Articolo in rivista, 1995, ENG, 10.1111/j.1751-1097.1995.tb05259.x

SPECTROSCOPIC AND PHOTOACOUSTIC STUDIES OF HYPERICIN EMBEDDED IN LIPOSOMES AS A PHOTORECEPTOR MODEL

F. Lenci, N. Angelini, F. Ghetti, A. Sgarbossa, A. Losi, A. Vecli, C. Viappiani, P. Taroni, A. Pifferi, R. Cubeddu

Istituto Biofisica CNR, Via S. Lorenzo 26, 56127 Pisa, Italy Dipartimento Fisica Universita, V, le Scienze, 43100 Parma, Italy CEQSE CNR e Dip. Fisica Politecnico, P. le Da Vinci, 20131 Milano, Italy

In photoresponsive ciliates, like Blepharisma japonicum and Stenter coeruleus, the photoreceptor pigments responsible for photomotile reactions are hypericin-type chromophores packed in highly osmiophilic subpellicular granules. Liposomes loaded with hypericin can constitute a simple model system, appropriate for understanding the primary light-induced molecular events triggering the sensory chain in these microorganisms. Optical absorption, steady-state and time-resolved fluorescence and pulsed photoacoustic calorimetry have been used to measure spectral distributions, fluorescence lifetimes, radiative and radiationless transition quantum yields of hypericin when assembled into egg L-alpha-phosphatidylcholine liposomes. With respect to hypericin ethanol solutions, both absorption and fluorescence maxima are 5 nm red shifted when the pigment is inserted into the lipidic microenvironment, regardless of the hypericin local concentration. Increasing by 100 times the hypericin local concentration decreases the relative fluorescence quantum yield by a factor of around 150 and the fraction of thermally released energy, conversely, increases from 0.6 to 0.9. From the analysis of fluorescence lifetimes and their relative amplitudes it appears that a subnanosecond living component is predominant at the highest hypericin local concentrations.

Photochemistry and photobiology 62 (1), pp. 199–204

Keywords

CNR authors

Cubeddu Rinaldo, Pifferi Antonio Giovanni, Taroni Paola, Viappiani Cristiano, Sgarbossa Antonella, Angelini Nicola, Lenci Francesco, Ghetti Francesco

CNR institutes

IBF – Istituto di biofisica

ID: 266818

Year: 1995

Type: Articolo in rivista

Creation: 2013-10-27 16:16:50.000

Last update: 2022-11-17 15:51:50.000

External IDs

CNR OAI-PMH: oai:it.cnr:prodotti:266818

DOI: 10.1111/j.1751-1097.1995.tb05259.x

ISI Web of Science (WOS): A1995RJ71000029