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Melatonin is a neurohormone that ameliorates many health conditions when it is administered as a drug, but its drawbacks are its oral and intravenous fast release. To overcome the limitations associated with melatonin release, cyclodextrin-based nanosponges (CD-based NSs) can be used. Under their attractive properties, CD-based NSs are well-known to provide the sustained release of the drug. Green cyclodextrin (CD)-based molecularly imprinted nanosponges (MIP-NSs) are successfully synthesized by reacting β-Cyclodextrin (β-CD) or Methyl-β Cyclodextrin (M-βCD) with citric acid as a cross-linking agent at a 1:8 molar ratio, and melatonin is introduced as a template molecule. In addition, CD-based non-molecularly imprinted nanosponges (NIP-NSs) are synthesized following the same procedure as MIP-NSs without the presence of melatonin. The resulting polymers are characterized by CHNS-O Elemental, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric (TGA), Differential Scanning Calorimetry (DSC), Zeta Potential, and High-Performance Liquid Chromatography (HPLC-UV) analyses, etc. The encapsulation efficiencies are 60–90% for MIP-NSs and 20–40% for NIP-NSs, whereas melatonin loading capacities are 1–1.5% for MIP-NSs and 4–7% for NIP-NSs. A better-controlled drug release performance (pH = 7.4) for 24 h is displayed by the in vitro release study of MIP-NSs (30–50% released melatonin) than NIP-NSs (50–70% released melatonin) due to the different associations within the polymeric structure. Furthermore, a computational study, through the static simulations in the gas phase at a Geometry Frequency Non-covalent interactions (GFN2 level), is performed to support the inclusion complex between βCD and melatonin with the automatic energy exploration performed by Conformer-Rotamer Ensemble Sampling Tool (CREST). A total of 58% of the CD/melatonin interactions are dominated by weak forces. CD-based MIP-NSs and CD-based NIP-NSs are mixed with cream formulations for enhancing and sustaining the melatonin delivery into the skin. The efficiency of cream formulations is determined by stability, spreadability, viscosity, and pH. This development of a new skin formulation, based on an imprinting approach, will be of the utmost importance in future research at improving skin permeation through transdermal delivery, associated with narrow therapeutic windows or low bioavailability of drugs with various health benefits.

This work reports for the first time a quantum mechanical study of the interactions of a model benzodiazepine drug, i.e., nitrazepam, with various models of amorphous silica surfaces, differing in structural and interface properties. The interest in these systems is related to the use of mesoporous silica as carrier in drug delivery. The adopted computational procedure has been chosen to investigate whether silica–drug interactions favor the drug degradation mechanism or not, hindering the beneficial pharmaceutical effect. Computed structural, energetics, and vibrational properties represent a relevant comparison for future experiments. Our simulations demonstrate that adsorption of nitrazepam on amorphous silica is a strongly exothermic process in which a partial proton transfer from the surface to the drug is observed, highlighting a possible catalytic role of silica in the degradation reaction of benzodiazepines.

There are different environments in the interstellar medium (ISM), depending on the density, temperature and chemical composition. Among them, molecular clouds, often referred to as the cradle of stars, are paradigmatic environments relative to the chemical diversity and complexity in space. Indeed, there, radio to far-infrared observations revealed the presence of several molecules in the gas phase, while near-infrared spectroscopy detected the existence of submicron sized dust grains covered by H2O -dominated ice mantles. The interaction between gas-phase species and the surfaces of water ices is measured by the binding energy (BE), a crucial parameter in astrochemical modelling. In this work, the BEs of a set of sulphur-containing species on water ice mantles have been computed by adopting a periodic ab initio approach using a crystalline surface model. The Density Functional Theory (DFT)-based B3LYP-D3(BJ) functional was used for the prediction of the structures and energetics. DFT BEs were refined by adopting an ONIOM-like procedure to estimate them at CCSD(T) level toward complete basis set extrapolation, in which a very good correlation between values has been found. Moreover, we show that geometry optimization with the computationally cheaper HF-3c method followed by single point energy calculations at DFT to compute the BEs is a suitable cost-effective recipe to arrive at BE values of the same quality as those computed at full DFT level. Finally, computed data were compared with the available literature data., Proceedings of the 21st International Conference on Computational Science and Its Applications, ICCSA 2021

Melatonin (MT) is a molecule of paramount importance in all living organisms, due to its presence in many biological activities, such as circadian (sleep–wake cycle) and seasonal rhythms (reproduction, fattening, molting, etc.). Unfortunately, it suffers from poor solubility and, to be used as a drug, an appropriate transport vehicle has to be developed, in order to optimize its release in the human tissues. As a possible drug-delivery system, β-cyclodextrin (βCD) represents a promising scaffold which can encapsulate the melatonin, releasing when needed. In this work, we present a computational study supported by experimental IR spectra on inclusion MT/βCD complexes. The aim is to provide a robust, accurate and, at the same time, low-cost methodology to investigate these inclusion complexes both with static and dynamic simulations, in order to study the main actors that drive the interactions of melatonin with β-cyclodextrin and, therefore, to understand its release mechanism.

