title: Unique roles of acidic amino acids in phase transformation of calcium phosphates.
abstract: Although phase transformation is suggested as a key step in biomineralization, the chemical scenario about how organic molecules mediate inorganic phase transformations is still unclear. The inhibitory effect of amino acids on hydroxyapatite (HAP, the main inorganic component of biological hard tissues such as bone and enamel) formation was concluded by the previous biomimetic modeling based upon direct solution crystallization. Here we demonstrate that acidic amino acids, Asp and Glu, could promote HAP crystallization from its precursor crystal, brushite (DCPD). However, such a promotion effect could not be observed when the nonacidic amino acids were applied in the transformation-based HAP formation. We found that the specific modification of acidic amino acid on crystal-solution interfaces played a key role in the phase transition. The distinct properties between DCPD and HAP in the solution resulted in an interfacial energy barrier to suppress the spontaneous formation of HAP phase on DCPD phase. Different from the other amino acids, the carboxylate-rich amino acids, Asp and Glu, could modify the interfacial characteristics of these two calcium phosphate crystals to make them similar to each other. The experiments confirmed that the involvement of Asp or Glu reduced the interfacial energy barrier between DCPD and HAP, leading to a trigger effect on the phase transformation. An in-depth understanding about the unique roles of acidic amino acids may contribute to understanding phase transformation controls druing biomineralization.
authors.affiliation: Center for Biomaterials and Biopathways, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang, China.
authors.forename: Xiaobin
authors.initials: X
authors.lastname: Chu
authors.forename: Wenge
authors.initials: W
authors.lastname: Jiang
authors.forename: Zhisen
authors.initials: Z
authors.lastname: Zhang
authors.forename: Yang
authors.initials: Y
authors.lastname: Yan
authors.forename: Haihua
authors.initials: H
authors.lastname: Pan
authors.forename: Xurong
authors.initials: X
authors.lastname: Xu
authors.forename: Ruikang
authors.initials: R
authors.lastname: Tang
mesh_terms: D024342:Amino Acids, Acidic / Q000737:chemistry / Q000502:physiology*; D002130:Calcium Phosphates / Q000737:chemistry*; D003460:Crystallization; D018625:Microscopy, Atomic Force; D044367:Phase Transition
chemical_list: D024342:Amino Acids, Acidic; D002130:Calcium Phosphates