| Biomineralization are ubiquitous in biological systems, understanding the mechanismsby which organisms direct or limit crystallization has long been a central challenge to thebiomineralization community. Because biomineral structures exhibit complex topologies,hierarchical design, and unique materials properties, and understanding of the underlyingmechanisms of biomolecular controls over mineral growth presents an opportunity to developnew strategies towards synthesis of novel materials for applications across a wide range oftechnologies. In particular, biomolecules that present carboxyl groups to the growing crystalhave been implicated as primary modulators of growth, have been revealed to play pivotalroles in the regulations of biomineral formation, presumably via molecular recognitions andinteractions at organic-inorganic interfaces. Therefore, a systematic study was carried out onthe interactions between different hierarchical structured biomolecules (amino acid, peptide,protein) and the growth of inorganic crystal.Proteins obtained from biological systems can obtain direct experimental evidence tostudy the interface mechanism. The composition of polypeptide and protein molecules is thesame, but due to the relatively small number of its constituent amino acids, it is easy tomodulate the molecular properties, secondary structure, and therefore polypeptide is an idealchoice to study the organic-inorganic interface at the molecular level. Amino acids are thebasic building blocks of proteins and peptides, and carry some functional groups that are thesame as macromolecules, such as carboxyl, amino, hydroxyl, etc, but in a much shorterbackbone structure. Amino acids are therefore ideal probes for crystal functional groupinteractions. Previous studies have paid much attention to the influence of acidic amino acids,on the contrary, the little study on the basic and netural amino acids. By using the atomicforce microscopy to undertake the interactions at the interface to understand the effect ofgroup, secondary structure, molecular properties.Investigated the influence on the growth of the (104) hillock step in the control calciumcarbonate supersaturated solution. The results show that, the velocity of the obtuse and acutesteps are significantly accelerated with the increased supersaturation. The smaller the ionicstrength, the wider the hillock terrace. The change of the temperature can also affect themorphology and the rate of the spiral growth hillock. The critical step length on supersaturation in precisely controlled solutions was messured and provided the step edge freeenergies for calcite.Study the interfacial interaction between the calcite (104) surface and amino acids, theneutral achiral amino acid (Gly), the acidic chiral amino acids (L/D-Asp, L/D-Glu) and thebasic amino acid (L-Lys). Analysis the role of active functional group (α-NH3+, α-COO-andthe side chain functional group) in the interface interaction. So far, the solid-liquid interfacemolecular recognition interaction including electrostatic attraction, geometrical matching andstereochemical correspondence. In the presence of achiral Gly, the effect of calcite (104) faceremains symmetrical with respect to the c-glide plane, expression of the [421] direction. Uponthe introduction of L/D-Asp, the hillock was no longer symmetrical with regard to the c-glideplane, presumably resulting for the chirality of Asp, expression the [010] direction. Growthhillocks formed in the presence of D-and L-forms of Asp are mirror images of one another.L-Asp bind more stronger on the [481]_direction, while the D-Asp bind more stronger on the[441]_direction. The growth hillocks developed in Glu were quite different from those in Aspdespite the small different in side chain length. The new step edge vetor [421] emerged in Glu.The overall effects caused by L-Glu were much stronger on the right part of the hillock, andthe [421] step edge only appeared on the right side, never on the left side. It is opposite withthe presence of D-Glu. The geometrical matching between adjacent Ca atoms and the α-NH3+and α-COO-plays a central role in the stabilization of the [421] direction. The bindinggeometry of L/D-Glu to the step reflects the chirality of the adsorbate, and the symmetryabout the glide plane is broken due to the presence of side chain group. With the introductionof L-Lys, the [421] direction appeared on the right side of the c-glide plane, while no effecton the left step of the c-glide plane. The geometrical matching between adjacent Ca atoms andthe α-NH3+and α-COO-plays a central role in the stabilization of the [421] direction. Themorphology of calcite step loses the symmetry of the c-glide plane due to the presence of theside chain group. The greater the supersaturation of the solution, the weaker the influence ofthe amino acids, that is the larger the supersaturation will weaken the effect of the additives.The morphology of the spiral growth hillock mainly depend on the spatial struction of theadditive, especially the distance between functional groups. In the calcite-amino acidsinterfacial interactions, geometrical matching plays a crucial role in solid-liquid recognition,while the stereochemical correspondence, molecular chirality are also important, whileelectrostatic interaction plays a minor role. The effect of amphiphilic polypeptide on cacite (104) face is that with the increase ofhydrophobicity of the hydrophobic portion, the weaken influence of the morphology and therate of calcite spiral growth hillock. Ac-G4D-OH has more effect on the acute step directionand accelerates the rate of the step velocity. Addition the same concentration of Ac-A4D-OHand Ac-V4D-OH separately, has no significantly effect on the spiral hillock. The α-helixcontent of the α-helix peptide is sensitive to the temperature.3E,3D can have a dramaticeffect on calcite crystal morphology and the effect is conformation dependent. At lowerconcentration, the crystal elonged along the [010](c-axis) direction with bind to the {110}prism faces of calcite at3℃; with little effect at25℃. At higher concentration, themodification of calcite crystal are basically the same at3℃and25℃. Maybe at highconcentration, even at the high temperature, the content of the α-helix is even enough to affectthe crystals elongated along the [001] direction (c-axis) with rhombohedral {104} caps.Ovalbumin and lysozyme are two major egg white proteins and putatively related to theformation of the mammillary layer of eggshells. Our studies identified two roles forovalbumin, favoring the formation of amorphous calcium carbonate protein clusters onterrace surface and accelerating the step growth kinetics via reduction of the energy barrier forion attachment to crystal steps. The two effects are intimately linked to the inherentcharacteristics of ovalbumin, i.e., being acidic and amphiphilic. In contrast, lysozyme as abasic protein did not induce the formation of any moldable transient phases. Instead, itinteracted with step edges and pinned them, leading to step bunching and even stepadvancement stop at higher concentrations. |
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