Poly(Dibenzothiophene-Terphenyl Piperidinium) for High-performance Anion Exchange Membrane Water Electrolysis.

The anion exchange membrane water electrolysis is widely regarded as the next-generation technology for producing green hydrogen. The OH- conductivity of the anion exchange membrane plays a key role in the practical implementation of this device. Here, we present a series of Z-S-x membranes with dibenzothiophene groups. These membranes contain sulfur-enhanced hydrogen bond networks that link surrounding surface site hopping regions, forming continuous OH- conducting highways. Z-S-20 has a high through-plane OH- conductivity of 182 ± 28 mS cm-1 and ultralong stability of 2650 h in KOH solution at 80 °C. Based on rational design, we achieved a high PGM-free alkaline water electrolysis performance of 7.12 A cm-2 at 2.0 V in a flow cell and demonstrated durability of 650 h at 2 A cm-2 at 40 °C with a cell voltage increase of 0.65 mV/h.

Stable Anion Exchange Membrane Bearing Quinuclidinium for High-performance Water Electrolysis.

Anion exchange membranes (AEMs) are core components in anion exchange membrane water electrolyzers (AEM-WEs). However, the stability of functional quaternary ammonium cations, especially under high temperatures and harsh alkaline conditions, seriously affects their performance and durability. Herein, we synthesized a 1-methyl-3,3-diphenylquinuclidinium molecular building unit. Density functional theory (DFT) calculations and accelerated aging analysis indicated that the quinine ring structure was exceedingly stable, and the SN2 degradation mechanism dominated. Through acid-catalyzed Friedel-Crafts polymerization, a series of branched poly(aryl-quinuclidinium) (PAQ-x) AEMs with controllable molecular weight and adjustable ion exchange capacity (IEC) were prepared. The stable quinine structure in PAQ-x was verified and retained in the ex situ alkaline stability. Furthermore, the branched polymer structure reduces the swelling rate and water uptake to achieve a tradeoff between dimensional stability and ionic conductivity, significantly improving the membrane's overall performance. Importantly, PAQ-5 was used in non-noble metal-based AEM-WE, achieving a high current density of 8 A cm-2 at 2 V and excellent stability over 2446 h in a gradient constant current test. Based on the excellent alkaline stability of this diaryl-quinuclidinium group, it can be further considered as a multifunctional building unit to create multi-topological polymers for energy conversion devices used in alkaline environments.

The mechanism of gut-lung axis in pulmonary fibrosis.

Pulmonary fibrosis (PF) is a terminal change of a lung disease that is marked by damage to alveolar epithelial cells, abnormal proliferative transformation of fibroblasts, excessive deposition of extracellular matrix (ECM), and concomitant inflammatory damage. Its characteristics include short median survival, high mortality rate, and limited treatment effectiveness. More in-depth studies on the mechanisms of PF are needed to provide better treatment options. The idea of the gut-lung axis has emerged as a result of comprehensive investigations into the microbiome, metabolome, and immune system. This theory is based on the material basis of microorganisms and their metabolites, while the gut-lung circulatory system and the shared mucosal immune system act as the connectors that facilitate the interplay between the gastrointestinal and respiratory systems. The emergence of a new view of the gut-lung axis is complementary and cross-cutting to the study of the mechanisms involved in PF and provides new ideas for its treatment. This article reviews the mechanisms involved in PF, the gut-lung axis theory, and the correlation between the two. Exploring the gut-lung axis mechanism and treatments related to PF from the perspectives of microorganisms, microbial metabolites, and the immune system. The study of the gut-lung axis and PF is still in its early stages. This review systematically summarizes the mechanisms of PF related to the gut-lung axis, providing ideas for subsequent research and treatment of related mechanisms.

The characteristics of trimethylamine N-oxide content in different classes of marine animals over the coastal and offshore areas of China.

