Single Atom Engineered Antibiotics Overcome Bacterial Resistance.

The outbreak of antibiotic-resistant bacteria, or "superbugs", poses a global public health hazard due to their resilience against the most effective last-line antibiotics. Identifying potent antibacterial agents capable of evading bacterial resistance mechanisms represents the ultimate defense strategy. This study shows that -the otherwise essential micronutrient- manganese turns into a broad-spectrum potent antibiotic when coordinated with a carboxylated nitrogen-doped graphene. This antibiotic material (termed NGA-Mn) not only inhibits the growth of a wide spectrum of multidrug-resistant bacteria but also heals wounds infected by bacteria in vivo and, most importantly, effectively evades bacterial resistance development. NGA-Mn exhibits up to 25-fold higher cytocompatibility to human cells than its minimum bacterial inhibitory concentration, demonstrating its potential as a next-generation antibacterial agent. Experimental findings suggest that NGA-Mn acts on the outer side of the bacterial cell membrane via a multimolecular collective binding, blocking vital functions in both Gram-positive and Gram-negative bacteria. The results underscore the potential of single-atom engineering toward potent antibiotics, offering simultaneously a long-sought solution for evading drug resistance development while being cytocompatible to human cells.

Bimetallic Single-Atom Catalysts for Water Splitting.

Green hydrogen from water splitting has emerged as a critical energy vector with the potential to spearhead the global transition to a fossil fuel-independent society. The field of catalysis has been revolutionized by single-atom catalysts (SACs), which exhibit unique and intricate interactions between atomically dispersed metal atoms and their supports. Recently, bimetallic SACs (bimSACs) have garnered significant attention for leveraging the synergistic functions of two metal ions coordinated on appropriately designed supports. BimSACs offer an avenue for rich metal-metal and metal-support cooperativity, potentially addressing current limitations of SACs in effectively furnishing transformations which involve synchronous proton-electron exchanges, substrate activation with reversible redox cycles, simultaneous multi-electron transfer, regulation of spin states, tuning of electronic properties, and cyclic transition states with low activation energies. This review aims to encapsulate the growing advancements in bimSACs, with an emphasis on their pivotal role in hydrogen generation via water splitting. We subsequently delve into advanced experimental methodologies for the elaborate characterization of SACs, elucidate their electronic properties, and discuss their local coordination environment. Overall, we present comprehensive discussion on the deployment of bimSACs in both hydrogen evolution reaction and oxygen evolution reaction, the two half-reactions of the water electrolysis process.

Postmelting Encapsulation of Glass Microwires for Multipath Light Waveguiding within Phosphate Glasses.

Glass waveguides are the fundamental component of advanced photonic circuits and play a pivotal role in diverse applications, including quantum information processing, light generation, imaging, data storage, and sensing platforms. Up to date, the fabrication of glass waveguides relies mainly on demanding chemical processes or on the employment of expensive ultrafast laser equipment. In this work, we demonstrate an advanced, simple, low-temperature, postmelting encapsulation procedure for the development of glass waveguides. Specifically, silver iodide phosphate glass microwires (MWs) are drawn from splat-quenched glasses. These MWs are then incorporated in a controlled manner within transparent silver phosphate glass matrices. The judicious selection of glass compositions ensures that the refractive index of the host phosphate glass is lower than that of the embedded MWs. This facilitates the propagation of light inside the encapsulated higher refractive index MWs, leading to the facile development of waveguides. Importantly, we substantially enhance the light transmission within the MWs by leveraging the plasmon resonance effects due to the presence of silver nanoparticles spontaneously generated owing to the silver iodide phosphate glass composition. Employing this innovative approach, we have successfully engineered waveguide devices incorporating either one or two MWs. Remarkably, the dual MW devices are capable of transmitting light of different colors and in multipath direction, rendering the developed waveguides outstanding candidates for extending the functionalities of diverse photonic and optoelectronic circuits, as well as in intelligent signaling applications in smart glass technologies.

Real Time Tracking of Nanoconfined Water-Assisted Ion Transfer in Functionalized Graphene Derivatives Supercapacitor Electrodes.

