Infrared Spectroscopic Observation of Oxo- and Superoxo-Intermediates in the Water Oxidation Cycle of a Molecular Ir Catalyst.

Molecular Ir catalysts have emerged as an important class of model catalysts for understanding structure-activity relationships in water oxidation, a reaction that is central to renewable fuel synthesis. Prior efforts have mostly focused on controlling and elucidating the emergence of active species from prepared precursors. However, the development of efficient and stable molecular Ir catalysts also necessitates probing of reaction intermediates. To date, relatively little is known about the key intermediates in the cycles of the molecular Ir catalysts. Herein, we probed the catalytic cycle of a homogeneous Ir catalyst ("blue dimer") at a Au electrode/aqueous electrolyte interface by combining surface-enhanced infrared absorption spectroscopy (SEIRAS) with phase-sensitive detection (PSD). Cyclic voltammograms (CVs) from 1.4 to 1.7 VRHE (RHE = reversible hydrogen electrode) give rise to a band at ∼818 cm-1, whereas CVs from 1.4 to ≥1.85 VRHE generate an additional band at ∼1146 cm-1. Isotope labeling experiments indicate that the bands at ∼818 and ∼1146 cm-1 are attributable to oxo (IrV═O) and superoxo (IrIV-OO•) moieties, respectively. This study establishes PSD-SEIRAS as a sensitive tool for probing water oxidation cycles at electrode/electrolyte interfaces and demonstrates that the relative abundance of two key intermediates can be tuned by the thermodynamic driving force of the reaction.

Highly Selective Electrochemical Baeyer-Villiger Oxidation through Oxygen Atom Transfer from Water.

The Baeyer-Villiger oxidation of ketones is a crucial oxygen atom transfer (OAT) process used for ester production. Traditionally, Baeyer-Villiger oxidation is accomplished by thermally oxidizing the OAT from stoichiometric peroxides, which are often difficult to handle. Electrochemical methods hold promise for breaking the limitation of using water as the oxygen atom source. Nevertheless, existing demonstrations of electrochemical Baeyer-Villiger oxidation face the challenges of low selectivity. We report in this study a strategy to overcome this challenge. By employing a well-known water oxidation catalyst, Fe2O3, we achieved nearly perfect selectivity for the electrochemical Baeyer-Villiger oxidation of cyclohexanone. Mechanistic studies suggest that it is essential to produce surface hydroperoxo intermediates (M-OOH, where M represents a metal center) that promote the nucleophilic attack on ketone substrates. By confining the reactions to the catalyst surfaces, competing reactions (e.g., dehydrogenation, carboxylic acid cation rearrangements, and hydroxylation) are greatly limited, thereby offering high selectivity. The surface-initiated nature of the reaction is confirmed by kinetic studies and spectroelectrochemical characterizations. This discovery adds nucleophilic oxidation to the toolbox of electrochemical organic synthesis.

Exploring Prenatal Exposure to Halogenated Compounds and Its Relationship with Birth Outcomes Using Nontarget Analysis.

Halogenated organic compounds (HOCs) are a class of contaminants showing high toxicity, low biodegradability, and high bioaccumulation potential, especially chlorinated and brominated HOCs (Cl/Br-HOCs). Knowledge gaps exist on whether novel Cl/Br-HOCs could penetrate the placental barrier and cause adverse birth outcomes. Herein, 326 cord blood samples were collected in a hospital in Jinan, Shandong Province from February 2017 to January 2022, and 44 Cl/Br-HOCs were identified with communicating confidence level above 4 based on a nontarget approach, covering veterinary drugs, pesticides, and their transformation products, pharmaceutical and personal care products, disinfection byproducts, and so on. To our knowledge, the presence of closantel, bromoxynil, 4-hydroxy-2,5,6-trichloroisophthalonitrile, 2,6-dibromo-4-nitrophenol, and related components in cord blood samples was reported for the first time. Both multiple linear regression (MLR) and Bayesian kernel machine regression (BKMR) models were applied to evaluate the relationships of newborn birth outcomes (birth weight, length, and ponderal index) with individual Cl/Br-HOC and Cl/Br-HOCs mixture exposure, respectively. A significantly negative association was observed between pentachlorophenol exposure and newborn birth length, but the significance vanished after the false discovery rate correction. The BKMR analysis showed that Cl/Br-HOCs mixture exposure was significantly associated with reduced newborn birth length, indicating higher risks of fetal growth restriction. Our findings offer an overview of Cl/Br-HOCs exposome during the early life stage and enhance the understanding of its exposure risks.

