Electrostatic loading and photoredox-based release of molecular cargo from oligoviologen-crosslinked microparticles

Although on-demand cargo release has been demonstrated in a wide range of microparticle platforms, many existing methods lack specific loading interactions and/or undergo permanent damage to the microparticle to release the cargo. Here, we report a novel method for electrostatically loading negatively charged molecular cargo in oligoviologen-crosslinked microparticles, wherein the cargo can be released upon activation by visible light. A water-in-oil (W/O) emulsion polymerization method was used to fabricate narrowly dispersed microparticles crosslinked by a dicationic viologen-based dimer and a poly(ethylene glycol) diacrylate. A zinc-tetraphenyl porphyrin photocatalyst was also polymerized into the microparticle and used to photochemically reduce the viologen subunits to their monoradical cations through a visible-light-mediated photoredox mechanism with triethanolamine (TEOA) as a sacrificial reductant. The microparticles were characterized by microscopy methods revealing uniform, spherical microparticles 481 ± 20.9 nm in diameter. Negatively charged molecular cargo (methyl orange, MO) was electrostatically loaded into the microparticles through counteranion metathesis. Upon irradiation with blue (450 nm) light, the photo-reduced viologen crosslinker subunits lose positive charges, resulting in release of the anionic MO cargo. Controlled release of the dye, as tracked by absorption spectroscopy, was observed over time, yielding release of up to 40% of the cargo in 2d and 60% in 5d in single dynamic dialysis experiment. However, full release of cargo was achieved upon transferring the microparticles to a fresh TEOA solution after the initial 5d period.

Drug delivery systems for the photodynamic application of two photosensitizers belonging to the porphyrin family

Photodynamic therapy involves the concomitant action of three components, light with an appropriate wavelength, molecular oxygen, and a molecule, able to absorb an electromagnetic radiation, called photosensitizer (PS). A fundamental aspect is the bioavailability of the PS that is directly related to some physicochemical properties of the PS itself as it should feature a certain degree of lipophilicity to easily cross the cell membrane, however, at the same time, should be sufficiently water-soluble to navigate in the bloodstream. Consequently, the use of a system for drug delivery becomes essential when photosensitizers with a high degree of lipophilicity are considered. In this work, we present three different drug delivery systems, microemulsions, emulsions and liposomes all capable of carrying a PS belonging to the porphyrin family: the tetraphenyl porphyrin (TPP) and the 4-hydroxyphenyl porphyrin (THPP), which show a relevant different degree of lipophilicity. A series of microemulsions (ME) and emulsions (E) were prepared, among which two formulations, one for THPP and one for TPP, have been chosen. The stability of these two carriers was monitored over time and under various temperature conditions. With the same criteria, two liposomal formulations have been also identified and analyzed. The four formulations mentioned above (one ME, one E and two liposomes) have been tested on SKOV3 tumor cell line comparing the photodynamic activity of the porphyrin formulations versus the aqueous/organic (DMSO) solution of the same two PSs. The results show that all the formulations have proved to be excellent carriers and that the liposomal formulation enhance the photodynamic efficacy of both porphyrins.

PALLADIUM(II)-PORPHYRIN COMPLEXES AS EFFICIENT SENSITIZERS FOR SOLAR ENERGY CONVERSION

The dye-sensitized solar cells (DSSC) and thin-layer heterojunctional solar cells have attracted much attention as an alternative to relatively expensive silicon-based solar cells. Among the various photosensitizers used to build these cells, porphyrins have proven to be outstanding candidates due to their strong absorption in the visible region and have established basic and peripheral modification methods to adjust their geometry and electronic structures. Due to the improved spectral properties, the electronic spectra of these materials have been extensively studied. In this paper, the information obtained using both ultraviolet-visible (UV-VIS) and Fourier Transform Infrared (FTIR) spectroscopy have been used to evaluate the use of Pd-TPP (palladium-5,10,15,20-tetraphenyl porphyrin) as sensitizer dye on different glass substrate coated with transparent conducting oxides. The electrical characterization and quantum efficiency results, related with Pd-TPP-sensitized heterojunctional supramolecular solar cells, are also highlighted.

