Divergent Syntheses of Near-Infrared Light-Activated Molecular Jackhammers for Cancer Cell Eradication.

Aminocyanines incorporating Cy7 and Cy7.5 moieties function as molecular jackhammers (MJH) through vibronic-driven action (VDA). This mechanism, which couples molecular vibrational and electronic modes, results in picosecond-scale concerted stretching of the entire molecule. When cell-associated and activated by near-infrared light, MJH mechanically disrupts cell membranes, causing rapid necrotic cell death. Unlike photodynamic and photothermal therapies, the ultrafast vibrational action of MJH is unhindered by high concentrations of reactive oxygen species scavengers and induces only a minimal temperature increase. Here, the efficient synthesis of a library of MJH is described using a practical approach to access a key intermediate and facilitating the preparation of various Cy7 and Cy7.5 MJH with diverse side chains in moderate to high yields. Photophysical characterization reveals that structural modifications significantly affect molar extinction coefficients and quantum yields while maintaining desirable absorption and emission wavelengths. The most promising compounds, featuring dimethylaminoethyl and dimethylcarbamoyl substitutions, demonstrate up to sevenfold improvement in phototherapeutic index compared to Cy7.5 amine across multiple cancer cell lines. This synthetic strategy provides a valuable platform for developing potent, light-activated therapeutic agents for cancer treatment, with potentially broad applicability across various cancer types.

Continuous Synthesis and Processing of Covalent Organic Frameworks in a Flow Reactor.

Covalent organic frameworks (COFs) are typically prepared in the form of insoluble microcrystalline powders using batch solvothermal reactions that are energy-intensive and require long annealing periods (>120 °C, >72 h). Thus, their wide-scale adoption in a variety of potential applications is impeded by complications related to synthesis, upscaling, and processing, which also compromise their commercialization. Here we report a strategy to address both the need for scalable synthesis and processing approaches through the continuous, accelerated synthesis, and processing of imine- and hydrazone-linked COFs using a flow microreactor. The flow microreactor is capable of unprecedented COF productivities, up to 61,111 kg m-3 day-1, and provides control over key stages of COF formation, including nanoparticle growth, self-assembly, and precipitation. Additionally, the technique successfully yields highly crystalline and porous COFs in versatile macroscopic structures such as monoliths, membranes, prints, and packed beds. We also show that a COF synthesized using the flow microreactor acts as an excellent photocatalyst for the photocatalytic degradation of perfluorooctanoic acid (PFOA) outperforming the degradation efficiency of its batch analogue and other classical photocatalysts such as titanium dioxide (TiO2).

Brownian Diffusion of Hexagonal Boron Nitride Nanosheets and Graphene in Two Dimensions.

Two-dimensional (2D) nanomaterials have numerous interesting chemical and physical properties that make them desirable building blocks for the manufacture of macroscopic materials. Liquid-phase processing is a common method for forming macroscopic materials from these building blocks including wet-spinning and vacuum filtration. As such, assembling 2D nanomaterials into ordered functional materials requires an understanding of their solution dynamics. Yet, there are few experimental studies investigating the hydrodynamics of disk-like materials. Herein, we report the lateral diffusion of hexagonal boron nitride nanosheets (h-BN and graphene) in aqueous solution when confined in 2-dimensions. This was done by imaging fluorescent surfactant-tagged nanosheets and visualizing them by using fluorescence microscopy. Spectroscopic studies were conducted to characterize the interactions between h-BN and the fluorescent surfactant, and atomic force microscopy (AFM) was conducted to characterize the quality of the dispersion. The diffusion data under different gap sizes and viscosities displayed a good correlation with Kramers' theory. We propose that the yielded activation energies by Kramers' equation express the magnitude of the interaction between fluorescent surfactant tagged h-BN and glass because the energies remain constant with changing viscosity and decrease with increasing confinement size. The diffusion of graphene presented a similar trend with similar activation energy as the h-BN. This relationship suggests that Kramers' theory can also be applied to simulate the diffusion of other 2D nanomaterials.

Hexagonal boron nitride exfoliation and dispersion.

Research on hexagonal boron nitride (hBN) 2-dimensional nanostructures has gained traction due to their unique chemical, thermal, and electronic properties. However, to make use of these exceptional properties and fabricate macroscopic materials, hBN often needs to be exfoliated and dispersed in a solvent. In this review, we provide an overview of the many different methods that have been used for dispersing hBN. The approaches that will be covered in this review include solvents, covalent functionalization, acids and bases, surfactants and polymers, biomolecules, intercalating agents, and thermal expansion. The properties of the exfoliated sheets obtained and the dispersions are discussed, and an overview of the work in the field throughout the years is provided.

