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Titanium dioxide nanotubes (TNT) have been extensively studied because of their unique properties, which make such systems ideal candidates for biomedical application, especially for the targeted release of drugs. However, knowledge about the properties of TiO2 nanotubes with typical dimensions of the order of the nanometer is limited, especially concerning the adsorption of molecules that can be potentially loaded in actual devices. In this work, we investigate, by means of simulations based on hybrid density functional theory, the adsorption of Vitamin C molecules on different nanotubes through a comparative analysis of the properties of different structures. We consider two different anatase TiO2 surfaces, the most stable (101) and the more reactive (001)A; we evaluate the role of the curvature, the thickness and of the diameter as well as of the rolling direction of the nanotube. Different orientations of the molecule with respect to the surface are studied in order to identify any trends in the adsorption mechanism. Our results show that there is no preferential functional group of the molecule interacting with the substrate, nor any definite spatial dependency, like a rolling orientation or the concavity of the nanotube. Instead, the adsorption is driven by geometrical factors only, i.e., the favorable matching of the position and the alignment of any functional groups with undercoordinated Ti atoms of the surface, through the interplay between chemical and hydrogen bonds. Differently from flat slabs, thicker nanotubes do not improve the stability of the adsorption, but rather develop weaker interactions, due to the enhanced curvature of the substrate layers.

In the field of nanomedicine, significant attention is directed toward near-infrared (NIR) light-responsive inorganic nanosystems, primarily for their applications in photodynamic therapy and fluorescence bioimaging. The crucial role of the NIR range lies in enabling optimal tissue penetration, which is essential for both irradiating and detecting nanoparticles deep within the human body. In this study, we employed density functional theory (DFT) and time-dependent DFT (TDDFT) calculations to explore the structural and electronic properties of cyanine-functionalized TiO2 spherical nanoparticles (NPs) with a realistic diameter of 2.2 nm. We revealed that different adsorption configurations of cyanine (VG20-C1) on the TiO2 NP surface exhibit distinct features in the optical spectra. These cyanine dyes, serving as bifunctional linkers with two carboxylic end groups, can adsorb in either a side-on mode (binding with both end groups) or an end-on mode (binding only one end group). In end-on adsorption structures, low-energy excitations are exclusive to dye-to-dye electronic transitions, while side-on structures exhibit electron charge transfer excitations from the dye to the TiO2 NP at low energy. This thorough analysis provides a rational foundation for designing cyanine-functionalized TiO2 nanosystems with optimal optical characteristics tailored for specific nanomedical applications such as photodynamic therapy or fluorescence bioimaging.

Experimental and theoretical studies have demonstrated that the use of single atom catalysts (SACs) for energy conversion processes is very promising. However, their stability under catalytic conditions is the main issue that hinders their commercial use. In this work, we report an oxygen evolution catalyst based on single nickel atoms stabilized in triazine-based carbon nitride (CN) and a detailed study of the evolution of the Ni centers under catalytic conditions. The nanostructured materials have been characterized by combining experimental techniques, such as X-ray diffraction, transmission electron microscopy, X-ray absorption and X-ray photoemission spectroscopy, with DFT theoretical calculations to determine the CN structure, the metal adsorption sites, the coordination of the Ni atoms, and the changes undergone under catalytic conditions. Electrochemical characterization showed a linear increase of the catalytic activity with Ni loading. The stability of the materials was studied by HR-TEM and XAS post-catalysis measurements and DFT simulations. Results indicated a partial chemical restructuring of the single Ni atoms under catalytic conditions with the formation of Ni-O-Ni moieties, stabilized in the CN cavities, which are the real catalytic species.

Nanoparticles' (NPs) permeation through cell membranes, whether it happens via passive or active transport, is an essential initial step for their cellular internalization. The NPs' surface coating impacts the way they translocate through the lipid bilayer and the spontaneity of the process. Understanding the molecular details of NPs' interaction with cell membranes allows the design of nanosystems with optimal characteristics for crossing the lipid bilayer: computer simulations are a powerful tool for this purpose. In this work, we have performed coarse-grained molecular dynamics simulations and free energy calculations on spherical titanium dioxide NPs conjugated with polymer chains of different chemical compositions. We have demonstrated that the hydrophobic/hydrophilic character of the chains, more than the nature of their terminal group, plays a crucial role in determining the NPs' interaction with the lipid bilayer and the thermodynamic spontaneity of NPs' translocation from water to the membrane. We envision that this computational work will be helpful to the experimental community in terms of the rational design of NPs for efficient cell membrane permeation.By coarse-grained molecular dynamics simulations, we have unveiled that nanoparticles coated with mixed hydrophobic/hydrophilic polymer chains spontaneously penetrate lipid membranes, unlike those covered with chains of hydrophilic character only.

