Internal Redox Research Articles

A Novel Near-Infrared Ytterbium Complex [Yb(DPPDA)2](DIPEA) with Φ = 0.46% and τobs = 105 μs.

The luminescent performances of near-infrared (NIR) lanthanide (Ln) complexes were restricted greatly by vibration quenching of X-H (X = C, N, O) oscillators, which are usually contained in ligands and solvents. Encapsulating Ln3+ into a cavity of coordination atoms is a feasible method of alleviating this quenching effect. In this work, a novel ytterbium complex [Yb(DPPDA)2](DIPEA) coordinated with 4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylic acid (DPPDA) was synthesized and characterized by FT-IR, ESI-MS and elemental analysis. Under the excitation of 335 nm light, [Yb(DPPDA)2](DIPEA) showed two emission peaks at 975 and 1011 nm, respectively, which were assigned to the characteristic 2F5/2 → 2F7/2 transition of Yb3+. Meanwhile, this ytterbium complex exhibited a plausible absolute quantum yield of 0.46% and a luminescent lifetime of 105 μs in CD3OD solution. In particular, its intrinsic quantum yield was calculated to be 12.5%, and this considerably high value was attributed to the near-zero solvent molecules bound to Yb3+ and the absence of X-H oscillators in the first coordination sphere. Based on experimental results, we further proposed that the sensitized luminescence of [Yb(DPPDA)2](DIPEA) occurred via an internal redox mechanism instead of an energy transfer process.

Ratiometric sensing of redox environments inside individual carboxysomes trapped in solution.

The rapid diffusion of biological nanoparticles in solution impedes our ability to continuously monitor individual particles and measure their physical and chemical properties. To overcome this, we previously developed the interferometric scattering anti-Brownian electrokinetic (ISABEL) trap, which uses scattering to localize a particle and applies electrokinetic forces to counteract Brownian motion, thus enabling extended observation. Here we present an improved ISABEL trap that incorporates a near-infrared scatter illumination beam and rapidly interleaves 405- and 488-nm fluorescence excitation beams, and apply this trap to the study of carboxysomes. Carboxysomes are bacterial microcompartments that self-assemble to sequester the enzyme rubisco and provide a favorable chemical environment for the fixation of carbon dioxide. With the ISABEL trap, we monitored the internal redox environment of individual carboxysomes labeled with the ratiometric redox reporter roGFP2. Carboxysomes were observed to vary widely in both redox-dependent fluorescence and scattering contrast (reporting on mass). Furthermore, we used redox sensing to explore the chemical kinetics within intact carboxysomes, where bulk measurements may contain unwanted contributions from aggregates or interfering fluorescent proteins. Overall, we demonstrate the ISABEL trap's ability to sensitively monitor chemical information inside single nanoscale biological objects, enabling new experiments on these systems.

Self‐Driven Ni‐Based Electrochromic Devices for Energy‐Efficient Smart Windows

AbstractElectrochromic devices (ECDs) with adjustable transmittance have opened new opportunities to the development of smart windows for energy‐efficiency building. However, the switching between colored and bleached state of conventional ECD will bring extra energy consumption, the design of high‐performance ECD with low consumption is still an elusive goal. To address this issue, a self‐driven and energy‐saving Ni anode‐based ECD using Prussian blue as electrochromic material is developed. During the day, it can be colored by solar energy. By contrast, it can spontaneously bleach when the ECD's anode and cathode are short‐circuiting using the internal redox potential during the night. It is worth noting that no extra energy is inputted in the coloring‐bleaching cycle. In comparison with the ECD using electrolyte with high Ni2+ (K+:Ni2+ = 1:9) or high K+ (K+:Ni2+ = 9:1) concentration with poor optical contrast and cyclic stability (failed <100 cycles), the Ni‐based ECD with the electrolyte containing equal amount of K+ and Ni2+ exhibits a high optical contrast (39.45%), good coloration response time (6 s), and excellent stability (1000 cycles). These properties suggest that the Ni‐based electrochromic configuration is expected to be a catalyst for the development of energy‐storage EC smart window in the future.

