Cation Anion Research Articles

Computational Exploration of the Nature of Li+-Ureide Anion Catalysis on Formation of Highly Reactive Vinyl Carbocations and Subsequent C-C Bond Forming Reactions.

The mechanisms of the C-H insertion reactions of vinyl carbocations formed by heterolysis of vinyl trifluoromethanesulfonates (triflates) by catalytic lithiated 1,3-bis[3,5-bis(trifluoromethyl)phenyl]urea (Li+-ureide) have been studied with ωB97X-D density functional theory. The ionization promoted by the Li+-ureide forms a metastable intimate ion pair complex of Li+-ureide-triflate anion and vinyl cation. The relative thermodynamic stabilities of isomeric alkyl cations are impacted by ion-pairing with the Li+-ureide-triflate anion. We show that the C-H insertion reaction of the vinyl cation intermediate is the rate-determining step and explain the effect of the aryl substituents on the formation of the vinyl cation and its C-H insertion reactivity as well as the regioselectivity of C-H activation by the vinyl cation.

Revealing the Correlation between the Solvation Structures and the Transport Properties of Water-in-Salt Electrolytes

Water-in-salt (WIS) electrolytes containing 21 m lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) have been considered as a safe and environment-friendly alternative to common organic electrolytes used in lithium-ion batteries. However, the relation between the solvation structures and transport properties of these materials remains elusive. Herein, we performed small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS), and X-ray pair distribution function (PDF) measurements of LiTFSI aqueous solutions at a wide range of concentrations. Combined with molecular dynamics simulations, the detailed solvation structures from long to short length scale were resolved. We found that the TFSI– solvation structures consist of TFSI– solvated structures and TFSI– networks; the former corresponds to solvent separated ion pairs, while the latter corresponds to contact ion pairs and cation–anion aggregates. In addition, we found that the relaxation time in the q range associated with the anion network structure exhibits the same concentration dependence as the viscosity. By combining the results from the experiments and simulations, this study revealed a correlation between the solvation structures of LiTFSI and the transport properties of the solutions, which is critical to understand the relation between the transport properties and the dynamics of the ions for imide-based lithium-ion salt aqueous electrolytes.

Solar‐Triggered Engineered 2D‐Materials for Environmental Remediation: Status and Future Insights

AbstractModern‐day society requires advanced technologies based on renewable and sustainable energy resources to face the challenges regarding environmental remediation. Solar‐inspired photocatalytic applications for water purification, hydrogen and oxygen evolution, carbon dioxide reduction, nitrogen fixation, and removal of bacterial species seem to be unique solutions based on green and efficient technologies. Considering the unique electronic features and larger surface area, 2D photocatalysts have been broadly explored for the above‐mentioned applications in the past few years. However, their photocatalytic potential has not been optimized yet to the adequate level of practical and commercial applications. Among many strategies available, surface and interface engineering and the hybridization of different materials have revealed pronounced potential to boost the photocatalytic potential of 2D materials. This feature review recapitulates recent advancements in engineered materials that are 2D for various photocatalysis applications for environmental remediation. Various surface and interface engineering technologies are briefly discussed, like anion–cation vacancies, pits, distortions, associated vacancies, etc., along with rules and parameters. In addition, several hybridization approaches, like 0D/2D, 1D/2D, 2D/2D, and 3D/2D hybridization, etc., are also deeply investigated. Lastly, the application of these engineered 2D materials for various photocatalytic applications, challenges, and future perspectives is extensively explored.

Adaptation and removal mechanism of anion chromium and cation cadmium by sulfate-reducing bacteria culture systems under different carbon sources

A major factor limiting the application of sulfate-reducing bacteria culture systems (SRBs) to the removal of heavy metals is the requirement to supply carbon and energy to drive the process. In this study, the effects of carbon sources on the SRBs under Cr(VI) and Cd(II) domestication conditions were comprehensively investigated, and two dominant groups with humic acid and sodium lactate as carbon sources were selected to study the mechanisms of transformation. Results showed that the order of carbon source utilization was humic acid > sodium lactate > glycerol > mixed carbon sources > glucose. Differences in the rate and extent of utilization of carbon sources resulted in different diversity, structure, and function of SRBs. Differences in carbon sources can lead to an increase or decrease in certain functions, e.g., nitrogen fixation is enhanced in the humic acid group. The fermentative bacteria play a key role in degrading macro-organics to volatile fatty acids, which are then utilized by SRBs to reduce sulfate. For the anion Cr(VI), the SRBs culture system reduced Cr(VI) to Cr(III) mainly through the H2S pathway; for the cation Cd(II), the EPS pathway, electron transport pathway, and H2S pathway all had good removal effects. These findings provide a new perspective on strain screening and heavy metal removal.

