Synthesis, Photophysical Properties and Application of New Porphyrin Derivatives for Use in Photodynamic Therapy and Cell Imaging

The art of simplicity: Water-soluble porphyrin-like carbon dots self-assemble into mesmerizing red glow

In this new study, we present an intriguing development in the field of theranostics: the simplistic self-assembly of red-emissive amphiphilic porphyrin-like carbon dots (P-CDs). By harnessing their exceptional photophysical properties, we have revealed a strong candidate as the ideal photosensitizer (PS) for applications, particularly in the realm of imaging. Spanning a remarkable size average between 1-4 nm, these particles exhibit both highly stable and unparalleled emission characteristics between 650 and 715 nm in water in comparison to current carbon dots (CDs) available. Lastly, these CDs were fairly non-toxic when tested against normal human cell lines as well as were found to have favorable imaging capabilities in zebrafish embryo.

Metal Modulation: An Effortless Tactic for Refining Photoredox Catalysis in Living Cells

The remarkable impact of photoredox catalytic chemistries has sparked a wave of innovation, opening doors to novel biotechnologies in the realm of catalytic antitumor therapy. Yet, the quest for novel photoredox catalysts (PCs) suitable for living systems, or the enhancement of catalytic efficacy in existing biocompatible PC systems, persists as a formidable challenge. Within this context, we introduce a readily applicable metal modulation strategy that significantly augments photoredox catalysis within living cells, exemplified by a set of metalloporphyrin complexes termed M-TCPPs (M = Zn, Mn, Ni, Co, Cu). Among these complexes, Zn-TCPP emerges as an exceptional catalyst, displaying remarkable photocatalytic activity in the oxidation of nicotinamide adenine dinucleotide (NADH), nicotinamide adenine dinucleotide phosphate (NADPH), and specific amino acids. Notably, comprehensive investigations reveal that Zn-TCPP's superior catalytic prowess primarily arises from the establishment of an efficient oxidative cycle for PC, in contrast to previously reported PCs engaged in reductive cycles. Moreover, theoretical calculations illuminate that amplified intersystem crossing rates and geometry alterations in Zn-TCPP contribute to its heightened photocatalytic performance. In vitro studies demonstrated that Zn-TCPP exhibits therapeutic potential and is found to be effective for photocatalytic antitumor therapy in both glioblastoma G98T cells and 3D multicellular spheroids. This study underscores the transformative role of "metal modulation" in advancing high-performance PCs for catalytic antitumor therapy, marking a significant stride toward the realization of this innovative therapeutic approach.

Development of water-soluble phenazine-2,3-diol-based photosensitizers for singlet oxygen generation

Phenazine-2,3-diol-based dyes, KY-1Na and KY-2Na bearing one and two carboxylic acid sodium salts, respectively, have been newly developed as water-soluble photosensitizers (PSs) possessing the ability to generate singlet oxygen (¹O₂). In order to evaluate the solubility of KY-1Na and KY-2Na in water, the hydrophobicity/hydrophilicity of the two PSs was investigated by experimental measurement of the logarithms (log P_o/w) of the 1-octanol/water partition coefficient (P_o/w) for the PS. The log P_o/w values of both KY-1Na and KY-2Na were determined to be -0.9, indicating that both the PSs are more hydrophilic than Rose Bengal (-0.6) and have hydrophilicity equivalent to methylene blue (-0.9). Both the PSs in water show a broad photoabsorption band in the range of 500 to 600 nm. Thus, we estimated the ¹O₂ quantum yields (Φ_Δ) of KY-1Na and KY-2Na in water by using 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) as a water-soluble ¹O₂ scavenger. It was found that in water the Φ_Δ value (0.19) of KY-2Na is higher than that of KY-1Na (0.06). Density functional theory (DFT) calculations suggested that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributions for the molecular structure of KY-2Na are adequately separated, leading to a decrease in the energy gap (ΔE_ST) between the singlet state (S₁) and the triplet state (T₁) that causes efficient intersystem crossing (ISC), compared to that for the molecular structure of KY-1Na. Indeed, time-dependent DFT (TD-DFT) calculations demonstrated that the ΔE_ST(S₁-T₁) value (0.82 eV) of KY-2Na is smaller than that (0.98 eV) of KY-1Na, resulting in a relatively high Φ_Δ value of KY-2Na. Consequently, we demonstrate that phenazine-2,3-diol-based PSs bearing carboxylic acid salts possess high solubility and moderate ¹O₂ generation ability in water.

