Spectroscopic, photophysical and thermodynamic studies of inclusion complexes of beta-cyclodextrin and 2-hydroxypropyl-beta-cyclodextrin with 10-methylbenzophenothiazine
Mdg. Seye et al., Spectroscopic, photophysical and thermodynamic studies of inclusion complexes of beta-cyclodextrin and 2-hydroxypropyl-beta-cyclodextrin with 10-methylbenzophenothiazine, NEW J CHEM, 25(10), 2001, pp. 1290-1296
The inclusion complexes of 10-methyl-12H-benzo[a]phenothiazine (10-MeBPHT)
with beta -cyclodextrin (beta -CD) and with 2-hydroxypropyl-beta -cyclodext
rin (HP-beta -CD) were investigated by electronic absorption and fluorescen
ce spectroscopies in aqueous solutions. 10-MeBPHT fluorescence quantum yiel
ds were significantly larger in the presence of HP-beta -CD (Phi (F) = 0.09
7 +/-0.02) and beta -CD (Phi (F) = 0.025 +/-0.004) than in water (Phi (F) =
0.00435 +/-0.00007). A 1:1 stoichiometry was found for these CD complexes
and formation constants (K-f, evaluated by means of the Benesi-Hildebrand t
reatment) ranged from 14 +/-7 to 50 +/- 11 M-1 (at 20 degreesC), depending
on the nature of the CD. In the case of the 10-MeBPHT: HP-beta -CD complex,
the complexation reaction was endothermic (DeltaH(0) = 12.4 kJ mol(-1)) an
d presented a positive entropy value (DeltaS(0) = 75 J mol(-1) K-1). AM1 se
miempirical calculations of the 10-MeBPHT geometry indicate a partial inclu
sion of this molecule in HP-beta -CD, in agreement with our experimental re
sults.