The effects of cation and halide anion on the stability, electronic and optical properties of double perovskite Cs2NaMX6 (M = In, Tl, Sb, bi; X = Cl, Br, I)

In recent years, the application of inorganic lead-free double perovskite halides in optoelectronic devices has attracted extensive attention because they can solve the toxicity problems of traditional perovskite materials and exhibit excellent environmental stability. The photoluminescence properties of the structure can be significantly improved by doping Cs2NaInCl6 with VA group elements. The geometrical and optoelectronic characteristics of the double perovskite Cs2NaMX6 (M = In, Tl, Sb, Bi; X = Cl, Br, I) were studied using first-principles calculations in this work. It is found by calculation that the doping substitution of M-site cations can change the energy band characteristics due to the change of the M-p orbital. The X-site anion substitution can adjust the structural band gap while maintaining the energy band structure shape. Our study shows that by compositional modulation of the M3+ site of Cs2NaInCl6 by 1:1 substitution of VA groups, the maximum light absorption in the near-ultraviolet region can be increased up to three times compared to undoped Cs2NaInCl6. Therefore, Cs2NaInCl6 can be widely used in the fields of luminescent and ultraviolet detectors through compositional modulation.

Co-Sputtering Crystal Lattice Selection for Rare Earth Metal-Based Multi Cation and Mixed Anion Photochromic Films

Rare-earth oxyhydride (ReOxHy) films are novel inorganic photochromic materials that have strong potential for applications in windows and optical sensors. Cations greatly influence many material properties and play an important role in the photochromic performance of ReOxHy. Here we propose a strategy for obtaining Gd1-zYzOxHy films (z = 1, 0.7, 0.5, 0.4, 0.35, 0.25, 0.15, 0) using one-step direct-current (DC) magnetron co-sputtering. Distinct from the mixed anion systems, such material would belong to the class of mixed anion and mixed cation materials. For Gd1-zYzOxHy films, different co-doping ratios can help tune the contrast ratio (that is, the difference between coloration and bleaching transmittance) and cycling degradation, which may be related to the lattice constant. X-ray diffraction (XRD) patterns show that the lattice constant increases from 5.38 Å for YOxHy to 5.51 Å, corresponding to Gd0.75Y0.25OxHy. The contrast ratio, in particular, can be enhanced to 37% from 6.3% by increasing the lattice constant, directly controlled by the co-sputtering power. When the lattice constant decreases, the surface morphology of the sample with the smallest lattice constant is essentially unchanged by testing in air with normal oxidation for 100 days, suggesting great improvement in environment durability. However, the crystal structure cannot be overly compressed, and co-sputtering with Cr gives black opaque films without photochromic properties. Moreover, because the atomic mass of different rare earth elements is different, the critical pressure p* (films deposited at p < p* remain metallic dihydrides) is different, and the preparation window is enlarged. Our work provides insights into innovative photochromic materials that can help to achieve commercial production and application.

Anion Effect on Forward Osmosis Performance of Tetrabutylphosphonium-Based Draw Solute Having a Lower Critical Solution Temperature

The applicability of ionic liquids (ILs) as the draw solute in a forward osmosis (FO) system was investigated through a study on the effect of the structural change of the anion on the FO performance. This study evaluated ILs composed of tetrabutylphosphonium cation ([P4444]+) and benzenesulfonate anion ([BS]-), para-position alkyl-substituted benzenesulfonate anions (p-methylbenzenesulfonate ([MBS]-) and p-ethylbenzenesulfonate ([EBS-]), and methanesulfonate anion ([MS]-). The analysis of the thermo-responsive properties suggested that the [P4444][MBS] and [P4444][EBS] ILs have lower critical solution temperatures (LCSTs), which play a beneficial role in terms of the reusability of the draw solute from the diluted draw solutions after the water permeation process. At 20 wt% of an aqueous solution, the LCSTs of [P4444][MBS] and [P4444][EBS] were approximately 36 °C and 25 °C, respectively. The water flux and reverse solute flux of the [P4444][MBS] aqueous solution with higher osmolality than [P4444][EBS] were 7.36 LMH and 5.89 gMH in the active-layer facing the draw solution (AL-DS) mode at osmotic pressure of 25 atm (20 wt% solution), respectively. These results indicate that the [P4444]+-based ionic structured materials with LCST are practically advantageous for application as draw solutes.

