Titanium Dioxide in the Service of the Biomedical Revolution

Defect Chemistry of Titanium Dioxide (Rutile). Progress Toward Sustainable Energy

This work, which overviews defect chemistry of TiO2 (rutile), is focused on atomic-size structural defects that are thermodynamically reversible. Here it is shown that thermodynamics can be used in defect engineering of TiO2-based energy materials, such as photoelectrodes and photocatalysts. We show that surface segregation of defects leads to the building-up of new surface structures that are responsible for reactivity. Since rational design of surface properties requires in situ surface characterization in operational conditions, expansion of bulk defect chemistry to surface defect chemistry requires a defect-related surface-sensitive tool for in situ monitoring of defect-related properties at elevated temperatures corresponding to defect equilibria and in a controlled gas-phase environment. Here we show that the high-temperature electron probe is a defect-related surface-sensitive tool that is uniquely positioned to aid surface defect engineering and determine unequivocal surface properties. The related applied aspects are considered for photoelectrochemical water splitting and the performance of solid oxide fuel cells. Here we report that trail-blazing studies on in situ surface monitoring of TiO2 during gas/solid equilibration, along with in situ characterization of surface semiconducting properties, leads to the discovery of a segregation-induced low-dimensional surface structure that is responsible for stable performance of oxide semiconductors, such as TiO2, in operational conditions.

Progress and Challenges of Monometallic Titanium Coordination Polymers

The realm of titanium coordination polymer research is still in its nascent stages and presents a formidable challenge in the field of coordination chemistry. In recent decades, the focus has predominantly been on manipulating titanium reactions in solution, resulting in the synthesis of ≈60 targeted compounds. Despite the limited number of documented instances, these materials showcase a diverse array of structures, encompassing 1D chains, 2D layers, and 3D frameworks. This suggests potential for fine-tuning coordination modes and structural features in future investigations. Moreover, titanium coordination polymers not only exhibit photo-active and photo-responsive properties but also hold promise for various other significant applications. This article offers an exhaustive review tracing the evolution of titanium coordination polymer development while providing an update on recent advancements. The review encompasses a synopsis of reported synthetic strategies, methodologies, structural diversity, and associated applications. Additionally, it delves into critical issues that necessitate attention for future progressions and proposes potential avenues to effectively propel this research field forward at an accelerated pace.

Recent Advances in Antibacterial Strategies Based on TiO2 Biomimetic Micro/Nano-Structured Surfaces Fabricated Using the Hydrothermal Method

Ti and its alloys, widely utilized in orthopedic and dental implants, inherently lack antibacterial properties, posing significant infection risks, especially in the context of growing antibiotic resistance. This review critically evaluates non-antibiotic antibacterial strategies, with a particular focus on surface modifications and micro/nano-structured surfaces. Micro/nano-structured surfaces, inspired by natural topographies, utilize physical mechanisms to eradicate bacteria. Despite their potential, the antibacterial efficacy of these surfaces remains insufficient for clinical application. Titanium dioxide (TiO2), known for its excellent photocatalytic antibacterial activity and biocompatibility, is emerging as an ideal candidate for enhancing micro/nano-structured surfaces. By combining the photocatalytic antibacterial effects of TiO2 with the mechanical bactericidal properties of micro/nano-structured surfaces, superior antibacterial performance can be achieved. The hydrothermal method is frequently employed to fabricate TiO2 micro/nano-structured surfaces, and this area of research continues to thrive, particularly in the development of antibacterial strategies. With demonstrated efficacy, combined antibacterial strategies based on TiO2 micro/nano-structured surfaces have become a prominent focus in current research. Consequently, the integration of physical stimulation and chemical release mechanisms may represent the future direction for TiO2 micro/nano-structured surfaces. This review aims to advance the study of TiO2 micro/nano-structured surfaces in antibacterial applications and to inspire more effective non-antibiotic antibacterial solutions.

Adsorption of Glycine on TiO2 in Water from On-the-fly Free-Energy Calculations and In Situ Electrochemical Impedance Spectroscopy

We report here an experimental-computational study of hydrated TiO2 anatase nanoparticles interacting with glycine, where we obtain quantitative agreement of the measured adsorption free energies. Ab initio simulations are performed within the tight binding and density functional theory in combination with enhanced free-energy sampling techniques, which exploit the thermodynamic integration of the unbiased mean forces collected on-the-fly along the molecular dynamics trajectories. The experiments adopt a new and efficient setup for electrochemical impedance spectroscopy measurements based on portable screen-printed gold electrodes, which allows fast and in situ signal assessment. The measured adsorption free energy is -30 kJ/mol (both from experiment and calculation), with preferential interaction of the charged NH3+ group which strongly adsorbs on the TiO2 bridging oxygens. This highlights the importance of the terminal amino groups in the adsorption mechanism of amino acids on hydrated metal oxides. The excellent agreement between computation and experiment for this amino acid opens the doors to the exploration of the interaction free energies for other moderately complex bionano systems.

Methyl contributes to the directed phosphorus doping of g-C3N4: pH-dependent selective reactive oxygen species enable customized degradation of organic pollutants

In the photocatalytic degradation process, constructing a controllable composite oxidation system with radicals and nonradicals to meet the requirement for efficient and selective degradation of diverse pollutants is significant. Herein, a methylated and phosphorus-doped g-C3N4 (NPEA) can exhibit selective radical and nonradical species formation depending on the pH values. The NPEA can spontaneously switch the production of active species according to the pH value of the reaction system, exhibiting steady-state concentrations of ·O2- for 11.83 × 10-2 µmol L-1 s-1 (with 92.7 % selectivity) under alkaline conditions (pH = 11), and steady-state concentrations of 1O2 for 5.18 × 10-2 µmol L-1 s-1 (with 88.7 % selectivity) under acidic conditions (pH = 3). The NPEA exhibits stability and universality in the degradation of pollutants with rate constant for sulfamethazine (k = 0.261 min-1) and atrazine (k = 0.222 min-1). Moreover, the LC-MS and Fukui function demonstrated that the NPEA can tailor degradation pathways for pollutants, achieving selective degradation. This study offers a comprehensive insight into the mechanism of the photocatalytic oxidation system, elucidating the intricate interplay between pollutants and reactive oxygen species.

Screening 2D Materials for Their Nanotoxicity toward Nucleic Acids and Proteins: An In Silico Outlook

Since the discovery of graphene, two-dimensional (2D) materials have been anticipated to demonstrate enormous potential in bionanomedicine. Unfortunately, the majority of 2D materials induce nanotoxicity via disruption of the structure of biomolecules. Consequently, there has been an urge to synthesize and identify biocompatible 2D materials. Before the cytotoxicity of 2D nanomaterials is experimentally tested, computational studies can rapidly screen them. Additionally, computational analyses can provide invaluable insights into molecular-level interactions. Recently, various "in silico" techniques have identified these interactions and helped to develop a comprehensive understanding of nanotoxicity of 2D materials. In this article, we discuss the key recent advances in the application of computational methods for the screening of 2D materials for their nanotoxicity toward two important categories of abundant biomolecules, namely, nucleic acids and proteins. We believe the present article would help to develop newer computational protocols for the identification of novel biocompatible materials, thereby paving the way for next-generation biomedical and therapeutic applications based on 2D materials.

