Luminescence spectra of harmine, harmaline, reserpiline and 3-dehydroreserpines

Photophysical and spectroscopic features of 3,4-dihydro-β-carbolines: a combined experimental and theoretical approach

The spectroscopic and photophysical properties of 3,4-dihydro-β-carboline alkaloids in aqueous were revisited. Absorbing and emitting species present in aqueous solution in the entire pH range were reassigned by DFT calculations.

Fluorescence quenching ofβ-carboline alkaloids in micellar media. A study to select the adequate surfactant to use in analytical techniques

The study of fluorescence quenching of the fluorophores allows the localization of the alkaloids (harmane and harmine) in the micelles (SDS, CTAB, Brij-35) to be established. In aqueous micellar solutions (SDS and Brij-35) at pH 13.0, emission corresponding to the neutral or zwitterionic forms can be observed. In the presence of CTAB (pH = 13.0) it was possible to observe the emission of anionic form. These species are not present in buffered aqueous solutions at these pH values. Bromide ion was added to the different surfactant solutions and the quenching effect was studied according to the Stern-Volmer equation. In the presence of SDS the quenching effect is considerably reduced compared to the aqueous solutions without surfactants, while for Brij-35 micelles were similar to those observed in homogeneous aqueous solution. For CTAB micelles a notable fluorescence quenching was observed for the different pH values studied. The fluorescence quenching studies show that the neutral species are associated inside the micelles, instead of the ionic species (cationic, zwitterionic or anionic) remaining on the surface of the micelles. The anionic surface of SDS micelles prevents the quenching effect by anionic quenchers for both neutral and charged species.

Detection and characterization of cyclodextrin complexes with beta-carboline derivatives by spectroscopic techniques

beta-Carboline alkaloids exhibit a great variety of pharmacological activities. The solid inclusion complexes of harmane and harmine with beta-cyclodextrin and also with hydroxypropyl-beta-cyclodextrin, have been prepared following different procedures. IR and NMR spectroscopies were employed to verify the interaction of the guest molecules with the cyclodextrin cavities. The differences observed in the IR and NMR spectra are in agreement with those described in the literature for other guest molecules. The shifts in the 13C- and 1H-NMR spectra confirm the existence of the inclusion complexes. The fluorescence emission spectra of these complexes dissolved in buffered aqueous solution (pH 7.3) exhibit the characteristic peaks of the cationic form for harmane alkaloids. The neutral bands are not present for the free alkaloids in aqueous solutions. Fluorescence quenching emission of the complexes is compared to that of the corresponding free alkaloids.

Fluorescence of harmol, harmalol and 2-hydroxycarbazole in concentrated hydroxide solutions

Room temperature electronic absorption and fluorescence spectra of harmol, harmalol and 2-hydroxycarbazole have been obtained in concentrated aqueous potassium hydroxide solutions. The appearance of a new fluorescence band for all these compounds in media of H- greater than 16, has been ascribed to the emission of excited dianions formed by deprotonation. Acidity constants have been estimated from the Föster-Weller method.