Abstract
While searching for adequate sol-gel methodologies for successfully trapping in monomeric and stable form either porphyrins or phthalocyanines, inside translucent monolithic silica xerogels, it was discovered that the interactions of these trapped tetrapyrrole macrocycles with Si-OH surface groups inhibit or spoil the efficient display of physicochemical, especially optical, properties of the confined species. Consequently, we have developed strategies to keep the inserted macrocycle species as far as possible from these interferences by substituting the surface-OH groups foralkylorarylgroups or trapping these species inside alternative metal oxide networks, such as ZrO2, TiO2, and Al2O3. In the present manuscript, we present, for the first time to our knowledge, a methodology for preserving the spectroscopic characteristics of metal tetrasulfophthalocyanines and cobalt tetraphenylporphyrins trapped inside the pores of ZrO2xerogels. The results obtained are contrasting with analogous silica systems and demonstrate that, in ZrO2networks, the macrocyclic species remain trapped in stable and monomeric form while keeping their original spectroscopic characteristics in a better way than when captured inside silica systems. This outcome imply a lower hydrophilic character linked to the existence of a smaller amount of surface hydroxyl groups in ZrO2networks, if compared to analogous SiO2xerogel systems. The development and study of the possibility of trapping or fixing synthetic or natural tetrapyrrole macrocycles inside inorganic networks suggest the possibility of synthesizing hybrid solid systems suitable for important applications in technological areas such as optics, catalysis, sensoring and medicine
Highlights
Tetrapyrrole macrocyclic compounds are molecules that perform transcendental functions in nature, since these species constitute the main part of molecules such as chlorophyll, blood, cyanocobalamine (Vitamin B12), and cytochromes [1,2,3]
We show the first results concerning the possibility of optimizing the displaying of physicochemical properties of macrocyclic species trapped or bonded inside inorganic networks that are different from SiO2, inside ZrO2 xerogels, prepared by the sol-gel method
VOL ads Conclusions The aluminium tetrasulfo-phthalocyanine, (OH)AlTSPc, was used as a probe to find that molar ratios of Zr(OPrn)4: H2O: HOPrn: acac, equivalent to 2: 4: 8: 1, render translucent, monolithic ZrO2 xerogels
Summary
Tetrapyrrole macrocyclic compounds are molecules that perform transcendental functions in nature, since these species constitute the main part of molecules such as chlorophyll, blood (heme group), cyanocobalamine (Vitamin B12), and cytochromes [1,2,3]. The presence of organic chains attached to the pore walls induces an internal physicochemical environment in which the electronic transitions of the trapped macrocycles occur in an easier way Through this procedure, it has been possible to optimize the fluorescence of synthetic porphyrins and, more recently, that of natural tetrapyrrole macrocycles, such as chlorophyll a [33]. Due to its convenient properties, the (OH)AlTSPc species was chosen as a spectroscopic tracer or probe to determine the optimal conditions required to synthesize translucent and monolithic ZrO2 xerogels having tetrapyrrole macrocyclic species physically trapped or covalently fixed (in a disaggregated and stable form) within the pores of xerogel networks. Pore size distributions (PSD), inherent to the ZrO2 matrix entrapping macrocyclic species, were calculated by the NLDFT method applied to the boundary desorption curve of the N2 isotherms [38] while assuming spherical pore cavities
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