In this work, we model thin films of β-Ca(BH4)2 to understand how nanostructuration of the material can be an effective way to decrease the dehydrogenation enthalpy. Two different crystallographic faces of Ca(BH4)2 have been investigated (i.e., (001) and (101)), and two reaction pathways have been considered that release hydrogen through the formation of CaH2 and CaB6, respectively. Quantum mechanical calculations predict that size reduction from bulk to nanoscale leads to a sizeable decrease of the decomposition enthalpy of the borohydride of about 5 kJ/molH2. Therefore, the present results corroborate the evidence that nanostructured metal borohydrides show advantages for energy storage applications compared to their bulk counterparts.

ACS applied energy materials 4(7), 7327-7337 (2021). doi:10.1021/acsaem.1c01455, Because substitutions of BH$_4$$^–$ anion with Br$^–$ can stabilize the hexagonal structure of the LiBH$_4$ at room temperature, leading to a high Li-ion conductivity, its thermodynamic stability has been investigated in this work. The binary LiBH$_4$–LiBr system has been explored by means of X-ray diffraction and differential scanning calorimetry, combined with an assessment of thermodynamic properties. The monophasic zone of the hexagonal Li(BH$_4$)$_{1–x}$(Br)$_x$ solid solution has been defined equal to 0.30 ≤ x ≤ 0.55 at 30 °C. Solubility limits have been determined by in situ X-ray diffraction at various temperatures. For the formation of the h-Li(BH$_4$)$_{0.6}$(Br)$_{0.4}$ solid solution, a value of the enthalpy of mixing ($ΔH_{mix}$) has been determined experimentally equal to −1.0 ± 0.2 kJ/mol. In addition, the enthalpy of melting has been measured for various compositions. Lattice stabilities of LiBH$_4$ and LiBr have been determined by ab initio calculations using CRYSTAL and VASP codes. Combining results of experiments and theoretical calculations, the LiBH$_4$–LiBr phase diagram has been determined in all composition and temperature ranges by the CALPHAD method., Published by ACS Publications, Washington, DC

Interstellar Grains (IGs) spread in the Interstellar Medium (ISM) host a multitude of chemical reactions that could lead to the production of interstellar Complex Organic Molecules (iCOMs), relevant in the context of prebiotic chemistry. These IGs are composed of a silicate-based core covered by several layers of amorphous water ice, known as a grain mantle. Molecules from the ISM gas-phase can be adsorbed at the grain surfaces, diffuse and react to give iCOMs and ultimately desorbed back to the gas phase. Thus, the study of the Binding Energy (BE) of these molecules at the water ice grain surface is important to understand the molecular composition of the ISM and its evolution in time. In this paper, we propose to use a recently developed semiempirical quantum approach, named GFN-xTB, and more precisely the GFN2 method, to compute the BE of several molecular species at the crystalline water ice slab model. This method is very cheap in term of computing power and time and was already showed in a previous work to be very accurate with small water clusters. To support our proposition, we decided to use, as a benchmark, the recent work published by some of us in which a crystalline model of proton-ordered water ice (P-ice) was adopted to predict the BEs of 21 molecules relevant in the ISM. The relatively good results obtained confirm GFN2 as the method of choice to model adsorption processes occurring at the icy grains in the ISM. The only notable exception was for the CO molecule, in which both structure and BE are badly predicted by GFN2, a real pity due to the relevance of CO in astrochemistry.

A density functional theory (PBE functional) investigation is carried out, in which a model of an amorphous silica surface is functionalized by ortho-benzoquinone. Surface functionalization with catechol and quinone-based compounds is relevant in biomedical fields, from prosthetic implants to dentistry, to develop multifunctional coatings with antimicrobial properties. The present study provides atomistic information on the specific interactions between the functionalizing agent and the silanol groups at the silica surface. The distinct configurations of the functional groups, the hydrogen bond pattern, the role of dispersion forces and the simulated IR spectra provide detailed insight into the features of this model surface coating. Ab initio molecular dynamics gives further insights into the mobility of the functionalizing groups. As a final step, we studied the condensation reaction with allylamine, via Schiff base formation, to ground subsequent simulations on condensation with model peptides of antimicrobial activity.

