Cl Coordination Research Articles

Atomically Engineered Chlorine Coordination of Iron in Active Centers for Selectively Catalytic H2O2 Decomposition Toward Efficient Antitumor-Specific Therapy.

The intervention of endogenous H2O2 via nanozymes provides a potential antitumor-specific therapy; however, the role of the nanozyme structure in relation to the selective decomposition of H2O2 to hydroxyl radicals (•OH) is yet to be fully understood, which limits the development of this therapeutic approaches. Herein, an iron single-atom nanozyme (Fe─N2Cl2─C SAzyme) is reported, which is prepared through precise Fe─Cl coordination based on the construction of a characteristic Fe-containing molecule. Fe─N2Cl2─C exhibits efficient catalytic H2O2 decomposition (2.19 × 106 mm-1 s-1), which is the highest among reported SAzymes. More importantly, it is found that H2O2 selectively decomposed into •OH on the Fe─N2Cl2─C surface, which is attributable to the d orbitals of the Fe active center matching the O-2p electrons of the adsorbed hydroxide (*OH) intermediate. Fe─N2Cl2─C is strongly cytotoxic toward a variety of cancer-cell lines in vitro but not to normal cells. Furthermore, Fe─N2Cl2─C shows an outstanding specific therapeutic effect in vivo; it efficiently destroys solid malignant tumors without injuring normal tissue. Altogether, these findings highlight the selective catalytic decomposition of H2O2 to •OH, which is achieved by engineering the active center on the atomic level, thereby providing an avenue for the development of specific nanomedicines with efficient antitumor activities.

Dual-functional metal-organic framework for chemisorption and colorimetric monitoring of cyanogen chloride

Given the growing concern over the deployment of toxic chemicals in warfare, the rapid and accurate removal and detection of cyanogen chloride (CK) as a blood agent has become increasingly critical. However, conventional physisorbents and chemisorbents used in military respirators are insufficient for the effective removal of CK. In this study, we demonstrate the chemisorption and sensing abilities of Co2(m-DOBDC) (m-DOBDC4− = 4,6-dioxo-1,3-benzenedicarboxylate) for CK via electrophilic aromatic substitution (EAS) in humid environments. Unlike the chemisorption in triethylenediamine (TEDA) impregnated carbon materials, which generates by-products through hydrolysis, the electron-rich C5 sites in m-DOBDC4− ligands give rise to cyano substitution with CK. This leads to the formation of stable C–C bonds and chloride ions (Cl−) coordinating with open Co2+ sites. Such a mechanism prevents the generation of toxic by-products like cyanic acid and hydrochloric acid. Breakthrough experiments conducted in a packed-bed system conclusively demonstrated the superior CK removal capacity of Co2(m-DOBDC) (1662 min/g), compared to TEDA-impregnated activated carbon (323 min/g) under humid conditions. Considering that MOF-74 series, isostructural with Co2(m-DOBDC), barely adsorb CK under similar conditions, this finding marks a significant advancement in developing novel sorbents for CK removal. Moreover, this chemisorption not only exhibited rapid and highly efficient CK removal but also enabled colorimetric monitoring via the distinctive color change induced by the coordination of Cl− acting as σ donors. These findings facilitate the development of adsorption and sensing equipment to protect military personnel from toxic chemical threats.

Unraveling promoter effect in enhancing Rh-catalyzed hydroformylation of formaldehyde

Hydroformylation is one of the most important homogenous reactions, especially formaldehyde hydroformylation is of critical importance for synthesis of ethylene glycol. Due to lack of mechanistic analysis on promoters, we have employed a combined experimental and theoretical approach to reveal the promoter effect in the Rh-catalyzed hydroformylation of formaldehyde. The base promoter was suggested to be a bifunctional promoter. The mechanism of Cl-promoted formaldehyde hydroformylation was established, which significantly different from Cl-free system, and HCHO insertion was illustrated to be the rate-determining step. The distortion/interaction-activation strain analysis and mechanism calculations of halogen types demonstrate that Cl-containing catalyst has superior promotion effects compare to F, Br, and I-containing systems. The investigation on the effect of Cl coordination number shows that one-coordinated catalyst exhibits lower energy barriers and higher reactivity.

