Study Of Nucleation And Growth Of Asparticacid Crystals On Self-assembled Monolayers

The Self-assembled Monolayers (SAMs) were employed as ordering interface to inducethe nucleation and growth of Aspartic acid.In this article, we investigated the regulative effectof the self-assembled monolayer on controlling the nucleation, orientation, chiral recognition,morphology and size of Aspartic acid crystallized in different conditions. X-ray Diffraction(XRD), Scanning Electron Microscope (SEM), High Performance Liquid Chromatography(HPLC) were used as characterization methods.D-and L-Aspartic acid have the almost same physical and chemical properties in achiralenvironment. The self-assembled monolayer of Cysteine own the chiral center and can serveas chiral temple to induce the crystallization of Aspartic acid enantiomers. The resultsindicated that SAMs have a significant effect on the crystallization habit of Aspartic acidenantiomers. First, the chiral surface can induce modification in orientation of crystal growthand lead to preferential orientation [100]. But in the crystallization rate and quantity respects,D-and L-Aspartic acid show great individual difference. XRD and HPLC all revealedL-Aspartic acid has a obvious advantage over D-Aspartic acid in present of D-Cysteine SAMs.In addition, thought D and L-Aspartic acid have the nearly identical lattice parameters, thereis a mirror symmetry relationship in them. We hold that large differences exist in the latticematch between enantiomers Aspartic acid and D-Cysteine. These may be the main reason leadto crystallization rate difference.Even in the mixed solution of D-and L-Aspartic acid with initial enantiomeric excess,the SAMs of Cysteine show great performance as chiral temple. The crystals grown on theSAMs have the same chirality with the one enantiomeric excess in the initial solution. But weshould note that the crystals grown on SAMs from enantiomers mixed solution precent a moresimple orientation, named [100]. Moreover, D-Aspatic acid crystals grown on SAMs ofL-Cysteine have a greater amount than the L-Aspartic acid after a rather long growth time.The result verified that the SAMs of Cysteine have a enantioselective effect on thecrystallization ofAspartic acid enantiomers once again.And we tried to study the effect of SAMs on the crystallization of DL-Aspartic acid in a mixed solvent environment. The experiment results show that both the SAMs and mixedsolvent have impacts on the crystallization. The solvent has a direct influence on themorphology. Furthermore, it can make a difference on the structure and properties of SAMs.And the SAMs play a more significant role as ordering interface in the mixed solvent oforganic and inorganic. The crystals morphology and size of DL-Aspartic acid were effectivelycontrolled by SAMs in H2O/C2H5OH mixed solvent.