Barrier For Cleavage Research Articles

Programmable DNA-Based Nanodevices for Next-Generation Clinical and Healthcare Applications.

Deoxyribonucleic acid (DNA) nanotechnology has brought an unparalleled set of possibilities for self-assembled structures emerging as an independent branch of synthetic biology. The field of science uses the molecular properties of DNA to build nanoparticles and nanodevices that have the potential to bring breakthroughs in medical science. On the one hand, their biocompatibility, precision, synthetic ease, and programmability make them an ideal choice in drug delivery and healthcare. On the other, the lack of proper biodistribution profiles, stability inside the system, enzymatic cleavage, immune recognition, and translational barriers are some of the hurdles it faces. Many recent technological advancements are in progress to tackle these challenges, while some already have been used. These tools and technologies need to be understood and studied for the successful transition of these intelligent DNA nanostructures (DNs) to healthcare applications. This review thus, highlights some of the challenges being faced by the DNs in healthcare. Additionally, it provides an overview of the recent trends in using these devices in disease detection and remission and finally talks about the future scope and opportunities for an effective transition from bench to bedside.

Oxygen reduction reaction kinetics of platinum-based catalysts under stress induction.

The ORR kinetic optimization for PtNi and PtPb catalysts is conferred by stress induction. First principles calculation shows the cleavage barrier reduction of the key intermediate *OOH to 28.48 and 0 kJ mol-1, respectively. Proper kinetic tuning led to a mass activity promotion of PtNi to 3.57 times that of Pt/C, whereas excessive modulation induced activity degradation for PtPb and shifted the rate-determining step to the first electron transfer, which was verified by in situ infrared spectroscopy and electrochemical characterization.

Cis-Dihydroxylation by Synthetic Iron(III)-Peroxo Intermediates and Rieske Dioxygenases: Experimental and Theoretical Approaches Reveal the Key O-O Bond Activation Step.

Dioxygen (O2) activation by iron-containing enzymes and biomimetic compounds generates iron-oxygen intermediates, such as iron-superoxo, -peroxo, -hydroperoxo, and -oxo, that mediate oxidative reactions in biological and abiological systems. Among the iron-oxygen intermediates, iron(III)-peroxo species are less frequently implicated as active intermediates in oxidation reactions. In this study, we present the combined experimental and theoretical investigations on cis-dihydroxylation reactions mediated by synthetic mononuclear nonheme iron-peroxo intermediates, demonstrating the importance of supporting ligands and metal centers in activating the peroxo ligand toward the O-O bond homolysis for the cis-dihydroxylation reactions. We found a significant ring size effect of the TMC ligand in [FeIII(O2)(n-TMC)]+ (TMC = tetramethylated tetraazacycloalkane; n = 12, 13, and 14) on the cis-dihydroxylation reactivity order: [FeIII(O2)(12-TMC)]+ > [FeIII(O2)(13-TMC)]+ > [FeIII(O2)(14-TMC)]+. Additionally, we found that only [FeIII(O2)(n-TMC)]+, but not other metal-peroxo complexes such as [MIII(O2)(n-TMC)]+ (M = Mn, Co, and Ni), is reactive for the cis-dihydroxylation of olefins. Using density functional theory (DFT) calculations, we revealed that electron transfer from the Fe dxz orbital to the peroxo σ*(O-O) orbital facilitates the O-O bond homolysis, with the O-O bond cleavage barrier well correlated with the energy gap between the frontier molecular orbitals of dxz and σ*(O-O). Further computational studies showed that the reactivity of the synthetic [FeIII(O2)(12-TMC)]+ complex is comparable to that of Rieske dioxygenases in cis-dihydroxylation, providing compelling evidence of the potential involvement of Fe(III)-peroxo species in Rieske dioxygenases. Thus, the present results significantly advance our understanding of the cis-dihydroxylation mechanisms by Rieske dioxygenases and synthetic nonheme iron-peroxo models.

Cascade Synthesis of Fe-N2-Fe Dual-Atom Catalysts for Superior Oxygen Catalysis.