Charge transfer excitons and directional fluorescence of in-plane lateral MoSe2-WSe2 heterostructures

In this article, the linear and nonlinear optical properties of in-plane lateral MoSe2-WSe2 heterostructures are theoretically investigated. The polarization-dependent strongest optical absorption in one-photon absorption occurs in charge transfer excited states, where electrons transfer from WSe2 to MoSe2. This phenomenon is supported by the LUMO (lowest unoccupied molecular orbital) and HUMO (highest occupied molecular orbital) imaging obtained through scanning tunneling microscopy. The charge difference density and transition density matrix are used to interpret the electronic transitions, and these interpretations rely on the concept of transition density. The optical properties of two-photon absorption in its nonlinear optical process are significantly different from the excitation in one-photon absorption, where the strongest optical absorption is contributed from direct transition from the ground state to the final state without going through an intermediate excited state, due to the very large difference of permanent dipole moments between the excited and ground states. Our results also reveal directional fluorescence and physical mechanism of in-plane lateral MoSe2-WSe2 heterostructures. Our work can provide insights into the physical mechanism of the optical properties of in-plane lateral MoSe2-WSe2 heterostructures.

Mechanism of RGD-conjugated nanodevice binding to its target protein integrin αVβ3 by atomistic molecular dynamics and machine learning

Active targeting strategies have been proposed to enhance the selective uptake of nanoparticles (NPs) by diseased cells, and recent experimental findings have proven the effectiveness of this approach. However, no mechanistic studies have yet revealed the atomistic details of the interactions between ligand-activated NPs and integrins. As a case study, here we investigate, by means of advanced molecular dynamics simulations (MD) and machine learning methods (namely equilibrium MD, binding free energy calculations and training of self-organized maps), the interaction of a cyclic-RGD-conjugated PEGylated TiO2 NP (the nanodevice) with the extracellular segment of integrin αVβ3 (the target), the latter experimentally well-known to be over-expressed in several solid tumors. Firstly, we proved that the cyclic-RGD ligand binding to the integrin pocket is established and kept stable even in the presence of the cumbersome realistic model of the nanodevice. In this respect, the unsupervised machine learning analysis allowed a detailed comparison of the ligand/integrin binding in the presence and in the absence of the nanodevice, which unveiled differences in the chemical features. Then, we discovered that unbound cyclic RGDs conjugated to the NP largely contribute to the interactions between the nanodevice and the integrin. Finally, by increasing the density of cyclic RGDs on the PEGylated TiO2 NP, we observed a proportional enhancement of the nanodevice/target binding. All these findings can be exploited to achieve an improved targeting selectivity and cellular uptake, and thus a more successful clinical outcome.

Enhancement in photocatalytic selectivity of TiO2-based nano-catalyst through molecular imprinting technology

Improvement in the photocatalytic selectivity is imperative for the effective and efficient utilization of catalysts. In this study, a molecularly imprinted polymer-coated iron-doped titanium dioxide (Fe-TiO2@MIP) nanocomposite was successfully synthesized by precipitation polymerization while using RB-19 as a template. The synthesized nanocomposites (Fe-TiO2@MIP and Fe-TiO2@NIP) were characterized by Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) with energy dispersive X-ray (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer-EMMETT-Teller (BET), and UV-visible spectrophotometry. The optimized binding experiments revealed a high imprinting factor of 5.0 for RB-19. The catalytic degradation efficiency and selectivity of Fe-TiO2@MIP enhanced to almost complete degradation of RB-19 from 70% for the parent Fe-TiO2 and 76% for Fe-TiO2@NIP. An outstanding degradation selectivity of RB-19 was achieved compared to other competitive dyes. Finally, the analysis of the non-degraded and degraded RB-19 by ESI-MS revealed the presence of different intermediates that fits well with the proposed degradation mechanism. The study opens new possibilities of selective photo-degradation of targeted contaminants that may ultimately lead to efficient use of photocatalysts.

Mechanistic insight into humic acid-enhanced sonophotocatalytic removal of 17β-estradiol: Formation and contribution of reactive intermediates

In this study, humic acid (HA) enhanced 17β-estradiol (17β-E2) degradation by Er3+-CdS/MoS2 (ECMS) was investigated under ultrasonic and light conditions. The degradation reaction rate of 17β-E2 was increased from (14.414 ± 0.315) × 10-3 min-1 to (122.677 ± 1.729) × 10-3 min-1 within 90 min sonophotocatalytic (SPC) reaction with the addition of HA. The results of quenching coupled with chemical probe experiments indicated that more reactive intermediates (RIs) including reactive oxygen species (ROSs) and triplet-excited states were generated in the HA-enhanced sonophotocatalytic system. The triplet-excited states of humic acid (3HA*), hydroxyl radical (•OH), and superoxide radical (•O2-) were the dominant RIs for 17β-E2 elimination. In addition, the energy- and electron-transfer process via coexisting HA also account for 12.86% and 29.24% contributions, respectively. The quantum yields of RIs in the SPC-ECMS-HA system followed the order of 3HA* > H2O2 > 1O2 > •O2-> •OH. Moreover, the spectral and fluorescence characteristics of HA were further analyzed during the sonophotocatalytic reaction process. The study expanded new insights into the comprehension of the effects of omnipresent coexisting HA and RIs formation for the removal of 17β-E2 during the sonophotocatalytic process.

Effect of Plasma Excitation Power on the SiOxCyHz/TiOx Nanocomposite

Titanium dioxide has attracted a great deal of attention in the field of environmental purification due to its photocatalytic activity under ultraviolet light. Photocatalytic efficiency and the energy required to initiate the process remain the drawbacks that hinder the widespread adoption of the process. Consistently with this, it is proposed here the polymerization of hexamethyldisiloxane fragments simultaneously to TiO₂ sputtering for the production of thin films in low-pressure plasma. The effect of plasma excitation power on the molecular structure and chemical composition of the films was evaluated by infrared spectroscopy. Wettability and surface energy were assessed by a sessile drop technique, using deionized water and diiodomethane. The morphology and elemental composition of the films were determined using scanning electron microscopy and energy dispersive spectroscopy, respectively. The thickness and roughness of the resulting films were measured using profilometry. Organosilicon-to-silica films, with different properties, were deposited by combining both deposition processes. Titanium was detected from the structures fabricated by the hybrid method. It has been observed that the proportion of titanium and particles incorporated into silicon-based matrices depends on the plasma excitation power. In general, a decrease in film thickness with increasing power has been observed. The presence of Ti in the plasma atmosphere alters the plasma deposition mechanism, affecting film deposition rate, roughness, and wettability. An interpretation of the excitation power dependence on the plasma activation level and sputtering yield is proposed. The methodology developed here will encourage researchers to create TiO₂ films on a range of substrates for their prospective use as sensor electrodes, water and air purification systems, and biocompatible materials.

