Scm. Gandini et al., Interaction of Fe(III)- and Zn(II)-tetra(4-sulfonatophenyl) porphyrins with ionic and nonionic surfactants: aggregation and binding, J INORG BIO, 85(4), 2001, pp. 263-277
Interactions of the water soluble Fe(III)- and Zn(II)-tetra(4-sulfonatophen
yl) porphyrins, FeTPPS4 and ZnTPPS4, with ionic and nonionic micelles in aq
ueous solutions have been studied by optical absorption, fluorescence, reso
nance light-scattering (RLS), and H-1 NMR spectroscopies. The presence of t
hree different species of both Fe(III)- and Zn(II)TPPS4 in cationic cetyltr
imethylammonium chloride (CTAC) solution has been unequivocally demonstrate
d: free metalloporphyrin monomers or dimers (pH 9), metalloporphyrin monome
rs or aggregates (possibly mu -oxo dimers) bound to the micelles, and nonmi
cellar metalloporphyrin/surfactant aggregates. The surfactant:metalloporphy
rin ratio for the maximum nonmicellar aggregate formation is around 5-8 for
Fe(III)TPPS4 both at pH 4.0 and 9.0; for Zn(II)TPPS4 this ratio is 8, and
the spectral changes are practically independent of pH. In the case of zwit
terionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and no
n-ionic polyoxyethylene lauryl ether (Brij-35) and t-octylphenoxypolyethoxy
etanol (Triton X-100), the nonmicellar aggregates were not observed in the
pH range from 2.0 to 12.0. Binding constants were calculated from optical a
bsorption data and are of the order of 10(4) M-1 for both CTAC and HPS, val
ues which are similar to those previously obtained for the porphyrin in the
free base form. For Brij-35 and Triton X-100 the binding constant for ZnTP
PS4 at pH 4.0 is a factor of 3-5 lower than those for CTAC and HPS, while i
n the case of FeTPPS4 they are two orders of magnitude lower. Our data show
that solubilization of ZnTPPS4 within nonpolar regions of n-ticelles is de
termined, in general, by nonspecific hydrophobic interactions, yet it is mo
dulated by electrostatic factors. In the case of FeTPPS4, the electrostatic
factor seems to be more relevant. NMR data indicated that Fe(III)TPPS4 is
bound to the micelles predominantly as a monomer at pH 4.0, and at pH 9.0 t
he bound aggregated form (possibly mu -oxo dimers) remains. The metalloporp
hyrins were incorporated into the micelles near the terminal part of their
hydrocarbon chains, as evidenced by a strong upfield shift of the correspon
ding peaks of the surfactants. (C) 2001 Elsevier Science B.V. All rights re
served.