Selective Formation of Acetic Acid and Methanol by Direct Methane Oxidation Using Rhodium Single-Atom Catalysts.

Atomically dispersed catalysts such as single-atom catalysts have been shown to be effective in selectively oxidizing methane, promising a direct synthetic route to value-added oxygenates such as acetic acid or methanol. However, an important challenge of this approach has been that the loading of active sites by single-atom catalysts is low, leading to a low overall yield of the products. Here, we report an approach that can address this issue. It utilizes a metal-organic framework built with porphyrin as the linker, which provides high concentrations of binding sites to support atomically dispersed rhodium. It is shown that up to 5 wt% rhodium loading can be achieved with excellent dispersity. When used for acetic acid synthesis by methane oxidation, a new benchmark performance of 23.62 mmol·gcat-1·h-1 was measured. Furthermore, the catalyst exhibits a unique sensitivity to light, producing acetic acid (under illumination, up to 66.4% selectivity) or methanol (in the dark, up to 65.0% selectivity) under otherwise identical reaction conditions.

Genome-wide identification and characterization of the BBX gene family in pineapple reveals that candidate genes are involved in floral induction and flowering.

B-box zinc finger proteins contain one or two B-box domains, and sometimes, a CCT domain, which are involved in many biological processes, such as photomorphogenesis, flowering, anthocyanin synthesis and abiotic stress resistance. But the BBX gene family in pineapple has not been systematically studied. Nineteen BBX genes were detected in pineapple genome and divided into five groups according to phylogenetic analysis. The results of transcriptome analysis and RT-qPCR showed that most of AcBBX members were highly expressed during the flowering process, indicating that AcBBX gene may be involved in flower bud differentiation and morphogenesis. Transcriptional activation analysis showed that AcBBX6 and AcBBX18 had transcriptional activity and were located in the nucleus. Overexpression of AcBBX18 promoted flowering in Arabidopsis thaliana. These results provided a basis for further study functions and regulatory mechanism of BBX members in pineapple floral induction and flower development.

Methane Carboxylation Using Electrochemically Activated Carbon Dioxide.

Direct synthesis of CH3 COOH from CH4 and CO2 is an appealing approach for the utilization of two potent greenhouse gases that are notoriously difficult to activate. In this Communication, we report an integrated route to enable this reaction. Recognizing the thermodynamic stability of CO2 , our strategy sought to first activate CO2 to produce CO (through electrochemical CO2 reduction) and O2 (through water oxidation), followed by oxidative CH4 carbonylation catalyzed by Rh single atom catalysts supported on zeolite. The net result was CH4 carboxylation with 100 % atom economy. CH3 COOH was obtained at a high selectivity (>80 %) and good yield (ca. 3.2 mmol g-1 cat in 3 h). Isotope labelling experiments confirmed that CH3 COOH is produced through the coupling of CH4 and CO2 . This work represents the first successful integration of CO/O2 production with oxidative carbonylation reaction. The result is expected to inspire more carboxylation reactions utilizing preactivated CO2 that take advantage of both products from the reduction and oxidation processes, thus achieving high atom efficiency in the synthesis.

Three-Dimensional Mass Spectrometry Imaging Reveals Distributions of Lipids and the Drug Metabolite Associated with the Enhanced Growth of Colon Cancer Cell Spheroids Treated with Triclosan.