Dual-atom catalysts (DACs) have been proposed to break the limitation of single-atom catalysts (SACs) in the synergistic activation of multiple molecules and intermediates, offering an additional degree of freedom for catalytic regulation. However, it remains a challenge to synthesize DACs with high uniformity, atomic accuracy, and satisfactory loadings. Herein, we report a facile cascade synthetic strategy for DAC via precise electrostatic interaction control and neighboring vacancy construction. We synthesized well-defined, uniformly dispersed dual Fe sites which were connected by two nitrogen bonds (denoted as Fe-N2-Fe). The as-synthesized DAC exhibited superior catalytic performances towards oxygen reduction reaction, including good half-wave potential (0.91 V), high kinetic current density (21.66 mA cm-2), and perfect durability. Theoretical calculation revealed that the DAC structure effectively tunes the oxygen adsorption configuration and decreases the cleavage barrier, thereby improving the catalytic kinetics. The DAC-based zinc-air batteries exhibited impressive power densities of 169.8 and 52.18 mW cm-2 at 25 °C and -40 °C, which is 1.7 and 2.0 times higher than those based on Pt/C+Ir/C, respectively. We also demonstrated the universality of our strategy in synthesizing other M-N2-M DACs (M=Co, Cu, Ru, Pd, Pt, and Au), facilitating the construction of a DAC library for different catalytic applications.

Cascade Synthesis of Fe‐N2‐Fe Dual‐Atom Catalysts for Superior Oxygen Catalysis

AbstractDual‐atom catalysts (DACs) have been proposed to break the limitation of single‐atom catalysts (SACs) in the synergistic activation of multiple molecules and intermediates, offering an additional degree of freedom for catalytic regulation. However, it remains a challenge to synthesize DACs with high uniformity, atomic accuracy, and satisfactory loadings. Herein, we report a facile cascade synthetic strategy for DAC via precise electrostatic interaction control and neighboring vacancy construction. We synthesized well‐defined, uniformly dispersed dual Fe sites which were connected by two nitrogen bonds (denoted as Fe‐N2‐Fe). The as‐synthesized DAC exhibited superior catalytic performances towards oxygen reduction reaction, including good half‐wave potential (0.91 V), high kinetic current density (21.66 mA cm−2), and perfect durability. Theoretical calculation revealed that the DAC structure effectively tunes the oxygen adsorption configuration and decreases the cleavage barrier, thereby improving the catalytic kinetics. The DAC‐based zinc‐air batteries exhibited impressive power densities of 169.8 and 52.18 mW cm−2 at 25 °C and −40 °C, which is 1.7 and 2.0 times higher than those based on Pt/C+Ir/C, respectively. We also demonstrated the universality of our strategy in synthesizing other M‐N2‐M DACs (M=Co, Cu, Ru, Pd, Pt, and Au), facilitating the construction of a DAC library for different catalytic applications.

Reduction of molecular oxygen in flavodiiron proteins - Catalytic mechanism and comparison to heme-copper oxidases

The family of flavodiiron proteins (FDPs) plays an important role in the scavenging and detoxification of both molecular oxygen and nitric oxide. Using electrons from a flavin mononucleotide cofactor molecular oxygen is reduced to water and nitric oxide is reduced to nitrous oxide and water. While the mechanism for NO reduction in FDPs has been studied extensively, there is very little information available about O2 reduction. Here we use hybrid density functional theory (DFT) to study the mechanism for O2 reduction in FDPs. An important finding is that a proton coupled reduction is needed after the O2 molecule has bound to the diferrous diiron active site and before the OO bond can be cleaved. This is in contrast to the mechanism for NO reduction, where both NN bond formation and NO bond cleavage occurs from the same starting structure without any further reduction, according to both experimental and computational results. This computational result for the O2 reduction mechanism should be possible to evaluate experimentally. Another difference between the two substrates is that the actual OO bond cleavage barrier is low, and not involved in rate-limiting the reduction process, while the barrier connected with bond cleavage/formation in the NO reduction process is of similar height as the rate-limiting steps. We suggest that these results may be part of the explanation for the generally higher activity for O2 reduction as compared to NO reduction in most FDPs. Comparisons are also made to the O2 reduction reaction in the family of heme‑copper oxidases.

Selective Upcycling of Polyethylene Terephthalate towards High-valued Oxygenated Chemical Methyl p-Methyl Benzoate using a Cu/ZrO2 Catalyst.