Development of Red-Emissive Porphyrin Graphene Quantum Dots (PGQDs) for Biological Cell-Labeling Applications

Red and near-infrared emission is a highly desirable feature for fluorescent nanoparticles in biological applications mainly due to longer wavelengths more easily being able to deeply penetrate tissues, organs, skin, and other organic components, while less autofluorescence interference would be produced. Additionally, graphene quantum dots (GQDs) that contain unique optical and electrical features have been targeted for their use in cell labeling applications as well as environmental analysis. Their most desirable features come in the form of low toxicity and biocompatibility; however, GQDs are frequently reported to have blue or green emission light and not the more advantageous red/NIR emission light. Furthermore, porphyrins are a subgroup of heterocyclic macrocycle organic compounds that are also naturally occurring pigments in nature that already contain the desired red-emission fluorescence. Therefore, porphyrins have been used previously to synthesize nanomaterials and for nanoparticle doping in order to incorporate the red/NIR emission light property into particles that otherwise do not contain the desired emission light. Meso-tetra(4-carboxyphenyl)porphine (TCPP) is one type of porphyrin with a large conjugated π-electron system and four carboxyl groups on its exterior benzene rings. These two key characteristics of TCPP make it ideal for incorporation into GQDs, as it would design and synthesize red-emissive material as well as give rise to excellent water solubility. In this work, TCPP is used in tangent with cis-cyclobutane-1,2-dicarboxylic acid (CBDA-2), a biomass derived organic molecule, to synthesize "green" porphyrin-based graphene quantum dots (PGQDs) with red-emission. The obtained PGQDs were characterized by various analytical methods. Utilizing TEM, HRTEM, and DLS the size distribution of the particles was determined to be 7.9 ± 4.1, well within the quantum dot range of 2-10 nm. FT-IR, XPS, and XRD depicted carbon, nitrogen, and oxygen as the main elemental components with carbon being in the form of graphene and the main porphyrin ring of TCPP remaining present in the final PGQDs product. Lastly, absorption and fluorescence spectroscopy determined the excitation wavelength at 420 nm and the emission at 650 nm which was successfully utilized in the imaging of HeLa cells using confocal microscopy.

Photo- and radio-luminescence of porphyrin functionalized ZnO/SiO2 nanoparticles

The development of hybrid nanoscintillators is hunted for the implementation of modern detection technologies, like in high energy physics, homeland security, radioactive gas sensing, and medical imaging, as well as of the established therapies in radiation oncology, such as in X-ray activated photodynamic therapy. Engineering of the physico-chemical properties of nanoparticles (NPs) enables the manufacture of hybrids in which the conjugation of inorganic/organic components leads to increased multifunctionality and performance. However, the optimization of the properties of nanoparticles in combination with the use of ionizing radiation is not trivial: a complete knowledge on the structure, composition, physico-chemical features, and scintillation property relationships in hybrid nanomaterials is pivotal for any applications exploiting X-rays. In this paper, the design of hybrid nanoscintillators based on ZnO grown onto porous SiO₂ substrates (ZnO/SiO₂) has been performed in the view to create nanosystems potentially suitable in X-ray activated photodynamic therapy. Indeed, cytotoxic porphyrin dyes with increasing concentrations have been anchored on ZnO/SiO₂ nanoparticles through amino-silane moieties. Chemical and structural analyses correlated with photoluminescence reveal that radiative energy transfer between ZnO and porphyrins is the principal mechanism prompting the excitation of photosensitizers. The use of soft X-ray excitation results in a further sensitization of the porphyrin emission, due to augmented energy deposition promoted by ZnO in the surroundings of the chemically bound porphyrin. This finding unveils the cruciality of the design of hybrid nanoparticles in ruling the efficacy of the interaction between ionizing radiation and inorganic/organic moieties, and thus of the final nanomaterial performances towards the foreseen application.

