Amorphous Calcium Phosphates: Solvent-Controlled Growth and Stabilization through the Epoxide Route.

Calcium phosphates stand among the most promising nanobiomaterials in key biomedical applications, such as bone repairment, signalling or drug/gene delivery. Their intrinsic properties as crystalline structure, composition, particle shape and size define their successful use. Among these compounds, metastable amorphous calcium phosphate (ACP) is currently gaining particular attention due to its inherently high reactivity in solution, which is crucial in bone development mechanisms. However, the preparation of this highly desired (bio)material with control over its shape, size and phase purity remains as a synthetic challenge. In this work, the epoxide route was adapted for the synthesis of pure and stable ACP colloids. By using biocompatible solvents, such as ethylene glycol and/or glycerine, it was possible to avoid the natural tendency of ACP to maturate into more stable and crystalline apatites. Moreover, this procedure offers size control, ranging from small nanoparticles (60 nm) to micrometric spheroids (>500 nm). The eventual fractalization of the internal mesostructured can be tuned, by simply adjusting the composition of the ethylene glycol:glycerine solvent mixture. These findings introduce the use of green solvents as a new tool to control crystallinity and/or particle size in the synthesis of nanomaterials, avoiding the use of capping agents and preserving the natural chemical reactivity of the pristine surface.

The Missing Link in the Magnetism of Hybrid Cobalt Layered Hydroxides: The Odd-Even Effect of the Organic Spacer.

A dramatic change in the magnetic behaviour, which solely depends on the parity of the organic linker molecules, has been found in a family of layered CoII hydroxides covalently functionalized with dicarboxylic molecules. These layered hybrid materials have been synthesized at room temperature using a one-pot procedure through the epoxide route. While hybrids connected by odd alkyl chains exhibit coercive fields (Hc ) below ca. 3500 Oe and show spontaneous magnetization at temperatures (TM ) below 20 K, hybrids functionalized with even alkyl chains behave as hard magnets with Hc >5500 Oe and display a TM higher than 55 K. This intriguing behaviour was studied by density functional theory with the incorporation of a Hubbard term (DFT+U) calculations, unveiling the structural subtleties underlying this observation. Indeed, the different molecular orientation exhibited by the even/odd alkyl chains, and the orientation of the covalently linked carboxylic groups modify the intensity of the magnetic coupling of both octahedral and tetrahedral in-plane sublattices, thus strongly affecting the magnetic properties of the hybrid. These findings offer an outstanding level of tuning in the molecular design of hybrid magnetic materials based on layered hydroxides.