An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
A novel class of dinucleating ligands has been introduced into manganese chemistry to study the reactivity of this metal towards dioxygen under strictly controlled conditions. Such N4 ligands combine some of the major peculiarities of tetradentate Schiff bases and the porphyrin skeleton. They are derived from the condensation between 2-pyrrolaldehyde and ethylenediamine or o-phenylenediamine, leading to pyrenH2 (LH2, 1), pyrophenH2 (L'H2, 2) and Me2pyrophenH2, (L"H2, 3), respectively. Their metallation with [Mn3-(Mes)6] (Mes = 2,4,6-trimethylphenyl) led to [Mn2L2] (4), [MnL'(thf)2] (5) and [MnL"(thf)2] (6). Complex 4 displays a double-stranded helical structure, while 5 and 6 are mononuclear complexes containing hexacoordinated metals. Regardless of their structure, complexes 5 and 6 behave in a similar manner to 4 in their reaction with dioxygen, namely, as a dimetallic unit inside a cavity defined by two dinucleating ligands. These reactions led to dinuclear MnIII/MnIV oxo-hydroxo derivatives, [Mn2L2(mu-O)(mu-OH)] (7), [Mn2L'2(mu-O)(mu-OH)] (8) and [Mn2L"2(mu-O)(mu-OH)] (9), in which the two Mn ions are strongly antiferromagnetically coupled [J = -53 (7), J = -64 (8), J = -60 cm(-1) (9)]. The crystal structure of 7 could only be solved with synchrotron radiation as the crystals diffracted very poorly and suffered from twisting and disorder. The formation of 7-9 has been proposed to occur through the formation of an intermediate dinuclear hydroperoxo species.
Composite materials, both biominerals such as bone or shells but also increasingly synthetic materials, often have a complex hierarchical 3D structure ranging over several length scales. To fully understand the structure of such materials, a method for probing the nanoscale structure in 3D is needed. Materials such as bone are particularly challenging due to their complex composition and hierarchical structure. Recent developments in synchrotron x-ray focusing optics have paved the way for smaller x-ray beams with high brilliance. Herein, we present how we probe the 3D elemental distribution and crystallographic properties of human bone using combined fluorescence and diffraction tomography (F-CT and XRD-CT) with a 50 nm pencil X-ray beam. The 2.6×3.1 µm2 cross section sample was a FIB-cut rod of human iliac crest bone. We recorded 2D diffraction patterns and fluorescence spectra for each point in a 50 nm raster scan grid pattern from 92 projection angles covering 0-182°. This allowed us to reconstruct tomographically both x-ray diffraction patterns and the elemental composition in a ∼5×5×3 µm3 volume encompassing the sample. We show that tomographic reconstruction of x-ray diffraction and fluorescence information is possible at <140 nm spatial resolution estimated from features in reconstructed images. Thereby it is possible to probe crystalline structure and elemental composition in 3D at length scales an order of magnitude smaller than hitherto available. This allows studying a very broad range of materials from biominerals to energy materials in more detail than ever before.
A helix that expands on cooling: The crystal structure of TrpGly⋅H2O consists of helical peptide nanotubes extending throughout the crystal. The thermal expansion is negative in the helical direction (see graph; a axis: red, c axis: blue). This effect is believed to be linked to the increasing order of water molecules enclosed in the helices.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Abstract Crystallization from amorphous phases is an emerging pathway for making advanced materials. Biology has made use of amorphous precursor phases for eons and used them to produce structures with remarkable properties. Herein, we show how the design of the amorphous phase greatly influences the nanocrystals formed therefrom. We investigate the transformation of mixed amorphous calcium phosphate/amorphous calcium carbonate phases into bone‐like nanocrystalline apatite using in situ synchrotron X‐ray diffraction and IR spectroscopy. The speciation of phosphate was controlled by pH to favor HPO 4 2− . In a carbonate free system, the reaction produces anisotropic apatite crystallites with large aspect ratios. The first formed crystallites are highly calcium deficient and hydrogen phosphate rich, consistent with thin octacalcium phosphate (OCP)‐like needles. During growth, the crystallites become increasingly stoichiometric, which indicates that the crystallites grow through addition of near‐stoichiometric apatite to the OCP‐like initial crystals through a process that involves either crystallite fusion/aggregation or Ostwald ripening. The mixed amorphous phases were found to be more stable against phase transformations, hence, the crystallization was inhibited. The resulting crystallites were smaller and less anisotropic. This is rationalized by the idea that a local phosphate‐depletion zone formed around the growing crystal until it was surrounded by amorphous calcium carbonate, which stopped the crystallization.
Bone has a complex hierarchical structure, which is essential for its performance. Bone is typically replete with cells called osteocytes that are embedded in the mineralized bone matrix in osteocyte lacunae, which are interconnected by canaliculi only a few hundred nanometer wide to form a vast cellular network. Our understanding of the osteocyte lacuno-canalicular network has been limited because of difficulties to image the cellular network within the opaque bone matrix in 3D. Synchrotron X-ray computed tomography is ideally suited to study the lacuno-canalicular network in bone because it combines the high penetration power of X rays with sub-micron resolution while retaining a fast acquisition time and thus high throughput. We discuss how synchrotron radiation-based tomography techniques have given insights into the osteocyte network in bone both in the form of regular tomography and, for higher resolution studies, in the form of nanotomography such as holotomography. These studies have provided quantitative measures of osteocyte lacunar properties and their relation to location within bones and bone challenges such as immobilization or lactation. Nanotomography revealed new features of the canalicular network that we term canalicular junctions, which are likely to play an important but hitherto hidden role in fluid flow dynamics within the bone cellular network. The examples illustrate how tomography provides information on complex biological materials like bone and we foresee that these capabilities will continue to improve with future/upgraded synchrotron X-ray sources.
