Origami metamaterials for ultra-wideband and large-depth reflection modulation.

The dynamic control of electromagnetic waves is a persistent pursuit in modern industrial development. The state-of-the-art dynamic devices suffer from limitations such as narrow bandwidth, limited modulation range, and expensive features. To address these issues, we fuse origami techniques with metamaterial design to achieve ultra-wideband and large-depth reflection modulation. Through a folding process, our proposed metamaterial achieves over 10-dB modulation depth over 4.96 - 38.8 GHz, with a fractional bandwidth of 155% and tolerance to incident angles and polarizations. Its ultra-wideband and large-depth reflection modulation performance is verified through experiments and analyzed through multipole decomposition theory. To enhance its practical applicability, transparent conductive films are introduced to the metamaterial, achieving high optical transparency (>87%) from visible to near-infrared light while maintaining cost-effectiveness. Benefiting from lightweight, foldability, and low-cost properties, our design shows promise for extensive satellite communication and optical window mobile communication management.

Fabrication of hyaluronic acid-altered gold complex delivery for head and neck squamous cell carcinoma therapy with high antitumor efficacy and low in vivo toxicity.

The use of multifunctional nanomedicines in the treatment of tumors is gaining popularity. Here, we constructed a nanodrug delivery system (HA/Au-PDA@CZT) that targets tumors and responds to pH and near-infrared (NIR) dual stimuli. By precisely interacting with an overexpressed CD44 receptor in specific cancer cells, hyaluronic acid (HA) is coated on the Au-PDA NP surface for tumor-targeting abilities. When exposed to NIR radiation, polydopamine (PDA) and gold nanoshells exhibit exceptional photothermal performance that has the potential to both accelerate and kill HLAC 78 head and neck squamous cell carcinoma cells. Antitumor investigations conducted in vivo and in vitro demonstrated that nanomedicine had remarkable synergistic benefits with chemotherapy and photothermal treatment. Only 25.2% of the cells in the HA/Au-PDA@CZT with a NIR irradiation group were viable. Any group's lowest tumor volume was shown in the tumor mice subjected to HA/Au-PDA@CZT with NIR at 0.3 ± 0.1. Consequently, for synergistic chemo-photothermal therapy, our logically designed nanoplatform would be the potential for a head and neck squamous tumor-targeting drug delivery system.

WSB1/2 target chromatin-bound lysine-methylated RelA for proteasomal degradation and NF-κB termination.

Proteasome-mediated degradation of chromatin-bound NF-κB is critical in terminating the transcription of pro-inflammatory genes and can be triggered by Set9-mediated lysine methylation of the RelA subunit. However, the E3 ligase targeting methylated RelA remains unknown. Here, we find that two structurally similar substrate-recognizing components of Cullin-RING E3 ligases, WSB1 and WSB2, can recognize chromatin-bound methylated RelA for polyubiquitination and proteasomal degradation. We showed that WSB1/2 negatively regulated a subset of NF-κB target genes via associating with chromatin where they targeted methylated RelA for ubiquitination, facilitating the termination of NF-κB-dependent transcription. WSB1/2 specifically interacted with methylated lysines (K) 314 and 315 of RelA via their N-terminal WD-40 repeat (WDR) domains, thereby promoting ubiquitination of RelA. Computational modeling further revealed that a conserved aspartic acid (D) at position 158 within the WDR domain of WSB2 coordinates K314/K315 of RelA, with a higher affinity when either of the lysines is methylated. Mutation of D158 abolished WSB2's ability to bind to and promote ubiquitination of methylated RelA. Together, our study identifies a novel function and the underlying mechanism for WSB1/2 in degrading chromatin-bound methylated RelA and preventing sustained NF-κB activation, providing potential new targets for therapeutic intervention of NF-κB-mediated inflammatory diseases.

Infection with 'Candidatus Liberibacter asiaticus' improves the fecundity of Diaphorina citri aiding its proliferation: A win-win strategy.

