Marta Corno | Università degli Studi di Torino (original) (raw)

Papers by Marta Corno

Langmuir : the ACS journal of surfaces and colloids, Jan 26, 2015

In silico modeling of acidic (CH2COOH) or basic (CH2NH2) functionalized silica surfaces has been ... more 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 gradient corrected functional to provide insight in the characterization of experimentally functionalized surfaces via atmospheric pressure dielectric barrier discharge AP-DBD plasma method. Hydroxylated surfaces of crystalline cristobalite (sporting 4.8 OH/nm(2)) mimic an amorphous silica interface as un-substituted 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 Reax-FF reactive force field to assess the mobi...

The Journal of Physical Chemistry C, 2015

ABSTRACT Ordered mesoporous silicas have been widely investigated as drug carriers in several fie... more ABSTRACT Ordered mesoporous silicas have been widely investigated as drug carriers in several fields, from tis-sue 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. Ex-perimentally the drug was loaded through supercritical CO2 and its adsorption investigated through infrared spectroscopy, N2 adsorption isotherms and thermogravimetric analysis. Modelling involved static and dynamic Density Functional Theory simulations of clotrimazole adsorbed on realistic mod-els of amorphous silica surfaces. A good agreement between the computational and experimental re-sults was obtained, concerning the energies of adsorption, the infrared spectra and the distribution of drug inside the mesopores. However, a complete interpretation of the experimental results was possi-ble only when simultaneously considering all the complex aspects of the drug-silica interaction. In-deed, the combination of both approaches allowed us to describe the drug-silica interface as a mix of multiple interaction configurations, based on a subtle balance of hydrogen bonding and dispersion interactions. Furthermore, at high drug loading, clotrimazole molecules are statistically distributed on the pore walls forming an adsorbed molecular layer. Finally, notwithstanding the stable interactions, the drug still exhibits a significant mobility at room temperature, moving on a complex potential en-ergy surface, as revealed by molecular dynamics simulations.

The Journal of Physical Chemistry C, 2014

The atomistic details of the interaction between ibuprofen (one of the most common nonsteroidal a... more The atomistic details of the interaction between ibuprofen (one of the most common nonsteroidal anti-inflammatory drugs) and a realistic model of MCM-41 (one of the most studied mesoporous silica materials for drug delivery) were elucidated by quantum mechanical modeling inclusive of London forces. Calculations are based on periodic density functional theory adopting all-electron Gaussian-type basis functions of polarized double-ζ quality and the B3LYP hybrid functional. By docking the drug on different sites of the MCM-41 pore walls, we have sampled different local features of the potential energy surface of the drug–silica system, both for low and high loadings (one and seven drug molecules per unit cell, respectively). For all cases, ibuprofen adsorption in MCM-41 is exothermic (average ΔH = −99 kJ·mol–1) and exergonic (average ΔG = −33 kJ·mol–1), exclusively when London interactions are taken into account due to their dominant role in dictating all features of this system. The comparison between simulated IR and NMR spectra suggests that static disorder of the adsorbed ibuprofen due to surface sites heterogeneity can also be invoked together with the current interpretation based on a dynamic behavior of the adsorbed ibuprofen to interpret the spectral features. Analysis of H-bond patterns exhibited by the drug interacting with the MCM-41 surface silanol (SiOH) groups revealed the importance of cooperativity in the H-bond strength. The present work shows that large-scale all-electron full quantum mechanical simulations employing accurate hybrid functionals can soon become competitive over modeling studies based on molecular mechanics methods, both in terms of superior accuracy and absence of the problematic parametrization, due to organic/inorganic interface.

The Journal of Physical Chemistry C, 2014

ABSTRACT Carbonate apatite is a material of the utmost importance as it represents the inorganic ... more ABSTRACT 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 fiinctionals. The static calculations reveal a number of almost energetically equivalent carbonate configurations in the channel, leading to cell parameters compatible with the P-(3) over bar 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.

