Substituent Effect on Ligand-Centered Electrocatalytic Hydrogen Evolution of Phosphorus Corroles.

There have been few reports on the substituent effect of main-group-element corrole complexes as ligand-centered homogeneous electrocatalysts for the hydrogen evolution reaction (HER). The key to comprehend the catalytic mechanism and develop efficient catalysts is the elucidation of the effects of electronic structure on the performance of energy-related small molecules. In this work, the "push-pull" electronic effect of the substituents on electrocatalytic HER of phosphorus corroles was investigated by using 5,10,15-tris(phenyl) corrole phosphorus (1P), 10-pentafluorophenyl-5,15-bis(phenyl) corrole phosphorus (2P), 10-phenyl-5,15-bis(pentafluorophenyl) corrole phosphorus (3P), 5,10,15-tris(pentafluorophenyl) corrole phosphorus (4P) complexes bearing hydroxyl axial ligands and different numbers of fluorine atoms on the meso-aryl substituents. The results revealed that the catalytic HER activity of phosphorus corroles decreased with the increasing of fluorine atom numbers, it follows in the order 1P>2P>3P>4P. Density functional theory (DFT) calculations show that the corrole 1P has the lowest free energy barrier in catalytic HER.

Non-Metallic Phosphorus Corrole as Efficient Electrocatalyst in Hydrogen Evolution Reaction.

The economical consideration of using an electrocatalyst in energy-related field, composed of non-precious/sustainable elements is quite noteworthy. In this work, the phosphorus(V) complex of tris-(pentafluorophenyl)corrole [(TPFC)PV (OH)2 ] was reported as electrocatalyst for the hydrogen evolution reaction (HER). The electrochemical studies revealed that the HER experienced a ECEC pathway (E: electron transfer step, C: chemical step), and the possible intermediate [PV ]-H species was suggested. (TPFC)PV (OH)2 displayed excellent HER activity in dimethylformamide (DMF) with trifluoroacetic acid (TFA) as the proton source, and the turnover frequency (TOF) reached 31.75 s-1 at an overpotential of 900 mV. Interestingly, the HER electrocatalytic performance remained extraordinary even applying water as a proton source in acetonitrile/water (v/v=2 : 3), with a TOF of 18.40 mol H 2 ${{_{{\rm H}{_{2}}}}}$ molcat -1 h-1 at an overpotential of 900 mV.

A yceI Gene Involves in the Adaptation of Ralstonia solanacearum to Methyl Gallate and Other Stresses.

Ralstonia solanacearum is a plant-pathogenic bacterium causing plant bacterial wilt, and can be strongly inhibited by methyl gallate (MG). Our previous transcriptome sequencing of MG-treated R. solanacearum showed that the yceI gene AVT05_RS03545 of Rs-T02 was up-regulated significantly under MG stress. In this study, a deletion mutant (named DM3545) and an over-expression strain (named OE3545) for yceI were constructed to confirm this hypothesis. No significant difference was observed among the growth of wild-type strain, DM3545 and OE3545 strains without MG treatment. Mutant DM3545 showed a lower growth ability than that of the wild type and OE3545 strains under MG treatment, non-optimal temperature, or 1% NaCl. The ability of DM3545 for rhizosphere colonization was lower than that of the wild-type and OE3545 strains. The DM3545 strain showed substantially reduced virulence toward tomato plants than its wild-type and OE3545 counterpart. Moreover, DM3545 was more sensitive to MG in plants than the wild-type and OE3545 strains. These results suggest that YceI is involved in the adaptability of R. solanacearum to the presence of MG and the effect of other tested abiotic stresses. This protein is also possibly engaged in the virulence potential of R. solanacearum.

Physiological and Transcriptional Response of Xanthomonas oryzae pv. oryzae to Berberine, an Emerging Chemical Control.

Berberine, a botanical drug, has great ability to inhibit the growth of Xanthomonas oryzae pv. oryzae. However, the antibacterial mechanism of berberine against X. oryzae pv. oryzae remains poorly understood. In this study, we investigated the physiological and transcriptional response of X. oryzae pv. oryzae to berberine. When strain X. oryzae pv. oryzae GX13 was treated with berberine (10 µg/ml), the hypersensitive response in tobacco, virulence to rice, pathogen population in the rice xylem, production of extracellular polysaccharide (EPS), and activity of extracellular hydrolases decreased, but the levels of pyruvate and ATP increased. Moreover, biofilm formation was inhibited, and the cell membrane was damaged. Transcriptome sequencing analysis showed downregulated expression of gspD, gspE, and gspF, involved in the type II secretion system (T2SS); hrcC, hrcJ, hrcN, and others, involved in the type III secretion system (T3SS); gumB and gumC, associated with EPS; zapE, ftsQ, and zapA, associated with cell division; lpxH, lpxK, kdtA, and others, associated with the membrane; and pyk, pgk, and mdh, encoding pyruvate kinase, phosphoglycerate kinase, and malate dehydrogenase, respectively. Upregulated expression was observed for nuoA, nuoB, and nuoH, encoding the NADH dehydrogenase complex, and atpF, atpC, and atpB, encoding ATP synthase. An adenylate cyclase (CyaA) fusion assay showed that berberine affects type three effector protein secretion via the T3SS and reduces effector translocation in X. oryzae pv. oryzae. It is speculated that the negative growth and virulence phenotypes of berberine-treated X. oryzae pv. oryzae GX13 may involve differentially expressed genes associated with cytoarchitecture and energy metabolism, and these effects on primary cell function may further dampen virulence and result in differential expression of T3SS- and T2SS-related genes.

Isolation of Methyl Gallate from Toxicodendron sylvestre and Its Effect on Tomato Bacterial Wilt.

We determined that the methanol extract of Toxicodendron sylvestre could significantly inhibit Ralstonia solanacearum in vitro and in planta. One compound responsible for the antibacterial activity was isolated from the ethyl ether extract and identified as methyl gallate (MG) based on its 1H and 13C nuclear magnetic resonance data as well as mass spectroscopy. MG displayed broad-spectrum activity against plant-pathogenic bacteria, and strong inhibitory effects on the growth of plant-pathogenic oomycetes. The half inhibition concentration of MG on R. solanacearum was 8.3 mg/liter, which was tested by the agar dilution method. Disease control trials in planta showed that both natural and synthetic MG could effectively reduce the incidence of tomato bacterial wilt, and there was no significant difference between them in control efficacy. This is the first report on the use of MG for the control of a plant bacterial disease. Because of its broad-spectrum antimicrobial activity and significant control efficacy on tomato bacterial wilt in planta, MG shows potential to be used as a bactericide to control plant bacterial wilt.