The evolution of insect vector-pathogen relationships has long been of interest in the field of molecular ecology. One system of special relevance, due to its economic impacts, is that between Diaphorina citri and 'Candidatus Liberibacter asiaticus' (CLas), the cause of the severe Asian form of huanglongbing. CLas-positive D. citri are more fecund than their CLas-negative counterparts, boosting opportunities for pathogens to acquire new vector hosts. The molecular mechanism behind this life-history shift remains unclear. Here, we found that CLas promoted ovarian development and increased the expression of the vitellogenin receptor (DcVgR) in ovaries. DcVgR RNAi significantly decreased fecundity and CLas titer in ovaries, extended the preoviposition period, shortened the oviposition period and blocked ovarian development. Given their importance in gene regulation, we explored the role of miRNAs in shaping these phenotypes and their molecular triggers. Our results showed that one miRNA, miR-275, suppressed DcVgR expression by binding to its 3' UTR. Overexpression of miR-275 knocked down DcVgR expression and CLas titer in ovaries, causing reproductive defects that mimicked DcVgR knockdown phenotypes. We focused, further, on roles of the Juvenile Hormone (JH) pathway in shaping the observed fecundity phenotype, given its known impacts on ovarian development. After CLas infection, this pathway was upregulated, thereby increasing DcVgR expression. From these combined results, we conclude that CLas hijacks the JH signalling pathway and miR-275, thereby targeting DcVgR to increase D. citri fecundity. These changes simultaneously increase CLas replication, suggesting a pathogen-vector host mutualism, or a seemingly helpful, but cryptically costly life-history manipulation.

Repellent effect of two anthranilates against the tropical bed bug Cimex hemipterus (Hemiptera: Cimicidae) demonstrated in laboratory assays.

BACKGROUND: The bites and blood sucking of bed bugs (Cimex spp.) (Hemiptera: Cimicidae) pose a serious threat to human physical and mental health. Application of an effective repellent can prevent or reduce bed bug bites. Previous studies on repellent screening mainly focused on Cimex lectularius L. In this study, we investigated the repellent effect of two safe food additives, ethyl anthranilate (EA) and butyl anthranilate (BA), against Cimex hemipterus (F.), and also explored the role of antennae and mouthparts on C. hemipterus perception of repellents. RESULTS: Both EA and BA had a strong repellent effect against tropical bed bugs and their repellency was similar or lower than that of N,N-diethyl-3-methyl benzoyl amide, depending on whether or not a CO2 source was present. EA had higher repellency than BA and exhibited repellency to C. hemipterus for 3 days when a CO2 source was present. C. hemipterus avoided resting on 20% EA- and BA-treated harborages. Applying 20% EA and BA on rabbit skin significantly reduced the blood intake of C. hemipterus within 2 h. C. hemipterus could perceive EA and BA after their antennae or mouthparts or both antennae and mouthparts were removed. CONCLUSION: Both EA and BA had strong repellency against C. hemipterus, with EA being more repellent. Ablation of antennae and mouthparts did not affect the perception of EA and BA by C. hemipterus. © 2023 Society of Chemical Industry.

Performance Exploration of Ni-Doped MoS2 in CO2 Hydrogenation to Methanol.

The preparation of methanol chemicals through CO2 and H2 gas is a positive measure to achieve carbon neutrality. However, developing catalysts with high selectivity remains a challenge due to the irreversible side reaction of reverse water gas shift (RWGS), and the low-temperature characteristics of CO2 hydrogenation to methanol. In-plane sulfur vacancies of MoS2 can be the catalytic active sites for CH3OH formation, but the edge vacancies are more inclined to the occurrence of methane. Therefore, MoS2 and a series of MoS2/Nix and MoS2/Cox catalysts doped with different amounts are prepared by a hydrothermal method. A variety of microscopic characterizations indicate that Ni and Co doping can form NiS2 and CoS2, the existence of these substances can prevent CO2 and H2 from contacting the edge S vacancies of MoS2, and the selectivity of the main product is improved. DFT calculation illustrates that the larger range of orbital hybridization between Ni and MoS2 leads to CO2 activation and the active hydrogen is more prone to surface migration. Under optimized preparation conditions, MoS2/Ni0.2 exhibits relatively good methanol selectivity. Therefore, this strategy of improving methanol selectivity through metal doping has reference significance for the subsequent research and development of such catalysts.

