Electronic excitations of C60 aggregates.

Excitation properties of the isolated C(60) and (C(60))(N) model clusters (N = 2, 3, 4, 6 and 13) are studied using an a priori parameterized and self-consistent Hamiltonian, the Complete Neglect of Differential Overlap considering the l azimuthal quantum number method. This method properly describes electron excitations of the isolated C(60) after the configuration interaction of singles (CIS) procedure, when those are compared with experimental data in n-hexane solution and in a molecular beam. Geometry models of (C(60))(N) clusters to model the effect of aggregation were obtained from the fullerene fcc crystal. Some peaks in the low energy edge of the absorption spectrum appear corresponding to clustering effects, as well as small increases of bandwidths in the strong bands at the UV region. An analysis of the theoretical absorption spectrum for dimer models has been carried out, taking into account the influence of the distance between fullerene centers. The density of states of CIS for fullerene clusters in the range from 2.0 to 6.5 eV shows the possibility of electron transitions as functions of the size of the clusters.

Glutathione-dependent oxidative modification of protoporphyrin and other dicarboxylic porphyrins by mammalian and plant peroxidases.

Protoporphyrin, an intermediate in heme and chlorophyll biosynthesis, can accumulate in human and plant tissues under certain pathological conditions and is a photosensitizer used in cancer phototherapy. We previously showed that protoporphyrin and the related non-natural dicarboxylic porphyrin deuteroporphyrin are rapidly oxidized by horseradish peroxidase in the presence of some thiols, especially glutathione. This study reports that bovine lactoperoxidase, but not leucocyte myeloperoxidase, can also catalyze this reaction and that Tween and ascorbic acid are inhibitors. Exogenous hydrogen peroxide is not required and cannot replace glutathione. Deuteroporphyrin was oxidized to a unique green chlorin product with two oxygen functions added directly to the characteristic reduced pyrrole ring of the chlorin. Spectroscopic and chromatographic results suggest that protoporphyrin was oxidized not to a green chlorin, but to a much more polar red porphyrin modified by oxidative addition to the two vinyl side chains. Two related nonnatural dicarboxylic porphyrins, with ethyl or hydroxyethyl instead of vinyl side chains, are not substrates or products for this enzymatic conversion.

In vitro photo-activation of newly synthesized chlorin derivatives with red-light-emitting diodes.

We investigated the in vitro photo-activation properties of two chlorin derivatives, i.e. 8-cis-heptylchlorin dicarboxylic acid and 3-trans-heptylchlorin bisamidoglucose derivative, which exhibit lipophilic properties similar to those of the active fractions of Photofrin II, on a normal epithelial cell line (FRTL-5). We used as an irradiation source an array of diodes emitting red light (lambda = 675 nm), which produced a fluence of 7mW cm-2 on the cells. We found that photo-activation with chlorin derivatives in the concentration range 1-100 ng ml-1 greatly enhanced the mortality of the irradiated cells (energy density, 0.25 J cm-2) with respect to the control cells kept in the dark. This response is immediate and appears to be an "all or none' effect. Taking into account that compounds exhibit a strong absorbance peak in the long wavelength region of visible light where tissues are relatively transparent, our results suggest that chlorins can be considered to be good candidates for application in photodynamic therapy.

Potential photosensitizers for photodynamic therapy. IV. Photophysical and photochemical properties of azaporphyrin and azachlorin derivatives.

The photophysical and photochemical properties of a 5-azaprotoporphyrin derivative ([5]AZPP), a zinc-15-azaporphyrin derivative (Zn-[15]AZIDP) and an E-Z isomeric mixture of a 5-azachlorin derivative ([5]AZCH) were studied in various solvents. The quantum yields of fluorescence phi F0, S1-T1 intersystem crossing phi T0 and singlet oxygen (1 delta g) formation phi delta were measured and the Stern-Volmer constants for the quenching of the S1 states by oxygen and the rate constants of quenching of O2(1 delta g) by the different azaporphyrinoid compounds were obtained. The fluorescence quantum yield (phi F0 = 0.23), the strong absorption in the red (lambda max = 674 nm, epsilon max = 66,000 M-1 cm-1) and the high value of the quantum yield for singlet oxygen (1 delta g) formation (phi delta = 0.65) observed for [5]AZCH recommend azachlorin derivatives as potential markers and photosensitizers for tumour therapy.

Potential photosensitizers for photodynamic therapy. III. Photophysical properties of a lipophilic chlorin and its zinc and tin chelates.

Photophysical properties of a lipophilic chlorin derivative and its zinc and tin chelates were investigated in chloroform. The quantum yields of the fluorescence phi F, of the S1----T1 intersystem crossing phi T and of singlet oxygen (1 delta g) formation phi delta, as well as the Stern-Volmer constants for the quenching of the S1 states by oxygen and the rate constants of quenching of O2(1 delta g) by the chlorins were measured. In comparison to the metal-free chlorin an increase of phi T and a decrease of phi F have been observed for the metal-containing derivatives, whereas the phi delta values remain constant.