Antimicrobial Potency of Fmoc-Phe-Phe Dipeptide Hydrogels with Encapsulated Porphyrin Chromophores Is a Promising Alternative in Antimicrobial Resistance.

Antimicrobial resistance (AMR) poses a significant global health risk as a consequence of misuse of antibiotics. Owing to the increasing antimicrobial resistance, it became imperative to develop novel molecules and materials with antimicrobial properties. Porphyrins and metalloporphyrins are compounds which present antimicrobial properties especially after irradiation. As a consequence, porphyrinoids have recently been utilized as antimicrobial agents in antimicrobial photodynamic inactivation in bacteria and other microorganisms. Herein, we report the encapsulation of porphyrins into peptide hydrogels which serve as delivery vehicles. We selected the self-assembling Fmoc-Phe-Phe dipeptide, a potent gelator, as a scaffold due to its previously reported biocompatibility and three different water-soluble porphyrins as photosensitizers. We evaluated the structural, mechanical and in vitro degradation properties of these hydrogels, their interaction with NIH3T3 mouse skin fibroblasts, and we assessed their antimicrobial efficacy against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria. We found out that the hydrogels are cytocompatible and display antimicrobial efficiency against both strains with the zinc porphyrins being more efficient. Therefore, these hydrogels present a promising alternative for combating bacterial infections in the face of growing AMR concerns.

Highly efficient light-driven hydrogen evolution utilizing porphyrin-based nanoparticles.

We developed dye-sensitized photocatalytic systems (DSPs) by utilizing porphyrins as a photosensitizer (PS) or as a photosensitizer-catalyst (PS/CAT) upon their chemisorption onto platinum-doped titanium dioxide nanoparticles (Pt-TiO2 NPs). The DSPs coated with Pt-Tc3CP (PS/CAT entity) exhibited a record-high stability (25 500 TONs) and H2 evolution activity (707 mmol g-1 h-1) compared to similar DSPs in the literature.

A covalently linked nickel(II) porphyrin-ruthenium(II) tris(bipyridyl) dyad for efficient photocatalytic water oxidation.

Visible-light-induced oxidation of water to dioxygen, catalyzed by a newly synthesized NiP-Ru dyad consisting of a ruthenium tris(bipyridyl), [Ru(bpy)3]2+ as a photosensitizer, and a low-cost nickel porphyrin, NiP as a water oxidation catalyst is reported.

Porphyrins and phthalocyanines as biomimetic tools for photocatalytic H2 production and CO2 reduction.

The increasing energy demand and environmental issues caused by the over-exploitation of fossil fuels render the need for renewable, clean, and environmentally benign energy sources unquestionably urgent. The zero-emission energy carrier, H2 is an ideal alternative to carbon-based fuels especially when it is generated photocatalytically from water. Additionally, the photocatalytic conversion of CO2 into chemical fuels can reduce the CO2 emissions and have a positive environmental and economic impact. Inspired by natural photosynthesis, plenty of artificial photocatalytic schemes based on porphyrinoids have been investigated. This review covers the recent advances in photocatalytic H2 production and CO2 reduction systems containing porphyrin or phthalocyanine derivatives. The unique properties of porphyrinoids enable their utilization both as chromophores and as catalysts. The homogeneous photocatalytic systems are initially described, presenting the various approaches for the improvement of photosensitizing activity and the enhancement of catalytic performance at the molecular level. On the other hand, for the development of the heterogeneous systems, numerous methods were employed such as self-assembled supramolecular porphyrinoid nanostructures, construction of organic frameworks, combination with 2D materials and adsorption onto semiconductors. The dye sensitization on semiconductors opened the way for molecular-based dye-sensitized photoelectrochemical cells (DSPECs) devices based on porphyrins and phthalocyanines. The research in photocatalytic systems as discussed herein remains challenging since there are still many limitations making them unfeasible to be used at a large scale application before finding a large-scale application.

Design and Synthesis of Porphyrin-Nitrilotriacetic Acid Dyads with Potential Applications in Peptide Labeling through Metallochelate Coupling.

The need to detect and monitor biomolecules, especially within cells, has led to the emerging growth of fluorescent probes. One of the most commonly used labeling techniques for this purpose is reversible metallochelate coupling via a nitrilotriacetic acid (NTA) moiety. In this study, we focus on the synthesis and characterization of three new porphyrin-NTA dyads, TPP-Lys-NTA, TPP-CC-Lys-NTA, and Py 3 P-Lys-NTA composed of a porphyrin derivative covalently connected with a modified nitrilotriacetic acid chelate ligand (NTA), for possible metallochelate coupling with Ni2+ ions and histidine sequences. Emission spectroscopy studies revealed that all of the probes are able to coordinate with Ni2+ ions and consequently can be applied as fluorophores in protein/peptide labeling applications. Using two different histidine-containing peptides as His6-tag mimic, we demonstrated that the porphyrin-NTA hybrids are able to coordinate efficiently with the peptides through the metallochelate coupling process. Moving one step forward, we examined the ability of these porphyrin-peptide complexes to penetrate and accumulate in cancer cells, exploring the potential utilization of our system as anticancer agents.

Controlling Solar Hydrogen Production by Organizing Porphyrins.