Revealing the Selective Bifunctional Electrocatalytic Sites via In Situ Irradiated X-Ray Photoelectron Spectroscopy for Lithium-Sulfur Battery.

The electrocatalysts are widely applied in lithium-sulfur (Li-S) batteries to selectively accelerate the redox kinetics behavior of Li2 S, in which bifunctional active sites are established, thereby improving the electrochemical performance of the battery. Considering that the Li-S battery is a complex closed "black box" system, the internal redox reaction routes and active sites cannot be directly observed and monitored especially due to the distribution of potential active-site structures and their dynamic reconstruction. Empirical evidence demonstrates that traditional electrochemical test methods and theoretical calculations only probe the net result of multi-factors on an average and whole scale. Herein, based on the amorphous TiO2- x @Ni selective bifunctional model catalyst, these limitations are overcome by developing a system that couples the light field and in situ irradiated X-ray photoelectron spectroscopy to synergistically convert the "black box" battery into a "see-through" battery for direct observation of the charge transportation, thus revealing that amorphous TiO2- x and Ni nanoparticle as the oxidation and reduction sites selectively promote the decomposition and nucleation of Li2 S, respectively. This work provides a universal method to achieve a deeper mechanistic understanding of bidirectional sulfur electrochemistry.

Cobalt-doped tin disulfide catalysts for high-capacity lithium-air batteries with high lifetime.

Dual electrolyte lithium-air batteries have received widespread attention for their ultra-high energy density. However, the low internal redox efficiency of these batteries results in a relatively short operating life. SnS2 is widely used in Li-S batteries, Li-ion batteries, photocatalysis, and other fields due to the high discharge capacity in batteries. However, SnS2 suffers from low electrical conductivity and slow redox kinetics. In this study, Co-doped SnS2 is prepared by hydrothermal method for application in dual-electrolyte lithium-air batteries to study its electrochemical performance and its catalytic reaction process by DFT theory. Conductivity tests show that the Co doping enhances the electrical conductivity of the material and high transmission electron microscopy (HRTEM) results demonstrate that the Co doping of SnS2 increases the grain plane spacing and the material indicates that defects are created on the surface of the material, which is more beneficial to the electrochemical performance of the cell. Co-doped SnS2 exhibits excellent good cycling stability and high discharge capacity in a dual electrolyte lithium-air battery, maintaining a 0.7 V overpotential for 120 h at a current density of 0.1 mA cm-2, with a cell life of over 500 h and an initial discharge capacity showing excellent results up to 16 065 mA h g-1. In addition, this study explores the catalytic activity of Co-doped SnS2 based on density flooding theory (DFT). The results show that Co atoms have a synergistic effect with Sn atoms to perturb the lattice parameters. The calculations show that the catalytic activity is enhanced with the increasing of Co doping content and 3Co-Sn exhibits minimal overpotential.

A Synthesis of Alstonlarsine A via Alstolucines B and F Demonstrates the Chemical Feasibility of a Proposed Biogenesis.

We offer a new biogenetic proposal for the origin of the complex alkaloid alstonlarsine A, through rearrangement of the Strychnos alkaloids alstolucines B and F. Further, we provide evidence of the chemical feasibility of this proposal in the facile conversion of synthetic alstolucines into alstonlarsine A through a short, efficient sequence of N-methylation, β-elimination, and a cascade 1,7-hydride shift/Mannich cyclization. We believe that this is the first biogenetic proposal involving the "tert-amino effect", a hydride-shift-based internal redox trigger of a Mannich cyclization. A further interesting feature of the cascade is that its stereochemical outcome most likely originates in conformational preferences during the hydride shift.

A Synthesis of Alstonlarsine A via Alstolucines B and F Demonstrates the Chemical Feasibility of a Proposed Biogenesis

AbstractWe offer a new biogenetic proposal for the origin of the complex alkaloid alstonlarsine A, through rearrangement of the Strychnos alkaloids alstolucines B and F. Further, we provide evidence of the chemical feasibility of this proposal in the facile conversion of synthetic alstolucines into alstonlarsine A through a short, efficient sequence of N‐methylation, β‐elimination, and a cascade 1,7‐hydride shift/Mannich cyclization. We believe that this is the first biogenetic proposal involving the “tert‐amino effect”, a hydride‐shift‐based internal redox trigger of a Mannich cyclization. A further interesting feature of the cascade is that its stereochemical outcome most likely originates in conformational preferences during the hydride shift.

