Response surface methodology toward the optimization of high-energy carotenoid extraction from Aristeus antennatus shrimp

High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE.     

Transport of Neutrally Buoyant and Dense Variably Sized Colloids in a Two-Dimensional Fracture with Anisotropic Aperture

The transport of monodisperse as well as polydisperse colloid suspensions in a two-dimensional, water saturated fracture with spatially variable and anisotropic aperture is investigated with a particle tracking model. Both neutrally buoyant and dense colloid suspensions are considered. Although flow and transport in fractured subsurface formations have been studied extensively by numerous investigators, the transport of dense, polydisperse colloid suspensions in a fracture with spatially variable and anisotropic aperture has not been previously explored. Simulated snapshots and breakthrough curves of ensemble averages of several realizations of a log-normally distributed aperture field show that polydisperse colloids exhibit greater spreading than monodisperse colloids, and dense colloids show greater retardation than neutrally buoyant colloids. Moreover, it is demonstrated that aperture anisotropy oriented along the flow direction substantially increases colloid spreading; whereas, aperture anisotropy oriented transverse to the flow direction retards colloid movement.     

Novel cytotoxic brominated diterpenes from the red alga Laurencia obtusa

Five new brominated diterpenes, along with two known, have been isolated from the organic extract of the red alga Laurencia obtusa, collected from the coastal rocks of Preveza in the Ionean Sea, Greece. The novel metabolites prevezols B-E possess two new carbon skeletons, to the best of our knowledge, unprecedented in the literature. The structures and the relative stereochemistry of the new natural products were established by means of spectral data analyses. The new metabolites were tested for their cytotoxic activity against five human cell lines. Two metabolites have exhibited significant cytotoxicity.     

All-solid-state potentiometric sensors for ascorbic acid by using a screen-printed compatible solid contact

The development of all-solid-state potentiometric ion selective electrodes for monitoring of ascorbic acid, by using a screen-printed compatible solid contact is described. The applied methodology is based on the use of PVC membrane modified with some firstly-tested ionophores (triphenyltin(IV)chloride, triphenyltin(IV)hydroxide and palmitoyl-l-ascorbic acid) and a novel one synthesized in our laboratory (dibutyltin(IV) diascorbate). Synthesis protocol and some preliminary identification studies are given. A conductive graphite-based polymer thick film ink was used as an internal solid contact between the graphite electrode and the PVC membrane. The presence and the nature of the solid contact (plain or doped with lanthanum 2,6-dichlorophenolindophenol (DCPI)) seem to enhance the analytical performance of the electrodes in terms of sensitivity, dynamic range, and response time. The analytical performance of the constructed electrodes was evaluated with potentiometry, constant-current chronopotentiometry and electrochemical impedance spectroscopy (EIS). The interference effect of various compounds was also tested. The potential response of the optimized Ph₃SnCl-based electrode was linear against ascorbic acid concentration range 0.005-5.0 mM. The applicability of the proposed sensors in real samples was also tested. The detection limit was 0.002 mM ascorbic acid (50 mM phosphate, pH 5 in 50 mM KCl). The slope of the electrodes was super-Nernstian and pH dependent, indicating a mechanism involving a combination of charge transfer and ion exchange processes. Fabrication of screen-printed ascorbate ISEs has also been demonstrated.     

Intrazeolite photooxygenation of chiral alkenes. Control of facial selectivity by confinement and cation-π interactions

Depending on the nature of the substituents on the stereogenic carbon atom, the ene reaction of singlet oxygen with several chiral alkenes by confinement within thionin-supported zeolite NaY, may exhibit significant changes on facial selectivity by comparison to their photooxygenation reaction in solution. It is proposed that, apart from the conformational consequences as a result of the alkene confinement within the zeolite cavities, a synergism between Na⁺-π interactions and singlet oxygen-Na⁺ interactions plays a significant role in the transition states of ene hydroperoxidation. Within NaY, the diastereoselectivity may significantly depend on the site selectivity, as probed through specific deuterium labelling of trisubstituted alkenes bearing a gem-dimethyl group. In certain cases, a remote stereogenic centre relative to the reacting double bond may induce enhanced diastereoselection and regioselectivity.     

Remarkable change of the diastereoselection in the dye-sensitized ene hydroperoxidation of chiral alkenes by zeolite confinement

[reaction: see text] The ene reaction of singlet oxygen with chiral trisubstituted alkenes bearing an alkyl and a phenyl group at the stereogenic center is erythro diastereoselective in solution and threo diastereoselective if carried out within zeolite Na-Y. The change of the diastereoselection trend by zeolite confinement is attributed to a synergism of steric effects and cation-pi interactions.     

Synthesis and thermal stability of the resins prepared from the reactions of 1,4-bis(2,2-dicyanovinyl)benzene with aromatic diamines and electrical conductivity of the resulting materials following pyrolysis

New thermosetting resins were prepared from the reaction of 1,4-bis(2,2-dicyanovinyl)benzene with aromatic diamines in varying molar ratios. The thermal stability of these resins was correlated with their composition and the curing conditions. They were stable in N₂ up to 370–448°C and afforded anaerobic char yields of 73–84% at 800°C after curing at 300°C for 20–60 h. The temperature dependence of the electrical resistivity of all resins pyrolyzed at 700°C for 15 h was studied in the temperature range from ?173–327°C (100–600 K). The results showed that at room temperature the unpyrolyzed polymers have insulating properties, whereas a dramatic decrease in the electrical resistivity is observed following pyrolysis. The temperature dependence of the electrical resistivity suggests that all of the materials studied have semiconducting properties. The observed electrical conductivity is thermally activated with activation energies ranging from 0.03–0.06 eV. © 1994 John Wiley & Sons, Inc.     

Mechanism for large first hyperpolarizabilities of phosphonic acid stilbene derivatives

This paper presents calculations of dipole moments (mu), static polarizabilities (alpha), and first hyperpolarizabilities (beta) of phosphonic acid stilbene derivatives calculated in the framework of density functional theory. These calculations were performed using a finite field approach implemented in the density functional program ALLCHEM and were of an all-electron type using local exchange-correlation functional and specially designed basis sets. The molecular structures have been fully optimized using the semiempirical program MSINDO. Some of the investigated stilbenes have been synthesized very recently while others are described for the first time. Donor and acceptor groups of these analogues have been modified and the influence of these changes on the first hyperpolarizabilities has been investigated. This work demonstrates that the nonlinear optical response beta of these compounds increases dramatically when the acceptor moiety is displaced by analogues containing alkali metal groups. A general mechanism for the design of novel nonlinear optical materials with large first hyperpolarizabilities is described.