The Journal of Physical Chemistry A, 2014

Silica-based materials find applications as excipients and, particularly for those of mesoporous ... more Silica-based materials find applications as excipients and, particularly for those of mesoporous nature, as drug delivery agents for pharmaceutical formulations. Their performance can be crucially affected by water moisture, as it can modify the behavior of these formulations, by limiting their shelf life. Here we describe the role of water microsolvation on the features of ibuprofen adsorbed on a model of amorphous silica surface by means of density functional theory (DFT) simulations. Starting from the results of the simulation of ibuprofen in interaction with a dry hydrophobic amorphous silica surface, a limited number of water molecules has been added to study the configurational landscape of the microsolvated system. Structural and energetics properties, as well as the role of dispersive forces, have been investigated. Our simulations have revealed that the silica surface exhibits a higher affinity for water than for ibuprofen, even if several structures coexist at room temperature, with an active competition of ibuprofen and water for the exposed surface silanols. Dispersive interactions play a key role in this system, as pure DFT fails to correctly describe its potential energy surface. Indeed, van der Waals forces are the leading contribution to adsorption, independently of whether the drug is hydrogen-bonded directly to the surface or via water molecules.

Journal of Chemical Theory and Computation, 2013

Amorphous silica is widely employed in pharmaceutical formulations both as a tableting, anticakin... more 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.

American Mineralogist, 2013

ABSTRACT Apatite minerals draw the attention of many researchers not only in mineralogy, but also... more ABSTRACT Apatite minerals draw the attention of many researchers not only in mineralogy, but also in biology, biochemistry, and medicine because hydroxylapatite [Ca-10(PO4)(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 P6(3)) and type A carbonated apatite [Ca-10(PO4)(6)(CO3), space group P1] have been modeled by density function method using the hybrid B3LYP functional and an all-electron polarized double-zeta 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.

American Mineralogist, 2014

ABSTRACT In nature, hydroxylapatite [Ca-10(PO4)(6)(OH)(2)] is mostly present with various stoichi... more ABSTRACT 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.

Biomaterials - Physics and Chemistry, 2011

... As for bioactive glasses, the first synthesis was performed in 1969-71 by Larry Hench in Flor... more ... As for bioactive glasses, the first synthesis was performed in 1969-71 by Larry Hench in Florida (Hench et al., 1971). ... For all the images displayed in this Chapter, MOLDRAW (Ugliengo et al., 1993), J-ICE (Canepa et al., 2011b) and VMD (Humphrey et al., 1996) programs were ...

T he simulation of matter at the atomic level by computer is now an essential tool of contemporar... more T he simulation of matter at the atomic level by computer is now an essential tool of contemporary science. Atomic modelling techniques are used routinely in the study of proteins and pharmaceuticals and in the conformational analysis of organic molecules. Computational methodologies have, however, an equally important and diverse role in the study of inorganic materials, especially in complex systems such as microporous catalysts (zeolites and metalorganic frameworks, MOF), high temperature superconductors, ternary and quaternary oxides and biomaterials. Nowadays, computational methods are routinely applied in several different fields: a) modelling crystal structures: such methods are used to assist the refinement of crystal structure data but the real challenge in this field is to develop procedures for predicting structures; b) there is perhaps an even greater incentive for the development of methods for modelling amorphous structures owing to the well-known difficulties in the determination of accurate and unambiguous atomistic structures for non-crystalline solids from experimental data alone; c) modelling inorganic surface chemistry is a field of growing importance and activity, since most of the reactivity of material with the surrounding environment occurs at their surfaces. In this paper a review of recent progresses obtained in the field of computer simulations of biomaterials properties is provided. Far to be

ABSTRACT Fluorine substitution in CaH2 has been studied by means of experimental and theoretical ... more ABSTRACT Fluorine substitution in CaH2 has been studied by means of experimental and theoretical methods. Samples with various compositions have been prepared by ball milling. In situ X-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 initio DFT calculations have been performed to estimate the thermodynamic mixing properties of both orthorhombic and cubic solid solutions. On the basis of ab initio results and literature information, a thermodynamic assessment within the CALPHAD framework has been performed and the pseudo binary CaH2-CaF2 phase diagram has been calculated. The formation of orthorhombic and cubic terminal solid solutions in the CaH2-CaF2 system is predicted, in good agreement with experimental findings.

