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1. Impacts of Initial Ca/P on Amorphous Calcium Phosphate

   https://doi.org/10.1021/acs.cgd.1c00058  

   Hoeher, Alexandria J.; Mergelsberg, Sebastian T.; Borkiewicz, Olaf J.; Michel, F. Marc (June 2021, Crystal Growth & Design)

   null (Ed.)

   Amorphous calcium phosphate (ACP) is a metastable phase in the crystallization pathway of calcium phosphates. Understanding its chemical and structural properties could provide critical insights into biomineralization mechanisms. Of particular interest is the impact of the initial Ca/P on the structure of ACP. Further, the influence of Ca/P on the size, precipitate chemistry, and transformation of ACP is crucial to understanding the metastability of amorphous phosphates. In situ pair distribution function (PDF) analysis results 5 min after mixing show that the Ca–P bonding geometry varies from predominantly monodentate, to mixed monodentate and bidentate, to predominantly bidentate as Ca/P increases from 0.2 to 5.0. This relationship is consistent across a pH range of 6–11. Samples with only monodentate Ca–P geometries transform directly to hydroxylapatite, while samples some or all bidentate geometries form brushite. Regardless of the initial ratio, the Ca/P of precipitates is close to 1.0. In situ small-angle X-ray scattering shows particle size increases with increasing Ca/P. This is the first evidence of structural variations in ACP and is directly linked to system chemistry. Synthesis of ACP with monodentate Ca–P geometries is a promising method to control the crystallization pathway to form hydroxylapatite at circumneutral pH without stabilizing ions. 

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2. Life Cycle Impacts and Techno-economic Implications of Flash Hydrolysis in Algae Processing

   Kumar, S (February 2018, ACS sustainable chemistry & engineering)

   Generation of coproducts from nutrients is purported to improve the sustainability of algae-derived transportation fuels by minimizing life cycle impacts and improving economic sustainability. Although algae cultivation produces lipids that is upgraded to drop-in transportation fuel products, life cycle assessment and techno-economic analysis have shown that without coproducts, energy/economic returns are diminishing regardless of processing methods. This study utilizes a combined flash hydrolysis (FH), hydrothermal liquefaction (HTL), and coproduct conversion technology (atmospheric precipitation/AP; hydrothermal mineralization/HTM) to conserve the most recyclable nutrients for coproduct marketability. Six biofuel pathways were developed and compared in terms of “well-to-pump” energy, life cycle greenhouse gas (LC-GHG) emissions, and economic profitability: renewable diesel II (RDII), renewable gasoline (RG), and hydroprocessed renewable jet (HRJ) fuel, each were modeled for AP and HTM coproduct conversion. A functional unit of 1 MJ usable energy was employed. RG showed a promising energy-return-on-investment (EROI) due to multiple coproducts. All models demonstrated favorable EROI (EROI > 1). LC-GHG emissions tie in with EROI such that RG produced the least emissions. HRJ-HTM was determined to be the most profitable model with a profitability index (PI) of 0.75. Sensitivity analyses revealed that dewatering affects EROI and PI significantly. To achieve break-even, gasoline must sell at $4.10/gal, diesel at $5.64/gal, and jet fuel at $3.43/gal. 

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3. Shear and endothelial induced late-stage calcific aortic valve disease-on-a-chip develops calcium phosphate mineralizations

   https://doi.org/10.1039/d1lc00931a  

   Mendoza, Melissa; Chen, Mei-Hsiu; Huang, Peter; Mahler, Gretchen J. (March 2022, Lab on a Chip)

   Calcific aortic valve disease (CAVD) is an active pathobiological process leading to severe aortic stenosis, where the only treatment is valve replacement. Late-stage CAVD is characterized by calcification, disorganization of collagen, and deposition of glycosaminoglycans, such as chondroitin sulfate (CS), in the fibrosa. We developed a three-dimensional microfluidic device of the aortic valve fibrosa to study the effects of shear stress (1 or 20 dyne per cm 2 ), CS (1 or 20 mg mL −1 ), and endothelial cell presence on calcification. CAVD chips consisted of a collagen I hydrogel, where porcine aortic valve interstitial cells were embedded within and porcine aortic valve endothelial cells were seeded on top of the matrix for up to 21 days. Here, we show that this CAVD-on-a-chip is the first to develop human-like calcified nodules varying in calcium phosphate mineralization maturity resulting from high shear and endothelial cells, specifically di- and octa-calcium phosphates. Long-term co-culture microfluidic studies confirmed cell viability and calcium phosphate formations throughout 21 days. Given that CAVD has no targeted therapies, the creation of a physiologically relevant test-bed of the aortic valve could lead to advances in preclinical studies. 