Carbon monoxide (CO) is the second most abundant gas-phase molecule after molecular hydrogen (H2) of the interstellar medium (ISM). In molecular clouds, an important component of the ISM, it adsorbs at the surface of core grains, usually made of Mg/Fe silicates, and originates complex organic molecules through the catalytic power of active sites at the grain surfaces. To understand the atomistic, energetic, and spectroscopic details of the CO adsorption on core grains, we resorted to density functional theory based on the hybrid B3LYP-D* functional inclusive of dispersion contribution. We modeled the complexity of interstellar silicate grains by studying adsorption events on a large set of infinite extended surfaces cut out from the bulk Mg2SiO4 forsterite, the Mg end-member of olivines (Mg2xFe2–2xSiO4), also a very common mineral on the Earth’s crust. Energetic and structural features indicate that CO is exclusively physisorbed with binding energy values in the 23–68 kJ mol–1 range. Detailed analysis of ...

A comparative assessment of the accuracy of different quantum mechanical methods for evaluating the structure and the cohesive energy of molecular crystals is presented. In particular, we evaluate the performance of the semiempirical HF-3c method in comparison with the B3LYP-D* and the Local MP2 (LMP2) methods by means of a fully periodic approach. Three benchmark sets have been investigated: X23, G60, and the new K7; for a total of 82 molecular crystals. The original HF-3c method performs well but shows a tendency at overbinding molecular crystals, in particular for weakly bounded systems. For the X23 set, the mean absolute error for the cohesive energies computed with the HF-3c method is comparable to the LMP2 one. A refinement of the HF-3c has been attempted by tuning the dispersion term in the HF-3c energy. While the performance on cohesive energy prediction slightly worsens, optimized unit cell volumes are in excellent agreement with experiment. Overall, the B3LYP-D* method combined with a TZP basis set gives the best results. For cost-effective calculations on molecular crystals, we propose to compute cohesive energies at the B3LYP-D*/TZP level of theory on the dispersion-scaled HF-3c optimized geometries (i.e., B3LYP-D*/TZP//HF-3c(0.27) also dubbed as SP-B3LYP-D*). Besides, for further benchmarking on molecular crystals, we propose to combine the three test sets in a new one denoted as MC82.

Confinement in mesoporous silica can greatly increase the solubility of pharmaceutical compounds. Propionic acid derivatives (a very popular class of drugs that include ibuprofen and ketoprofen) would greatly benefit from such technology, given their common apolar character. However, it is still debated whether, after confinement, these drugs are adsorbed on the pore walls as individual molecules or they keep the H-bonded dimeric structure that exists in their crystalline form. Their physical state inside the mesopores could have important consequences on the final performances of the drug delivery system. We employed accurate periodic density functional theory simulations, both static and dynamic, to investigate the issue. We simulated ibuprofen, as a model for all propionic acid derivatives, adsorbed both as a monomer and as a dimer inside a realistic model for the MCM-41 mesoporous silica. We found that adsorption is energetically favored in both cases, driven by both vdW and H-bond interactions. However, through ab initio molecular dynamics, we observed a continuous forming, breaking and reforming of these interactions. In the end, by comparing computed energetics, vibrational spectra and mobility, we were able to provide some important clues on the physical state of this class of drugs inside mesoporous silica, helping to define which drug family (monomer or dimer) is more probable after confinement.

The LiBH4–NaBH4 pseudo-binary system has been investigated by X-ray diffraction, temperature-programmed photographic analysis, and differential scanning calorimetry, in order to establish the phase diagram. The polymorphic orthorhombic-to-hexagonal phase transition of LiBH4 was observed at 94 °C in samples containing NaBH4, i.e. 15 °C lower than for pure LiBH4, which indicates the dissolution of sodium into LiBH4. The formation of solid solutions was confirmed by powder X-ray diffraction measurements performed as a function of temperature. A new eutectic composition between Li0.65Na0.35BH4 and Li0.70Na0.30BH4, with a melting temperature of 216 °C, is observed. Ab initio calculations have been performed to establish the relative stabilities of the pure compounds in orthorhombic, hexagonal and cubic structures. The obtained experimental and calculated data were compared with available literature values and they were used for a thermodynamic assessment of the LiBH4–NaBH4 system by the calphad method. The enthalpy of mixing for solid and liquid solutions has been estimated on the basis of experimental data.

Ordered mesoporous silicas have been widely investigated as drug carriers in several fields, from tissue engineering to cancer therapy. The knowledge of the specific interactions between the surface of mesoporous silicas and drugs is necessary to guide development of new and improved drug delivery systems. However, such knowledge is still scarce, due to the arduous interpretation of experimental results. In this work, we characterize the incorporation of clotrimazole, a common antifungal drug, inside ordered mesoporous silica by means of a joint computational and experimental approach. Experimentally the drug was loaded through supercritical CO2 and its adsorption investigated through infrared spectroscopy, N2 adsorption isotherms, and thermogravimetric analysis. Modeling involved static and dynamic Density Functional Theory simulations of clotrimazole adsorbed on realistic models of amorphous silica surfaces. A good agreement between the computational and the experimental results was obtained, concerning...