Trimethylamine N-oxide (TMAO) is widely present in marine animals. However, the characteristics of TMAO content in different classes of marine animals are insufficiently understood. In this study, the TMAO content in 79 marine animals (48 species, 7 classes) collected in the coastal and offshore areas of China during year 2019-2022 was analysed. The results showed that the TMAO content of the total samples varied from 0 to 139.19 mmol kg-1. The TMAO content in the classes Bivalvia, Gastropoda, Polychaeta and Holothuroidea varied from 0.06 ± 0.09 to 0.38 ± 0.63 mmol kg-1, but it varied from 30.20 ± 24.20 to 75.90 ± 38.59 mmol kg-1 in the classes Crustacea, Cephalopoda, and Osteichthyes. The TMAO content in the latter 3 classes was 2-3 orders of magnitude higher than that of the former 4 classes. It was inferred that the significant difference was related to the food sources or physiological metabolic mechanisms of different classes.

Complexation of a Nitrilotriacetate-Derived Triamide Ligand with Trivalent Lanthanides: A Thermodynamic and Crystallographic Study.

Non-heterocyclic N-donor nitrilotriacetate-derived triamide ligands are one of the most promising extractants for the selective extraction separation of trivalent actinides over lanthanides, but the thermodynamics and mechanism of the complexation of this kind of ligand with actinides and lanthanides are still not clear. In this work, the complexation behaviors of N,N,N',N',N″,N″-hexaethylnitrilotriacetamide (NTAamide(Et)) with four representative trivalent lanthanides (La3+, Nd3+, Eu3+, and Lu3+) were systematically investigated by using 1H nuclear magnetic resonance (1H NMR), ultraviolet-visible (UV-vis) and fluorescence spectrophotometry, microcalorimetry, and single-crystal X-ray diffractometry. 1H NMR spectroscopic titration of La3+ and Lu3+ indicates that two species of 1:2 and 1:1 metal-ligand complexes were formed in NO3- and ClO4- media. The stability constants of NTAamide(Et) with Nd3+ and Eu3+ obtained by UV-vis and fluorescence titration show that the complexing strength of NTAamide(Et) with Nd3+ is lower than that with Eu3+ in the same anionic medium, while that of the same lanthanide complex is higher in ClO4- medium than in NO3- medium. Meanwhile, the formation reactions for all metal-ligand complexes are driven by both enthalpy and entropy. The structures of lanthanide complexes in the single ClO4- and NO3- medium and the mixed one were determined to be [LnL2(MeOH)](ClO4)3 (Ln = La, Nd, Eu, and Lu), [LaL2(EtOH)2][La(NO3)6], and [LaL2(NO3)](ClO4)2, separately. The average bond lengths of lanthanide complexes decrease gradually with the decrease in ionic radii of Ln3+, indicating that heavier lanthanides form stronger complexes due to the lanthanide contraction effect, which coincides with the trend of the complexing strength obtained by spectroscopic titration. This work not only reveals the thermodynamics and mechanism of the complexation between NTAamide ligands and lanthanides but also obtains the periodic tendency of complexation between them, which may facilitate the separation of trivalent lanthanides from actinides.

Electron-hopping across dye-sensitized mesoporous NiO surfaces.

To gain a deeper understanding of the underlying charge processes in dye sensitized photocathodes, lateral electron hopping across dye-sensitized NiO photocathodes was investigated. For dye-sensitized systems, hole hopping across photoanodes has been studied extensively in the literature but no expansive studies on electron hopping in sensitized photocathodes exist today. Therefore, an organic p-type dye (TIP) with donor-linker-acceptor design, showing high stability and electrochemical reversibility, was used to study the electron transfer dynamics (electron-hopping) between dyes with temperature dependent spectroelectrochemistry and computational simulations. Besides intermolecular electron-hopping across the surface with a rate constant in the order of 105 s-1, our results show a second electron hopping pathway between NiO surface states with a rate constant in the order of 107 s-1, which precedes the electron hopping between the dyes. Upon application of a potential step negative enough to reduce both the dye and NiO surface states, the majority of NiO surface states need to be reduced before intermolecular electron transfer can take place. The results indicate that, in contrast to sensitized photoanodes where intermolecular charge transfer is known to influence recombination kinetics, intermolecular charge transport processes in TIP dye sensitized NiO photocathodes is less relevant because the fast electron transport between NiO surface states likely dominates recombination kinetics.

