Apparent Stability Constant Of Complex Research Articles

The Influence of Cyclodextrin and pH on the Solubility of Ketoprofen

Cyclodextrin complexation and pH adjustments have been reported as useful tools to increase the solubility of drug. The aim of this study was to investigate the influence of both cyclodextrin and pH on the overall solubility of ketoprofen. β-cyclodextrin (β-CD) and hydroxypropyl β-cyclodextrin (HP-β-CD) were used for the preparation of inclusion complex by shaking method in aqueous solution at pH 2, 5, 7 and 10. It was found that the solubility of ketoprofen significantly increased with increasing pH and cyclodextrin concentration, showing AL type phase solubility diagram. However, the apparent stability constant of complex (KC) was found to decrease with increasing pH due to the decreased affinity of ionized drug to cyclodextrin cavity. The ionization of ketoprofen increased when the pH was raised, corresponding with its higher zeta potential. The result indicated that the solubility of ketoprofen could be improved by using a combined approach of pH adjustments and complexation with cyclodextrin. Moreover, the unionized drug that was formed by pH adjustments interacted with cyclodextrin more strongly than the ionized drug.

Influence of Sodium Dodecyl Sulfate on the Protolytic Properties of N,N-Dimethyl-N′-(2-hydroxybenzyl) Ethylenediamine and Its Complexation with Copper(II)

To investigate the effect of sodium dodecyl sulfate (concentration Cs = 5 and 10 mM) on the acid–base properties of N,N-dimethyl-N′-(2-hydroxybenzyl) ethylenediamine and its complexation with copper(II) (Cs = 10 mM) was studied using the methods of potentiometry, spectrophotometry (at 298 K), and mathematical simulation of equilibria in solutions. The sodium dodecyl sulfate contributes to the formation of a monomeric form of N,N-dimethyl-N′-(2-hydroxybenzyl)ethylenediamine, while this compound exists in 40% isopropyl alcohol predominantly in the form of a dimer. The acidic properties of protonated monomeric and dimeric species are weaker than those in an aqueous alcohol solution. Sodium dodecyl sulfate facilitates the coordination of the deprotonated form of ligand. The region of the predominant accumulation of an uncharged complex of 1 : 2 composition is shifted to lower pH values (11.0 and 7.5, respectively), whereas the molar absorption coefficient of the complex increases by approximately 1.7 times. The apparent stability constants of complexes of the same type increase.

Reaction in ion exchangers. Apparent stability constants of complexes and salting-in (out) effects

Abstract The reaction qS + nTz ⇄ SqTnnZ is considered in ion exchangers. Variations of the apparent stability constants of complexes are shown in three ion exchange membranes. A corrective term KdTST is introduced to take the variations into account. KdTST is compared to a selectivity coefficient relative to a complex (ST) and a complexing counterion (T). The equilibrium distribution of ammonia, Ag+ and NH4+ between a sulfonic membrane (Nafion) and a solution was studied first. With an increase of ammonia concentration, the Ag+ / NH4+ ion exchange isotherms show a change in the order of selectivity. Our hypothesis is that the change in interactions is due to a substitution of molecules of water by molecules of ammonia. Next, the fixation of boric acid by two anion exchange membranes (RPA Rhone Poulenc and Permion) initially in the OH− form was studied. The amounts of sorbed boron and the simultaneous conductivity change are in agreement with the non-formation of triborates and the formation of mono- and bivalent tetra- and pentaborates. With regard to Permion membranes an additional correction (the same KdTST = 0.33 for every polyborate ST referring to borate T) must be made to take account of the lower apparent stability of polyborates. The present study is the first step in the modelling of facilitated transport and extraction involving the species considered above.