In silico modeling of acidic (CH2COOH) or basic (CH2NH2) functionalized silica surfaces has been carried out by means of a density functional approach based on a gradient-corrected functional to provide insight into the characterization of experimentally functionalized surfaces via a plasma method. Hydroxylated surfaces of crystalline cristobalite (sporting 4.8 OH/nm2) mimic an amorphous silica interface as unsubstituted material. To functionalize the silica surface we transformed the surface Si-OH groups into Si-CH2COOH and Si-CH2NH2 moieties to represent acidic/basic chemical character for the substitution. Structures, energetics, electronic, and vibrational properties were computed and compared as a function of the increasing loading of the functional groups (from 1 to 4 per surface unit cell). Classical molecular dynamics simulations of selected cases have been performed through a Reax-FF reactive force field to assess the mobility of the surface added chains. Both DFT and force field calculations identify the CH2NH2 moderate surface loading (1 group per unit cell) as the most stable functionalization, at variance with the case of the CH2COOH group, where higher loadings are preferred (2 groups per unit cell). The vibrational fingerprints of the surface functionalities, which are the ?(C=O) stretching and ?(NH2) bending modes for acidic/basic cases, have been characterized as a function of substitution percentage in order to guide the assignment of the experimental data. The final results highlighted the different behavior of the two types of functionalization. On the one hand, the frequency associated with the ?(C=O) mode shifts to lower wavenumbers as a function of the H-bond strength between the surface functionalities (both COOH and SiOH groups), and on the other hand, the ?(NH2) frequency shift seems to be caused by a subtle balance between the H-bond donor and acceptor abilities of the NH2 moiety. Both sets of data are in general agreement with experimental measurements on the corresponding silica-functionalized materials and provide finer details for a deeper interpretation of experimental spectra.

Halide substitution in Ca(BH4)2 has been investigated in ball milled mixtures of Ca(BH4)2 and CaX2 (X = F, Cl, Br) with different molar ratios. In situ synchrotron radiation powder X-ray diffraction measurements of Ca(BH4)2 + CaCl2 with 1:0.5, 1:1 and 1:2 molar ratios reveal that no substitution of Cl− for BH4− occurs from the ball milling process. However, substitution readily occurs after the transitions from α- to β-Ca(BH4)2 and from orthorhombic to tetragonal CaCl2 upon heating above ∼250 °C, which is evident from both contraction of the unit cell and changes in the relative Bragg peak intensities, in agreement with theoretical calculations. Rietveld analyses of the obtained β-Ca((BH4)1−xClx)2 solid solutions indicate compositions from x = 0 to 0.6, depending on the amount of CaCl2 in the parent mixtures. β-Ca((BH4)0.5Cl0.5)2 was investigated by differential scanning calorimetry and has a slightly higher decomposition temperature compared to pure Ca(BH4)2. No substitution with CaF2 or CaBr2 is observed.

Carbonate apatite is a material of the utmost importance as it represents the inorganic fraction of biological hard tissues in bones and teeth. Here we study the static and dynamic features of CO 3 2 − ion in the apatitic channel of carbonate apatite (A- type substitution), by applying both static and dynamic quantum mechanical calculations based on density functional methods with B3LYP-D * and PBE functionals. The static calculations reveal a number of almost energetically equivalent carbonate con fi gurations in the channel, leading to cell parameters compatible with the P 3 ̅space group assigned by the experimental X-ray structure determination. Ab initio isothermal − isobaric molecular dynamics simulations provide insights on the CO 3 2 − mobility, showing that at the temperature of the experimental structural determination the CO 3 2 − moiety undergoes a dynamic disorder, as the carbonate group is almost free to move within the apatitic channel enhancing its exchangeability with other anions. Carbonate apatite is a material of the utmost importance as it represents the inorganic fraction of biological hard tissues in bones and teeth. Here we study the static and dynamic features of CO32- ion in the apatitic channel of carbonate apatite (A-type substitution), by applying both static and dynamic quantum mechanical calculations based on density functional methods with B3LYP-D* and PBE functionals. The static calculations reveal a number of almost energetically equivalent carbonate configurations in the channel, leading to cell parameters compatible with the P3Ì... space group assigned by the experimental X-ray structure determination. Ab initio isothermal-isobaric molecular dynamics simulations provide insights on the CO32- mobility, showing that at the temperature of the experimental structural determination the CO32- moiety undergoes a dynamic disorder, as the carbonate group is almost free to move within the apatitic channel enhancing its exchangeability with other anions. © 2013 American Chemical Society.

