Diatom biosilica is an inorganic/organic hybrid with interesting properties. The molecular architecture of the organic material at the atomic and nanometer scale has so far remained unknown, in particular for intact biosilica. A DNP-supported ssNMR approach assisted by microscopy, MS, and MD simulations was applied to study the structural organization of intact biosilica. For the first time, the secondary structure elements of tightly biosilica-associated native proteins in diatom biosilica were characterized in situ. Our data suggest that these proteins are rich in a limited set of amino acids and adopt a mixture of random-coil and β-strand conformations. Furthermore, biosilica-associated long-chain polyamines and carbohydrates were characterized, thereby leading to a model for the supramolecular organization of intact biosilica.
Highly reflective
crystals of the nucleotide base guanine are widely
distributed in animal coloration and visual systems. Organisms precisely
control the morphology and organization of the crystals to optimize
different optical effects, but little is known about how this is achieved.
Here we examine a fundamental question that has remained unanswered
after over 100 years of research on guanine:
what are the
crystals made of
? Using solution-state and solid-state chemical
techniques coupled with structural analysis by powder XRD and solid-state
NMR, we compare the purine compositions and the structures of seven
biogenic guanine crystals with different crystal morphologies, testing
the hypothesis that intracrystalline dopants influence the crystal
shape. We find that biogenic “guanine” crystals are
not pure crystals but
molecular alloys
(aka solid
solutions and mixed crystals) of guanine, hypoxanthine, and sometimes
xanthine. Guanine host crystals occlude homogeneous mixtures of other
purines, sometimes in remarkably large amounts (up to 20% of hypoxanthine),
without significantly altering the crystal structure of the guanine
host. We find no correlation between the biogenic crystal morphology
and dopant content and conclude that dopants do not dictate the crystal
morphology of the guanine host. The ability of guanine crystals to
host other molecules enables animals to build physiologically “cheaper”
crystals from mixtures of metabolically available purines, without
impeding optical functionality. The exceptional levels of doping in
biogenic guanine offer inspiration for the design of mixed molecular
crystals that incorporate multiple functionalities in a single material.
Diatom-templated noble metal (Ag, Pt, Au) and semiconductor (CdTe) nanoparticle arrays were synthesized by the attachment of prefabricated nanoparticles of defined size. Two different attachment techniques-layer-by-layer deposition and covalent linking-could successfully be applied. The synthesized arrays were shown to be useful for surface-enhanced Raman spectroscopy (SERS) of components, for catalysis, and for improved image quality in scanning electron microscopy (SEM).
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