpropenoic acid, 2-methylpropionic acid, and pentanoic acid were determined at 25.0 °C (I = 0.1 mol dm -3 KNO 3 ) by potentiometric pH titration in pure water and water + methanol, water + ethanol, water + dimethylformamide, water + dimethyl sulfoxide, and water + acetonitrile. pK a values increase with an increase in the concentration of the organic compounds. These results are discussed in terms of solvent characteristics. Solvent basicity and stabilization of the conjugate acid free base by hydrogen-bonding interactions in hydroorganic solvent media relative to pure aqueous media as well as proton-solvent interaction play an important role in the acid dissociation equilibrium.