Molecular dynamics simulation techniques have been in the spotlight of recent nanomedicine research, becoming an indispensable tool for unveiling complex molecular mechanisms that are sometimes unreachable by experimental methods. Here, we demonstrate how MD simulations can complement existing experimental knowledge or provide new mechanistic insights into relevant aspects of nanoscale devices designed for nanomedicine. Through some case studies - from how thermodynamic variables (e.g., pH and ionic strength) affect the protein corona formation onto organic-functionalized nanoparticles to the impact of lipid composition in the permeation process of anti-tumoral drugs in membranes - this work compilation illustrates how classical MD simulations can be helpful bridging the simulated microscopic behaviors to their corresponding macroscopic manifestation.

Molecular dynamics simulation techniques have been in the spotlight of recent nanomedicine research, becoming an indispensable tool for unveiling complex molecular mechanisms that are sometimes unreachable by experimental methods. Here, we demonstrate how MD simulations can complement existing experimental knowledge or provide new mechanistic insights into relevant aspects of nanoscale devices designed for nanomedicine. Through some case studies - from how thermodynamic variables (e.g., pH and ionic strength) affect the protein corona formation onto organic-functionalized nanoparticles to the impact of lipid composition in the permeation process of anti-tumoral drugs in membranes - this work compilation illustrates how classical MD simulations can be helpful bridging the simulated microscopic behaviors to their corresponding macroscopic manifestation.

The pertechnetate ion TcVIIO4- is a nuclear fission product whose major issue is the high mobility in the environment. Experimentally, it is well known that Fe3O4 can reduce TcVIIO4- to TcIV species and retain such products quickly and completely, but the exact nature of the redox process and products is not completely understood. Therefore, we investigated the chemistry of TcVIIO4- and TcIV species at the Fe3O4(001) surface through a hybrid DFT functional (HSE06) method. We studied a possible initiation step of the TcVII reduction process. The interaction of the TcVIIO4- ion with the magnetite surface leads to the formation of a reduced TcVI species without any change in the Tc coordination sphere through an electron transfer that is favored by the magnetite surfaces with a higher FeII content. Furthermore, we explored various model structures for the immobilized TcIV final products. TcIV can be incorporated into a subsurface octahedral site or adsorbed on the surface in the form of TcIVO2·xH2O chains. We propose and discuss three model structures for the adsorbed TcIVO2·2H2O chains in terms of relative energies and simulated EXAFS spectra. Our results suggest that the periodicity of the Fe3O4(001) surface matches that of the TcO2·2H2O chains. The EXAFS analysis suggests that, in experiments, TcO2·xH2O chains were probably not formed as an inner-shell adsorption complex with the Fe3O4(001) surface.

Strategies based on the active targeting of tumor cells are emerging as smart and efficient nanomedical procedures. Folic acid (FA) is a vitamin and a well-established tumor targeting agent because of its strong affinity for the folate receptor (FR), which is an overexpressed protein on the cell membranes of the tumor cells. FA can be successfully anchored to several nanocarriers, including inorganic nanoparticles (NPs) based on transition metal oxides. Among them, TiO2 is extremely interesting because of its excellent photoabsorption and photocatalytic properties, which can be exploited in photodynamic therapy. However, it is not yet clear in which respects direct anchoring of FA to the NP or the use of spacers, based on polyethylene glycol (PEG) chains, are different and whether one approach is better than the other. In this work, we combine Quantum Mechanics (QM) and classical Molecular Dynamics (MD) to design and optimize the FA functionalization on bare and PEGylated TiO2 models and to study the dynamical behavior of the resulting nanoconjugates in a pure water environment and in physiological conditions. We observe that they are chemically stable, even under the effect of increasing temperature (up to 500 K). Using the results from long MD simulations (100 ns) and from free energy calculations, we determine how the density of FA molecules on the TiO2 NP and the presence of PEG spacers impact on the actual exposure of the ligands, especially by affecting the extent of FA–FA intermolecular interactions, which are detrimental for the targeting ability of FA towards the folate receptor. This analysis provides a solid and rational basis for experimentalists to define the optimal FA density and the more appropriate mode of anchoring to the carrier, according to the final purpose of the nanoconjugate.