Spatial Distribution and Temporal Dynamics of Candidatus Liberibacter Asiaticus in Different Stages of Embryos, Nymphs and Adults of Diaphorina citri.

Huanglongbing, a globally devastating citrus disease, is associated with Candidatus Liberibacter asiaticus (CLas) and is mainly transmitted by Diaphorina citri. Verification of the distribution and dynamics of CLas in D. citri is critical to understanding CLas transmitted by vectors in nature. Here, the distribution and titers of CLas in different sexes and tissues of D. citri adults were investigated by fluorescence in-situ hybridization (FISH) and quantitative real-time PCR (qRT-PCR). Results showed that CLas had widespread distribution in the brain, salivary glands, digestive system, and reproductive system of both females and males, indicating a systemic infection of CLas in D. citri. Moreover, CLas fluorescence intensity and titers were significantly increased in both the digestive system and the female reproductive system with development and there was a marked decreased in both the salivary glands and the male brain, but there was no significant change in the female brain or the male reproductive system. Furthermore, the distribution and dynamics of CLas in embryos and nymphs were investigated. CLas was observed in all laid eggs and subsequent first-second-instar nymphs, indicating that a high percentage of embryos and nymphs resulting from infected D. citri mothers were infected with CLas.

Prevention of hypoparathyroidism: A step-by-step near-infrared autofluorescence parathyroid identification method.

Background: Hypoparathyroidism is an important factor that seriously affects the quality of life of patients after thyroidectomy. This study aimed to optimize the surgical procedure for parathyroid identification using near-infrared autofluorescence (NIRAF) during thyroidectomy. Methods: This was a prospective controlled study that included 100 patients with primary papillary thyroid carcinoma diagnosed in Beijing Tongren Hospital between June 2021 and April 2022 who were awaiting total thyroidectomy and bilateral neck dissection. The patients were randomly divided into an experimental group in whom step-by-step NIRAF imaging was used to identify parathyroid glands, and a control group in whom NIRAF was not used. Results: The number of parathyroid glands identified in the NIRAF group was higher than that in the control group (195 vs. 161, p=0.000, Z=-5.186). The proportion of patients with parathyroid glands inadvertently removed in the NIRAF group was lower than that in the control group (2.0% vs. 18.0%, respectively; p=0.008, χ2 = 7.111). In the NIRAF group, we found that more than 95% of the superior parathyroid glands and more than 85% of the inferior parathyroid glands were identified before the dangerous phase, which was much higher than that in the control group. The incidences of temporary hypoparathyroidism, hypocalcemia, and symptomatic hypocalcemia were higher in the control group than those in the NIRAF group. On the first postoperative day, the average parathyroid hormone (PTH) level in the NIRAF group decreased to 38.1% of the preoperative level and that in the control group decreased to 20.0% of the preoperative level (p=0.000, Z=-3.547). On the third postoperative day, the PTH level in 74% of the patients in the NIRAF group recovered to normal levels, whereas it recovered in only 38% of the patients in the control group (p=0.000, χ2 = 13.149). The PTH levels in all patients in the NIRAF group had recovered within 30 days after surgery, whereas one patient in the control group failed to return to the normal level 6 months after surgery and was diagnosed with permanent parathyroidism. Conclusions: The step-by-step NIRAF parathyroid identification method can effectively locate the parathyroid gland and protect its function.

A Case Study on Tropical Bed Bug, Cimex hemipterus (Hemiptera: Cimicidae) Infestation and Management in Dormitories.

