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PEGylation of metal oxide nanoparticles is the common approach to improve their biocompatibility and in vivo circulation time. In this work, we present a combined experimental and theoretical study to determine the operating condition that guarantee very high grafting densities, which are desirable in any biomedical application. Moreover, we present an insightful conformational analysis spanning different coverage regimes and increasing polymer chain lengths. Based on 13C NMR measurements and molecular dynamics simulations, we show that classical and popular models of polymer conformation on surfaces fail in determining the mushroom-to-brush transition point and prove that it actually takes place only at rather high grafting density values.

Functionalizing nanoparticles (NPs) with biological molecules is a promising modern strategy in bionanotechnology to build up smart bioinorganic devices for medical applications. Bifunctional linkers provide an interesting and ductile bioconjugation approach especially because they behave not only as anchoring and tethering agents but also as spacers between the NP and the biomolecules, which helps in maintaining their 3D structural and functional properties. In this work, by means of a wide set of density functional theory (DFT) electronic structure calculations and density functional tight binding (DFTB) molecular dynamics simulations, we provide an all-round investigation of the functionalization of realistic curved TiO2NPs (2–3 nm size with ∼800 atoms) with a catechol derivative, such as dopamine and DOPAC. We span from single-molecule adsorption to the full coverage regime. For the low coverage, we achieve a detailed description of the mechanisms of molecular adsorption, of the interfacial electronic charge-transfer effects, and of the processes following visible light irradiation (exciton formation, trapping, charge carrier diffusion, or recombination). We then consider a growing molecular layer on the NP and analyze the self-assembling mechanism and the effects on the electronic properties of the complex. Finally, for the maximum coverage (46 molecules per NP) we perform molecular dynamics runs at 300 K to compare the molecular configuration and electronic properties of the NP/linker complex interface before and after thermal treatment to better account for the competition between molecule/surface and molecule/molecule interactions. The use of curved NP surfaces combined with dopamine, with respect to a flat one and DOPAC, respectively, is found to be more effective for bioconjugation.

Despite the many successful syntheses and applications of dopamine-functionalized TiO2nanohybrids, there has not yet been an atomistic understanding of the interaction of this 1,2-dihydroxybenzene derivative ligand with the titanium dioxide surfaces. In this work, on the basis of a wide set of dispersion-corrected hybrid density functional theory (DFT) calculations and density functional tight binding (DFTB) molecular dynamics simulations, we present a detailed study of the adsorption modes, patterns of growth, and configurations of dopamine on the anatase (101) TiO2surface, with reference to the archetype of 1,2-dihydroxybenzene ligands, i.e., catechol. At low coverage, the isolated dopamine molecule prefers to bend toward the surface, coordinating the NH2group to a Ti5cion. At high coverage, the packed molecules succeed in bending toward the surface only in some monolayer configurations. When they do, we observe a proton transfer from the surface to the ethyl-amino group, forming terminal NH3+species, which highly interact with the O atoms of a neighboring dopamine molecule. This strong Coulombic interaction largely stabilizes the self-assembled monolayer. On the basis of these results, we predict that improving the probability of dopamine molecules being free to bend toward the surface through thermodynamic versus kinetic growth conditions will lead to a monolayer of fully protonated dopamine molecules.

In the confined zone between a bidimensional material and a metal surface, unexpected effects can take place. In this study, we show that when a nonregular two-dimensional h-BN layer is grown on a Cu(111) surface, metal adatoms spontaneously pop up from the bulk to fill the holes in the structure. We provide ample theoretical support to our findings based on a large set of dispersion-corrected density functional theory calculations and on a detailed analysis of the electronic properties and of the chemical processes at this peculiar interface. The observation can be rationalized in terms of a high affinity of Cu adatoms toward N-donor species. Defective h-BN, exposing N-terminated edges, behaves like a giant multi-N-donor macrocyclic ligand that can encapsulate metal atoms as a consequence of a huge stabilization deriving from the Cu–N bond formation. Our conclusions could apply to other metal surfaces and could even stimulate the idea of trapping different metal atoms from those of the underlying surface (e.g., more precious but more active metals) for catalytic purposes.

In most technological applications, nanoparticles are immersed in a liquid environment. Understanding nanoparticles/liquid interfacial effects is extremely relevant. This work provides a clear and detailed picture of the type of chemistry and physics taking place at the prototypical TiO2nanoparticles/water interface, which is crucial in photocatalysis and photoelectrochemistry. We present a multistep and multiscale investigation based on hybrid density functional theory (DFT), density functional tight-binding, and quantum mechanics/molecular mechanics calculations. We consider increasing water partial pressure conditions from ultra-high vacuum up to the bulk water environment. We first investigate single water molecule adsorption modes on various types of undercoordinated sites present on a realistic curved nanoparticle (2–3 nm) and then, by decorating all the adsorption sites, we study a full water monolayer to identify the degree of water dissociation, the Brønsted–Lowry basicity/acidity of the nanoparticle in water, the interface effect on crystallinity, surface energy, and electronic properties, such as the band gap and work function. Furthermore, we increase the water coverage by adding water multilayers up to a thickness of 1 nm and perform molecular dynamics simulations, which evidence layer structuring and molecular orientation around the curved nanoparticle. Finally, we clarify whether these effects arise as a consequence of the tension at the water drop surface around the nanosphere by simulating a bulk water up to a distance of 3 nm from the oxide surface. We prove that the nanoparticle/water interfacial effects go rather long range since the dipole orientation of water molecules is observed up to a distance of 5 Å, whereas water structuring extends at least up to a distance of 8 Å from the surface.

