Synthesis, properties, and photodynamic inactivation of Escherichia coli using a cationic and a noncharged Zn(II) pyridyloxyphthalocyanine derivatives
作者:Inés Scalise、Edgardo N. Durantini
DOI:10.1016/j.bmc.2005.01.063
日期:2005.4
The photodynamic effect of a cationic Zn(II) N-methylpyridyloxyphthalocyanine (ZnPc 2) and a noncharged Zn(II) pyridyloxyphthalocyanine (ZnPc 1) has been compared in both homogeneous media bearing photooxidizable substrates and in vitro using a typical Gram-negative bacterium Escherichia coli. Absorption and fluorescence spectroscopic studies were analyzed in different media. Fluorescence quantum yields (phi(F)) of 0.23 for ZnPc 1 and 0.22 for ZnPc 2 were calculated in N,N-dimethylformamide (DMF). The singlet molecular oxygen, O-2((1)Delta(g)), production was evaluated using 9,10-dimethylanthracene (DMA) in DMF yielding values of Phi(Delta) = 0.56 for ZnPc 1 and 0.59 for ZnPc 2. A faster decomposition Of (L)-tryptophan (Trp), which was used as biological substrate model, was obtained using ZnPc 2 as a sensitizer with respect to ZnPc 1. In biological medium, the E coli cultures were treated with 10 mu M of sensitizer for different times at 37 degrees C in the dark. Both ZnPcs 1 and 2 are rapidly bound to E. coli cells in 5 min and the amount of cell-bound sensitizer is not appreciably changed incubating the cultures for longer times. The recovered ZnPc 2 after one washing step is similar to 3 times higher than 1, reaching a value of similar to 3 nmol/10(6) cells. After irradiation with visible light, a higher photoinactivation of cells was found for ZnPc 2. Thus, a similar to 4.5 log (99.997%) decrease of cell survival was obtained after 30 min of irradiation. On the other hand, a very low photodamage was found for cells treated with ZnPc 1 (similar to 0.5 log). Also, these results were established by stopping of growth curves for E coli. In the structure of ZnPc 2, the cationic centers are isolated from the phthalocyanine ring by an ether bridge, which also provides a higher mobility of the charges facilitating the interaction with the outer membrane of the Gram-negative bacteria. These studies show that cationic ZnPc 2 is an efficient phototherapeutic agent with potential applications in photodynamic inactivation of bacteria. (c) 2005 Elsevier Ltd. All rights reserved.