Christel Pierlot

Naphthalene endoperoxides as generators of singlet oxygen in biological media.

Publisher Summary Singlet oxygen is generated in biological systems and can be implicated in defense mechanisms against viruses and bacteria by phagocytic cells. Dark reactions (chemiexcitation), such as reactions catalyzed by peroxidases (myeloperoxidase) or oxygenases (lipoxygenase or cyclooxygenase), or the reaction of hydrogen peroxide with hypochlorite or peroxynitrite or thermodecomposition of dioxetanes can be responsible for 1 O 2 generation in biological systems. Singlet oxygen is one of the major species mediating cytotoxic effects of photodynamic treatment. In addition to these cytotoxic effects, 1 O 2 can be responsible for ultraviolet A-induced activation of gene expression. Due to the difficulties involved in obtaining 1 O 2 free from other reactive contaminants, there is a paucity of detailed studies on the aspects of 1 O 2 biochemistry mentioned earlier. This chapter presents a useful tool to generate 1 O 2 using endoperoxides of water-soluble naphthalene derivatives. The physicochemical properties are suitable as chemical sources of 1 O 2 in biological media.

Panorama of sustainable solvents using the COSMO-RS approach

Recent regulations have banned numerous common organic solvents that have been recognized as hazardous to human health and environment. There is thus a pressing need for alternatives, often called “green” or “sustainable” solvents, which have a good HSE (Health Safety Environment) profile and are preferably obtained from the biomass feedstock. A number of such green solvents are already on the market or under advanced development and have been listed in this work. To use this set of solvents as effective alternatives, a tool is needed to compare their physico–chemical properties to the ones of the solvents they are supposed to replace. The COnductor-like Screening MOdel for Real Solvents (COSMO-RS) approach was used to model the solvents, which were located in a pseudo 3D-space thanks to Principal Components Analysis and clustering procedures. This approach had already been successfully applied to the classification of classical organic solvents into ten families in which the green solvents have been positioned. This pseudo 3D-representation of green solvents helps in the search of potential alternatives to a questionable solvent. It also sheds light on paucity or even a complete lack of green solvents in some families (e.g. strong electron pair donor bases). There is thus a need to develop new green solvents with the prerequisite properties. As the COSMO-RS approach can be applied to almost any potential candidate, it could be a powerful tool for the design in silico of new sustainable solvents.

Structure-interfacial properties relationship and quantification of the amphiphilicity of well-defined ionic and non-ionic surfactants using the PIT-slope method.

The Phase Inversion Temperature of a reference C10E4/n-Octane/Water system exhibits a quasi-linear variation versus the mole fraction of a second surfactant S2 added in the mixture. This variation was recently proposed as a classification tool to quantify the Hydrophilic-Lipophilic Balance (HLB) of commercial surfactants. The feasibility of the so-called PIT-slope method for a wide range of well-defined non-ionic and ionic surfactants is investigated. The comparison of various surfactants having the same dodecyl chain tail allows to rank the polar head hydrophilicity as: SO3Na⩾SO4Na⩾NMe3Br>E2SO3Na≈CO2Na⩾E1SO3Na⩾PhSO3Na>Isosorbide(exo)SO4Na≫IsosorbideendoSO4Na≫E8⩾NMe2O>E7>E6⩾Glucosyl>E5⩾Diglyceryl⩾E4>E3>E2≈Isosorbide(exo)>Glyceryl>Isosorbide(endo). The influence on the surfactant HLB of other structural parameters, i.e. hydrophobic chain length, unsaturation, replacement of Na(+) by K(+) counterion, and isomerism is also investigated. Finally, the method is successfully used to predict the optimal formulation of a new bio-based surfactant, 1-O-dodecyldiglycerol, when performing an oil scan at 25 °C.

Effects of oxygenated substituents on the [4+2] cycloaddition of singlet oxygen in the photooxygenation of water-soluble naphthyl ethers

Abstract Water-soluble ethers 2 and 5 undergo [4+2] cycloaddition of singlet oxygen to afford endoperoxides. Compound 2 is extremely reactive ( k r + k q =2.0×10 8 M −1 /s −1 in D 2 O) due to the mesomeric interactions between oxygen and the naphthalene ring. However, the unstable endoperoxide was immediately and quantitatively decomposed into the aldehyde ester 6 . When a methylene linker separates the oxygen from the aromatic core ( 5 ), photooxidation leads to a mixture of 1,4 and 5,8-endoperoxides.

First evidence of the formation of 5,8-endoperoxide from the oxidation of 1,4-disubstituted naphthalene by singlet oxygen

Bulky water-soluble 1,4-disubstituted naphthalenes react with singlet oxygen giving the usual 1,4- and the unexpected 5,8-endoperoxides and showing that the regioselectivity of the [4 + 2] cycloaddition of singlet oxygen depends on the steric hindrance of the substrate.

One pot flame retardant and weathering resistant coatings for plastics: a novel approach

The self-stratifying approach is a one step process allowing the formation of a complex laminated coating structure at the surface of plastics or other substrates, combining optimized surface and adhesion properties. These coatings have already been developed for various application fields but have never been considered for fire retardant purposes, whatever the substrate involved. In this work, the self-layering concept has been used to make polycarbonate fire retardant, using a mixture of epoxy and fluoropolymer resins, and iron oxide as flame retardant additive (10 wt%). Self-stratification was evidenced by microscopic analyses. The flame retardant properties were evaluated according to Limiting Oxygen Index (LOI), UL-94 and Mass Loss Calorimetry (MLC). Weathering resistance by accelerated UV, thermal and humidity exposure was also considered. In the first part, the effect of solvent on the self-layering process was investigated. It was shown that the system diluted in a blend of butylacetate : xylene (1 : 1 ratio) exhibits a perfect stratification and excellent adhesion onto polycarbonate. In such a system, an outstanding improvement of the fire retardant properties (V0 rating at UL-94 and 32 vol% at LOI), unaffected by weathering (both UV and temperature/humidity exposure), was observed when a 200 μm wet thick coating was applied. The coating allows the formation of a protective barrier and the presence of metal particles avoids dripping and promotes a charring effect.

Catastrophic Emulsion Inversion Process of Highly Viscous Isosorbide Biobased Polyester Monitored in situ by Torque and Light Backscattering

Highly viscous hydrophobic isosorbide biobased polyester O/W emulsions are prepared through catastrophic phase inversion. The process is followed in situ with two different methods: torque and light backscattering (LBS). Considering high viscosity of the system, only discontinuous conductivity monitoring is performed for comparison. Torque and LBS allow to highlight the emulsion inversion point (EIP) with relatively close water weight fraction values (fw≈0.20). The torque and LBS signals are rather noisy before inversion (evolution of different structures) and more smooth after phase inversion (continuous aqueous phase). Torque gives a more macroscopic information, representative of the global state of the dispersion. Consistent conductivity and torque measurements suggest indeed an inversion pathway through multiple o/W/O emulsions leading to multiple complex structures before getting continuous aqueous final emulsion. This hypothesis is confirmed with continuous LBS monitoring and microscopic observations. LBS signal seems more complete because it combines the information of conductivity and torque and allows to clearly follow in situ the inversion from the beginning to the end of the process.