Contrasting impacts of mixed nonionic surfactant micelles on plant growth in the delivery of fungicide and herbicide.

HYPOTHESIS: Nonionic alkyl ethoxylate surfactants are widely used in agrochemicals to facilitate the permeation of systemic herbicides and fungicides across the plant waxy film. Industrial grade surfactants are often highly mixed and how the mixing affects their interactions with pesticides and wax films remains largely unexplored. A better understanding could enable design of mixed nonionic surfactants for herbicides and fungicides to maximize their efficiency and reduce wastage whilst controlling their impact on plant wax films. EXPERIMENT: In this study, nonionic surfactants with general structure n-oxyethylene glycol monododecyl ether (C12En) were used to form surfactant mixtures with the same average ethoxylate numbers but different hydrophilic-lipophilic balance (HLB) values. Their mixed micellar systems were then used to solubilize a herbicide diuron (DN) and a fungicide cyprodinil (CP), followed by plant wax solubilization upon contact with wax films. These processes were monitored by 1H NMR and SANS. FINDING: Pesticide solubilization made surfactant micelles effectively more hydrophobic but subsequent wax dissolution caused pesticide release and the restoration of the micellar amphiphilicity. Nonionic surfactants with lower HLBs form larger nanoaggregates, show enhanced wettability, and have better ability to solubilize and permeate pesticides across the wax film, but may cause significant damage to plant growth. These observations help explain why herbicides applied on weeds would benefit from surfactants with lower HLB values while fungicides require surfactants with HLBs to balance between delivery efficiency and potential phytotoxicity risks.

How does substrate hydrophobicity affect the morphological features of reconstituted wax films and their interactions with nonionic surfactant and pesticide?

HYPOTHESIS: Surfactants are widely used in agri-sprays to improve pesticide efficiency, but the mechanism underlying their interactions with the surface wax film on plants remains poorly understood. To facilitate physical characterisations, we have reconstituted wheat cuticular wax films onto an optically flat silicon substrate with and without octadecyltrimethoxysilane modification to control surface hydrophobicity. EXPERIMENTS: Imaging techniques including scanning electron microscopy (SEM) unravelled morphological features of the reconstituted wax films similar to those on leaves, showing little impact from the different substrates used. Neutron reflection (NR) established that reconstituted wax films were comprised of an underlying wax film decorated with top surface wax protrusions, a common feature irrespective of substrate hydrophobicity and highly consistent with what was observed from natural wax films. NR measurements, with the help of isotopic H/D substitutions to modify the scattering contributions of the wax and solvent, revealed different wax regimes within the wax films, illustrating the impact of surface hydrophilicity on the nanostructures within the wax films. FINDINGS: It was observed from both spectroscopic ellipsometry and NR measurements that wax films formed on the hydrophobic substrate were more robust and durable against attack by nonionic surfactant C12E6 solubilised with pesticide Cyprodinil (CP) than films coated on the bare hydrophilic silica. Thus, the former could be a more feasible model for studying the wax-surfactant-pesticide interactions.

Room-temperature synthesis of water-dispersible sulfur-doped reduced graphene oxide without stabilizers.

Sulfur-Doped graphene has attracted significant attention because of its potential uses in sensors, catalysts, and energy storage applications. In conventional approaches, the sulfur-doped graphene is fabricated with graphene oxide and sulfur-containing compounds through thermal annealing or hydrothermal process, which generally involves special equipment and heat treatment, and requires additional stabilizers to make it solution-processable. In this work, we report a facile one-step approach to synthesize water-dispersible sulfur-doped reduced graphene oxide (S-rGO). Graphene oxide (GO) could be readily reduced and converted to S-rGO simultaneously by directly mixing GO dispersion with hydrosulfide hydrate (NaSH·xH2O) at room temperature. The sulfur doping is confirmed by high resolution S 2p XPS spectrum and element mapping. The colloidal dispersion state of S-rGO is confirmed by the investigation of Tyndall effect, the zeta potential and particle size distribution measurement. Compared with previously reported strategies, NaSH can initiate the reduction and sulfur doping at room temperature, demand no heat treatment, require no equipment and form stable aqueous S-rGO dispersion without using any stabilizer. These advantages will facilitate large-scale production of water-dispersible (sulfur doped) graphene and further boost their applications in sensors, catalysts and energy storage devices.

New shape-selectivity discovered on graphene-based materials in catching tobacco specific nitrosamines.

New shape-selectivity of graphene-based materials was discovered on this article. To explore the new selectivity, the structure and surface state of graphene and carbon nanotube were examined firstly, and their specific selectivity was verified and was compared with that of ZSM-5 zeolite in aqueous solutions of tobacco specific nitrosamines (TSNA) along with dyes. These two adsorbents trapped about 55% and 70% of 4-methylnitrosamino-1-3-pyridyl-1-butanone (NNK) but only 3% of N'-nitrosonornicotine (NNN) in solution, having an obvious selectivity for the former, due to its stronger interaction with graphene. NNK on graphene sheet obtained more electrons (0.015 e) and owned larger adsorption energy (15.63 kcal mol-1) than that of NNN (0.003 e, 9.19 kcal mol-1), according to theoretical calculation and FTIR results. More 95 or 136 mg g -1 acid red 88 than methyl orange was captured by graphene or carbon nanotube, demonstrating this special and abnormal selectivity again. With new selectivity, graphene showed a higher capacity (6.9%) and shorter adorption equilibrium time (5 min) for TSNA than the typical selecive sorbent ZSM-5 zeolite (1.7% and 20 min) in tobacco solution but kept the similar selctivity to NNK, paving a new way to control the carcinogens like TSNA in environment.

