Complete Resolution of the Microscopic Protonation Equilibria of D-myo-Inositol 1,2,6-Tris(phosphate) and Related Compounds by 31P NMR and Potentiometry

Abstract

31P NMR and potentiometric titration experiments allowed the complete microconstant system to be resolved

3‐Hydroxybenzene 1,2,4‐Trisphosphate, a Novel Second Messenger Mimic and unusual Substrate for Type‐I myo‐Inositol 1,4,5‐Trisphosphate 5‐Phosphatase: Synthesis and Physicochemistry

“…Such an effect, noted in many cases, [16,25,[35][36][37] was also ascribed to hydrogen bonding and an increase of the effective local dielectric constant resulting from introduction of the OH-3 group. By considering the interactivity parameters of compound 4, (see Table 1) phosphate-1 and phosphate-2 strongly interact.…”

“…[7] Potentiometric studies and NMR determinations of compounds 2 and 4: Potentiometric and NMR experiments were carried out as reported previously. [16,37] The experiments were performed in two steps; the solution concentration of compounds 2 and 4 was approximately 3 10 À3 mol dm À3 and they were subjected to potentiometric and …”

“…For benzene polyphosphates, 31 P NMR spectroscopy is a good method to study individual protonation, [16][17][18][19][20][21][22][23][24][25][26][27] provided the observed chemical shifts for the phosphorus resonances mainly depend on the electronic effects accompanying the variations in the protonation states. [16,23,[28][29][30][31][32] In this case, the protonated fraction f i,p of a phosphate group in position i on the benzene polyphosphate can be calculated by the equation below:…”

“…We have previously demonstrated that for trifunctional compounds, [16] the individual protonation fractions f i,p may be expressed as a function of the macro-and micro-protonation constants, allowing the determination of the latter ones by nonlinear regression. The microconstants may also be obtained using the criteria on the cluster expansion method by Borkovec et al [33] This study was performed in 0.2 mm KCl at 37 8C, a medium that mimics the ionic strength and temperature conditions encountered in cells.…”

“…To account for the extent of interaction between phosphate groups, we previously proposed the calculation of interactivity parameters. [16] Thus, the equation, Dlog k 1À2 = log k 1 À log k 21 = log k 2 Àlog k 12 characterises the interaction between phosphate-1 and phosphate-2. The calculated parameters, reported in Table 1 indicate that no preferential interaction between the three phosphates can be proposed from the microconstants in most of the pH range.…”