Cation functional group effect on SO2 absorption in amino acid ionic liquids.

Introduction: The effect of the functional group of the cation on SO2 acidic gas absorption by some designed amino acid ionic liquids (AAILs) was studied. Methods: An isolated pair of glycinate anion and pristine imidazolium-based cation, as well as decorated cation functionalized by hydroxyl (OH), amine (NH2), carboxylic acid (COOH), methoxy (OCH3), and acetate (CH3COO) groups, were structurally optimized by density functional theory (DFT) using split-valence triple-zeta Pople basis set. Results and Discussion: The binding and Gibbs free energy (ΔGint) values of SO2 absorption show the AAIL functionalized by the COOH group is the most thermodynamically favorable green solvent and this functional group experiences the closest distance between anion and captured SO2 and vice versa in the case of cation … SO2 which may be the main reason for being the best absorbent; in addition, the highest net charge-transfer amount of SO2 is observed. Comparing the non-covalent interaction of the systems demonstrates that the strongest hydrogen bond between captured gas and anion, as well as π-hole, and van der Waals (vdW) interaction play critical roles in gas absorption; besides, the COOH functional group decreases the steric effect while the CH3COO functional group significantly increases steric effect after absorption that declines the hydrogen bond.

Temperature and Pressure Dependence of the Transport Properties of the Ionic Liquid Triethyloctylphosphonium Bis(trifluoromethanesulfonyl)amide, [P222,8][Tf2N

Viscosities of triethyloctylphosphonium bis(trifluoromethanesulfonyl)amide, [P222,8][Tf2N], are reported as a function of temperature [(273 to 363) K] and pressure (maximum 302 MPa) with a falling-body viscometer together with electrical conductivities (κ) measured by impedance spectroscopy at (283 to 348) K, to 250 MPa maximum pressure. pVT data were determined with a vibrating tube densimeter from (298 to 353) K to 50 MPa. Ion self-diffusion coefficients (DSi) were measured by steady-gradient spin-echo NMR [(313 to 365) K], and densities [(273 to 363) K] were determined with a vibrating tube densimeter, both at atmospheric pressure. The results were correlated with Walden and Stokes–Einstein–Sutherland relations. Velocity cross-correlation coefficients (VCC), distinct diffusion coefficients (DDC) and Laity resistance coefficients (LRC) were calculated from DSi and κ at 0.1 MPa. The DDC and LRC for [P222,8][Tf2N] and the pentyl-substituted analogue, [P222,5][Tf2N], showed differences for cation–cation and cation–anion velocity anti correlations, presumably due to the different cation structures. The high-pressure viscosities were used to predict the pressure dependence of the glass-transition temperature for [P222,5][Tf2N] and [P222,8][Tf2N]. Density scaling was applied to the high-pressure viscosities and conductivities of [P222,8][Tf2N] for comparison with [P222,5][Tf2N]. The scaling parameters are consistent with the theoretical treatment of Knudsen et al. for ionic liquids.

Synthesis of pH-responsive polyzwitterions for activated cellular uptake and tumor accumulation of gold nanoparticles at tumorous acidity

The response sensitivity of surface material plays an important role in adjustable nano-bio interaction in vivo. In this present, a zwitterionic polymer (polyzwitterion) containing quaternary ammonium cation and sulfonamide anion poly(4-((4-(3-(methacryloyloxy)propoxy)phenyl) sulfonamido)-N, N, N-trimethyl-4-oxobutan-1-aminium chloride) (PMPTSA) was synthesized by Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT) polymerization to explore the pH responsive behavior in tumors. The PMPTSA-coated gold nanoparticles (PMPTSA-@-Au NPs) showed zwitterionic nature such as antifouling ability, low cellular uptake and prolonged circulation time similar with common hydrophilic polymers, including polyethylene glycol (PEG), poly(carboxybetaine methacrylate) and poly(sulfobetaine methacrylate) functional gold nanoparticles in physiological environment (pH 7.4). A high sensitivity and reversible positive charge conversion of P(MPTSA)-@-Au NPs at tumor slight acidic microenvironment (∼pH 6.8) leaded to an enhanced cellular internalization than that at pH 7.4 and increased tumor accumulation compared with PEG, polycarboxybetaines and polymer sulphobetaine (PSB) functional gold nanoparticles. The highly pH responsive PMPTSA will provide the promising application in cancer nanomedicine.