Numerous bed bug research papers have been published in the past 20 yr as a result of bed bug (Cimex spp.) (Hemiptera: Cimicidae) resurgence in the world. Yet, few of them focused on the management of the tropical bed bug, C. hemipterus (F.). Here, we describe a case of tropical bed bug infestation in two dormitory buildings and effectiveness of a tropical bed bug treatment program. The study site consisted of 125 dormitories in two buildings. An initial building-wide monitoring with ClimbUp interceptors revealed 25 infestations. The spatial distribution of bed bug infested rooms showed a significant aggregated distribution pattern with same infestation status for neighboring units sharing walls. All infested rooms were monitored every 2 wk and treated using a combination of steam and diatomaceous earth (DE) dust application if bed bugs were still found. For the 25 initially identified infested rooms, after 14 wk treatment, 44% of them no longer had bed bugs, and the mean number of bed bugs captured per room decreased by 94.1%. A combination of steam and DE dust treatment is an effective strategy for suppressing tropical bed bug infestations in dormitory environment.

Comparison between free posterior tibial flap and free radial forearm flap for head and neck reconstruction: an anatomical study and a retrospective comparative cohort study.

Background: Both free posterior tibial flap (FPTF) and free radial forearm flap (FRFF) are commonly used for head and neck defects. They have many similarities in embryology, histology, and anatomy, but their advantages and disadvantages in head and neck repair have not been fully recognized. This study aimed to compare the cadaveric anatomy and clinical application of FPTF and FRFF for the reconstruction of head and neck defects after tumor resection. Methods: Anatomical dissection was performed on 10 fresh adult cadavers. The general characteristics of both flaps and the sites of recipients and donors were collected. A total of 31 and 25 patients underwent FPTF and FRFF construction, respectively. The patient medical records were assessed to obtain the clinical characteristics. Characteristics of the flap such as size, pedicle length, and clinical process data were collected and compared. The appearance, sensory disturbance, and effect on quality of life and daily activity were evaluated. Results: The posterior tibial artery was present and observed in all patients. The posterior vascular pedicle was longer than the radial artery. There was no difference between the diameters of arteries of FPTF and FRFF; however, the diameters of their veins differed. In terms of flap characteristics, FPTF was significantly larger and had a longer vascular pedicle than FRFF (40.68±11.07 vs. 53.77±29.02 cm2, P=0.03; 8.48±1.66 vs. 11.10±2.39 cm, P=0.00). Patients in the FPTF group had a significantly shorter total hospital stay (FRFF: 26.48±8.33 d; FPTF: 18.58±6.68 d), postoperative hospital stay (FRFF: 17.60±5.53 d; FPTF: 10.94±3.62 d), and flap harvest time (FRFF: 87.00±20.92 min; FPTF: 65.00±17.56 min) than FRFF group. There were far more complications of the donor site in the FRFF group than in the FPTF group. Also, according to the patients' subjective evaluations of the donor site, FPTF was superior to FRFF (P=0.00). Conclusions: FPTF is a reliable alternative to FRFF for head and neck reconstruction. These techniques share similar certain embryogenesis and anatomical characteristics but FPTF possesses unique aesthetic and clinical application advantages.

High Nitrile Yields of Aerobic Ammoxidation of Alcohols Achieved by Generating •O2- and Br• Radicals over Iron-Modified TiO2 Photocatalysts.

