Mesoporous Electrocatalysts with p-n Heterojunctions for Efficient Electroreduction of CO2 and N2 to Urea.

The electrocatalytic synthesis of high-value-added urea by activating N2 and CO2 is a green synthesis technology that has achieved carbon neutrality. However, the chemical adsorption and C-N coupling ability of N2 and CO2 on the surface of the catalyst are generally poor, greatly limiting the improvement of electrocatalytic activity and selectivity in electrocatalytic urea synthesis. Herein, novel hierarchical mesoporous CeO2/Co3O4 heterostructures are fabricated, and at an ultralow applied voltage of -0.2 V, the urea yield rate reaches 5.81 mmol g-1 h-1, with a corresponding Faraday efficiency of 30.05%. The hierarchical mesoporous material effectively reduces the mass transfer resistance of reactants and intermediates, making it easier for them to access active centers. The emerging space-charge regions at the heterointerface generate local electrophilic and nucleophilic regions, facilitating CO2 targeted adsorption in the electrophilic region and activation to produce *CO intermediates and N2 targeted adsorption in the nucleophilic region and activation to generate *N ═ N* intermediates. Then, the electrons in the σ orbitals of *N ═ N* intermediates can be easily accepted by the empty eg orbitals of Co3+ in CeO2/Co3O4, which presents a low-spin state (LS: t2g6eg0). Subsequently, *CO couples with *N ═ N* to produce the key intermediate *NCON*. Interestingly, it was discovered through in situ Raman spectroscopy that the CeO2/Co3O4 catalyst has a reversible spinel structure before and after the electrocatalytic reaction, which is due to the surface reconstruction of the catalyst during the electrocatalytic reaction process, producing amorphous active cobalt oxides, which is beneficial for improving electrocatalytic activity.

Developing an ultra-intensified fed-batch cell culture process with greatly improved performance and productivity.

Intensified fed-batch (IFB), a popular cell culture intensification strategy, has been widely used for productivity improvement through high density inoculation followed by fed-batch cultivation. However, such an intensification strategy may counterproductively induce rapidly progressing cell apoptosis and difficult-to-sustain productivity. To improve culture performance, we developed a novel cell culture process intermittent-perfusion fed-batch (IPFB) which incorporates one single or multiple cycles of intermittent perfusion during an IFB process for better sustained cellular and metabolic behaviors and notably improved productivity. Unlike continuous perfusion or other semi-continuous processes such as hybrid perfusion fed-batch with only early-stage perfusion, IPFB applies limited times of intermittent perfusion in the mid-to-late stage of production and still inherits bolus feedings on nonperfusion days as in a fed-batch culture. Compared to IFB, an average titer increase of ~45% was obtained in eight recombinant CHO cell lines studied. Beyond IPFB, ultra-intensified IPFB (UI-IPFB) was designed with a markedly elevated seeding density of 20-80 × 106 cell/mL, achieved through the conventional alternating tangential flow filtration (ATF) perfusion expansion followed with a cell culture concentration step using the same ATF system. With UI-IPFB, up to ~6 folds of traditional fed-batch and ~3 folds of IFB productivity were achieved. Furthermore, the application grounded in these two novel processes showed broad-based feasibility in multiple cell lines and products of interest, and was proven to be effective in cost of goods reduction and readily scalable to a larger scale in existing facilities.

Identification of ammonium source for groundwater in the piedmont zone with strong runoff of the Hohhot Basin based on nitrogen isotope.

