Unravelling the specific site preference in doping of calcium hydroxyapatite with strontium from ab initio investigations and Rietveld analyses

Strontium can be substituted into the calcium sublattice of hydroxyapatite without a solubility limit. However, recent ab initio simulations carried out at 0 K report endothermic nature of this process. There is also striking discrepancy between experimentally observed preference of Sr doping at Ca-II sites and the first principles calculations, which indicate that a Ca-I site is preferred energetically for the Sr substitution. In this paper we combine insights from Density Functional Theory simulations and regular configurational entropy calculations to determine the site preference of Sr doping in the range of 0-100 at% at finite temperatures. In addition, samples of Sr-HA are synthesized and refinement of the relevant structural information provides benchmark information on the experimental unit cell parameters of Sr-HA. We find that the contribution of the entropy of mixing can efficiently overcome the endothermic excess energy at a temperature typical of the calcining step in the synthesis route of hydroxyapatite (700-950 degrees C). We observe that the most preferential substitution pattern is mixed substitution of Sr regardless of the concentration. For a wet chemical method, carried out at a moderate temperature (90 degrees C), the mixed doping is still slightly favourable at higher Sr-concentrations, except the range at 20% Sr, where Site II substitution is not restricted energetically and equally possible as the mixed doping. We observe a close correspondence between our theoretical results and available experimental data. Hence it should be possible to apply this theory to other divalent dopants in HA, such as Zn2+, Mg2+, Pb2+, Cu2+, Ba2+, Cd2+ etc

Chemical features and bioactivities of cornflower (Centaurea cyanus L.) capitula: The blue flowers and the unexplored non-edible part

Cornflower is a flowering weed and ornamental plant whose blue flowers have been used for food, decorative and colouring purposes. In this study, the upper (edible flowers) and lower (non-edible receptacle and involucre) parts of the capitulum were studied and compared for their chemical composition and bioactive properties. The flowers were richer in tocopherols, organic acids, and apigenin derivatives (mainly apigenin-7-O-glucuronide-4′-O-(6-O-malonylglucoside)) than the non-edible bristly part (where syringic acid predominated). Four cyanidin derivatives were identified in the flowers. The extract of the non-edible part was more efficient in inhibiting the formation of thiobarbituric acid reactive substances (TBARS), the bleaching of β-carotene, and the haemolysis of the erythrocytes membrane. In general, the extracts were more active against Gram-positive bacteria and had no cytotoxicity against non-tumour liver PLP2 cells. Therefore, while flowers are a potential source of natural cyanidin-based colorants, the lower part of the capitulum has bioactive properties to be exploited in different food or pharmaceutical formulations.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support to CIMO ( UID/AGR/00690/2013 ); to FCT for the grants of C.L. Roriz ( SFRH/BD/129551/2017 ) and C. Pereira ( SFRH/BPD/122650/2016 ) (awarded under the Programa Operacional Capital Humano (POCH) supported by the European Social Fund and National Funds of MCTES (Ministério da Ciência, Tecnologia e Ensino Superior) , and the research contracts of J. Pinela (Project AllNatt , POCI-01-0145-FEDER-030463 ) and L. Barros. This work is also funded by the European Regional Development Fund (ERDF) through the Regional Operational Program North 2020, within the scope of Project NORTE-01-0145-FEDER-023289: DeCodE and project Mobilizador Norte-01-0247-FEDER-024479: ValorNatural®; and FEDER-Interreg España-Portugal through the project 0377_Iberphenol_6_E.info:eu-repo/semantics/publishedVersio

Three-dimensionally ordered hierarchically porous tin dioxide inverse opals and immobilization of palladium nanoparticles for catalytic applications

A high surface area 3D ordered SnO2 inverted opal with walls composed of interconnected nanocrystals is reported using a facile approach with tin acetate precursors. The hierarchically porous structure exhibits porosity on multiple lengths scales (cm down to nm). The thickness of the IO wall structure comprising nanocrystals of the oxide can be tuned by multiple infilling of the precursor. Using highly monodisperse Pd nanoparticles, we show how the SnO2 IO can be functionalized with immobilized Pd NP assemblies. We show that the Pd NP size dispersion is controlled by utilizing weak ligand–metal interactions and strong metal-oxide interactions for the immobilization step. The resulting SnO2–Pd IOs were investigated X-ray photoelectron spectroscopy indicating electronic interactions between the Pd and SnO2 and alterations to NP surface chemistry. Pd NPs assembled with excellent dispersion on the ordered SnO2 IOs show superior catalytic performance for liquid phase chemical synthesis via Suzuki coupling reactions and allow easy removal of the catalyst substrate post reaction. Higher mass electrocatalytic activity is also demonstrated for formic acid oxidation, compared to commercial Pd/C catalysts, which is shown to be due to better access to the catalytically active sites on SnO2–Pd IOs. The high surface area interconnected phase-pure SnO2 IO, with programmable porosity forms a functional material for catalytic applications

ANALISIS BANJIR RANCANGAN DENGAN METODE HSS NAKAYASU PADA BENDUNGAN GINTUNG

Jebolnya Situ Gintung merupakan akibat dari perubahan debit banjir yang terus bertambah. Hal tersebut perlu diana/isis terhadap debit banjir rancangan yang selanjutnya dapat digunakan untuk merencanakan Bendungan Gintung yang baru. Berdasarkan permasalahan di atas, maka perlu dikembangkan perhitungan banjir rancangan dengan metode HSS Nakayasu. Perhitungan dengan menggunaan data hujan. Pada penelitian ini digunakan 18 Pos stasiun penangkar hujan yang diseleksi menurut kelayakan data menjadi 9 pos stasiun hujan dengan memasukan nilai hujan harian maksimum tahunan. Data curah hujan yang disaring memilki tingkat kepercayaan yang rendah, namun masih masuk ke dalam data aman. Dalam penentuan debit banjir rencana terlebih dahulu dilakukan ana/isa frekuensi dan penetapan sebaran data curah hujan kemudian diuji dengan chi-kuadrat. Distribusi yang sesuai adalah distribusi Log Pearson Type III. Dari hasil ana/isa debit banjir rancangan, untuk merencanakan bendungan digunakan debit banjir kala ulang Ql000 = 289,348 m3/dt