Anion substitution is at present one of the pathways to destabilize metal borohydrides for solid ... more Anion substitution is at present one of the pathways to destabilize metal borohydrides for solid state hydrogen storage. In this work, a solid solution of LiBH 4 and LiCl is studied by density functional theory (DFT) calculations, thermodynamic modeling, X-ray diffraction, and infrared spectroscopy. It is shown that Cl substitution has minor effects on thermodynamic stability of either the orthorhombic or the hexagonal phase of LiBH 4 . The transformation into the orthorhombic phase in LiBH 4 shortly after annealing with LiCl is for the first time followed by infrared measurements. Our findings are in a good agreement with an experimental study of the LiBH 4 -LiCl solid solution structure and dynamics. This demonstrates the validity of the adopted combined theoretical (DFT calculations) and experimental (vibrational spectroscopy) approach, to investigate the solid solution formation of complex hydrides.

RSC Advances, 2014

ABSTRACT As also observed for conventional silicate glasses, water can be incorporated in the bul... more ABSTRACT As also observed for conventional silicate glasses, water can be incorporated in the bulk interstitial regions of a bioactive glass (BG) matrix during the glass preparation and/or upon exposure to an aqueous environment. However, in the case of BGs, very little is known about the effect of hydration on the bulk structure, and then on key properties of these materials, such as biodegradation and bioactivity, that depend on the bulk structure itself. Here we employ a combination of atomistic simulation techniques to explore the nature and effects of water–BG interactions in the bulk of a bioactive glass. The fate of water inserted in the bulk interstitial region of 45S5 bioglass has been studied by ab initio geometry relaxations and Molecular Dynamics (AIMD) simulations. We probed the interaction of a water molecule with silica rings and cages of different size, as well as the stability of potentially relevant configurations involving manually dissociated water and opened rings. The local stability of selected configurations was further assessed by subjecting them to AIMD runs, in order to overcome possible kinetic barriers for water diffusion and dissociation. Small rings do not appear as favourable absorption sites in the bulk of a bioactive glass as they are for bioinert glasses. Moreover, water dissociation through rupture of Si–O bonds of silica rings formed in the bulk was thermodynamically unfavourable. However, a high-temperature AIMD run led to a dissociated state involving no broken Si–O bonds and a free hydroxyl: because re-optimization of this state produced the most favourable hydration energy identified in this study, dissociative absorption through this mechanism appears a likely outcome of the water–45S5 interaction at low water content. We discuss the structural and dynamical basis for the stability of this and other water–glass adducts identified, and the potential consequences of these interactions for the behaviour of the glass in a biological context.

Theoretical Chemistry Accounts, 2007

A first step towards a computational multiscale approach has been adopted here to deal with the c... more 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

The Journal of Physical Chemistry C, 2013

The adsorption of CO at hydroxyapatite (HA) surfaces has been studied by combining quantum mechan... more 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/nm 2 , 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 terminations exposed by HA crystalline nanoparticles.

The Journal of Physical Chemistry C, 2012

ABSTRACT The synthesis of halide-substituted Mg(BH4)2 by ball-milling, and characterization with ... more ABSTRACT The synthesis of halide-substituted Mg(BH4)2 by ball-milling, and characterization with respect to thermodynamics and crystal structure, has been addressed. The ball-milled mixture of Mg(BH4)2 and MgX2 (X = Cl, Br) has been investigated by in situ/ex situ synchrotron powder X-ray diffraction (SR-PXD), differential scanning calorimetry (DSC), and infrared and Raman spectroscopy. High resolution SR-PXD patterns reveal that the unit cell volume of β-Mg(BH4)2 in milled and annealed mixtures of Mg(BH4)2 with MgCl2/MgBr2 is smaller than that of pure β-Mg(BH4)2. This is due to substitution of BH4– by Cl–/Br– ions which have ionic radii smaller than that of BH4–. For comparison, ab initio calculations were run to simulate Cl substitution in α-Mg(BH4)2. The α-polymorph was used rather than the β-polymorph because the size of the unit cell was more manageable. Electronic energy data and thermodynamic considerations confirm the miscibility of MgCl2 and Mg(BH4)2, both in α- and β-polymorphs.

The Journal of Physical Chemistry C, 2011

In this work vibrational properties of alkaline-metal borohydrides and of the corresponding tetra... more 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 IR-ATR (infrared attenuated total ...

The Journal of Physical Chemistry C, 2009

ABSTRACT Different models of hydroxylated surfaces of quartz, cristobalite, and tridymite have be... more ABSTRACT 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) stretching frequency with respect to the value for a free surface OH group. Simulation of the vibrational spectra in the OH stretching region for all surfaces of each polymorph showed a general good agreement with the experimental spectra recorded on polycrystalline powdered samples validating the present surface models for further studies on molecular adsorption.