Creating an Optimal Microenvironment within Mesoporous Silica MCM-41 for Capture of Tobacco-Specific Nitrosamines in Solution.

To meet the requirement of capturing tobacco-specific nitrosamines (TSNA) for environment protection, a unique microenvironment was carefully created inside the channels of mesoporous silica MCM-41. In situ carbonization of template micelles at 923 K, combined with the excess aluminum used in one-pot synthesis of MCM-41, is adopted to tailor the tortuosity of mecsoporous channels, while loaded metal oxides (5 wt %) and the Al component in the framework are employed to exert the necessary electrostatic interaction toward the target carcinogens TSNA in solution. The elaborated microenvironment created in mesoporous sorbents was characterized with XRD, N2 adsorption-desorption, TEM, XPS, and TG-DSC methods. Various solutions of Burley- and Virginia-type tobaccos were used to assess the adsorption performance of new mesoporous sorbents, and the influence of the solid-to-liquid ratio, adsorption time, and loading amount of CuO on the adsorption was carefully examined. The representative sample 5%Cu/AM-10c could capture 27.2% of TSNA in Burley tobacco solution, and its capacity reached 0.3 mg g-1 in Snus tobacco extract solution, offering a promising candidate for the protection of the environment and public health.

One-Step Preparation of Oxygen/Fluorine Dual Functional MWCNTs with Good Water Dispersibility by the Initiation of Fluorine Gas.

It is still a challenge to prepare water-dispersible carbon nanotubes which are proved to have great potential in numerous applications. In this present work, as low as 2% fluorine gas was used as initiator to prepare oxygen/fluorine dual functional MWCNTs (OF-MWCNTs) with good water dispersibility through a one-step method under oxygen atmosphere. The aromatic structure of OF-MWCNTs is reserved to some extent resulting in better electrical conductivity than pure fluorinated MWCNTs (F-MWCNTs). The amount of oxygen atoms and fluorine atoms (hereinafter referred to as "O-content" and "F-content") of OF-MWCNTs is up to 8.8% and 7.5%. Fourier transform infrared spectroscopy (FTIR) manifests that - COOH is covalently bonded onto the surface of OF-MWCNTs. In addition, the OF-MWCNTs sample is pH-sensitive, which further validates the successful introduction of -COOH. The successful covalent attachment of -COOH onto MWCNTs dramatically improves the hydrophilia of MWCNTs which always present hydrophobic character. It is deduced that fluorine creates reactive sites for oxygen, increases the oxygen content, and eventually results in the dispersibility of OF-MWCNTs in water. The corresponding hydrophilic OF-MWCNTs film shows good performance for separating oil-in-water emulsions. Meanwhile, the good dispersibility of OF-MWCNTs in organic solvents also makes it possible to be applied in various composites.

Characterization of Conformation and Locations of C-F Bonds in Graphene Derivative by Polarized ATR-FTIR.

It is still a challenge to explore the orientation and location of chemical groups in the two-dimensional derivative of graphene. In this study, polarized attenuated total reflectance Fourier transform infrared spectroscopy (polarized ATR-FTIR) was employed to investigate the orientation and location of C-F groups in the corresponding graphene derivative sheets, which facilitates building a relationship between the bonding nature and fine structure. There were two types of C-F bonding, (C-F)I and (C-F)II, in fluorinated graphene sheets. It was found that (C-F)II bonds were linked at the coplanar carbon atoms in the weakly fluorinated region (CxF, x ≥ 2), whereas the (C-F)I bonds cluster at the strongly deformed carbon framework with a F/C ratio of about 1. The thermostability of (C-F)II is lower than that of (C-F)I bonds. This is because the coplanar structure of the weakly fluorinated region tends to transform to the planar aromatic ring with the breaking of the C-F bond as compared with the strong fluorinated nonplanar region.

Controllable defluorination of fluorinated graphene and weakening of C-F bonding under the action of nucleophilic dipolar solvent.