Heterogeneous catalysis is an essential aspect for actual industrialization of chemical processes. Here a TiO2-based powder, typically used in photocatalysis, is exploited for the first time for visible-light-regulated Photoinduced Electron/Energy (PET)-reversible addition–fragmentation chain-transfer (RAFT). Titania is a non-toxic, low-cost, and heterogeneous catalyst that can offer several advantages in terms of sustainable polymerization and photocatalyst (PC) recovery. In this work, we aim not only at unraveling the mechanism of photopolymerization and the important interactions involved, but also at red-shifting the absorption region to achieve vis-light polymerization. The combination of the experimental investigation with Density Functional Theory (DFT) calculations provides new insights into the interactions between the chain transfer agents (CTAs) and the TiO2 surface, unveiling their pivotal role on the reaction rate and polymerization control. Moreover, to shift the polymerization under the less energetic blue light, high-surface area N-doped TiO2 nanoparticles are employed, avoiding the CTA degradation often observed with UV irradiation and increasing the overall sustainability of the process.

Doping magnetite surfaces with transition-metal atoms is a promising strategy to improve the catalytic performance toward the oxygen evolution reaction (OER), which governs the overall efficiency of water electrolysis and hydrogen production. In this work, we investigated the Fe3O4(001) surface as a support material for single-atom catalysts of the OER. First, we prepared and optimized models of inexpensive and abundant transition-metal atoms, such as Ti, Co, Ni, and Cu, trapped in various configurations on the Fe3O4(001) surface. Then, we studied their structural, electronic, and magnetic properties through HSE06 hybrid functional calculations. As a further step, we investigated the performance of these model electrocatalysts toward the OER, considering different possible mechanisms, in comparison with the pristine magnetite surface, on the basis of the computational hydrogen electrode model developed by Nørskov and co-workers. Cobalt-doped systems were found to be the most promising electrocatalytic systems among those considered in this work. Overpotential values (∼0.35 V) were in the range of those experimentally reported for mixed Co/Fe oxide (0.2-0.5 V).

Although graphitic-carbon nitride (gCN) is a highly investigated inorganic semiconductor, especially in the field of photocatalysis, it is still the object of many controversial discussions. The possibility to easily synthesize a homogeneous heterostructure through the condensation and the polymerization of simple molecules allows the growth of a variety of structures with different electronic and optical properties. With the aim of driving the development of the catalyst toward improved performances or newer applications, it is paramount to understand the optically-driven excitation process within each polymer. In this work, we focus on two models of melem-based gCN, i.e. the fully and the partially polymerized structures, and we perform a computational investigation, based on hybrid density functional theory calculations, of their optical properties in terms of vibrational and electronic excitations. First, we determine the normal modes of the ground state and we interpret the IR absorption spectrum. Then, we simulate the electronic excited state with an electron–hole pair model and we determine the exciton binding energy, the self-trapping energy and the photo-emission energy. We compare these numerical results with the experimental data available in literature and in addition we discuss the role of the different polymeric arrangements.

Fabrication of ordered structures at the nanoscale limit poses a cornerstone challenge for modern technologies. In this work we show how naturally occurring moiré patterns in Ir(111)-supported graphene template the formation of 2D ordered arrays of substitutional boron species. A complementary experimental and theoretical approach provides a comprehensive description of the boron species distribution, bonding configurations, interfacial interaction with Ir(111) and the impact on graphene's electronic structure. Atomically-resolved scanning tunnelling microscopy images and density functional theory calculations reveal that boron preferably forms small aggregates of substitutional defects in geometrically low regions of the moiré superlattice of graphene, by inducing local bending of graphene towards the underlying Ir(111). Surprisingly, calculations reveal that the incorporation of electron deficient boron does not lead to an enhanced p-type doping, as the local rippling of the graphene layer prompts electron uptake from the iridium substrate that compensates the initial electron loss due to substitutional boron. Scanning tunnelling spectroscopy and angle-resolved photoemission spectroscopy measurements corroborate that the arrays of boron species do not modify the electronic structure of graphene near the Fermi level, hence preserving the slight p-type doping induced by Ir(111).