Photochemical iron-catalyzed decarboxylative azidation via the merger of ligand-to-metal charge transfer and radical ligand transfer catalysis.

Ligand-to-metal charge transfer (LMCT) using stoichiometric copper salts has recently been shown to permit decarboxylative C-N bond formation via an LMCT/radical polar crossover (RPC) mechanism; however, this method is unable to function catalytically and cannot successfully engage unactivated alkyl carboxylic acids, presenting challenges to the general applicability of this approach. Leveraging the concepts of ligand-to-metal charge transfer (LMCT) and radical-ligand-transfer (RLT), we herein report the first photochemical, iron-catalyzed direct decarboxylative azidation. Simply irradiating an inexpensive iron nitrate catalyst in the presence of azidotrimethylsilane allows for a diverse array of carboxylic acids to be converted to corresponding organic azides directly with broad functional group tolerance and mild conditions. Intriguingly, no additional external oxidant is required for this reaction to proceed, simplifying the reaction protocol. Finally, mechanistic studies are consistent with a radical mechanism and suggest that the nitrate counteranion serves as an internal oxidant for turnover of the iron catalyst.

Evaluating the inhibitory activity of ferrocenyl Schiff bases derivatives on 5-lipoxygenase: Computational and biological studies.

In the search for new 5-LOX inhibitors, two ferrocenyl Schiff base complexes functionalized with catechol ((ƞ5-(E)-C5H4-NCH-3,4-benzodiol)Fe(ƞ5-C5H5) (3a)) and vanillin ((ƞ5-(E)-C5H4-NCH-3-methoxy-4-phenol)Fe(ƞ5-C5H5) (3b)) were obtained. Complexes 3a and 3b were biologically evaluated as 5-LOX inhibitors showed potent inhibition compared to their organic analogs (2a and 2b) and known commercial inhibitors, with IC50 = 0.17 ± 0.05 µM for (3a) and 0.73 ± 0.06 µM for (3b) demonstrated a highly inhibitory and potent effect against 5-LOX due to the incorporation of the ferrocenyl fragment. Molecular dynamic studies showed a preferential orientation of the ferrocenyl fragment toward the non-heme iron of 5-LOX, which, together with electrochemical and in-vitro studies, allowed us to propose a competitive redox deactivation mechanism mediated by water, where Fe(III)-enzyme can be reduced by the ferrocenyl fragment. An Epa/IC50 relationship was observed, and the stability of the Schiff bases was evaluated by SWV in the biological medium, observing that the hydrolysis does not affect the high potency of the complexes, making them interesting alternatives for pharmacological applications.

Deconvoluting binding sites in amyloid nanofibrils using time-resolved spectroscopy.

Steady-state fluorescence spectroscopy has a central role not only for sensing applications, but also in biophysics and imaging. Light switching probes, such as ruthenium dipyridophenazine complexes, have been used to study complex systems such as DNA, RNA, and amyloid fibrils. Nonetheless, steady-state spectroscopy is limited in the kind of information it can provide. In this paper, we use time-resolved spectroscopy for studying binding interactions between amyloid-ß fibrillar structures and photoluminescent ligands. Using time-resolved spectroscopy, we demonstrate that ruthenium complexes with a pyrazino phenanthroline derivative can bind to two distinct binding sites on the surface of fibrillar amyloid-ß, in contrast with previous studies using steady-state photoluminescence spectroscopy, which only identified one binding site for similar compounds. The second elusive binding site is revealed when deconvoluting the signals from the time-resolved decay traces, allowing the determination of dissociation constants of 3 and 2.2 µM. Molecular dynamic simulations agree with two binding sites on the surface of amyloid-ß fibrils. Time-resolved spectroscopy was also used to monitor the aggregation of amyloid-ß in real-time. In addition, we show that common polypyridine complexes can bind to amyloid-ß also at two different binding sites. Information on how molecules bind to amyloid proteins is important to understand their toxicity and to design potential drugs that bind and quench their deleterious effects. The additional information contained in time-resolved spectroscopy provides a powerful tool not only for studying excited state dynamics but also for sensing and revealing important information about the system including hidden binding sites.