Atomically engineered Al-doped LaOCl for chlorine-ion batteries

LaOCl belongs to one kind of promising solid electrolyte for chlorine-ion batteries due to its excellent electric insulation performance and special layered structure. However, LaOCl still suffers from poor chlorine-ion conductivity. Then, we proposed microstructure modulation of LaOCl to solve this problem based on Al doping method. Firstly, we carried out first-principles and ab-initio molecular dynamics (AIMD) calculations to investigate the internal relation among structure stability, chlorine-ion conductivity and related physicochemical properties of Al doped LaOCl(La1-xAlxOCl). It is found that La0.75Al0.25OCl not only possesses most stable structure but also demonstrates the best ductility. Moreover, La0.75Al0.25OCl also possesses much lower chlorine-ion diffusion energy barrier than LaOCl(0.40 eV vs.0.78 eV) and its chlorine-ion conductivity goes as high as 5.4 × 10−3 S/cm at 300K. This is attributed to the optimal reconstruction of La–Cl coordination structure induced by Al dopant, which weakens the limiting effect of La–Cl bond as far as possible. Meanwhile,La0.75Al0.25OCl exhibits excellent electrical insulating property due to its wide band gap of 5.87 eV. In addition, La0.75Al0.25OCl exhibits wide electrochemical window with La and Al metal acted as anode materials, respectively (1.92–9.66 V for La and 0–7.74 V for Al). At this stage, La0.75Al0.25OCl solid electrolyte requires no chlorine-ion uptake and loss in the process of oxidation and reduction, indicating its excellent electrochemical stability.

Pinpointing the Cl Coordination Effect on Mn-N3-Cl Moiety Toward Boosting Reaction Kinetics and Suppressing Shuttle Effect in Li-S Batteries.

Single atom catalysts (SACs) are highly favored in Li-S batteries due to their excellent performance in promoting the conversion of lithium polysulfides (LiPSs) and inhibiting their shuttling. However, the intricate and interrelated microstructures pose a challenge in deciphering the correlation between the chemical environment surrounding the active site and its catalytic activity. Here, a novel SAC featuring a distinctive Mn-N3-Cl moiety anchored on B, N co-doped carbon nanotubes (MnN3Cl@BNC) is synthesized. Subsequently, the selective removal of the Cl ligands while inheriting other microstructures is performed to elucidate the effect of Cl coordination on catalytic activity. The Cl coordination effectively enhances the electron cloud density of the Mn-N3-Cl moiety, reducing the band gap and increasing the adsorption capacity and redox kinetics of LiPSs. As a modified separator for Li-S batteries, MnN3Cl@BNC exhibits high capacities of 1384.1 and 743mAhg-1 at 0.1 and 3C, with a decay rate of only 0.06% per cycle over 700cycles at 1C, which is much better than that of MnN3OH@BNC. This study reveals that Cl coordination positively contributes to improving the catalytic activity of the Mn-N3-Cl moiety, providing a fresh perspective for the design of high-performance SACs.

Comprehensive Study on the Adsorption and Degradation of Dichlorodiphenyltrichloroethane on Bifunctional Adsorption-Photocatalysis Material TiO2/MCM-41 Using Quantum Chemical Methods.