Strategies based on the active targeting of tumor cells are emerging as smart and efficient nanomedical procedures. Folic acid (FA) is a vitamin and a well-established tumor targeting agent because of its strong affinity for the folate receptor (FR), which is an overexpressed protein on the cell membranes of the tumor cells. FA can be successfully anchored to several nanocarriers, including inorganic nanoparticles (NPs) based on transition metal oxides. Among them, TiO2 is extremely interesting because of its excellent photoabsorption and photocatalytic properties, which can be exploited in photodynamic therapy. However, it is not yet clear in which respects direct anchoring of FA to the NP or the use of spacers, based on polyethylene glycol (PEG) chains, are different and whether one approach is better than the other. In this work, we combine Quantum Mechanics (QM) and classical Molecular Dynamics (MD) to design and optimize the FA functionalization on bare and PEGylated TiO2 models and to study the dynamical behavior of the resulting nanoconjugates in a pure water environment and in physiological conditions. We observe that they are chemically stable, even under the effect of increasing temperature (up to 500 K). Using the results from long MD simulations (100 ns) and from free energy calculations, we determine how the density of FA molecules on the TiO2 NP and the presence of PEG spacers impact on the actual exposure of the ligands, especially by affecting the extent of FA-FA intermolecular interactions, which are detrimental for the targeting ability of FA towards the folate receptor. This analysis provides a solid and rational basis for experimentalists to define the optimal FA density and the more appropriate mode of anchoring to the carrier, according to the final purpose of the nanoconjugate.

Although the immobilization of oligonucleotides (nucleic acid) on mineral surfaces is at the basis of different biotechnological applications, an atomistic understanding of the interaction of the nucleic acid components with the titanium dioxide surfaces has not yet been achieved. Here, the adsorption of the phosphate anion, of the four DNA bases (adenine, guanine, thymine, and cytosine) and of some entire nucleotides and dinucleotides on the TiO2 anatase (1 0 1) surface is studied through dispersion-corrected hybrid density functional theory (DFT) calculations. Several adsorption configurations are identified for the separated entities (phosphate anion or base) and then considered when studying the adsorption of the entire nucleotides. The analysis shows that both the phosphate anion and each base may anchor the nucleotides to the surface in a collaborative and synergistic adsorption mode. The tendency is that the nucleotides containing the guanine base present the strongest adsorption while those made up with the thymine base have the lowest adsorption energies. Nucleotides based on adenine and cytosine have a similar intermediate behavior. Finally, we investigated the adsorption of competing water molecules to understand whether in the presence of the aqueous solvent, the nucleotides would remain bonded to the surface or desorb.

Doxorubicin (DOX) is one of the most efficient antitumor drugs employed in numerous cancer therapies. Its incorporation into lipid-based nanocarriers, such as liposomes, improves the drug targeting into tumor cells and reduces drug side effects. The carriers' lipid composition is expected to affect the interactions of DOX and its partitioning into liposomal membranes. To get a rational insight into this aspect and determine promising lipid compositions, we use numerical simulations, which provide unique information on DOX- membrane interactions at the atomic level of resolution. In particular, we combine classical molecular dynamics simulations and free energy calculations to elucidate the mechanism of penetration of a protonated Doxorubicin molecule (DOX+) into potential liposome membranes, here modeled as lipid bilayers based on mixtures of phosphatidylcholine (PC), sphingomyelin (SM) and cholesterol lipid molecules, of different compositions and lipid phases. Moreover, we analyze DOX+ partitioning into relevant regions of SM-based lipid bilayer systems using a combination of free energy methods. Our results show that DOX+ penetration and partitioning are facilitated into less tightly packed SM-based membranes and are dependent on lipid composition. This work paves the way to further investigations of optimal formulations for lipid-based carriers, such as those associated with pH-responsive membranes.

