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Open AccessArticle

Crystallographic and Physicochemical Analysis of Bovine and Human Teeth Using X-ray Diffraction and Solid-State Nuclear Magnetic Resonance

by Noriko Hiraishi, Tadamu Gondo, Yasushi Shimada, Robert Hill and Fumiaki Hayashi

J. Funct. Biomater. 2022, 13(4), 254; https://doi.org/10.3390/jfb13040254 - 19 Nov 2022

Cited by 10 | Viewed by 2819

Abstract

Dental research often uses bovine teeth as a substitute for human teeth. The aim of this study was to evaluate differences in the crystalline nanostructures of enamel and dentin between bovine and human teeth, using X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (NMR). The crystallite size (crystallinity) and microstrains were analyzed using XRD with the Rietveld refinement technique and the Halder–Wagner method. The ³¹P and ¹H NMR chemical environments were analyzed by two-dimensional (2D) ¹H-³¹P heteronuclear-correlation (HETCOR) magic-angle spinning (MAS) NMR spectroscopy. Enamel had a greater crystallite size and fewer microstrains than dentin for both bovine and human teeth. When compared between the species, the bovine apatite had a smaller crystallite size with more microstrains than the human apatite for both dentin and enamel. The 2D HETCOR spectra demonstrated that a water-rich layer and inorganic HPO₄²⁻ ions were abundant in dentin; meanwhile, the hydroxyl group in the lattice site was more dominant in enamel. A greater intensity of the hydroxyl group was detected in human than in bovine for both dentin and enamel. For ³¹P projections, bovine dentin and bovine enamel have wider linewidths than human dentin and human enamel, respectively. There are differences in the crystallite profile between human and bovine. The results of dental research should be interpreted with caution when bovine teeth are substituted for human teeth. Full article

(This article belongs to the Special Issue Functional Materials for Dental Restorations)

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19 pages, 2317 KB

Open AccessArticle

2D Solid-State HETCOR ¹H-¹³C NMR Experiments with Variable Cross Polarization Times as a Tool for a Better Understanding of the Chemistry of Cellulose-Based Pyrochars—A Tutorial

by Heike Knicker, Marta Velasco-Molina and Michael Knicker

Appl. Sci. 2021, 11(18), 8569; https://doi.org/10.3390/app11188569 - 15 Sep 2021

Cited by 12 | Viewed by 5100

Abstract

The chemistry and nature of biochars are still far from being well understood. In the present work, solid-state 2D HETCOR ¹H-¹³C NMR spectroscopy is introduced for an improved characterization of the aromatic network in biochars. To that end, a pyrochar obtained from the pyrolysis of cellulose at 350 °C for 1 h was used as an example. Variation of the contact time during cross polarization from 50 µs, to 200 µs and 1000 µs gave information about the protonation degree of the different C groups and their interactions. We demonstrated that carbohydrates did not survive the used pyrolysis conditions. Therefore, O-alkyl C was assigned to ethers. Phenols were not identified to a higher extent suggesting that furan and benzofuran-type units determine the O-functionality of the aromatic domains. The latter are directly connected to alkyl chains. Those features are expected to affect chemical but also physical properties of the biochar. Based on our results, we developed a new concept describing the nature of the aromatic network in the studied cellulose-based pyrochars. The latter contrasts common views about the chemical nature of biochar, possibly because pyrolysis temperatures > 350 °C are required for achieving advanced condensation of the aromatic domains. Full article

(This article belongs to the Special Issue Composts and Organic Wastes: Analytical Methods and Applications)

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14 pages, 3491 KB

Open AccessReview

Structural Changes of Hydroxylapatite during Plasma Spraying: Raman and NMR Spectroscopy Results

by Robert B. Heimann

Coatings 2021, 11(8), 987; https://doi.org/10.3390/coatings11080987 - 19 Aug 2021

Cited by 16 | Viewed by 4330

Abstract

Functional osseoconductive coatings based on hydroxylapatite (HAp) and applied preferentially by atmospheric plasma spraying to medical implant surfaces are a mainstay of modern implantology. During contact with the hot plasma jet, HAp particles melt incongruently and undergo complex dehydration and decomposition reactions that alter their phase composition and crystallographic symmetry, and thus, the physical and biological properties of the coatings. Surface analytical methods such as laser-Raman and nuclear magnetic resonance (NMR) spectroscopies are useful tools to assess the structural changes of HAp imposed by heat treatment during their flight along the hot plasma jet. In this contribution, the controversial information is highlighted on the existence or non-existence of oxyapatite, i.e., fully dehydrated HAp as a thermodynamically stable compound. Full article

(This article belongs to the Special Issue Calcium Phosphate and Bioglass Materials for Bone Implant Applications)

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2 pages, 15 KB

Open AccessAbstract

Synthesis and Characterization of New Naphthoquinonic Derivatives Containing the Pyrazole Ring: Pyrazolylnaphthoquinones

by Norma R. Sperandeo and María M. De Bertorello

Molecules 2000, 5(3), 508-509; https://doi.org/10.3390/50300508 - 22 Mar 2000

Cited by 2 | Viewed by 5731

Abstract

The reaction of 3-aminopyrazole (1) with 1,2-naphthoquinone-4-sulfonic acid sodium salt (2) was studied in different aqueous media. The novel pyrazolylnaphthoquinones synthesized were physical and spectroscopically characterized, including 2D NMR spectroscopy (HETCOR). The possible reaction mechanism is proposed. Full article

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