Effect of protonation on the singlet–singlet excited-state absorption of meso-tetrakis(p-sulphonatophenyl) porphyrin

Daylight photodynamic inactivation of cattle tick Rhipicephalus microplus by porphyrins: An alternative for the ectoparasite control

The bovine tick Rhipicephalus microplus, a primary ectoparasite of veterinary concern, contributes significantly to disease transmission and reduced cattle productivity, resulting in substantial economic losses. The overuse of chemical acaricides has led to the emergence of resistant strains, posing a considerable challenge to veterinary medicine. Consequently, the development of alternative parasite control methods is essential to ensure livestock quality and enhance food safety worldwide. Our study introduces an innovative approach to photodynamic inactivation (PDI) of the bovine tick, harnessing natural daylight for a potential field application. Reproductive parameters (female and egg mass, egg production index, and larval hatch) were evaluated in engorged female ticks under photodynamic action using the hematoporphyrin (HP) and tetra-cationic porphyrins free-base meso-tetra-ruthenated (4-pyridyl) (RuTPyP) and its zinc(II) complex (ZnRuTPyP) as photosensitizers (PS). The results showed that there was no significant difference between the groups treated with tetra‑ruthenium porphyrins and the control group. However, HP exhibits a control percentage of 97.9% at a concentration of 2.5 μmol.L-1, aligning with the expected control rates achieved by conventional chemical acaricides. Photophysical and physicochemical parameters such as the number of singlet oxygen produced and lipophilicity were discussed for each PS and related to tick control percentages. Furthermore, the interaction between HP and chitin, an important macromolecule presents in the tick's cuticle, considered as the primary target tick structure during PDI was observed by the absorption and fluorescence emission spectroscopic techniques. Therefore, the results presented here extend the potential for controlling R. microplus through photodynamic inactivation while utilizing sunlight as a source of natural irradiation.

Synergic vascular photodynamic activity by methylene blue-curcumin supramolecular assembly

A supramolecular assembly was obtained by combining methylene blue (MB) with a natural plant extract, curcumin (Curc), in a stoichiometric ratio of 1:4 in aqueous solution (90% PBS + 10% ethanol) at room temperature. The MB-Curc supramolecular assembly was evidenced by absorption and fluorescence spectroscopies, and the stoichiometry and bonding constant were obtained using Cieleńs model. Its stability and photostability were evaluated by chromatographic analysis and UV-Vis absorption. The MB-Curc avoids the aggregation of both isolated compounds and efficiently produces singlet oxygen (ΦΔ= 0.52 ± 0.03). Its potential for photodynamic antiangiogenic treatments was evaluated through the vascular effect observed in chicken chorioallantoic membrane (CAM) assay. The results showed intense damage in CAM vascular network by MB-Curc after irradiation, which is higher than the effect of isolated compounds, indicating a synergistic vascular effect. This combination can be essential to prevent cancer revascularization after photodynamic application and improve the efficacy of this approach. The characteristics exhibited by MB-Curc make it a potential candidate for use in cancer treatments through photodynamic antiangiogenic therapy.

Effects of meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS4) aggregation on its spectral and kinetic characteristics and singlet oxygen production

The present work reports the effects of meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS₄) aggregation on its excited states absorption spectra, triplet states quenching by molecular oxygen and singlet oxygen production. Experimental techniques such as optical absorption, Z-scan with a white light continuum source and the Laser Flash Photolysis were used to fulfil the study. J-aggregates possess reverse saturable absorption in the 505-660 nm spectral range with a peak centered close to 540 nm. These facts together with their fast relaxation time suggest that they can be employed as material for ultrafast optical limiting and switching. Even though aggregation reduces the porphyrin excited-state lifetimes and quantum yields, it does not reduce the probability of the contact between the quencher and the excited aggregate. Aggregation does not change the contribution of energy transfer mechanisms to triplet state quenching by molecular oxygen. The production of singlet oxygen, the intense absorption in the phototherapeutic window and the high efficiency of conversion of light energy into heat, allow consider J-aggregates as a theranostic agent for photomedicine. It is proposed to use J-aggregates for diagnostics by photoacoustic images and in combination with a near-infrared photodynamic/photothermal dual mode therapy, thus improving synergistically the therapeutic response.

Effects of bovine serum albumin (BSA) on the excited-state properties of meso-tetrakis(sulfonatophenyl) porphyrin (TPPS4)

To infer changes in the photophysical properties of porphyrins due to complexation with albumin, a combination of Z-scan and conventional spectroscopic techniques was employed. We measured the characteristics of excited states of meso-tetrakis(sulfonatophenyl) porphyrin bound to bovine serum albumin and observed that the binding reduces the intersystem crossing quantum yield and increases the internal conversion one. A reverse saturable absorption process was observed in the nanosecond timescale. These results are important for prediction of the efficiency of this complex in medical and optical applications, because associating porphyrins to proteins enables better accumulation in tumors and improves its stability in optical devices, but at the same time, decreases its triplet quantum yield.