Saturation magnetization values close to the bulk have been reported for coated magnetite nanoparticles with organic acids. The mechanism of this effect is not yet understood. Here, we show that a previously proposed rationalization in Nano Letters 12 (2021) 2499–2503 was based on electronic structure properties that are not consistent with several existing density functional theory studies. Our study is based on a wide set of Hubbard-corrected density-functional tight-binding (DTFB + U) and hybrid density functional theory (HSE06) calculations on Fe3O4 nanocubes of more than 400 atoms. We provide a new explanation for the spin ordering in coated nanoparticles, through the investigation of spin-flipping phenomena. In particular, we show that the spin-flip of d electrons at octahedral Fe3+ sites, which is confirmed to be more favorable near the surface, especially where atomic reorganization can take place such as at corner sites, can be hampered by the presence of adsorbed organic acids because they do not only limit the surface reconstruction but also allow for additional ferromagnetic superexchange interaction between octahedral Fe sites as a consequence of the carboxylates bridging binding mode. The proof-of-concept of this mechanism is given by a simplified model of the Fe(III) tert-butoxide dimer.

Inorganic nanoparticles (NPs) are gaining increasing attention in nanomedicine because of their stimuli responsiveness, which allows combining therapy with diagnosis. However, little information is known about their interaction with intracellular or plasma proteins when they are introduced in a biological environment. Here we present atomistic molecular dynamics (MD) simulations investigating the case study of dopamine-functionalized TiO2 nanoparticles and two proteins that are overexpressed in cancer cells, i.e. PARP1 and HSP90, since experiments proved them to be the main components of the corona in cell cultures. The mechanism and the nature of the interaction (electrostatic, van der Waals, H-bonds, etc.) is unravelled by defining the protein residues that are more frequently in contact with the NPs, the extent of contact surface area and the variations in the protein secondary structures, at different pH and ionic strength conditions of the solution where they are immersed to simulate a realistic biological environment. The effects of the NP surface functionalization and charge are also considered. Our MD results suggest that less acidic intracellular pH conditions in the presence of cytosolic ionic strength enhance PARP1 interaction with the nanoparticle, whereas the HSP90 contribution is partly weakened, providing a rational explanation to existing experimental observations.

The pertechnetate ion TcVIIO4− is a nuclear fission product whose major issue is the high mobility in the environment. Experimentally, it is well-known that Fe3O4 can reduce TcVIIO4− to TcIV species and retain such products quickly and completely, but the exact nature of the redox process and products is not completely understood. Therefore, we investigated the chemistry of TcVIIO4− and TcIV species at the Fe3O4(001) surface through a hybrid DFT functional (HSE06) method. We studied a possible initiation step of the TcVII reduction process. The interaction of the TcVIIO4− ion with magnetite surface leads to the formation of a reduced TcVI species without any change in the Tc coordination sphere, through an electron transfer that is favored by the magnetite surfaces with a higher FeII content. Furthermore, we explored various model structures for the immobilized TcIV final products. TcIV can be incorporated into a subsurface octahedral site or adsorbed on the surface in the form of TcIVO2·xH2O chains. We propose and discuss three model structures for the adsorbed TcIVO2·2H2O chains in terms of relative energies and simulated EXAFS spectra. Our results suggest that the periodicity of the Fe3O4(001) surface matches that of the TcO2·2H2O chains. The EXAFS analysis suggests that in experiments TcO2·xH2O chains were probably not formed as an inner-shell adsorption complex with the Fe3O4(001) surface.

Nonequilibrium molecular dynamics simulations were performed to study the electrokinetic properties of five mainstream TIPxP water models (namely, TIP3P-FB, TIP3Pm, TIP4P-FB, TIP4P-Ew, and TIP4P/2005) in NaCl aqueous solutions in the presence of a negatively charged TiO2 surface. The impact of solvent flexibility and system geometry on the electro-osmotic (EO) mobility and flow direction was systematically assessed and compared. We found that lack of water flexibility decelerates the forward EO flow of aqueous solutions at moderate (0.15 M) or high (0.30 M) NaCl concentrations, in some special cases to such an extent that EO flow reversal occurs. Zeta potential (ZP) values were then determined from the bulk EO mobilities using the Helmholtz-Smoluchowski formula. The straight comparison against available experimental data strongly suggests that water flexibility improves the ZP determination of NaCl solutions adjacent to a realistic TiO2 surface under neutral pH conditions.

