Phytochemical and antioxidant studies of Laurera benguelensis growing in Thailand.
The aim of this study was to investigate metabolites of the lichen Laurera benguelensis. A high-performance liquid chromatographic (HPLC) method has been developed for the characterization of xanthones and anthraquinones in extracts of this lichen. Lichexanthone, secalonic acid D, norlichexanthon, parietin, emodin, teloschistin and citreorosein were detected in the lichen samples, which were collected from two places in Thailand. Components of the lichen were identified by relative retention time and spectral data. This is the first time that a detailed phytochemical analysis of the lichen L. benguelensis was reported and this paper has chemotaxonomic significance because very little has been published on the secondary metabolites present in Laurera species. Some of the metabolites were detected for the first time in the family Trypetheliaceae. The results of preliminary testing of benzene extract and its chloroform and methanol fractions showed that all samples showed a weak radical scavenging activity. The chloroform extract showed the highest antioxidant activity.
Biopharmaceutical potential of lichens
Context: Lichens are composite organisms consisting of a symbiotic association of a fungus (the mycobiont) with a photosynthetic partner (the phytobiont), usually either a green alga or cyanobacterium. The morphology, physiology and biochemistry of lichens are very different from those of the isolated fungus and alga in culture. Lichens occur in some of the most extreme environments on the Earth and may be useful to scientists in many commercial applications. Objective: Over the past 2 decades, there has been a renewed and growing interest in lichens as a source of novel, pharmacologically active biomolecules. This review summarizes the past and current research and development trends in the characterization and use of lichens and their bioactive compounds in traditional medicine and other biopharmaceutical applications of commercial interest. Methods: The present review contains 10 illustrations and 188 references compiled from major databases including Science Direct, Chemical Abstracts, PubMed and Directory of Open Access Journals. Results: Lichen morphology, symbiosis, diversity and bioactivities including enzyme inhibitory, antimicrobial, antifungal, antiviral, anticancer, anti-insecticidal and antioxidant actions were reviewed and summarized. Recent progress in lichens and lichen-forming fungi was discussed with emphasis on their potential to accelerate commercialization of lichen-based products. Conclusions: Lichens are an untapped source of biological activities of industrial importance and their potential is yet to be fully explored and utilized. Lichen-derived bioactive compounds hold great promise for biopharmaceutical applications as antimicrobial, antioxidant and cytotoxic agents and in the development of new formulations or technologies for the benefit of human life.
Suppressed Light Emission of the Reaction Zone in Detonation
THE detonation of high explosives in water can be photographed with an open camera and a flash light as the explosive gases do not emit light. The method has been used1 to investigate the spread of shock waves and explosive gases, and to investigate the initiation by shock waves2. We have found that it can be used also in certain gases such as butane and propane. The method is not suitable, on the other hand, for explosives with two levels of detonation velocity in the case of low velocity. A great part of the reaction then occurs after the reaction zone has passed and the expanding explosive gases are very luminous even in water.