Isolation and Characterization of Putative Endophytic Bacteria Antagonistic to Phoma tracheiphila and Verticillium albo-atrum

A collection of 200 bacterial isolates recovered from citrus plants (Citrus limon, Citrus sinensis, and Citrus reticulata), Medicago truncatula and Laurus nobilis, was established. In vitro screening indicated that 28 isolates exhibited an inhibitory activity against the vascular pathogens Phoma tracheiphila and Verticillium albo-atrum. Isolates were screened according to their hydrolytic activities, plant growth-promoting bacteria (PGPB) abilities, as well as for the presence of nonribosomal peptide synthetase (NRPS) genes responsible of the lipopeptide biosynthesis. The results were positive for 16 isolates which exhibited at least two PGPB activities and a single NRPS gene. Genetic diversity of the selected isolates was studied using random amplified polymorphic DNA (RAPD) and repetitive element PCR (REP) tools that showed clustering of strains into three major groups (I, II, and III) (i, ii, and iii), respectively. Clustering was further confirmed by the 16S rDNA sequencing that assigned nine isolates to Bacillus velezensis, four isolates to Bacillus methyltrophicus, one isolate to Bacillus amyloliquefaciens, and two isolates to Bacillus mojavensis. Organ-bacterial genotype interaction as well as positive correlation with NRPS genes are discussed.     

New separation method for organic and inorganic selenium compounds based on anion exchange chromatography followed by inductively coupled plasma mass spectrometry

We describe a new method for separating the organic and inorganic selenocompounds methaneseleninic acid, selenite, selenate, methylselenocysteine, selenocystine as well as both selenomethionine and its oxidized form. The separation is performed on a Hamilton PRP-X100 column. According to the literature, the oxidized form of selenomethionine—which is easily formed—is eluted close to the dead volume when this column is used. The choice of parahydroxybenzoic acid as mobile phase enabled us to elute all of these species after this oxidized form, resulting in better identification and quantification. The factors determining separation (eluent concentration, pH, gradient) were optimized via an experimental design. Application of the method to yeast and commercial tablets showed that the principal Se compound present was selenomethionine, which was also present in its oxidized form.     

Straightforward and Highly Diastereoselective Synthesis of a New Set of Functionalized Dispiropyrrolidines Involving Multicomponent 1,3‐Dipolar Cycloaddition with Azomethine Ylides

The diastereoselective synthesis of novel series of dispiropyrrolidines has been achieved by a one‐pot three‐component [3 + 2] cycloaddition reaction of (E)‐2‐arylideneindanones, glycine ethyl ester, and the cyclic diketones 1H‐indole‐2,3‐dione (isatin) or acenaphthenequinone. Moreover, we disclose an unprecedented epimerization of spiroadducts leading to a new family of dispiropyrrolidines with an unusual relative stereochemistry.     

Catalytic charring-volatilization competition in organoclay nanocomposites

The thermal behaviour of organoclays, and especially their organic treatment, is an important issue in polymer nanocomposite preparation and their fire retardant properties. The thermal behaviour of the organomodifier is strongly affected by the different composition parameters of the clays. Thus the thermal degradation, in inert and in oxidative atmosphere, of natural montmorillonite and synthetic fluorohectorite both exchanged with polar and non-polar organomodifiers was studied using a combined thermogravimetry/Fourier transform infrared and a flash pyrolysis GC-MS system. Decomposition and charring mechanisms of the organic molecules in the clays are proposed for each kind of clay and a relationship between the composition of the clays and the kinetics of the decomposition reactions is found. Furthermore, it is shown that the charring-volatilization competition on heating organoclays in the presence of oxygen depends on the structure of the clay, the confined or unconfined position of the organic molecules and their polarity.     