Langmuir : the ACS journal of surfaces and colloids, Jan 26, 2015

In silico modeling of acidic (CH2COOH) or basic (CH2NH2) functionalized silica surfaces has been ... more 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 gradient corrected functional to provide insight in the characterization of experimentally functionalized surfaces via atmospheric pressure dielectric barrier discharge AP-DBD plasma method. Hydroxylated surfaces of crystalline cristobalite (sporting 4.8 OH/nm(2)) mimic an amorphous silica interface as un-substituted 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 Reax-FF reactive force field to assess the mobi...

The Journal of Physical Chemistry C, 2015

ABSTRACT Ordered mesoporous silicas have been widely investigated as drug carriers in several fie... more ABSTRACT Ordered mesoporous silicas have been widely investigated as drug carriers in several fields, from tis-sue 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. Ex-perimentally the drug was loaded through supercritical CO2 and its adsorption investigated through infrared spectroscopy, N2 adsorption isotherms and thermogravimetric analysis. Modelling involved static and dynamic Density Functional Theory simulations of clotrimazole adsorbed on realistic mod-els of amorphous silica surfaces. A good agreement between the computational and experimental re-sults was obtained, concerning the energies of adsorption, the infrared spectra and the distribution of drug inside the mesopores. However, a complete interpretation of the experimental results was possi-ble only when simultaneously considering all the complex aspects of the drug-silica interaction. In-deed, the combination of both approaches allowed us to describe the drug-silica interface as a mix of multiple interaction configurations, based on a subtle balance of hydrogen bonding and dispersion interactions. Furthermore, at high drug loading, clotrimazole molecules are statistically distributed on the pore walls forming an adsorbed molecular layer. Finally, notwithstanding the stable interactions, the drug still exhibits a significant mobility at room temperature, moving on a complex potential en-ergy surface, as revealed by molecular dynamics simulations.

The Journal of Physical Chemistry C, 2014

The atomistic details of the interaction between ibuprofen (one of the most common nonsteroidal a... more The atomistic details of the interaction between ibuprofen (one of the most common nonsteroidal anti-inflammatory drugs) and a realistic model of MCM-41 (one of the most studied mesoporous silica materials for drug delivery) were elucidated by quantum mechanical modeling inclusive of London forces. Calculations are based on periodic density functional theory adopting all-electron Gaussian-type basis functions of polarized double-ζ quality and the B3LYP hybrid functional. By docking the drug on different sites of the MCM-41 pore walls, we have sampled different local features of the potential energy surface of the drug–silica system, both for low and high loadings (one and seven drug molecules per unit cell, respectively). For all cases, ibuprofen adsorption in MCM-41 is exothermic (average ΔH = −99 kJ·mol–1) and exergonic (average ΔG = −33 kJ·mol–1), exclusively when London interactions are taken into account due to their dominant role in dictating all features of this system. The comparison between simulated IR and NMR spectra suggests that static disorder of the adsorbed ibuprofen due to surface sites heterogeneity can also be invoked together with the current interpretation based on a dynamic behavior of the adsorbed ibuprofen to interpret the spectral features. Analysis of H-bond patterns exhibited by the drug interacting with the MCM-41 surface silanol (SiOH) groups revealed the importance of cooperativity in the H-bond strength. The present work shows that large-scale all-electron full quantum mechanical simulations employing accurate hybrid functionals can soon become competitive over modeling studies based on molecular mechanics methods, both in terms of superior accuracy and absence of the problematic parametrization, due to organic/inorganic interface.

The Journal of Physical Chemistry C, 2014

ABSTRACT Carbonate apatite is a material of the utmost importance as it represents the inorganic ... more ABSTRACT 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 fiinctionals. The static calculations reveal a number of almost energetically equivalent carbonate configurations in the channel, leading to cell parameters compatible with the P-(3) over bar 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.