Water molecules confined in nanoscale spaces of 2D graphene layers have fascinated researchers worldwide for the past several years, especially in the context of energy storage applications. The water molecules exchanged along with ions during the electrochemical process can aid in wetting and stabilizing the layered materials resulting in an anomalous enhancement in the performance of supercapacitor electrodes. Engineering of 2D carbon electrode materials with various functionalities (oxygen (─O), fluorine (─F), nitrile (─C≡N), carboxylic (─COOH), carbonyl (─C═O), nitrogen (─N)) can alter the ion/water organization in graphene derivatives, and eventually their inherent ion storage ability. Thus, in the current study, a comparative set of functionalized graphene derivatives-fluorine-doped cyanographene (G-F-CN), cyanographene (G-CN), graphene acid (G-COOH), oxidized graphene acid (G-COOH (O)) and nitrogen superdoped graphene (G-N) is systematically evaluated toward charge storage in various aqueous-based electrolyte systems. Differences in functionalization on graphene derivatives influence the electrochemical properties, and the real-time mass exchange during the electrochemical process is monitored by electrochemical quartz crystal microbalance (EQCM). Electrogravimetric assessment revealed that oxidized 2D acid derivatives (G-COOH (O)) are shown to exhibit high ion storage performance along with maximum water transfer during the electrochemical process. The complex understanding of the processes gained during supercapacitor electrode charging in aqueous electrolytes paves the way toward the rational utilization of graphene derivatives in forefront energy storage applications.

Single Atom Catalysts Based on Earth-Abundant Metals for Energy-Related Applications.

Anthropogenic activities related to population growth, economic development, technological advances, and changes in lifestyle and climate patterns result in a continuous increase in energy consumption. At the same time, the rare metal elements frequently deployed as catalysts in energy related processes are not only costly in view of their low natural abundance, but their availability is often further limited due to geopolitical reasons. Thus, electrochemical energy storage and conversion with earth-abundant metals, mainly in the form of single-atom catalysts (SACs), are highly relevant and timely technologies. In this review the application of earth-abundant SACs in electrochemical energy storage and electrocatalytic conversion of chemicals to fuels or products with high energy content is discussed. The oxygen reduction reaction is also appraised, which is primarily harnessed in fuel cell technologies and metal-air batteries. The coordination, active sites, and mechanistic aspects of transition metal SACs are analyzed for two-electron and four-electron reaction pathways. Further, the electrochemical water splitting with SACs toward green hydrogen fuel is discussed in terms of not only hydrogen evolution reaction but also oxygen evolution reaction. Similarly, the production of ammonia as a clean fuel via electrocatalytic nitrogen reduction reaction is portrayed, highlighting the potential of earth-abundant single metal species.

Development of Iron-Based Single Atom Materials for General and Efficient Synthesis of Amines.

Earth abundant metal-based heterogeneous catalysts with highly active and at the same time stable isolated metal sites constitute a key factor for the advancement of sustainable and cost-effective chemical synthesis. In particular, the development of more practical, and durable iron-based materials is of central interest for organic synthesis, especially for the preparation of chemical products related to life science applications. Here, we report the preparation of Fe-single atom catalysts (Fe-SACs) entrapped in N-doped mesoporous carbon support with unprecedented potential in the preparation of different kinds of amines, which represent privileged class of organic compounds and find increasing application in daily life. The optimal Fe-SACs allow for the reductive amination of a broad range of aldehydes and ketones with ammonia and amines to produce diverse primary, secondary, and tertiary amines including N-methylated products as well as drugs, agrochemicals, and other biomolecules (amino acid esters and amides) utilizing green hydrogen.

Correction: α-Fe2O3/TiO2 3D hierarchical nanostructures for enhanced photoelectrochemical water splitting.

Correction for 'α-Fe2O3/TiO2 3D hierarchical nanostructures for enhanced photoelectrochemical water splitting' by Hyungkyu Han et al., Nanoscale, 2017, 9, 134-142, https://doi.org/10.1039/C6NR06908H.

Solvent Controlled Generation of Spin Active Polarons in Two-Dimensional Material under UV Light Irradiation.

