The methylpyropheophorbide-fullerene[60] dyad was synthesized by 1,3-dipolar cycloadditions of the corresponding azomethine ylide to C 60 (Prato reaction). Using the mass spectrometric method with soft matrix-activated ionization it was possible to achieve a significant reduction in fragmentation processes by the retro-Diels-Alder reaction, which allows to reliably detect the presence of polyadducts of azomethine ylide cycloadditions to fullerene. The use of gel permeation chromatography under conditions of weakening of the intermolecular π-π interaction between methylpyropheophorbide and fullerene moieties makes it possible to effectively separate mixed products with ~ 1.5 fold difference in molecular weight. It has been shown that the fluorescence of the dyad is quenched more than 5000 times (compared to the native dye). The singlet oxygen quantum yield of the dyad is 360 times less than that for the native methylpyropheophorbide a, however, its efficiency of superoxide generation increases by 18.5 times. The obtained result agrees well with the previously reported mechanism of relaxation of the excited state of the dyad through a charge-separated state, which can lead to the formation of superoxide. The observed effects indicate a change in the mechanism of photodynamic activity from type II (generation of singlet oxygen) for the native dye to type I (generation of superoxide) for the dyad, which shows a promising method of creation of highly efficient photosensitizers based on similar dye-fullerene[60] dyads.
Traditional soft ionization methods are not always suitable for mass spectral analysis of complex compounds. Factors such as laser radiation and heating resulting in fragmentations of sample molecules in the case of matrix-assisted laser desorption/ionization and difficulties in preparing suitable sample solutions in the case of electrospray ionization make it impossible to use these methods in some cases. Matrix-assisted ionization was used to analyze products of chemical synthesis involving pyropheophorbide and fullerene. Mass spectra were acquired using a simple effective modification of the Exactive Orbitrap mass spectrometer electrospray interface. Reliable identification of pyropheophorbide-fullerene dyad ions and its derivatives was carried out. An experimental comparison of a matrix-assisted ionization and an electrospray ionization technique demonstrated the significant advantage in sensitivity to the ions under study (approximately 20 times higher) of the matrix-assisted ionization method in this particular study.
A new type of pyropheophorbide-fullerene [60] dyad was synthesized by their attachment by the cyclopropane backbone at the 13(1)-position of the chlorin macrocycle using the Hummelen-Wudl method. Here we report a complex analysis of the structure influence on the photophysical properties of the newly obtained dyad and its comparison with another pyropheophorbide-fullerene [60] dyad. The latter dyad was previously obtained by the attachment of the tetrahydropyrrole backbone at the third position of the macrocycle using the Prato reaction. It was shown by quantum-chemical modeling that the studied dyads have drastically different spatial positions of the fullerene core relative to the dye macrocycle plane: "parallel" for the former and "perpendicular" -for the latter. The influence of structural differences on various properties of dyads was studied: the aggregation properties, absorption spectra, the fluorescence quenching of the dye moiety in the dyads, and the lifetimes of excited states. The data obtained are important for the further development of methods for the directional design of the photoactive fullerene-dye structures -highly effective photosensitizers for photodynamic therapy.
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