The adsorption and degradation capacities of dichlorodiphenyltrichloroethane (DDT) on a photocatalyst composed of TiO2 supported on the mesoporous material MCM-41 (TiO2/MCM-41) were investigated using density functional theory and real-time density functional theory methods. The van der Waals interactions within the PBE functional were adjusted by using the Grimme approach. The adsorption of DDT was evaluated through analyses involving adsorption energy, Hirshfeld atomic charges, Wiberg bond orders, molecular electrostatic potential, noncovalent interaction analysis, and bond path analysis. The findings reveal that DDT undergoes physical adsorption on pristine MCM-41 or MCM-41 modified with Al or Fe due to the very small bond order (only about 0.15-0.18) as well as the change in total charge of DDT after adsorption is close to 0. However, it chemically adsorbs onto the TiO2/MCM-41 composite through the formation of Ti···Cl coordination bonds because the maximum bond order is very large, about 1.0 (it can be considered as a single bond). The adsorption process is significantly influenced by van der Waals interactions (accounting for approximately 30-40% of the interaction energy), hydrogen bonding, and halogen bonding. MCM-41 is demonstrated to concurrently function as a support for the TiO2 photocatalyst, creating a synergistic effect that enhances the photocatalytic activity of TiO2. Based on the computational results, a novel photocatalytic mechanism for the degradation of DDT on the TiO2/MCM-41 catalyst system was proposed.

A Reusable Fluorescent Molecular Self-Assembly Cage for Simultaneous Detection and Recycling of Silver(I) Ion.

Although molecular self-assembled porous materials capable of ratiometric fluorescence probing and recycling of metal ions are both economically and environmentally attractive, very few current efforts have been devoted. Herein, we demonstrated a three-dimensional pure organic cage, namely 4-cage, which can serve as a fluorescent probe for simultaneous ratiometric detection and recycling of Ag+ ion. Taking advantage of the promising emission behavior of its rigidified tetraphenylethylene scaffolds and the chelating ability of its dynamically reversible imine moieties, on one hand, upon the addition of Ag+ , 4-cage undergoes coordination to form a stable but poorly soluble fluorescent complex, Ag+ @4-cage, accompanied by a fluorescence color change from bluish-green to yellowish-green. This allows us to differentiate Ag+ from other cations with high selectivity. On the other hand, upon the addition of Cl- anion, Ag+ @4-cage can be effectively converted into free 4-cage due to the competitive coordination of Cl- with Ag+ . Through this process, secondary usage of 4-cage and the recycling of Ag+ ion can be achieved.

Both chloride-binding sites are required for KCC2-mediated transport

The K+-Cl- cotransporter 2 (KCC2) plays an important role in inhibitory neurotransmission, and its impairment is associated with neurological and psychiatric disorders, including epilepsy, schizophrenia, and autism. Although KCCs transport K+ and Cl- in a 1:1 stoichiometry, two Cl- coordination sites were indicated via cryo-EM. In a comprehensive analysis, we analyzed the consequences of point mutations of residues coordinating Cl- in Cl1 and Cl2. Individual mutations of residues in Cl1 and Cl2 reduce or abolish KCC2WT function, indicating a crucial role of both Cl- coordination sites for KCC2 function. Structural changes in the extracellular loop 2 by inserting a 3xHA tag switches the K+ coordination site to another position. To investigate, whether the extension of the extracellular loop 2 with the 3xHA tag also affects the coordination of the two Cl- coordination sites, we carried out the analogous experiments for both Cl- coordinating sites in the KCC2HA construct. These analyses showed that most of the individual mutation of residues in Cl1 and Cl2 in the KCC2HA construct reduces or abolishes KCC2 function, indicating that the coordination of Cl- remains at the same position. However, the coupling of K+ and Cl- in Cl1 is still apparent in the KCC2HA construct, indicating a mutual dependence of both ions. In addition, the coordination residue Tyr569 in Cl2 shifted in KCC2HA. Thus, conformational changes in the extracellular domain affect K+ and Cl--binding sites. However, the effect on the Cl--binding sites is subtler.

Long-term durability of metastable β-Fe2O3 photoanodes in highly corrosive seawater

Durability is one prerequisite for material application. Photoelectrochemical decomposition of seawater is a promising approach to produce clean hydrogen by using solar energy, but it always faces the problem of serious Cl− corrosion. We find that the main deactivation mechanism of the photoanode is oxide surface reconstruction accompanied by the coordination of Cl− during seawater splitting, and the stability of the photoanode can be effectively improved by enhancing the metal-oxygen interaction. Taking the metastable β-Fe2O3 photoanode as an example, Sn added to the lattice can enhance the M–O bonding energy and hinder the transfer of protons to lattice oxygen, thereby inhibiting excessive surface hydration and Cl− coordination. Therefore, the bare Sn/β-Fe2O3 photoanode delivers a record durability for photoelectrochemical seawater splitting over 3000 h.