Polarons belong to a class of extensively studied quasiparticles that have found applications spanning diverse fields, including charge transport, colossal magnetoresistance, thermoelectricity, (multi)ferroism, optoelectronics, and photovoltaics. It is notable, though, that their interaction with the local environment has been overlooked so far. We report an unexpected phenomenon of the solvent-induced generation of polaronic spin active states in a two-dimensional (2D) material fluorographene under UV light. Furthermore, we present compelling evidence of the solvent-specific nature of this phenomenon. The generation of spin-active states is robust in acetone, moderate in benzene, and absent in cyclohexane. Continuous wave X-band electron paramagnetic resonance (EPR) spectroscopy experiments revealed a massive increase in the EPR signal for fluorographene dispersed in acetone under UV-light irradiation, while the system did not show any significant signal under dark conditions and without the solvent. The patterns appeared due to the generation of transient magnetic photoexcited states of polaronic character, which encompassed the net 1/2 spin moment detectable by EPR. Advanced ab initio calculations disclosed that polarons are plausibly formed at radical sites in fluorographene which interact strongly with acetone molecules in their vicinity. Additionally, we present a comprehensive scenario for multiplication of polaronic spin active species, highlighting the pivotal role of the photoinduced charge transfer from the solvent to the electrophilic radical centers in fluorographene. We believe that the solvent-tunable polaron formation with the use of UV light and an easily accessible 2D nanomaterial opens up a wide range of future applications, ranging from molecular sensing to magneto-optical devices.

Magnetically Recyclable Borane Lewis Acid Catalyst for Hydrosilylation of Imines and Reductive Amination of Carbonyls.

Fluorinated arylborane-based Lewis acid catalysts have shown remarkable activity and serve as ideal examples of transition metal-free catalysts for diverse organic transformations. However, their homogeneous nature poses challenges in terms of recyclability and separation from reaction mixtures. This work presents an efficient technique for the heterogenization of boron Lewis acid catalysts by anchoring Piers' borane to allyl-functionalized iron oxide. This catalyst demonstrates excellent activity in the hydrosilylation of imines and the reductive amination of carbonyls using various silanes as reducing agents under mild reaction conditions. The catalyst exhibits broad tolerance towards a wide range of functional substrates. Furthermore, it exhibits good recyclability and can be easily separated from the products using an external magnetic field. This work represents a significant advance in the development of sustainable heterogenous metal-free catalysts for organic transformations.

Correction to "Band Gap and Morphology Engineering of Hematite Nanoflakes from an Ex Situ Sn Doping for Enhanced Photoelectrochemical Water Splitting".

[This corrects the article DOI: 10.1021/acsomega.2c04028.].

Linear-Structure Single-Atom Gold(I) Catalyst for Dehydrogenative Coupling of Organosilanes with Alcohols.

A strategy for the synthesis of a gold-based single-atom catalyst (SAC) via a one-step room temperature reduction of Au(III) salt and stabilization of Au(I) ions on nitrile-functionalized graphene (cyanographene; G-CN) is described. The graphene-supported G(CN)-Au catalyst exhibits a unique linear structure of the Au(I) active sites promoting a multistep mode of action in dehydrogenative coupling of organosilanes with alcohols under mild reaction conditions as proven by advanced XPS, XAFS, XANES, and EPR techniques along with DFT calculations. The linear structure being perfectly accessible toward the reactant molecules and the cyanographene-induced charge transfer resulting in the exclusive Au(I) valence state contribute to the superior efficiency of the emerging two-dimensional SAC. The developed G(CN)-Au SAC, despite its low metal loading (ca. 0.6 wt %), appear to be the most efficient catalyst for Si-H bond activation with a turnover frequency of up to 139,494 h-1 and high selectivities, significantly overcoming all reported homogeneous gold catalysts. Moreover, it can be easily prepared in a multigram batch scale, is recyclable, and works well toward more than 40 organosilanes. This work opens the door for applications of SACs with a linear structure of the active site for advanced catalytic applications.

Single atom catalyst-mediated generation of reactive species in water treatment.

