Complexation Behavior of Guanine with Th⁴⁺, UO₂²⁺, and Ce³⁺ at Various Temperatures

Abstract

The complexation of guanine with Th4+, UO2 2+, and Ce3+ was investigated using the potentiometric method at a constant ionic strength of I = 0.10 mol·dm−3 (KCl) in aqueous solutions at elevated temperatures. For each metal ion, stability constants were obtained from the pH-metric data using the program HYPERQUAD2006. The formation of monomeric and polymeric species was taken into consideration for each ion at (25, 37, and 45) °C. The thermodynamic parameters for the formation of the guanine complexes were calculated. In conclusion, it is indicated that the values of the stability constants change at various temperatures.

Complex Equilibria in Aqueous Solutions of Chromium(III) with Some Biological pH Buffers

“…The [H] is obtained from potentiometric titration. The ionic product of water (p K w = 13.46 at 310.15 K and ionic strength I = 0.10 mol·dm –3 KCl) was maintained constant during all refinements. The T L : T Cr ratios (1:1, 2:1, or 3:1) used to characterize Cr–(buffer) x -–(OH) y systems, as well as the pH range used in the refinement by the HYPERQUAD program, are presented in Table .…”

Leucine Complexes with Cerium: Stability Constants and Thermodynamic Parameters

“… a The data taken from Teksoz et al’s study b Measurements were taken in the pH range 3.15−10.58 (for 85 data) at 25 °C, 3.75−10.58 (for 82 data) at 37 °C, and 4.52−9.99 (for 82 data) at 45 °C for I = 1.00 mol dm −3 KCl. …”

“…Ligand protonation constants and cerium hydrolysis constants were held constant for all three titrations with leucine. Cerium hydrolysis constants were calculated in a previous study for I = 0.1 . Measurements were carried out to determine the hydrolytic constants of Ce 3+ ion at a 1.00 mol dm −3 ionic strength, and the hydrolysis constants were calculated from obtained data at (25, 37, and 45) °C.…”

“…To determine the hydrolysis constants of the Ce 3+ ion at 1.00 mol dm −3 ionic strength, experiments were designed and carried out at (25, 37, and 45) °C according to the method reported before. The hydrolysis constants of Ce 3+ ion at 0.1 mol dm −3 ionic strength were obtained from a previous study . Finally, the potentiometric results were transferred to HYPERQUAD2006 computer program and stability constants were calculated.…”

“…Errors in fixed values are not introduced in HYPERQUAD, so that error propagation is not considered in optimizing the protonation constants. Statistical data refer to protonation constants: N = total number of experimental data points used; χ 2 = observed statistical parameter based on weighted residuals of the pH readings (values <12.6 indicate a confidence level >95%), σ = ratio of the root-mean-square of the weighted residuals to the estimated error in the actual working conditions (σ V and σ E ) …”