In nature, hydroxylapatite [Ca-10(PO4)(6)(OH)(2)] is mostly present with various stoichiometric defects. The most abundant is the carbonate ion that can occupy different crystallographic sites (namely A and B types), however, its effects on the apatite structure is still an object of debate. Type A carbonated apatite was quantum mechanically simulated in a previous study, here we extend the simulation to bulk structural and vibrational features of Na-bearing type B and mixed type A-B carbonated hydroxylapatite [Ca10-xNax(PO4)(6-x)(CO3)(x+y)(OH)(2(1-y)), space group P1]. The simulation has been performed by ab initio density functional methods. The geometry of the models (lattice parameters and internal coordinates) have been fully optimized exploring different positions of the sodium ion in the apatite unit cell. The results, in agreement with XRD data, suggest that in each crystallographic cell in the biological mineral there is at least one calcium ion substitution or vacancy per cell. The carbonate ion presence in the apatite structure is in good agreement with biological/chemical data. Furthermore, there is also a very good agreement with FTIR data reported in literature. In nature, hydroxylapatite [Ca10(PO4) 6(OH)2] is mostly present with various stoichiometric defects. The most abundant is the carbonate ion that can occupy different crystallographic sites (namely A and B types), however, its effects on the apatite structure is still an object of debate. Type A carbonated apatite was quantum mechanically simulated in a previous study, here we extend the simulation to bulk structural and vibrational features of Na-bearing type B and mixed type A-B carbonated hydroxylapatite [Ca10-xNa x(PO4)6-x(CO3)x+y(OH) 2(1-y), space group P1]. The simulation has been performed by ab initio density functional methods. The geometry of the models (lattice parameters and internal coordinates) have been fully optimized exploring different positions of the sodium ion in the apatite unit cell. The results, in agreement with XRD data, suggest that in each crystallographic cell in the biological mineral there is at least one calcium ion substitution or vacancy per cell. The carbonate ion presence in the apatite structure is in good agreement with biological/chemical data. Furthermore, there is also a very good agreement with FTIR data reported in literature. © 1997 - 2014 Mineralogical Society of America. All rights reserved.

The properties of hydroxyapatite can be improved by substitution of biologically relevant ions, such as magnesium (Mg) and strontium (Sr), into its structure. Previous work in the literature has not reached agreement as to site preferences in these substitutions, and there are suggestions that these may change with differing levels of substitution. The current work adopted a quantum mechanical approach based on density functional theory using the CRYSTAL09 code to investigate the structural changes relating to, and site preferences of, magnesium and strontium substitution (to 10 mol%) in hydroxyapatites and also to predict the corresponding vibrational spectra in the harmonic approximation. The structures underwent full geometrical optimisation within the P63 space group, indicating an energetic site preference for the Ca (2) site in the case of Mg substitution, and the Ca (1) site in the case of Sr. Shrinkage of the unit cell was observed in the case of Mg substitution, and expansion in the case of Sr substitution, in agreement with the corresponding ionic radii. Thermodynamic properties of the structures obtained from the harmonic vibrational frequency calculations confirmed that the structures were minima on the potential energy surface. Isotopic substitutions indicated that the main contribution of Sr and Mg to vibrational modes is at frequencies < 400 cm-1.

The adsorption of CO at hydroxyapatite (HA) surfaces has been studied by combining quantum mechanical modeling with experimental IR results. To model the adsorption, the hybrid B3LYP-D*, inclusive of dispersive interactions, has been adopted within the periodic boundary conditions, using the CRYSTAL09 program and a polarized Gaussian type basis set. Four HA surfaces have been investigated using slabs of finite thickness: two stoichiometric HA(001) and HA(010)R surfaces and two nonstoichiometric HA(010) in which the value of the Ca/P ratio was either higher (HA(010)_Ca-rich) or lower (HA(010)_P-rich) than the bulk value. Geometrical, energetic, and vibrational features of the adsorption process have been fully investigated, by considering CO coverage ranging from 1.5 to 6 CO/nm2, respectively. By combining the results from the modeling study with experimental IR data, it was assessed that the vibrational features of adsorbed CO can be proposed as a potential tool for the recognition of types of surface ter...

The reactivity of bioglasses, which is related to the dissolution of cations and orthosilicate groups in the physiological fluid, strongly depends on the key structural features present at the glass surfaces. On the basis of the composition and the synthetic routes employed to make the glass, surfaces with very different characteristics and thus presenting different mechanisms of dissolution can be observed. In this paper, the surface structures of two very different bioglass compositions, namely 45S5 (46.1 SiO2, 24.4 Na2O, 26.9 CaO, and 2.6 P2O5 mol %) and 77S (80.0 SiO2, 16.0 CaO, and 4.0 P2O5 mol %), have been investigated by means of periodic DFT calculations based on a PBE functional and localized Gaussian basis set as encoded in the CRYSTAL code. Our calculations show that the two glass surfaces differ by the relative amount of key structural sites such as NBOs, exposed ions, orthosilicate units, and small rings. We have demonstrated how the number of these sites affects the surface stability and reactivity (bioactivity).

