Facilitating Hot Electron Injection from Graphene to Semiconductor by Rectifying Contact for Vis-NIR-Driven H2 O2 Production.

Solar-driven production of hydrogen peroxide (H2 O2 ), as an important industrial chemical oxidant with an extensive range of applications, from oxygen reduction is a sustainable alternative to mainstream anthraquinone oxidation and direct hydrogenation of dioxygen methods. The efficiency of solar to hydrogen peroxide over semiconductor-based photocatalysts is still largely limited by the narrow light absorption to visible light. Here, the authors proposed and demonstrate the proof-of-concept application of light-generated hot electrons in a graphene/semiconductor (exemplified with widely used TiO2 ) dyad to largely extend visible light spectra up to 800 nm for efficient H2 O2 production. The well-designed graphene/semiconductor heterojunction has a rectifying interface with a zero barrier for the hot electron injection, largely boosting excited hot electrons with an average lifetime of ≈0.5 ps into charge carriers with a long fluorescent lifetime (4.0 ns) for subsequent H2 O2 production. The optimized dyadic photocatalyst can provide an H2 O2 yield of 0.67 mm g-1  h-1 under visible light irradiation (λ ≥ 400 nm), which is 20 times of the state-of-the-art noble-metal-free titanium oxide-based photocatalyst, and even achieves an H2 O2 yield of 0.14 mm g-1  h-1 upon photoexcitation by near-infrared-region light (≈800 nm).

Light-driven Oxidative Demethylation Reaction Catalyzed by a Rieske-type Non-heme Iron Enzyme Stc2.

Rieske-type non-heme iron oxygenases/oxidases catalyze a wide range of transformations. Their applications in bioremediation or biocatalysis face two key barriers: the need of expensive NAD(P)H as a reductant and a proper reductase to mediate the electron transfer from NAD(P)H to the oxygenases. To bypass the need of both the reductase and NAD(P)H, using Rieske-type oxygenase (Stc2) catalyzed oxidative demethylation as the model system, we report Stc2 photocatalysis using eosin Y/sulfite as the photosensitizer/sacrificial reagent pair. In a flow-chemistry setting to separate the photo-reduction half-reaction and oxidation half-reaction, Stc2 photo-biocatalysis outperforms the Stc2-NAD(P)H-reductase (GbcB) system. In addition, in a few other selected Rieske enzymes (NdmA, CntA, and GbcA), and a flavin-dependent enzyme (iodotyrosine deiodinase, IYD), the eosin Y/sodium sulfite photo-reduction pair could also serve as the NAD(P)H-reductase surrogate to support catalysis, which implies the potential applicability of this photo-reduction system to other redox enzymes.

Proofreading and DNA Repair Assay Using Single Nucleotide Extension and MALDI-TOF Mass Spectrometry Analysis.

The maintenance of the genome and its faithful replication is paramount for conserving genetic information. To assess high fidelity replication, we have developed a simple non-labeled and non-radio-isotopic method using a matrix-assisted laser desorption ionization with time-of-flight (MALDI-TOF) mass spectrometry (MS) analysis for a proofreading study. Here, a DNA polymerase [e.g., the Klenow fragment (KF) of Escherichia coli DNA polymerase I (pol I) in this study] in the presence of all four dideoxyribonucleotide triphosphates is used to process a mismatched primer-template duplex. The mismatched primer is then proofread/extended and subjected to MALDI-TOF MS. The products are distinguished by the mass change of the primer down to single nucleotide variations. Importantly, a proofreading can also be determined for internal single mismatches, albeit at different efficiencies. Mismatches located at 2-4-nucleotides (nt) from the 3' end were efficiently proofread by pol I, and a mismatch at 5 nt from the primer terminus showed only a partial correction. No proofreading occurred for internal mismatches located at 6 - 9 nt from the primer 3' end. This method can also be applied to DNA repair assays (e.g., assessing a base-lesion repair of substrates for the endo V repair pathway). Primers containing 3' penultimate deoxyinosine (dI) lesions could be corrected by pol I. Indeed, penultimate T-I, G-I, and A-I substrates had their last 2 dI-containing nucleotides excised by pol I before adding a correct ddN 5'-monophosphate (ddNMP) while penultimate C-I mismatches were tolerated by pol I, allowing the primer to be extended without repair, demonstrating the sensitivity and resolution of the MS assay to measure DNA repair.

Application of single nucleotide extension and MALDI-TOF mass spectrometry in proofreading and DNA repair assay.