Probing the Rotary Cycle of Amine-Substituted Molecular Motors.

An understanding of the rotary cycle of molecular motors (MMs), a key component of an approach to opening cells using mechanical motion, is important in furthering the research. Nuclear magnetic resonance (NMR) spectroscopy was used for in situ analysis of illuminated light-active MMs. We found that the presence of a N,N-dimethylethylenediamine in a position conjugated to the central olefin results in changes to the rotation of a second-generation Feringa-type MM. Importantly, the addition decreases the photostability of the compound. The parent compound 1 can withstand >2 h of illumination with no signs of decomposition, while the amino 7 decomposes after 10 min. We found that the degradation can be mitigated by implementing the simple techniques of modulating the light dose, dilution, and stirring the sample while illuminating. Additionally, the presence of moisture affects the rate of the motor's rotation. The addition of the amino group to 1, without moisture present, makes the rotation of motor 7 three times slower than the unfunctionalized parent compound. We also report the use of a method that can be used to determine the molar extinction coefficient of a light-generated metastable species. This method can be used when in situ NMR illumination is not available.

Liquid crystals of neat boron nitride nanotubes and their assembly into ordered macroscopic materials.

Boron nitride nanotubes (BNNTs) have attracted attention for their predicted extraordinary properties; yet, challenges in synthesis and processing have stifled progress on macroscopic materials. Recent advances have led to the production of highly pure BNNTs. Here we report that neat BNNTs dissolve in chlorosulfonic acid (CSA) and form birefringent liquid crystal domains at concentrations above 170 ppmw. These tactoidal domains merge into millimeter-sized regions upon light sonication in capillaries. Cryogenic electron microscopy directly shows nematic alignment of BNNTs in solution. BNNT liquid crystals can be processed into aligned films and extruded into neat BNNT fibers. This study of nematic liquid crystals of BNNTs demonstrates their ability to form macroscopic materials to be used in high-performance applications.

A simple graphene modified electrode for the determination of antimony(III) in edible plants and beverage.

Antimony(III) is a rare electroactive specie present on Earth, whose concentration is not typically determined. The presence of high concentrations of antimony is responsible for a variety of diseases, which makes it desirable to find convenient and reliable methods for its determination. We have developed a convenient glassy carbon modified electrode with electroreduced graphene oxide GC/rGO for the first time determination of Sb(III) in commercial lettuce, celery, and beverages. The surface of the electrode was characterized by scanning electron microscopy (SEM) and cyclic voltammetry, indicating a heterogeneous and rough surface with a real area of 0.28 cm2, which is ~2.5 times the area of GC. The optimal chemical and electrochemical parameters used were: sodium acetate buffer (pH = 4.3), an accumulation potential of -1.0 V and an accumulation time of 150 s. The analytical validation was developed evaluating the linear range (10-60 µg L-1), limit of detection (2.5 µg L-1), accuracy, repetibility and reproducibility with satisfactory results (relative standard deviation (RSD) values lower than 10%). All the analyzes performed in real samples by stripping voltammetry were compared with GF-AAS, showing statistically similar values, demonstrating that GC/rGO could be effectively applied in the analysis of food samples.

Real-Time Visualization and Dynamics of Boron Nitride Nanotubes Undergoing Brownian Motion.

We report the first real-time imaging of individualized boron nitride nanotubes (BNNTs) via stabilization with a rhodamine surfactant and fluorescence microscopy. We study the rotational and translational diffusion and find them to agree with predictions based on a confined, high-aspect-ratio rigid rod undergoing Brownian motion. We find that the behavior of BNNTs parallels that of individualized carbon nanotubes (CNTs), indicating that BNNTs could also be used as model rigid rods to study soft matter systems, while avoiding the experimental disadvantages of CNTs due to their strong light absorption. The use and further development of our technique and findings will accelerate the application of BNNTs from material engineering to biological studies.

Defect-Engineering-Enabled High-Efficiency All-Inorganic Perovskite Solar Cells.