Apatite minerals draw the attention of many researchers not only in mineralogy, but also in biology, biochemistry, and medicine because hydroxylapatite [Ca 10 (PO 4 ) 6 (OH) 2 ] is the main component of the mineral phase of mammalian bones. However, in nature this mineral is mostly present with various stoichiometric defects. The carbonate ion is found commonly in its structure where it can occupy different crystallographic sites; however, its configurational energy and relative orientation in the apatite lattice is still debated. In this work, bulk structural features of hexagonal hydroxylapatite (space group P 6 3 ) and type A carbonated apatite [Ca 10 (PO 4 ) 6 (CO 3 ), space group P 1] have been modeled by density function method using the hybrid B3LYP functional and an all-electron polarized double-ζ quality Gaussian-type basis set using the CRYSTAL09 computer program. The effect on the structural parameters due to the adoption of the present all-electron basis set for the Ca ion compared to the pseuodpotential adopted in previous work has also been discussed. Different orientations of the carbonate ion in the apatite unit cell have been considered. The B3LYP functional and Gaussian-type basis set with polarization have been adopted. The geometry of the model (lattice parameters and internal coordinates) has been fully optimized and resulted in very good agreement with XRD data reported in literature that suggest a “close” configuration (type A1) of the carbonate ion, i.e., with a C-O bond perpendicular to the c -axis of the apatite cell.

Amorphous silica is widely employed in pharmaceutical formulations both as a tableting, anticaking agent and as a drug delivery system, whereas MCM-41 mesoporous silica has been recently proposed as an efficient support for the controlled release of drugs. Notwithstanding the relevance of this topic, the atomistic details about the specific interactions between the surfaces of the above materials and drugs and the energetic of adsorption are almost unknown. In this work, we resort to a computational ab initio approach, based on periodic Density Functional Theory (DFT), to study the adsorption behavior of two popular drugs (aspirin and ibuprofen) on two models of an amorphous silica surface characterized by different hydrophilic/hydrophobic properties due to different SiOH surface groups' density. Particular effort was devoted to understand the role of dispersive (vdW) interactions in the adsorption mechanism and their interplay with H-bond interactions. On the hydrophilic silica surface, the H-bond pattern of the Si-OH groups rearranges to comply with the formation of new H-bond interactions triggered by the adsorbed drug. The interaction energy of ibuprofen with the hydrophilic model of the silica surface is computed to be very close to the sublimation energy of the ibuprofen molecular crystal, accounting for the experimental evidence of ibuprofen crystal amorphization induced by the contact with the mesoporous silica material. For both surface models, dispersion interactions play a crucial role in dictating the features of the drug/silica system, and they become dominant for the hydrophobic surface. It was proved that a competition may exist between directional H-bonds and nonspecific dispersion driven interactions, with important structural and energetic consequences for the adsorption. The results of this work emphasize the inadequacy of plain DFT methods to model adsorption processes involving inorganic surfaces and drugs of moderate size, due to the missing term accounting for London dispersion interactions.

The affinity towards water of a selection of well-defined, nanostructured hydroxyapatite (HA) samples was investigated by H 2 O vapour adsorption microcalorimetry and infrared (IR) spectroscopy. A large hydrophilicity of all investigated materials was confirmed. The surface features of hydrated HA were investigated on the as-synthesized samples pre-treated in mild conditions at T =303 K, whereas dehydrated HA features were characterized on samples activated at T =573 K. The relatively large hydrophilicity of the hydrated surface (−Δ ads H∼100–50 kJ mol −1 ) was due to the interaction of water with the highly polarized H 2 O molecules strongly coordinated to the surface Ca 2+ cations. At the dehydrated surface, exposing coordinatively unsaturated ( cus ) Ca 2+ cations, H 2 O was still molecularly adsorbed but more strongly (−Δ ads H∼120–90 kJ mol −1 ). The use of CO adsorption to quantify the Lewis acidic strength of HA surface sites revealed only a moderate strength of cus Ca 2+ cations, as confirmed by both microcalorimetric and IR spectroscopic measurements and ab initio calculations. This result implies that the large HA/H 2 O interaction energy is due to the interplay between cus Ca 2+ sites and nearby hydrophilic PO 4 groups, not revealed by the CO probe. The lower density of cus Ca 2+ cations at the 573 K activated HA surface with respect to the pristine one did not affect the whole hydrophilicity of the surface, as the polarizing effect of Ca sites is so strong to extend up to the fourth hydrated layer, as confirmed by both high-coverage microcalorimetric and IR spectroscopic data. No specific effects due to the investigated specimen preparation method and/or different morphology were observed.

Fluorine substitution in CaH2has been studied by means of experimental and theoretical methods. Samples with various compositions have been prepared by ball milling.In situX-ray diffraction analysis has been carried out as a function of temperature by synchrotron radiation experiments. An increase of mixing has been observed during heating, suggesting that mixing is thermodynamically favoured but it is kinetically hindered at low temperatures.Ab initioDFT calculations have been performed to estimate the thermodynamic mixing properties of both orthorhombic and cubic solid solutions. On the basis ofab initioresults and literature information, a thermodynamic assessment within the CALPHAD framework has been performed and the pseudo binary CaH2-CaF2phase diagram has been calculated. The formation of orthorhombic and cubic terminal solid solutions in the CaH2-CaF2system is predicted, in good agreement with experimental findings.