The application of mass spectrometry imaging (MSI) to explore the responses of cancer cell spheroids (CCS) after treatment of exogenous molecules has attracted growing attention. Increasing studies have utilized MSI to image the two-dimensional distributions of exogenous and endogenous molecules in planar CCS sections. However, because CCS are volumetric and heterogenous, maintaining their three-dimensional (3D) information is essential for acquiring a better understanding of the tumor microenvironment and mechanisms of action of exogenous molecules. Here, an established method of 3D MSI was applied to distinguish the distributions of triclosan sulfate and endogenous lipids in three microregions of colon CCS with an enhanced growth induced by the treatment of triclosan, a common antimicrobial agent. The results of 3D MSI showed that triclosan sulfate gradually accumulated from the periphery to the entire structure of CCS and finally localized in the core region. Spatial lipidomics analysis revealed that the upregulated phosphatidylethanolamine (fold change (FD) = 1.26, p = 0.0021), phosphatidylinositol (FD = 1.17, p = 0.0180), and phosphatidylcholine (FD = 1.22, p = 0.0178) species mainly distributed in the outer proliferative region, while the upregulated sphingomyelin (FD = 1.18, p = 0.024) species tended to distribute in the inner necrotic region. Our results suggest that a competitive mechanism between inhibiting and promoting CCS growth might be responsible for the proliferation of CCS treated with triclosan.

Metabolomics Reveal Nanoplastic-Induced Mitochondrial Damage in Human Liver and Lung Cells.

Plastic debris in the global biosphere is an increasing concern, and nanoplastic (NPs) toxicity in humans is far from being understood. Studies have indicated that NPs can affect mitochondria, but the underlying mechanisms remain unclear. The liver and lungs have important metabolic functions and are vulnerable to NP exposure. In this study, we investigated the effects of 80 nm NPs on mitochondrial functions and metabolic pathways in normal human hepatic (L02) cells and lung (BEAS-2B) cells. NP exposure did not induce mass cell death; however, transmission electron microscopy analysis showed that the NPs could enter the cells and cause mitochondrial damage, as evidenced by overproduction of mitochondrial reactive oxygen species, alterations in the mitochondrial membrane potential, and suppression of mitochondrial respiration. These alterations were observed at NP concentrations as low as 0.0125 mg/mL, which might be comparable to the environmental levels. Nontarget metabolomics confirmed that the most significantly impacted processes were mitochondrial-related. The metabolic function of L02 cells was more vulnerable to NP exposure than that of BEAS-2B cells, especially at low NP concentrations. This study identifies NP-induced mitochondrial dysfunction and metabolic toxicity pathways in target human cells, providing insight into the possibility of adverse outcomes in human health.

Physical Characterization, Nutrient, Phenolic Profiles and Antioxidant Activities of 16 litchi Cultivars Grown in the Upper Yangtze River Region.

Litchi grown in the upper Yangtze River region have the advantage of being late-maturing owing to the geographical location. This study aimed to evaluate the physical characteristics, nutritional values, phenolic composition and antioxidant activities of 16 litchi cultivars grown in the upper Yangtze River region. Litchi grown in this region had total soluble solid and ascorbic acid contents comparable with those of cultivars grown in other locations. The total polyphenol contents were determined using the Folin-Ciocalteu assay, and the phenolic profiles were determined using UPLC-QqQ-MS/MS. Nine phenolic compounds were identified and quantified in this study. Naringin, rutin and p-coumaric acid were the major phenolic compounds in all the litchi cultivars. Statistical analysis of all the physiochemical results was performed using principal component analysis. Our results indicated that litchi grown in the upper Yangtze River region not only showed the late-maturity characteristic but were also good dietary sources of phenolic compounds and antioxidants. In particular, 'Fei Zi Xiao' and 'Jing Gang Hong Nuo', characterized by high polyphenol contents and high antioxidant capacities, were of superior comprehensive quality. This study provides important information for the development of late-maturing litchi industry.

Genome-wide analysis of AP2/ERF transcription factors in pineapple reveals functional divergence during flowering induction mediated by ethylene and floral organ development.