UV-vis absorption spectra of Sn(IV)tetrakis(4-pyridyl) porphyrins on the basis of axial ligation and pyridine protonation

The present study highlights the structural and electronic spectra of Sn(IV)tetrakis(4-pyridyl) porphyrins (SnTP) using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The impact of axial ligands (OH^-, Cl^-, and H₂O) and protonation at pyridine sites on the excitation properties of SnTP is also explored. The considered SnTPs were optimized at B3LYP/6-31+G* level of theory with LANL2DZ basis set for Sn metal. The effects of tetrahydrofuran (THF) and dimethylformamide (DMF) solvents were also assessed employing conductor-like polarizable continuum (C-PCM) model. The observed structural effects correlate well with the experimental data and clearly depict the impact of axial ligands on the SnTP ring. The absorption spectra along with the frontier orbitals in all three phases show noticeable dependence of axial ligation on the photophysical properties of SnTPs. The transition character of molecular orbitals and their respective density of states (DOS) were explored to infer the orbitals involved in electronic transitions. Graphical abstract The structural and electronic spectra of Sn(IV)tetrakis(4-pyridyl) porphyrins (SnTP) were examined using time-dependent density functional theory (TDDFT). Axial ligation and pyridine protonation significantly affects the absorption properties of Sn complexes. The overall results suggest the application of [(OH^-)Sn (OH^-)TP] and [(Cl^-)Sn (Cl^-)TP] as photosensitizers.

Use of Spectroscopic Techniques for Evaluating the Coupling of Porphyrins on Biocompatible Nanoparticles. A Potential System for Photodynamics, Theranostics, and Nanodrug Delivery Applications

Modern medicine has been searching for new and more efficient strategies for diagnostics and therapeutics applications. Considering this, porphyrin molecules have received great interest for applications in photodiagnostics and phototherapies, even as magnetic nanoparticles for drug-delivery systems and magnetic-hyperthermia therapy. Aiming to obtain a multifunctional system, which combines diagnostics with therapeutic functions on the same platform, the present study employed UV/vis absorption and fluorescence spectroscopies to evaluate the interaction between meso-tetrakis(p-sulfonatofenyl)porphyrin (TPPS) and maghemite nanoparticles (γ-Fe₂O₃). These spectroscopic techniques allowed us to describe the dynamics of coupling porphyrins on nanoparticles and estimate the number of 21 porphyrins per nanoparticle. Also, the binding parameters, such as the association constants (K_a = 8.89 × 10⁵ M^-1) and bimolecular quenching rate constant (k_q = 2.54 × 10¹⁴ M^-1 s^-1) were obtained. These results suggest a static quenching process where the electrostatic attraction plays an essential role. The work shows that spectroscopic techniques are powerful tools to evaluate the coupling of organic molecules and nanoparticles. Besides, the system studied provides a relevant background for potential applications in bionanotechnology and nanomedicine, such as (1) nanodrug delivery system, (2) photodiagnostics/theranostics, and/or (3) a combined action of photodynamic and hyperthermia therapies, working in a synergetic way.

Laser induced protonation of free base porphyrin in chloroform results in the enhancement of positive nonlinear absorption due to conformational distortion

Free base porphyrin in chloroform solution irradiated with focused laser beam, in an open Z-scan set-up, changed color from purple to green, which was associated with protonation of the porphyrin with protonic species from photodegradation of the solvent. Protonation is demonstrated as a simple means to improve the optical limiting performance of free base porphyrin nonlinear optical (NLO) materials.

Effect of interaction with micelles on the excited-state optical properties of zinc porphyrins and J-aggregates formation

This work reports on the photophysical properties of zinc porphyrins meso-tetrakis methylpyridiniumyl (Zn(2+)TMPyP) and meso-tetrakis sulfonatophenyl (Zn(2+)TPPS) in homogeneous aqueous solutions and in the presence of sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) micelles. The excited-state dynamic was investigated with the Z-scan technique, UV-Vis absorption, and fluorescence spectroscopy. Photophysical parameters were obtained by analyzing the experimental data with a conventional five-energy-level diagram. The interaction of the charged side porphyrin groups with oppositely charged surfactants can reduce the electrostatic repulsion between porphyrin molecules leading to aggregation, which affected the porphyrin characteristics such as absorption cross-sections, lifetimes and quantum yields. The interaction between anionic ZnTPPS with cationic CTAB micelles induced the formation of porphyrin J-aggregates, while this effect was not observed in the interaction of ZnTMPyP with SDS micelles. This difference is, probably, due to the difference in electrostatic repulsion between the porphyrin molecules. The insights obtained by these results are important for the understanding of the photophysical behavior of porphyrins, regarding potential applications in pharmacokinetics as encapsulation of photosensitizer for drug delivery systems and in its interaction with cellular membrane.

Effects of environment on the photophysical characteristics of mesotetrakis methylpyridiniumyl porphyrin (TMPyP)

Porphyrins are an important class of organic molecules, with interesting linear and nonlinear optical properties given mainly by their extended π-conjugation structure. Their photophysical properties can be greatly affected by the surrounding environment, which can be used to tune its final properties. Here we report on an experimental study of the photophysical properties of meso-tetrakis (methylpyridiniumyl) porphyrin (TMPyP) in aqueous and in several organic solvents and its interaction with micelles formed from negatively charged sodium dodecylsulphate (SDS), positively charged cetyl trimethyl ammonium bromide (CTAB) and neutral TRITON X-100. By using the Z-scan technique, flash-photolysis and time-resolved fluorescence techniques, we were able to evaluate the excited state dynamics of the TMPyP, and observed that the tetrapyrrole ring plays important role due to hydrogen bonds formation between nitrogen atom and water, while the side groups determine the porphyrin localization in non-aqueous micelle part.