Inhibition Of Crystallization Kinetics Of Calcium Oxalates By Phosphorylated Calsequestrin Peptides

Biomineralization is a process by which organisms produce materials solutions for their own functional requirements. Due to the addition of protein molecule, inorganic process of organisms can be promoted or inhibited. In order to simulate biomolecule effect in process of calcium oxalate monohydrate(COM) nucleation and growth, firstly, we synthesized the COM which is suited to experiment of atomic force microscopy(AFM). Then we chose the calsequestrin(CS-2) with different number of phosphorylation sites and synthesized them in vitro. At last, combined with the experiment of ion electrode and AFM, we summarize the main results as following:(1) According to the experiment of COM synthesized in silica and clay gel, we found the synthesis conditions which is suited to COM observation by AFM as follows: silica-gel, room-temperature, 60 d, 0.5 mol·L-1; clay-gel, room-temperature, 90 d, 0.75 mol·L-1 and 62℃, 60 d, 0.5 mol·L-1. The crystals we got are stable, smooth and size-suited(width ≥ 20 μm).(2) Under near-physiological condition(σCOM = 1.62, I = 0.15 mol·L-1, p H = 7.0, 25 °C), we study the effect of peptide CS containing 14 amino acid on the nucleation and growth of COM in KCl or Na Cl background electrolyte. According to the experiment of calcium oxalate nucleation, the speed of calcium oxalate nucleation in KCl background electrolyte is faster than the speed in Na Cl.(2p)CS-2 inhibitory effect is stronger than CS-2 in the process of COM nucleation. With the two peptides concentration increasing, their inhibitory becomes more and more stronger. CS-2 and(2p)CS-2 all modifie the COM shape, furthermore(2p)CS-2 can weaken crystallinity and be incorporated into the crystal structure.(3) The result of atomic force microscopy(AFM) showed the different inhibitory effect of CS-2 and(2p)CS-2 in process of COM surface growing(σCOM = 0.816, I = 0.15 mol·L-1, p H 7.0, 25 °C). Due to Na Cl affected the hillock morphologies which was affected least by KCl, for the calsequestrin experiments, KCl was selected as the background electrolyte. CS-2 and(2p)CS-2 block step movement and the growth rate drops with increasing peptides concentration.CS-2 inhibitory effect on(-101) face is stronger than(2p)CS-2, and they can pin the moving of steps in the high peptide concentration(≥30 nmol·L-1). The inhibitory effect of(2p)CS-2 on(010) face is stronger than CS-2, especially in [0-2-1] direction. Therefore, the selective binding on different face of crystal is determined by the composition and stereochemical structure of peptides.