The effect of solvent on the chemical structure and properties of fluorinated graphene (FG) was particularly investigated in this work. It is found that the reduction of FG and the weakening of strong covalent C-F bonding take place under the action of some dipolar solvents even at room temperature. The rate of the C-F bond rupture reaction is positively influenced by the dipole moment of solvent and fluorine coverage of FG sheets. Meanwhile, defluorination of FG is controllable through the time and temperature of solvent treatment. These solvents function as the nucleophilic catalysts, promoting chemical transformation, which leads to a series of changes in the structure and properties of FG, such as a decline of fluorine concentration of about 40% and the reduction of thermal stability and band gap from 3 to 2 eV. After the treatment with dipolar solvent N-methyl-2-pyrrolidinone, FG maintained a capacity of 255 mA h g(-1) and a power density of 2986 W kg(-1) at a high discharge rate, while the pristine FG could not be discharged at all. This is called the "solvent activation" effect on the electrochemical performance of FG. The finding may draw attention to the effect of various external factors on the chemical structure and properties of FG, which is of great importance for the realization of the FG's potential.

A new prenylated indole diketopiperazine alkaloid from Eurotium cristatum.

A new prenylated indole diketopiperazine alkaloid, cristatumin F (1), and four known metabolites, echinulin (2), dehydroechinulin (3), neoechinulin A (4) and variecolorin O (5), were isolated from the crude extract of the fungus Eurotium cristatum. The structure of 1 was elucidated primarily by NMR and MS methods. The absolute configuration of 1 was assigned using Marfey's method applied to its acid hydrolyzate. Cristatumin F (1) showed modest radical scavenging activity against DPPH radicals, and exhibited marginal attenuation of 3T3L1 pre-adipocytes.

Fluorographene with high fluorine/carbon ratio: a nanofiller for preparing low-κ polyimide hybrid films.

Sufficient amounts of fluorographene sheets with different sheet-size and fluorine/carbon ratio were synthesized for preparing of fluorographene/polyimide hybrids in order to explore the effect of fluorographene on the dielectric properties of hybrid materials. It is found that the fluorine/carbon ratio, width of band gap, and sheet-size of fluorographene play the important roles in determining the final dielectric properties of hybrids. The fluorographene with high fluorine/carbon ratio (F/C ≈ 1) presents broaden band gap, enhanced hydrophobicity, good dispersity and thermal stability, etc. Even at a very low filling, only 1 wt %, its polyimide hybrids exhibited drastically reduced dielectric constants as low as 2.1 without sacrificing thermal stability, improved mechanical properties obviously and decreased water absorption by about 120% to 1.0 wt %. This provides a novel route for improving the dielectric properties of materials and a new thought to carry out the application of fluorographene as an advanced material.

Development of a rapid method for the simultaneous separation and determination of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its N- and O-glucuronides in human urine by liquid chromatography-tandem mass spectrometry.

Determination of the tobacco-specific nitrosamine metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its N- and O-glucuronides (NNAL-N-Gluc and NNAL-O-Gluc) is important for toxicology analysis of tobacco smoke induced carcinogenicity and the understanding of detoxification mechanisms of the carcinogenic nitrosamine in humans. But previously reported indirect measurement methods involving enzymolysis and base treatment steps were tedious and time-consuming. In this work, a direct measurement method for simultaneous determination of urinary NNAL, NNAL-N-Gluc and NNAL-O-Gluc by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in a single run was developed for the first time without the need to perform enzymatic or base hydrolysis. Urine samples were purified using dichloromethane and further extracted by solid-phase extraction. Then they were analyzed by LC-MS/MS operated in electrospray positive ionization mode. Chromatographic separation was achieved on a Phenomenex Kinetex PFP column within 6 min. The proposed method was validated and the results demonstrated that the method can produce satisfactory recoveries and reproducibility for the analytes. The applicability of this newly developed method was investigated for the simultaneous analysis of the three metabolites in smokers' urine and the obtained results were comparable to those detected using the conventional enzymolysis method.

Development, validation, and application of a liquid chromatography-tandem mass spectrometry method for the determination of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in human hair.

The tobacco-specific nitrosamine metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is a valuable biomarker for human exposure to the carcinogenic nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in tobacco and tobacco smoke. In this work, an efficient and sensitive method for the analysis of NNAL in human hair was developed and validated. The hair sample was extracted by NaOH solution digestion, purified by C(18) solid-phase extraction (SPE) and molecularly imprinted solid-phase extraction, further enriched by reverse-phase ultrasound-assisted dispersive liquid-liquid microextraction (USA-DLLME) into 1.0 % aqueous formic acid, and finally analyzed by liquid chromatography-electrospray ionization tandem mass spectrometry. Good linearity was obtained in the range of 0.24-10.0 pg/mg hair with a correlation coefficient of 0.9982, when 150 mg hair was analyzed. The limit of detection and lower limit of quantification were 0.08 and 0.24 pg/mg hair, respectively. Accuracies determined from hair samples spiked with three different levels of NNAL ranged between 87.3 and 107.7 %. Intra- and inter-day relative standard deviations varied from 4.1 to 8.5 % and from 6.9 to 11.3 %, respectively. Under the optimized conditions, an enrichment factor of 20 was obtained. Finally, the developed method was applied for the analysis of NNAL in smokers' hair. The proposed sample preparation procedure combining selectivity of two-step SPE and enrichment of DLLME significantly improves the purification and enrichment of the analyte and should be useful to analyze NNAL in hair samples for cancer risk evaluation and cancer prevention in relation to exposure to the tobacco-specific carcinogen NNK.