The APETALA2/ethylene-responsive factor (AP2/ERF) has important roles in regulating developmental processes and hormone signaling transduction in plants. Pineapple demonstrates a special sensitivity to ethylene, and AP2/ERFs may contribute to this distinct sensitivity of pineapples to ethylene. However, little information is available on the AP2/ERF of pineapple. In this study, 97 AP2/ERF family members were identified from the pineapple genome. The AcAP2/ERF superfamily could be further divided into five subfamilies, and different subfamily existed functional divergence in multifarious biological processes. ERF and RAV subfamily genes might play important roles in the process of ethylene response of pineapple; ERF and DREB subfamily genes had particular functions in the floral organ development. This study is the first to provide detailed information on the features of AP2/ERFs in pineapple, provide new insights into the potential functional roles of the AP2/ERF superfamily members, and will facilitate a better understanding of the molecular mechanism of flower in pineapple.

Incorporating MOOC and COVID-19-Related Scientific Papers into Veterinary Microbiology Teaching to Enhance Students' Learning Performance and Professional Recognition.

The COVID-19 pandemic has exerted a huge adverse influence on global teaching activities and students' psychological status. Veterinary microbiology is mainly concerned with bacterial and viral diseases, including coronavirus diseases. An innovative online-to-offline teaching approach for this course was established to stimulate students' learning initiative and mitigate their anxiety about COVID-19. A well-established massive open online course (MOOC) was first adopted as preview material before class, followed by in-person teaching. Additionally, COVID-19-related scientific papers were also used as pre-class reading material in veterinary microbiology and were further explained in class. The effect of this innovative teaching mode was systematically evaluated by final examination scores and questionnaires. The average score (81.75) and excellence score rating (> 85 scores, 37.3%) resulting from this blended teaching mode were not statistically higher than those of the online-only (79.19, p = .115; 28.6%, p = .317) or offline-only (79.47, p = .151; 27.9%, p = .269) teaching modes. This may be due to the sample size investigated; however, the results indicate that the innovative teaching mode did not decrease teaching quality. Additionally, most subjects (72.9%) were satisfied with the blended mode and supported its future use. Intriguingly, the introduction of COVID-19-related scientific papers helped students understand virology, relieve their anxiety, and increase their professional identity. Collectively, the innovative approach to teaching veterinary microbiology in this study provides a beneficial reference for other teachers to maintain and improve teaching quality.

Simultaneous determination of triclosan, triclocarban, triclocarban metabolites and byproducts in urine and serum by ultra-high-performance liquid chromatography/electrospray ionization tandem mass spectrometry.

RATIONALE: Triclosan (TCS) and triclocarban (TCC) are ubiquitous antimicrobial agents incorporated in consumer and personal care products. Due to their human health risks, it is essential to develop a sensitive and accurate analytical method to simultaneously quantify TCS, TCC, as well as their metabolites and byproducts in urine and serum samples. METHODS: The quantitative parameters of TCS, TCC, TCC metabolites and byproducts (2'-OH-TCC, 3'-OH-TCC, 6-OH-TCC, DHC, DCC, NCC) were optimized by using ultra-high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (UHPLC/ESI-MS/MS). Enzymatic hydrolysis of the samples was optimized based on enzyme dosage and incubation time. The efficiencies of solid-phase extraction (SPE) and liquid-liquid extraction (LLE) were compared. The effectiveness of the established method was evaluated, and method application was validated using real urine and serum samples. RESULTS: The conjugates were sufficiently hydrolyzed under 500 U/mL ß-glucuronidase and 80 U/mL sulfatase at 37°C for 4 h. Compared with the LLE method, SPE achieved higher extraction efficiency in both urine and serum samples. The optimized SPE-UHPLC/ESI-MS/MS method showed low limits of detection (LODs) in the range 0.001-0.3 ng/mL and good linearity (R2 > 0.99) at 0.01-150 ng/mL in both matrices. Excellent recoveries of 82.0%-120.7% (urine) and 76.7%-113.9% (serum) were obtained with low relative standard deviation (RSD, <7.6%) for inter-day and intra-day injections. This method was applicable to quantify target compounds in multiple biological urine and serum samples. Notably, TCS and TCC were detected with average concentrations of 8.37 and 10.46 ng/mL, respectively, in 15 Chinese female urine samples, with the simultaneous detection of TCC metabolites and byproducts. CONCLUSIONS: A reliable method was established to simultaneously determine TCS, TCC, TCC metabolites and byproducts in urine and serum samples by using UHPLC/ESI-MS/MS. This sensitive methodology provides the basis for the evaluation of TCS and TCC exposure at the metabolic level.