Proofreading and DNA repair are important factors in maintaining the high fidelity of genetic information during DNA replication. Herein, we designed a non-labeled and non-radio-isotopic simple method to measure proofreading. An oligonucleotide primer is annealed to a template DNA forming a mismatched site and is proofread by Klenow fragment of Escherichia coli DNA polymerase I (pol I) in the presence of all four dideoxyribonucleotide triphosphates. The proofreading excision products and re-synthesis products of single nucleotide extension are subjected to MALDI-TOF mass spectrometry (MS). The proofreading at the mismatched site is identified by the mass change of the primer. We examined proofreading of Klenow fragment with DNAs containing various base mismatches. Single mismatches at the primer terminus can be proofread efficiently. Internal single mismatches can also be proofread at different efficiencies, with the best correction for mismatches located 2-4-nucleotides from the primer terminus. For mismatches located 5-nucleotides from the primer terminus there was partial correction and extension. No significant proofreading was observed for mismatches located 6-9-nucleotides from the primer terminus. We also subjected primers containing 3' penultimate deoxyinosine (dI) lesions, which mimic endonuclease V nicked repair intermediates, to pol I repair assay. The results showed that T-I was a better substrate than G-I and A-I, however C-I was refractory to repair. The high resolution of MS results clearly demonstrated that all the penultimate T-I, G-I and A-I substrates had been excised last 2 dI-containing nucleotides by pol I before adding a correct ddNMP, however, pol I proofreading exonuclease tolerated the penultimate C-I mismatch allowing the primer to be extended by polymerase activity.

Three new anthraquinones from the twigs of Cassia fistula and their bioactivities.

Three previously unreported anthraquinones, fistulaquinones A-C (1-3), together with three known ones (4-6) were isolated from the twigs of Cassia fistula. Their structures were determined by means of extensive NMR and MS spectroscopic analyses. All the isolated compounds were tested for their anti-tobacco mosaic virus (anti-TMV) activity, and compound 3 showed significant activity with inhibition rate of 34.5% at 20 µM concentration, even more potent than positive control. Additionally, compounds 1-6 exhibited moderate cytotoxicity with IC50 values ranging from 2.8 to 9.4 µM for some tested human tumor cell lines.

Mariniluteicoccus endophyticus sp. nov., an endophytic actinobacterium isolated from root of Ocimum basilicum.

Two strains of Gram-stain-positive, aerobic, non-motile, irregular coccus-shaped bacteria, designated YIM 2617T and YIM 2617-2, were isolated from the root of Ocimum basilicum. Phylogenetic analysis on the basis of 16S rRNA gene sequence comparison revealed that the two strains were closely related to Mariniluteicoccus flavus YIM M13146T (98.1 and 98.0 % similarities, respectively) and formed a robust clade with M. flavus in the neighbour-joining tree. Optimum growth of the strains was observed at 28-32 °C, at pH 7.0-8.0 and in the presence of 0-2 % (w/v) NaCl. The chemotaxonomic profiles of the strains comprised anteiso-C15 : 0 as the major cellular fatty acid, MK-9(H4) as the predominant menaquinone, alanine, glycine, glutamic acid and ll-diaminopimelic acid as peptidoglycan components, and phosphatidylcholine and diphosphatidylglycerol as the major polar lipids. The G+C contents of the genomic DNA of strains YIM 2617T and YIM 2617-2 were 66.4 and 66.6 mol%, respectively. DNA-DNA hybridizations of the two strains with M. flavus YIM M13146T gave mean relatedness values of 47.6 ± 2.0 and 43.2 ± 1.5 %, respectively, while the relatedness value between them was 92.1 ± 2.2 %. On the basis of the data recorded from the present study, strains YIM 2617T and YIM 2617-2 represent a novel species of the genus Mariniluteicoccus, for which the name Mariniluteicoccus endophyticus sp. nov. is proposed. The type strain is YIM 2617T ( = KCTC 29482T = DSM 28728T = JCM 30097T).

An antialgal compound produced by Streptomyces jiujiangensis JXJ 0074(T).

Previous investigations suggested that Streptomyces jiujiangensis JXJ 0074(T) can secrete antialgal compounds. In this study, an antialgal compound was isolated from the cultured broth of S. jiujiangensis JXJ 0074(T) by using bioassay methods. Based on spectroscopic data, the active compound was identified as 2'-deoxyadenosine, which exhibited a greater antialgal activity against cyanobacteria than its analogues such as adenosine, guanosine, and 2'-deoxyguanosine. The antialgal activity of 2'-deoxyadenosine increased with the content and time. 2'-Deoxyadenosine severely damaged the vegetative cells of cyanobacteria, causing crumpling, collapse, expanding, perforation, breakage of filamentous cyanobacteria, and decrease of the chlorophyll. However, 2'-deoxyadenosine seemed to have less impact on the morphology of heterocysts of filamentous cyanobacteria. The superoxide dismutase (SOD) activity in the treated cells of M. aeruginosa FACHB-905 initially increased with 31.14 ± 2.00% higher than that of the control after 36 h and then decreased quickly. On the same time, there were rapid increases in superoxide anion radical (O2 (-)) and malondialdehyde (MDA) contents with 315.53 ± 12.81 and 84.72 ± 6.15% higher than these of the controls at 60 h, respectively. The intracellular microcystin-LR (MC-LR) content in the treated cells of M. aeruginosa FACHB-905 increased by 36.34 ± 7.35% 1 day later, followed by a rapid decrease with a rate of 90.50 ± 1.08% 8 days later, while the extracellular MC-LR content showed no significant difference with the control. Five days after adding 15 µg/ml of 2'-deoxyadenosine to the culture of M. aeruginosa FACHB-905, there was no 2'-deoxyadenosine detected by HPLC, suggesting that 2'-deoxyadenosine completely degraded. This study provides a new clue to screen natural-based antialgal compounds from nucleoside analogues.