The synthetic tetrapyrrole macrocycles, such as porphyrins (H2P) and phthalocyanines (H2Pc), exhibit interesting physicochemical properties suitable to be used in modern technology. For many applications, those species should be trapped or fixed inside graphite, hydrotalcites, silica, TiO2, or polymers. Methodologies for the optimization of the properties of porphyrins, trapped or fixed inside polymers, have been barely developed. Our research works in the development of methodologies for the optimization of incorporation and display of properties of tetrapyrrole macrocycles inside inorganic, polymeric, or hybrid networks. This paper shows some results about the effect of the spatial disposition of the amine (–NH2) groups attached on the periphery of substituted tetraphenylporphyrins, on the Nylon 66 structure and on the display of the physicochemical properties of the trapped macrocycles. Nylon 66 was synthesized from adipoyl chloride and hexamethylenediamine in presence of tetraphenylporphyrins substituted with –NH2groups localized at theortho- orpara-positions of the phenyls. Cobalt complexes formation was used to quantify the amount of porphyrins in the polymer fibers. Characterization results show that the spatial position of amine groups of the porphyrins has important structural and textural effect on the Nylon 66 fibers and on the fluorescence of the porphyrins integrated into the fibers.

The crossed and linked histories of tetrapyrrolic macrocycles, interwoven with new research discoveries, suggest that Nature has found in these structures a way to ensure the continuity of life. For diverse applications porphyrins or phthalocyanines must be trapped inside solid networks, but due to their nature, these compounds cannot be introduced by thermal diffusion; the sol-gel method makes possible this insertion through a soft chemical process. The methodologies for trapping or bonding macrocycles inside pristine or organo-modified silica or inside ZrO2 xerogels were developed by using phthalocyanines and porphyrins as molecular probes. The sizes of the pores formed depend on the structure, the cation nature, and the identities and positions of peripheral substituents of the macrocycle. The interactions of the macrocyclic molecule and surface Si-OH groups inhibit the efficient displaying of the macrocycle properties and to avoid this undesirable event, strategies such as situating the macrocycle far from the pore walls or to exchange the Si-OH species by alkyl or aryl groups have been proposed. Spectroscopic properties are better preserved when long unions are established between the macrocycle and the pore walls, or when oligomeric macrocyclic species are trapped inside each pore. When macrocycles are trapped inside organo-modified silica, their properties result similar to those displayed in solution and their intensities depend on the length of the alkyl chain attached to the matrix. These results support the prospect of tuning up the pore size, surface area, and polarity inside the pore cavities in order to prepare efficient catalytic, optical, sensoring, and medical systems. The most important feature is that research would confirm again that tetrapyrrolic macrocycles can help in the development of the authentic pore engineering in materials science.

Abstract:The entrapping of physicochemical active molecules inside mesoporous networks is an appealing field of research due to the myriad of potential applications in optics, photocatalysis, chemical sensing, and medicine. One of the most important reasons for this success is the possibility of optimizing the properties that a free active species displays in solution but now trapped inside a solid substrate. Additionally it is possible to modulate the textural characteristics of substrates, such as pore size, specific surface area, polarity and chemical affinity of the surface, toward the physical or chemical adhesion of a variety of adsorbates. In the present document, two kinds of non-silicon metal alkoxides, Zr and Ti, are employed to prepare xerogels containing entrapped tetrapyrrolic species that could be inserted beforehand in analogue silica systems. The main goal is to develop efficient methods for trapping or binding tetrapyrrole macrocycles inside TiO2 and ZrO2 xerogels, while comparing the properties of these systems against those of the SiO2 analogues. Once the optimal synthesis conditions for obtaining translucent monolithic xerogels of ZrO2 and TiO2 networks were determined, it was confirmed that these substrates allowed the entrapment, in monomeric form, of macrocycles that commonly appear as aggregates within the SiO2 OPEN ACCESSMolecules 2015, 20 19464 network. From these experiments, it could be determined that the average pore diameters, specific surface areas, and water sorption capacities depicted by each one of these substrates, are a consequence of their own nature combined with the particular structure of the entrapped tetrapyrrole macrocycle. Furthermore, the establishment of covalent bonds between the intruding species and the pore walls leads to the obtainment of very similar pore sizes in the three different metal oxide (Ti, Zr, and Si) substrates as a consequence of the templating effect of the encapsulated species.

The physicochemical and luminescent properties of tetrapyrrole macrocycles, such as the porphyrins (H 2 P) and phthalocyanines (H 2 Pc), were preserved by trapping or bonding these species in silica matrices. The method involved used hydroxy-aluminium tetrasulphophthalocyanine OH(Al)TSPc as a probe to find optimal conditions for the entrapment of tetrapyrrole molecules. This methodology made possible the trapping or fixing of macrocyclic species or their respective complexes in the interior of pores existing in monolithic, translucent, normal, or organo-modified silica xerogels. The average pore sizes ranged from 2.0 to 3.6 nm in these systems and depended on the structure, the nature of the cation in the complex and on the identity and position of the substituents at the periphery of the macrocyclic species. Under appropriate conditions, the tetrapyrrolic species can be trapped or bonded to the pore network in stable and monomeric form; however, the interactions with Si-OH groups on the pore walls inhibit the efficient displaying of its properties. To avoid this deleterious effect, some strategies are used, such as to place the macrocycle far from the pore walls through long bridges or by substituting Si-OH groups with alkyl or aryl species. Average pore diameters vary from 3.5 to 9.4 nm when long unions are established between the macrocycle and the pore walls or when more of one macrocyclic species are trapped inside each pore. The spectroscopic properties of the macrocycles trapped in these systems are similar to those displayed by the same species in solution. When phthalocyanines or porphyrins are trapped or bonded to the pore walls of organo-modified silica, the spectroscopic properties are better preserved and their intensities are a function of the chain length of the alkyl group present in the silica matrix. This last result suggests the possibility of tuning the pore size and polarity inside them by choosing the tetrapyrrole species that can be trapped or bonded; in this way, it is possible to create more efficient systems for catalytic, optical, sensoring and medical applications.

Crossed and Linked Histories of Tetrapyrrolic Macrocycles and Their Use for Engineering Pores Within Sol-Gel Matrices -[454 refs.]. -(GARCIA-SANCHEZ, M. A.; ROJAS-GONZALEZ, F.; MENCHACA-CAMPOS, E. C.; TELLO-SOLIS, S. R.; QUIROZ-SEGOVIANO, R. I. Y.; DIAZ-ALEJO, L. A.; SALAS-BANALES, E.; CAMPERO, A.; Molecules 18 (2013) 588-653, http://dx.doi.org/10.3390/molecules18010588 ; Dep. Quim., Univ. Auton. Metrop.-Iztapalapa, 09340 Mexico, Mex.; Eng.) -Lindner 32-268