Symmetry‐Driven Assembly of a Penta‐Shell Keplerate Cuprofullerene for Metallofullerene Frameworks

AbstractTwo metallofullerene frameworks (MFFs) constructed from a penta‐shell Keplerate cuprofullerene chloride, C60@Cu24@Cl44@Cu12@Cl12, have been successfully prepared via a C60‐templated symmetry‐driven strategy. The icosahedral cuprofullerene chloride is assembled on a C60 molecule through [η2‐(C=C)]−CuI and CuI−Cl coordination bonds, resulting in the penta‐shell Keplerate with the C60 core canopied by 24 Cu, 44 Cl, 12 Cu and 12 Cl atoms that fulfill the tic@rco@oae@ico@ico penta‐shell polyhedral configuration. By sharing the outmost‐shell Cl atoms, the cuprofullerene chlorides are connected into 2D or 3D (snf net) frameworks. TD‐DFT calculations reveal that the charge transfer from the outmost CuI and Cl to C60 core is responsible for their light absorption expansion to near‐infrared region, implying anionic halogenation may be an effective strategy to tune the light absorption properties of metallofullerene materials.

Symmetry-Driven Assembly of a Penta-Shell Keplerate Cuprofullerene for Metallofullerene Frameworks.

Two metallofullerene frameworks (MFFs) constructed from a penta-shell Keplerate cuprofullerene chloride, C60 @Cu24 @Cl44 @Cu12 @Cl12 , have been successfully prepared via a C60 -templated symmetry-driven strategy. The icosahedral cuprofullerene chloride is assembled on a C60 molecule through [η2 -(C=C)]-CuI and CuI -Cl coordination bonds, resulting in the penta-shell Keplerate with the C60 core canopied by 24 Cu, 44 Cl, 12 Cu and 12 Cl atoms that fulfill the tic@rco@oae@ico@ico penta-shell polyhedral configuration. By sharing the outmost-shell Cl atoms, the cuprofullerene chlorides are connected into 2D or 3D (snf net) frameworks. TD-DFT calculations reveal that the charge transfer from the outmost CuI and Cl to C60 core is responsible for their light absorption expansion to near-infrared region, implying anionic halogenation may be an effective strategy to tune the light absorption properties of metallofullerene materials.

Boosting the CO2 adsorption performance by defect-rich hierarchical porous Mg-MOF-74

Adsorbents with high adsorption capacity and high selectivity are crucial for carbon capture, utilization and storage (CCUS) technology applied to industrial flue gas to reduce carbon emissions. In this paper, a defect-rich hierarchical porous Mg-MOF-74 was synthesized successfully with MgCl2·6H2O used as a metal source considering that the weak coordination of Cl− may interfere with the normal coordination process of metal centers and organic ligands, which causes the formation of crystal defects. Through the analysis of a series of characterizations, ligand deletion of Mg-MOF-74 prepared with MgCl2·6H2O was confirmed, and the deleted ligand was estimated to be approximately 20% compared with the traditional Mg-MOF-74 prepared with Mg(NO3)2·6H2O, which led to mesopores accounting for 36.9%, and the width of mesopores reached 13.1 nm. Compared with traditional Mg-MOF-74, the adsorption heat of CO2 at zero load of the defect-rich hierarchical porous Mg-MOF-74 increased from 36 kJ·mol−1 to 46 kJ·mol−1, and the saturated adsorption capacity of CO2 under ambient pressure was improved by 15%. Interestingly, the IAST selective adsorption performance of CO2/N2 was increased by 20 times. Compared with the saturated adsorption capacity for traditional Mg-MOF-74, the equivalent adsorption capacity of hierarchical porous Mg-MOF-74 only needs 17 kPa, indicating that it is suitable for carbon capture operation in a real flue environment. Calculations of density functional theory (DFT) confirmed that the active site of the hierarchical porous Mg-MOF-74 has a lower adsorption energy with CO2 due to the presence of defects, which is regarded to play a key role in improving the CO2 capture performance.