The adsorption of glycine on the Ca-rich and P-rich HA(010) nonstoichiometric surfaces has been studied at B3LYP level using a polarized triple-ζ basis set within periodic boundary conditions. Although the Ca-rich and P-rich HA(010) nonstoichiometric surfaces exhibit different terminations, giving rise to different electrostatic features in the adsorption regions, glycine preferentially adsorbs as a zwitterion on both surfaces. When adsorbed in a canonical form, the proton of the COOH group is always transferred to the HA(010) surface except for one case, which, in turn, is also the least stable one. Glycine adsorbs by favorable electrostatic interactions between COO–/Ca2+ and NH3+/PO42– species, while dispersion interactions play a minor role. The harmonic B3LYP vibrational spectrum is in very good agreement with the experimental one and, when merged with contributions due to glycine adsorbed on stoichiometric HA(010) surfaces, allows one to explain the origin of the “squat shape” of the COO– stretching ...

The features of the ferroelectric (proton ordered) hydroxyapatite HA (001) surface as derived from the P63 hexagonal HA bulk have been studied by periodic density functional calculations using the ...

In this work vibrational properties of alkaline-metal borohydrides and of the corresponding tetrafluorborates are studied by comparing DFT harmonic vibrational IR and Raman spectra of the crystals with the experimental ones, obtained by infrared attenuated total reflection and Raman techniques. The computed internal bending frequencies of the [BX4]− anions are found to be in good agreement with the experiment, and the computed stretching frequencies of tetrafluorborates are slightly underestimated. As expected, due to the neglecting of anharmonicity in the DFT spectra, the computed stretching frequencies of borohydrides are overestimated. The peak assignment of the experimental spectra is carried out in terms of factor group theory. For borohydrides, it is mostly in agreement with previously published data but for a peak observed at ca. 1400 cm–1. The peak assignment for KBF4 and LiBF4 was carried out for the first time in terms of factor group theory. This work is the first step on the way to determining...

Different models of hydroxylated surfaces of quartz, cristobalite, and tridymite have been studied with the hybrid B3LYP functional using the Gaussian basis set of polarized double-ζ quality with periodic boundary conditions. Starting from the optimized bulk structures of the polymorphs, 2D slabs exhibiting low (hkl) crystallographic planes have been cut, dangling bonds healed by hydroxyl groups, and the final structures fully optimized. The H-bond pattern at a given surface depends on the (hkl) plane and on the OH group density, exhibiting isolated, weakly interacting pairs, short chains, or strings extending through the whole surface. Cases in which no H-bonds are present envisage either a very low OH density or slab structural rigidity which hinders the OH groups to establish H-bond contacts. The thermodynamics of surface hydroxylation of the considered polymorphs has been shown to correlate with the strength of the H-bonds formed at the surfaces measured by the bathochromic shift of the ν(OH) stretchi...

H(2)O adsorption on hexagonal hydroxyapatite (001) and (010) stoichiometric surfaces has been studied at B3LYP level with a localized Gaussian basis set of polarized double-zeta quality using the periodic CRYSTAL06 code. Because four Ca(2+) cations are available at both surfaces, the considered H(2)O coverages span the 1/4 = 49 cm(-1)) and a bathochromic shift of the OH stretching modes larger than 1700 cm(-1) ( = 427 cm(-1)), which are both in good agreement with literature experimental data

The IR spectrum of the Bioglass 45S5 (of composition 46.1 SiO2, 24.4 Na2O, 26.9 CaO, and 2.6 P2O5 mol %) has been simulated by means of periodic ab initio B3LYP calculations. The initial glass structure unit cell envisaging 78 atoms was generated through a melt quench process by means of classical molecular dynamics simulations. The molecular mechanics optimized unit cell has then been fully reoptimized (both unit-cell parameters and internal coordinates) at B3LYP level in a periodic approach using Gaussian basis sets of double-ζ quality by means of the CRYSTAL06 code. Although long-range structural properties cannot be modeled by using this ab initio approach because of the intrinsic amorphous nature of the glass, the quantum mechanical simulation proved to be extremely effective in predicting and analyzing the vibrational features of this biomaterial. The effect of modifiers Na and Ca cations on the network dynamics has been assessed by comparing the 45S5 vibrational spectrum with that of amorphous v-Si...

