Effects of fluorine content on the elastic behavior of topaz [Al 2 SiO 4 (F,OH) 2 ]

Int J of Quantum Chemistry

2017

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Hydroxylapatite is an important calcium phosphate phase whose knowledge is useful in different fields, for instance in bone biology, development of biomaterials and even cultural heritage. In this work, the equation of state of this mineral was calculated by using the quasi-harmonic approximation, also including for the first time the temperature effect. In athermal conditions (0 K), we found that the pressure dependence of the hydroxylapatite unit cell volume is well described by a third-order Birch-Murnaghan formulation, with parameters K 0 5 115.9(1), K' 5 4.47(6), and V 0 5 524.323 (27). The inclusion of temperature led to a lower bulk modulus, for example, KT 0 5 109.55 GPa at 300 K. The thermal expansion coefficient between 0 and 1000 K was also reported. The results are in good agreement with the few available experimental data reported in literature and further extend the knowledge of the mechanical and thermal behavior of this important mineral. K E Y W O R D S DFT/B3LYP-D*, equation of state, hydroxylapatite, quasi-harmonic approximation, thermal expansion coefficient | I N TR ODU C TI ONThe growing interest in biomaterials and biominerals led, in recent years, to several researches aimed to unravel the mechanical properties of calcium phosphates among which hydroxylapatite (OHAp, space group P6 3 /m, Figure 1) is one of the most investigated because of its similarities to the mineral phase of bone and dental tissues. For instance, specific and peculiar experimental Raman piezo-spectroscopy were employed to better understand the microscopic processes governing the behavior of natural bone tissues (sane and osteoporotic) as well as the mechanochemical framework describing how the microstructure of synthetic biomaterials affects the failure of artificial joints. [1,2] This method can analyse the mechanical stress as stored in the apatite crystals belonging to both natural bone (sane and osteoporotic) and synthetic biomaterials by the Raman shift of the apatite (compared to unstressed apatite). Another example regards the mechanical stability and failure of hydroxylapatite/collagen fibrils nano-composite, which was simulated by molecular mechanics methods in several works of Dubey and Tomar. [3][4][5] Finally, the effects of carbonate ion on the OHAp unit cell was studied from both the structural [6][7][8][9][10] and vibrational [11][12][13][14] points of view, to better understand the differences between stoichiometric hydroxylapatite and biological apatite (which contains several CO 22 3 and other ionic substitutions). Hexagonal OHAp is known to be a piezoelectric material, a property related to the ordered hydroxyl group alignment in the calcium channel.According to recent studies in literature, [15][16][17][18] OHAp exhibits also a ferroelectric behavior. Being a piezoelectric compound, a detailed knowledge on the mechanical properties of hydroxylapatite could be important.Hydroxylapatite is also a valued material for cultural heritage purposes. Recently, it was found that this mineral could be used to...

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Equation of state of hexagonal hydroxylapatite (P6₃) as obtained from density functional theory simulations

Int J of Quantum Chemistry

2017

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“…The chosen basis sets are well balanced and, in particular the one of the hydrogen atom, allow accurate calculations in both molecular and crystal structures with sustainable computational costs. Furthermore, they have been employed with good results in previous investigations on other phyllosilicates (Ulian & Valdrè, 2015a; Ulian & Valdrè, 2015b) and topaz (Ulian & Valdrè, 2017).…”

Section: Methodsmentioning

confidence: 99%

Nano‐atomic scale hydrophobic/philic confinement of peptides on mineral surfaces by cross‐correlated SPM and quantum mechanical DFT analysis

Moro

2020

Journal of Microscopy

The fundamental knowledge of the interaction between biomolecules and mineral surfaces is of utmost importance to drive new technological advancements, particularly for condensation, aggregation, catalysis and exchange of biomolecules. The mineral surface can be used in several fields and applications, for instance in biotechnology, environmental science and remediation, soil science, agro-food and related technology. This kind of knowledge may also provide several suggestions and have implications also for the prebiotic chemistry field, namely the study of the abiotic physicochemical steps that could have led to the 'creation' of the first known living organism. Nowadays, this kind of information at the micro and nanometric scale can be explored with several experimental and theoretical techniques and, among them, atomic force microscopy (AFM)-related methods and density functional theory (DFT) are particularly suited to investigate adsorption processes at single molecule level. In the present work, the specific interaction at the atomic scale between a small peptide (di-glycine) and the (001) surface of clinochlore, a mineral presenting alternately stacked talc-like layers (hydrophilic) and brucite-like sheets (hydrophobic), was characterized by means of a cross-correlated approach combining AFM and DFT simulations. The experiments evidenced the preferential adsorption of di-glycine onto the hydrophobic brucite-like sheet of the mineral, with the observed molecules organized as dot-like (single-molecules), agglomerates, filament-like and network structures by the surface, whereas only very few peptides were imaged onto the hydrophilic talc-like layer. From the theoretical analysis, the most stable conformation of the

“…Each model was then geometrically optimized. This approach has been successfully adopted for other mineral phases [6] , [19] .…”

Section: Experimental Design Materials and Methodsmentioning

confidence: 99%

Crystal-chemical and structural data related to the equation of state and second-order elastic constants of portlandite Ca(OH)2 and brucite Mg(OH)2

2018

Data in Brief

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This data article reports crystal-chemical and structural data (unit cell parameters and internal coordinates) of two hydroxyl minerals, namely brucite [magnesium hydroxide, Mg(OH)2] and portlandite [calcium hydroxide, Ca(OH)2], which were calculated and employed to derive the mechanical behavior of these solid phases under hydrostatic compression (Ulian and Valdrè, 2018). The dataset has been obtained by ab initio quantum mechanical means, by employing Density Functional Theory methods, in particular the B3LYP hybrid functional, all-electron Gaussian-type orbitals basis sets and a correction to take into account the effects of dispersive forces. Equilibrium and expanded/compressed models of both minerals were realized and geometrically optimized within two space group settings, Pnormal3¯m1 and Pnormal3¯.