Upgrading of polyethylene terephthalate (PET) waste into valuable oxygenated molecules is a fascinating process, yet it remains challenging. Herein, we developed a two-step strategy involving methanolysis of PET to dimethyl terephthalate (DMT), followed by hydrogenation of DMT to produce the high-valued chemical methyl p-methyl benzoate (MMB) using a fixed-bed reactor and a Cu/ZrO2 catalyst. Interestingly, we discovered the phase structure of ZrO2 significantly regulates the selectivity of products. Cu supported on monoclinic ZrO2 (5 %Cu/m-ZrO2 ) exhibits an exceptional selectivity of 86 % for conversion of DMT to MMB, while Cu supported on tetragonal ZrO2 (5 %Cu/t-ZrO2 ) predominantly produces p-xylene (PX) with selectivity of 75 %. The superior selectivity of MMB over Cu/m-ZrO2 can be attributed to the weaker acid sites present on m-ZrO2 compared to t-ZrO2 . This weak acidity of m-ZrO2 leads to a moderate adsorption capability of MMB, and facilitating its desorption. Furthermore, DFT calculations reveal Cu/m-ZrO2 catalyst shows a higher effective energy barrier for cleavage of second C-O bond compared to Cu/t-ZrO2 catalyst; this distinction ensures the high selectivity of MMB. This catalyst not only presents an approach for upgrading of PET waste into fine chemicals but also offers a strategy for controlling the primary product in a multistep hydrogenation reaction.

Selective Upcycling of Polyethylene Terephthalate towards High‐valued Oxygenated Chemical Methyl p‐Methyl Benzoate using a Cu/ZrO2 Catalyst

AbstractUpgrading of polyethylene terephthalate (PET) waste into valuable oxygenated molecules is a fascinating process, yet it remains challenging. Herein, we developed a two‐step strategy involving methanolysis of PET to dimethyl terephthalate (DMT), followed by hydrogenation of DMT to produce the high‐valued chemical methyl p‐methyl benzoate (MMB) using a fixed‐bed reactor and a Cu/ZrO2 catalyst. Interestingly, we discovered the phase structure of ZrO2 significantly regulates the selectivity of products. Cu supported on monoclinic ZrO2 (5 %Cu/m‐ZrO2) exhibits an exceptional selectivity of 86 % for conversion of DMT to MMB, while Cu supported on tetragonal ZrO2 (5 %Cu/t‐ZrO2) predominantly produces p‐xylene (PX) with selectivity of 75 %. The superior selectivity of MMB over Cu/m‐ZrO2 can be attributed to the weaker acid sites present on m‐ZrO2 compared to t‐ZrO2. This weak acidity of m‐ZrO2 leads to a moderate adsorption capability of MMB, and facilitating its desorption. Furthermore, DFT calculations reveal Cu/m‐ZrO2 catalyst shows a higher effective energy barrier for cleavage of second C−O bond compared to Cu/t‐ZrO2 catalyst; this distinction ensures the high selectivity of MMB. This catalyst not only presents an approach for upgrading of PET waste into fine chemicals but also offers a strategy for controlling the primary product in a multistep hydrogenation reaction.

Mechanistic insights of electrocatalytic CO2 reduction by Mn complexes: synergistic effects of the ligands.

The electrocatalytic mechanisms of CO2 reduction catalyzed by pyridine-oxazoline (pyrox)-based Mn catalysts were investigated by DFT calculations. In-depth comparative analyses of pyrox-based and bipyridine-based Mn complexes were carried out. C-OH cleavage is the rate-determining step for both the protonation-first path and the reduction-first path. The free energy of CO2 activation (ΔG1) and the electrons donated by CO ligands in this step are effective descriptors in regulating the C-OH cleavage barrier. The reduction of carboxylate complex 6 (E6) is the potential-determining step for the reduction-first path. Meanwhile, for the protonation-first path, the initial generation (E2) or the regeneration (E8) of active catalyst might be potential-determining. Hirshfeld charge and orbital contribution analysis indicate that E6 is definitely based on the heterocyclic ligand and E2 is related to both the heterocyclic ligand and three CO ligands. Therefore, replacement of the CO ligand by a stronger electron donating ligand can effectively boost the catalytic activity of CO2 reduction without increasing the overpotential in the reduction-first path. This hypothesis is supported by the mechanism calculations of the Mn complex in which the axial CO ligand is replaced by a pyridine or PMe3.

The electron-rich [ZnH]+ species stabilized by titanium silicalite-1 zeolite for propane dehydrogenation

The electron-rich [ZnH]+ species stabilized by titanium silicalite-1 zeolite for propane dehydrogenation

Calpain Promotes LPS-induced Lung Endothelial Barrier Dysfunction via Cleavage of Talin.

