PDT-related photophysical properties of conformationally distorted palladium(II) porphyrins

Secure transplantation by tissue purging using photodynamic therapy to eradicate malignant cells

The field of photodynamic therapy (PDT) for treating various malignant neoplasms has been given researchers' attention due to its ability to be a selective and minimally invasive cancer therapy strategy. The possibility of tumor cell infection and hence high recurrence rates in cancer patients tends to restrict autologous transplantation. So, the photodynamic tissue purging process, which consists of selective photoinactivation of the malignant cells in the graft, is defined as a compromising strategy to purify contaminated tissues before transplantation. In this strategy, the direct malignant cells' death results from the reactive oxygen species (ROS) generation through the activation of a photosensitizer (PS) by light exposure in the presence of oxygen. Since new PS generations can effectively penetrate the tissue, PDT could be an ideal ex vivo tissue purging protocol that eradicates cancer cells derived from various malignancies. The challenge is that the applied pharmacologic ex vivo tissue purging should efficiently induce tumor cells with minor influence on normal tissue cells. This review aims to provide an overview of the current status of the most effective PDT strategies and PS development concerning their potential application in ex vivo purging before hematopoietic stem cell or ovarian tissue transplantation.

Synthesis and Redox Properties of Superbenzene Porphyrin Conjugates

Superbenzene porphyrin conjugates find wide range of applications from nonlinear optical materials to semiconductors. Herein, we report the synthesis and characterization of 5,15-bis(3,5-di-tert-butylphenyl)-10,20-bis(pentaphenylphenyl)phenylporphyrin and its Zinc-metallated complex. Oxidative planarization of 5,15-bis(3,5-di-tert-butylphenyl)-10,20-bis(pentaphenylphenyl)phenylporphyrin and its metallated complex was carried out by using NOBF₄ as an oxidizing agent. The formation of superbenzene porphyrin conjugates validates its Scholl type reactions. The laboratory-synthesized porphyrin conjugates were characterized experimentally using spectroscopic techniques such as ¹H NMR, ¹³C NMR, electron spin resonance, and ultraviolet-visible spectroscopy for structural conformation. In addition, density functional theory calculations were carried out to validate the experimental results. The theoretical and experimental results show that the 4-(pentaphenylphenyl)phenyl ligand increases the stability, optical properties, and rate of planarization of synthesized porphyrins. The conjugates exhibited intense and distant electronic communication between two hexabenzocoronene sites, taking advantage of porphyrin as a π-spacer. The π-radical cation has also been found to be an intermediate in oxidative C-C bond formation. NICS calculations support such a conclusion.

Effect of Toxic Metal Ions on Photosensitized Singlet Oxygen Generation for Photodegradation of Polyaromatic Hydrocarbon Derivatives and Inactivation of Escherichia coli

Here, we report an experimental study of the effect of toxic metal ions on photosensitized singlet oxygen generation for photodegradation of PAH derivatives, Anthracene-9,10-dipropionic acid disodium salt (ADPA) and 1,5-dihydroxynapthalene (DHN) and photoinactivation of Escherichia coli bacteria by using cationic meso-tetra(N-methyl-4-pyridyl)porphine tetrachloride (TMPyP) as a singlet oxygen photosensitizer. Three s-block metals ions, such as Na⁺ , K⁺ and Ca²⁺ and five toxic metals such as Cd²⁺ , Cu²⁺ , Hg²⁺ , Zn²⁺ and Pb²⁺ were studied. The s-block metal ions showed no change in the rate of photodegradation of ADPA or DHN by TMPyP, whereas a dramatic change in the photodegradation of ADPA and DHN was observed in the presence of toxic metals. The maximum photodegradation rate constants of ADPA and DHN were observed for Cd²⁺ ions [(3.91 ± 0.20) × 10^-3 s^-1 and (7.18 ± 0.35) × 10^-4 s^-1 , respectively]. Strikingly, the photodegradation of ADPA and DHN was almost completely inhibited in the presence of Hg²⁺ ions and Cu²⁺ ions. A complete inhibition of growth of E. coli was observed upon visible light irradiation of E. coli solutions with TMPyP and toxic metal ions particularly, Cd²⁺ , Hg²⁺ , Zn²⁺ and Pb²⁺ ions, except for Cu²⁺ ions where a significantly slow inhibition of E. coli's growth was observed.