Receptor-Mediated Redox Imbalance: An Emerging Clinical Avenue against Aggressive Cancers.

Cancer cells are more vulnerable to abnormal redox fluctuations due to their imbalanced antioxidant system, where cell surface receptors sense stress and trigger intracellular signal relay. As canonical targets of many targeted therapies, cell receptors sensitize the cells to specific drugs. On the other hand, cell target mutations are commonly associated with drug resistance. Thus, exploring effective therapeutics targeting diverse cell receptors may open new clinical avenues against aggressive cancers. This paper uses focused case studies to reveal the intrinsic relationship between the cell receptors of different categories and the primary cancer hallmarks that are associated with the responses to external or internal redox perturbations. Cold atmospheric plasma (CAP) is examined as a promising redox modulation medium and highly selective anti-cancer therapeutic modality featuring dynamically varying receptor targets and minimized drug resistance against aggressive cancers.

Suitability of lectin binding studies for the characterization of redox-active microbial environmental biofilms

Aquatic environmental microbial biofilms grow in a broad range of redox environments from oxic to methanogenic, and they often also establish internal redox gradients. In technical applications, biofilms are also subjected to controlled redox conditions. Studies on biofilms often make use of fluorescence microscopic imaging techniques together with lectin binding analysis to gain insights into structure, composition, and functions of the biofilms. Here we studied the direct influence of redox potentials on fluorescence lectin binding analyses (FLBA) for two commonly used lectin-fluorophore conjugates. An effect of the electrical potential on signal intensity was observed and found to be statistically significant. The signal intensity changes however, remained within the range of a few percent total. A significant drop in intensity was only observed for extremely oxidizing potentials, typically not found under environmental conditions. Our results showed that the fluorophore itself and not the lectin binding to the respective glycoconjugate causes fluorescence changes. The two tested lectin-fluorophores are shown to be suitable for studying the distribution and composition of EPS in environmental biofilms or technical applications and under varying redox conditions.

Ion-Pairing Effects on the Absolute Oxidation Potential of the Fc/Fc+ Redox Couple in Complex Non-Aqueous Environments

Ferrocene (Fc) is commonly used as an internal redox couple in electrochemical measurements. Therefore, understanding how the absolute oxidation potential of Fc is modulated by different solvents and ion concentrations is important for facilitating the comparison between different experimental measurements. Standard implicit solvation models are unable to examine these systems since they lack atomistic detail of the solvent structure and ion coordination. Using polarizable forcefields fit to ab initio quantum chemistry calculations, we have computed the absolute oxidation potential of the Fc/Fc+ redox couple in water, acetonitrile, 1,2-dichloroethane, and trichloromethane. Since experimental measurements are often taken in mixtures of nonaqueous solvents and ionic liquids, we have computed the oxidation potential of Fc in mixtures of acetonitrile and 1,2-dichloroethane with an ionic liquid, [BMIM+][BF4-]. In order to elucidate the effect ion-pairing has on the thermodynamics of this electron transfer process, we relate the differential solvation free energy of Fc/Fc+ to anion coordination sampled in molecular simulations. Quantification of these solvation/environmental effects has important implications in how the thermodynamics of electron transfer processes are modulated by ion concentration fluctuations in the electrical double layer at electrode interfaces.

Hydride shift mediated C(sp3)–H bond functionalization starting from non-aniline/phenol type substrates: Evolution into a sequential system

Hydride shift mediated C(sp3)–H bond functionalization, namely, internal redox reaction, is an useful synthetic tool for the construction of fused cycles. Most of the reactions reported so far have focused on the reactions with aniline and phenol derivatives (a heteroatom is directly connected to an aromatic ring), and reactions using substrates having a carbon linker between the aromatic ring and the heteroatom have been overlooked. Recently, various novel reactions starting from the latter type of substrates have been developed, paving the way for new opportunities for the internal redox reaction. In this digest, we summarize recent progress in internal redox reactions that have enabled the unprecedented double C(sp3)–H bond functionalization, the combination of other organic transformations, and the construction of a medium-sized ring.