Water is one of the most essential components in the sustainable development goals (SDGs) of the United Nations. With worsening global water scarcity, especially in some developing countries, water reuse is gaining increasing acceptance. A key challenge in water treatment by conventional treatment processes is the difficulty of treating low concentrations of pollutants (micromolar to nanomolar) in the presence of much higher levels of inorganic ions and natural organic matter (NOM) in water (or real water matrices). Advanced oxidation processes (AOPs) have emerged as an attractive treatment technology that generates reactive species with high redox potentials (E0) (e.g., hydroxyl radical (HO˙), singlet oxygen (1O2), sulfate radical (SO4˙-), and high-valent metals like iron(IV) (Fe(IV)), copper(III) (Cu(III)), and cobalt(IV) (Co(IV))). The use of single atom catalysts (SACs) in AOPs and water treatment technologies has appeared only recently. This review introduces the application of SACs in the activation of hydrogen peroxide and persulfate to produce reactive species in treatment processes. A significant part of the review is devoted to the mechanistic aspects of traditional AOPs and their comparison with those triggered by SACs. The radical species, SO4˙- and HO˙, which are produced in both traditional and SACs-activated AOPs, have higher redox potentials than non-radical species, 1O2 and high-valent metal species. However, SO4˙- and HO˙ radicals are non-selective and easily affected by components of water while non-radicals resist the impact of such constituents in water. Significantly, SACs with varying coordination environments and structures can be tuned to exclusively generate non-radical species to treat water with a complex matrix. Almost no influence of chloride, carbonate, phosphate, and NOM was observed on the performance of SACs in treating pollutants in water when nonradical species dominate. Therefore, the appropriately designed SACs represent game-changers in purifying water vs. AOPs with high efficiency and minimal interference from constituents of polluted water to meet the goals of water sustainability.

Lewis Acid Catalyzed Amide Bond Formation in Covalent Graphene-MOF Hybrids.

Covalent hybrids of graphene and metal-organic frameworks (MOFs) hold immense potential in various technologies, particularly catalysis and energy applications, due to the advantageous combination of conductivity and porosity. The formation of an amide bond between carboxylate-functionalized graphene acid (GA) and amine-functionalized UiO-66-NH2 MOF (Zr6O4(OH)4(NH2-bdc)6, with NH2-bdc2- = 2-amino-1,4-benzenedicarboxylate and UiO = Universitetet i Oslo) is a highly efficient strategy for creating such covalent hybrids. Previous experimental studies have demonstrated exceptional properties of these conductive networks, including significant surface area and functionalized hierarchical pores, showing promise as a chemiresistive CO2 sensor and electrode materials for asymmetric supercapacitors. However, the molecular-level origin of the covalent linkages between pristine MOF and GA layers remains unclear. In this study, density functional theory (DFT) calculations were conducted to elucidate the mechanism of amide bond formation between GA and UiO-66-NH2. The theoretical calculations emphasize the crucial role of zirconium within UiO-66, which acts as a catalyst in the reaction cycle. Both commonly observed hexa-coordinated and less common hepta-coordinated zirconium complexes are considered as intermediates. By gaining detailed insights into the binding interactions between graphene derivatives and MOFs, strategies for tailored syntheses of such nanocomposite materials can be developed.

Ultrasound-Driven Defect Engineering in TiO2-x Nanotubes─Toward Highly Efficient Platinum Single Atom-Enhanced Photocatalytic Water Splitting.

Single-atom catalysts (SACs) have demonstrated superior catalytic activity and selectivity compared to nanoparticle catalysts due to their high reactivity and atom efficiency. However, stabilizing SACs within hosting substrates and their controllable loading preventing single atom clustering remain the key challenges in this field. Moreover, the direct comparison of (co-) catalytic effect of single atoms vs nanoparticles is still highly challenging. Here, we present a novel ultrasound-driven strategy for stabilizing Pt single-atomic sites over highly ordered TiO2 nanotubes. This controllable low-temperature defect engineering enables entrapment of platinum single atoms and controlling their content through the reaction time of consequent chemical impregnation. The novel methodology enables achieving nearly 50 times higher normalized hydrogen evolution compared to pristine titania nanotubes. Moreover, the developed procedure allows the decoration of titania also with ultrasmall nanoparticles through a longer impregnation time of the substrate in a very dilute hexachloroplatinic acid solution. The comparison shows a 10 times higher normalized hydrogen production of platinum single atoms compared to nanoparticles. The mechanistic study shows that the novel approach creates homogeneously distributed defects, such as oxygen vacancies and Ti3+ species, which effectively trap and stabilize Pt2+ and Pt4+ single atoms. The optimized platinum single-atom photocatalyst shows excellent performance of photocatalytic water splitting and hydrogen evolution under one sun solar-simulated light, with TOF values being one order of magnitude higher compared to those of traditional thermal reduction-based methods. The single-atom engineering based on the creation of ultrasound-triggered chemical traps provides a pathway for controllable assembling stable and highly active single-atomic site catalysts on metal oxide support layers.