[Pathogen Distribution,Imaging Characteristics,and Establishment and Verification of Risk Prediction Model of Pulmonary Infection with Multi-drug Resistant Organism in Patients with Severe Craniocerebral Injury].

Objective To investigate the pathogen distribution,imaging characteristics,and risk factors of pulmonary infection with multi-drug resistant organism (MDRO) in patients with severe craniocerebral injury,and establish and verify the risk prediction model. Methods A total of 230 patients with severe craniocerebral injury complicated with pulmonary infection were collected retrospectively.According to the 7∶3 ratio,they were randomly assigned into a modeling group (161 patients) and a validation group (69 patients).The risk factors of MDRO pulmonary infection were predicted with the data of the modeling group for the establishment of the risk prediction model.The data of the validation group was used to validate the performance of the model. Results Among the 230 patients,68 patients developed MDRO pulmonary infection.The isolated drug-resistant bacteria mainly included multi-drug resistant Acinetobacter baumannii,multi-drug resistant Klebsiella pneumoniae,multi-drug resistant Pseudomonas aeruginosa,and methicillin-resistant Staphylococcus aureus,which accounted for 45.21%,23.29%,16.44%,and 15.07%,respectively.The imaging characteristics included pleural effusion,lung consolidation,and ground-glass shadow,which accounted for 72.06%,63.24%,and 45.59%,respectively.Multivariate Logistic regression analysis showed that the independent risk factors for MDRO pulmonary infection included age ≥60 years (P=0.003),history of diabetes (P=0.021),history of chronic obstructive pulmonary disease (P=0.038),mechanical ventilation ≥7 d (P=0.001),transfer from other hospitals (P=0.008),and coma (P=0.002).A risk scoring model was established with the ß value (rounded to the nearest integer) corresponding to each index in the regression equation.Specifically,the ß values of age ≥60 years,history of diabetes,history of chronic obstructive pulmonary disease,mechanical ventilation ≥7 d,transfer from other hospitals,and coma were 1,1,1,2,2,and 1,respectively (value ≥4 indicated a high-risk population).The areas under the receiver operating characteristic curve of the modeling group and validation group were 0.845 and 0.809,respectively. Conclusions Multi-drug resistant Acinetobacter baumannii is the most common pathogen of MDRO pulmonary infection in patients with severe craniocerebral injury.Pleural effusion,lung consolidation,and ground-glass shadow were the most common imaging characteristics.The established risk model has high discriminant validity in both the modeling group and the validation group.

Extraction and Complexation Investigation of Palladium(II) by a Nitrilotriacetate-Derived Triamide Ligand.

Effective and selective separation and recovery of the fission product palladium from high-level liquid waste are conducive not only to reducing its hazards to the public health and environment but also to alleviate the pressure on the increasing demand for natural palladium. Herein, the Pd2+ extraction in an HNO3 solution with a nitrilotriacetate-derived triamide ligand NTAamide(n-Oct) and the complexation between them were investigated. Using n-octanol as a diluent, NTAamide(n-Oct) demonstrated an excellent selectivity, strong extractability, and high loading capacity for Pd2+ extraction. Combined with the results of single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, electrospray ionization-mass spectroscopy, microcalorimetric titration, and slope analysis, the extracted complexes were determined as [PdL2](NO3)2 and [PdL2][Pd(NO3)4] (where L denotes the NTAamide ligand) in 0.10 and 3.0 mol/L HNO3 solutions, respectively. The extraction model closely depended on the solvation state of Pd2+ in the HNO3 solution. An ion-pair extraction model was proposed and discussed.