Flower-like spherical Ni-benzimidazole derived Ni-NiO-C complexed with carbon nanotubes as electrocatalysts for lithium-sulfur battery

In this work, we design and fabricate a novel Ni-NiO-C@CNT composite with synergetic features combining a new metal organic framework-Ni-Benzimidazole (Ni-PhIm) derived Ni-NiO-C and high conductive carbon nanotube (CNT). The Ni-NiO-C was synthesized by carbonizing Ni-PhIm, which used benzimidazole as the organic ligand. The carbon skeleton of Ni-NiO-C provides numerous active sites for adsorbing and chemical anchoring for polysulfides. Meanwhile, the uniformly dispersed Ni and NiO in Ni-NiO-C ensure the integrity of the internal redox process. In addition, the interconnected CNT networks offer good conductivity throughout the entire structure, contributing to fast electron transfer. Hence, the Ni-NiO-C@CNT@S electrode exhibits a remarkable initial specific capacity of 1468 mAh g−1 at 0.2 C, and maintains 904.4 mAh g−1 even at a high discharge rate of 2 C. Moreover, Ni-NiO-C@CNT@S presents outstanding cycle stability with capacity retention of 76.20% and a decay rate of 0.05% per cycle after 500 cycles at 2 C. This work provides a new avenue and an excellent example to design and fabricate cathode material of LSB with outstanding ion/charge transmissive capability to enhance electrochemical performance.

La2NiO4+δ‐Based Memristive Devices Integrated on Si‐Based Substrates

AbstractValence change memories, in which internal redox reactions control the change in resistance are promising candidates for resistive random access memories (ReRAMs) and neuromorphic computing elements. In this context, La2NiO4+δ (L2NO4), a mixed ionic‐electronic conducting oxide, well known for its highly mobile oxygen interstitial ions, emerges as a potential switching material for novel L2NO4‐based memristive devices. However, their integration in complementary metal oxide semiconductor (CMOS) technology still has to be demonstrated, as the major focus of previous studies has been carried out on epitaxial films grown on single crystals. In this work, the optimization of the deposition temperature and precursor solution composition is presented, allowing to obtain high‐quality polycrystalline L2NO4 thin films grown by metal organic chemical vapor deposition on a platinized silicon substrate, and to use these films to build memristive devices in vertical configuration with Ti top electrodes. A bipolar analog‐type transition in resistance can be achieved in Ti/L2NO4/Pt memristive devices. While the “forming” process required for the devices based on nonoptimized L2NO4 thin films is considered as a drawback, the Ti/optimized L2NO4/Pt devices are forming‐free and exhibit a good cyclability. These results prove the switching response of L2NO4‐based devices in a vertical configuration for the first time.

Intramolecular Phosphine-Promoted Knoevenagel Based Redox-Reaction.

A Knoevenagel based redox-reaction promoted by intramolecular phosphine sources is presented for the first time. The influence of different diketones, aldehydes, bases and acids was investigated. The effects of different substituents were evaluated based on their electronical influence on the diketone structure. With the obtained results a mechanism is proposed, giving information about transition states formed during the reaction, which can lead to different products. This type of an internal redox transformation with a phosphine oxide moiety remaining in the molecule after the redox reaction represents a new type of reaction.

