LOW-TEMPERATURE PHOTCOXIDATION OF CHLOROPHYLL-A*

Abstract— Illumination of chlorophyll at low temperature, in solvents containing organic Lewis bases and oxygen, leads to oxidation of the C-2 vinyl group. This oxidation proceeds through a series of thermal and photochemical changes, including initial formation of a new compound (I) absorbing at 620 nm. This undergoes further rapid photochemical (or thermal) conversion back to a chlorin-like substance (II), and much slower phototransformation to a third intermediate (III) absorbing near 500 nm. The reaction requires complexed metal (Mg or Zn), but not an intact cyclopentanone ring. The ‘620’ photoproduct is assigned to a cyclic peroxide involving C-1 of chlorophyll and the vinyl group.     

Molecular Dynamics simulation of aqueous ZnC12 solutions

An important medium for ore transport within the Earth is by hydrothermal fluids. To understand ore transportation processes by hydrothermal fluids it is necessary to determine the clustering of dissolved ionic species in aqueous solution. We have chosen sphalerite, an important zinc containing mineral, as an example. We describe the results of Molecular Dynamics simulations to predict which chlorozinc complexes will occur at the pressures and temperatures found in the Earth's crust. Potentials have been derived for zinc-water and zinc-chloride interactions using density functional calculations. Although the DFT calculations provide good gas-phase clusters, the resulting potentials do not work well when modelling aqueous solutions. We therefore describe attempts to modify the potential to compensate for these effects. We show that at low chloride concentrations the dominant species are Zn(H₂O)²⁺ ₆, and ZnC1(H₂O)⁺ ₅. At higher temperatures there are a significant number of clusters which contain more than one zinc with bridging chloride ions. In aqueous solutions with a high chloride concentration the dominant species are Zn(H₂O)²⁺ ₆, ZnC1₂(H₂O)⁰ ₄ and ZnC1₃(H₂O)^? ₃. There are almost no clusters containing more than one zinc.