The emergence of cesium lead iodide (CsPbI3 ) perovskite solar cells (PSCs) has generated enormous interest in the photovoltaic research community. However, in general they exhibit low power conversion efficiencies (PCEs) because of the existence of defects. A new all-inorganic perovskite material, CsPbI3 :Br:InI3 , is prepared by defect engineering of CsPbI3 . This new perovskite retains the same bandgap as CsPbI3 , while the intrinsic defect concentration is largely suppressed. Moreover, it can be prepared in an extremely high humidity atmosphere and thus a glovebox is not required. By completely eliminating the labile and expensive components in traditional PSCs, the all-inorganic PSCs based on CsPbI3 :Br:InI3 and carbon electrode exhibit PCE and open-circuit voltage as high as 12.04% and 1.20 V, respectively. More importantly, they demonstrate excellent stability in air for more than two months, while those based on CsPbI3 can survive only a few days in air. The progress reported represents a major leap for all-inorganic PSCs and paves the way for their further exploration in order to achieve higher performance.

Interrogating Amyloid Aggregates using Fluorescent Probes.

Amyloids are a broad class of proteins and peptides that can misfold and assemble into long unbranched fibrils with a cross-ß conformation. These misfolding and aggregation events are associated with the onset of a variety of human diseases, among them, Alzheimer's disease, Parkinson's disease, and Huntington disease. Our understanding of amyloids has been greatly supported by fluorescent molecular probes, such as thioflavin-T, which shows an increase in fluorescence emission upon binding to fibrillar aggregates. Since the first application of thioflavin-T in amyloid studies nearly 30 years ago, many probes have emerged exhibiting a variety of responses to amyloids, such as intensity changes, shifts in fluorescence maxima, and variations in lifetimes, among many others. These probes have shed light on a variety of topics including the kinetics of amyloid aggregation, the effectiveness of amyloid aggregation inhibitors, the elucidation of binding sites in amyloid structures, and the staining of amyloids aggregates in vitro, ex vivo, and in vivo. In this Review, we discuss the design, properties, and application of photoactive probes used to study amyloid aggregation, as well as the challenges faced by current probes and techniques, and the novel approaches that are emerging to address these challenges.

Monitoring the Formation of Amyloid Oligomers Using Photoluminescence Anisotropy.

The formation of oligomeric soluble aggregates is related to the toxicity of amyloid peptides and proteins. In this manuscript, we report the use of a ruthenium polypyridyl complex ([Ru(bpy)2(dpqp)]2+) to track the formation of amyloid oligomers at different times using photoluminescence anisotropy. This technique is sensitive to the rotational correlation time of the molecule under study, which is consequently related to the size of the molecule. [Ru(bpy)2(dpqp)]2+ presents anisotropy values of zero when free in solution (due to its rapid rotation and long lifetime) but larger values as the size and concentration of amyloid-ß (Aß) oligomers increase. Our assays show that Aß forms oligomers immediately after the assay is started, reaching a steady state at ∼48 h. SDS-PAGE, DLS, and TEM were used to confirm and characterize the formation of oligomers. Our experiments show that the rate of formation for Aß oligomers is temperature dependent, with faster rates as the temperature of the assay is increased. The probe was also effective in monitoring the formation of α-synuclein oligomers at different times.

Lead-Free Double Perovskite Cs2 SnX6 : Facile Solution Synthesis and Excellent Stability.

Long-term instability and possible lead contamination are the two main issues limiting the widespread application of organic-inorganic lead halide perovskites. Here a facile and efficient solution-phase method is demonstrated to synthesize lead-free Cs2 SnX6 (X = Br, I) with a well-defined crystal structure, long-term stability, and high yield. Based on the systematic experimental data and first-principle simulation results, Cs2 SnX6 displays excellent stability against moisture, light, and high temperature, which can be ascribed to the unique vacancy-ordered defect-variant structure, stable chemical compositions with Sn4+ , as well as the lower formation enthalpy for Cs2 SnX6 . Additionally, photodetectors based on Cs2 SnI6 are also fabricated, which show excellent performance and stability. This study provides very useful insights into the development of lead-free double perovskites with high stability.

Adverse Effect of PTFE Stir Bars on the Covalent Functionalization of Carbon and Boron Nitride Nanotubes Using Billups-Birch Reduction Conditions.

The functionalization of nanomaterials has long been studied as a way to manipulate and tailor their properties to a desired application. Of the various methods available, the Billups-Birch reduction has become an important and widely used reaction for the functionalization of carbon nanotubes (CNTs) and, more recently, boron nitride nanotubes. However, an easily overlooked source of error when using highly reductive conditions is the utilization of poly(tetrafluoroethylene) (PTFE) stir bars. In this work, we studied the effects of using this kind of stir bar versus using a glass stir bar by measuring the resulting degree of functionalization with 1-bromododecane. Thermogravimetric analysis studies alone could deceive one into thinking that reactions stirred with PTFE stir bars are highly functionalized; however, the utilization of spectroscopic techniques, such as Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, tells otherwise. Furthermore, in the case of CNTs, we determined that using Raman spectroscopy alone for analysis is not sufficient to demonstrate successful chemical modification.