Exploring the parameters of central redox hub for screening salinity tolerant rice landraces of coastal Bangladesh

Regulation of oxidative stress towards origin of favorable internal redox cue plays a decisive role in salinity stress acclimation and least studied in rice and hence is the subject of present investigation. Redox landscaping of seedlings of ten experimental land races of rice of coastal Bangladesh grown under post imbibitional salinity stress (PISS) has been done through characterization of ROS-antioxidant interaction dynamics at metabolic interface, transcriptional reprogramming of redox-regulatory genes along with the assessment of biomarkers of oxidative threat for standardizing redox strategies and quality parameters for screening. The results exhibited a strong correlation between salinity induced redox status (pro-oxidant/antioxidant ratio, efficacy of H2O2 turnover through integrated RboH-Ascorbate–Glutathione/Catalase pathway and estimation of sensitive redox biomarkers of oxidative deterioration) and germination phenotypes of all landraces of rice. Transcript abundance of the marker genes of the enzymes associated with central antioxidant hub for H2O2 processing (CatA, OsAPx2, SodCc2, GRase and RboH) of all experimental landraces of the rice advocate the central role of H2O2 turnover dynamics in regulating redox status and salinity tolerance. Landraces suffering greater loss of abilities of decisive regulation of H2O2 turnover dynamics exhibited threat on the oxidative windows of the germinating seeds under salinity.

Multivalent Ce-MOFs as biomimetic laccase nanozyme for environmental remediation

Nanozyme has emerged as promising alternative to natural enzyme during recent years. Currently, laccase nanozyme is mainly limited to Cu-containing materials with catalytic Cu as active site. Noncopper laccase nanozyme, however, has not attracted extensive attention. Herein, inspired by multicopper active site and redox Cu2+/Cu+ electron transfer pathway of natural laccase, a range of multivalent cerium-based metal–organic frameworks (Ce-MOFs) with considerable laccase-mimicking activity were designed, where the internal cerium redox (Ce4+/Ce3+) reactivity could mimic the active center and catalytic function of natural laccase. Compared with natural laccase, Ce-UiO-66 and Ce-MOF-808 exhibited not only better catalytic efficiency (at identical mass concentration) but also superior stability and recyclability toward the oxidation of phenolic compounds. Accordingly, they were applied for detection of mercaptan contaminants and degradation of bisphenol A, showing great potential in environmental catalysis. This work provides new deep insights for rational design of advanced nanozymes and demonstrates the huge potential of applying nanozymes for environmental remediation.

Active Sulfur-Host Material VS4 with Surface Defect Engineering: Intercalation-Conversion Hybrid Cathode Boosting Electrochemical Performance of Li-S Batteries.

Transition-metal sulfides as late-model electrocatalysts usually remain inactive in lithium-sulfur (Li-S) batteries in spite of their advantages to accelerate the rapid conversion of lithium polysulfides (LiPSs). Herein, a series of cobalt-doped vanadium tetrasulfide/reduced graphene oxide (x%Co-VS4/rGO) composites with an ultrathin layered structure as an active sulfur-host material are prepared by a one-pot hydrothermal method. The well-designed two-dimensional ultrathin 3%Co-VS4/rGO with heteroatom architecture defects (defect of Co-doping and defect of S-vacancies) can significantly improve the adsorption ability on LiPSs, the electrocatalytic activity in the Li2S potentiostatic deposition, and the active sulfur reduction/oxidation conversion reactions and greatly boost the electrochemical performances of Li-S batteries. On the one hand, the ultrathin 3%Co-VS4/rGO possesses good conductivity inheriting from rGO which contributes to the capacity of internal redox reactions on lithiation from VS4. On the other hand, the hybrid architectures provide strong adsorption and excellent electrocatalytic ability on LiPSs, which benefit from the surface defects caused by heteroatom doping. The S@3%Co-VS4/rGO cathode displays a high specific capacity of 1332.6 mA h g-1 at 0.2 C and a low-capacity decay of only 0.05% per cycle over 1000 cycles at 3 C with a primary capacity of 633.1 mA h g-1. Furthermore, when the sulfur loading (single-side coating) reaches 4.48 mg cm-2, it still can deliver 756.2 mA h g-1 after the 100th cycle at 0.2 C with 89.5% capacity retention. In addition, the in situ X-ray diffraction test reveals that the sulfur conversion mechanism is the processes of α-S8 → Li2S → β-S8 (first cycle) and then β-S8 ↔ Li2S during the subsequent cycles. The designing strategy with heteroatom doping and self-intercalation capacity adopted in this work would provide novel inspiration for fabricating advanced sulfur-host materials to achieve excellent electrochemical capability in Li-S batteries.

