The components of bone assemble hierarchically to provide stiffness and toughness. However, the organization and relationship between bone's principal components-mineral and collagen-has not been clearly elucidated. Using three-dimensional electron tomography imaging and high-resolution two-dimensional electron microscopy, we demonstrate that bone mineral is hierarchically assembled beginning at the nanoscale: Needle-shaped mineral units merge laterally to form platelets, and these are further organized into stacks of roughly parallel platelets. These stacks coalesce into aggregates that exceed the lateral dimensions of the collagen fibrils and span adjacent fibrils as continuous, cross-fibrillar mineralization. On the basis of these observations, we present a structural model of hierarchy and continuity for the mineral phase, which contributes to the structural integrity of bone.

A metal-decorated alkene-linked covalent organic framework is a robust, selective photocatalyst for CO2 reduction.

In the nacre or aragonite layer of the mollusk shell there exist proteomes which regulate both the early stages of nucleation and nano-to-mesoscale assembly of nacre tablets from mineral nanoparticle precursors. Several approaches have been developed to understand protein-associated mechanisms of nacre formation, yet we still lack insight into how protein ensembles or proteomes manage nucleation and crystal growth. To provide additional insights we have created a proportionally-defined combinatorial model consisting of two nacre-associated proteins, C-RING AP7 (shell nacre, H. rufescens) and pseudo-EF hand PFMG1 (oyster pearl nacre, P. fucata) whose individual in vitro mineralization functionalities are well-documented and distinct from one another. Using SEM, flow cell STEM, AFM, Ca(II) potentiometric titrations and QCM-D quantitative analyses, we find that both nacre proteins are functionally active within the same mineralization environments, and at 1:1 mole ratios, synergistically create calcium carbonate mesoscale structures with ordered intracrystalline nanoporosities, extensively prolong nucleation times and introduce an additional nucleation event. Further, these two proteins jointly create nanoscale protein aggregates or phases that under mineralization conditions further assemble into protein-mineral PILP-like phases with enhanced ACC stabilization capabilities, and there is evidence for intermolecular interactions between AP7 and PFMG1 under these conditions. Thus, a combinatorial model system consisting of more than one defined biomineralization protein dramatically changes the outcome of the in vitro biomineralization process.

Covalent organic framework nanosheets (CONs), fabricated from two dimensional covalent organic frameworks (COFs), present a promising strategy for incorporating atomically distributed catalytic metal centers into welldefined pore structures with desirable chemical environments. Here, a series of CONs was synthesized embedding single cobalt sites that were then evaluated for photocatalytic carbon dioxide reduction. A partially fluorinated, cobalt-loaded CON produced 10.1 µmol carbon monoxide with a selectivity of 76%, over 6 hours irradiation under visible light (turnover number = 28.1) and a high external quantum efficiency of 6.6% under 420 nm irradiation in the presence of an iridium dye. The CONs appear to act as a semiconducting support, facilitating charge-carrier transfer between the dye and the cobalt centers, and this results in a performance comparable with the state-of-the-art heterogeneous catalysts in the literature under similar conditions. The ultra-thin CONs outperformed their bulk counterparts in all cases, suggesting a general strategy to enhance the photocatalytic activities of COF materials.