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Chemical equilibria in aqueous solutions of disodium adenosinetriphosphate (Na2H2ATP), high-molecular-weight heparin (H4Hep) and Na2H2ATP and in MCl2-H4Hep-Na2H2ATP-H2O-NaCl (M = Ca2+ or Mg2+) solutions in the 0.15 M NaCl background were studied using computer simulation and pH titration at 2.3 ≤ pH ≤ 10.5. Formation constants were determined for two protonated ATP species, three protonated complex species of heparin with ATP of equimolar stoichiometry, and mixed-ligand calcium and magnesium complexes with heparin and adenosinetriphosphate. The formation constants for mixed-ligand calcium(II) complexes with heparin are more than two times those of homoligand calcium complexes with heparin. As a result, the Ca2+ ion concentration at 6.8 ≤ pH ≤ 7.4 (the pH range of blood plasma stability) decreases from 40 to 100 wt % depending on the ratio of the initial concentrations of CaCl2, H4Hep, and Na2H2ATP. [ABSTRACT FROM AUTHOR]

Chemical equilibria in the heterogeneous system Tb(NO3)3-H2O, physiological saline solutions containing terbium nitrate, and unfractionated heparin ((H4L) Tb(NO3)3-H4L-H2O-NaCl), and solutions containing calcium chloride, terbium nitrate, and unfractionated heparin (CaCl2-Tb(NO3)3-H4L-H2O-NaCl) were studied by mathematical modeling and pH titration. A physicochemical model was designed for two-phase equilibria in the system Tb(NO3)3-H2O, which consists of an aqueous solution and a solid phase of precipitated terbium hydroxide. Formation constants were calculated for terbium hydroxide ions Tb(OH) ( i = 1, 2, 3) in an aqueous phase, and a correlation was found between the amount of precipitated Tb(OH) and pH. The four-component solution Tb(NO3)3-H4L-H2O-NaCl in the range 2.3 ≤ pH ≤ 10.4 is homogeneous; as a result of its investigation, the formation constants were ascertained for significant terbium complexes with heparin: TbL, TbHL, and Tb(OH)2L3−. Chemical equilibria in the five-component solution CaCl2-Tb(NO3)3-H4L-H2O-NaCl were modeled proceeding from the models developed for equilibria in the four-component solution subsystems Tb(NO3)3-H4L-H2O-NaCl and CaCl2-H4L-H2O-NaCl. The modeling showed that the Tb3+ ion is an efficient competitive complex former to the Ca2+ ion, which forms complexes with heparin, and decreases tenfold the concentration of the major complex NaCaL at 6.8 ≤ pH ≤ 7.4 (the pH range of blood plasma stability). [ABSTRACT FROM AUTHOR]