Groundwater with high ammonium concentration (HANC groundwater), mostly caused by anthropogenic pollution, is widely distributed in China, which could also result from natural geological genesis. Groundwater in the piedmont zone with strong runoff in the central Hohhot Basin has featured its excessive ammonium concentration since the 1970s. Currently, chemical factories also serve as potential pollution sources. In this study, based on the nitrogen isotopic technique and combined with hydrochemical methods, the sources of high concentration ammonium in the groundwater was identified. The HANC groundwater is mainly distributed in the alluvial-proluvial fan and the interfan depression in the western and central parts of the study area, and a maximum ammonium concentration of 529.32 mg/L was observed in the groundwater in the mid-fan of the Baishitou Gully (BSTG) alluvial-proluvial fan. Although the BSTG mid-fan is part of the piedmont zone with strong runoff, some of the HANC groundwater in this area still presents the typical hydrochemical characteristics in the discharge area. Moreover, an extremely high concentration of volatile organic compounds was observed in groundwater in the BSTG alluvial-proluvial fan, which indicated significant anthropogenic pollution. Besides, 15N-NH4+ is enriched in groundwater in the BSTG root-fan and the interfan depression, which is consistent with the situation of organic nitrogen and exchangeable ammonium in natural sediments, as well as the natural HANC groundwater in other regions of China. These δ15N-NH4+ values indicate that the ammonium of the groundwater in the BSTG root-fan and the interfan depression is derived from natural sediments. The 15N-NH4+ in groundwater is depleted in the BSTG mid-fan, and the δ15N-NH4+ values are similar with those of the pollution sources from the chemical factories in the mid-fan. Both hydrochemical and nitrogen isotopic characteristics indicate significant pollution in the mid-fan, but the ammonium pollution is limited to the area near the chemical factories.

Modulating and optimizing Pluronic F-68 concentrations and feeding for intensified perfusion Chinese hamster ovary cell cultures.

Perfusion culture is often performed with micro-sparger to fulfill the high oxygen demand from the densified cells. Protective additive Pluronic F-68 (PF-68) is widely used to mitigate the adverse effect in cell viability from micro-sparging. In this study, different PF-68 retention ratio in alternating tangential filtration (ATF) columns was found to be crucial for cell performance of different perfusion culture modes. The PF-68 in the perfusion medium was found retained inside the bioreactor when exchanged through ATF hollow fibers with a small pore size (50 kD). The accumulated PF-68 could provide sufficient protection for cells under micro-sparging. On the other hand, with large-pore-size (0.2 µm) hollow fibers, PF-68 could pass through the ATF filtration membranes with little retention, and consequently led to compromised cell growth. To overcome the defect, a PF-68 feeding strategy was designed and successfully verified on promoting cell growth with different Chinese hamster ovary (CHO) cell lines. With PF-68 feeding, enhancements were observed in both viable cell densities (20%-30%) and productivity (~30%). A threshold PF-68 concentration of 5 g/L for high-density cell culture (up to 100 × 106 cells/mL) was also proposed and verified. The additional PF-68 feeding was not observed to affect product qualities. By designing the PF-68 concentration of perfusion medium to or higher than the threshold level, a similar cell growth enhancement was also achieved. This study systematically investigated the protecting role of PF-68 in intensified CHO cell cultures, shedding a light on the optimization of perfusion cultures through the control of protective additives.

Optimized process operations reduce product retention and column clogging in ATF-based perfusion cell cultures.

Product retention in hollow fibers is a common issue in ATF-based cell culture system. In this study, the effects of four major process factors on product (therapeutic antibody/recombinant protein) retention were investigated using Chinese hamster ovary cell. Hollow fibers made of polysulfone presented a product retention rate from 15% ± 8 to 43% ± 18% higher than those made of polyether sulfone varying with specific processes. Higher harvest flowrate and ATF exchange rate increased product retention by 13% ± 10% and up to 31% ± 13%, respectively. Hollow fibers with larger pore sizes (0.65 µm) appeared to have increased product retention by 38% ± 7% compared with smaller ones (0.2 µm) in this study. Further investigation revealed that the effects of pore size on retention could be correlated to the particle size distribution in the cell culture broth. A hollow fiber with a larger pore size (>0.5 µm) may reduce protein retention when small particles (approximately 0.01-0.2 µm in diameter) are dominant in the culture. However, if majority of the particles are larger than 0.2 µm in diameter, hollow fiber with smaller pore sizes (0.2 µm) could be a solution to reducing product retention. Alternatively, process optimization may modulate particle size distribution towards reduced production retention with selected ATF hollow fibers. This study for the first time highlights the importance of matching proper pore sizes of hollow fibers with the cell culture particles distribution and offers methods to reducing product retention and ATF column clogging in perfusion cell cultures. KEY POINTS: The material of ATF column could impact product retention during perfusion culture. Higher harvest flowrate and ATF exchange rate increased product retention. Matching culture particle size and ATF pore size is critical for retention modulation.