Sensing Temperature in Vitro and in Cells Using a BODIPY Molecular Probe.

Boron dipyrromethene (BODIPY) molecular rotors have shown sensitivity toward viscosity, polarity, and temperature. Here, we report a 1,3,5,7-tetramethyl-8-phenyl-BODIPY modified with a polyethylene glycol (PEG) chain, for temperature sensing and live cell imaging. This new PEG-BODIPY dye presents an increase in nonradiative decay as temperature increases, which directly influences its lifetime. This change in lifetime is dependent on changes in both temperature and viscosity at low viscosity values, but is only dependent on temperature at high viscosity values. The dependence of fluorescence lifetime with temperature allows for temperature monitoring in vitro and in cells, with sub degree resolution. When in contact with cells, the PEG-BODIPY spontaneously penetrates and stains the cell but not the nucleus. Furthermore, no significant cell toxicity was found even at 100 µM concentration. Using fluorescence lifetime imaging microscopy (FLIM), we were able to observe the changes in the lifetime of PEG-BODIPY within the cell at different temperatures. The use of FLIM and molecular probes such as PEG-BODIPY can provide important information about cellular temperature and heat dissipation upon medically relevant stimuli, such as radiofrequency ablation and photodynamic therapy.

Surfactant-assisted individualization and dispersion of boron nitride nanotubes.

Boron nitride nanotubes (BNNTs) belong to a novel class of material with useful thermal, electronic and optical properties. However, the study and the development of applications of this material requires the formation of stable dispersions of individual BNNTs in water. Here we address the dispersion of BNNT material in water using surfactants with varying properties. The surfactants were compared based on the quantity of BNNTs dispersed and the quality of the dispersions, as visualized by AFM and cryo-TEM. All surfactants produce dispersions of individualized or small bundles of BNNTs. Of the surfactants tested, high molecular weight, nonionic surfactants suspend the most BNNTs, while ionic surfactants remove the most h-BN impurities. The surfactant dispersions were further characterized by ensemble measurements, such as UV absorption and photoluminescence, dynamic light scattering (DLS), and zeta potential to investigate dispersion stability and quality. These techniques provide a facile strategy for testing future BNNT dispersions. The results of this study reveal that BNNT dispersions in aqueous solution can be tuned to fit a specific application through surfactant selection.

Soft-Lithographic Patterning of Luminescent Carbon Nanodots Derived from Collagen Waste.

Luminescent carbon dots (Cdots) synthesized using inexpensive precursors have inspired tremendous research interest because of their superior properties and applicability in various fields. In this work, we report a simple, economical, green route for the synthesis of multifunctional fluorescent Cdots prepared from a natural, low-cost source: collagen extracted from animal skin wastes. The as-synthesized metal-free Cdots were found to be in the size range of ∼1.2-9 nm, emitting bright blue photoluminescence with a calculated Cdot yield of ∼63%. Importantly, the soft-lithographic method used was inexpensive and yielded a variety of Cdot patterns with different geometrical structures and significant cellular biocompatibility. This novel approach to Cdot production highlights innovative ways of transforming industrial biowastes into advanced multifunctional materials which offer exciting potential for applications in nanophotonics and nanobiotechnology using a simple and scalable technique.

An Insight into the Phase Transformation of WS2 upon Fluorination.

The transformation from semiconducting to metallic phase, accompanied by a structural transition in 2D transition metal dichalcogenides has attracted the attention of the researchers worldwide. The unconventional structural transformation of fluorinated WS2 (FWS2 ) into the 1T phase is described. The energy difference between the two phases debugs this transition, as fluorination enhances the stability of 1T FWS2 and makes it energetically favorable at higher F concentration. Investigation of the electronic and optical nature of FWS2 is supplemented by possible band structures and bandgap calculations. Magnetic centers in the 1T phase appear in FWS2 possibly due to the introduction of defect sites. A direct consequence of the phase transition and associated increase in interlayer spacing is a change in friction behavior. Friction force microscopy is used to determine this effect of functionalization accompanied phase transformation.