The Effects of Rso2 and PI Monitoring Images on the Treatment of Premature Infants Based on Deep Learning.

In recent years, due to the combined effects of individual behavior, psychological factors, environmental exposure, medical conditions, biological factors, etc., the incidence of preterm birth has gradually increased, so the incidence of various complications of preterm infants has also become higher and higher. This article is aimed at studying the therapeutic effects of preterm infants and proposing the application of rSO2 and PI image monitoring based on deep learning to the treatment of preterm infants. This article introduces deep learning, blood perfusion index, preterm infants, and other related content in detail and conducts experiments on the treatment of rSO2 and PI monitoring images based on deep learning in preterm infants. The experimental results show that the rSO2 and PI monitoring images based on deep learning can provide great help for the treatment of preterm infants and greatly improve the treatment efficiency of preterm infants by at least 15%.

Pyrene-Based Dopant-Free Hole-Transport Polymers with Fluorine-Induced Favorable Molecular Stacking Enable Efficient Perovskite Solar Cells.

A new class of polymeric hole-transport materials (HTMs) are explored by inserting a two-dimensionally conjugated fluoro-substituted pyrene into thiophene and selenophene polymeric chains. The broad conjugated plane of pyrene and "Lewis soft" selenium atoms not only enhance the π-π stacking of HTM molecules greatly but also render a strong interaction with the perovskite surface, leading to an efficient charge transport/transfer in both the HTM layer and the perovskite/HTM interface. Note that fluorine substitution adjacent to pyrene boosts the stacking of HTMs towards a more favorable face-on orientation, further facilitating the efficient charge transport. As a result, perovskite solar cells (PSCs) employing PE10 as dopant-free HTM afford an excellent efficiency of 22.3 % and the dramatically enhanced device longevity, qualifying it among the best PSCs based on dopant-free HTMs.

A Phenanthrocarbazole-Based Dopant-Free Hole-Transport Polymer with Noncovalent Conformational Locking for Efficient Perovskite Solar Cells.

Adequate hole mobility is the prerequisite for dopant-free polymeric hole-transport materials (HTMs). Constraining the configurational variation of polymer chains to afford a rigid and planar backbone can reduce unfavorable reorganization energy and improve hole mobility. Herein, a noncovalent conformational locking via S-O secondary interaction is exploited in a phenanthrocarbazole (PC) based polymeric HTM, PC6, to fix the molecular geometry and significantly reduce reorganization energy. Systematic studies on structurally explicit repeats to targeted polymers reveals that the broad and planar backbone of PC remarkably enhances π-π stacking of adjacent polymers, facilitating intermolecular charge transfer greatly. The inserted "Lewis soft" oxygen atoms passivate the trap sites efficiently at the perovskite/HTM interface and further suppress interfacial recombination. Consequently, a PSC employing PC6 as a dopant-free HTM offers an excellent power conversion efficiency of 22.2 % and significantly improved longevity, rendering it as one of the best PSCs based on dopant-free HTMs.

The dynamics of light-induced interfacial charge transfer of different dyes in dye-sensitized solar cells studied by ab initio molecular dynamics.