Local Photochemical Nanoscopy of Hot-Carrier-Driven Catalytic Reactions Using Plasmonic Nanosystems.

Nanoscale investigation of the reactivity of photocatalytic systems is crucial for their fundamental understanding and improving their design and applicability. Here, we present a photochemical nanoscopy technique that unlocks the local spatial detection of molecular products during plasmonic hot-carrier-driven photocatalytic reactions with nanometric precision. By applying the methodology to Au/TiO2 plasmonic photocatalysts, we experimentally and theoretically determined that smaller and denser Au nanoparticle arrays present lower optical contribution with quantum efficiency in hot-hole-driven photocatalysis closely related to the population heterogeneity. As expected, the highest quantum yield from a redox probe oxidation is achieved at the plasmon peak. Investigating a single plasmonic nanodiode, we unravel the areas where oxidation and reduction products are evolved with subwavelength resolution (∼200 nm), illustrating the bipolar behavior of such nanosystems. These results open the way to quantitative investigations at the nanoscale to evaluate the photocatalytic reactivity of low-dimensional materials in a variety of chemical reactions.

Magnetic Polaron States in Photoluminescent Carbon Dots Enable Hydrogen Peroxide Photoproduction.

Photoactivation of aspartic acid-based carbon dots (Asp-CDs) induces the generation of spin-separated species, including electron/hole (e- /h+ ) polarons and spin-coupled triplet states, as uniquely confirmed by the light-induced electron paramagnetic resonance spectroscopy. The relative population of the e- /h+ pairs and triplet species depends on the solvent polarity, featuring a substantial stabilization of the triplet state in a non-polar environment (benzene). The electronic properties of the photoexcited Asp-CDs emerge from their spatial organization being interpreted as multi-layer assemblies containing a hydrophobic carbonaceous core and a hydrophilic oxygen and nitrogen functionalized surface. The system properties are dissected theoretically by density functional theory in combination with molecular dynamics simulations on quasi-spherical assemblies of size-variant flakelike model systems, revealing the importance of size dependence and interlayer effects. The formation of the spin-separated states in Asp-CDs enables the photoproduction of hydrogen peroxide (H2 O2 ) from water and water/2-propanol mixture via a water oxidation reaction.

Acidic graphene organocatalyst for the superior transformation of wastes into high-added-value chemicals.

Our dependence on finite fossil fuels and the insecure energy supply chains have stimulated intensive research for sustainable technologies. Upcycling glycerol, produced from biomass fermentation and as a biodiesel formation byproduct, can substantially contribute in circular carbon economy. Here, we report glycerol's solvent-free and room-temperature conversion to high-added-value chemicals via a reusable graphene catalyst (G-ASA), functionalized with a natural amino acid (taurine). Theoretical studies unveil that the superior performance of the catalyst (surpassing even homogeneous, industrial catalysts) is associated with the dual role of the covalently linked taurine, boosting the catalyst's acidity and affinity for the reactants. Unlike previous catalysts, G-ASA exhibits excellent activity (7508 mmol g-1 h-1) and selectivity (99.9%) for glycerol conversion to solketal, an additive for improving fuels' quality and a precursor of commodity and fine chemicals. Notably, the catalyst is also particularly active in converting oils to biodiesel, demonstrating its general applicability.

Antibacterial Nanomaterials: Mechanisms, Impacts on Antimicrobial Resistance and Design Principles.

Antimicrobial resistance (AMR) is one of the biggest threats to the environment and health. AMR rapidly invalidates conventional antibiotics, and antimicrobial nanomaterials have been increasingly explored as alternatives. Interestingly, several antimicrobial nanomaterials show AMR-independent antimicrobial effects without detectable new resistance and have therefore been suggested to prevent AMR evolution. In contrast, some are found to trigger the evolution of AMR. Given these seemingly conflicting findings, a timely discussion of the two faces of antimicrobial nanomaterials is urgently needed. This review systematically compares the killing mechanisms and structure-activity relationships of antibiotics and antimicrobial nanomaterials. We then focus on nano-microbe interactions to elucidate the impacts of molecular initiating events on AMR evolution. Finally, we provide an outlook on future antimicrobial nanomaterials and propose design principles for the prevention of AMR evolution.