Acid-base and complexation properties of gem-diphosphonic and gem-diphosphinic acids in aqueous solutions and micellar media of surfactants

Abstract

Acid base and complexation properties of gem disubstituted phosphorus acids, viz., methylenediphosphonic, 1 hydroxyethylidene 1,1 diphosphonic, P,P´ diphenylmethylene diphosphinic, and P,P´ diphenyl 1 hydroxyethylidene 1,1 diphosphinic acids, were studied in aqueous solutions and in the presence of biomimetics (micelles of ionic surfactants). The dissociation constants of the acids and stability constants of complexes with magnesium(II) and copper(II) ions were determined in aqueous solutions and microheterogeneous media contain ing sodium dodecyl sulfate, cetylpyridinium chloride, or cetylpyridinium nitrate (ionic strength 0.1 mol L -1 , temperature 25 °С).

Re-evaluated data of dissociation constants of alendronic, pamidronic and olpadronic acids

“…This was done because the problem of ionic strength calculation for micellar solutions has not been resolved, although it is known that ionic strength in micellar solutions is somewhat lower than total concentration of ionic surfactant [40]. The micellar media effect on pK a3 , pK a4 , pK a5 of investigated acids agreed with obtained in work [23] for structurally related gem-diphosphonic acids. The shift of pK a3 is especially important for developing a method of titrimetric determination of alendronate by acid-base titration.…”

“…The three dissociation constants of olpadronic and pamidronic acids were calculated by titration of their solutions with concentration 1.00 × 10 -3 М with 4.00 × 10 -3 М KОН. The potassium hydroxide was used as titrant to prevent the formation of complexes with Na + that was observed for some bisphosphonic acids [23,25]. The concentration of KCl as supporting electrolyte was 0.10 M for titrations in aqueous solutions.…”

“…The standard solutions of NaOH are often used for routine analysis in pharmaceutical laboratories because their carbonate-free solutions can be prepared more easily than KOH solution [24]. However, some bisphosphonic acids form complexes with sodium ions that influence on shape and localization of titration curve [22,23]. These effects were investigated by comparison 3.1 Dissociation constants of alendronic, olpadronic and pamidronic acids in aqueous solution 3.2 Effect of CPC micellar media on protolytic properties of aminobisphosphonic acids 3.3 Determination of sodium alendronate in pharmaceutical substance and tablets (1) of titrations of sodium alendronate by 0.0100 M NaOH solution or (С 2 Н 5 ) 4 NOH solution, which cation can not form complexes with bisphosphonic acids [25].…”

“…This should confirm or reject the possibility of sodium alendronate determination by acid-base titration in aqueous solutions. The dissociation constants of alendronic, olpadronic and pamidronic acid were also determined in micellar solutions of cationic surfactant cetylpyridinium chloride (CPC), because it is known that the strength of an acid increases in the presence of cationic micelles [23]. This observation allows the development of simple titrimetric methods of aminobisphosphonates determination in pharmaceutical formulations.…”

Synthesis of glycolurils and hydantoins by reaction of urea and 1, 2‐dicarbonyl compounds using etidronic acid as a “green catalyst”

“…To explain the observed changes, we believe that the initial stage includes the process of complete hydration of glyoxal 2a in water with the formation of bishemdiol 2a' (Figures S7 and S8 in Data S1) and then HEDP, that is prone to hydrate formation, [ 45 ] binds one water molecule to the formation of an intermediate complex A (Scheme 2, Figures 1 and 2), which is stabilized due to the appearance of a developed system of hydrogen bonds.…”