The charge-transport dynamics at the dye-TiO2 interface plays a vital role for the resulting power conversion efficiency (PCE) of dye sensitized solar cells (DSSCs). In this work, we have investigated the charge-exchange dynamics for a series of organic dyes, of different complexity, and a small model of the semiconductor substrate TiO2. The dyes studied involve L1, D35 and LEG4, all well-known organic dyes commonly used in DSSCs. The computational studies have been based on ab initio molecular dynamics (aiMD) simulations, from which structural snapshots have been collected. Estimates of the charge-transfer rate constants of the central exchange processes in the systems have been computed. All dyes show similar properties, and differences are mainly of quantitative character. The processes studied were the electron injection from the photoexcited dye, the hole transfer from TiO2 to the dye and the recombination loss from TiO2 to the dye. It is notable that the electronic coupling/transfer rates differ significantly between the snapshot configurations harvested from the aiMD simulations. The differences are significant and indicate that a single geometrically optimized conformation normally obtained from static quantum-chemistry calculations may provide arbitrary results. Both protonated and deprotonated dye systems were studied. The differences mainly appear in the rate constant of recombination loss between the protonated and the deprotonated dyes, where recombination losses take place at significantly higher rates. The inclusion of lithium ions close to the deprotonated dye carboxylate anchoring group mitigates recombination in a similar way as when protons are retained at the carboxylate group. This may give insight into the performance-enchancing effects of added salts of polarizing cations to the DSSC electrolyte. In addition, solvent effects can retard charge recombination by about two orders of magnitude, which demonstrates that the presence of a solvent will increase the lifetime of injected electrons and thus contribute to a higher PCE of DSSCs. It is also notable that no simple correlation can be identified between high/low transfer rate constants and specific structural arrangements in terms of atom-atom distances, angles or dihedral arrangements of dye sub-units.

Identification of lnc RNAs Related to Prognosis of Patients With Colorectal Cancer.

The purpose of this study was to identify long noncoding RNAs (lncRNAs) related to prognosis of patients with colorectal cancer (CRC) and develop a prognostic prediction model for CRC. Transcriptome data and survival information of CRC patients were downloaded from The Cancer Genome Atlas. The differentially expressed lncRNAs (DElncRNAs) between CRC and normal colorectal tissues were identified by the edgeR package. The association of DElncRNAs expression with prognosis of CRC patients was analyzed by the survival package. A nomogram predicting 3- and 5- year overall survival of CRC patients was drawn by the rms package. A total of 1046 DElncRNAs were identified, including 271 down-regulated and 775 up-regulated lncRNAs in CRC. Multivariate Cox regression analysis showed 10 lncRNAs related to the prognosis of CRC patients. Thereinto high expression of AC004009.1, LHX1-DT, ELFN1-AS1, AL136307.1, AC087379.2, RBAKDN and AC078820.1 was associated with poorer prognosis of CRC patients. High expression of LINC01055, AL590483.1 and AC008514.1 was associated with better prognosis of CRC patients. Furthermore, the risk score model developed based on the 10 lncRNAs could effectively predict overall survival of CRC patients. In conclusion, 10 prognostic biomarkers for CRC were identified, which would be helpful to understand the role of lncRNAs in CRC progression.

Conformational and Compositional Tuning of Phenanthrocarbazole-Based Dopant-Free Hole-Transport Polymers Boosting the Performance of Perovskite Solar Cells.

Conjugated polymers are regarded as promising candidates for dopant-free hole-transport materials (HTMs) in efficient and stable perovskite solar cells (PSCs). Thus far, the vast majority of polymeric HTMs feature structurally complicated benzo[1,2-b:4,5-b']dithiophene (BDT) analogs and electron-withdrawing heterocycles, forming a strong donor-acceptor (D-A) structure. Herein, a new class of phenanthrocarbazole (PC)-based polymeric HTMs (PC1, PC2, and PC3) has been synthesized by inserting a PC unit into a polymeric thiophene or selenophene chain with the aim of enhancing the π-π stacking of adjacent polymer chains and also to efficiently interact with the perovskite surface through the broad and planar conjugated backbone of the PC. Suitable energy levels, excellent thermostability, and humidity resistivity together with remarkable photoelectric properties are obtained via meticulously tuning the conformation and elemental composition of the polymers. As a result, PSCs containing PC3 as dopant-free HTM show a stabilized power conversion efficiency (PCE) of 20.8% and significantly enhanced longevity, rendering one of the best types of PSCs based on dopant-free HTMs. Subsequent experimental and theoretical studies reveal that the planar conformation of the polymers contributes to an ordered and face-on stacking of the polymer chains. Furthermore, introduction of the "Lewis soft" selenium atom can passivate surface trap sites of perovskite films by Pb-Se interaction and facilitate the interfacial charge separation significantly. This work reveals the guiding principles for rational design of dopant-free polymeric HTMs and also inspires rational exploration of small molecular HTMs.

