Protonation of Tetrakis(4-sulfonatophenyl)porphyrin in Aqueous Solutions of Acetonitrile and Dioxane

Abstract

The protonation constants of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin were determined in binary mixtures of water with acetonitrile and 1,4-dioxane at 25°C and 0.1 mol·dm −3 sodium perchlorate. The pK a values decrease with addition of organic solvent to the media. The lack of a significant relationship between the protonation constants and dielectric constant of these solvent mixtures reveals the existence of specific solute-solvent interactions. Therefore the solvent effects were analyzed in terms of linear solvation energy relationships using the model of Kamlet, Abboud and Taft (KAT). Multiple linear regressions correlated the protonation constants with the microscopic parameters α (hydrogenbond acidity), π * (dipolarity/polarizability) and β (hydrogen-bond basicity). In the all cases, an equation with two solvatochromic parameters gave the best correlations. For pK 1 values, the most significant parameters were found to be α and π * , whereas for pK 2 values, π * and β were the most predominant descriptors.

Solvent Effects on the Dissociation Constants of Hydroxyflavones in Organic–Water Mixtures. Determination of the Thermodynamic pKa Values by UV–Visible Spectroscopy and DFT Calculations

“… a Notation: w , organic solvent fraction (w/w); α, hydrogen-bond donor capacity of the solvent mixtures. b Reference ; D , solvent relative permittivity at 298.15 K. c Reference . d Reference . e Reference and R 2 is the square regression coefficient of the least-squares linear fit. The standard uncertainties u are u ( w ) = 0.001, u ( T ) = 0.01 K. Values in parentheses are standard fitting deviations at the 95 % confidence level. …”

“…Now, the stock solution of 7­(OH)­Fl was prepared in ACN and the buffer solutions of pH 6.20 to 8.0, pH 2, and pH 13 were prepared in ACN-W mixtures ( w ACN = 0.118, 0.136, 0.175, 0.214 and 0.280). The relative permittivity values of these solutions were 74.12, 73.39, 71.67, 69.85 and 66.61, respectively. The analytic concentration of 7­(OH)­Fl in these standard solutions was 3.29·10 –5 mol·kg –1 .…”

Solvent effect on protonation of tpps in water-DMF mixtures

“…In continuous of our previous studies on porphyrin [12][13][14][15][16][17], in this work the protonation constants of 5,10,15,20-tetrakis(4-sulfonatophenyl) porphyrin were determined by spectroscopic titration in binary mixtures of water with N,N-dimethylformamide, DMF, to examine the solvent dependence of its acid-base properties. Spectroscopic titration is a convenient way for accurate determination of equilibrium constants [18][19][20].…”