Person: Martín Carmona, María Antonia
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First Name
María Antonia
Last Name
Martín Carmona
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Farmacia
Department
Química en Ciencias Farmacéuticas
Area
Química Analítica
Identifiers
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Item Fluorescence properties of the anti-tumour alkaloid luotonin A and new synthetic analogues: pH modulation as an approach to their fluorimetric quantitation in biological samples(Journal of Luminescence, 2012) González Ruiz, Víctor; González-Cuevas, Yamisley; Arunachalam, Sankaralingam; Martín Carmona, María Antonia; Olives Barba, Ana Isabel; Ribelles, Pascual; Ramos García, María Teresa; Menéndez Ramos, José CarlosLuotonin A is an alkaloid structurally related to the natural anti-tumour agent camptothecin. The fluorescence behaviour of luotonin A and a series of six analogues is described in the present work. The influence of solvent polarity and pH on the native fluorescence properties of these alkaloids was studied, finding that in organic solvents or in aqueous solutions (pH 5.5–7.2) the neutral form of the luotonin derivatives emit in the region of 410–450 nm but, in both media, acidification to pH values below 3.0 causes a new emission band to appear at about 500 nm. An ESPT reaction occurs due to the protonation of the basic nitrogen atoms of the pentacyclic ring. Acid-base titrations of luotonin A and its derivatives in aqueous and acetonitrile media were carried out in order to determine their pKa n values which were around 2, showing these compounds to be very weak bases. In aqueous media, the absence of an iso-emissive point in the emission spectra suggests the existence of more than two species in the proton transfer equilibria. The basicity of the luotonin A derivatives is increased in organic media, and a good correlation between the pKa n values and the chemical structure was found. The protonation of luotonin A was also studied by 1 H-NMR and 13C-NMR experiments, which proved the protonation of the nitrogen atoms at the positions 5 and 6 of the pentacyclic ring. The fluorescence quantum yields were determined in ethanol and in aqueous solutions under neutral and acidic conditions. The fluorescence quantum yields were higher in water for the case of the more polar compounds, and the opposite result was obtained for the more hydrophobic ones. The remarkable and interesting fluorescence properties of luotonin A prompted the development of its fluorimetric analytical quantitation, obtaining very good analytical features