A new ascorbate-induced chloroplast absorbance change which has the characteristics of a carotenoid shift is described. The absorbance change was light-dependent at pH 7 but not at pH 5. The difference spectra for the light and dark changes were similar, showing a large absorbance peak at 505 nanometers, smaller peaks near 468 and 437 nanometers, and a sharp valley around 483 nanometers. The ab...

The epoxidation reaction using heterogeneous solid catalysts with H2O2 as oxidants are environmentally friendly routes to produce extensively useful epoxides which are traditionally obtained from capital-intensive or environmentally polluted processes. In this paper, various types of solid catalysts for the epoxidation of olefins with H2O2 as oxidants are reviewed. The efficient catalysts repor...

Samples of particulate organic matter from the water column and anoxic Holocene sediment layers from the Small Meromictic Basin (SMB) in Ellis Fjord (eastern Antarctica) were analyzed to study the early incorporation of reduced inorganic sulfur species into highly branched isoprenoid (HBI) alkenes. HBIs were not detected in the water column samples from austral winter, whereas compounds contain...

Metallocalixarenes were grafted onto silica using a surface organometallic approach and shown to be active and selective catalysts for epoxidation of alkenes using organic hydroperoxides. Calixarene-Ti(IV) precursors were anchored at surface densities from 0.1 to near-monolayer coverages (0.025-0.25 calixarene nm(-2)). Several spectroscopic methods independently detected calixarene-Ti(IV) conne...

A new chiral binaphthyl-strapped iron-porphyrin 4 b that exhibits unprecedented catalytic activity toward the enantioselective epoxidation of terminal olefins was synthesized. Typical enantiomeric excesses (ee) of 90 % were measured with a maximum of 97 % for the epoxidation of styrene, whereas the turnover numbers (TON) averaged 16000.

The key factors for carbonyl-stabilised ammonium ylide-mediated epoxidation reactions were systematically investigated by experimental and computational means and the hereby obtained energy profiles provide explanations for the observed experimental results. In addition, we were able to identify the first tertiary amine-based chiral auxiliary that allows for high enantioselectivities and high y...

The cytochromes P450 are versatile enzymes involved in various catalytic oxidation reactions, such as hydroxylation, epoxidation and dehydrogenation. In this work, we present combined experimental and theoretical studies on the change of regioselectivity in cyclohexadiene oxidation (i.e., epoxidation vs dehydrogenation) by oxoiron(IV) porphyrin complexes bearing different porphyrin ligands. Our...

The mechanism and origin of asymmetric induction in the Mn(III)(salen)-catalyzed epoxidation by peracetic acid have been elucidated by the density functional [Becke three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional (B3LYP)] method in two different regimes: with and without an axial ligand. The acylperoxo complexes of Mn(II,III,IV) in cisON cisNO and trans geom...

Reversible nonphotochemical fluorescence quenching depends on thylakoid lumen acidification and violaxanthin de-epoxidation and is correlated with photoprotection of photosynthesis. The O2-dependent electron flow in the coupled Mehler-ascorbate peroxidase reaction (MP-reaction) mediates the electron flow necessary for lumen acidification and violaxanthin de-epoxidation in isolated, intact chlor...