Ratiometric Sensing of Redox Environments Inside Individual Carboxysomes Trapped in Solution.

Diffusion of biological nanoparticles in solution impedes our ability to continuously monitor individual particles and measure their physical and chemical properties. To overcome this, we previously developed the interferometric scattering anti-Brownian electrokinetic (ISABEL) trap, which uses scattering to localize a particle and applies electrokinetic forces that counteract Brownian motion, thus enabling extended observation. Here we present an improved ISABEL trap that incorporates a near-infrared scatter illumination beam and rapidly interleaves 405 and 488 nm fluorescence excitation reporter beams. With the ISABEL trap, we monitored the internal redox environment of individual carboxysomes labeled with the ratiometric redox reporter roGFP2. Carboxysomes widely vary in scattering contrast (reporting on size) and redox-dependent ratiometric fluorescence. Furthermore, we used redox sensing to explore the chemical kinetics within intact carboxysomes, where bulk measurements may contain unwanted contributions from aggregates or interfering fluorescent proteins. Overall, we demonstrate the ISABEL trap’s ability to sensitively monitor nanoscale biological objects, enabling new experiments on these systems.

Electrochemical DNA Biosensor to Detect Glycopeptidolipids of Nontuberculous Mycobacteria

In many regions, nontuberculous Mycobacteria (NTM) pulmonary infections have outnumbered tuberculosis infections over the past 30 years, yet NTM infections are frequently misdiagnosed. One critical challenge is that the current “gold standard” for NTM diagnosis involves a weeks‐to‐month long microbiological culture‐based method. To provide a more efficient diagnostic method, we have developed a novel electrochemical DNA‐based (E‐DNA) biosensor to detect NTM. Our E‐DNA biosensor targets a mycobacterial glycopeptidolipid (GPL) found on the exterior cell wall of NTM, which demonstrates high exclusivity for NTM. To create the E‐DNA biosensor, we successfully generated a GPL‐specific single‐stranded DNA aptamer through a modified SELEX (systematic evolution of ligands by exponential enrichment) process followed by high throughput sequencing to quantify potential aptamer sequences. The putative aptamers were then synthesized and screened via fluorescence, with the best candidate aptamer displaying a dissociation constant in the low nanomolar range (KDapp = 0.73 nM). Computational analysis was used to predict secondary and tertiary structure of the aptamer, allowing optimization of that aptamer sequence to find the minimum binding domain and engineer in a two‐state folding mechanism. The aptamer will then be synthesized with a 5’ thiol linkage to facilitate attachment to a gold electrode along with an internal redox reporter (methylene blue). This will enable an electrochemical interrogation method wherein changes in the peak current in square wave voltametric analysis correlate to a conformational rearrangement of the aptamer upon binding to GPL. In future studies, this E‐DNA biosensor will be verified against NTM‐positive patient samples. Ultimately, this approach should provide a rapid, point‐of‐care diagnostic method that eliminates the current lengthy culturing requirements to shorten the duration between the onset of symptoms and correctly targeted treatment of patients infected with NTM.

Structure-Function-Environment Relationship of the Isomers Zeaxanthin and Lutein

A synthesis is provided of the roles of the carotenoids zeaxanthin and/or lutein in opposing (i) photodamage in plants, (ii) photodamage to the human eye as well as cognitive dysfunction and a host of human diseases and disorders, and (iii) damage to extremophile microorganisms in the most inhospitable environments on earth. Selected examples are used to examine microenvironments and basic biological structures with which these xanthophylls associate as well as the effect of the organisms’ external environment. An overview is presented of the multiple principal mechanisms through which these xanthophylls can directly or indirectly impact organisms’ internal redox (oxidant/antioxidant) balance that provides input into the orchestration of growth, development, and defense in prokaryotic microorganisms, plants, and humans. Gaps in the research are identified, specifically with respect to the need for further in vivo assessment of the mechanisms.