In this study, a highly efficient photocatalytic H2 production system is developed by employing porphyrins as photocatalysts. Palladium and platinum tetracarboxyporphyrins (PdTCP and PtTCP) are adsorbed or coadsorbed onto TiO2 nanoparticles (NPs), which act as the electron transport medium and as a scaffold that promotes the self-organization of the porphyrinoids. The self-organization of PdTCP and PtTCP, forming H- and J-aggregates, respectively, is the key element for H2 evolution, as in the absence of TiO2 NPs no catalytic activity is detected. Notably, J-aggregated PtTCPs are more efficient for H2 production than H-aggregated PdTCPs. In this approach, a single porphyrin, which self-organizes onto TiO2 NPs, acts as the light harvester and simultaneously as the catalyst, whereas TiO2 serves as the electron transport medium. Importantly, the concurrent adsorption of PdTCP and PtTCP onto TiO2 NPs results in the most efficient catalytic system, giving a turnover number of 22,733 and 30.2 mmol(H2 ) g(cat)-1 .

Supramolecular Nanodrugs Constructed by Self-Assembly of Peptide Nucleic Acid-Photosensitizer Conjugates for Photodynamic Therapy.

Two hybrid materials were designed by conjugating peptide nucleic acids (PNAs) to porphyrin or boron-dipyrromethene, generating PNA-porphyrin (PNA-TPP) and PNA-BODIPY (PNA-BDP) conjugates, respectively. Because of the combination of the supramolecular characteristics of PNAs and photosensitizers, the two hybrid conjugates readily self-assemble in aqueous solutions and produce well-defined nanoparticles with uniform particle sizes. The resulting two kinds of nanoparticles show good stability in biological solutions and upon dilution. Importantly, the nanoparticles can efficiently interact with cancer cells and the internalized nanoparticles are mainly distributed in the cytoplasm without discernible cytotoxicity in the dark, enabling them to be applied as photodynamic nanoagents for selective killing cells. Hence, self-assembly of PNA-photosensitizer conjugates may hold promise for advancing the rational design and construction of photodynamic nanoagents for cancer therapy.

Self-assembly of aliphatic dipeptides coupled with porphyrin and BODIPY chromophores.

In this work, the self assembly ability of chromophores covalently linked to aliphatic dipeptides is described. Altering various parameters such as the protecting group, the solvent mixture, the dipeptide and the chromophore resulted in different nanostructures. Interestingly, a peptide-porphyrin hybrid is capable of forming a hydrogel in HFIP-water solvent mixture.

A self-assembly study of PNA-porphyrin and PNA-BODIPY hybrids in mixed solvent systems.

In this work a peptide nucleic acid (PNA) was covalently connected with two different chromophores, namely porphyrin and boron-dipyrromethene. To the best of our knowledge, this is the first example in the literature where a PNA unit is covalently linked to such chromophores. The self-assembly properties of the hybrids were examined through electron microscopy experiments by adopting the "good-bad" solvent self-assembly protocol. For both hybrids (PNA-TPP and PNA-BDP) we were able to observe distinctive supramolecular architectures. During these studies we investigated the influence of the solvent system, the concentration and the deposition method on the morphology of the formed nanostructures. In the case of PNA-TPP under all examined conditions well-formed nanospheres were obtained. Interestingly, in the PNA-BDP hybrid by simply altering the solvent mixture, self-assemblies of two different morphologies were formed (spherical and flake shaped). Absorption and emission studies suggested the formation of J-aggregates in all the obtained nanostructures. The nano-architectures assembled by PNA conjugates are capable of light-harvesting and producing hydrogen using Pt nanoparticles as a photocatalyst.

Self-assembly study of nanometric spheres from polyoxometalate-phenylalanine hybrids, an experimental and theoretical approach.

Herein, we report on the study of supramolecular assemblies based on polyoxometalates (POMs) upon their modification with amino acids. Two POM-amino acid hybrids were synthesized by coupling a functionalized Keggin type polyoxoanion [PW11O39{Sn(C6H4)C[triple bond, length as m-dash]C(C6H4)COOH}]4- with carboxyl-protected (methyl-ester) phenylalanine or diphenylalanine peptides. Surprisingly, all compounds, including the initial POM, formed supramolecular nanospheres in different solvent mixtures, which were examined by scanning electron microscopy (SEM). Molecular dynamics (MD) simulations for the POM-amino acid species revealed that the hydrophobic forces are mainly responsible for the initial aggregation into incipient micelle type structures, in which the organic arms are buried inside the aggregate while POM polar heads are more exposed to the solvent with tetrabutyl-ammonium counter cations acting as linkers.

Self-assembly of (boron-dipyrromethane)-diphenylalanine conjugates forming chiral supramolecular materials.

Herein, we present the synthesis of a series of boron-dipyrromethane (BDP) derivatives bearing diphenylalanine (FF) at their meso position via amide bond coupling. The BDP-FF bioconjugates are able to form self-assembled materials with different morphologies. By altering various parameters such as the protecting group of the FF peptide or the solvent system of the self-assembly process, we were able to obtain either fibrillar or spherical nanostructures. Furthermore, we confirmed that both the formation as well as the dissociation of the self-assemblies is a reversible procedure that can be achieved by simply altering the solvent mixture. Electronic circular dichroism (ECD) studies demonstrated a characteristic mirror image relationship regarding the FLFL and FDFD enantiomers, revealing the chiral nature of the obtained materials. Interestingly, an intense excitonic bisignate signal was observed in the ECD spectrum of the fibrillar structures, whereas the spherical assemblies remained ECD silent. What is more, the electronic circular dichroism studies were supported by quantum chemical calculations.