Acid Dissociation Constants of 5,5-Diphenylpyrrolidine N-Aroylthioureas and Stability Constants of their Pt(II) and Ni(II) Complexes in Acetonitrile-Water Hydroorganic Solvent

Abstract

In this study, acid dissociation constants of 5,5-diphenylpyrrolidine N-aroylthiourea derivatives, exhibiting anti(myco)bacterial activity, were determined by potentiometric titration in 30% (v/v) acetonitrile-water hydroorganic solventat 25 ± 0.1 °C, at an ionic background of 0.1 mol / L of NaCl using the HYPERQUAD computer program. Three acid dissociation constants were determined for each compound 1a-e and we suggest that these acid dissociation constants are related to the carboxyl, enol and enthiol groups. Stability constants of their Pt(II) and Ni(II) complexes were also determined by potentiometric titration under the same conditions stated above using the HYPERQUAD computer program. The ligands behave as bidentate and bind to the metal atom via the S and O atoms. In various pH conditions, the different complex forms were formulated as ML2, MHL2, MH2L2, MH3L2, MH4L2, MH5L2 and MH-4L2 between Pt 2+ /Ni 2+ ions and 5,5-diphenylpyrrolidine N-aroylthioureas. Stability constants of the complexes show that the ligands 1a-e form complexes with Pt(II) and Ni(II) metals as 2:1. The stability of the complexes formed by the ligands and platinum were found to follow the order: 3d > 3a > 3e > 3c > 3b. The stability of the complexes formed by the ligands and nickel were found to follow the order: 4d > 4c > 4a > 4b > 4e. As a result, generally the platinum complexes formed with these ligands are more stable than their nickel complexes.

Synthesis and Determination of Acid Dissociation Constants of Bis-Acyl Thiourea Derivatives

“…In studies on the determination of pKa values of acyl thiourea derivative compounds, potentiometrically, one pKa value in the range of 9.82-10.19 for each of the benzoylthiourea derivatives in 75:25 (v/v) dioxane-water was reported by Schröder et al (65). In addition, for each 5,5-diphenylpyrrolidine Naroylthiourea compound in 30:70 (v/v) acetonitrilewater, potentiometrically two pKa values, which were in the range of 6.96±0.03 to 7.84±0.04 associated with enol and in the range of 8.29±0.02 to 9.94±0.08 associated with enthiol groups, were reported (66). In other study, for each pyrrolidine Naroylthioureas in 25:75 (v/v) DMSO-water, potentiometrically two pKa values, which were in the range of 5.85±0.08 to 6.06±0.06 associated with enol, in the range of 8.37±0.05 to 8.87±0.05 associated with enthiol groups, and in the range of 10.11±0.03 to 11.62±0.03 associated with NH, were reported (67).…”

Synthesis and Determination of Acid Dissociation Constants in Dimethyl Sulfoxide–Water Hydroorganic Solvent of 5,5-Diphenylpyrrolidine N-Aroylthiourea Derivatives

“…As a continuation of our previous studies (5,41), this study reports the synthesis and determination of acid dissociation constants of 5,5-diphenylpyrrolidine N-aroylthiourea derivatives in dimethyl sulfoxide-water hydro-organic solvent.…”

“…The pKa values of (2S, 4S)-5,5-diphenylpyrrolidine N-aroylthioureas 3a-d were determined potentiometrically in a 25% (v/v) DMSO-water hydro-organic solvent system at 25.0±0.1 °C ( for each N-aroylthiourea compound in a 50% (v/v) dioxane-water mixture. The previous study [41] reported three potentiometrically different pKa values for each (2S, 4S)-5,5diphenylpyrrolidine N-aroylthiourea compound in the 30% (v/v) acetonitrile-water hydroorganic solvent system. The present study suggested that the pKa1 values in the range of 3.49±0.07 to 5.19±0.04 were related to carboxyl, the pKa2 values in the range of 6.96±0.03 to 7.84±0.04 were related to enol, and the pKa3 values in the range of 8.29±0.02 to 9.94±0.08 were related to enthiol groups.…”

EQUILIBRIUM STUDIES ON Ni(II) and Cu(II) COMPLEXES with 4,7- DIMETHYL-1,10-PHENANTHROLINE and ACIDIC AMINO ACIDS in AQUEOUS SOLUTION

“…Aspartic acid (asp) and glutamic acid (glu), being acidic amino acids, play significant roles in the enzyme active centers, along with in sustaining the solubility and ionic character of proteins. Many studies in the literature have focused on experimentally and computationally determining the protonation constant of ligands and their stability constants of the complexes formed with metal ions (6)(7)(8). Recently, we have reported that (1:1) and (1:1:1) palladium(II) and copper(II) complexes of amino acids, 1,10-phenanthroline, and derivatives in aqueous solution (9)(10)(11)(12)(13)(14).…”