The Journal of Physical Chemistry A, 2014

Silica-based materials find applications as excipients and, particularly for those of mesoporous ... more Silica-based materials find applications as excipients and, particularly for those of mesoporous nature, as drug delivery agents for pharmaceutical formulations. Their performance can be crucially affected by water moisture, as it can modify the behavior of these formulations, by limiting their shelf life. Here we describe the role of water microsolvation on the features of ibuprofen adsorbed on a model of amorphous silica surface by means of density functional theory (DFT) simulations. Starting from the results of the simulation of ibuprofen in interaction with a dry hydrophobic amorphous silica surface, a limited number of water molecules has been added to study the configurational landscape of the microsolvated system. Structural and energetics properties, as well as the role of dispersive forces, have been investigated. Our simulations have revealed that the silica surface exhibits a higher affinity for water than for ibuprofen, even if several structures coexist at room temperature, with an active competition of ibuprofen and water for the exposed surface silanols. Dispersive interactions play a key role in this system, as pure DFT fails to correctly describe its potential energy surface. Indeed, van der Waals forces are the leading contribution to adsorption, independently of whether the drug is hydrogen-bonded directly to the surface or via water molecules.

Journal of Chemical Theory and Computation, 2013

Amorphous silica is widely employed in pharmaceutical formulations both as a tableting, anticakin... more 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.

American Mineralogist, 2013

ABSTRACT Apatite minerals draw the attention of many researchers not only in mineralogy, but also... more ABSTRACT Apatite minerals draw the attention of many researchers not only in mineralogy, but also in biology, biochemistry, and medicine because hydroxylapatite [Ca-10(PO4)(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 P6(3)) and type A carbonated apatite [Ca-10(PO4)(6)(CO3), space group P1] have been modeled by density function method using the hybrid B3LYP functional and an all-electron polarized double-zeta 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.

American Mineralogist, 2014

ABSTRACT In nature, hydroxylapatite [Ca-10(PO4)(6)(OH)(2)] is mostly present with various stoichi... more ABSTRACT 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.

Biomaterials - Physics and Chemistry, 2011

... As for bioactive glasses, the first synthesis was performed in 1969-71 by Larry Hench in Flor... more ... As for bioactive glasses, the first synthesis was performed in 1969-71 by Larry Hench in Florida (Hench et al., 1971). ... For all the images displayed in this Chapter, MOLDRAW (Ugliengo et al., 1993), J-ICE (Canepa et al., 2011b) and VMD (Humphrey et al., 1996) programs were ...

T he simulation of matter at the atomic level by computer is now an essential tool of contemporar... more T he simulation of matter at the atomic level by computer is now an essential tool of contemporary science. Atomic modelling techniques are used routinely in the study of proteins and pharmaceuticals and in the conformational analysis of organic molecules. Computational methodologies have, however, an equally important and diverse role in the study of inorganic materials, especially in complex systems such as microporous catalysts (zeolites and metalorganic frameworks, MOF), high temperature superconductors, ternary and quaternary oxides and biomaterials. Nowadays, computational methods are routinely applied in several different fields: a) modelling crystal structures: such methods are used to assist the refinement of crystal structure data but the real challenge in this field is to develop procedures for predicting structures; b) there is perhaps an even greater incentive for the development of methods for modelling amorphous structures owing to the well-known difficulties in the determination of accurate and unambiguous atomistic structures for non-crystalline solids from experimental data alone; c) modelling inorganic surface chemistry is a field of growing importance and activity, since most of the reactivity of material with the surrounding environment occurs at their surfaces. In this paper a review of recent progresses obtained in the field of computer simulations of biomaterials properties is provided. Far to be

ABSTRACT Fluorine substitution in CaH2 has been studied by means of experimental and theoretical ... more ABSTRACT Fluorine substitution in CaH2 has been studied by means of experimental and theoretical methods. Samples with various compositions have been prepared by ball milling. In situ X-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 initio DFT calculations have been performed to estimate the thermodynamic mixing properties of both orthorhombic and cubic solid solutions. On the basis of ab initio results and literature information, a thermodynamic assessment within the CALPHAD framework has been performed and the pseudo binary CaH2-CaF2 phase diagram has been calculated. The formation of orthorhombic and cubic terminal solid solutions in the CaH2-CaF2 system is predicted, in good agreement with experimental findings.

Anion substitution is at present one of the pathways to destabilize metal borohydrides for solid ... more Anion substitution is at present one of the pathways to destabilize metal borohydrides for solid state hydrogen storage. In this work, a solid solution of LiBH 4 and LiCl is studied by density functional theory (DFT) calculations, thermodynamic modeling, X-ray diffraction, and infrared spectroscopy. It is shown that Cl substitution has minor effects on thermodynamic stability of either the orthorhombic or the hexagonal phase of LiBH 4 . The transformation into the orthorhombic phase in LiBH 4 shortly after annealing with LiCl is for the first time followed by infrared measurements. Our findings are in a good agreement with an experimental study of the LiBH 4 -LiCl solid solution structure and dynamics. This demonstrates the validity of the adopted combined theoretical (DFT calculations) and experimental (vibrational spectroscopy) approach, to investigate the solid solution formation of complex hydrides.