Effect of anions and cations on the self-assembly of ionic liquid surfactants in aqueous solution

Ionic liquid surfactants have shown increasing promise for substituting the traditional amphiphiles due to their flexible tunability and superior physicochemical properties. However, the effect of cationic structure and anion type on the surface properties of ionic liquid surfactants remains unclear. Herein, four ionic liquid surfactants [C12mim][BF4], [PyC12][Br], [C12mim][Br] and [PyC12][BF4] with the same alkyl side chain length were designed and synthesized. Their surface properties, such as micelle-free energy (ΔGmθ), surface tension reduction efficiency (ПCMC), and adsorption efficiency (pC20), and the influence of the type and structure of the anion and cation on their micellar physicochemical properties in aqueous solution were discussed according to the data. The proposed approach demonstrates that the critical micelle concentration (CMC) is determined by combining electrostatic and hydrophobic effects. When the anion is BF4−, the ionic liquid has a lower CMC, and BF4− has a superior hydrophobic effect, which allows the ionic liquid to form micelles more easily. In addition, the ionic liquid of tetrafluoroborate has higher interfacial activity (larger pC20) at the same temperature and its aqueous solution has lower surface tension, making it a more desirable surfactant. All four types of ionic liquids have negative values of ΔGmθ, implying that micelle formation is a spontaneous process. The surface activity of imidazolium- and pyridinium-based ionic liquids was slightly different from the critical micelle concentration under the same anion and carbon chain length. Imidazole and pyridine have highly similar hydrophobic and electrostatic effects, and the cation may not be the most critical factor affecting the surface properties.

The Physics of Twin Boundary Termination in Cu(In, Ga)Se2 Absorbers

The grain boundaries (GBs) in the absorber of a Cu(In,Ga)(S,Se)2 (CIGS) solar cell play a vital role in its efficiency and cells with polycrystalline absorbers exhibit high conversion efficiency (&gt;23%). Previous investigations confirm that the traits of GBs in CIGS are directly connected to their composition. However, such a relationship cannot be established for twin boundaries (TBs). This is because although electron beam‐induced current (EBIC) highlights the existence of both electrically inactive and active TBs, atom probe tomography is not able to detect composition fluctuations in a very limited volume (one or two monolayers). Therefore, herein, high‐resolution scanning transmission electron microscopy at TBs to investigate their differences and correlate them with their traits is used. It is found that the electrically neutral TBs are cation–anion‐terminated boundaries, whereas the electrically beneficial TBs are cation–cation terminated. Density functional theory results show that the formation of point defects next to cation–cation TBs is more favorable compared to the case with cation–anion TBs. The presence of Cu vacancies can result in a passivated TB and a hole‐depletion region next to the cation–cation TBs, and consequently a better electron transport, as the bright contrast observed in the EBIC map suggests.

Glucose dehydration reaction over metal halides supported on activated charcoal catalysts

Different metal halide catalysts supported on a commercial active charcoal have been synthesized, activated, characterized and tested in glucose dehydration to 5-hydroxymethylfurfural using a biphasic water/methyl isobutyl ketone media. The influence of the cation nature (K+, Ca2+, Sr2+, Mg2+) and anion nature (F-, Cl-, Br-) on the catalytic performance of the solid is discussed in terms of glucose conversion, HMF yield and products selectivity. The activation of the impregnated catalysts results in a great diversity of active sites, such as Bronsted sites (carboxylic groups), basic sites (metal oxide), and Lewis acid site (Mn+). Their distribution within the samples determinates the resulting products and the final HMF yield.

Entropy-Driven Ultrafast Ion Conduction Via Confining Organic Plastic Crystals in Ordered Nanochannels of Covalent Organic Frameworks.

Low conductivity over a wide temperature region due to ultra-slow ion migration dynamics is a key issue in the field of solid-state electrolytes (SSE), which needs to be solved and improved. Covalent organic frameworks (COFs), a rapidly growing class of porous crystalline materials, emerge as a new research hotspot in the field of SSEs. This is due to their homogeneously dispersed sites and well-defined pathways for ion diffusion, demonstrating great advantages over conventional non-porous solids. Herein, a composite solid electrolyte by confining organic ionic plastic crystal (OIPC) in the 1D ordered nanochannels of COFs as the host matrix for solid-state lithium-ion conduction, is reported. Due to the loss of coupling between PBu4 + cations and TFSI- anions, the cation-anion interaction is weakened; and thus, the lithium-ion transportation is facilitated. As a result, the COF-confining OIPC SSEs show ultra-high lithium-ion conductivity of 0.048 S cm-1 at 30 °C and 0.021 S cm-1 at the extremely low temperature of -30 °C. The dynamic origin of this fast ion conduction is characterized by differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and variable temperature solid-state nuclear magnetic resonance (NMR) spectroscopy.