Antioxidant hepatic lipid metabolism can be promoted by orally administered inorganic nanoparticles

Accumulation of inorganic nanoparticles in living organisms can cause an increase in cellular reactive oxygen species (ROS) in a dose-dependent manner. Low doses of nanoparticles have shown possibilities to induce moderate ROS increases and lead to adaptive responses of biological systems, but beneficial effects of such responses on metabolic health remain elusive. Here, we report that repeated oral administrations of various inorganic nanoparticles, including TiO₂, Au, and NaYF₄ nanoparticles at low doses, can promote lipid degradation and alleviate steatosis in the liver of male mice. We show that low-level uptake of nanoparticles evokes an unusual antioxidant response in hepatocytes by promoting Ces2h expression and consequently enhancing ester hydrolysis. This process can be implemented to treat specific hepatic metabolic disorders, such as fatty liver in both genetic and high-fat-diet obese mice without causing observed adverse effects. Our results demonstrate that low-dose nanoparticle administration may serve as a promising treatment for metabolic regulation.

Metadynamics simulations for the investigation of drug loading on functionalized inorganic nanoparticles

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.

Photon-Controlled Pyroptosis Activation (PhotoPyro): An Emerging Trigger for Antitumor Immune Response

Pyroptosis refers to the process of gasdermin-mediated lytic programmed cell death (PCD) characterized by the release of pro-inflammatory cytokines. Our knowledge of pyroptosis has expanded beyond the cellular level and now includes extracellular responses. In recent years, pyroptosis has attracted considerable attention due to its potential to induce host immunity. For instance, at the 2022 International Medicinal Chemistry of Natural Active Ligand Metal-Based Drugs (MCNALMD) conference, numerous researchers demonstrated an interest in photon-controlled pyroptosis activation ("PhotoPyro"), an emerging pyroptosis-engineered approach for activating systemic immunity via photoirradiation. Given this enthusiasm, we share in this Perspective our views on this emerging area and expound on how and why "PhotoPyro" could trigger antitumor immunity (i.e., turning so-called "cold" tumors "hot"). In doing so, we have tried to highlight cutting-edge breakthroughs in PhotoPyro while suggesting areas for future contributions. By providing insights into the current state of the art and serving as a resource for individuals interested in working in this area, it is hoped that this Perspective will set the stage for PhotoPyro to evolve into a broadly applicable cancer treatment strategy.

Titanium(IV) Surface Complexes Bearing Chelating Catecholato Ligands for Enhanced Band-Gap Reduction

Protonolysis reactions between dimethylamido titanium(IV) catecholate [Ti(CAT)(NMe₂)₂]₂ and neopentanol or tris(tert-butoxy)silanol gave catecholato-bridged dimers [(Ti(CAT)(OCH₂tBu)₂)(HNMe₂)]₂ and [Ti(CAT){OSi(OtBu)₃}₂(HNMe₂)₂]₂, respectively. Analogous reactions using the dimeric dimethylamido titanium(IV) (3,6-di-tert-butyl)catecholate [Ti(CATtBu₂-3,6)(NMe₂)₂]₂ yielded the monomeric Ti(CATtBu₂-3,6)(OCH₂tBu)₂(HNMe₂)₂ and Ti(CATtBu₂-3,6)[OSi(OtBu)₃]₂(HNMe₂)₂. The neopentoxide complex Ti(CATtBu₂-3,6)(OCH₂tBu)₂(HNMe₂)₂ engaged in further protonolysis reactions with Si-OH groups and was consequentially used for grafting onto mesoporous silica KIT-6. Upon immobilization, the surface complex [Ti(CATtBu₂-3,6)(OCH₂tBu)₂(HNMe₂)₂]@[KIT-6] retained the bidentate chelating geometry of the catecholato ligand. This convergent grafting strategy was compared with a sequential and an aqueous approach, which gave either a mixture of bidentate chelating species with a bipodally anchored Ti(IV) center along with other physisorbed surface species or not clearly identifiable surface species. Extension of the convergent and aqueous approaches to anatase mesoporous titania (m-TiO₂) enabled optical and electronic investigations of the corresponding surface species, revealing that the band-gap reduction is more pronounced for the bidentate chelating species (convergent approach) than for that obtained via the aqueous approach. The applied methods include X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and solid-state UV/vis spectroscopy. The energy-level alignment for the surface species from the aqueous approach, calculated from experimental data, accounts for the well-known type II excitation mechanism, whereas the findings indicate a distinct excitation mechanism for the bidentate chelating surface species of the material [Ti(CATtBu₂-3,6)(OCH₂tBu)₂(HNMe₂)₂]@[m-TiO₂].

Triggering cell death in cancers using self-illuminating nanocomposites

Bioinspired photocatalysis has resulted in efficient solutions for many areas of science and technology spanning from solar cells to medicine. Here we show a new bioinspired semiconductor nanocomposite (nanoTiO₂-DOPA-luciferase, TiDoL) capable of converting light energy within cancerous tissues into chemical species that are highly disruptive to cell metabolism and lead to cell death. This localized activity of semiconductor nanocomposites is triggered by cancer-generated activators. Adenosine triphosphate (ATP) is produced in excess in cancer tissues only and activates nearby immobilized TiDoL composites, thereby eliminating its off-target toxicity. The interaction of TiDoL with cancerous cells was probed in situ and in real-time to establish a detailed mechanism of nanoparticle activation, triggering of the apoptotic signaling cascade, and finally, cancer cell death. Activation of TiDoL with non-cancerous cells did not result in cell toxicity. Exploring the activation of antibody-targeted semiconductor conjugates using ATP is a step toward a universal approach to single-cell-targeted medical therapies with more precision, efficacy, and potentially fewer side effects.

Molecular dynamics simulations of cRGD-conjugated PEGylated TiO2 nanoparticles for targeted photodynamic therapy

The conjugation of high-affinity cRGD-containing peptides is a promising approach in nanomedicine to efficiently reduce off-targeting effects and enhance the cellular uptake by integrin-overexpressing tumor cells. Herein we utilize atomistic molecular dynamics simulations to evaluate key structural-functional parameters of these targeting ligands for an effective binding activity towards α_Vβ₃ integrins. An increasing number of cRGD ligands is conjugated to PEG chains grafted to highly curved TiO₂ nanoparticles to unveil the impact of cRGD density on the ligand's presentation, stability, and conformation in an explicit aqueous environment. We find that a low density leads to an optimal spatial presentation of cRGD ligands out of the "stealth" PEGylated layer around the nanosystem, favoring a straight upward orientation and spaced distribution of the targeting ligands in the bulk-water phase. On the contrary, high densities favor over-clustering of cRGD ligands, driven by a concerted mechanism of enhanced ligand-ligand interactions and reduced water accessibility over the ligand's molecular surface. These findings strongly suggest that the ligand density modulation is a key factor in the design of cRGD-targeting nanodevices to maximize their binding efficiency into over-expressed α_Vβ₃ integrin receptors.