Catalytic ammoxidation of alcohols into nitriles is an essential reaction in organic synthesis. While highly desirable, conducting the synthesis at room temperature is challenging, using NH3 as the nitrogen source, O2 as the oxidant, and a catalyst without noble metals. Herein, we report robust photocatalysts consisting of Fe(III)-modified titanium dioxide (Fe/TiO2) for ammoxidation reactions at room temperature utilizing oxygen at atmospheric pressure, NH3 as the nitrogen source, and NH4Br as an additive. To the best of our knowledge, this is the first example of catalytic ammoxidation of alcohols over a photocatalyst using such cheap and benign materials. Various (hetero) aromatic nitriles were synthesized at high yields, and aliphatic alcohols could also be transformed into corresponding nitriles at considerable yields. The modification of TiO2 with Fe(III) facilitates the formation of active •O2- radicals and increases the adsorption of NH3 and amino intermediates on the catalyst, accelerating the ammoxidation to yield nitriles. The additive NH4Br impressively improves the catalytic efficiency via the formation of bromine radicals (Br•) from Br-, which works synergistically with •O2- to capture H• from Cα-H, which is present in benzyl alcohol and the intermediate aldimine (RCH═NH), to generate the active carbon-centered radicals. Further, the generation of Br• from the Br- additive consumes the photogenerated holes and OH• radicals to prevent over-oxidation, significantly improving the selectivity toward nitriles. This amalgamation of function and synergy of the Fe(III)-doped TiO2 and NH4Br reveals new opportunities for developing semiconductor-based photocatalytic systems for fine chemical synthesis.

Evaluation of proton transport and solvation effect in hydrated Nafion membrane with degradation.

In proton exchange membrane fuel cells (PEMFCs), free radicals easily attack ionomers, resulting in membrane degradation. In this work, the multistate empirical valence bond (MS-EVB) method is employed to investigate the chemical degradation impact of Nafion membranes on proton transport and the solvation effect. The hydrophilic domain and its connectivity are analyzed. The numbers of surrounding water and hydronium ions as well as the location of the solvation shell are evaluated. The results demonstrate that the membrane degradation does not change the interaction with the hydronium ions and water molecules but alters the coordination number, leading to a larger hydrophilic domain and a poorer connectivity. The acid groups and protons are distributed more at the edge of the hydrophilic region to accelerate the proton motion, which is not conducive to the proton transport along the membrane side chain.

Modified radius-weighted lattice Boltzmann model to address singularities in axisymmetric multiphase flows.

The radius-weighted lattice Boltzmann model has achieved great success in the simulation of axisymmetric flows. However, severe spurious currents near the axis are observed when this model is extended to simulate axisymmetric multiphase flows. In this study, to determine the origin of this singularity, we conducted a truncation error analysis based on high-order Taylor series expansion and identified the leading error terms through dimensionless analysis. By neglecting the error terms in proportion to the radius, we obtained the final forms of the singular terms in the axisymmetric lattice Boltzmann model. We proposed a modified model by including an additional correction term, to remove the singularity at the third order. We validated the proposed model using numerical tests for flat and spherical interfaces. Results showed that the present modified model reduced the spurious currents near the axis by two orders of magnitude compared with the original model. This modified model also has been successfully applied to predict bubble dynamics in an air-water system. Our numerical results are in excellent agreement with available experimental observations in terms of bubble shapes and terminal velocities.

Identification and Validation of Reference Genes for Expression Analysis Using qRT-PCR in Cimex hemipterus (Hemiptera: Cimicidae).

The tropical bed bug, Cimex hemipterus (F.) (Hemiptera: Cimicidae) is an important public-health pest that feeds on the blood of humans and some other animals. To explore the function of the target genes of C. hemipterus, it is essential to select suitable reference genes for the accurate quantification of gene expression. Here, we selected 10 frequently used reference genes in insects and evaluated their stability in C. hemipterus under various biotic (developmental stage, sex, and tissue) and abiotic (gas stimulation and temperature) conditions through RefFinder (which integrates four computational programs: geNorm, NormFinder, BestKeeper, and ∆Ct). Results indicate that the optimal combination of reference genes for each experimental condition was as follows: RPL8 and EF1α for the developmental stage (eggs, early instar nymphs, late instar nymphs, and adults), RPL8 and RPS16 for adult sex, RPL8 and RPL11 for adult tissue (head, thorax, abdomen, and legs), RPL8 and ß-tubulin for gas stimulation (air and carbon dioxide), and RPL8 and NADH for temperature (0, 5, 17, 30, and 37 °C). Finally, the expression pattern of the HSP70 and GR21 genes were analyzed, and the results highlight the importance of appropriate reference-gene selection. Our results provide a comprehensive list of optimal reference genes from C. hemipterus for the first time, which will contribute to accurately analyzing the expression of target genes.

