Synthesis of graft copolymers. II. Synthesis of polystyrene‐g‐poly(methyl methacrylate)

The thermolysis of labile 1,2‐bis(trimethylsilyloxy)tetraphenylethane groups pendant along polystyrene chains in the presence of various vinyl monomers leads to the direct synthesis of graft copolymers. Depending on the monomer chosen, the polymerization temperature, and the number of active sites by the macroinitiator molecule, crosslinked or total soluble graft copolymers can be prepared. Several conditions were studied in order to attain soluble polystyrene‐g‐poly(methyl methacrylate) copolymers under a controlled polymerization mechanism. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 12–18, 2002     

Melatonin is a phytochemical in olive oil

Given the numerous observations regarding the positive effects of olive oil consumption and the presence of melatonin in edible plants, we addressed for the first time the question of melatonin determination in virgin olive oil. All the extra virgin olive oil registered designation of origins from Spain and commercial samples of refined olive and sunflower oil were used. Immunoprecipitation and ELISA were combined for melatonin determination. Melatonin is present in olive oil at higher levels in extra virgin olive oil than in refined olive or sunflower oil samples. We concluded that melatonin is part of the phytochemical profile of the olive oil. Particularly, extra virgin olive oil had almost double the melatonin contents of the other refined oils analysed. Thus, melatonin may account for the healthy effects of the Mediterranean diet in which olive oil is the main source of fat.     

Micro‐ and macrophase separation of thermosetting systems modified with epoxidized styrene‐block‐butadiene‐ block‐styrene linear triblock copolymers and their influence on final mechanical properties

BACKGROUND: The goal of this work was to establish the minimum degree of epoxidation needed to develop nanostructured epoxy systems by modification with poly(styrene‐block‐butadiene‐block‐styrene) (SBS) triblock copolymers epoxidized to several degrees, and also to investigate the effect of polystyrene (PS) content on the final morphologies. By using two SBS copolymers, the influence of the weight ratio of the two blocks on the generated morphologies and mechanical properties was also analysed. RESULTS: Nanostructured thermosets were effectively obtained through reaction‐induced microphase separation of PS blocks from the matrix. A minimum of 27 mol% of epoxidation, which corresponds to 4.8 wt% of epoxidized polybutadiene (PB) units in the overall mixture, was needed to ensure nanostructuring of final mixtures and thus their transparency. Hexagonally ordered nanostructures were achieved for PS contents of around 16–20 wt%, which agrees with our previous results for mixtures with other SBS copolymers with different ratios between blocks. The fracture toughness of the epoxy matrix was improved or at least retained with mixing. CONCLUSION: The degree of epoxidation of PB blocks needed to switch epoxy/SBS mixtures from a macrophase‐separated to a nanostructured state has been established. The generated morphologies in the epoxy systems are mainly dependent on the PS content in the mixture. Copyright © 2008 Society of Chemical Industry     

Rheokinetic analysis of the hydration of pentasodium triphosphate in a detergent slurry

The main objective of this research was to analyze, from a rheokinetic point of view, the hydration of pentasodium triphosphate (TPP) in a detergent slurry with a standard composition. A torque rheometer (Brabender Plastograph) with a roller-type measuring system was used. The influence of temperature, TPP quality, system agitation and concentration of dry substances on the total torque of the samples has been studied. From the experimental results it can be concluded that all of these parameters, as well as the reaction time, influence the consistency of the samples. The kinetics of the process are controlled by diffusional resistances.     

Specific viscosity of Newtonian aqueous solutions containing an anionic surfactant and an alkaline pyrophosphate

The effects that both temperature and solute concentrations exert on specific viscosity are studied in this paper. The products used were sodium or triethanolammonium dodecylsulfates or dodecylbenzenesulfonates, as surfactants, and tetrasodium or tetrapotassium pyrophosphates, as electrolytes. All are of technical quality. As temperature decreases, within the temperature range studied, a phase separation or an appearance of non-Newtonian behavior is noted in many solutions. The solutions studied fit, within the accuracy range for experimental measurements, an empirical equation that agrees with what is called the activated diffusive relaxation model. For this model, the relative viscosity is a linear superposition of stresses coming from hydrodynamic interactions and from activation energy due to structural relaxation of the uniform distribution of micelles in the quiescent micellar solution. Solutions containing a dodecylsulfate show very slight hydrodynamic effects. Their activation energy, which is independent of temperature, becomes greater by increasing the concentrations of surfactant and pyrophosphate. The specific viscosities of these solutions also increase by replacing the triethanolammonium counter-ion with sodium. Solutions containing sodium dodecylbenzenesulfonate show considerable hydrodynamic effects, which increase with the addition of tetrasodium pyrophosphate. The activation energy is independent of temperature. Solutions containing triethanolammonium dodecylbenzenesulfonate show decreasing activation energy values when temperature is increased. Consequently, a maximum for specific viscosity appears at a certain temperature. This maximum diminishes progressively with the addition of pyrophosphate, while the corresponding temperature becomes higher. From the investigation carried out, the necessity for further basic studies remains clear. Research should be done on concentrated aqueous solutions containing surfactants and electrolytes, taking into consideration the variations that their dynamic viscosities present along with composition and temperature. All of this, naturally, must be carried out before developmental research on manufacturing, commercialization and usage of such solutions proceeds.     

Modified 5'-trityl nucleosides as inhibitors of Plasmodium falciparum dUTPase

2'-Deoxyuridine triphosphate nucleotidohydrolase (dUTPase) is a potential drug target for the treatment of malaria. We previously reported the discovery of 5'-tritylated analogues of deoxyuridine as selective inhibitors of this Plasmodium falciparum enzyme. Herein we report further structure-activity studies; in particular, variations of the 5'-trityl group, the introduction of various substituents at the 3'-position of deoxyuridine, and modifications of the base. Compounds were tested against both the enzyme and the parasite. Variations of the 5'-trityl group and of the 3'-substituent were well tolerated and yielded active compounds. However, there is a clear requirement for the uracil base for activity, because modifications of the uracil ring result in loss of enzyme inhibition and significant decreases in antiplasmodial action.     

Design, synthesis, and evaluation of 5'-diphenyl nucleoside analogues as inhibitors of the Plasmodium falciparum dUTPase

Deoxyuridine 5'-triphosphate nucleotidohydrolase (dUTPase) is a potential drug target for malaria. We previously reported some 5'-tritylated deoxyuridine analogues (both cyclic and acyclic) as selective inhibitors of the Plasmodium falciparum dUTPase. Modelling studies indicated that it might be possible to replace the trityl group with a diphenyl moiety, as two of the phenyl groups are buried, whereas the third is exposed to solvent. Herein we report the synthesis and evaluation of some diphenyl analogues that have lower lipophilicity and molecular weight than the trityl lead compound. Co-crystal structures show that the diphenyl inhibitors bind in a similar manner to the corresponding trityl derivatives, with the two phenyl moieties occupying the predicted buried phenyl binding sites. The diphenyl compounds prepared show similar or slightly lower inhibition of PfdUTPase, and similar or weaker inhibition of parasite growth than the trityl compounds.