For some unknown reasons LiPc crystals are not very stable under certain conditions. For example it is well known that these crystals are sensitive to oxygen after a few months in pure water and in brain but in a muscle lose their sensitivity to oxygen in a few days. Dr. Sutcliffe observed apparent instability of LiPc when in use but it was not clear if this was due only to the quality of the LiPc available to him. In studies at the Institute of Food Research in the U.K., it was found that the oxygen sensitive properties of lithium phthalocyanine appeared to vary more than expected when placed in different types of oils. Therefore a systematic study of the stability of LiPc crystals in sunflower oil was undertaken using well characterized LiPc. Five crystals from two different batches were placed in a Teflon tube filled with sunflower oil. Three crystals (from one batch) had the same and the usual sensitivity to oxygen on the first day and two months later. Two LiPc crystals (from a different batch) had only half of the sensitivity on the first day and no sensitivity at all after two months. This experiment indicates that we do not yet fully understand the factors which affect the stability of the oxygen-sensitive properties of LiPc crystals. While this is problematic, it also raises hope that with such understanding, we may be able to improve further their stability in tissues such as muscles where currently they cannot be used for more than a few days.
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