Homogeneous and Heterogeneous Free-Based Porphyrins Incorporated to Silica Gel as Fluorescent Materials and Visible Light Catalysts Mimic Monooxygenases

The use of enzymes and whole cells as biocatalysts in biotechnology and organic chemistry is recognized as being of great economic potential in the increasing production of unique and valuable compounds present in nature in an insufficient amount. Bioconversion with living microbial cells, which have the ability to regenerate their own respective cofactors and exhibit a spectrum of enzymatic activity, is a very useful tool in bioorganic synthesis. There is no doubt that the advantage of microbial biotransformations is the possibility to induce enzymes of defined, desired activity, simply by the suitable preincubation methods (Griffin et al., 2001). However, this kind of biocatalysts has several limitations in application to oxidative biotransformations, including stability and activities, especially to those substrates and products that are toxic and require being performed in reaction media other than water. A disadvantage might be the membrane barrier and diffusion problems. Recent advances in addressing these problems include molecular and reaction engineering approaches (Burton, 2003). A broad field of activity of biological heme-containing oxygenases like cytochromes P450 has provoked the development of the invention of artificial catalytic systems based on porphyrins mimicking the controlled and selective oxidation reactions of these hemoproteins. The concept of artificial enzymes and biomimetic chemistry was introduced by Breslow in 1972 (Breslow, 1972), that started the field of bioinspired or biomimetic catalysis, wherein researchers try to copy Nature in designing the catalyst with the structure and properties similar to those of the active sites of enzymes. Such biomimetic systems are expected to work in organic media and have high stability toward toxic organic compounds in comparison with traditional catalysis employing enzymes or microorganisms. The porphyrins, due to their synthetic versatility and reactivity, are especially attractive in the construction of biomimetic analogues of monooxygenases through elaboration of the