Design of two-photon molecular tandem architectures for solar cells by ab initio theory

We present new two-photon molecular architectures for photovoltaics where atomic precision can be obtained by synthetic chemistry.

An extensive database of spectroscopic properties of molecules from ab initio calculations is used to design molecular complexes for use in tandem solar cells that convert two photons into a single electron–hole pair, thereby increasing the output voltage while covering a wider spectral range. Three different architectures are considered: the first two involve a complex consisting of two dye molecules with appropriately matched frontier orbitals, connected by a molecular diode. Optimized combinations of dye molecules are determined by taking advantage of our computational database of the structural and energetic properties of several thousand porphyrin dyes. The third design is a molecular analogy of the intermediate band solar cell, and involves a single dye molecule with strong intersystem crossing to ensure a long lifetime of the intermediate state. Based on the calculated energy levels and molecular orbitals, energy diagrams are presented for the individual steps in the operation of such tandem solar cells. We find that theoretical open circuit voltages of up to 1.8 V can be achieved using these tandem designs. Questions about the practical implementation of prototypical devices, such as the synthesis of the tandem molecules and potential loss mechanisms, are addressed.

Riboflavin interactions with oxygen-a survey from the photochemical perspective

In this short review we provide some insights to the main processes that riboflavin is involved in upon absorption of a photon. We describe riboflavin properties in its interactions with oxygen, comparing them to the properties of some other singlet oxygen sensitizers. Data are provided on riboflavin photosensitizing properties in vivo and in vitro, and its properties as an endogenous singlet oxygen sensitizer are discussed. We additionally report flavin catalytic role in organic synthesis and photochemical reactivity in solutions of riboflavin and some of its derivatives.

Successful full term pregnancy and delivery after concurrent chemo-photodynamic therapy (CCPDT) for the uterine cervical cancer staged 1B1 and 1B2: Preserving fertility in young women

► Photodynamic therapy can treat lesions with highly reactive single oxygen. ► CCPDT (Concurrent Chemo Photodynamic Therapy) is defined as PDT with chemotherapy. ► CCPDT can treat larger and deeper lesions than PDT due to PCI concept. ► Complete remission would be possible in uterine cervical cancer by CCPDT. ► Uterine cervix and corpus can be preserved in CCPDT.

The photophysics of metalloporphyrins excited in their Soret and higher energy UV absorption bands

Photophysical processes involving the higher electronic excited states of diamagnetic porphyrins and metalloporphyrins are critically reviewed. Intramolecular electronic relaxation of one-photon Soret-excited molecules in solution is now known to involve processes other than S 2 - S 1 internal conversion; dark electronic states are implicated. Sequential two-photon excitation to produce gerade excited singlet states ( S n , n > 2) results in relaxation dynamics that are quantitatively different from those resulting from one-photon excitation to ungerade states of about the same energy. Intermolecular electron and electronic energy transfer involving Soret-excited metalloporphyrins and intramolecular electron and electronic energy transfer in Soret-excited dyads and larger arrays containing porphyrins are reviewed. Metalloporphyrins containing main group metals or transition metals with filled d orbitals exhibit relaxation dynamics that differ from metalloporphyrins containing transition metals with unfilled d orbitals. Non-linear phenomena associated with multi-photon excitation of diamagnetic metalloporphyrins are also reviewed.

Syntheses and cellular investigations of 17(3)-, 15(2)-, and 13(1)-amino acid derivatives of chlorin e(6)

A series of amino acid conjugates of chlorin e(6), containing lysine or aspartic acid residues in positions 17(3), 15(2), or 13(1) of the macrocycle were synthesized and investigated as photosensitizers for photodynamic therapy of tumors. All three regioisomers were synthesized in good yields and in five steps or less from pheophytin a (1). In vitro investigations using human carcinoma HEp2 cells show that the 15(2)-lysyl regioisomers accumulate the most within cells, and the most phototoxic are the 13(1) regioisomers. The main determinant of biological efficacy appears to be the conjugation site, probably because of molecular conformation. Molecular modeling investigations reveal that the 17(3)-substituted chlorin e(6) conjugates are L-shaped, the 15(2) and 13(1) regioisomers assume extended conformations, and the 13(1) derivatives are nearly linear. It is hypothesized that the 13(1)-aspartylchlorin e(6) conjugate may be a more efficient photosensitizer for PDT than the commercial currently used 15(2) derivative.