"Three-in-One" Structural-Building-Mode-Based Ti16-Type Titanium Oxo Cluster Entirely Protected by the Ligands Benzoate and Salicylhydroxamate

Titanium oxo clusters (TOCs) with accurate molecular structures have potential applications in photocatalysis, such as photocatalytic degradation, hydrogen production, and water oxidation. The hydrolytic stability and light absorption ability of TOCs have important impacts on photocatalysis, where the selection of peripheral organic ligands plays a significant role. In this regard, salicylhydroxamic acid (abbreviated as H₃L) attracts our attention, acting as a ligand for its multidentate and dye-functional features, which can increase the hydrolytic stability and broaden light absorption for TOCs. Herein, two TOCs were solvothermally synthesized and structurally characterized using H₃L, formulated as [Ti₈(μ₂-O)₂(μ₃-O)₂(OⁱPr)₁₂(L)₄]·2CH₃CN (1) and [Ti₁₆(μ₂-O)₁₀(μ₃-O)₄(PhCOO)₁₄(L)₆(HL)₂]·4CH₃CN·2ⁱPrOH (2). Complex 2 was obtained by adding excessive benzoic acid over the reaction system of 1, resulting in enhanced hydrolytic stability via the replacement of all alkoxy ligands by multidentate ligands for protection. Interestingly, for the first time, the "three-in-one" structural building mode with {Ti₆} + {Ti₄} + {Ti₆} by the common subunits in 2 was observed among all reported TOCs. Moreover, complex 2 can strongly absorb visible light reaching up to 700 nm and exhibit obvious activity for the photodegradation of methyl orange.

Nonlinear plexcitons: excitons coupled with plasmons in two-photon absorption

The nonlinear optical properties of a D-A (donor-acceptor) conjugated organic molecule with polythiophene (PT) as the donor and indene-C₆₀ bisadduct (IC₆₀BA) as the acceptor are theoretically investigated, which exhibits a large two-photon absorption (TPA) cross-section up to 8000 GM at the wavelength of 780 nm. Combining surface plasmon resonances (SPRs) with nonlinear optics, nonlinear properties can be strongly enhanced. In this paper, an appropriate nonlinear plexciton method by the coupling of Au@Ag nanorods and an Ag film is designed, in which the TPA properties of the PT:IC₆₀BA complex can be increased by 10⁶ times. The angle dependence on polarization and incidence is investigated to obtain the maximum of plasmonic enhancement. Our results emphasize the physical mechanism of nonlinear plexcitons and provide a feasible method to improve the nonlinear properties of organic solar cell materials.

Synthesis, modification and application of titanium dioxide nanoparticles: a review

Titanium dioxide (TiO₂) has been heavily investigated owing to its low cost, benign nature and strong photocatalytic ability. Thus, TiO₂ has broad applications including photocatalysts, Li-ion batteries, solar cells, medical research and so on. However, the performance of TiO₂ is not satisfactory due to many factors such as the broad band gap (3.01 to 3.2 eV) and fast recombination of electron-hole pairs (10^-12 to 10^-11 s). Plenty of work has been undertaken to improve the properties, such as structural and dopant modifications, which broaden the applications of TiO₂. This review mainly discusses the aspects of TiO₂-modified nanoparticles including synthetic methods, modifications and applications.

S-scheme BiVO4/CQDs/β-FeOOH photocatalyst for efficient degradation of ofloxacin: Reactive oxygen species transformation mechanism insight

Photocatalysis technology exhibited promising application for advanced treatment of wastewater. Nevertheless, the design of efficient photocatalyst and the mechanism of free radicals in pollutant degradation still remained to be further investigated. Herein, BiVO₄/CQDs/β-FeOOH photocatalyst was fabricated by electrostatic self-assembly method, which exhibited the excellent photocatalytic performance. Under visible-light irradiation, the removal rate of ofloxacin by BiVO₄/CQDs/β-FeOOH (0.25 min^-1) was 1.93 times than pristine BiVO₄, and the removal efficiency in 15 min reached 99.21%. The perfect reusability of BiVO₄/CQDs/β-FeOOH was ascribed to the persistent catalytic active centers provided by the renewable surface oxygen vacancies on the β-FeOOH. As electron transfer channels, CQDs facilitated the transfer of BiVO₄ photogeneration electrons. The matched band structure allowed the construction of S-scheme heterojunctions, and the higher conduction band position was retained while the carrier separation was promoted. More importantly, this work firstly reported the phenomenon that the main reactive groups in the photocatalysis process would be directionally transformed with the change of pH conditions. Based on the analysis of capture and electron paramagnetic resonance experiments, ·O₂^- was the main free radicals to photodegrade OFL in neutral and alkaline conditions. However, when the solution pH turned into acidic, the photodegradation of OFL was dominated by ¹O₂. This innovative phenomenon was due to that acidic condition accelerated the reaction kinetics of spontaneous transformation of ·O₂^- to ¹O₂ and inhibited the direct oxidation of pollutants by ·O₂^-. Accordingly, this research could inspire theoretical study of free radical reaction and the design of S-scheme heterojunction photocatalysts.

Complementary Powerful Techniques for Investigating the Interactions of Proteins with Porous TiO2 and Its Hybrid Materials: A Tutorial Review

Understanding the adsorption and interaction between porous materials and protein is of great importance in biomedical and interface sciences. Among the studied porous materials, TiO₂ and its hybrid materials, featuring distinct, well-defined pore sizes, structural stability and excellent biocompatibility, are widely used. In this review, the use of four powerful, synergetic and complementary techniques to study protein-TiO_2-based porous materials interactions at different scales is summarized, including high-performance liquid chromatography (HPLC), atomic force microscopy (AFM), surface-enhanced Raman scattering (SERS), and Molecular Dynamics (MD) simulations. We expect that this review could be helpful in optimizing the commonly used techniques to characterize the interfacial behavior of protein on porous TiO₂ materials in different applications.