Inorganic nanoparticles show promising properties that allow them to be efficiently used as drug carriers. The main limitation in this type of application is currently the drug loading capacity, which can be overcome with a proper functionalization of the nanoparticle surface. In this study, we present, for the first time, a computational approach based on metadynamics to estimate the binding free energy of the doxorubicin drug (DOX) to a functionalized TiO2 nanoparticle under different pH conditions. On a thermodynamic basis, we demonstrate the robustness of our approach to capture the overall mechanism behind the pH-triggered release of DOX due to environmental pH changes. Notably, binding free energy estimations align well with what is expected for a pH-sensitive drug delivery system. Based on our results, we envision the use of metadynamics as a promising computational tool for the rational design and in silico optimization of organic ligands with improved drug carrier properties.

Melem (2,6,10-triamino-s-heptazine) is the building block of melon, a carbon nitride (CN) polymer that is proven to produce H2from water under visible illumination. With the aim of bringing additional insight into the electronic structure of CN materials, we performed a spectroscopic characterization of gas-phase melem and of a melem-based self-assembled 2D H-bonded layer on Au(111) by means of ultraviolet and X-ray photoemission spectroscopy (UPS, XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In parallel, we performed density functional theory (DFT) simulations of the same systems to unravel the molecular charge density redistribution caused by the in-plane H-bonds. Comparing the experimental results with the spectroscopic DFT simulations, we can correlate the induced charge accumulation on the Naminoatoms to the red-shift of the corresponding N 1s binding energy (BE) and of the Namino1s → LUMO+n transitions. Moreover, when introducing a supporting Au(111) surface in the computational simulations, we observe a molecule-substrate interaction that almost exclusively involves the out-of-plane molecular orbitals, leaving those engaged in the in-plane H-bonded network rather unperturbed.

We investigated the adsorption of severe acute respiratory syndrome corona virus 2 (SARS-CoV-2), the virus responsible for the current pandemic, on the surface of the model catalyst TiO2(101) using atomic force microscopy, transmission electron microscopy, fluorescence microscopy, and X-ray photoelectron spectroscopy, accompanied by density functional theory calculations. Three different methods were employed to inactivate the virus after it was loaded on the surface of TiO2(101): (i) ethanol, (ii) thermal, and (iii) UV treatments. Microscopic studies demonstrate that the denatured spike proteins and other proteins in the virus structure readsorb on the surface of TiO2 under thermal and UV treatments. The interaction of the virus with the surface of TiO2 was different for the thermally and UV treated samples compared to the sample inactivated via ethanol treatment. AFM and TEM results on the UV-treated sample suggested that the adsorbed viral particles undergo damage and photocatalytic oxidation at the surface of TiO2(101) which can affect the structural proteins of SARS-CoV-2 and denature the spike proteins in 30 min. The role of Pd nanoparticles (NPs) was investigated in the interaction between SARS-CoV-2 and TiO2(101). The presence of Pd NPs enhanced the adsorption of the virus due to the possible interaction of the spike protein with the NPs. This study is the first investigation of the interaction of SARS-CoV-2 with the surface of single crystalline TiO2(101) as a potential candidate for virus deactivation applications. Clarification of the interaction of the virus with the surface of semiconductor oxides will aid in obtaining a deeper understanding of the chemical processes involved in photoinactivation of microorganisms, which is important for the design of effective photocatalysts for air purification and self-cleaning materials.

Molecular dynamics simulation techniques have been in the spotlight of recent nanomedicine research, becoming an indispensable tool for unveiling complex molecular mechanisms that are sometimes unreachable by experimental methods. Here, I will exemplify how MD simulations can complement existing experimental knowledge or provide new mechanistic insights into relevant aspects of nanoscale devices designed for nanomedicine. Through some case studies - from how thermodynamic variables (e.g., pH and ionic strength) affect the protein corona formation onto organic-functionalized nanoparticles to the impact of lipid composition in the permeation process of anti-tumoral drugs in membranes - this presentation will address how classical MD simulations can be helpful bridging the simulated microscopic behavior to their corresponding macroscopic manifestation.

