The mollusk shell is a hard tissue consisting of calcium carbonate crystals and an organic matrix. The nacre of the shell is characterized by a stacked compartment structure with a uniformly oriented c axis of aragonite crystals in each compartment. Using a calcium carbonate-binding assay, we identified an acidic matrix protein, Pif, in the pearl oyster Pinctada fucata that specifically binds to aragonite crystals. The Pif complementary DNA (cDNA) encoded a precursor protein, which was posttranslationally cleaved to produce Pif 97 and Pif 80. The results from immunolocalization, a knockdown experiment that used RNA interference, and in vitro calcium carbonate crystallization studies strongly indicate that Pif regulates nacre formation.
Gone fishing: Unidirectionally oriented CaCO3 crystalline films have been prepared on chitin matrices in the presence of calcification‐associated peptide (CAP‐1), which was isolated from the exoskeleton of the red swamp crayfish. The interactions of CAP‐1 with the matrix and the acidic nature of the peptide lead to a filmlike assembly of CaCO3 nanocrystals through transformation of amorphous calcium carbonate (see picture).
Unidirectionally aligned hybrids consisting of chitin and calcite were obtained by template crystallization of CaCO3 in an ordered chitin film with nematic liquid‐crystalline molecular alignment. The picture shows the resulting chitin matrix containing CaCO3 rods, schematically and in the form of an optical micrograph, and the selected‐area electron diffraction pattern of a thin section of a single rod.
The Z-scheme process in chlorophyll-based natural photosynthesis shows the pathway of photoinduced electron transport from photosystem II (PSII) to photosystem I (PSI) through an electron transfer chain. Inspired by the interesting Z-scheme of oxygenic photosynthesis, we imitated the dual photosynthesis systems into biosolar cells (BSCs). The device structure fabricated here is ITO/ZnO/Chl-A/Chl-D1, -D2, -D3, or -D4 (Chl-Ds)/MoO 3 /Ag. Due to higher HOMO/LUMO energy levels of Chl-A than those of Chl-Ds, the sublayer Chl-A corresponds to PSI, and the upper layer Chl-Ds are equivalent to PSII, leading to double photoexcited electron transfer from Chl-Ds to Chl-A. The energy alignment of the photoactive layers here is in conflict with the traditional comprehension of photovoltaic devices. Interestingly, such an uncommon device can still work well. A power conversion efficiency of 1.30% was reached based on the Chl-A/Chl-D4 device under standard AM1.5 illumination.
CaCO 3 /chitin-whisker hybrids were prepared using the liquid-crystalline suspension of the chitin whisker. Suspensions of chitin nanowhiskers were obtained by acid hydrolysis of chitin powder. The suspension containing about 5 wt% of whiskers exhibited lyotropic liquid-crystalline behavior. The suspension was converted to a gel form when it was exposed to ammonium carbonate vapor. CaCO 3 crystals were formed for 30 days in chitin gels as templates. The nucleation of CaCO 3 occurred in the liquidcrystalline chitin matrix and the CaCO 3 crystals deposited in the chitin gels to form hybrids with an interpenetrated threedimensional structure. Scanning electron microscopy image of the fractured sample of the hybrid showed that the gel matrix was filled with CaCO 3 crystals. Thermogravimetric analysis revealed that the composition of CaCO 3 /polymer/H 2 O is about 2:6:2 in weight. This approach inspired by biomineralization may be useful for the development of inorganic/organic hybrid materials. Polymer Journal (2010) 42, 583-586; doi:10.1038/pj.2010.32; published online 5 May 2010Keywords: biomineralization; CaCO 3 ; chitin; hybrid; liquid crystal INTRODUCTIONThe process used by living organisms to produce inorganic/organic hybrids is called biomineralization. 1-3 Natural biominerals such as bone, teeth and the nacre of the shell have high mechanical strength and optical properties. In these biominerals, the properties are closely related to their hierarchically ordered structures. For instance, the nacre of the shell has a layered structure composed of about 95 wt% CaCO 3 and about 5 wt % organic matrices. 4-6 The layered structure induces high mechanical strength and pearl luster. Another type of biomineral that is softer than the nacre of the shell is the exoskeleton of the crayfish. 7 It is composed of about 50 wt% CaCO 3 and about 50 wt% organic macromolecules such as chitin and proteins. In the exoskeleton, chitin fibers have a helical structure 8,9 that is analogous to the cholesteric liquid-crystalline order. These chitin fibers are complexed with proteins and CaCO 3 . These natural biominerals offer ideas for new inorganic/organic hybrid materials. [10][11][12][13][14][15][16] A variety of calcium-based hybrid materials have been reported. [17][18][19][20][21][22][23][24][25][26] We previously reported that CaCO 3 thin-film crystals were formed on chitin matrices in the presence of acidic polymers. [17][18][19][20][21] Moreover, oriented CaCO 3 crystals were obtained in an oriented chitin matrix. 27 This result shows that the ordered matrix is important for further structure control of inorganic/organic hybrid materials. Our intention here is to use ordered chitin whiskers for the formation of hybrids. Herein, we report on the formation of CaCO 3 crystals/ chitin-whisker hybrids using the liquid-crystalline suspension of the chitin whisker.
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