Efficient Naphthalene Imide-Based Interface Engineering Materials for Enhancing Perovskite Photovoltaic Performance and Stability.

The ways to overcome surface charge recombination and poor interface contact are still the central challenges for the development of inorganic-organic hybrid halide perovskite solar cells (PSCs). [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) is commonly employed in PSCs, but it has some disadvantages including high charge recombination and poor surface coverage. Therefore, the addition of an interfacial engineering layer showing efficient surface passivation, electron extraction, and excellent interface contact can solve the above problems. Furthermore, by employing interface engineering with a spike structure of the energy levels, the reduced energy losses are beneficial to elevating the open-circuit voltage (Voc) in PSCs. Herein, the linear naphthalene imide dimer containing an indacenodithiophene unit (IDTT2NPI) has been developed as an excellent interface engineering material to strengthen the perovskite performance. The introduction of a spike interface on the top of a methylammonium lead triiodide (MAPbI3) film resulted in a high Voc of 1.12 V with the optimal efficiency reaching 20.2%. The efficiency enhancement can be traced to the efficient surface passivation and enhanced interface contact. The mechanism of IDTT2NPI as the interface engineering layer was investigated by both experiments and theoretical calculations. This work provides a promising naphthalene imide-based interfacial material for high-efficiency and stable PSCs.

Association of sarcopenia and muscle mass with both peripheral neuropathy and nerve function in patients with type 2 diabetes.

AIM: This study aimed to investigate the association of sarcopenia and muscle mass with both peripheral neuropathy and nerve function in type 2 diabetes mellitus. METHODS: A total of 1794 patients (937 men and 857 women) with type 2 diabetes, with a mean age of 60.22 years, were enrolled for a cross-sectional study; of these, 183 patients were enrolled for a follow-up study with a median follow-up of 2.7 years. All participants underwent nerve conduction studies and muscle mass index (ASM/HT2) measurements. The composite Z scores for the sensory nerve conduction velocity (SCV) and the motor nerve conduction velocity (MCV) were calculated. The changes in ASM/HT2, SCV, and MCV were calculated from the measurements nearly 2 years apart and classified into three groups: a decrease in ASM/HT2 of >3%, a minor change within ±3%, and an increase in ASM/HT2 of >3%. RESULTS: The ASM/HT2 of men was positively associated with the composite Z scores of MCV and SCV, and sarcopenia highly correlated with DPN after adjusting for confounding factors. The optimal cutoff point for ASM/HT2 that indicated DPN was 7.09 kg/m2. Furthermore, increases in ASM/HT2 independently predicted a greater benefit of MCV and SCV increment outcomes, whereas a minor change in ASM/HT2 only significantly associated with lower benefit in terms of SCV increment. However, this phenomenon was not observed in women. CONCLUSIONS: Sarcopenia and DPN exhibited a close association. The increased muscle mass improved the partial MCVs and SCVs. However, a sex-related discrepancy was observed in this phenomenon.

Theoretical reflections on the structural polymorphism of the oxygen-evolving complex in the S2 state and the correlations to substrate water exchange and water oxidation mechanism in photosynthesis.

