Selective inhibition of aragonite growth by citrate and isocitrate at moderate supersaturations, as measured by an optical-microscope flow-cell assay

摘要

An optical flow-cell assay was developed which allowed for simultaneous measurement of calcite and aragonite growth under conditions of constant concentrations of constituent ions and growth-modifying additives. Using this assay, it was determined that L-citrate and D,L-isocitrate selectively inhibited the growth of aragonite crystal seeds, while having little or no effect on calcite growth rates at supersaturations in the range of σ = 2.5 + 0.4. Tricarballylate, which differs from citrate and isocitrate by the absence of a hydroxide functionality, had very little effect on calcite or aragonite growth. For citrate on aragonite, an effective surface binding constant of K= 2.5 ± 0.6 × 10~5M~(-1) was derived from the kinetic data; for isocitrate, K= 2.9 ± 0.8 × 10~5M~(-1). The similarity of these effective binding constants argues against precise stereochemical recognition of the aragonite surface.