Inkjet-Printed Phospholipid Bilayers on Titanium Oxide Surfaces: Towards Functional Membrane Biointerfaces

Functional biointerfaces hold broad significance for designing cell-responsive medical implants and sensor devices. Solid-supported phospholipid bilayers are a promising class of biological materials to build bioinspired thin-film coatings, as they can facilitate interactions with cell membranes. However, it remains challenging to fabricate lipid bilayers on medically relevant materials such as titanium oxide surfaces. There are also limitations in existing bilayer printing capabilities since most approaches are restricted to either deposition alone or to fixed microarray patterning. By combining advances in lipid surface chemistry and on-demand inkjet printing, we demonstrate the direct deposition and patterning of covalently tethered lipid bilayer membranes on titanium oxide surfaces, in ambient conditions and without any surface pretreatment process. The deposition conditions were evaluated by quartz crystal microbalance-dissipation (QCM-D) measurements, with corresponding resonance frequency (Δf) and energy dissipation (ΔD) shifts of around −25 Hz and <1 × 10−6, respectively, that indicated successful bilayer printing. The resulting printed phospholipid bilayers are stable in air and do not collapse following dehydration; through rehydration, the bilayers regain their functional properties, such as lateral mobility (>1 µm2/s diffusion coefficient), according to fluorescence recovery after photobleaching (FRAP) measurements. By taking advantage of the lipid bilayer patterned architectures and the unique features of titanium oxide’s photoactivity, we further show how patterned cell culture arrays can be fabricated. Looking forward, this work presents new capabilities to achieve stable lipid bilayer patterns that can potentially be translated into implantable biomedical devices.

Self-Photopolymerizable Hydrogel-Ceramic Composites with Scavenger Properties

The photocatalytic behaviours of semiconductive ceramic nanoparticles such as TiO₂, ZnO, Fe₂O₃, and Fe₃O₄, have been extensively studied in photocatalysis and photopolymerization, due to their ability to produce radical species under ultraviolet-visible light, and even in dark conditions. In addition, in the form of microparticles, TiO₂ and its Magnéli phases are capable of neutralizing radical species, and a heterogeneous catalytic process has been suggested to explain this property, as it is well known as scavenging activity. Thus, in this study, we demonstrate that these ceramic powders, in the form of microparticles, could be used as photoinitiators in UV polymerization in order to synthesize a hydrogel matrix. Them, embedded ceramic powders could be able to neutralize radical species of physiological media once implanted. The hydrogel matrix would regulate the exchange of free radicals in any media, while the ceramic particles would neutralize the reactive species. Therefore, in this work, the scavenger activities of TiO₂, ZnO, Fe₂O₃, and Fe₃O₄ microparticles, along with their photoinitiation yield, were evaluated. After photopolymerization, the gel fraction and swelling behaviour were evaluated for each hydrogel produced with different ceramic initiators. Gel fractions were higher than 60%, exhibiting variation in their scavenging activity. Therefore, we demonstrate that ceramic photoinitiators of TiO₂, ZnO, Fe₂O₃, and Fe₃O₄ can be used to fabricate implantable devices with scavenger properties in order to neutralize radical species involved in inflammatory processes and degenerative diseases.

Selectively Lighting Up Singlet Oxygen via Aggregation-Induced Electrochemiluminescence Energy Transfer

Singlet oxygen (¹O₂) is an important reactive oxygen species (ROS) that is intensively involved in natural photochemical and photobiological processes. Herein, selectively lighting up ¹O₂ is achieved in the aggregation-induced emission (AIE) of electrochemiluminescence (ECL) from the Zn²⁺-mediated AIE assembly of Au nanoclusters (Zn²⁺-AIE-AuNCs). Zn²⁺-AIE-AuNCs can exhibit efficient AIE ECL and photoluminescence (PL) along with ¹O₂ generation in energy and charge transfer routes, respectively. The AIE ECL of the Zn²⁺-AIE-AuNCs/tripropylamine (TEA) system in carbonate buffer is located around 703 nm with the dimeric aggregate of ¹O₂ as an emitter because electrochemically oxidizing coexisted Zn²⁺-AIE-AuNCs and TEA in carbonate buffer would promote the oxygen vacancy (O_v) of Zn²⁺-AIE-AuNCs, which could selectively enable the generation of emissive singlet oxygen in the energy transfer route by effectively transferring the energy from excited singlet Zn²⁺-AIE-AuNCs to the triplet ground state of dissolved oxygen (³O₂). No emissive ¹O₂ is detected via electrochemically oxidizing the Zn²⁺-AIE-AuNCs in the case without either carbonate buffer or TEA, and the Zn²⁺-AIE-AuNCs/TEA system can only exhibit AIE ECL around 485 nm with Zn²⁺-AIE-AuNCs as the emitter in carbonate-free buffers. Photoexciting Zn²⁺-AIE-AuNCs merely brings out band-gap-engineered AIE PL around ∼485 nm with Zn²⁺-AIE-AuNCs as the emitter, which manifests that the ¹O₂ generated in the charge transfer route via photoexciting Zn²⁺-AIE-AuNCs is un-emissive. This work not only proposes an effective strategy for AIE with ¹O₂ as an emitter but also opens a promising way to selectively light up ¹O₂.

Dopamine Adsorption on Rutile TiO2(110): Geometry, Thermodynamics, and Core-Level Shifts from First Principles

The modification of the rutile TiO₂(110) surface with dopamine represents the best example of the functionalization of TiO₂-based nanoparticles with catecholamines, which is of great interest for sunlight harvesting and drug delivery. However, there is little information on the dopamine-TiO₂(110) adsorption complex in terms of thermodynamic properties and structural parameters such as bond coordination and orientation of the terminal ethyl-amino group. Here, we report a density functional theory (DFT) investigation of dopamine adsorption on the TiO₂(110) surface using the optB86b-vdW functional with a Hubbard-type correction to the Ti 3d orbitals, where U _eff = 3 eV. Guided by available X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) data, our simulations identify enolate species with bidentate coordination at a submonolayer coverage, which are bonded to two neighboring 5-fold-coordinated Ti atoms at the TiO₂(110) surface through both deprotonated oxygen atoms of the dopamine, i.e., in a bridging fashion. The process is highly exothermic, involving an adsorption energy of -2.90 eV. Calculated structural parameters suggest that the molecule sits approximately upright on the surface with the amino group interacting with the π-like orbitals of the aromatic ring, leading to a gauche-like configuration. The resulting NH···π hydrogen bond in this configuration can be broken by overcoming an energy barrier of 0.22 eV; in this way, the amino group rotation leads to an anti-like conformation, making this terminal group able to bind to other biomolecules. This mechanism is endothermic by 0.07 eV. Comparison of existing spectroscopic data with DFT modeling shows that our computational setup can reproduce most experimentally determined parameters such as tilt angles from NEXAFS and chemical shifts in XPS, which allows us to identify the preferred mode of adsorption of dopamine on the TiO₂(110) surface.

