Biologically Controlled Morphology and Twinning in Guanine Crystals. Issue 32 (6th July 2017)

• Record Type: Journal Article
• Authors: Hirsch, Anna; Palmer, Benjamin A.; Elad, Nadav; Gur, Dvir; Weiner, Steve; Addadi, Lia; Kronik, Leeor; Leiserowitz, Leslie
• Is Part Of: Angewandte Chemie international edition. Volume 56:Issue 32(2017)
• Page Start: 9420
• Page End: 9424
• Publication Date: 2017-07-06
• Subjects: crystal twinning -- electron diffraction -- morphological engineering -- photonic crystals -- tiling; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201704801
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Guanine crystals are widely used in nature as components of multilayer reflectors. Guanine‐based reflective systems found in the copepod cuticle and in the mirror of the scallop eye are unique in that the multilayered reflectors are tiled to form a contiguous packed array. In the copepod cuticle, hexagonal crystals are closely packed to produce brilliant colors. In the scallop eye, square crystals are tiled to obtain an image‐forming reflecting mirror. The tiles are about 1 μm in size and 70 nm thick. According to analysis of their electron diffraction patterns, the hexagon and square tiles are not single crystals. Rather, each tile type is a composite of what appears to be three crystalline domains differently oriented and stacked onto one another, achieved through a twice‐repeated twinning about their ⟨011⟩ and ⟨021⟩ crystal axes, respectively. By these means, the monoclinic guanine crystal mimics higher symmetry hexagonal and tetragonal structures to achieve unique morphologies. Abstract : Guanignma : The brilliant colors of the copepod and the image‐forming reflecting mirror in the eye of the scallop are both the result of guanine‐based multilayer reflectors. Both systems form tessellated arrays composed of guanine monoclinic crystals biologically engineered into symmetrical hexagon and square tiles. Electron diffraction patterns reveal that their morphologies are achieved by crystal twinning, each forming a composite of three domains.