A mechanistic study on homo- and copolymerization of L-Lactide and ε-caprolactone catalyzed by an aluminum complex bearing a Bis(phenoxy)amine ligand: A DFT study

Polymerization of biodegradable lactide and lactone has been the subject of intense research during the past decade. We used density functional theory (DFT) calculations to investigate the initiation and first propagation for ring-opening polymerization (ROP) mechanisms of L-lactide (LA) and ε-caprolactone (CL) on aluminum complexes bearing the bis(phenoxy)-amine ligand with pyridine (Catalyst I) and diethylamine (Catalyst II) sidearm. Here, the ROP mechanisms of LA and CL on both catalysts were classified into 3 parts: (1) LA homopolymerization, (2) CL homopolymerization, and (3) LA and CL copolymerization. For homopolymerization, Catalyst I shows a greater performance than Catalyst II on both LA and CL due to its less bulky sidearm. However, CL homopolymerization on Catalyst I is more favorable than that of LA, which is caused by the stronger CL coordination on the catalyst. For LA and CL copolymerization, the amine sidearm variation and the vdW interactions of monomers on Catalysts I and II provide different copolymer products, the tapered and random copolymers, respectively. These calculated results are in good agreement with our previous experimental reports. The understanding gained in the current study might be helpful in the development of high-performance catalysts for the ROP reaction of biodegradable lactide and lactone.

Thermodynamic analysis of decomposing Bi2S3 in acidic system and its application in treatment of molybdenite-bismuthinite mixed ore

Through thermodynamic calculations, the E-pH diagrams of the Bi-S-H2O and Bi-S-Cl-H2O systems at 298 K were plotted, the dominant regions of the components in the system and their changes with pH were clarified, and the mechanism and thermodynamic conditions for the decomposition of Bi2S3 in acidic systems were clarified. The key to the decomposition of Bi2S3 in acidic systems was based on the coordination of Cl− and Bi3+. The formation of BiCl4− can promote the decomposition of Bi2S3 in acidic systems, based on this characteristic, HCl was used to achieve efficient leaching of bismuth in molybdenite-bismuthinite mixed ore. Under the optimized conditions of hydrochloric acid concentration of 6 mol/L, liquid-to-solid ratio of 5:1, temperature of 95 °C, stirring speed of 400 rpm, and time of 300 min, the leaching efficiency of bismuth reached 97.64 %, and the bismuth content in the leaching residue was 0.93 %, while molybdenum remained in the form of MoS2 in the residue, The efficient separation of molybdenum and bismuth has been achieved, providing a new process to solve the traditional separation of molybdenite-bismuthinite mixed ores.

One, Two Three - Phosphaalkene Decoration Tailoring Solubility and Electronic Properties of Truxene-Based Electron Acceptors.

We report the functionalization and deplanarization of truxenes using pnictaalkene fragments. Selective introduction of one, two, or three Mes*-Pn fragments provides up to three fully reversible reductions based on the Pn=C fragments. The incorporation of the unsaturated heteroelement fragment as well as the contortion of the truxene core result in significantly red-shifted absorption spectra and interesting opto-electronic properties which are studied by electrochemistry and spectro-electrochemistry. Incorporation of arsaalkene (As=C) motifs gives significantly milder reduction potentials and red-shifted absorption, while phosphaalkene decorated truxene P3 can be functionalized using Au(I)Cl coordination. Furthermore, solubility is markedly increased upon incorporation of the Pn-Mes* fragments which renders these materials suitable for solution processing.

