Strong interactions through the highly polar "Early-Late" metal-metal bonds enable single-atom catalysts good durability and superior bifunctional ORR/OER activity.

Simultaneously enhancing the durability and catalytic performance of metal-nitrogen-carbon (M-Nx-C) single-atom catalysts is critical to boost oxygen electrocatalysis for energy conversion and storage, yet it remains a grand challenge. Herein, through the combination of early and late metals, we proposed to enhance the stability and tune the catalytic activity of M-Nx-C SACs in oxygen electrocatalysis by their strong interaction with the M2'C-type MXene substrate. Our density functional theory (DFT) computations revealed that the strong interaction between "early-late" metal-metal bonds significantly improves thermal and electrochemical stability. Due to considerable charge transfer and shift of the d-band center, the electronic properties of these SACs can be extensively modified, thereby optimizing their adsorption strength with oxygenated intermediates and achieving eight promising bifunctional catalysts for ORR/OER with low overpotentials. More importantly, the constant-potential analysis demonstrated the excellent bifunctional activity of SACs supported on MXene substrate across a broad pH range, especially in strongly alkaline media with record-low overpotentials. Further machine learning analysis shows that the d-band center, the charge of the active site, and the work function of the formed heterojunctions are critical to revealing the ORR/OER activity origin. Our results underscore the vast potential of strong interactions between different metal species in enhancing the durability and catalytic performance of SACs.

Holey penta-hexagonal graphene: a promising anode material for Li-ion batteries.

Carbon allotropes are widely used as anode materials in Li batteries, with graphite being commercially successful. However, the limited capacity and cycling stability of graphite impede further advancement and hinder the development of electric vehicles. Herein, through density functional theory (DFT) computations and ab initio molecular dynamics (AIMD) simulations, we proposed holey penta-hexagonal graphene (HPhG) as a potential anode material, achieved through active site designing. Due to the internal electron accumulation from the π-bond, HPhG follows a single-layer adsorption mechanism on each side of the nanosheet, enabling a high theoretical capacity of 1094 mA h g-1 without the risk of vertical dendrite growth. HPhG also exhibits a low open circuit voltage of 0.29 V and a low ion migration barrier of 0.32 eV. Notably, during the charge/discharge process, the lattice only expands slightly by 1.1%, indicating excellent structural stability. This work provides valuable insights into anode material design and presents HPhG as a promising two-dimensional material for energy storage applications.

Machine-learning-accelerated screening of single metal atoms anchored on MnPS3 monolayers as promising bifunctional oxygen electrocatalysts.

Searching for bifunctional oxygen electrocatalysts with good catalytic performance to promote the oxygen evolution/reduction reactions (OER/ORR) is of great significance to the development of sustainable and renewable clean energy. Herein, we performed density functional theory (DFT) and machine-learning (DFT-ML) hybrid computations to investigate the potential of a series of single transition metal atoms anchored on the experimentally available MnPS3 monolayer (TM/MnPS3) as the bifunctional electrocatalysts for the ORR/OER. The results revealed that the interactions of these metal atoms with MnPS3 are rather strong, thus guaranteeing their high stability for practical applications. Remarkably, the highly efficient ORR/OER can be achieved on Rh/MnPS3 and Ni/MnPS3 with lower overpotentials than those of metal benchmarks, which can be further rationalized by establishing the volcano and contour plots. Furthermore, the ML results showed that the bond length of TM atoms with the adsorbed O species (dTM-O), the number of d electrons (Ne), the d-center (εd), the radius (rTM) and the first ionization energy (Im) of the TM atoms are the primary descriptors featuring the adsorption behavior. Our findings not only suggest novel highly efficient bifunctional oxygen electrocatalysts, but also provide cost-effective opportunities for the design of single-atom catalysts using the DFT-ML hybrid method.

Large Pressure Effects Caused by Internal Rotation in the s-cis-syn-Acrolein Stabilized Criegee Intermediate at Tropospheric Temperature and Pressure.

