title: Effects of initial supersaturation on spontaneous precipitation of calcium carbonate in the presence of charged poly-L-amino acids.
abstract: Spontaneous precipitation of calcium carbonate was investigated in two precipitation systems: (1) with initial supersaturation lower than that corresponding to the solubility of amorphous calcium carbonate (ACC), at which vaterite precipitated, and (2) with initial supersaturation higher than that of ACC solubility, at which a mixture of calcite and vaterite was formed. After the addition of an acidic polypeptide, poly-L-glutamic acid (pGlu) or poly-L-aspartic acid (pAsp), into (1) a significant inhibition of nucleation, expressed as an increase in induction time, and growth of vaterite, perceived as a dead zone, was observed. Extent of inhibition decreased in the order: Inh(pAps)>Inh(pGlu)>>Inh(pLys). The addition of a polypeptide into (2) caused the inhibition of precipitation and changed the morphology and polymorphic composition of the precipitate; only vaterite appeared at approximately c(pAsp)=3 ppm, c(pGlu)=6 ppm, or c(pLys)=7 ppm. This finding is explained as a consequence of kinetic constraints through the inhibition of calcite nucleation and stronger binding of acidic polypeptide by the calcite surfaces than by the vaterite surfaces. Laboratory precipitation studies using conditions that resemble those in living organism should be run at an initial supersaturation corresponding to the solubility of ACC as a limiting condition.
authors.affiliation: Laboratory for Precipitation Processes, Division of Materials Chemistry, Ruder Bosković Institute, P.O. Box 180, HR-10002 Zagreb, Croatia. bnjeg@irb.hr
authors.forename: Branka
authors.initials: B
authors.lastname: Njegić-Dzakula
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Falini
authors.forename: Ljerka
authors.initials: L
authors.lastname: Brecević
authors.forename: Zeljko
authors.initials: Z
authors.lastname: Skoko
authors.forename: Damir
authors.initials: D
authors.lastname: Kralj
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002119:Calcium Carbonate / Q000737:chemistry*; D011232:Chemical Precipitation; D011108:Polymers / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D055672:Static Electricity
chemical_list: D000596:Amino Acids; D011108:Polymers; D002119:Calcium Carbonate