The presence of defects in the graphenic layers deposited on metal surfaces modifies the nature of the interaction. Unsaturated carbon atoms, due to vacancies in the lattice, form strong organometallic bonds with surface metal atoms that highly enhance the binding energy between the two materials. We investigate by means of a wide set of dispersion-corrected density functional theory calculations how such strong chemical bonds affect both the electronic properties of these hybrid interfaces and the chemical reactivity with water, which is commonly present in the working conditions. We compare different metal substrates (Cu vs Pt) that present a different type of interaction with graphene and with defective graphene. This comparative analysis allows us to unravel the controlling factors of water reactivity, the role played by the carbon vacancies and by the confinement or “graphene cover effect”. Water is capable of breaking the C–Cu bond by dissociating at the undercoordinated carbon atom of the vacancy, restoring the weak van der Waals type of interaction between the two materials that allows for an easy detachment of graphene from the metal, but the same is not true in the case of Pt, where C–Pt bonds are much stronger. These conclusions can be used to rationalize water reactivity at other defective graphene/metal interfaces.

A water/(101) anatase TiO2interface has been investigated with the DFT-based self-consistent-charge density functional tight-binding theory (SCC-DFTB). By comparison of the computed structural, energetic, and dynamical properties with standard DFT-GGA and experimental data, we assess the accuracy of SCC-DFTB for this prototypical solid–liquid interface. We tested different available SCC-DFTB parameters for Ti-containing compounds and, accordingly, combined them to improve the reliability of the method. To better describe water energetics, we have also introduced a modified hydrogen-bond-damping function (HBD). With this correction, equilibrium structures and adsorption energies of water on (101) anatase both for low (0.25 ML) and full (1 ML) coverages are in excellent agreement with those obtained with a higher level of theory (DFT-GGA). Furthermore, Born–Oppenheimer molecular dynamics (MD) simulations for mono-, bi-, and trilayers of water on the surface, as computed with SCC-DFTB, evidence similar ordering and energetics as DFT-GGA Car–Parrinello MD results. Finally, we have evaluated the energy barrier for the dissociation of a water molecule on the anatase (101) surface. Overall, the combined set of parameters with the HBD correction (SCC-DFTB+HBD) is shown to provide a description of the water/water/titania interface, which is very close to that obtained by standard DFT-GGA, with a remarkably reduced computational cost. Hence, this study opens the way to the future investigations on much more extended and realistic TiO2/liquid water systems, which are extremely relevant for many modern technological applications.

Understanding magnetism in defective graphene is paramount to improve and broaden its technological applications. A single vacancy in graphene is expected to lead to a magnetic moment with both a σ (1 μB) and a π (1 μB) component. Theoretical calculations based on standard LDA or GGA functional on periodic systems report a partial quenching of the π magnetization (0.5 μB) due to the crossing of two spin split bands at the Fermi level. In contrast, STS experiments (Phys. Rev. Lett.2016, 117, 166801) have recently proved the existence of two defect spin states that are separated in energy by 20–60 meV. In this work, we show that self-interaction corrected hybrid functional methods (B3LYP-D*) are capable of correctly reproducing this finite energy gap and, consequently, provide a π magnetization of 1 μB. The crucial role played by the exact exchange is highlighted by comparison with PBE-D2 results and by the magnetic moment dependence with the exact exchange portion in the functional used. The ground state ferromagnetic planar solution is compared to the antiferromagnetic and to the diamagnetic ones, which present an out-of-plane distortion. Periodic models are then compared to graphene nanoflakes of increasing size (up to C383H48). For large models, the triplet spin configuration (total magnetization 2 μB) is the most stable, independently of the functional used, which further corroborates the conclusions of this work and puts an end to the long-debated issue of the magnetic properties of an isolated C monovacancy in graphene.

In biomedical applications, TiO2nanoparticles are generally coated with polymers to prevent agglomeration, improve biocompatibility, and reduce cytotoxicity. Although the synthesis processes of such composite compounds are well established, there is still a substantial lack of information on the nature of the interaction between the titania surface and the organic macromolecules. In this work, the adsorption of polyethylene glycol (PEG) on the TiO2(101) anatase surface is modeled by means of dispersion-corrected density functional theory (DFT-D2) calculations. The two extreme limits of an infinite PEG polymer [−(OCH2CH2)n], on one side, and of a short PEG dimer molecule [H(OCH2CH2)2OH], on the other, are analyzed. Many different molecular configurations and modes of adsorption are compared at increasing surface coverage densities. At low and medium coverage, PEG prefers to lay down on the surface, while at full coverage, the adsorption is maximized when PEG molecules bind perpendicularly to the surface and interact with each other through lateral dispersions, following a mushroom to brush transition. Finally, we also consider the adsorption of competing water molecules at different coverage densities, assessing whether PEG would remain bonded to the surface or desorb in the presence of the aqueous solvent.

Finite-length models of chiral semiconducting carbon nanotubes based on Clar sextet theory allowed carrying out accurate calculations, performed by application of gradient-corrected density functional theory, on the energetic of sidewall reactions. In particular, we analyzed the addition of atomic fluorine and carbene (CH2) to (6,4) and (6,5) nanotubes, finding excellent convergence of reaction energies with respect to the model length and good agreement with literature data. Our study demonstrates the importance of using models of carbon nanotubes based on chemical considerations to evaluate consistently the electronic and reactive properties of the sidewall.