Responsive Peptide Nanofibers with Theranostic and Prognostic Capacity

Photodynamic therapy (PDT) is a highly promising therapeutic modality for cancer treatment. The development of stimuli-responsive photosensitizer nanomaterials overcomes certain limitations in clinical PDT. Herein, we report the rational design of a highly sensitive PEGylated photosensitizer-peptide nanofiber (termed PHHPEG 6 NF) that selectively aggregates in the acidic tumor and lysosomal microenvironment. These nanofibers exhibit acid-induced enhanced singlet oxygen generation, cellular uptake, and PDT efficacy in vitro , as well as fast tumor accumulation, long-term tumor imaging capacity and effective PDT in vivo . Moreover, based on the prolonged presence of the fluorescent signal at the tumor site, we demonstrate that PHHPEG 6 NFs can also be applied for prognostic monitoring of the efficacy of PDT in vivo , which would potentially guide cancer treatment. Therefore, these multifunctional PHHPEG 6 NFs allow control over the entire PDT process, from visualization of photosensitizer accumulation, via actual PDT to the assessment of the efficacy of the treatment.

Fundamental electronic changes upon intersystem crossing in large aromatic photosensitizers: free base 5,10,15,20-tetrakis(4-carboxylatophenyl)porphyrin

Free base 5,10,15,20-tetrakis(4-carboxylatophenyl)porphyrin stands for the class of powerful porphyrin photosensitizers for singlet oxygen generation and light-harvesting. The atomic level selectivity of dynamic UV pump – N K-edge probe X-ray absorption spectroscopy in combination with time-dependent density functional theory (TD-DFT) gives direct access to the crucial excited molecular states within the unusual relaxation pathway. The efficient intersystem crossing, that is El-Sayed forbidden and not facilitated by a heavy atom is confirmed to be the result of the long singlet excited state lifetime (Q_x 4.9 ns) and thermal effects. Overall, the interplay of stabilization by conservation of angular momenta and vibronic relaxation drive the de-excitation in these chromophores.

The crucial transient states of free-base porphyrins are characterized by time-resolved X-ray absorption spectroscopy unraveling their unusual relaxation pathway.

An Anti-inflammatory Fe3 O4 -Porphyrin Nanohybrid Capable of Apoptosis through Upregulation of p21 Kinase Inhibitor Having Immunoprotective Properties under Anticancer PDT Conditions

We report the influence of Fe₃ O₄ nanoparticles (NPs) on porphyrins in the development of photosensitizers (PSs) for efficient photodynamic therapy (PDT) and possible post-PDT responses for inflicting cancer cell death. Except for Au, most metal-based nanomaterials are unsuitable for clinical applications. The US Food and Drug Administration and other agencies have approved Feraheme and a few other iron oxide NPs for clinical use, paving the way for novel biocompatible immunoprotective superparamagnetic iron oxide nanohybrids to be developed as nanotherapeutics. A water-soluble nanohybrid, referred to here as E-NP, comprising superparamagnetic Fe₃ O₄ NPs functionalised with tripyridyl porphyrin PS was introduced through a rigid 4-carboxyphenyl linker. As a PDT agent, the efficacy of E-NP toward the AGS cancer cell line showed enhanced photosensitising ability as determined through in vitro photobiological assays. The cellular uptake of E-NPs by AGS cells led to apoptosis by upregulating ROS through cell-cycle arrest and loss of mitochondrial membrane potential. The subcellular localisation of the PSs in mitochondria stimulated apoptosis through upregulation of p21, a proliferation inhibitor capable of preventing tumour development. Under both PDT and non-PDT conditions, this nanohybrid can act as an anti-inflammatory agent by decreasing the production of NO and superoxide ions in murine macrophages, thus minimising collateral damage to healthy cells.

Photodynamic activity attained through the ruptured π-conjugation of pyridyl groups with a porphyrin macrocycle: synthesis and the photophysical and photobiological evaluation of 5-mono-(4-nitrophenyl)-10,15,20-tris-[4-(phenoxymethyl)pyridine]-porphyrin and its Zn(ii) complex