The structural polymorphism of the oxygen-evolving complex is of great significance to photosynthetic water oxidation. Employing density functional theory calculations, we have made further advisement on the interconversion mechanism of O5 transfer in the S2 state, mainly focusing on the potentiality of multi-state reactivity and spin transitions. Then, O5 protonation is proven impossible in S2 for irreversibility of the interconversion, which serves as an auxiliary judgment for the protonation state of O5 in S1. Besides, the structural polymorphism could also be archived by alternative mechanisms involving Mn3 ligand exchange, one of which with Mn3(III) makes sense to substrate water exchange in S2, although being irresponsible for the derivations of the observed EPR signals. During the water exchange, high-spin states would prevail to facilitate electron transfer between the ferromagnetically coupled Mn centers. In addition, water exchange in S1 could account for the closed-cubane structure as the initial form entering S2 at cryogenic temperatures. With regard to water oxidation, the structural flexibility and variability in both S2 and S3 guarantee smooth W2-O5 coupling in S4, according to the substrate assignments from water exchange kinetics. Within this theoretical framework, the new XFEL findings on S1-S3 can be readily rationalized. Finally, an alternative mechanistic scenario for OO bond formation with ·OH radical near O4 is presented, followed by water binding to the pivot Mn4(III) from O4 side during S4-S0. This may diversify the substrate sources combined with the Ca channel in water delivery for the forthcoming S-cycle.

The open-cubane oxo-oxyl coupling mechanism dominates photosynthetic oxygen evolution: a comprehensive DFT investigation on O-O bond formation in the S4 state.

The dioxygen formation mechanism of biological water oxidation in nature has long been the focus of argument; many diverse mechanistic hypotheses have been proposed. Based on a recent breakthrough in the resolution of the electronic and structural properties of the oxygen-evolving complex in the S3 state, our density functional theory (DFT) calculations reveal that the open-cubane oxo-oxyl coupling mechanism, whose substrates preferably originate from W2 and O5 in the S2 state, emerges as the best candidate for O-O bond formation in the S4 state. This is justified by the overwhelming energetic superiority of this mechanism over alternative mechanisms in both the isomeric open and closed-cubane forms of the Mn4CaO5 cluster; spin-dependent reactivity rooted in variable magnetic couplings was found to play an essential role. Importantly, this oxygen evolution mechanism is supported by the recent discovery of femtosecond X-ray free electron lasers (XFEL), and the origin of the observed structural changes from the S1 to S3 state has been analyzed. In this view, we corroborate the proposed water binding mechanism during S2-S3 transition and correlate the theoretical models with experimental findings from aspects of substrate selectivity according to water exchange kinetics. This theoretical consequence for native metalloenzymes may serve as a significant guide for improving the design and synthesis of biomimetic materials in the field of photocatalytic water splitting.

How does ammonia bind to the oxygen-evolving complex in the S2 state of photosynthetic water oxidation? Theoretical support and implications for the W1 substitution mechanism.

Ammonia as a water analogue can bind to the Mn4CaO5 cluster of the oxygen-evolving complex in concomitance with ligand substitution and underlying structural transformation. On account of current controversies of the binding site and the absence of the viewpoint of reactivity and mechanistic proofs, we have investigated three modes of NH3 binding based on our elaborations of the possible reaction mechanisms, in correspondence with experimental observation for the NH3-altered g ≈ 2.0 EPR multiline signal. Broken-symmetry density functional theory was employed to construct all the spin surfaces. As a result, we rule out the O5 substitution strategy owing to the impenetrable free energy barrier exceeding 30 kcal mol-1, and alternative routes to destroy the O5 bridge are also blocked. The W1 substitution mechanism is shown to be quite facile, with the barrier not above 11.4 kcal mol-1. For the Mn4 addition scheme, the 'redox switch mechanism' was not implemented by our model, and the effective ways found render 15-22 kcal mol-1 energetic disadvantage by contrast. Consequently, it is strongly in favor of the W1 substitution mechanism for its overwhelming superiority in reactivity, reaching a consensus with the new pulse EPR conclusion. Then, we point out that ammonia departure occurs in the S4' state, with the O-O bonding but unreleased molecular O2. In the meantime, we propose two alternative channels for water binding in the S0' state and expound the significance to substrate selectivity. Ultimately, implications for the mechanism of O-O bond formation are discussed and all the remaining options are listed for future explorations.