Acute lung injury (ALI) is characterized by lung vascular endothelial cell (EC) barrier compromise resulting in increased endothelial permeability and pulmonary edema. The infection of gram-negative bacteria that produce toxins like LPS is one of the major causes of ALI. LPS activates Toll-like receptor 4, leading to cytoskeleton reorganization, resulting in lung endothelial barrier disruption and pulmonary edema in ALI. However, the signaling pathways that lead to the cytoskeleton reorganization and lung microvascular EC barrier disruption remain largely unexplored. Here we show that LPS induces calpain activation and talin cleavage into head and rod domains and that inhibition of calpain attenuates talin cleavage, RhoA activation, and pulmonary EC barrier disruption in LPS-treated human lung microvascular ECs invitro and lung EC barrier disruption and pulmonary edema induced by LPS in ALI invivo. Moreover, overexpression of calpain causes talin cleavage and RhoA activation, myosin light chain (MLC) phosphorylation, and increases in actin stress fiber formation. Furthermore, knockdown of talin attenuates LPS-induced RhoA activation and MLC phosphorylation and increased stress fiber formation and mitigates LPS-induced lung microvascular endothelial barrier disruption. Additionally, overexpression of talin head and rod domains increases RhoA activation, MLC phosphorylation, and stress fiber formation and enhances lung endothelial barrier disruption. Finally, overexpression of cleavage-resistant talin mutant reduces LPS-induced increases in MLC phosphorylation in human lung microvascular ECs and attenuates LPS-induced lung microvascular endothelial barrier disruption. These results provide the first evidence that calpain mediates LPS-induced lung microvascular endothelial barrier disruption in ALI via cleavage of talin.

Facile Synthesis of Ni-Doped WO3-x Nanosheets with Enhanced Visible-Light-Responsive Photocatalytic Performance for Lignin Depolymerization into Value-Added Biochemicals

Lignin is the only renewable resource composed of aromatic hydrocarbons in nature that can be used as raw materials for preparing chemicals. However, due to the existence of stable C–O bonds and C−C bonds in the lignin, the high-value resource utilization of lignin is still challenging work. Herein, we reported efficient lignin depolymerization using a Ni-doped WO3-x nanosheet photocatalyst that was prepared via the two-step hydrothermal treatment. The optimized catalyst (Ni-doped WO3-x) successfully depolymerized sodium lignosulfonate to vanillic acid and guaiacol under visible-light irradiation. The active radicals of photocatalytic depolymerization of sodium lignosulfonate were superoxide radicals, photogenic holes, and hydroxyl radicals under visible-light irradiation. Furthermore, the introduction of Ni significantly decreased the activation energy barrier for selective cleavage of the C−C bond, which was the essential step to promote lactic acid production. This work presented an effective and promising strategy for lignin depolymerization and value-added biochemical production.

Towards selective glycerol hydrodeoxygenation to 1,3-propanediol with effective Pt-WOx catalyst design: Insights from first principles

DFT simulations predicted the C-O bond cleavage in glycerol on Brønsted acidic Pt-WOx catalyst under a hydrogen atmosphere to be via a “protonation dehydration” mechanism. Interfacial Pt-WOx sites facilitate Brønsted acid (BA) site formation by hydrogen spillover and synergistic activity of Pt and WOx. At strong BA sites, selective formation of 1,3-PDO is likely due to the large difference of over 40 kJ/mol in primary and secondary C-O bond cleavage barriers. The secondary C-O bond cleavage has a linear relation with NH3 binding energy while there is a non-monotonic trend for the primary C-O cleavage. Hence, Brønsted acid strength is a potential descriptor for the catalyst activity and 1,3-PDO selectivity. Synthetic strategies enabling fine dispersion of WOx to trimeric units on the Pt nanoparticles, while preventing W doping and agglomeration of WOx to 3D WO3 on small Pt nanoparticles are desirable for high BA strength and thereby 1,3-PDO yield.

