Departamento de Estratigrafía y Paleontología, Universidad de Granada, 18071, Granada, Spain.
Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, 18100, Armilla, Spain.
Sci Rep. 2020 Oct 8;10(1):16784. doi: 10.1038/s41598-020-73804-8.
The calcite grains forming the wall plates of the giant barnacle Austramegabalanus psittacus have a distinctive surface roughness made of variously sized crystalline nanoprotrusions covered by extremely thin amorphous pellicles. This biphase (crystalline-amorphous) structure also penetrates through the crystal's interiors, forming a web-like structure. Nanoprotrusions very frequently elongate following directions related to the crystallographic structure of calcite, in particular, the <- 441> directions, which are the strongest periodic bond chains (PBCs) in calcite. We propose that the formation of elongated nanoprotrusions happens during the crystallization of calcite from a precursor amorphous calcium carbonate (ACC). This is because biomolecules integrated within the ACC are expelled from such PBCs due to the force of crystallization, with the consequent formation of uninterrupted crystalline nanorods. Expelled biomolecules accumulate in adjacent regions, thereby stabilizing small pellicle-like volumes of ACC. With growth, such pellicles become occluded within the crystal. In summary, the surface roughness of the biomineral surface reflects the complex shape of the crystallization front, and the biphase structure provides evidence for crystallization from an amorphous precursor. The surface roughness is generally explained as resulting from the attachment of ACC particles to the crystal surface, which later crystallised in concordance with the crystal lattice. If this was the case, the nanoprotrusions do not reflect the size and shape of any precursor particle. Accordingly, the particle attachment model for biomineral formation should seek new evidence.
形成巨型藤壶 Austramegabalanus psittacus 壁板的方解石晶粒具有独特的表面粗糙度，由各种大小的结晶纳米突起组成，表面覆盖着极薄的无定形包膜。这种双相（结晶-无定形）结构也贯穿晶体内部，形成网状结构。纳米突起非常频繁地沿着与方解石结晶结构有关的方向伸长，特别是与方解石最强的周期性键链（PBC）相关的<-441>方向。我们提出，纳米突起的形成发生在从前驱体无定形碳酸钙（ACC）结晶形成方解石的过程中。这是因为由于结晶的力，整合在 ACC 中的生物分子被从这些 PBC 中挤出，从而形成了连续的结晶纳米棒。被挤出的生物分子在相邻区域积聚，从而稳定了小的包膜状 ACC 体积。随着生长，这些包膜被包含在晶体中。总之，生物矿化表面的粗糙度反映了结晶前沿的复杂形状，而双相结构为从无定形前驱体结晶提供了证据。表面粗糙度通常被解释为 ACC 颗粒附着在晶体表面上，然后与晶格一致结晶。如果是这样，纳米突起就不能反映任何前驱体颗粒的大小和形状。因此，生物矿化形成的颗粒附着模型应该寻找新的证据。