On the importance of spectral responsivity of Robertson-Berger-type ultraviolet radiometers for long-term observations

A system to determine the spectral responsivity of ultraviolet (UV) radiometers has been developed and is routinely operated at the Central Ultraviolet Calibration Facility, at the National Oceanic and Atmospheric Administration. The instrument and the measurement methodologies are described. Results of measurements from thermally controlled broadband UV radiometers of the Robertson-Berger (R-B)-type are described. Systematic differences in the spectral response curves for these instruments have been detected. The effect of these differences on the field operation of UV-B radiometers has been studied by calculating the instrumental response from modeled UV spectra. The differences of the weighted spectral UV irradiances, measured by two radiometers with different spectral response functions, caused by the daily variation in the position of the sun were estimated for fixed values of total ozone, altitude and albedo, and for cloud-free conditions. These differences increase with the solar zenith angle and are as large as 8%. Larger differences in the instrumental response may be produced by ozone variations. Thus, care must be taken when analyzing data from R-B radiometers and comparing results from different instruments. Routine cycling of UV-B radiometers in operative networks without a careful determination of the spectral responsivity, or small drifts of the spectral responsivity, may strongly affect the accuracy of UV radiation measurements and produce an erroneous trend. Because of the possible differences among radiometers, it would not be practical to derive the long-term behavior of UV radiation without routine and thorough characterization of the spectral responsivities of the instruments.     

Role of Basic Surface Groups of Activated Carbon in Chlordecone and β-Hexachlorocyclohexane Adsorption: A Molecular Modelling Study

The influence of nitrogen-containing surface groups (SGs) onto activated carbon (AC) over the adsorption of chlordecone (CLD) and β-hexachlorocyclohexane (β-HCH) was characterized by a molecular modelling study, considering pH (single protonated SGs) and hydration effect (up to three water molecules). The interactions of both pollutants with amines and pyridine as basic SGs of AC were studied, applying the multiple minima hypersurface (MMH) methodology and using PM7 semiempirical Hamiltonian. Representative structures from MMH were reoptimized using the M06-2X density functional theory. The quantum theory of atoms in molecules (QTAIM) was used to characterize the interaction types in order understanding the adsorption process. A favorable association of both pesticides with the amines and pyridine SGs onto AC was observed at all pH ranges, both in the absence and presence of water molecules. However, a greater association of both pollutants with the primary amine was found under an acidic pH condition. QTAIM results show that the interactions of CLD and β-HCH with the SGs onto AC are governed by Cl···C interactions of chlorine atoms of both pesticides with the graphitic surface. Electrostatic interactions (H-bonds) were observed when water molecules were added to the systems. A physisorption mechanism is suggested for CLD and β-HCH adsorption on nitrogen-containing SGs of AC.     

Diazonium salt-derived 4-(dimethylamino)phenyl groups as hydrogen donors in surface-confined radical photopolymerization for bioactive poly(2-hydroxyethyl methacrylate) grafts

In this paper we describe a novel methodology for grafting polymers via radical photopolymerization initiated on gold surfaces by aryl layers from diazonium salt precursors. The parent 4-(dimethylamino)benzenediazonium salt was electroreduced on a gold surface to provide 4-(dimethylamino)phenyl (DMA) hydrogen donor layers; free benzophenone in solution was used as a photosensitizer to strip hydrogen from the grafted DMA. This system permitted efficient surface initiation of photopolymerization of 2-hydroxyethyl methacrylate. The resulting poly(2-hydroxyethyl methacrylate) (PHEMA) grafts were found to be very adherent to the surface as they resist total failure after being soaked in the well-known paint stripper methyl ethyl ketone. The PHEMA grafts were reacted with 1,1'-carbonyldiimidazole to yield carbamate groups that are able to react readily with amino groups from proteins. The final surface consisted of protein-functionalized PHEMA grafts where bovine serum albumin (BSA) protein is specifically linked to the grafts by covalent bonds. We used X-ray photoelectron spectroscopy to monitor the chemical changes at the gold surface all along the process from the neat gold to the end-protein-functionalized polymer grafts: the PHEMA graft thickness ranged from 7 to 27 nm, and the activation by 1,1'-carbonyldiimidazole reached 37% of the OH groups, which was sufficient for 90% surface coverage of the grafts by BSA. This work conclusively provides a new approach for bridging reactive and functional polymers to surfaces via aryl diazonium salts in a simple, fast, and efficient approach of importance in biomedical and other applications.