Near-IR phosphorescence of iridium(III) corroles at ambient temperature

The photophysical properties of Ir(III) corroles differ from those of phosphorescent porphyrin complexes, cyclometalated and polyimine Ir(III) compounds, and other luminescent metallocorroles. Ir(III) corrole phosphorescence is observed at ambient temperature at wavelengths much longer (>800 nm) than those of most Ir(III) phosphors. The solvatochromic behavior of Ir(III)-corrole Soret and Q absorption bands suggests that the lowest singlet excited states (S(2) and S(1)) are substantially more polar than the ground state.

Polymeric micelles of zinc protoporphyrin for tumor targeted delivery based on EPR effect and singlet oxygen generation

Polymeric micelles of zinc protoporphyrin (ZnPP) with water soluble biocompatible and amphiphilic polymer, polyethylene glycol (PEG) demonstrated unique characteristics to target tumor tissues selectively based on the enhanced permeability and retention (EPR) effect. The micellar macromolecular drug of ZnPP (SMA-ZnPP and PEG-ZnPP) previously showed notable anticancer activity as a consequence of selective tumor targeting ability and its potent HO-1 inhibitory potential, resulting in suppressed biliverdin/bilirubin production in tumors thereby leading to oxystress induced tumor cell killing. Furthermore, recent findings also showed that ZnPP efficiently generated reactive singlet oxygen under illumination of visible light, laser, or xenon light source, which could augment its oxystress induced cell killing abilities. In the present paper, we report the synergistic effects of light induced photosensitizing capabilities and HO-1 inhibitory potentials of these unique micelles when tested in vitro and in vivo on tumor models under localized, mild illumination conditions using a tungsten-xenon light source. The results indicate that these water soluble polymeric micelles of ZnPP portend to be promising candidates for targeted chemotherapy as well as photodynamic therapy against superficial tumors as well as solid tumors located at light penetrable depths.

Model Systems for Fluorescence and Singlet Oxygen Quenching by Metalloporphyrins

Next-generation photodynamic therapy agents will minimize extraneous phototoxicity by being active only at the target site. To this end, we have developed a model system to systematically investigate the excited-state quenching ability of a number of metalloporphyrins. Central metal ions that prefer four-coordinate, square planar orientations (Ag(II), Cu(II), Ni(II), Pd(II), and Zn(II)) were used. Porphyrin dimers based on 5-(4-aminophenyl)-10,15,20-triphenylporphyrin and comprising both a free base porphyrin and a metalloporphyrin covalently linked through a five-carbon alkyl chain were synthesized. The fluorescence and singlet oxygen quantum yields for the dimers were probed at 630 and 650 nm, respectively, resulting in the excitation of only the free base porphyrin and allowing a comparison of the quenching efficacy of each central metal ion. These results demonstrate that metalloporphyrins can serve as efficient quenchers, and may be useful in the design of novel light-activated therapeutic agents.

Singlet oxygen quantum yields of potential porphyrin-based photosensitisers for photodynamic therapy

The singlet oxygen formation quantum yield (Phi(Delta)) for solutions of the di-cation, free-base and metallated forms of hematoporphyrin derivative (HpD), hematoporphyrin IX (Hp9) and a boronated protoporphyrin (BOPP) are reported using the method of direct detection of the characteristic phosphorescence following polychromatic excitation. Values of Phi(Delta) for the free-base form of all the porphyrins and the di-cation forms of Hp9 and HpD are in the range of 0.44 to 0.85 in the solvents investigated. Incorporation of zinc ions into the macrocycle reduces Phi(Delta) for all three porphyrins. BOPP facilitates the coordination of certain transition metals (Mn, Co and Cu) compared to Hp9 and HpD and results in a dramatic decrease in Phi(Delta). The experimental data suggest the introduction of low energy charge transfer states associated with the disruption of the planarity of the macrocyclic ring provides alternative non-radiative deactivation pathways. In BOPP, this non-planarity is augmented by the large closo-carborane peripheral substituent groups.

Exercises in molecular gymnastics--bending, stretching and twisting porphyrins

The functional versatility of tetrapyrroles as natural cofactors is related to their conformational flexibility where manipulation of the macrocycle conformation allows a fine-tuning of their physicochemical properties. This feature article gives a personal account of the synthesis and solid state structural characterization of highly substituted, non-planar porphyrins. Their conformational analysis identifies sterically strained tetrapyrroles as a versatile class of biomimetic compounds with tailor-made properties.