Fast interfacial charge transfer in α-Fe2O3-δCδ/FeVO4-x+δCx-δ@C bulk heterojunctions with controllable phase content.

The novelties in this paper are embodied in the fast interfacial charge transfer in α-Fe2O3-δCδ/FeVO4-x+δCx-δ@C bulk heterojunctions with controllable phase compositions. The carbon source-glucose plays an important role as the connecting bridge between the micelles in the solution, forming interfacial C-O, C-O-Fe and O-Fe-C bonds through dehydration and polymerization reactions. Then the extra VO3- around the FeVO4 colloidal particles can react with unstable Fe(OH)3, resulting the phase transformation from α-Fe2O3 (47.99-7.16%) into FeVO4 (52.01-92.84%), promoting photocarriers' generation capacities. After final carbonization, a part of C atoms enter into lattices of α-Fe2O3 and FeVO4, forming impurity levels and oxygen vacancies to increase effective light absorptions. Another part of C sources turn into interfacial carbon layers to bring fast charge transfer by decreasing the charge transition resistance (from 53.15 kΩ into 8.29 kΩ) and the surface recombination rate (from 64.07% into 7.59%). The results show that the bulk heterojunction with 90.29% FeVO4 and 9.71% α-Fe2O3 shows ideal light absorption, carriers' transfer efficiency and available photocatalytic property. In general, the synergistic effect of optimized heterojunction structure, carbon replacing and the interface carbon layers are critical to develop great potential in stable and recoverable use.

Scalable biocatalytic synthesis of optically pure ethyl (R)-2-hydroxy-4-phenylbutyrate using a recombinant E. coli with high catalyst yield.

Ethyl (R)-2-hydroxy-4-phenylbutanoate [(R)-HPBE] is a versatile and important chiral intermediate for the synthesis of angiotensin-converting enzyme (ACE) inhibitors. Recombinant E. coli strain coexpressing a novel NADPH-dependent carbonyl reductase gene iolS and glucose dehydrogenase gene gdh from Bacillus subtilis showed excellent catalytic activity in (R)-HPBE production by asymmetric reduction. IolS exhibited high stereoselectivity (>98.5% ee) toward α-ketoesters substrates, whereas fluctuant ee values (53.2-99.5%) for ß-ketoesters with different halogen substitution groups. Strategies including aqueous/organic biphasic system and substrate fed-batch were adopted to improve the biocatalytic process. In a 1-L aqueous/octanol biphasic reaction system, (R)-HPBE was produced in 99.5% ee with an exceptional catalyst yield (g product/g catalyst) of 31.7 via bioreduction of ethyl 2-oxo-4-phenylbutyrate (OPBE) at 330 g/L.

[Diagnosis value of nasopharyngo-fiberscope and CT for microfocal nasopharyngeal carcinoma].

OBJECTIVE: To explore the value of nasopharyngo-fiberscope and CT in diagnosing microfocal Nasopharyngeal Carcinoma (NPC) and the prevalent area, the nasopharynx, where the NPC usually initially developed from. METHOD: From October, 2003 to October,2005, the data of original microfocus of 36 pathologically confirmed NPC were reviewed retrospectively. These cases were examined by nasopharyngo-fiberscope and CT strengthening scanning. RESULT: On clinical examination, only 2 cases (5.6%) were found to have original micro-tumor in the recess, the other 34 cases (94.4%) had developed from the other regions including 25 (69.4%) from the roof and 9 cases (25.0%) from the posterior wall, all with smooth and symmetrical mucosa in the recess. Positive rate of nasopharyngeal mass were 100% by nasopharyngo-fiberscope and by CT. CONCLUSION: The data suggested that the roof of nasopharyngeal cavity be the most possible area that the original NPC micro-focus developed from, followed by the posterior wall and the recess. Nasopharyngo-fiberscope and CT is very helpful for the correct clinical diagnosis of NPC.