Dual hydrogen production from electrocatalytic water reduction coupled with formaldehyde oxidation via a copper-silver electrocatalyst

The broad employment of water electrolysis for hydrogen (H2) production is restricted by its large voltage requirement and low energy conversion efficiency because of the sluggish oxygen evolution reaction (OER). Herein, we report a strategy to replace OER with a thermodynamically more favorable reaction, the partial oxidation of formaldehyde to formate under alkaline conditions, using a Cu3Ag7 electrocatalyst. Such a strategy not only produces more valuable anodic product than O2 but also releases H2 at the anode with a small voltage input. Density functional theory studies indicate the H2C(OH)O intermediate from formaldehyde hydration can be better stabilized on Cu3Ag7 than on Cu or Ag, leading to a lower C-H cleavage barrier. A two-electrode electrolyzer employing an electrocatalyst of Cu3Ag7(+)||Ni3N/Ni(–) can produce H2 at both anode and cathode simultaneously with an apparent 200% Faradaic efficiency, reaching a current density of 500 mA/cm2 with a cell voltage of only 0.60 V.

Insight into the solvent effects on ethanol oxidation on Ir(100).

Solvent effects have always been a non-negligible factor for aqueous catalytic reactions, though few studies have been devoted towards the molecular understanding and impact of solvent effects on catalysis. In this work, we investigated ethanol dehydrogenation and C-C bond cleavage over Ir(100) in an aqueous solution using density functional theory calculations with both the implicit and explicit solvent models and transition state theory-based kinetics simulations. The results show that solvent polarization assists the α- and β-dehydrogenation of ethanol on Ir(100) in the aqueous solution and hydrogen bonding also assists the ethanol β-dehydrogenation and C-C bond cleavage in CH2CO. The hydrogen bond between the ethanol and water molecule hinders ethanol hydroxyl dehydrogenation while the CHCO⋯H2O hydrogen bond radically alters the adsorption configuration of CHCO, which leads to an increase in the C-C cleavage barrier by 2.5 fold. Furthermore, the solvent changes the reaction pathways significantly. In an aqueous solution, ethanol β-dehydrogenation on Ir(100) is the dominant ethanol dehydrogenation pathway and C-C bond cleavage occurs predominantly via CH2CO species.

How Nitrogen and Sulfur Doping Modified Material Structure, Transformed Oxidation Pathways, and Improved Degradation Performance in Peroxymonosulfate Activation.

Current research has widely applied heteroatom doping for the promotion of catalyst activity in peroxymonosulfate (PMS) systems; however, the relationship between heteroatom doping and stimulated activation mechanism transformation is not fully understood. Herein, we introduce nitrogen and sulfur doping into a Co@rGO material for PMS activation to degrade tetracycline (TC) and systematically investigate how heteroatom doping transformed the activation mechanism of the original Co@rGO/PMS system. N was homogeneously inserted into the reduced graphene oxide (rGO) matrix of Co@rGO, inducing a significant increase in the degradation efficiency without affecting the activation mechanism transformation. Additionally, S doping converted Co3O4 to Co4S3 in Co@rGO and transformed the cooperative oxidation pathway into a single non-radical pathway with stronger intensity, which led to a higher stability against environmental interferences. Notably, based on density functional theory (DFT) calculations, we demonstrated that Co4S3 had a higher energy barrier for PMS adsorption and cleavage than Co3O4, and therefore, the radical pathway was not easily stimulated by Co4S3. Overall, this study not only illustrated the improvement due to the heteroatom doping of Co@rGO for TC degradation in a PMS system but also bridged the knowledge gap between the catalyst structure and degradation performance through activation mechanism transformation drawn from theoretical and experimental analyses.

Mechanisms of the carbon deposition at the Ni/YSZ interface: A combination study of microscopic observation and first-principles calculation

Carbon deposition mechanisms at the Ni/YSZ interface in the CH 4 environment were studied through microscale observation and density functional theory calculation. SEM and STEM observation showed that carbon deposition occurred at some Ni/YSZ interfaces but was not found at others at the early stage. The carbon deposition in the calculation was modeled by absorbing and bonding CH fragments, and the impact of vacancy configuration at the Ni/YSZ interfaces was studied using the Vienna Ab-initio Simulation Package code. Consequently, the CH–CH bonding barrier was approximately 0.6 eV in the Ni/YSZ, which is lower than the CH cleavage barrier at the last step of CH 4 decomposition, indicating that CH–CH bonding occurred as the nascent carbon deposition. Some vacancy configurations made the CH fragments absorption energy more stable mainly because the CH adsorption increased the adhesion bonding force between Ni and YSZ, leading to a stable interface structure. Calculations showed the carbon growth mechanisms at the Ni/YSZ interface, illustrating why the Ni/YSZ interface had a different reactivity against carbon deposition at the atomic scales. • Carbon deposition model considering CH–CH bonding was developed using DFT. • Some of the vacancy configuration made the adsorption of CH fragments more stable. • Interface adhesion force explained the carbon deposition near the interface.

