Competitive co-adsorption of bacteriophage MS2 and natural organic matter onto multiwalled carbon nanotubes.

A leading challenge in drinking water treatment is to remove small-sized viruses from the water in a simple and efficient manner. Multi-walled carbon nanotubes (MWCNT) are new generation adsorbents with previously demonstrated potential as filter media to improve virus removal. This study therefore aimed to evaluate the field applicability of MWCNT-filters for virus removal in water containing natural organic matter (NOM) as co-solute to viruses, using batch equilibrium experiments. Contrary to previous studies, our results showed with MS2 bacteriophages single-solute systems that the affinity of MWCNT for MS2 was low, since after 3 h of equilibration only 4 log10 reduction value (LRV) of MS2 (20 mL at an initial concentration of 106 PFU MS2/mL) were reached. Single solute experiments with Suwannee river NOM (SRNOM) performed with environmentally-relevant concentrations showed MWCNT surface saturation at initial SRNOM concentrations between 10 and 15 mgC/L, for water pH between 5.2 and 8.7. These results suggested that at NOM:virus ratios found in natural waters, the NOM would competitively suppress virus adsorption onto MWCNT, even at low NOM concentrations. We confirmed this expectation with SRNOM-MS2 co-solute experiments, which showed an exponential decrease of the MS2 LRV by MWCNT with an increase in the initial SRNOM concentration. More interestingly, we showed that pre-equilibrating MWCNT with a SRNOM solution at a concentration as low as 0.4 mgC/L resulted in a LRV decrease of 3 for MS2, due to the formation of a negatively charged SRNOM adlayer on the MWCNT surface. Complementary batch experiments with natural NOM-containing waters and competition experiments with SRNOM in the presence of CaCl2 confirmed that the presence of NOM in waters challenges virus removal by MWCNT-filters, irrespective of the concentration and type of NOM and also in the presence of Ca2+. We therefore conclude that MWCNT-filters produced with commercially available pristine MWCNT cannot be considered as a viable technology for drinking water virus removal.

Synthesis and antifungal evaluation of PCA amide analogues.

To improve the physical and chemical properties of phenazine-1-carboxylic acid (PCA) and find higher antifungal compounds, a series of PCA amide analogues were designed and synthesized and their structures were confirmed by 1H NMR, HRMS, and X-ray. Most compounds showed some antifungal activities in vitro. Particularly, compound 3d exhibited inhibition effect against Pyriculariaoryzac Cavgra with EC50 value of 28.7 µM and compound 3q exhibited effect against Rhizoctonia solani with EC50 value of 24.5 µM, more potently active than that of the positive control PCA with its EC50 values of 37.3 µM (Pyriculariaoryzac Cavgra) and 33.2 µM (Rhizoctonia solani), respectively.

Synthesis, fungicidal activity and phloem mobility of phenazine-1-carboxylic acid-alanine conjugates.

Phenazine-1-carboxylic acid (PCA) is a natural product that has been proven effective against a number of soil-borne fungal phytopathogens and registered for biofungicide against rice sheath blight in China. In order to improve the phloem mobility of phenazine-1-carboxylic acid (PCA), four PCA derivatives were designed and synthesized by conjugating PCA with l-alanine methyl ester, d-alanine methyl ester, l-alanine and d-alanine respectively. In vitro and planta bioassays results showed that conjugates L-PAM and D-PAM exhibited higher fungicidal activities against Rhizoctonia solani Kuhn than PCA while L-PA and D-PA were less active than PCA. The concentration of conjugates in Ricinus communis phloem sap was determined by HPLC. The results showed that only L-PA exhibited phloem mobility among these conjugates, and its concentration in Ricinus communis phloem sap increased with the increase of time (the maximum concentration was 12.69µM within 5h). However, the results of pot experiments showed that L-PA and other conjugates didn't exhibited the inhibition for the growth of Rhizoctonia solani Kuhn in the lower leaves after treatment in the upper leaves of rice seedlings. This may be due to the poor plant absorbility for them or their too little amount of accumulation in the lower leaves.