Evaluating the “wrong-way-round” electrospray ionization of antiretroviral drugs for improved detection sensitivity

The presence of antiretroviral drugs (ARVDs) in the aquatic environment poses a significant health risk to the ecosystem. The dilution of these compounds during wastewater treatment processes, followed by discharge into the environment, results in extremely low concentrations in the range of ng/L. Therefore, to enable detection of these low concentrations, it is important to determine the most efficient electrospray ionization (ESI) mode using the right mobile phase modifier and to establish a selective extraction procedure. In this study, we compared the ESI intensity in the positive and negative mode using both formic acid (FA) and ammonium hydroxide (NH4OH) as mobile phase modifiers. The results revealed a phenomenon known as the “wrong-way-round” (WWR) ESI in which high intensity [M + H]+ ions were detected under basic conditions using NH4OH as modifier and, similarly, high intensity [M-H]− ions were detected under acidic conditions using FA as modifier. Furthermore, mixed-mode strong cation (MCX) and mixed-mode strong anion (MAX) exchange sorbents were evaluated for extraction recoveries, which yielded extraction recoveries between 60 and 100%. Finally, the recoveries obtained using mixed-mode ion exchange sorbents compared to ion production during the ESI process provide evidence that ions produced in solution do not necessarily reflect the ions that are produced during the ESI process. Based on the results of this study, it is recommended to evaluate the optimal ionization mode under basic and acidic conditions, instead of defaulting to the use of acidic modifiers with positive ion detection.

Neutralization Short-Circuiting with Weak Electrolytes Erodes the Efficiency of Bipolar Membranes.

Bipolar membranes (BPMs) are critical components of a variety of electrochemical energy technologies. Many electrochemical applications require the use of buffers to maintain stable, nonextreme pH environments, yet the impact of buffers or weak acids/bases on the electrochemical behavior of BPMs remains poorly understood. Our data for a cell containing weak electrolytes is consistent with internal pH gradients within the anion exchange membrane (AEM) or cation exchange membrane (CEM) component of the BPM that form via ionic short-circuiting processes at open-circuit. Short-circuiting results from the coupling of co-ion crossover and parasitic neutralization and leads to buffering of the bipolar interface. This phenomenon, which we term neutralization short-circuiting, serves to erode BPM efficiency by attenuating the open-circuit membrane voltage and introducing parasitic reverse bias currents associated with weak acid/base dissociation at the interface. These findings establish a mechanistic basis for the operation of BPM cells in the presence of weak acid/base electrolytes.

Crystal host engineering for transition metal lasers

Much progress has been made in the power and energy scaling of mid-infrared lasers based on transition metal ions, such as Cr2 + , Co2 + , and Fe2 + , in zinc and cadmium chalcogenides. Still, the exploration of the physics of these devices is incomplete. In this work, we analyze absorption spectra collected from Fe2 + ions in several binary, ternary, and quaternary host crystals at temperatures from a few degrees Kelvin to room temperature. We use the zero-phonon lines of the low-temperature spectra to calculate the value of the crystal field energy of Fe2 + ions in these hosts. We plot these crystal field energies with respect to the anion–cation distance of the host crystal and show that their crystal field strengths deviate somewhat from the trend predicted by crystal field theory. We use a model which we previously developed to describe the upper state lifetime of Fe2 + ions to predict the steady-state radiative efficiency of Fe:II–VI materials with respect to temperature. The impact of relative crystalline disorder on the output characteristics of lasers based on Cr:ZnS, Cr:ZnSe, Fe:ZnSe, and Fe:CdMnTe is explored. The effect of decreased long-range order of the host crystal is observed in the broadening of the absorption spectra of Fe2 + -doped ternary and quaternary alloys, the broadening of the spectral linewidth of continuous-wave Fe:II–VI lasers, and a reduction in the portion of the Cr:ZnSe emission spectrum accessible for modelocked lasing. This survey provides a richer picture of the tradespaces that can be leveraged when producing laser devices based on transition metal chalcogenides.