Continuous Dermal Exposure to Triclocarban Perturbs the Homeostasis of Liver-Gut Axis in Mice: Insights from Metabolic Interactions and Microbiome Shifts.

Humans are constantly exposed to antimicrobial triclocarban (TCC) via direct skin contact with personal care and consumer products, but the safety of long-term dermal exposure to TCC remains largely unknown. Herein, we used a mouse model to evaluate the potential health risks from the continuous dermal application of TCC at human-relevant concentrations. After percutaneous absorption, TCC circulated in the bloodstream and largely entered the liver-gut axis for metabolic disposition. Nontargeted metabolomics approach revealed that TCC exposure perturbed mouse liver homeostasis, as evidenced by the increased oxidative stress and impaired methylation capacity, leading to oxidative damage and enhancement of upstream glycolysis and folate-dependent one-carbon metabolism. Meanwhile, TCC was transformed in the liver through hydroxylation, dechlorination, methylation, glucuronidation, sulfation, and glutathione conjugation. TCC-derived xenobiotics were subsequently excreted into the gut, and glucuronide and sulfate metabolites could be further deconjugated by the gut microbiota into their active free forms. In addition, microbial community analysis showed that the composition of gut microbiome was altered in response to TCC exposure, indicating the perturbation of gut homeostasis. Together, through tracking the xenobiotic-biological interactions in vivo, this study provides novel insights into the underlying impacts of dermally absorbed TCC on the liver and gut microenvironments.

Numerical Study on the Characteristics of Boger Type Viscoelastic Fluid Flow in a Micro Cross-Slot under Sinusoidal Stimulation.

The cross-slot geometry plays an important role in the study of nonlinear effects of viscoelastic fluids. The flow of viscoelastic fluid in a micro cross-slot with a high channel aspect ratio (AR, the ratio of channel depth to width) can be divided into three types, which are symmetric flow, steady-state asymmetric flow and time-dependent flow under the inlet condition with a constant velocity. However, the flow pattern of a viscoelastic fluid in the cross-slot when a stimulation is applied at inlets has been rarely reported. In this paper, the response of cross-slot flow under an external sinusoidal stimulation is studied by numerical simulations of a two-dimensional model representing the geometry with a maximum limit of AR. For the cases under constant inlet velocity conditions, three different flow patterns occur successively with the increase of Weissenberg number (Wi). For the cases under sinusoidal varying inlet velocity conditions, when the stimulation frequency is far away from the natural frequency of a viscoelastic fluid, the frequency spectrum of velocity fluctuation field shows the characteristics of a fundamental frequency and several harmonics. However, the harmonic frequency disappears when the stimulation frequency is close to the natural frequency of the viscoelastic fluid. Besides, the flow pattern shows spatial symmetry and changes with time. In conclusion, the external stimulation has an effect on the flow pattern of viscoelastic fluid in the 2D micro cross-slot channel, and a resonance occurs when the stimulation frequency is close to the natural frequency of the fluid.

A numerical study on viscoelastic droplet migration on a solid substrate due to wettability gradient.

This study investigates the viscoelastic effects on droplet migration induced by a wettability gradient on a rigid substrate by a numerical simulation based on OpenFOAM with the volume-of-fluid method. The droplets are set with different rheological properties to investigate the effect of the elastic parameters. The Oldroyd-B model was employed. Quantitative differences in the migration and deformation between Newtonian and viscoelastic droplets were investigated by changing the degree of elasticity. The droplet migration shows conspicuously higher mobility for high elasticity, especially during the accelerating period. Moreover, the displacement and velocity increased with the decrease of a viscoelasticity parameter, and the velocity enhancement was regulated by the elastic instability shown at a high Weissenberg number. In addition, the velocity of the droplet changes more significantly over the range of contact angles of 130° to 60° compared to other wettability-gradient surfaces.

