Crystal growth of calcium phosphates in the presence of magnesium ions

Abstract

tradiol in 50% v/v methanol/water 0.1 M buffer. However, when the percentage of methanol was reduced to 5% v/v, an adsorptive couple was observed even at "pH" 4.0.Cyclic voltammograms of -estradiol (Figure 16B), the stereoisomer of ß-estradiol in the 17-OH position, under identical conditions to the /3-estradiol experiments, showed significant differences in position and shape of the adsorptive responses relative to that of ß-estradiol (Figure 16A). Oestrone (a phenolic steroid not possessing a 17-OH group) did not show any peaks at all in CV. Obviously the addition of the 17-OH group played an important role in the manifestation of the capacitative phenomena observed in CV as did the 3-OH group of the "A" ring phenol. ConclusionsThe electron-transfer reactions of acetylenic steroid hormones at the mercury electrode are strongly influenced by interaction with the electrode surface. The surface interactions in turn are dependent upon the type and orientation of the substituents.The dichotomy in behavior between the oxidation process for the "phenolic" acetylenic steroid ethynylestradiol and the non-phenolic acetylene steroids can be rationalized in terms of their adsorptive properties at the mercury electrode. Phenolic steroids in general have specific reversible interactions with the mercury surface at high "pH". These interactions are presumably a result of specific orientations on the electrode surface and depend upon the surface charge, stereoisomerism of 17-OH group, phenol/phenolate A ring/"pH", and methanol content. Such physical and chemical considerations have been expressed for specific orientations of other aromatic compounds at the platinum electrode.21"23 Furthermore it is likely that these specific orientations for phenolic steroids facilitate the electrode process for the oxidation of mercury in the presence of ethynylestradiol, resulting in a comparatively well-defined process for the latter.However, at pH >10, the non-phenolic acetylenic steroids do not exhibit specific electrode adsorption behavior and are much more strongly adsorbed than the corresponding phenolic steroids. The preferred orientation and strong adsorption of this class of steroid is believed to induce the observed irreversible electrode reaction behavior. The orientation of adsorbed intermediates is known to exert profound effects on electrochemical processes.24

Preparation of amorphous calcium-magnesium phosphates at pH 7 and characterization by x-ray absorption and fourier transform infrared spectroscopy

“…The mechanism [1, 16,29]. In seeded growth experiments, however, of transformation probably involves the growth of it has been shown that magnesium ions strongly brushite from solution at the expense of the retard the growth of OCP whereas the growth of amorphous phase, rather than a direct solid to brushite is hardly affected [33,34]. Thus, while solid transformation.…”

Magnesium in Man: Implications for Health and Disease

“…In bone, Mg 2ϩ ions bind at the surface of the hydroxyapatite crystals. Mg 2ϩ increases the solubility of P i and Ca 2ϩ hydroxyapatite and thereby acts on the crystal size and formation (443). Mg 2ϩ induces osteoblast proliferation; therefore, Mg 2ϩ deficiency results in decreased bone formation (320) (FIGURE 4) Mg 2ϩ -deficient rats have reduced osteoblast numbers and decreased bone mass (434).…”

“…Mg 2ϩ increases the solubility of the minerals and thereby acts on the crystal size and formation (443). Crystals in Mg 2ϩ -deficient bone are larger, and the bone may therefore be brittle and more susceptible to fractures (89).…”

Degradation processes of reinforced concretes by combined sulfate–phosphate attack

“…Furthermore, the hypothesis of amorphous calcium phosphate occurrence in the first phases of alteration is consistent with high pH and reagent concentration, despite the meta-stability of this compound [17]. Moreover, the presence of Mg in the system from the dissolution of dolostones and magnesium limestones stabilizes the amorphous calcium phosphate and brushite, inhibiting the crystallization of apatite and less extensively of octacalcium phosphate [46]. The transformation of calcium phosphate precursors into apatite was locally inhibited by the acidic pH and the presence of stabilizing ions in solution [47].…”