Effects of Sublethal Concentrations of Insecticides on Survival and Reproduction of Two Bactrocera Species (Diptera: Tephritidae).

The melon fruit fly, Bactrocera cucurbitae (Coquillett) and the pumpkin fruit fly, Bactrocera tau (Walker) (Diptera: Tephritidae), are important invasive pests on Cucurbitaceous hosts. The acute toxicity of five insecticides to females of these two fruit fly species was bio-assayed by membrane method, and effects of their sublethal concentration on the survival, reproduction, and ovary development of females were evaluated in the laboratory. Results showed that based on the LC50 values, both B. cucurbitae and B. tau were the most susceptible to trichlorfon. After treatment with sublethal concentration (LC30) of trichlorfon, abamectin+ß-cypermethrin, spinetoram, and lambda-cyhalothrin, the female survival days of the two Bactrocera species were significantly shortened compared with the control. Moreover, the fecundity of two Bactrocera species was remarkably decreased, after exposure to abamectin+ß-cypermethrin and trichlorfon LC30. However, the sublethal concentration (LC30) of insecticides had no significant influence on the egg hatchability of the fruit flies. Furthermore, after treatment with abamectin+ß-cypermethrin LC30, the ovary length, width, and egg load of B. cucurbitae were significantly lower than that of the control; however, only the ovarian length and egg load of B. tau were significantly decreased on the 16th and 20th day. In conclusion, abamectin+ß-cypermethrin has an excellent insecticidal activity against B. cucurbitae and B. tau.

Effects of Sublethal Concentrations of Tetracycline Hydrochloride on the Biological Characteristics and Wolbachia Titer in Parthenogenesis Trichogramma pretiosum.

Trichogramma pretiosum Riley is an important natural enemy and biological control agent of lepidopteran pests. Wolbachia is an intracellular endosymbiont that induces parthenogenesis in the parasitoid T. pretiosum. In this paper, the sublethal effects of the antibiotic tetracycline hydrochloride on the development and reproduction of T. pretiosum were studied. Emerged females were fed with sublethal concentrations (LC5, LC15, and LC35) of tetracycline for ten generations. The biological parameters (longevity, parasitized eggs, and fecundity) of treated females significantly reduced compared with the control Moreover, the percentage of female offspring in the treatments significantly reduced, but the percentage of male offspring significantly increased. In addition, the Wolbachia titer sharply reduced after two generations of antibiotic treatments, but it could still be detected even after ten successive generations of antibiotic treatments, which indicated that Wolbachia was not completely removed by sublethal concentrations of tetracycline. The control lines with higher Wolbachia titers produced more female offspring than the tetracycline treatments with lower Wolbachia titers, indicating that the Wolbachia titer affected the sex determination of T. pretiosum. Our results show that sublethal concentrations of tetracycline had adverse effects on the development of T. pretiosum, and Wolbachia titers affected the sexual development of T. pretiosum eggs.

Identification of a Cordyceps fumosorosea Fungus Isolate and Its Pathogenicity against Asian Citrus Psyllid, Diaphorina citri (Hemiptera: Liviidae).