Synthesis of encapsulated fish oil using whey protein isolate to prevent the oxidative damage and cytotoxicity of titanium dioxide nanoparticles in rats

Fish oil exhibited several beneficial effects on human health; however, its applications face several challenges such as its effects on the organoleptic properties of food and its susceptibility to oxidation. Titanium dioxide NPs (TiO₂-NPs) are utilized widely in pharmaceutical and food applications although there are some reports about their oxidative damage to living organisms. The current work was undertaken to identify fatty acids content in mullet fish oil, encapsulation, and characterization of the oil, and to assess the protective efficiency of the encapsulated mullet fish oil (EMFO) against the oxidative damage and genotoxicity of TiO₂-NPs in rats. Sixty female Sprague-Dawley rats were distributed to 6 groups and treated for 21 days included the control group; TiO₂-NPs-treated group (50 mg/kg b.w); the groups treated with EMFO (50 or 100 mg/kg b.w) and the groups received TiO₂-NPs plus EMFO at the low or high dose. Samples of blood, liver, and kidney were taken for different assays and histological studies. The GC-FID analysis showed that a total of 14 different fatty acids were found in Mullet fish oil included 41.4% polyunsaturated fatty acids (PUFAs), 31.1% monounsaturated fatty acids (MUFAs), and 25.1% saturated fatty acids (SFAs). The structure of EMFO was spherical with an average diameter of 234.5 nm and a zeta potential of -6.24 mV and was stable up to 10 days at 25 °C with EE of 81.08%. The PV of EMFO was decreased at 5 days then increased at 15 days; however, TBARS was increased throughout the storage time over 15 days. The biological evaluation showed that TiO₂-NPs disturb the hepato-nephro functions, lipid profile, inflammatory cytokines, oxidative stress markers, antioxidant enzymes activity, and their corresponding gene expression along with severe pathological alterations in both hepatic and renal tissue. Co-administration of EMFO induced a strong antioxidant role, and the high level could normalize the majority of the parameters tested and the histological picture of the hepatic and renal tissues. These results pointed out that the encapsulation technology enhances the protective role of EMFO against oxidative stress and genotoxicity of TiO₂-NPs through the prevention of ω-3 PUFAs oxidation and controlling their release.

Interaction of KRSR Peptide with Titanium Dioxide Anatase (100) Surface: A Molecular Dynamics Simulation Study

Due to its tensile strength and excellent biocompatibility, titanium (Ti) is commonly used as an implant material in medicine and dentistry. The success of dental implants depends on the formation of a contact between the oxidized surface of Ti implant and the surrounding bone tissue. The adsorption of proteins and peptides to the implant surface allows the bone-forming osteoblast cells to adhere to such modified surfaces. Recently, it has been observed that tetrapeptide KRSR (Lys-Arg-Ser-Arg) functionalization could promote osteoblast adhesion to implant surfaces. This may facilitate the establishment of an efficient bone-to implant contact and improve implant stability during the healing process. GROMACS, a molecular dynamics software package was used to perform a 200 ns simulation of adsorption of the KRSR peptide to the TiO₂ (anatase) surface in an aqueous environment. The molecule conformations were mapped with Replica Exchange Molecular Dynamics (REMD) simulations to assess the possible peptide conformations on the anatase surface, and the umbrella sampling method was used to calculate the binding energy of the most common conformation. The simulations have shown that the KRSR peptide migrates and attaches to the surface in a stable position. The dominant amino acid residue interacting with the TiO₂ surface was the N-terminal charged lysine (K) residue. REMD indicated that there is a distinct conformation that is taken by the KRSR peptide. In this conformation the surface interacts only with the lysine residue while the ser (S) and arg (R) residues interact with water molecules farther from the surface. The binding free energy of the most common conformation of KRSR peptide to the anatase (100) surface was ΔG = −8.817 kcal/mol. Our result suggests that the N-terminal lysine residue plays an important role in the adhesion of KRSR to the TiO₂ surface and may influence the osseointegration of dental implants.

Inorganic Nanomaterials with Intrinsic Singlet Oxygen Generation for Photodynamic Therapy

Inorganic nanomaterials with intrinsic singlet oxygen (1 O2 ) generation capacity, are emerged yet dynamically developing materials as nano-photosensitizers (NPSs) for photodynamic therapy (PDT). Compared to previously reported nanomaterials that have been used as either carriers to load organic PSs or energy donors to excite the attached organic PSs through a Foster resonance energy transfer process, these NPSs possess intrinsic 1 O2 generation capacity with extremely high 1 O2 quantum yield (e.g., 1.56, 1.3, 1.26, and 1.09) than any classical organic PS reported to date, and thus are facilitating to make a revolution in PDT. In this review, the recent advances in the development of various inorganic nanomaterials as NPSs, including metal-based (gold, silver, and tungsten), metal oxide-based (titanium dioxide, tungsten oxide, and bismuth oxyhalide), metal sulfide-based (copper and molybdenum sulfide), carbon-based (graphene, fullerene, and graphitic carbon nitride), phosphorus-based, and others (hybrids and MXenes-based NPSs) are summarized, with an emphasis on the design principle and 1 O2 generation mechanism, and the photodynamic therapeutic performance against different types of cancers. Finally, the current challenges and an outlook of future research are also discussed. This review may provide a comprehensive account capable of explaining recent progress as well as future research of this emerging paradigm.

Converging 2D Nanomaterials and 3D Bioprinting Technology: State-of-the-Art, Challenges, and Potential Outlook in Biomedical Applications

The development of next-generation of bioinks aims to fabricate anatomical size 3D scaffold with high printability and biocompatibility. Along with the progress in 3D bioprinting, 2D nanomaterials (2D NMs) prove to be emerging frontiers in the development of advanced materials owing to their extraordinary properties. Harnessing the properties of 2D NMs in 3D bioprinting technologies can revolutionize the development of bioinks by endowing new functionalities to the current bioinks. First the main contributions of 2D NMS in 3D bioprinting technologies are categorized here into six main classes: 1) reinforcement effect, 2) delivery of bioactive molecules, 3) improved electrical conductivity, 4) enhanced tissue formation, 5) photothermal effect, 6) and stronger antibacterial properties. Next, the recent advances in the use of each certain 2D NMs (1) graphene, 2) nanosilicate, 3) black phosphorus, 4) MXene, 5) transition metal dichalcogenides, 6) hexagonal boron nitride, and 7) metal-organic frameworks) in 3D bioprinting technology are critically summarized and evaluated thoroughly. Third, the role of physicochemical properties of 2D NMSs on their cytotoxicity is uncovered, with several representative examples of each studied 2D NMs. Finally, current challenges, opportunities, and outlook for the development of nanocomposite bioinks are discussed thoroughly.

