Calcium hydroxy palmitate: Possible precursor phase in calcium precipitation by palmitate

Calcium(II) precipitates with palmitate (Pal(-)), a process affecting calcium absorption in the gut, in a first-order reaction, as followed by a calcium electrode in neutral aqueous solution for excess of calcium(II), with a rate constant showing a minimum at physiological ionic strength of 0.32 +/- 0.09 d(-1) at 25 degrees C with a stoichiometry of 1.79 +/- 0.03, lower than the expected 1:2. During ageing of precipitate, pH increases in the supernatant, while pH decreases for precipitation with excess of palmitate. Increasing pH, as in some aged food products, decreases the solubility, and K-sp' = [Ca2+[Pal(-)][OH-] is found constant rather than K-sp = [Ca2+][Pal(-)](2) in agreement with an initial precipitation of Ca(OH)(Pal), which slowly may convert into Ca(Pal)(2)center dot Ca(OH)(Pal) has a solubility minimum at physiological ionic strength with K-sp' = (1.4 +/- 0.4)10(-16) M-3. X-ray diffraction showed a d-spacing of 44.15 angstrom (different from 45.2 angstrom reported for Ca(Pal)(2)), and infrared spectroscopy confirmed the presence of a hydroxy group. (C) 2012 Elsevier Ltd. All rights reserved.