Inorganic nanoparticles are excellent tools to create smart bioinorganic nanodevices for drug delivery, targeting and imaging. To investigate these complex systems, we use multiscale approaches ranging from first-principles calculations to atomistic molecular dynamics simulations, metadynamics, umbrella sampling and machine learning.

An easy and cost-effective method is presented to functionalize graphene through thermally activated dimerization of 2,5-diaryltetrazoles. Consistently with the experimental spectroscopic results, theoretical calculations demonstrate that during the thermal treatment a dimerization process to tetrazine is energetically more favorable than covalent grafting. Since both the functionalization method by thermal activation and the use of tetrazoles have never been considered before to prepare graphene-based chemiresistors, this represents a promising approach to develop graphene-related sensing platforms. Five different 2,5-diaryltetrazoles have been tested here for the effective functionalization of low-defect graphene layers on silicon nitride. Based on these layers, an array of sensors has been prepared for testing upon ammonia exposure. The tests on the sensing performances clearly show sensitivity to ammonia, extending the current range of ammonia detection with a graphene-based chemiresistor down to the sub-ppm range, as results from a benchmarking with data available in the literature. Furthermore, all sensors perform better than bare graphene. Density functional theory (DFT) calculations, carried out on a model of the best performing layer of the array, provided the theoretical framework to rationalize the sensing mechanism and disclose a dual role played by the tetrazine molecules, (i) acting as ammonia concentrators and (ii) mediating the electron transfer between ammonia and graphene.

An easy and cost-effective method is presented to functionalize graphene through thermally activated dimerization of 2,5-diaryltetrazoles. Consistently with the experimental spectroscopic results, theoretical calculations demonstrate that during the thermal treatment a dimerization process to tetrazine is energetically more favorable than covalent grafting. Since both the functionalization method by thermal activation and the use of tetrazoles have never been considered before to prepare graphene-based chemiresistors, this represents a promising approach to develop graphene-related sensing platforms. Five different 2,5-diaryltetrazoles have been tested here for the effective functionalization of low-defect graphene layers on silicon nitride. Based on these layers, an array of sensors has been prepared for testing upon ammonia exposure. The tests on the sensing performances clearly show sensitivity to ammonia, extending the current range of ammonia detection with a graphene-based chemiresistor down to the sub-ppm range, as results from a benchmarking with data available in the literature. Furthermore, all sensors perform better than bare graphene. Density functional theory (DFT) calculations, carried out on a model of the best performing layer of the array, provided the theoretical framework to rationalize the sensing mechanism and disclose a dual role played by the tetrazine molecules, (i) acting as ammonia concentrators and (ii) mediating the electron transfer between ammonia and graphene.

Functionalized titanium dioxide (TiO2) nanoparticles (NPs) with intense fluorescent dyes are a promising tool for several technological applications ranging from photochemistry, photocatalysis, photovoltaics, photodynamic therapy, or bioimaging. Here, we present the case study of Alizarin adsorption on TiO2 NPs of different shapes and increasing size up to 2.2 nm (700 atoms), by means of density functional theory calculations. We find that Alizarin can bind in three different ways, depending on the number and the type of bonds between Alizarin and TiO2: ‘tridented’, ‘bidented’, and ‘chelated’. Next, we investigate the optical properties of these systems by time-dependent density functional theory calculations. Based on the absorption spectra and the Kohn–Sham orbitals analysis, we discovered that the mechanism of electron injection depends on the Alizarin binding mode to the TiO2 surface. While for bidented and chelated adsorption modes, a direct charge transfer is observed; for the tridented one, an indirect mechanism governs the charge transfer process following the excitation. Our results are in good agreement with existing experimental data and suggest that by tailoring the shape of the TiO2 NPs and, thus, determining the type of undercoordinated Ti atoms prevalently exposed at the surface, it is possible to control the predominant injection mechanism.

Surface functionalization is found to prevent the reduction of saturation magnetization in magnetite nanoparticles, but the underlying mechanism is still to be clarified. Through a wide set of hybrid density functional theory (HSE06) calculations on Fe3O4 nanocubes, we explore the effects of the adsorption of various ligands (containing hydroxyl, carboxylic, phosphonic, catechol, and silanetriol groups), commonly used to anchor surfactants during synthesis or other species during chemical reactions, onto the spin and structural disorder, which contributes to the lowering of the nanoparticle magnetization. The spin-canting is simulated through a spin-flip process at octahedral Fe ions and correlated with the energy separation between O2- 2p and FeOct3+ 3d states. Only multidentate bridging ligands hamper the spin-canting process by establishing additional electronic channels between octahedral Fe ions for an enhanced ferromagnetic superexchange interaction. The presence of anchoring organic acids also interferes with structural disorder, by disfavoring surface reconstruction.

