. Cell chemistry; a collection of papers dedicated to Otto Warburg on the occasion of his 70th birthday. Warburg, Otto Heinrich, 1883-; Biochemistry. VOL. 12 (1953) CARCINOGENIC COMPOUNDS, PURINES AND NUCLEIC ACID 85 10:, I 61 — ~o__ 70 80 90 % Ionization Fig. 10. lonisation of 3:4-6:7-dibenzacridine in purine solutions. X X, in 71/ tetramethyluric acid; O. -0, in DNA. , in -^^ caffeine; /O TABLE IV pKa VALUES OF THE DIBENZACRIDINES IN PURINE SOLUTIONS Dibenzacridine Solvent pKa 3:4-6:7 DBA ^ 1:2-6:7 DBA 1:2-8:9 DBA 25 %. 50% or 75% ethanol DNA 50% ethanolic
. Cell chemistry; a collection of papers dedicated to Otto Warburg on the occasion of his 70th birthday. Warburg, Otto Heinrich, 1883-; Biochemistry. VOL. 12 (1953) CARCINOGENIC COMPOUNDS, PURINES AND NUCLEIC ACID 85 10:, I 61 — ~o__ 70 80 90 % Ionization Fig. 10. lonisation of 3:4-6:7-dibenzacridine in purine solutions. X X, in 71/ tetramethyluric acid; O. -0, in DNA. , in -^^ caffeine; /O TABLE IV pKa VALUES OF THE DIBENZACRIDINES IN PURINE SOLUTIONS Dibenzacridine Solvent pKa 3:4-6:7 DBA ^ 1:2-6:7 DBA 1:2-8:9 DBA 25 %. 50% or 75% ethanol DNA 50% ethanolic DNA -^^ caffeine M tetramethyluric acid M tetramethyluric acid M tetramethyluric acid DISCUSSION The molecular compounds formed between caffeine (or tetramethyluric acid) and one of the dibenzcarbazoles (or dibenzacridines), which have so far been isolated, resemble the hydrocarbon-purine complexes isolated by Weil-Malherbe, in that only small changes in light absorption are associated with their formation. In this way they differ from the molecular compounds formed between nitro-compounds and hydrocarbons or amines. The change or intensification of colour which takes place in these cases has been ascribed to the formation of a complex molecule, essentially ionic in character, involving an electron transfer from the unsaturated hydrocarbon to the poly-nitro compound (Weiss^^; Kronberger and Weiss^^). The infrared absorption spectra of the complexes of purines with hydrocarbons and with aromatic nitrogenous substances (Booth, Boyland and Orr^^) are similar to those References p. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Burk, Dean. Amsterdam, Houston, Elsevier Pub. Co.
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