Integration of Metabolomics and Lipidomics Reveals Metabolic Mechanisms of Triclosan-Induced Toxicity in Human Hepatocytes.

Triclosan (TCS), an extensively used antimicrobial agent, has raised considerable concern due to its hepatocarcinogenic potential. However, previous hepatotoxicity studies primarily focused on the activation of specific intracellular receptors, the underlying mechanisms still warrant further investigation at the metabolic level. Herein, we applied metabolomics in combination with lipidomics to unveil TCS-related metabolic responses in human normal and cancerous hepatocytes. Endogenous and exogenous metabolites were analyzed for the identification of metabolic biomarkers and biotransformation products. In L02 normal cells, TCS exposure induced the up-regulation of purine metabolism and amino acid metabolism, caused lipid accumulation, and disturbed energy metabolism. These metabolic disorders in turn enhanced the overproduction of reactive oxygen species (ROS), leading to the alteration of antioxidant enzyme activities, down-regulation of endogenous antioxidants, and peroxidation of lipids. TCS-induced oxidative stress is thus considered to be one crucial factor for hepatotoxicity. However, in HepG2 cancer cells, TCS underwent fast detoxification through phase II metabolism, accompanied by the enhancement of energy metabolism and elevation of antioxidant defense system, which contributed to the potential effects of TCS on human hepatocellular carcinoma development. These different responses of metabolism between normal and cancerous hepatocytes provide novel and robust perspectives for revealing the mechanisms of TCS-triggered hepatotoxicity.

Rate-Limiting O-O Bond Formation Pathways for Water Oxidation on Hematite Photoanode.

Photoelectrochemical (PEC) water oxidation has attracted heightened interest in solar fuel production. It is well accepted that water oxidation on hematite is mediated by surface trapped holes, characterized to be the high valent -Fe═O species. However, the mechanism of the subsequent rate-limiting O-O bond formation step is still a missing piece. Herein we investigate the reaction order of interfacial hole transfer by rate law analysis based on electrochemical impedance spectroscopy (EIS) measurement and probe the reaction intermediates by operando Fourier-transform infrared (FT-IR) spectroscopy. Distinct reaction orders of ∼1 and ∼2 were observed in near-neutral and highly alkaline environments, respectively. The unity rate law in near-neutral pH regions suggests a mechanism of water nucleophilic attack (WNA) to -Fe═O to form the O-O bond. Operando observation of a surface superoxide species that hydrogen bonded to the adjacent hydroxyl group by FT-IR further confirmed this pathway. In highly alkaline regions, coupling of adjacent surface trapped holes (I2M) becomes the dominant mechanism. While both are operable at intermediate pHs, mechanism switch from I2M to WNA induced by local pH decrease was observed at high photocurrent level. Our results highlight the significant impact of surface protonation on O-O bond formation pathways and oxygen evolution kinetics on hematite surfaces.

Transcriptome profiling of litchi leaves in response to low temperature reveals candidate regulatory genes and key metabolic events during floral induction.

