Acid-base and tautomeric equilibria of harmol in the ground and first excited singlet states

UVA Photoactivation of Harmol Enhances Its Antifungal Activity against the Phytopathogens Penicillium digitatum and Botrytis cinerea

“…In the case of harmol, the most relevant equilibrium present under physiological pH involves the deprotonation of the pyridinic nitrogen (N-2), with an overall p K a value of 7.8 ( Figure 1 ). This p K a value is in agreement, within the experimental error, with the value previously reported ( Tomas et al, 1985 ). The other functional groups, i.e., the hydroxy-substituent placed at position 7 and the nitrogen of the indole ring, have p K a values higher than 9.6.…”

β-Carboline alkaloids as matrices for UV-matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in positive and negative ion modes. Analysis of proteins of high molecular mass, and of cyclic and acyclic oligosaccharides

“…), 20,21 crystalline structure, electronic properties (UV-visible absorption and fluorescence spectra; molar absorption coefficient; fluorescence life-time; fluorescence quantum yield; electron affinity; ionization potential), [22][23][24] as well as acid-basic behavior in the ground state (pK a ) and in the lower excited singlet state (pK a * ), depends strongly on the simultaneous presence of both the indolic acid NH and the pyridinic basic N groups. Besides, the well known dramatic increase of the basic character of the pyridinic N group in the excited singlet state, expressed as a high DpK a value (DpK a =pK a * -pK a , see Table 4), in both liquid solutions (water [25][26][27] and organic media [22][23][24]28 ) and in the solid state, [22][23][24] would account for the outstanding capability shown by bcarbolines to work as anionizing matrices in negative ion mode (Tables 2, 3 and 4). This property, together with the different capabilities shown by each individual b-carboline to produce homogeneous crystallization in the matrixanalyte film deposited on the stainless steel slides (see discussion in Experimental section), would account for the general behavior observed for b-carbolines and specially for that observed for harmaline, harmane and nor-harmane (see Tables 2,3 and 4).…”

Photochemical behaviour of β-carbolines. Part 4.1 Acid–base equilibria in the ground and excited states in organic media

“…Electronic excitation results in significant charge-density changes due to the presence of two different types of nitrogen atoms in their structure (pyridinic and pyrrolic). These acid-base equilibria have been extensively studied in aqueous solution as a function of pH; [11][12][13][14][15] the pK and the first excited state pK* values have been determined, [10][11][12][13][14][15][16] together with some kinetic parameters. 17, 18 In addition, fluorescence quantum yields and/or lifetimes have been determined in water at different pH values.…”