Structure and Morphology of Light-Reflecting Synthetic and Biogenic Polymorphs of Isoxanthopterin: A Comparison

Hirsch, Anna K. H.; Palmer, Benjamin A.; Ramasubramaniam, Ashwin; Williams, P. Andrew; Harris, Kenneth David Maclean; Pokroy, Boaz; Weiner, Steve; Addadi, Lia; Leiserowitz, Leslie; Kronik, Leeor

doi:10.1021/acs.chemmater.9b01039

Cited by 17 publications

(29 citation statements)

References 91 publications

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“…However, biogenic 7,8-dihydroxanthopterin adopts a different hydrogen-bonded network that does not incorporate cyclic hydrogen-bonded dimers but rather is composed of a zigzag motif of hydrogen-bonded molecular ribbons, juxtaposed to each other with a dihedral angle of about 105°. This motif is somewhat similar to that of the synthetic (as opposed to biogenic) crystals of isoxanthopterin . As a consequence of this packing motif, the orientation of the planar molecules is more isotropic.…”

Section: Discussionsupporting

confidence: 58%

“…The presence of a b -glide was independently proven based on a TEM stage tilt of the ( hk 0) pattern (Figure S3). The unit cell dimensions ( a ≈ 5 Å, b ≈ 8 Å c ≈ 17 Å, z = 4) yield a crystal density close to that of crystalline isoxanthopterin assuming four molecules in the unit cell. , …”

Section: Resultsmentioning

confidence: 75%

“…The molecules lie in the {120} planes, interlinked by b -glide symmetry along the two diagonals a ± (1/2) b (purple and green), and interlinked by H-bonds, forming a ribbon (purple molecules 1 and 2, green molecules 3 and 4). The model comprises juxtaposed criss-crossed ribbons along the a ± (1/2) b diagonals, reminiscent of the synthetic α-form of isoxanthopterin …”

Section: Resultsmentioning

confidence: 99%

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Guanine and 7,8-Dihydroxanthopterin Reflecting Crystals in the Zander Fish Eye: Crystal Locations, Compositions, and Structures

et al. 2019

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The eyes of many fish contain a reflecting layer of organic crystals partially surrounding the photoreceptors of the retina, which are commonly believed to be composed of guanine. Here we study an unusual fish eye from Stizostedion lucioperca that contains two layers of organic crystals. The crystals in the outer layer are thin plates, whereas the crystals in the inner tapetum layer are block-shaped. We show that the outer layer indeed contains guanine crystals. Analyses of solutions of crystals from the inner layer indicated that the block-shaped crystals are composed of xanthopterin. A model of the structure of the block-shaped crystals was produced using symmetry arguments based on electron diffraction data followed by dispersion-augmented DFT calculations. The resulting crystal structure of xanthopterin included, however, a problematic repulsive interaction between CO and N of two adjacent molecules. Knowing that dissolved 7,8-dihydroxanthopterin can oxidize to xanthopterin, we replaced xanthopterin with 7,8-dihydroxanthopterin in the model. An excellent fit was obtained with the powder X-ray diffraction pattern of the biogenic crystals. We then analyzed the biogenic block-shaped crystals in their solid state, using MALDI-TOF and Raman spectroscopy. All three methods unequivocally prove that the block-shaped crystals in the eye of S. lucioperca are crystals of 7,8-dihydroxanthopterin. On the basis of the eye anatomy, we deduce that the guanine crystals form a reflective layer producing the silvery color present on part of the eye surface, whereas the block-shaped crystals backscatter light into the retina in order to increase the light sensitivity of the eye.

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Section: Discussionsupporting

confidence: 58%

Section: Resultsmentioning

confidence: 75%

Section: Resultsmentioning

confidence: 99%

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Guanine and 7,8-Dihydroxanthopterin Reflecting Crystals in the Zander Fish Eye: Crystal Locations, Compositions, and Structures

et al. 2019

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“…guanine, [20] isoxanthopetrin [52] and 7,8dihydroxanthopterin [40] (Figure 5). The first step in determining the structures was to construct a plausible packing motif using crystal engineering principles.…”

Section: The Structures and Morphologies Of Biogenic Molecular Crystalsmentioning

confidence: 99%

“…Similar ribbon structure motifs can be found in the monoclinic crystal structures of synthetic isoxanthopterin and uric acid. [52,53] It is also interesting to note that in 7,8-dihydoxanthopterin and uric acid, unlike guanine and isoxanthopterin, the number of hydrogen-bond acceptors and donors is not equal, which probably brings about the need for this diagonal packing arrangement.…”

Section: The Structures and Morphologies Of Biogenic Molecular Crystalsmentioning

confidence: 99%

Functional Molecular Crystals in Biology

Wagner

Wen

Pinsk

et al. 2021

Israel Journal of Chemistry

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Highly reflective crystals of small organic molecules are the functional materials in a wide variety of optical systems in animals. We present a perspective on this field of organic biomineralization and review evidence for the widespread distribution of organic crystals in animals. These materials were, until recently, largely overlooked principally because the crystals are lost during conventional electron microscopy preparation procedures. We document the discovery of the crystalline pteridines as a new class of biological crystals and explain why many more organic biocrystals will likely be discovered and where they may be found. We examine the chemical basis for the extraordinary optical properties of the crystals and review some of their newly discovered biological functions. The study of biogenic molecular crystals promises to yield fascinating insights into photonic systems in animals and will inspire the development of artificial optical materials.

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Surface‐Guided Crystallization of Xanthine Derivatives for Optical Metamaterial Applications

Niazov‐Elkan,

Shepelenko,

Alus

et al. 2023

Advanced Materials

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Numerous bio‐organisms employ template‐assisted crystallization of molecular solids to yield crystal morphologies with unique optical properties that are difficult to reproduce synthetically. Here, a facile procedure is presented to deposit bio‐inspired birefringent crystals of xanthine derivatives on a template of single‐crystal quartz. Crystalline sheets that are several millimeters in length, several hundred micrometers in width, and 300–600 nm thick, are obtained. The crystal sheets are characterized with a well‐defined orientation both in and out of the substrate plane, giving rise to high optical anisotropy in the plane parallel to the quartz surface, with a refractive index difference Δn ≈ 0.25 and a refractive index along the slow axis of n ≈ 1.7. It is further shown that patterning of the crystalline stripes with a tailored periodic grating leads to a thin organic polarization‐dependent diffractive meta‐surface, opening the door to the fabrication of various optical devices from a platform of small‐molecule based organic dielectric crystals.

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Structure and Morphology of Light-Reflecting Synthetic and Biogenic Polymorphs of Isoxanthopterin: A Comparison

Cited by 17 publications

References 91 publications

Guanine and 7,8-Dihydroxanthopterin Reflecting Crystals in the Zander Fish Eye: Crystal Locations, Compositions, and Structures

Guanine and 7,8-Dihydroxanthopterin Reflecting Crystals in the Zander Fish Eye: Crystal Locations, Compositions, and Structures

Functional Molecular Crystals in Biology

Surface‐Guided Crystallization of Xanthine Derivatives for Optical Metamaterial Applications

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