Twin-like chiral configuration of a calcium oxalate monohydrate mesocrystal regulated with an organic framework in grape leaves

Biogenic calcium oxalate monohydrate (COM, CaC₂O₄·H₂O) needle crystals (raphides) having a pointed tip and two tails are arranged as a bundle in grape leaves. In this work, the specific hierarchical architecture was studied at the micrometric and nanometric scales. Raphides were macroscopically characterized as having a twin-like chiral configuration of COM divided by an organic central wall and covered with an organic enveloping membrane. The COM of the raphides has a mesocrystalline structure that consists of small grains ∼10 nm in diameter with a distorted single-crystal nature. The initially produced organic framework was suggested to control the specific crystal growth of COM under the construction of a raphide in a specific cell.