Tetraphenyl porphyrin films as selective detectors for amino acid molecules

The interaction of different amino acids and vacuum evaporated tetraphenyl porphyrin films was investigated by using kinetic isotherms, UV-vis spectroscopy, quartz crystal microbalance and density functional theory techniques. The adsorption process was analyzed by using pseudo-first-order and pseudo-second-order models. From these results, the adsorption order changed depending on the chemical characteristics of the porphyrin film, although most of the interactions were classified as pseudo-second-order at the films interface. From absorbance measurements, red shifts on the Soret peak positions were observed for all amino acids interacting with the metal free and the ZnTPP systems, while the position of the Soret peak barely change for the CuTPP surface, except for a slight bathocromic shift for arginine. On the other hand, the broadening of the Soret peak was more important for the ZnTPP and H2TPP surfaces, but the interaction with the CuTPP interfaces decreased the width of the peaks in all cases. In addition, a quartz crystal microbalance analysis was employed to investigate the film sensing performance during amino acid exposure. From these results, positively charged amino acids were more easily adsorbed on the films in contrast with the polar (serine) molecule. DFT calculations exhibited important deformations for H2TPP, the out-of-plane displacement of the Zn atom for ZnTPP, and hydrogen bond interactions with the CuTPP molecule. DFT also showed high binding energies for the positively charged amino acids but low binding energies for serine in agreement with experimental data. From these results, porphyrin films could be used as selective detectors for various L-amino acid molecules.

Early detection of Pseudomonas aeruginosa and Escherichia coli. using zinc tetraphenylporphyrin

The sensory characteristics of food are considerably effected by the metabolic processes of various micro-organisms in the food stored in the field or at ambient temperature. Also, this microbial contamination can pose serious health hazards to public health. Chemical analysis of the complex mixture of volatiles produced during bacterial growth and investigation methods of these microorganisms presents a big challenge. There remains major unmet need to shorten and improve detection methods. Therefore, early detection of the microorganisms will open many frontiers for quality control in the foodstuffs industry. Accordingly, the aim of this study was to assess the feasibility and performance of chemoreceptive sensors for the rapid detection of bacterial pathogens, specifically Pseudomonas aeruginosa and Escherichia coli. In Uv/vis study, zinc tetraphenyl porphyrin solutions (in DMF) was tested with various volatile compounds, such as propanal, hexanal and heptanal which are commonly found to be released during the growth of bacteria. These sensors were used to detect the bacterial odours of two pathogenic species (E.coli and P.aeruginosa) during their growth cycle at 4 °C and ambient temperature. Hypochromic shifts in Uv/vis and hydrogen bonding in FT-IR studies confirmed the interaction between the volatiles and porphyrin. The porphyrin used detected the presence of microorganisms after 12 hrs incubation and showed more sensitivity for volatiles released during aerobic activity P. aeruginosa as compared to E. coli at 4 °C and ambient temperature. Zinc tetraphenyl porphyrin based chemoreceptive membranes has been proved successful for the detection of P. aeruginosa. Hence, the present study proves wide scope of improvement over current laboratory techniques for the detection of pathogens in terms of speed, ease of use, and cost. Key messages The developed technique allows rapid detection of spoiled food. Chemoreceptive property of porphyrin has been exploited for the early detection of bacteria.

Amino acid adsorption on tetraphenyl porphyrin films

In this work, metal free, zinc and copper tetraphenyl porphyrin thin films were employed as substrates to study their interaction with glycine, serine, glutamate, lysine and argynine amino acids in order to investigate the effect of the metallic center and the amino acid characteristics in the adsorption phenomena. The amount of amino acid adsorbed on the films was quantified by using the Ruhemann method. Adsorption isotherms were obtained and analyzed in order to predict the adsorption mechanism for each case. In addition, the morphology of the films was investigated before and after the amino acid immersion by using scanning electron and atomic force microscopies. On the other hand, dynamic contact angle measurements were performed to monitor the spreading phenomena and changes in the hydrophobic nature of the surfaces after the amino acid interaction. From the results, it was observed that the largest deposited amino acid on all three surfaces corresponded to the positively charged compounds, while serine was the lowest adsorbed amino acid in all cases. These results can be attributed to electronic interactions between the amino acids’ lateral chains and the electronic [Formula: see text] distribution of the porphyrin macrocycle ring, and they provide important information regarding the amino acid selectivity of adsorption on tetraphenyl porphyrin films.