SPECTRAL CHARACTERISTICS AND ACID-BASE EQUILIBRIA OF 4,9-DIHYDROXY-5,10-DIOXO-4,5,9,10-TETRAHYDRO-4,9-DIAZAPYRENE AND ITS 2,7-DERIVATIVES Article Zaitsev B.E., Migachev G.I., Koval'chukova O.P., Matyushenko V.V. Chemistry of Heterocyclic Compounds. Латвийский институт органического синтеза Латвийской академии наук / Springer New York Consultants Bureau. Vol. 29. 1993. P. 81-86