In this paper we performed the deposition and self-assembly of a Pd-cyclometallated compound on Ag(1 1 0) surface for the first time. The system is investigated from the morphological and chemical point of view by scanning tunneling microscopy and x-ray photoemission spectroscopy, respectively, and the results are validated by ab-initio calculations. Our combined experimental and theoretical study aims at elucidating the atomistic details of the chemical steps following Pd cyclometallate deposition on the metallic substrate. To do that, we analyze the electronic and chemical properties of the species present on the surface at the end of the preparation process at room temperature and at 150 °C. We observe an unexpected complex chemistry: on one side, the organometallic molecules are found to dissociate into fragments, forming a well-ordered metal–carbon network; on the other side, Pd atoms become buried in the bulk of the metal substrate following metal exchange with surface Ag atoms. The details of this mechanistic study reveal the active role played by the metal substrate in promoting the chemistry of the deposited Pd cyclometallates and could open new perspectives for the application of this class of materials in heterogeneous catalysis.

Single atom catalysts (SACs) embedded in bidimensional (2D) materials are commonly viewed as chemically doped 2D systems whose electronic properties can be discussed in terms of solid state physics, where the doping atoms are perturbating agents to the semimetallic (graphene) or insulating (h-BN) character of the 2D material. In this Perspective, we present a different and closer viewpoint, where the SAC electronic properties are interpreted in terms of coordination chemistry concepts, as the transition metal (TM) atom is complexed by a giant macrocycle, which is the defective 2D layer. In the crystal/ligand field theories, both electrostatic and covalent interactions between SAC and the surrounding 2D material are accounted for defining the splitting and mixing of the TM d states. This analysis reveals the key role played by the type of 2D material not only in determining spin and charge of SAC but also in stabilizing several SAC oxidative states via charge delocalization for an enhanced catalytic activity.

Doxorubicin (DOX) is one of the most efficient antitumor drugs employed in numerous cancer therapies. Its incorporation into lipid-based nanocarriers, such as liposomes, improves the drug targeting into tumor cells and reduces drug side effects. The carriers' lipid composition is expected to affect the interactions of DOX and its partitioning into liposomal membranes. To get a rational insight into this aspect and determine promising lipid compositions, we use numerical simulations, which provide unique information on DOX-membrane interactions at the atomic level of resolution. In particular, we combine classical molecular dynamics simulations and free energy calculations to elucidate the mechanism of penetration of a protonated Doxorubicin molecule (DOX+) into potential liposome membranes, here modeled as lipid bilayers based on mixtures of phosphatidylcholine (PC), sphingomyelin (SM) and cholesterol lipid molecules, of different compositions and lipid phases. Moreover, we analyze DOX+ partitioning into relevant regions of SM-based lipid bilayer systems using a combination of free energy methods. Our results show that DOX+ penetration and partitioning are facilitated into less tightly packed SM-based membranes and are dependent on lipid composition. This work paves the way to further investigations of optimal formulations for lipid-based carriers, such as those associated with pH-responsive membranes.

Doxorubicin (DOX) is one of the most efficient antitumor drugs in numerous cancer therapies. Its incorporation into lipid-based nanocarriers, such as liposomes, improves the drug targeting into tumor cells and reduces drug side effects. The carriers' lipid composition is expected to affect the interactions of DOX and its partitioning into liposomal membranes. In this context, numerical simulation methods are of great value in designing and determining promising lipid compositions, providing unique information on drug-membrane interactions at the atomic/molecular level of resolution. This speed talk will highlight the capabilities of a theoretical framework developed in our research group combining classical molecular dynamics simulations and free energy calculations to elucidate the molecular mechanism of penetration and partitioning of DOX into potential liposome membrane compositions. Such molecular knowledge, synergically combined with experiments, can help the improvement of the therapeutic efficacy of liposomal anticancer drug products by optimizing their formulations.