RESUMEN
The aim of the present investigation was to immobilize zinc phthalocyanines in a silicate matrix and to test the photobactericidal properties of the matrices so prepared toward Esherichia coli in model aqueous media. For the purpose, tetra tertiary butyl zinc phthalocyanine (TBZnPc) and zinc phthalocyanine tetrasulfonic acid (ZnPcTS) were used. The abilities of these two photosensitizers to generate singlet oxygen in solution were compared by following the rate of photobleaching of 1,3-diphenylisobenzofuran (DPBF) at 430 nm in dimethylformamide (DMF). The results of this study show clearly that, under the conditions used here, the TBZnPc is the more effective generator of singlet oxygen; with it the DPBF was virtually completely photobleached in 4 min, while with the ZnPcTS under the same conditions, it took 12 min to reach this point. Glass conjugates with the two phthalocyanines were obtained by the sol-gel technique and were characterized by a well-defined color due to the phthalocyanine incorporated in the silicate matrix. Glasses with an intense, but inhomogeneous, green color were obtained when the tetrasulfonic derivative of the zinc phthalocyanine was used, while blue glasses of evenly distributed coloration were formed from the tetra tertiary butyl derivative. The ZnPcTS conjugate demonstrates more effective singlet oxygen evolution than is the case with the TBZnPc conjugate. These results are the opposite of those obtained for the free phthalocyanines in solution. The structural formulae of the compounds show that TBZnPc has a more pronounced hydrophobic character than the sulfonic derivative. In our view, the relative reactivities of the conjugates can be explained by the tetrasulfonic derivative being situated mainly in the surface parts of the glass matrix where the hydrophilic character is prevailing, while the tertiary butyl derivative is mainly present in the internal parts of the matrix as a result of which it is less accessible and therefore less active. The results obtained on the effect of zinc phthalocyanine conjugates on E. coli show a trend similar to that observed with singlet oxygen evolution shown. Thus, for the ZnPcTS conjugate, the log kill is 1.32 and for the TBZnPc conjugate, it is 0.98, in each case after 120 min. The results obtained show that phthalocyanines can be immobilized successfully in a silicate matrix and used for photodisinfection of microbially polluted waters. The silicate matrix has some advantages in comparison with other organic matrices. It is insoluble in water, resistant towards microorganisms, easy to fabricate, and might be developed successfully for the photodisinfection of water, e.g., in swimming pools and in other open water reservoirs.
Asunto(s)
Escherichia coli/citología , Escherichia coli/efectos de los fármacos , Indoles/química , Indoles/farmacología , Compuestos Organometálicos/química , Compuestos Organometálicos/farmacología , Silicatos/química , Adsorción , Antibacterianos/química , Antibacterianos/farmacología , Supervivencia Celular/efectos de los fármacos , Supervivencia Celular/efectos de la radiación , Materiales Biocompatibles Revestidos/química , Escherichia coli/efectos de la radiación , Isoindoles , Luz , Fármacos Fotosensibilizantes/química , Fármacos Fotosensibilizantes/farmacología , Compuestos de ZincRESUMEN
We have designed experiments to test the idea that the photodynamic effect can be used to lower microbial levels in a flow of water using a sensitizer incorporated into a polymeric membrane. We have selected a naturally derived, wettable polymer, chitosan, which can be reinforced with nylon. Photosensitizers of singlet oxygen formation were incorporated into translucent chitosan membranes by adsorption [5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin, p-THPP], by dissolution and casting [5,10,15,20-tetrakis(p-aminophenyl)porphyrin, p-TAPP], and by covalent attachment by reactive dyeing [zinc(II) phthalocyanine tetrasulfonic acid, ZnPcS]. Preliminary evaluation of photomicrobicidal activity in static systems against Escherichia coli revealed some activity in each case, and showed that the phthalocyanine/chitosan membrane was the most effective. A novel photodisinfection reactor was designed and constructed as a model for a large-scale water-flow system. Using the novel reinforced ZnPcS/chitosan membrane as the photosensitizing surface, a significant photokill of E. coli was observed, thus providing proof of concept.