Effect of Surface Functionalization on the Magnetization of Fe₃O₄ Nanoparticles by Hybrid Density Functional Theory Calculations

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

Functionalizing TiO₂ Nanoparticles with Fluorescent Cyanine Dye for Photodynamic Therapy and Bioimaging: A DFT and TDDFT Study

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

Molecular Dynamics for the Optimal Design of Functionalized Nanodevices to Target Folate Receptors on Tumor Cells

Atomistic details on the mechanism of targeting activity by biomedical nanodevices of specific receptors are still scarce in the literature, where mostly ligand/receptor pairs are modeled. Here, we use atomistic molecular dynamics (MD) simulations, free energy calculations, and machine learning approaches on the case study of spherical TiO2 nanoparticles (NPs) functionalized with folic acid (FA) as the targeting ligand of the folate receptor (FR). We consider different FA densities on the surface and different anchoring approaches, i.e., direct covalent bonding of FA γ-carboxylate or through polyethylene glycol spacers. By molecular docking, we first identify the lowest energy conformation of one FA inside the FR binding pocket from the X-ray crystal structure, which becomes the starting point of classical MD simulations in a realistic physiological environment. We estimate the binding free energy to be compared with the existing experimental data. Then, we increase complexity and go from the isolated FA to a nanosystem decorated with several FAs. Within the simulation time framework, we confirm the stability of the ligand–receptor interaction, even in the presence of the NP (with or without a spacer), and no significant modification of the protein secondary structure is observed. Our study highlights the crucial role played by the spacer, FA protonation state, and density, which are parameters that can be controlled during the nanodevice preparation step

Adsorption and Inactivation of SARS-CoV‑2 on the Surface of Anatase TiO₂(101)

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