Bifunctional electrolyte regulation towards low-temperature and high-stability Zn-ion hybrid capacitor

Aqueous Zinc-based energy storage devices are considered as one of the potential candidates in future power technologies. Nevertheless, poor low temperature performance and uncontrollable Zn dendrite growth lead to the limited energy storage capability. Herein, an anti-hydrolysis, cold-resistant, economical, safe, and environmentally friendly electrolyte is developed by utilizing water, ethylene glycol (EG), and ZnCl2 with high ionic conductivity (7.9 mS cm−1 in glass fiber membrane at −20 °C). The spectra data and DFT calculations show the competitive coordination of EG and Cl- to induce a unique solvation configuration of Zn2+, conducive to effectively inhibiting the hydrolysis of Zn2+, suppressing the dendrite growth, and broadening the working voltage range and temperature range of ZnCl2 electrolyte. The isotope tracing data confirm that Cl- could effectively destroy the ZnO passivation film, promoting the formation of Zn nuclei and improving its reaction activity. Compared to the corresponding ZnSO4 electrolyte, the Cu/Zn half-cell with the ZnCl2 electrolyte exhibits a stable cycle life of more than 1600 h at −20 °C, even at the current density of 5 mA cm−2. The assembled Zn-ion hybrid capacitor possesses an average capacity of 42.68 mA h g−1 under −20 °C at a current density of 5 A g−1, 3.5 times than that of the modified ZnSO4 electrolyte. Our work proposes a new approach for optimizing aqueous electrolytes to meet low temperature energy storage applications.

A computational study on the coordination modes and electron absorption spectra of the complexes U(iv) with N,N,N',N'-tetramethyl-diglycolamide and anions.

Lipophilic N,N,N',N'-tetraalkyl-diglycolamides (TRDGAs) are promising extractants for actinides separation in spent nuclear fuel reprocessing. Usually, in the extracted complexes of actinide and lanthanide ions of various oxidation states, the metal ions are completely surrounded by 2 or 3 TRDGA molecules, and the counter anions do not directly coordinate with them. In contrast, the extracted complexes of U(iv) from different media presenting different absorption spectra indicate that the anions (Cl- and NO3-) are directly involved in the coordination with U(iv) in the first inner sphere. Based on this exceptional observation in solvent extraction, taking the coordination of U(iv) with N,N,N',N'-tetramethyl-diglycolamide (TMDGA, the smallest analogue of TRDGA) as the research object, we mimic the behaviours of counterions (Cl- and NO3-) and the water molecule during coordination of TMDGA with U(iv), especially combining with the simulation of the absorption spectra. We demonstrate that during the complexing of TMDGA to U(iv), the counterion Cl- will occupy one coordination number in the inner coordination sphere, and NO3- will occupy two by bidentate type; however, the ubiquitous water cannot squeeze in the inner coordination sphere. In addition, the coordination of Cl- and NO3- is proved to favour the extraction with the lower binding energy. Moreover, the simulation of absorption spectra is in good agreement with the observation from experiments, further verifying the aforementioned conclusion. This work in some way will provide guidance to improve the computation methods in research of actinides by mimicking the absorption spectra of actinide ions in different complexes.

Selective adsorption mechanism of copper from nickel electrolytes by tert-butyl 2-(N-octyl-2-picolyamino) acetate functionalized chelating resin: A DFT study

Exploring the selective adsorption of Cu(II) from nickel electrolytes by tert-butyl 2-(N-octyl-2-picolyamino) acetate (AMPA) functionalized chelating resin is of great implication for accurately regulating the interface interaction. In this study, based on the first-principles density functional theory (DFT), the pKa values of functional group AMPA were calculated, the H2O and Cl− were considered as ligands, and the valence bond properties were elucidated by electron localization function (ELF) and ligand field theory. AMPA is protonated to AMPAH1H2 under acidic conditions, and Cu(II) could replace protons of AMPAH1H2 and be chelated to form AMPA-Cu(II) substrate while Ni(II) cannot. An irregular octahedral configuration is formed with the coordination of H2O and Cl− based on the AMPA-Cu(II) substrate. Cl− promotes Ni(II) to replace protons of AMPAH1H2 to form [AMPA-NiCln]2−n (n ≤ 2), while Ni(II) in [AMPA-NiCln]2−n (n = 2, 3) presents poor stability and will be further replaced by Cu(II). In addition, the interaction between Cl− and Ni(II) is stronger than that with Cu(II), and [NiCln]2−n (n > 2) clusters are not conducive to being adsorbed, while the Cu(II) with weak binding ability to Cl− is selectively adsorbed. Finally, an interface interaction model of selective adsorption of Cu(II) by AMPA-based chelating resin was proposed.

