Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany.
State Academy of Art and Design, Am Weißenhof 1, 70191, Stuttgart, Germany.
Angew Chem Int Ed Engl. 2020 Jun 8;59(24):9438-9442. doi: 10.1002/anie.202001609. Epub 2020 Apr 15.
Helical motifs are common in nature, for example, the DNA double or the collagen triple helix. In the latter proteins, the helical motif originates from glycine, the smallest amino acid, whose molecular confirmation is closely related to acetic acid. The combination of acetic acid with calcium and water, which are also omnipresent in nature, materializing as calcium acetate hemihydrate, was now revealed to exhibit a collagen-like triple helix structure. This calcium salt is observed as efflorescence phase on calcareous heritage objects, like historic Mollusca shells, pottery or marble reliefs. In a model experiment pure calcium acetate hemihydrate was crystallized on the surface of a terracotta vessel. Calcium acetate hemihydrate crystallizes in a surprisingly large unit cell with a volume of 11,794.5(3) Å at ambient conditions. Acetate ions bridge neighboring calcium cations forming spiral chains, which are arranged in a triple helix motif.
螺旋结构在自然界中很常见，例如 DNA 的双螺旋或胶原蛋白的三螺旋。在后者的蛋白质中，螺旋结构源于甘氨酸，即最小的氨基酸，其分子结构与乙酸密切相关。乙酸与钙和水的结合，这些在自然界中也无处不在，形成了二水合醋酸钙，现在被证明具有胶原蛋白样的三螺旋结构。这种钙盐以钙盐华的形式出现在钙质遗产物体上，如历史悠久的贝类、陶器或大理石浮雕。在一个模型实验中，纯二水合醋酸钙在一个赤陶容器的表面结晶。二水合醋酸钙在环境条件下结晶形成一个惊人的大单位细胞，体积为 11794.5(3)Å。乙酸根离子桥接相邻的钙离子，形成螺旋链，这些螺旋链排列成三螺旋结构。