Criegee intermediates are important atmospheric oxidants, and quantitative kinetics for stabilized Criegee intermediates are key parameters for atmospheric modeling but are still limited. Here we report barriers and rate constants for unimolecular reactions of s-cis-syn-acrolein oxide (scsAO), in which the vinyl group makes it a prototype for Criegee intermediates produced in the ozonolysis of isoprene. We find that the MN15-L and M06-2X density functionals have CCSD(T)/CBS accuracy for the unimolecular cyclization and stereoisomerization of scsAO. We calculated high-pressure-limit rate constants by the dual-level strategy that combines (a) high-level wave function-based conventional transition-state theory (which includes coupled-cluster calculations with quasiperturbative inclusion of quadruple excitations because of the strongly multiconfigurational character of the electronic wave function) and (b) canonical variational transition-state theory with small-curvature tunneling based on a validated density functional. We calculated pressure-dependent rate constants both by system-specific quantum Rice-Ramsperger-Kassel theory and by solving the master equation. We report rate constants for unimolecular reactions of scsAO over the full range of atmospheric temperature and pressure. We found that the unimolecular reaction rates of this larger-than-previously studied Criegee intermediate depend significantly on pressure. Particularly, we found that falloff effects decrease the effective unimolecular cyclization rate constant of scsAO by about a factor of 3, but the unimolecular reaction is still the dominant atmospheric sink for scsAO at low altitudes. The large falloff caused by the inclusion of the stereoisomerization channel in the master equation calculations has broad implications for mechanistic analysis of reactions with competitive internal rotations that can produce stable rotamers.

Enabling Lithium Metal Anode in Nonflammable Phosphate Electrolyte with Electrochemically Induced Chemical Reactions.

Lithium metal anode holds great promises for next-generation battery technologies but is notoriously difficult to work with. The key to solving this challenge is believed to lie in the ability of forming stable solid-electrolyte interphase (SEI) layers. To further address potential safety issues, it is critical to achieve this goal in nonflammable electrolytes. Building upon previous successes in forming stable SEI in conventional carbonate-based electrolytes, here we report that reversible Li stripping/plating could be realized in triethyl phosphate (TEP), a known flame retardant. The critical enabling factor of our approach was the introduction of oxygen, which upon electrochemical reduction induces the initial decomposition of TEP and produces Li3 PO4 and poly-phosphates. Importantly, the reaction was self-limiting, and the resulting material regulated Li plating by limiting dendrite formation. In effect, we obtained a functional SEI on Li metal in a nonflammable electrolyte. When tested in a symmetric Li∥Li cell, more than 300 cycles of stripping/plating were measured at a current density of 0.5 mA cm-2 . Prototypical Li-O2 and Li-ion batteries were also fabricated and tested to further support the effectiveness of this strategy. The mechanism by which the SEI forms was studied by density functional theory (DFT), and the predictions were corroborated by the successful detection of the intermediates and products.

Enhanced performance of Mo2P monolayer as lithium-ion battery anode materials by carbon and nitrogen doping: a first principles study.

By means of density functional theory (DFT) computations, we explored the potential of carbon- and nitrogen-doped Mo2P (CMP and NMP) layered materials as the representative of transition metal phosphides (TMPs) for the development of lithium-ion battery (LIB) anode materials, paying special attention to the synergistic effects of the dopants. Both CMP and NMP have exceptional stabilities and excellent electronic conductivity, and a high theoretical maximum storage capacity of ∼ 486 mA h g-1. Li-ion diffusion barriers on the two-dimensional (2D) CMP and NMP surfaces are extremely low (∼0.036 eV), and it is expected that on these 2D layers Li can diffuse 104 times faster than that on MoS2 and graphene at room temperature, and both monolayers have relatively low average open-circuit voltage (0.38 and 0.4 eV). All these exceptional properties make CMP and NMP monolayers as promising candidates for high-performance LIB anode materials, which also demonstrates that simple doping is an effective strategy to enhance the performance of anode materials in rechargeable batteries.

Metallic FeSe monolayer as an anode material for Li and non-Li ion batteries: a DFT study.