Diaphorina citri is the mainly transmitting vector of the citrus huanglongbing pathogen, which causes severe losses in in the citrus industry. In this study, we isolated a new entomopathogenic fungus, identified as member of Cordyceps fumosorosea based on morphology and ITS sequence analysis. We named C. fumosorosea SCAU-CFDC01 and evaluated its pathogenicity against D. citri nymphs and adults by immersion under laboratory and greenhouse conditions. Results showed that SCAU-CFDC01 was most pathogenic to young nymphs, followed by old nymphs and adults. The LC50 values of the fungus on nymphs and adults showed a declining trend over a 2-7-day period after inoculation. The LT50 (lethal time for a certain concentration to cause 50% mortality) values also presented a decreasing trend along with increasing conidia concentrations. For the results on greenhouse experiments, when 3rd and 5th instar nymphs were inoculated with 1 × 105 conidia mL-1, the survival rate of nymphs were lower, and the emergence rate of adults and female longevity was significantly reduced compared with the control. However, there were no significant effects on sex ratio of adults and male longevity. Our results showed SCAU-CFDC01 was highly pathogenic to D. citri, and may promote mycoparasite development for biological control of D. citri.

Role of the foraging gene in worker behavioral transition in the red imported fire ant, Solenopsis invicta (Hymenoptera: Formicidae).

BACKGROUND: Worker division of labor is predominant in social insects. The foraging (for) gene, which encodes cGMP-dependent protein kinase (PKG), has been implicated in the regulation of behavioral transitions in honeybees, but information regarding its function in other social insects is scarce. RESULTS: We investigated the role of the for (Sifor) gene in the red imported fire ant, Solenopsis invicta, and found that Sifor and PKG exhibited different expression patterns in different castes, body sizes, ages and tissues of fire ants, especially in foragers and nurses. Foragers displayed greater locomotor activity but showed no preference for larval or adult odors, whereas nurses showed lesser locomotor activity but had a strong preference for larval odors. We found that the expression of Sifor was significantly higher in the heads of foragers (compared to nurses). RNA interference-mediated Sifor knockdown in foraging workers induced behavioral transition of foragers toward the nurse phenotype characterized by reduced locomotor activity and a stronger preference for larval odors. By contrast, treating nurses with 8-Br-cGMP, an activator of PKG, resulted in behavioral transition toward the forager phenotype characterized by higher locomotor activity but reduced preference for larval odors. CONCLUSION: Our results suggest that Sifor plays a critical role in the behavioral transition between foragers and nurses of workers, which may be a promising target for RNAi-based management of worker caste organization in S. invicta. © 2022 Society of Chemical Industry.

Visualization of on-surface ethylene polymerization through ethylene insertion.

Polyethylene production through catalytic ethylene polymerization is one of the most common processes in the chemical industry. The popular Cossee-Arlman mechanism hypothesizes that the ethylene be directly inserted into the metal-carbon bond during chain growth, which has been awaiting microscopic and spatiotemporal experimental confirmation. Here, we report an in situ visualization of ethylene polymerization by scanning tunneling microscopy on a carburized iron single-crystal surface. We observed that ethylene polymerization proceeds on a specific triangular iron site at the boundary between two carbide domains. Without an activator, an intermediate, attributed to surface-anchored ethylidene (CHCH3), serves as the chain initiator (self-initiation), which subsequently grows by ethylene insertion. Our finding provides direct experimental evidence of the ethylene polymerization pathway at the molecular level.

The degradation effect on proton dissociation and transfer in perfluorosulfonic acid membranes.

In the operation of proton exchange membrane fuel cells (PEMFCs), the ionomer-perfluorosulfonic acid (PSFA) membrane side chains are easily attacked by free radicals, resulting in membrane degradation. In this work, the chemical degradation effect of side chains in the PSFA membrane on proton dissociation and transfer behaviors is investigated by means of the quantum chemistry calculation. The rotation of the H atom in the acid group after the degradation is evaluated. The impact of the electrostatic potential (ESP) and electronegativity of the side chains is analyzed. The results demonstrate that the membrane degradation decreases the positive potential of the proton in the acid group, leading to the proton being less active so that more water molecules are required for the spontaneous proton dissociation. The rotation of the H atom in the acid group affects the proton dissociation mode owing to the change of the hydrogen bond network. It is found that the ESP of the acid group in two side chain fragments influences each other and the water molecules between two side chains can be shared to reduce the number of water molecules for the proton dissociation.