Isolation and purification of the bioactive carotenoid zeaxanthin from the microalga Microcystis aeruginosa by high-speed counter-current chromatography

High-speed counter-current chromatography was successfully applied for the first time to the isolation and purification of the bioactive carotenoid zeaxanthin from the cyanobacterium Microcystis aeruginosa. The crude zeaxanthin was obtained by extraction with organic solvents after the microalgal sample had been saponified. Preparative high-speed counter-current chromatography with a two-phase solvent system composed of n-hexane-ethyl acetate-ethanol-water (8:2:7:3, v/v/v/v) was successfully performed yielding zeaxanthin at 96.2% purity from 150 mg of the crude extract in a one-step separation. The recovery of zeaxanthin was 91.4%. This was also the first report that zeaxanthin was successfully separated and purified from microalgae.     

Concepts of photochemical damage of Photosystem II and the role of excessive excitation

Photoinhibition is one of the most controversial topics in photophysiology. Well into the 21 st century, scientists have not agreed on the mechanism of action, primary site, and roles of excess energy absorbed by photosynthetic pigments. It is recognized that Photosystem II is the most fragile component during photoinhibition and that excess excitation absorbed by the photosynthetic pigments has a strong impact on it. Consensus is yet to come on terminology, guidelines to study photoinhibition, or boundaries of what can be considered photodamage. Some of these controversies are the result of how we understand the phenomenon of photoinhibition, as this is what determines a given experimental design. Thus, how we understand photodamage depends on the philosophical approach of each group. While some efforts have been made in the parametrization of Photosystem II photoinhibition, an updated review about the concepts of photoinhibition of Photosystem II and how to study it is still pending. In this work, a review of the concepts used in the field of photoinhibition is presented, accompanied by a synopsis on the history and mechanisms of action.     

Theoretical study of solvent effects on the structures and isomerization of silylenoid H<Subscript>2</Subscript>SiLiF

The structures and isomerization of silylenoid H₂SiLiF are investigated by density functional theory (DFT) at B3LYP/6-311+G(d,p) level. The solvent effects are modeled using the self-consistent reaction field (SCRF) method with Tomasi’s polarized continuum model (PCM). Five representative solvents, i.e. benzene, ether, THF, acetone, and DMSO, are chosen for this work. Special attention is paid to THF solvent. The results indicate that the polarity of solvents has played an important role on the structures and relative stabilities of different isomers. Contrary to the three-membered ring structure 1, the relative stability of the “classical” tetrahedron structure 4 increases with increasing dielectric constants (ε) of solvents. The σ-complex isomer 3 is most unstable structure. Although the relative energies are reduced with increasing dielectric constants (ε) of solvents, the p-complex structure 2 still has the lowest energy. The effects of solvents on the dipole moments and charge distributions are also discussed.