On the Comprehensive Precipitation of Hydroxyapatites Unraveled by a Combined Kinetic-Thermodynamic Approach.

The present study combines experimental and theoretical approaches to investigate the competitive precipitation of calcium phosphates (CaPs) in aqueous solution in order to understand and control both the structural and textural properties of the synthesized hydroxyapatites (HAps). Some of the precipitation reactions were followed by in situ Raman spectroscopy or achieved under kinetically controlled conditions. The CaP precursors of HAps were identified as a function of the precipitation pH of the medium and the order of introduction of the precursor ions in the synthesis reactor. Their formation was rationalized by calculations based on a homogeneous nucleation model. Depending on the synthesis conditions, precipitation reaction pathways of HAps are proposed by bringing together the kinetic model developed in the present study and our previous thermodynamic model. HAps are complex materials due to the ease with which large amounts of crystallographic defects, such as carbonates and hydrogen phosphates, can be incorporated in their structure. As these defects play a key role in material sciences (bone substitute, heterogeneous acid-base catalysis, etc.), the present work also includes the analysis of the formation of these crystallographic defects in the apatitic framework, allowing a better control of their incorporation through careful selection of operating parameters.

In-place molecular preservation of cellulose in 5,000-year-old archaeological textiles.

The understanding of fossilization mechanisms at the nanoscale remains extremely challenging despite its fundamental interest and its implications for paleontology, archaeology, geoscience, and environmental and material sciences. The mineralization mechanism by which cellulosic, keratinous, and silk tissues fossilize in the vicinity of archaeological metal artifacts offers the most exquisite preservation through a mechanism unexplored on the nanoscale. It is at the center of the vast majority of ancient textiles preserved under nonextreme conditions, known through extremely valuable fragments. Here we show the reconstruction of the nanoscale mechanism leading to the preservation of an exceptional collection of ancient cellulosic textiles recovered in the ancient Near East (4,000 to 5,000 years ago). We demonstrate that even the most mineralized fibers, which contain inorganic compounds throughout their histology, enclose preserved cellulosic remains in place. We evidence a process that combines the three steps of water transport of biocidal metal cations and soil solutes, degradation and loss of crystallinity of cellulosic polysaccharides, and silicification.

The Formation of Chemical Degraders during the Conservation of a Wooden Tudor Shipwreck.

Determining the nature, evolution, and impact of acid-generating sulfur deposits in the Mary Rose wooden hull is crucial for protecting Henry VIII's famous warship for generations to come. Here, a comprehensive X-ray absorption near-edge spectroscopy (XANES) and X-ray fluorescence (XRF) study sheds vital light on the evolution of complex sulfur-based compounds lodged in Mary Rose timbers as a function of drying time. Combining insights from infrared spectroscopy correlates the presence of oxidized sulfur species with increased wood degradation via the loss of major wood components (holocellulose). Intriguingly, zinc is found to co-exist with iron and sulfur in the most degraded wood regions, indicating its potential contributing role to wood degradation. This study provides crucial information on the degradation processes and resulting products within the wood, which can be used to develop remediation strategies to save the Mary Rose.

3D Coumarin Systems Based on [2.2]Paracyclophane: Synthesis, Spectroscopic Characterization, and Chiroptical Properties.

In this article, we report the preparation of a series of [2.2]paracyclophane-fused coumarin systems through a simple and general procedure involving a transition-metal-catalyzed cyclization of aryl alkynoates as the key step. We also highlight the influence of the [2.2]paracyclophane (pCp) motif and its "phane" interactions on the spectroscopic properties of the newly synthesized fluorophores, which emit in the blue-green region of the visible spectrum (λem up to 560 nm) and show extremely large Stokes shifts (up to 230 nm). Finally, we demonstrate that our straightforward approach can easily be used to access optically active planar chiral 3D coumarins. Compared to previously described fluorescent paracyclophanes and other organic dyes, our compact heteroaromatic derivatives show promising chiroptical properties, both in term of circular dichroism ( gabs ∼ 8 × 10 -3) and circularly polarized luminescence ( glum ∼ 5 × 10 -3), thus demonstrating a practical application of our synthetic method.