Molecular Mechanistic Insights into the Ionic-Strength-Controlled Interfacial Behavior of Proteins on a TiO2 Surface

By adjusting the ionic strengths through changing the concentration of the buffer ions, the molecular force and the interfacial behavior of cytochrome c (Cyt c) and TiO₂ are systematically studied. The molecular forces determined by combining the adhesion force and adsorption capacity are found to first increase and then decrease with the increasing ionic strength, with a peak obtained at an ionic strength between 0.8 and 1.0 M. The mechanism is explained based on the dissociation and hydration of ions at the interfaces, where the buffer ions could be completely dissociated at ionic strengths of <0.8 M but were partially associated when the ionic strength increased to a high value (>1.2 M), and the strongest hydration was observed around 1.0 M. The hydrodynamic size and the zeta potential value representing the effective contact area and protein stability of the Cyt c molecule, respectively, are also affected by the hydration and are proportional to the molecular forces. The interfacial behavior of Cyt c molecules on the TiO₂ surface, determined through surface-enhanced Raman scattering (SERS), is extremely affected by the ionic strength of the solution as the ion dissociation and hydration also increase the electron transfer ability, where the best SERS enhancement is observed at the ionic strength of around 1.0 M, corresponding to the largest molecular force. Our results provide a detailed understanding at the nanoscale on controlling the protein interfacial behavior with solid surfaces, adjusted by the buffer ions.

Synthesis, Structural and Physicochemical Characterization of a Titanium(IV) Compound with the Hydroxamate Ligand N,2-Dihydroxybenzamide

The siderophore organic ligand N,2-dihydroxybenzamide (H2dihybe) incorporates the hydroxamate group, in addition to the phenoxy group in the ortho-position and reveals a very rich coordination chemistry with potential applications in medicine, materials, and physical sciences. The reaction of H2dihybe with TiCl4 in methyl alcohol and KOH yielded the tetranuclear titanium oxo-cluster (TOC) [TiIV4(μ-O)2(HOCH3)4(μ-Hdihybe)4(Hdihybe)4]Cl4∙10H2O∙12CH3OH (1). The titanium compound was characterized by single-crystal X-ray structure analysis, ESI-MS, 13C, and 1H NMR spectroscopy, solid-state and solution UV-Vis, IR vibrational, and luminescence spectroscopies and molecular orbital calculations. The inorganic core Ti4(μ-O)2 of 1 constitutes a rare structural motif for discrete TiIV4 oxo-clusters. High-resolution ESI-MS studies of 1 in methyl alcohol revealed the presence of isotopic distribution patterns which can be attributed to the tetranuclear clusters containing the inorganic core {Ti4(μ-O)2}. Solid-state IR spectroscopy of 1 showed the presence of an intense band at ~800 cm-1 which is absent in the spectrum of the H2dihybe and was attributed to the high-energy ν(Ti2-μ-O) stretching mode. The ν(C=O) in 1 is red-shifted by ~10 cm-1, while the ν(N-O) is blue-shifted by ~20 cm-1 in comparison to H2dihybe. Density Functional Theory (DFT) calculations reveal that in the experimental and theoretically predicted IR absorbance spectra of the ligand and Ti-complex, the main bands observed in the experimental spectra are also present in the calculated spectra supporting the proposed structural model. 1H and 13C NMR solution (CD3OD) studies of 1 reveal that it retains its integrity in CD3OD. The observed NMR changes upon addition of base to a CD3OD solution of 1, are due to an acid-base equilibrium and not a change in the TiIV coordination environment while the decrease in the complex's lability is due to the improved electron-donating properties which arise from the ligand deprotonation. Luminescence spectroscopic studies of 1 in solution reveal a dual narrow luminescence at different excitation wavelengths. The TOC 1 exhibits a band-gap of 1.98 eV which renders it a promising candidate for photocatalytic investigations.

Exploring the drug loading mechanism of photoactive inorganic nanocarriers through molecular dynamics simulations

Inorganic nanoparticles are gaining increasing attention as drug carriers because they respond to external physical stimuli, allowing therapy to be combined with diagnosis. Their drawback is low drug loading capacity, which can be improved by proper and efficacious functionalization. In this computational study, we take TiO2 spherical nanoparticles as prototype photoresponsive inorganic nanoparticles and we fully decorate them with two different types of bifunctional ligands: TETTs and DOPACs, which present different surface anchoring groups (silanol or catechol) but the same drug tethering COOH group, although in different concentrations (3 vs. 1), thus causing different steric hindrances. Then, we put these two types of nanocarriers in bulk water and in the presence of several DOX molecules and let the systems evolve through molecular dynamics (MD) simulations, clearly observing drug loading on the nanocarriers. This comparative MD study allows the investigation of the loading mechanism, performance of a conformational analysis and establishment of the guiding interactions through an energy decomposition analysis. We learn that DOX mostly interacts with the functionalized NPs through electrostatics, as a consequence of the protonated amino group, although several H-bonds are also established both with the ligands and with the oxide surface. Different ligands induce a different electrostatic potential around the NP; therefore, those which lead to the formation of more negative hotspots (here TETTs) are found to favour DOX binding. The leading role of electrostatics can provide a rational explanation for a pH-dependent drug release mechanism that is often invoked for DOX when reaching diseased cells because under anomalous acidic conditions both the NP surface and the carboxylate groups of the ligands are expected to get protonated, which of course would weaken, if not totally quench, the interaction of the nanocarrier with protonated DOX.

Hydrogen Bonds and H3O+ Formation at the Water Interface with Formic Acid Covered Anatase TiO2

Carboxylic acid-modified TiO₂ surfaces in aqueous environment are of widespread interest, yet atomic-scale understanding of their structure is limited. We here investigate formic acid (FA) on anatase TiO₂ (101) (A-101) in contact with water using density functional theory (DFT) and ab initio molecular dynamics (AIMD). Isolated FA molecules adsorbed in a deprotonated bridging bidentate (BD) form on A-101 are found to remain stable at the interface with water, with the acid proton transferred to a surface oxygen to form a surface bridging hydroxyl (O_brH). With increasing FA coverage, adsorbed monolayers of only BD and successively of alternating monodentate (MD) and BD species give rise to a higher concentration of surface O_brH's. Simulations of these adsorbed monolayers in water environment show that some protons are released from the surface O_brH's to water resulting in a negatively charged surface with nearby solvated H₃O⁺ ions. These results provide insight into the complex acid-base equilibrium between an oxide surface, adsorbates and water and can also help obtain a better understanding of the wetting properties of chemically modified TiO₂ surfaces.

Photonic crystal light trapping for photocatalysis

The Achilles heel of wide-band photocatalysts such as TiO₂ is the insufficient photogeneration in the visible range under sunlight. This has been a longstanding impediment to large-scale, real-world deployment of titania-based photocatalysis applications. Instead of traditional band engineering through heavy-doping, we suggest enhancing photocatalytic efficiency of lightly-doped TiO₂ using photonic crystal (PC) structures. This strongly increases solar photogeneration through novel wave-interference-based light trapping. Four photocatalyst structures - simple cubic woodpile (wdp), square lattice nanorod (nrPC), slanted conical-pore (scPore), and face-centered cubic inverse opal (invop) - are optimized and compared for light harvesting in the sub- and above-gap (282 to 550 nm) regions of weakly absorbing TiO₂, with the imaginary part of the dielectric constant 0.01 in the visible range. The optimized lattice constants for the first three, and opal center-to-center distance for invop, are ∼300 - 350 nm. For fixed PC thickness, the ranking of visible light harvesting capability is: scPore > wdp ∼ nrPC > invop. The scPore PC deposited on highly reflective substrate is ideal for photocatalysis given its combination of enhanced light trapping and superior charge transport.