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4. Amyloid-like amelogenin nanoribbons template mineralization via a low-energy interface of ion binding sites

   https://doi.org/10.1073/pnas.2106965119  

   Akkineni, Susrut; Zhu, Cheng; Chen, Jiajun; Song, Miao; Hoff, Samuel E.; Bonde, Johan; Tao, Jinhui; Heinz, Hendrik; Habelitz, Stefan; De Yoreo, James J. (May 2022, Proceedings of the National Academy of Sciences)

   Protein scaffolds direct the organization of amorphous precursors that transform into mineralized tissues, but the templating mechanism remains elusive. Motivated by models for the biomineralization of tooth enamel, wherein amyloid-like amelogenin nanoribbons guide the mineralization of apatite filaments, we investigated the impact of nanoribbon structure, sequence, and chemistry on amorphous calcium phosphate (ACP) nucleation. Using full-length human amelogenin and peptide analogs with an amyloid-like domain, films of β-sheet nanoribbons were self-assembled on graphite and characterized by in situ atomic force microscopy and molecular dynamics simulations. All sequences substantially reduce nucleation barriers for ACP by creating low-energy interfaces, while phosphoserines along the length of the nanoribbons dramatically enhance kinetic factors associated with ion binding. Furthermore, the distribution of negatively charged residues along the nanoribbons presents a potential match to the Ca–Ca distances of the multi-ion complexes that constitute ACP. These findings show that amyloid-like amelogenin nanoribbons provide potent scaffolds for ACP mineralization by presenting energetically and stereochemically favorable templates of calcium phosphate ion binding and suggest enhanced surface wetting toward calcium phosphates in general. 

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5. The solubility of monazite (CePO4), SmPO4, and GdPO4 in aqueous solutions from 100 to 250 °C

   https://doi.org/https://doi.org/10.1016/j.gca.2018.08.038  

   Gysi, A.P.; Harlov, D.; Miron, G.D. (January 2018, Geochimica et cosmochimica acta)

   Monazite (CePO4) is a light rare earth element (REE) phosphate occurring as accessory mineral in metamorphic, igneous and sedimentary rocks, and is also a common mineral in REE mineral deposits. Metasomatism of monazite yields important clues about fluid-rock interaction in the crust, in particular, because its compositional variations may enable us to determine conditions of mineralization. The thermodynamic properties of monazite have been determined using several calorimetric methods, but up to the present time only a few solubility studies have been undertaken, which test the reliability of both, the thermodynamic properties of the REE phosphates and associated REE aqueous species. In this study, we have measured the solubility of the monoclinic REE phosphate end-members CePO4, SmPO4, and GdPO4 in aqueous perchloric acid solutions at temperatures from 100 to 250 °C at saturated water vapor pressure (swvp). The solubility products (Ks0) were determined according to the reaction: REEPO4 = REE3+ + PO43−. Combining available calorimetric data for the REE phosphates with the REE aqueous species from the Supcrt92 (slop98.dat) dataset, yields several orders of magnitude differences when compared with our solubility measurements. We have investigated ways to reconcile these discrepancies and propose a consistent set of provisional thermodynamic properties for REE aqueous species and REE phosphates that reproduce our measured solubility values. To reconcile these discrepancies, we have used the GEMS code package and GEMSFITS for parameter optimization by adjusting the standard Gibbs energy of REE3+ and REEOH2+ at 25 °C and 1 bar. An alternative optimization could involve adjustment of the standard Gibbs energy of REEPO4(s) and REEOH2+. Independently of the optimization method used, this study points to a need to revise the thermodynamic properties of REEOH2+ and possibly other REE hydroxyl species in future potentiometric studies. These revisions will have an impact on calculated solubilities of REE phosphates and our understanding of the mobility of REE in natural hydrothermal fluids. 

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