Monoammonium Trimetaphosphimate (NH4)H2(PO2NH)3

Trimetaphosphimates show a rich structural variability in both cation coordination and anion arrangement. They are precursors for crystalline, as well as amorphous oxonitridophosphates. The ammonium trimetaphosphimate (NH4)H2(PO2NH)3 is formed during the decomposition of the corresponding acid in solution. The monoclinic crystal structure of the monoammonium salt was elucidated by single crystal X-ray diffraction using synchrotron radiation. The trimetaphosphimate monoanions exhibit a twist conformation and form crankshaft-like stacks along [100], which have so far only been observed in (NH4)3(PO2NH)3·H2O and Ag3(PO2NH)3. (NH4)H2(PO2NH)3 decomposes at 170 °C, forming a poorly crystalline phase. Therefore, it is a model system and possible precursor for the synthesis of oxonitridophosphates.

Effect of Sugar Beet Pulp and Anionic Salts on Metabolic Status and Mineral Homeostasis during the Peri-Parturient Period of Dairy Sheep.

Sugar beet pulp is a popular by-product of sugar extraction; however, it can potentially cause depletion of Ca availability due to its oxalic content. The experiment examined the effect of sugar beet pulp and anionic salts administration during the dry period on the serum concentration of calcium, magnesium, phosphate, and potassium of dairy sheep. Eighty-seven sheep were divided into three groups (A, B, and C) according to their body condition score (BCS) and age at 40 days before the expected lambing. All groups received alfalfa hay, mixed grass straw, and a concentrate supplement. The concentrate fed to groups B and C contained sugar beet pulp. The nutritional value fed to all three groups was similar, except for Dietary Cation Anion Difference (DCAD). Animals of group A had a DCAD of +198 mEq/kg, animals of group B of +188 mEq/kg, and animals of group C were fed 20 gr/d ammonium chloride to achieve a negative DCAD (-52 mEq/kg). All groups were fed the same ration after lambing. Blood samples were collected 30 d, 20 d, 17 d, 14 d, 10 d, 7 d, and 4 d before lambing (a.p.), 6 h, 12 h, 24 h, 7 d, 10 d, and 15 d after lambing (p.p) for calcium, magnesium, phosphate, and potassium, and 30 d a.p., 7 d, and 15 d p.p. for beta hydroxybutyrate acid (BHBA) concentrations. Urine samples were also collected 20 d, 10 d, 4 d a.p., and 7 d p.p for the evaluation of pH levels. Ca levels of the control group decreased earlier and were lower at 4 d a.p. compared to those of group B and C. Additionally, the control group showed lower p values compared to group C at 20 d and 17 d a.p. P levels recovered earlier post parturition in young (age 1-1.5 years old) compared to older ewes. Group C had lower urine pH values throughout the pre-parturient period, reflecting the acidifying effect of the administered ammonium chloride, without any side effect on macromineral blood concentration. Feeding sugar beet pulp and systemic acidifying before parturition is considered safe and might even be beneficial in preventing hypocalcemia.

Identification and characterization of the key lethal toxin from jellyfish Cyanea nozakii

Jellyfish Cyanea nozakii venom is a complex mixture of various toxins, most of which are proteinous biological macromolecules and are considered to be responsible for clinical symptoms or even death after a severe sting. Previous transcriptome and proteome analysis identified hundreds of toxins in the venom, including hemolysins, C-type lectin, phospholipase A2, potassium channel inhibitor, metalloprotease, etc. However, it is not clear which toxin in the venom plays the most important role in lethality. Herein, we isolated the key lethal toxin (Letoxcn) from jellyfish Cyanea nozakii using anion exchange chromatography, size-exclusion chromatography, and cation exchange chromatography. The molecular weight of Letoxcn is ∼50 kDa with the N-terminal sequences of QADAEKVNLPVGVCV. Peptide mass fingerprinting analysis of Letoxcn shows that it may have some motifs of phospholipase, metalloproteinase, thrombin-like enzyme, potassium channel toxin, etc. However, only metalloproteinase activity but no hemolytic, PLA2, or blood coagulation activity was observed from in vitro toxicity analysis. Overall, this study uncovered and characterized the key lethal toxin in the venom of jellyfish Cyanea nozakii, which will not only help to reveal the molecule mechanism of the lethality, but also develop effective treatment like antivenom for this jellyfish sting in the future.