By means of density functional theory computations, we explored the electrochemical performance of an FeSe monolayer as an anode material for lithium and non-lithium ion batteries (LIBs and NLIBs). The electronic structure, adsorption, diffusion, and storage behavior of different metal atoms (M) in FeSe were systematically investigated. Our computations revealed that M adsorbed FeSe (M = Li, Na and K) systems show metallic characteristics that give rise to good electrical conductivity and mobility with low activation energies for diffusion (0.16, 0.13 and 0.11 eV for Li, Na, and K, respectively) of electrons and metal atoms in the materials, indicative of a fast charge/discharge rate. In addition, the theoretical capacities of the FeSe monolayer for Li, Na and K can reach up to 658, 473, and 315 mA h g-1, respectively, higher than that of commercial graphite (372 mA h g-1 for Li, 284 mA h g-1 for Na, and 273 mA h g-1 for K), and the average open-circuit voltage is moderate (0.38-0.88 V for Li, Na and K). All these characteristics suggest that the FeSe monolayer is a potential anode material for alkali-metal rechargeable batteries.

Tackling the Activity and Selectivity Challenges of Electrocatalysts toward the Nitrogen Reduction Reaction via Atomically Dispersed Biatom Catalysts.

Developing efficient catalysts for nitrogen fixation is becoming increasingly important but is still challenging due to the lack of robust design criteria for tackling the activity and selectivity problems, especially for electrochemical nitrogen reduction reaction (NRR). Herein, by means of large-scale density functional theory (DFT) computations, we reported a descriptor-based design principle to explore the large composition space of two-dimensional (2D) biatom catalysts (BACs), namely, metal dimers supported on 2D expanded phthalocyanine (M2-Pc or MM'-Pc), toward the NRR at the acid conditions. We sampled both homonuclear (M2-Pc) and heteronuclear (MM'-Pc) BACs and constructed the activity map of BACs by using N2H* adsorption energy as the activity descriptor, which reduces the number of promising catalyst candidates from over 900 to less than 100. This strategy allowed us to readily identify 3 homonuclear and 28 heteronuclear BACs, which could break the metal-based activity benchmark toward the efficient NRR. Particularly, using the free energy difference of H* and N2H* as a selectivity descriptor, we screened out five systems, including Ti2-Pc, V2-Pc, TiV-Pc, VCr-Pc, and VTa-Pc, which exhibit a strong capability of suppressing the competitive hydrogen evolution reaction (HER) with favorable limiting potential of -0.75, -0.39, -0.74, -0.85, and -0.47 V, respectively. This work not only broadens the possibility of discovering more efficient BACs toward N2 fixation but also provides a feasible strategy for rational design of NRR electrocatalysts and helps pave the way to fast screening and design of efficient BACs for the NRR and other electrochemical reactions.

Highly Efficient Photocatalytic Degradation of Dyes by a Copper-Triazolate Metal-Organic Framework.

A copper(I) 3,5-diphenyltriazolate metal-organic framework (CuTz-1) was synthesized and extensively characterized by using a multi-technique approach. The combined results provided solid evidence that CuTz-1 features an unprecedented Cu5 tz6 cluster as the secondary building unit (SBU) with channels approximately 8.3 Šin diameter. This metal-organic framework (MOF) material, which is both thermally and chemically (basic and acidic) stable, exhibited semiconductivity and high photocatalytic activity towards the degradation of dyes in the presence of H2 O2 . Its catalytic performance was superior to that of reported MOFs and comparable to some composites, which has been attributed to its high efficiency in generating . OH, the most active species for the degradation of dyes. It is suggested that the photogenerated holes are trapped by CuI , which yields CuII , the latter of which behaves as a catalyst for a Fenton-like reaction to produce an excess amount of . OH in addition to that formed through the scavenging of photogenerated electrons by H2 O2 . Furthermore, it was shown that a dye mixture (methyl orange, methyl blue, methylene blue, and rhodamine B) could be totally decolorized by using CuTz-1 as a photocatalyst in the presence of H2 O2 under the irradiation of a Xe lamp or natural sunlight.

Thiol-maleimide poly(ethylene glycol) crosslinking of L-asparaginase subunits at recombinant cysteine residues introduced by mutagenesis.