This article compares a reported hydrophobic and photobiologically inert porphyrin synthon, (NPh)TPyP, bearing a single meso-4-nitrophenyl group and three meso-pyridyl groups (A₃B type) with a new photobiologically active metal-free porphyrin, P₃N, and its zinc-complex, P₃NZn, which bear a meso-4-nitrophenyl group along with three distal pyridyl groups. Both P₃N and P₃NZn experience ruptured π-conjugation with the porphyrin macrocycle and attain hydrophilicity, as indicated via density functional theory (DFT) calculations, becoming photobiologically active under in vitro conditions. The non-invasive photodynamic activity (PDA) predominantly shown by the zinc-complex P₃NZn (with higher hydrophilicity) towards KRAS-mutated human lung-cancer cells (A549) was studied. The results indicate the existence of intracellular singlet oxygen inflicted anticancer PDA, which is apparent through the upregulation of intracellular reactive oxygen species (ROS) and the downregulation of both intracellular superoxide dismutase (SOD) and intracellular reduced glutathione (GSH) levels. The trends obtained from both SOD and GSH assays were indicators of therapeutic defence against oxidative stress via neutralizing superoxide anions (SOA).

meso-Thiophenium Porphyrins and Their Zn(II) Complexes: A New Category of Cationic Photosensitizers

A new category of cationic meso-thiophenium porphyrins are introduced as possible alternatives to the popular meso-pyridinium porphyrins. Combinations of cationic porphyrins bearing meso-2-methylthiophenium and meso-4-hydroxyphenyl moieties T₂(OH)₂M (A₂B₂ type) and T(OH)₃M (AB₃ type) along with their zinc(II) complexes T₂(OH)₂MZn and T(OH)₃MZn, are reported. The increase in the number of thienyl groups attached to the meso-positions of the porphyrin derivatives (A₂B₂ frame) has been shown to impart longer fluorescence lifetimes and stronger photocytotoxicity toward A549 lung cancer cells, as evident with T₂(OH)₂M and its corresponding diamagnetic metal complex T₂(OH)₂MZn. The photoactivated T₂(OH)₂MZn imparts an early stage reactive oxygen species (ROS) upregulation and antioxidant depletion in A549 cells and contributes to the strongest oxidative stress-induced cell death mechanism in the series. The DFT calculations of the singlet-triplet energy gap (ΔE) of all the four hydrophilic thiophenium porphyrin derivatives establish the potential applicability of these cationic photosensitizers as PDT agents.

Rhenium in the core of porphyrin and rhenium bound to the periphery of porphyrin: synthesis and applications

An overview of most of the well known rhenium porphyrins (rhenium in the core of porphyrins) is presented here reviewing their synthesis, coordination chemistry, and applications. The important features of oxorhenium(v) porphyrins are discussed elaborately taking into account their application in epoxidation reaction. Moreover, the chemistry of some recently known porphyrin-Re conjugates (rhenium bound to the periphery of porphyrin) is reported considering their applications in the photochemical carbon dioxide reduction process and photodynamic therapy. The number of well characterized rhenium porphyrinoids are limited but they show interesting diverse properties, some of which are also discussed in this review.

Synthesis of meso-tetra-(4-sulfonatophenyl) porphyrin (TPPS4) - CuInS/ZnS quantum dots conjugate as an improved photosensitizer

BACKGROUND

 Metal-free, water-soluble and highly stable meso-tetra-(4-sulfonatophenyl) porphyrin (TPPS4) has been studied for their singlet oxygen quantum yield. However, TPPS4 suffers from inherent shortcomings. To address these, TPPS4 was conjugated to ternary copper indium sulphide/ zinc sulphide (CuInS2/ZnS) quantum dots (QDs).

PURPOSE

 We herein report for the first time the synthesis of TPPS4-CuInS/ZnS QDs conjugate as an improved photosensitizer.

METHODS

 Water-soluble TPPS4 was synthesized from tetraphenylporphyrin (TPPH2) after silica-gel purification. The CuInS/ZnS QDs were synthesized by hydrothermal method at a Cu:In ratio of 1:4. The porphyrin-QDs conjugate was formed via the daggling sulfonyl bond of the porphyrin and amine bond of the QDs. The effect of pH on the optical properties of TPPS4 was evaluated. The effect of Zn:Cu + In ratio on the ZnS shell passivation was examined to reduce structural defects on the as-synthesized QDs.

RESULTS

Various spectroscopic techniques were used to confirm the successful conversion of the organic TPPH2 to water-soluble TPPS4. The singlet oxygen generation evaluation shows an improved singlet oxygen quantum yield from 0.19 for the porphyrin (TPPS4) alone to 0.69 after conjugation (CuInS/ZnS-TPPS4) with an increase in the reaction rate constant (k (s-1)).