Chemical Education Today
Letters More Thoughts on the Narra Tree Fluorescence Mark Muyskens, in his recent contribution (1) to the useful series “Tested Demonstrations”, presents an interesting and charming example of fluorescence from a natural product, the wood of narra tree (Pterocarpus indicus). As historical background the author noted that the narra tree was known as Lignum nephriticum,1 the mysterious medicinal wood that gave rise to the first reference to fluorescence in Europe in 1565 by Nicolás Monardes from Sevilla (2). In addition, Muyskens reports on his attempts to determine whether the pH-dependent fluorescence of the narra aqueous extract is due to an isoflavone related to formononetin, as was claimed before (3). He concluded finally “formononetin cannot by itself account for the fluorescence”. Muyskens should be praised for designing such a lucid demonstration of fluorescence, as well as for his efforts to excite the student’s interest on the history of luminescence. On the other hand, the two aspects commented above, the source of L. nephriticum and the substance responsible for the intense blue fluorescence of the wood water extract, may require further consideration. Regarding the unknown botanic origin of L. nephriticum we (and others) have argued (4) that the most likely source was the Mexican tree Eysenhardtia polystachya (kidneywood), which is also mentioned in Muyskens text.2 Eynsehardtia trees can be found today as high as 20 meters and even forming forests in some parts of Mexico. We also have shown that both the wood’s medicinal properties and its striking blue color (fluorescence) were already known by Aztec prehispanic doctors, who passed this information to pioneer anthropologist Bernardino de Sahagún, a Franciscan missionary. Of course, several 19th century Mexican professional naturalists and all of the traditional healers certainly knew kidneywood’s original source. Nowadays the wood can be easily obtained in different parts of Mexico, sold as “sweet wood” or “blue wood” by local vendors of medicinal plants. The wood’s easily water-soluble emitting dye is unlikely to be found in significant quantities in petrol extracts of the plant. On the contrary, Beltrami et al. (5) isolated from water extracts of E. polystachya large quantities of two non-fluorescent C-glucosyl dihydrochalcones, which they named Coatline A and B. We contend that the long-sought blueemitting compound of L. nephriticum is a Coatline B reaction product, which is formed in slightly alkaline water solution (4c, d).
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This quite scholarly discussion over a 400 years-old mystery of science, which attracted the keen interest of Kircher, Grimaldi, Boyle, Newton, Priestley, and many other classic scientists may add a bit of controversy to the excellent contribution of Muyskens to the teaching of fluorescence in the classroom. Notes 1. Lignum nephriticum is not a proper Linnaean botanic binomial, but just the common name of a commercial product. 2. Monardes’ Lignum nephriticum was described originally in 1565 and was being used in Europe from ca.1530. Its true botanic origin cannot be the wood of Pterocarpus indicus, which is a tree from the Republic of the Philippines, as the Philippines became a Spanish colony in 1565 and only a few years later regular traffic started between the Islands and Nueva España (Mexico).
Literature Cited 1. Muyskens, M. J. Chem. Educ. 2006, 83, 765–768. (b) Muyskens, M. J. Chem. Educ. 2006, 83, 768A–768B 2. Monardes, N. B. Dos Libros/El vno que trata de todas las cosas que traen de nuestras Indias Occidentales que siruen al uso de Medicina y como se ha de vsar la rayz de Mechoacan, purga excelentissima. El otro libro trata de dos medicinas marauillosas... En casa de Sebastián Trugillo, Sevilla, 1565 3. Burns, D. T.; Dalgarno, B. G.; Gargan, P. E.; Grimshaw, J. Phytochemistry 1984, 23, 167–169. 4. (a) Acuña, A. U. IV Congress on Photochemistry, Gandía, Spain, 1999. (b) Acuña, A. U., 9th International Conference on Methods and Applications of Fluorescence, Lisbon, Portugal, 2005. (c) Acuña, A. U.; Amat-Guerri, F. Early History of Solution Fluorescence: The Lignum Nephriticum of Nicolás Monardes. In Springer Series on Fluorescence Methods and Applications; Barberán-Santos, M. N., Ed.; Springer-Verlag: Berlin, in press. (d) Acuña, A. U.; Morcillo, P.; Amat-Guerri, F. to be submitted for publication. 2006. 5. Beltrami, E.; de Bernardi, M.; Fronza, G.; Mellerio, G.; Vidari, G.; Vita-Finzi, P. Phytochemistry 1982, 21, 2931–2933.
A. Ulises Acuña Institute of Physical Chemistry, CSIC 119 Serrano 28006-Madrid, Spain
[email protected] Vol. 84 No. 2 February 2007
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Journal of Chemical Education
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