A partial charge shell-ion model potential for silica polymorphs and their hydroxylated surfaces (FFSiOH) was parametrized in a self-consistent way using periodic B3LYP results for bulk α-cristobalite and the (100) and (001) hydroxylated surfaces. The reliability of the new potentials was checked by comparing structures, vibrational frequencies and relative phase stabilities of dense bulk silica polymorphs, namely α-quartz, α-cristobalite, α-tridymite, and Stishovite with both experimental and B3LYP data. The FFSiOH was also checked for computing structural and vibrational features of representative all-silica microporous materials, namely edingtonite, chabazite, and faujasite. As a last step, FFSiOH was adopted to predict OH stretching vibrational frequencies and relative thermodynamic stability of the most common fully hydroxylated surfaces of the dense silica polymorphs, the (100) and (001) faces of all-silica edingtonite, the features of the local Si-defect in chabazite and sodalite known as (SiOH)4 h...

A first step towards a computational multiscale approach has been adopted here to deal with the computational simulation of the Hench bioglass® 45S5, an amorphous material of 48.1% SiO2, 25.9% CaO, 22.2% Na2O and 3.7% P2O5 composition. Molecular dynamics simulations based on classical force fields followed by static minimizations on quenched structures have been run on a unit cell size suitable for subsequent ab initio calculations. The molecular mechanics optimized unit cell envisaging 78 atoms of Na12Ca7P2Si13 O44 composition and P1 symmetry has then been fully optimized (both unit cell parameters and internal coordinates) at B3LYP level in a periodic approach using gaussian basis sets of double-ζ quality and the development version of the CRYSTAL03 code. Comparison between the molecular mechanics and B3LYP optimized structures shows the latter to give a slightly higher density than the former, due to overestimation of the Si–O bonds and underestimation of the Si–O–Si and Si–O–P angles, respectively. Other geometrical features are in excellent agreement within the two approaches. Electronic properties of the Hench bioglass have been reported at B3LYP for the first time and both Mulliken charges and electronic band structure show a rather ionic character of the material, whereas a band gap of about 6.5 eV characterizes the bioglass as a strong insulator. Work presently in progress will soon allow the information to be transferred from the B3LYP calculations to the molecular mechanics engine in order to refine the presently available empirical force fields for complex ionic systems and their surfaces.

Phosphorous is ubiquitous in planet Earth and plays a fundamental role in all living systems. Finding a reasonable prebiotic source of phosphorous is not trivial, as common sources where it is present nowadays are in the form of phosphate minerals, which are rather insoluble and non-reactive materials, and, accordingly, unavailable for being readily incorporated in living organisms. A possible source of phosphorous is from the exogenous meteoritic bombardment and, in particular, in iron/nickel phosphites. These materials, by simple interaction with water, produce oxygenated phosphorous compounds, which can easily react with organic molecules, thus forming C-O-P bonds. In the present work, periodic ab-initio simulations at PBE level (inclusive of dispersive interactions) have been carried out on metallic Fe2NiP-schreibersite, as a relative abundant component of metallic meteorites, in order to characterize structural, energetics and vibrational properties of both bulk and surfaces of this material. The aim is to study the relative stability among different surfaces, to characterize both the nanocrystal morphology and the reactivity towards water molecules.

This paper aims at addressing the exploitation of solid-state carriers for hydrogen storage, with attention paid both to the technical aspects, through a wide review of the available integrated systems, and to the social aspects, through a preliminary overview of the connected impacts from a gender perspective. As for the technical perspective, carriers to be used for solid-state hydrogen storage for various applications can be classified into two classes: metal and complex hydrides. Related crystal structures and corresponding hydrogen sorption properties are reviewed and discussed. Fundamentals of thermodynamics of hydrogen sorption evidence the key role of the enthalpy of reaction, which determines the operating conditions (i.e., temperatures and pressures). In addition, it rules the heat to be removed from the tank during hydrogen absorption and to be delivered to the tank during hydrogen desorption. Suitable values for the enthalpy of hydrogen sorption reaction for operating conditions close to ambient (i.e., room temperature and 1–10 bar of hydrogen) are close to 30 kJ·molH2−1. The kinetics of the hydrogen sorption reaction is strongly related to the microstructure and to the morphology (i.e., loose powder or pellets) of the carriers. Usually, the kinetics of the hydrogen sorption reaction is rather fast, and the thermal management of the tank is the rate-determining step of the processes. As for the social perspective, the paper arguments that, as it occurs with the exploitation of other renewable innovative technologies, a wide consideration of the social factors connected to these processes is needed to reach a twofold objective: To assess the extent to which a specific innovation might produce positive or negative impacts in the recipient socioeconomic system and, from a sociotechnical perspective, to explore the potential role of the social components and dynamics in fostering the diffusion of the innovation itself. Within the social domain, attention has been paid to address the underexplored relationship between the gender perspective and the enhancement of hydrogen-related energy storage systems. This relationship is taken into account both in terms of the role of women in triggering the exploitation of hydrogen-based storage playing as experimenter and promoter, and in terms of the intertwined impact of this innovation in their current conditions, at work, and in daily life.