L-Asparaginase is an enzyme successfully being used in the treatment of acute lymphoblastic leukemia, acute myeloid leukemia, and non-Hodgkin's lymphoma. However, some disadvantages still limit its full application potential, e.g., allergic reactions, pancreatitis, and blood clotting impairment. Therefore, much effort has been directed at improving its performance. A popular strategy is to randomly conjugate L-asparaginase with mono-methoxy polyethylene glycol, which became a commercial FDA approved formulation widely used in recent years. To improve this formulation by PEGylation, herein we performed cysteine-directed conjugation of the L-asparaginase subunits to prevent dissociation-induced loss of activity. The recombinant cysteine conjugation sites were introduced by mutagenesis at surface-exposed positions on the protein to avoid affecting the catalytic activity. Three conjugates were obtained using different linear PEGs of 1000, 2000, and 5000 g/mol, with physical properties ranging from a semi-solid gel to a fully soluble state. The soluble-conjugate exhibited higher catalytic activity than the non-conjugated mutant, and the same activity than the native enzyme. The cysteine-directed crosslinking of the L-asparaginase subunits produced a higher molecular weight conjugate compared to the native tetrameric enzyme. This strategy might improve L-asparaginase efficiency for leukemia treatment by reducing glomerular filtration due to the increase in hydrodynamic size thus extending half-live, while at the same time retaining full catalytic activity.

Colorimetric detection of microcystin-LR based on disassembly of orient-aggregated gold nanoparticle dimers.

Recently we demonstrated oriented formation of gold nanoparticle (AuNP) dimers for ultrasensitive sensing oligonucleotides (J. Am. Chem. Soc. 2013, 135, 12338). Herein, we investigate the reverse process of this sensing mechanism using target analytes to disassemble the orient-aggregated AuNP dimers. This enables us to expand the analytes from oligonucleotides to other molecules, e.g. highly sensitive and selective determination of microcystin-LR (MC-LR) is selected for a demonstration in this work. Aptamers specific to the target molecules are used as linkers to prepare the AuNP dimers. In the presence of the target molecule, the aptamer changes its structure to bind the target molecule. Thus the pre-formed AuNP dimers are disassembled. As a result, the solution color is changed from blue to red. This sensing design retains the advantages of the previously developed sensors based on target molecules guided formation of AuNP dimers, e.g. the overwhelming sensitivity and stability comparing with those non-oriented sensors based on the formation of large aggregates, with the additional advantages as follows: 1) the target molecules are expanded from oligonucleotides to arbitrary molecules that can specifically bind to aptamers; 2) the color change is completed within 5 min, while the previous sensor based on the formation of AuNP dimers cost ~1 hour to obtain stable responses.

Head and neck cancer patients want us to support them psychologically in the posttreatment period: Survey results.

OBJECTIVES: No study systematically has investigated the supportive care needs of general head and neck cancer patients using validated measures. These needs include physical and daily living needs, health system and information needs, patient care and support needs, psychological needs, and sexuality needs. Identifying the unmet needs of head and neck cancer patients is a necessary first step to improving the care we provide to patients seen in our head and neck oncology clinics. It is recommended as the first step in intervention development in the Pan-Canadian Clinical Practice Guideline of the Canadian Partnership Against Cancer (see Howell, 2009). This study aimed to identify: (1) met and unmet supportive care needs of head and neck cancer patients, and (2) variability in needs according to demographics, disease variables, level of distress, and quality-of-life domains. METHODS: Participants were recruited from the otolaryngology-head and neck surgery clinics of two university teaching hospitals. Self-administered questionnaires included sociodemographic and medical questions, as well as validated measures such as the Supportive Care Needs Survey-Short Form (SCNS-SF34), the Hospital Anxiety and Depression Scale (HADS), and the Functional Assessment of Cancer Therapy-General (FACT-G) and Head and Neck Module (FACT-H&N) (quality of life measures). RESULTS: One hundred and twenty-seven patients participated in the survey. 68% of them experienced unmet needs, and 25% revealed a clinically significant distress level on the HADS. The highest unmet needs were psychological (7 of top 10 needs). A multiple linear regression indicated a higher level of overall unmet needs when patients were divorced, had a high level of anxiety (HADS subscale), were in poor physical condition, or had a diminished emotional quality of life (FACT-G subscales). SIGNIFICANCE OF RESULTS: The results of this study highlight the overwhelming presence of unmet psychological needs in head and neck cancer patients and underline the importance of implementing interventions to address these areas perceived by patients as important. In line with hospital resource allocation and cost-effectiveness, one may also contemplate screening patients for high levels of anxiety, as well as target patients who are divorced and present low levels of physical well-being, as these patients may have more overall needs to be met.