Antimicrobial nanomedicine for ocular bacterial and fungal infection

Ocular infection induced by bacteria and fungi is a major cause of visual impairment and blindness. Topical administration of antibiotics remains the first-line treatment, as effective eradication of pathogens is the core of the anti-infection strategy. Whereas, eye drops lack efficiency and have relatively low bioavailability. Intraocular injection may cause concurrent ocular damage and secondary infection. In addition, antibiotic-based management can be limited by the low sensitivity to multidrug-resistant bacteria. Nanomedicine is proposed as a prospective, effective, and noninvasive platform to mediate ocular delivery and combat pathogen or even resistant strains. Nanomedicine can not only carry antimicrobial agents to fight against pathogens but also directly active microbicidal capability, killing pathogens. More importantly, by modification, nanomedicine can achieve enhanced residence time and release time on the cornea, and easy penetration through corneal tissues into anterior and posterior segments of the eye, thus improving the therapeutic effect for ocular infection. In this review, several categories of antimicrobial nanomedicine are systematically discussed, where the efficiency and possibility of further embellishment and improvement to adapt to clinical use are also investigated. All in all, novel antimicrobial nanomedicine provides potent and prospective ways to manage severe and refractory ocular infections.

Supercooled liquid-like dynamics in water near a fully hydrated titania surface: Decoupling of rotational and translational diffusion

We report an ab initio molecular dynamics (MD) simulation investigating the effect of a fully hydrated surface of TiO₂ on the water dynamics. It is found that the universal relation between the rotational and translational diffusion characteristics of bulk water is broken in the water layers near the surface with the rotational diffusion demonstrating progressive retardation relative to the translational diffusion when approaching the surface. This kind of rotation-translation decoupling has so far only been observed in the supercooled liquids approaching glass transition, and its observation in water at a normal liquid temperature is of conceptual interest. This finding is also of interest for the application-significant studies of the water interaction with fully hydrated nanoparticles. We note that this is the first observation of rotation-translation decoupling in an ab initio MD simulation of water.

Mesoporous Materials-Based Electrochemical Biosensors from Enzymatic to Nonenzymatic

Mesoporous materials have drawn more and more attention in the field of biosensors due to their high surface areas, large pore volumes, tunable pore sizes, as well as abundant frameworks. In this review, the progress on mesoporous materials-based biosensors from enzymatic to nonenzymatic are highlighted. First, recent advances on the application of mesoporous materials as supports to stabilize enzymes in enzymatic biosensing technology are summarized. Special emphasis is placed on the effect of pore size, pore structure, and surface functional groups of the support on the immobilization efficiency of enzymes and the biosensing performance. Then, the development of a nonenzymatic strategy that uses the intrinsic property of mesoporous materials (carbon, silica, metals, and composites) to mimic the behavior of enzymes for electrochemical sensing of some biomolecules is discussed. Finally, the challenges and perspective on the future development of biosensors based on mesoporous materials are proposed.

Supramolecular Chemistry of Titanium Oxide Clusters

Titanium oxide clusters (TOCs) have been emerging as a new type of inorganic molecular entities of supramolecular chemistry. Herein, a perspective on the structures and functionalities of TOCs over the past three decades is given and the paramount roles of TOCs in serving supramolecular chemistry are demonstrated. Four types of supramolecular assemblies based on TOCs are reviewed, namely, TOC hosts for ion inclusion, mechanically interlocked molecular systems built from cyclic TOCs, reactivities of surface sites toward ligand exchange, and hierarchical structures of TOCs. The principles and advantages of TOCs toward each application are fully discussed, along with structural analyses. Following this path, more functional TOC-based supramolecular systems may be designed and synthesized in the future, which, in turn, will certainly enhance research into both supramolecular and coordination chemistry of titanium.

Reactive molecular dynamics simulations of hydration shells surrounding spherical TiO2 nanoparticles: implications for proton-transfer reactions

In many potential applications, nanoparticles are typically in an aqueous medium. This has strong influence on the stability, optical properties and reactivity, in particular for their functionalization. Therefore, the understanding of the chemistry at the interface between the solvent and the nanoparticle is of utmost importance. In this work, we present a comparative ReaxFF reactive molecular dynamics investigation on spherical TiO2 nanoparticles (NSs) of realistic size, with diameters from 2.2 to 4.4 nm, immersed in a large drop of bulk water. After force field validation for its use for a curved anatase TiO2 surface/water interface, we performed several simulations of the TiO2 nanoparticles of increasing size in a water drop. We found that water can be adsorbed jointly in a molecular and dissociative way on the surface. A Langmuir isotherm indicating an adsorption/desorption mechanism of water on the NS is observed. Regarding the dissociative adsorption, atomistic details reveal two different mechanisms, depending on the water concentration around the NS. At low coverage, the first mechanism involves direct dissociation of a single water molecule, whereas, at higher water coverage, the second mechanism is a proton transfer reaction involving two water molecules, also known as Grotthuss-like mechanism. Thermal annealing simulations show that several water molecules remain on the surface in agreement with the experimental reports. The capacity of adsorption is higher for the 2.2 and 3.0 nm NSs than for the 4.4 nm NS. Finally, a comparative investigation with flat surfaces indicates that NSs present a higher water adsorption capacity (undissociated and dissociated) than flat surfaces, which can be rationalized considering that NSs present many more low-coordinated Ti atoms available for water adsorption.

Aloe Vera-Mediated Te Nanostructures: Highly Potent Antibacterial Agents and Moderated Anticancer Effects

Cancer and antimicrobial resistance to antibiotics are two of the most worrying healthcare concerns that humanity is facing nowadays. Some of the most promising solutions for these healthcare problems may come from nanomedicine. While the traditional synthesis of nanomaterials is often accompanied by drawbacks such as high cost or the production of toxic by-products, green nanotechnology has been presented as a suitable solution to overcome such challenges. In this work, an approach for the synthesis of tellurium (Te) nanostructures in aqueous media has been developed using aloe vera (AV) extracts as a unique reducing and capping agent. Te-based nanoparticles (AV-TeNPs), with sizes between 20 and 60 nm, were characterized in terms of physicochemical properties and tested for potential biomedical applications. A significant decay in bacterial growth after 24 h was achieved for both Methicillin-resistant Staphylococcus aureus and multidrug-resistant Escherichia coli at a relative low concentration of 5 µg/mL, while there was no cytotoxicity towards human dermal fibroblasts after 3 days of treatment. AV-TeNPs also showed anticancer properties up to 72 h within a range of concentrations between 5 and 100 µg/mL. Consequently, here, we present a novel and green approach to produce Te-based nanostructures with potential biomedical applications, especially for antibacterial and anticancer applications.