Atomic cerium modulated palladium nanoclusters exsolved ferrite catalysts for lean methane conversion.

The active and stable palladium (Pd) based catalysts for CH4 conversion are of great environmental and industrial significance. Herein, we employed N2 as an optimal activation agent to develop a Pd nanocluster exsolved Ce-incorporated perovskite ferrite catalyst toward lean methane oxidation. Replacing the traditional initiator of H2, the N2 was found as an effective driving force to selectively touch off the surface exsolution of Pd nanocluster from perovskite framework without deteriorating the overall material robustness. The catalyst showed an outstanding T50 (temperature of 50% conversion) plummeting down to 350°C, outperforming the pristine and H2-activated counterparts. Further, the combined theoretical and experimental results also deciphered the crucial role that the atomically dispersed Ce ions played in both construction of active sites and CH4 conversion. The isolated Ce located at the A-site of perovskite framework facilitated the thermodynamic and kinetics of the Pd exsolution process, lowering its formation temperature and promoting its quantity. Moreover, the incorporation of Ce lowered the energy barrier for cleavage of C─H bond, and was dedicated to the preservation of highly reactive PdOx moieties during stability measurement. This work successfully ventures uncharted territory of in situ exsolution to provide a new design thinking for a highly performed catalytic interface.

Defect-induced decomposition of energetic nitro compounds at MgO Surface

• MgO surface F 0 -center triggers decomposition of energetic molecules due to an electron charge transfer. • The O-atom-oxygen vacancy recombination is highly exothermic causing reaction propagation. • This new decomposition mechanism is significantly different from ordinary decomposition nitro energetic molecules. • The activation barriers for N O cleavage are much lower than activation barriers of decomposition reactions in gas phase or solid state for nitro materials. We studied the role of F 0 centers at a MgO surface in decomposition of energetic nitro compounds which is critically important for the control of chemical explosion reactions in these materials as well as for their recycling. We found that the first step of the molecular decomposition is initiated by an electron charge transferring from one of the F 0 centers at the surface to the NO 2 group of the energetic molecule which results in the cleavage of one of the N O bonds. The O atom released from the nitro molecule goes to the oxygen vacancy thus liquidating the vacancy defect. The process of oxygen trapping in the F 0 center is highly exothermic, with a significant energy release. The released energy is sufficient to break other molecular bonds thus facilitating a further decomposition of the energetic molecules and propagating the decomposition reaction. This decomposition initiation mechanism is significantly different from decomposition in gas phase or solid state for all three considered nitro energetic molecules. In particular, the activation barriers for N O cleavage are much lower than activation barriers of the first step of decomposition reactions in gas phase or solid state (molecular crystals) for all three nitro materials.

Intrinsic Electron Localization of Metastable MoS2 Boosts Electrocatalytic Nitrogen Reduction to Ammonia.

The advancement of efficient electrocatalysts toward the nitrogen reduction reaction (NRR) is critical in sustainable ammonia synthesis under ambient pressure and temperature. Manipulating the electronic configuration of electrocatalysts is particularly vital to form metal-nitrogen (MN) bonds during the NRR through regulating the active electronic states of sites. Here, in sharp contrast to stable 2H MoS2 without metal chains, MoMo bonding in metastable polymorphs of MoS2 bulk (zigzag chain in the 1T' phase and diamond chain in the 1T″' phase) is discovered to significantly increase intrinsic electron localization around the metal chains. This can enhance the charge transfer from the adsorbed nitrogen molecule to the metal chains, allowing for boosted NRR kinetics. The electrochemical experiments show that the NH3 yield rate and the faradaic efficiency of the metastable 1T″' MoS2 rich with abundant Mo-Mo bonds are about 9 and 12 times above average than those of 2H MoS2 , correspondingly. Theoretical simulations reveal the high local electron density surrounding the MoMo chains and sites can promote π back-donation, which is beneficial for increasing nitrogen adsorption, strengthening the MN bonds, and reducing the cleavage barrier of the triple NN bond.