New insights into the photophysics and photochemistry of harmalol in aqueous media?

J. GABRIEL YAÑUK; M. PAULA DENOFRIO; M. LIS ALOMAR; M. MICAELA GONZALEZ; ROSA ERRA-BALSELLS; FRANCO M. CABRERIZO

Cordoba

Congreso; 16th International Congress on Photobiology; 2014

  Harmalol is a naturally occurring alkaloid that belongs to the family of b-carbolines (bCs). bCs comprise  both  fully  aromatic  alkaloids  and  partially  reduced  derivatives  such  as  3,4-dihydro- and 1,2,3,4-tetrahydro-bCs. In terms of its chemical structure, harmalol is a 3,4-dihydro-bC.  During the last decades, the photophysics and photochemistry of some bCs, in aqueous media, has been well investigated [1-3]. Briefly, in aqueous solution, these alkaloids may show several acid-base  equilibria.  However,  for  some  dihydro-  and  tetrahydro-bCs,  the  information published in the literature is, in somehow, contradictory, negligible or null [4-8].  In the present work we have investigated the acid-base equilibria and species present in the pH range  of  2-13.  The  corresponding  pKa  values,  chemical  structure  of  each  harmalol  acid-base specie,  as  well  as  the  corresponding  absorption  and  emission  spectra  observed  in  aqueous solution  are  reported.  Moreover,  the  pH-effect  on  the  thermal  and  photochemical  stability  of harmalol is also reported.   Scheme 1.Acid-base equilibria of harmalol, in its ground state, in aqueous solution under different pH conditions.