BACKGROUND: Litchi (Litchi chinensis Sonn.) is an economically important evergreen fruit tree widely cultivated in subtropical areas. Low temperature is absolutely required for floral induction of litchi, but its molecular mechanism is not fully understood. Leaves of litchi played a key role during floral induction and could be the site of low temperature perception. Therefore, leaves were treated under different temperature (15 °C/25 °C), and high-throughput RNA sequencing (RNA-Seq) performed with leaf samples for the de novo assembly and digital gene expression (DGE) profiling analyses to investigate low temperature-induced gene expression changes. RESULTS: 83,107 RNA-Seq unigenes were de novo assembled with a mean length of 1221 bp and approximately 61% of these unigenes (50,345) were annotated against public protein databases. Differentially-expressed genes (DEGs) under low temperature treatment in comparison with the control group were the main focus of our study. Hierarchical clustering analysis arranged 2755 DEGs into eight groups with three significant expression clusters (p-value ≤ 0.05) during floral induction. With the increasing contents of sugars and starch, the expression of genes involved in metabolism of sugars increased dramatically after low temperature induction. One FT gene (Unigene0025396, LcFT1) which produces a protein called 'florigen' was also detected among DEGs of litchi. LcFT1 exhibited an apparent specific tissue and its expression was highly increased after low temperature induction, GUS staining results also showed GUS activity driven by LcFT1 gene promoter can be induced by low temperature, which indicated LcFT1 probably played a pivotal role in the floral induction of litchi under low temperature. CONCLUSIONS: Our study provides a global survey of transcriptomes to better understand the molecular mechanisms underlying changes of leaves in response to low temperature induction in litchi. The analyses of transcriptome profiles and physiological indicators will help us study the complicated metabolism of floral induction in the subtropic evergreen plants.

Transcriptional sequencing and analysis of major genes involved in the adventitious root formation of mango cotyledon segments.

MAIN CONCLUSION: A total of 74,745 unigenes were generated and 1975 DEGs were identified. Candidate genes that may be involved in the adventitious root formation of mango cotyledon segment were revealed. Adventitious root formation is a crucial step in plant vegetative propagation, but the molecular mechanism of adventitious root formation remains unclear. Adventitious roots formed only at the proximal cut surface (PCS) of mango cotyledon segments, whereas no roots were formed on the opposite, distal cut surface (DCS). To identify the transcript abundance changes linked to adventitious root development, RNA was isolated from PCS and DCS at 0, 4 and 7 days after culture, respectively. Illumina sequencing of libraries generated from these samples yielded 62.36 Gb high-quality reads that were assembled into 74,745 unigenes with an average sequence length of 807 base pairs, and 33,252 of the assembled unigenes at least had homologs in one of the public databases. Comparative analysis of these transcriptome databases revealed that between the different time points at PCS there were 1966 differentially expressed genes (DEGs), while there were only 51 DEGs for the PCS vs. DCS when time-matched samples were compared. Of these DEGs, 1636 were assigned to gene ontology (GO) classes, the majority of that was involved in cellular processes, metabolic processes and single-organism processes. Candidate genes that may be involved in the adventitious root formation of mango cotyledon segment are predicted to encode polar auxin transport carriers, auxin-regulated proteins, cell wall remodeling enzymes and ethylene-related proteins. In order to validate RNA-sequencing results, we further analyzed the expression profiles of 20 genes by quantitative real-time PCR. This study expands the transcriptome information for Mangifera indica and identifies candidate genes involved in adventitious root formation in cotyledon segments of mango.

Pivotal Role and Regulation of Proton Transfer in Water Oxidation on Hematite Photoanodes.

Hematite is a promising material for solar water splitting; however, high efficiency remains elusive because of the kinetic limitations of interfacial charge transfer. Here, we demonstrate the pivotal role of proton transfer in water oxidation on hematite photoanodes using photoelectrochemical (PEC) characterization, the H/D kinetic isotope effect (KIE), and electrochemical impedance spectroscopy (EIS). We observed a concerted proton-electron transfer (CPET) characteristic for the rate-determining interfacial hole transfer, where electron transfer (ET) from molecular water to a surface-trapped hole was accompanied by proton transfer (PT) to a solvent water molecule, demonstrating a substantial KIE (∼3.5). The temperature dependency of KIE revealed a highly flexible proton transfer channel along the hydrogen bond at the hematite/electrolyte interface. A mechanistic transition in the rate-determining step from CPET to ET occurred after OH(-) became the dominant hole acceptor. We further modified the proton-electron transfer sequence with appropriate proton acceptors (buffer bases) and achieved a greater than 4-fold increase in the PEC water oxidation efficiency on a hematite photoanode.