Ustriyana Putu, Michel F Marc, Wilson Michael C, Harmon Emma, Chen Jiahui, Liu Tianbo, Sahai Nita
Department of Polymer Science, The University of Akron, Akron, Ohio 44325, United States.
Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States.
J Phys Chem B. 2020 Jul 23;124(29):6288-6298. doi: 10.1021/acs.jpcb.0c01690. Epub 2020 Jul 15.
Proteins and their mimics that contain negatively charged sequences are important in natural and biomimetic mineralization. The mechanism by which these sequences affect calcium phosphate mineralization is not well understood. Here, peptides containing different numbers of repeat units of contiguous glutamic acid residues, oligo(l-glutamic acid) ( = 3, 7, 8, 10), were investigated with regards to the mechanism in delaying the crystallization of amorphous calcium phosphate (ACP) while holding the amount of carboxylic acid groups in solution constant. Increasing peptide chain length increases the stability of ACP at a certain total amount of carboxylic acid groups in solution. This effect is shown to be due to stronger binding as well as binding to more calcium ions per peptide by the longer oligopeptides compared to the shorter ones. It is proposed that these associations delay the structural rearrangement of calcium ions and the dehydration of ACP, which are required for the crystallization of hydroxyapatite. The initial nucleation and the local structure of ACP, however, do not vary with chain length. This second part of a two-part series provides an improved mechanistic understanding of how organic additives, especially those with contiguous acidic amino acid sequences, modulate the kinetics of calcium phosphate precipitation and phase transformation.
含有带负电荷序列的蛋白质及其模拟物在天然矿化和仿生矿化过程中具有重要作用。这些序列影响磷酸钙矿化的机制尚未完全明晰。在此，研究了含有不同数量连续谷氨酸残基重复单元的肽，即聚（L-谷氨酸）（n = 3、7、8、10），在保持溶液中羧酸基团数量恒定的情况下，其延迟无定形磷酸钙（ACP）结晶的机制。在溶液中羧酸基团总量一定时，增加肽链长度可提高ACP的稳定性。结果表明，这种效应是由于较长的寡肽比较短的寡肽与钙离子的结合更强且每个肽结合的钙离子更多。据推测，这些结合作用延迟了钙离子的结构重排以及ACP的脱水过程，而这两个过程是羟基磷灰石结晶所必需的。然而，ACP的初始成核和局部结构并不随链长而变化。本系列文章的第二部分对有机添加剂，尤其是那些具有连续酸性氨基酸序列的添加剂如何调节磷酸钙沉淀和相变动力学提供了更深入的机理理解。
