Physical chemical studies of the kinetics and energetics of the nucleation and growth of calcium-containing biominerals
Zachowicz, William J
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The constant composition method was used to investigate the effect of polyaspartic acids on calcium oxalate monohydrate crystal (COM) growth. Three larger molecular weight (ranging from 6000--35000) polymers were first used, and it was found that a polyaspartic acid with a molecular weight of 13000 had the highest effect. The ability to inhibit molecular growth is similar on a molar level to osteopontin, a protein commonly found in urine that has been shown to significantly inhibit calcium oxalate monohydrate crystal growth. The effect of three smaller weight (around 3000) polyaspartic acids was also investigated. However, at such low molecular weights, polyaspartic acid is unstable; amino acid spacers must be added to the polymer. The spacer used markedly affects the effectiveness of the copolymer towards the inhibition of COM crystal growth. A copolymer with serine spacers is most effective, followed by one with a phosphoserine spacer and then one with a glycine spacer, although all three are less effective than the three higher molecular weight polymers. Atomic force microscopy studies show that the polyaspartic acid with serine spacers is much more effective at inhibiting COM growth on the (010) and (-101) faces than the copolymer with glycine spacers. Using a thin layer wicking technique, the interfacial energies of COM treated with various proteins and polyaspartic acids were determined. It was hoped that there would be a trend in either the Lewis base term and/or in the interfacial energy term that paralleled their effects on COM crystal growth (i.e. 13000 molecular weight polyaspartic acid would have a similar Lewis base term and/or interfacial energy). However, no trend was established. Constant composition experiments were also made in attempts to nucleate COM on dentin surfaces. The goal of these experiments was to nucleate COM crystals such that they occlude the open tubules in dentin (the condition in which a person has exposed tubules is called dentine sensitivity). At moderate supersaturations, COM crystals did nucleate on the surface of dentin disks. However, these crystals were not small enough and thus did not nucleate inside the tubules.