Controlled C–H bond activation leads to orthometalation and ring-hydroxylation in Ni(II) and Pd(II) complexes of a common tridentate azophenyl-salicylaldimine ligand

Using a common tridentate azophenyl-appended salicylaldimine ligand in its deprotonated form (L4)–, two classical coordination complexes [Ni(L4)2] (1) (NiIIO2N2N'2 coordination) and [Pd(L4)Cl]•CH2Cl2 (2) (PdIIONN'Cl coordination), two cyclometalated complexes [M(L4*)] (M = Ni 3 and Pd 4; MIIONN'C coordination), and two azophenyl ring-hydroxylated complexes [M(L4–O)] (M = Ni 5 and Pd 6; MIIONN'O' coordination), obtained due to selective oxidation of MII–C bond, have been synthesized. Complex 1 is paramagnetic (S = 1) but all other complexes are uniformly diamagnetic (S = 0). For 1–6, absorption spectral and redox properties have been investigated, along with single-crystal structural analysis. The regiospecific aryl ring-hydroxylation of M−C bonds in 3 and 4 are achieved due to H2O2 and m-CPBA oxidation, respectively, affording 5 and 6. Coulometically-generated one-electron oxidation and one-electron reduction have been done on 1–6, and the nature of the resulting species has been probed by EPR and absorption spectral studies. While oxidation of 1 and 3 generate Ni(III) species, it is a resonance hybrid between Ni(III) ⇔ Ni(II)-O(phenoxyl radical) species for 5. On the other hand, 2, 4, and 6 generate ligand radical species. Reduction of 1–6 generates ligand radical species uniformly. Density functional theory (DFT) calculations at the B3LYP level of theory have been done to extract information about the electronic structure of the complexes. Time-dependent (TD)-DFT calculations have been done to shed light on the origin of observed absorption spectra. Plausible mechanisms have been proposed for the observed orthometalation and ring-hydroxylation reactions.

Kinetic isotope effects of C and N indicate different transformation mechanisms between atzA- and trzN-harboring strains in dechlorination of atrazine.

Compound-specific stable isotope analysis provides an alternative method to insight into the biotransformation mechanisms of diffuse organic pollutants in the environment, e.g., the endocrine disruptor herbicide atrazine. Biotic hydrolysis process catalyzed by chlorohydrolase AtzA and TrzN plays an important role in the detoxification of atrazine, while the catalytic mechanism of AtzA is still speculative. To investigate the catalytic mechanism of AtzA and answer whether both enzymes catalyze hydrolytic dechlorination of atrazine by the same mechanism, in this study, apparent kinetic isotope effects (AKIE) for carbon and nitrogen were observed by three atzA-harboring bacterial isolates and their membrane-free extracts. The AKIEs obtained from atzA-harboring bacterial isolates (AKIEC = 1.021 ± 0.010, AKIEN = 0.992 ± 0.003) were statistically different from that of trzN-harboring strains (AKIEC = 1.040 ± 0.006, AKIEN = 0.983 ± 0.006), confirming the different activation mechanisms of atrazine preceding to nucleophilic aromatic substitution of Cl atom in actual enzymatic reaction catalyzed by AtzA and TrzN, despite the limitation of variable dual-element isotope plots. The lower degree of normal carbon and inverse nitrogen isotope fractionation observed from atzA-harboring strains, suggesting AtzA catalyzing hydrolytic dechlorination of atrazine by coordination of Cl and one aromatic N to the Fe2+ drawing electron density from carbon-chlorine bond that facilitating the nucleophilic attack, rather than in TrzN case that protonation of aromatic N increasing nucleophilic substitution of Cl atom. This study suggests considering the potential influences of phylogenetic diversity of bacterial isolates and evolution of enzymes on the applications of CSIA method in future study.