RSC Advances, 2014

ABSTRACT As also observed for conventional silicate glasses, water can be incorporated in the bul... more ABSTRACT As also observed for conventional silicate glasses, water can be incorporated in the bulk interstitial regions of a bioactive glass (BG) matrix during the glass preparation and/or upon exposure to an aqueous environment. However, in the case of BGs, very little is known about the effect of hydration on the bulk structure, and then on key properties of these materials, such as biodegradation and bioactivity, that depend on the bulk structure itself. Here we employ a combination of atomistic simulation techniques to explore the nature and effects of water–BG interactions in the bulk of a bioactive glass. The fate of water inserted in the bulk interstitial region of 45S5 bioglass has been studied by ab initio geometry relaxations and Molecular Dynamics (AIMD) simulations. We probed the interaction of a water molecule with silica rings and cages of different size, as well as the stability of potentially relevant configurations involving manually dissociated water and opened rings. The local stability of selected configurations was further assessed by subjecting them to AIMD runs, in order to overcome possible kinetic barriers for water diffusion and dissociation. Small rings do not appear as favourable absorption sites in the bulk of a bioactive glass as they are for bioinert glasses. Moreover, water dissociation through rupture of Si–O bonds of silica rings formed in the bulk was thermodynamically unfavourable. However, a high-temperature AIMD run led to a dissociated state involving no broken Si–O bonds and a free hydroxyl: because re-optimization of this state produced the most favourable hydration energy identified in this study, dissociative absorption through this mechanism appears a likely outcome of the water–45S5 interaction at low water content. We discuss the structural and dynamical basis for the stability of this and other water–glass adducts identified, and the potential consequences of these interactions for the behaviour of the glass in a biological context.

Theoretical Chemistry Accounts, 2007

A first step towards a computational multiscale approach has been adopted here to deal with the c... more 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

The Journal of Physical Chemistry C, 2013

The adsorption of CO at hydroxyapatite (HA) surfaces has been studied by combining quantum mechan... more 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/nm 2 , 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 terminations exposed by HA crystalline nanoparticles.

The Journal of Physical Chemistry C, 2012

ABSTRACT The synthesis of halide-substituted Mg(BH4)2 by ball-milling, and characterization with ... more ABSTRACT The synthesis of halide-substituted Mg(BH4)2 by ball-milling, and characterization with respect to thermodynamics and crystal structure, has been addressed. The ball-milled mixture of Mg(BH4)2 and MgX2 (X = Cl, Br) has been investigated by in situ/ex situ synchrotron powder X-ray diffraction (SR-PXD), differential scanning calorimetry (DSC), and infrared and Raman spectroscopy. High resolution SR-PXD patterns reveal that the unit cell volume of β-Mg(BH4)2 in milled and annealed mixtures of Mg(BH4)2 with MgCl2/MgBr2 is smaller than that of pure β-Mg(BH4)2. This is due to substitution of BH4– by Cl–/Br– ions which have ionic radii smaller than that of BH4–. For comparison, ab initio calculations were run to simulate Cl substitution in α-Mg(BH4)2. The α-polymorph was used rather than the β-polymorph because the size of the unit cell was more manageable. Electronic energy data and thermodynamic considerations confirm the miscibility of MgCl2 and Mg(BH4)2, both in α- and β-polymorphs.

The Journal of Physical Chemistry C, 2011

In this work vibrational properties of alkaline-metal borohydrides and of the corresponding tetra... more 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 IR-ATR (infrared attenuated total ...

The Journal of Physical Chemistry C, 2009

ABSTRACT Different models of hydroxylated surfaces of quartz, cristobalite, and tridymite have be... more ABSTRACT 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) stretching frequency with respect to the value for a free surface OH group. Simulation of the vibrational spectra in the OH stretching region for all surfaces of each polymorph showed a general good agreement with the experimental spectra recorded on polycrystalline powdered samples validating the present surface models for further studies on molecular adsorption.