Schatz et al.
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A. KHAN. Yes, there has been extensive work on that, particularly guanine is sensitive to reaction with singlet oxygen.
H. SELIGER. In the bioluminescent systems in biological organisms nature appears to have chosen an oxygenation mechanism which initially adds oxygen as
\
/c-c
/O
'\OH Then possibly by dioxetane or hydroxyl attack the C-C bond is split, and an excited state product molecule different from the parent substrate emits fluorescence or sensitizesthe fluorescenceof a suitable acceptor. There are many methods of achieving excited states and some of the ' 0 2 mechanism you have shown are possible. However, for biological chemiluminescence,singlet oxygen does not appear to be a necessary constituent. In the delayed luminescence of chloroplasts there are several experimental lines of evidence which imply
a chemical origin of the excited state emitter, Le., pH or ion gradient effects. This, of course, does not eliminate the necessity for initial excitation by light. The lifetimes observed are not exponential but appear to follow a log-log relation. Again singlet oxygen requirement would not be a unique pathway. A. KHAN. Only the basic physical process, the occurrence of a triplet state, for instance, of chlorophyll and the occurrenceof a singlet state of oxygen would be necessary. They could annihilate and elect to produce an excited state. Now, the sourceof singlet oxygen; we know, for instance, dioxetane decomposition could stimulate an excited state, which could generate by sensitization singlet oxygen. There are a large number of ways whereby one can generate singlet oxygen. B. WATSON.I would like to comment on the supposed involvement of singlet oxygen in various chemiluminescentreactions in biological systems, as observed by several groups using scintillation counters operated in out-of-coincidence mode. Contrary to the assertions of these authors, direct singlet oxygen contribution to the observed luminescence is quite unlikely and could be proved or disproved using a simple monochromator setup with photon counting.
Magnetic Circularly Polarized Emission from Crystalline Cs2ZrCI6:Re4+ H. G. Brittain, F. S. Richardson, J. P. Jasinski, W. C. Yeakel, and P. N. Schatz' Department of Chemistry, University of Virginia, Charlottesville, Virginia 2290 1 (Received January 29, 1976) Publication costs assisted by the Petroleum Research Fund
High resolution, low temperature magnetic circularly polarized emission (MCPE) and total emission spectra are reported for Re4+(5d3)doped into single crystals of Cs2ZrC16. With A,,
