Oxygen-containing polycyclic aromatic hydrocarbons (OPAHs) are potential contributors to the 11.3 m band in interstellar observations. To further explore their role in the interstellar medium, we have investigated their fate after photoprocessing by VUV radiation; in particular, we studied the dissociative photoionization of the simplest OPAH, benzofuran, with imaging photoelectron photoion coincidence spectroscopy, iPEPICO. Ionized benzofuran dissociates by loss of CO, followed by a sequential H atom loss. The parallel HCO-loss channel, leading to the same bicyclic C7H5+ fragment ion, is not competitive at low excess energies above the ionization threshold. However, the collision-induced dissociation tandem mass spectrometry results suggest that CO and HCO may be formed in parallel at higher energies. An RRKM fragmentation model reproduced the iPEPICO data well assuming the initial 1,2-H shift transition state to be rate determining to CO loss. The breakdown diagram and the measured dissociation rates agreed well at the CBS-QB3-calculated activation energy of 2.99 eV, which could be relaxed to 3.25 eV, and only a slight adjustment of the ab initio activation entropy. The model barrier to sequential H-loss is larger than the computed H-loss threshold and the breakdown diagram rises less steeply than predicted, which indicates suprastatistical kinetic energy release after the tight H-transfer transition state of the first step. HCO cleavage is possible after a ring-opening transition state, which is looser than and isoenergetic with the CO-loss transition state. However, a subsequent ring formation transition state at 3.85 eV is moderately tight, which suppresses HCO loss at low excess energies.
The Maya employed the k’an |K’AN| glyph in Late Classic (~750 CE) hieroglyphs on murals and polychrome pottery as an adjective meaning precious, yellow. On cacao drinking vessels, the k’an glyph was suggested as a descriptor for a flavoring ingredient, allspice, Pimenta dioica (L.) Merr. (Myrtaceae). However, our previous consensus ethnobotanical fieldwork with Q’eqchi’ Maya healers of Belize revealed another candidate among antidiabetic plants, Tynanthus guatemalensis Donn. Sm. (Bignoniaceae), which was the healers’ top selection for treatment of diabetes and an exceptionally active extract in an antidiabetic assay for inhibition of protein glycation. Traits of T. guatemalensis observed after cross sectioning the liana were: (1) a cross-shaped xylem organization similar to the k’an glyph; (2) an allspice-like aroma; and (3) yellow color. Based on taxonomy and ethnobotany, confirmation of the allspice-like aromatic compound eugenol, and antidiabetic activity, we determined the plant described by the k’an glyph to be T. guatemalensis (chib’ayal in Q’eqchi’), not P. dioica (allspice). In contemporary Q’eqchi’ tradition, the section of the chib’ayal vine with its cross is associated with the eighth day of their Tzolk’in calendar, which is called the “nawal” (energy) of “q’anil” (ripe, full yellow). This day is represented with a different glyph from the k’an glyph, but notably has a cross representing the four cardinal points. The identification of a potent medicinal plant used in the late classic as well as contemporary times may suggest the long-term preservation of traditional medicinal knowledge in Maya culture for pharmacologically significant plants.
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