Autoluminescent plants that express a bacterial bioluminescence gene cluster 1 have not been widely adopted due to requisite expression in plastids and low light output. Alternatively, we have engineered tobacco lines expressing a fungal bioluminescent system 2 , which converts caffeic acid present in all plants into luciferin, and report self-sustained luminescence easily visible to the naked eye. Our findings might underpin development of a suite of imaging tools for plants.

4-Hydroxycoumarin 1, 4,5-dihydroxycoumarin 2, and 4,7-dihydroxycoumarin 3 undergo H–D exchange at the C(3) atom of the lactone ring. Although only the 4-hydroxy-2-chromenone tautomeric forms are seen in the 1H and 13C NMR spectra of compounds 1–3, the equilibrium between the 4-hydroxy-2-chromenone and 2,4-chromandione forms is suggested to be the key step in the H–D exchange reaction. 4,5-Dihydroxycoumarin shows the highest rate of the reaction, since H-bonding between 5-hydroxyl and 4-keto functional groups can provide relative stability to the 5-hydroxy-2,4-chromandione tautomeric form, a probable intermediate of the exchange. NMR spectra and tautomeric transformations of 3-(4-methoxyphenylazo)-4-hydroxycoumarin 4 and 3-acetyl-4-hydroxycoumarin 5 are also discussed. The stabilities of different tautomeric forms of compounds 1–5 have been evaluated by MNDO calculations. Keywords: 4-hydroxycoumarin derivatives, keto-enol tautomerism, H–D-exchange.

No abstract

No abstract

The results of NMR-spectroscopy studies of the structure, dynamic stereochemistry, and intermoleeular interactions in solutions of organic derivatives of penta-and hexacoordinated silicon, germanium, and tin containing amidomethyl, lactamomethyl, and related bidentate ligands are surveyed.