Drought-induced changes in antioxidant system and osmolyte content of poplar cuttings

Poplars are widely utilized in the intensive and biomass production, as well as in breeding and environment protection programs. This experiment was performed to investigate the effect of drought stress on poplar clones (M-1, PE19/66 and B-229). Poplar clones were grown hydroponically under controlled conditions and exposed to drought stress by applying polyethylene glycol (PEG) 6000. The plant samples were collected and separated into roots and leaves. For estimation of antioxidant status, activities of different antioxidant enzymes were determined (superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), glutathione peroxidase (GPX), glutathione reductase (GR) and ascorbate peroxidase (APX)), as well as antiradical power (ARP) against hydroxyl (˙OH) radical using ESR spin-trapping. The water stress parameters proline (PRO) content, activity of proline dehydrogenase (PDH) and glycine betaine (GB) content were determined. Drought stress had significant effects on PRO and GB contents, SOD, APX and CAT activities when compared to control. All investigated extracts were determined as good inhibitors for ˙OH radical reduction, especially clone M-1where there was an increase of ARP against ˙OH radical in drought condition what could help to prevent or meliorate oxidative damage. Results indicated that the M-1 clone had a greater accumulation of substances for osmotic adjustment and a more efficient enzymatic detoxification cycle for eliminating the negative effects caused by ROS under drought stress than clones B-229 and PE19/66. This study provides valuable information for understanding drought - responsive mechanisms in leaves and roots of poplar clones M-1, B-229 and PE19/66. Key words: antioxidant enzymes, climate change, drought, glycine betaine, proline.

Synthesis of Fluorescent Dansyl Derivatives of Methoxyamine and Diphenylhydrazine as Free Radical Precursors

Starting from dansyl-chloride, in reaction with 1,1-diphenylhydrazine and methoxyamine, two new fluorescent derivatives 1 and 2 were obtained and characterized by NMR, IR, UV-Vis, HR-MS, and fluorescence spectroscopy. The single-crystal X-ray structure was obtained for compound 2. Both compounds generate free radicals by oxidation, as demonstrated by ESR spectroscopy. Compound 1 generates the corresponding hydrazyl-persistent free radical, evidenced directly by ESR spectroscopy, while compound 2 generates in the first instance the methoxyaminyl short-lived free radical, which decomposes rapidly with the formation of the methoxy radical, evidenced by the ESR spin-trapping technique. By oxidation of compounds 1 and 2, their fluorescence is quenched.

Thermal Initiators as Additives for Photopolymerization of Methacrylates upon Blue Light

Free radical polymerization is often performed by thermal initiation but also more and more by light-assisted polymerization processes. This second approach allows the polymerization to be carried out under mild conditions (under air, upon blue light exposure, under low light intensity). The aim and the originality of the present paper is to perform photopolymerization in the presence of a thermal initiator, i.e., we can take advantage of the exothermicity of the photopolymerization process to decompose the thermal initiator, leading to enhanced polymerization rates. The performance of the photoinitiating system is discussed in the present study based on real-time Fourier-transform infrared spectroscopy measurements (following the C=C bond content evolution vs. time) and by thermal imaging experiments. Mechanisms of the new system proposed in this work are also fully detailed using cyclic voltammetry, electron spin resonance (ESR) spin trapping, and UV-visible absorption properties.

Free Radical Photopolymerization and 3D Printing Using Newly Developed Dyes: Indane-1,3-Dione and 1H-Cyclopentanaphthalene-1,3-Dione Derivatives as Photoinitiators in Three-Component Systems

The design of photoinitiating systems with excellent photochemical reactivities at 405nm LED is one of the obstacles to efficiently promote free radical polymerization in mild conditions (e.g., low light intensity, under air). Here, our actual search for new multicomponent photoinitiating systems at 405nm LED prompts us to develop new dyes based on push–pull structures. In the present paper, we chose two series of new dyes which possess indane-1,3-dione and 1H-cyclopenta naphthalene-1,3-dione groups as the electron-withdrawing groups, since they have the great potential to behave as sensitive and remarkable photoinitiators in vat photopolymerization/3D printing. When incorporated with a tertiary amine (ethyl dimethylaminobenzoate EDB, used as electron/hydrogen donor) and an iodonium salt (used as electron acceptor) as the three-component photoinitiating systems (PISs), and among a series of 21 dyes, 10 of them could efficiently promote the free radical photopolymerization of acrylates. Interestingly, steady state photolysis experiments revealed different behaviors of the dyes. Fluorescence experiments and free energy change calculations for redox processes were also carried out to investigate the relevant chemical mechanisms. Additionally, the formation of radicals from the investigated PISs was clearly observed by electron spin resonance (ESR) spin-trapping experiments. Finally, stereoscopic 3D patterns were successfully fabricated by the laser writing technique. In this work, the use of push–pull dyes based on the naphthalene scaffold as photoinitiators of polymerization is reported for the first time in a systematic study aiming at investigating the structure–performance relationship for irradiation carried out at 405 nm. By carefully selecting the electron donors used in the two series of push–pull dyes, novel and high-performance photoinitiating systems operating at 405 nm are thus proposed.

Investigation into the Direct Photolysis Process of Photo-Induced RAFT Polymerization by ESR Spin Trapping

The direct photolysis of reversible addition fragmentation chain transfer (RAFT) agents under visible light was demonstrated by electron spin resonance (ESR) using 5,5-dimethyl-1-pyrroline N-oxide as a typical spin trap. The hyperfine coupling lines obtained by ESR spectroscopy showed the successful capture of the carbon-centered and the sulfur-centered radical. Photo-polymerization of vinyl acetate under different wavelengths was performed to verify the effects of wavelength on the process. The effect of the R group of RAFT agents on the photolysis was investigated by spin-trapping experiments using poly (butyl acrylate) and poly (vinyl acetate) as macroRAFT agents. The quantitative experiment showed the yield of photolysis of a xanthate to be only 0.023% under λ > 440 nm.