The influence of pH on charged porphyrins studied by fluorescence and photoacoustic spectroscopy

Probing mechanism of Rhodamine B decolorization under homogeneous conditions via pH-controlled photocatalysis with anionic porphyrin

Porphyrins are acknowledged for their efficacy as photosensitizers and show potential for the treatment of water contaminated with diverse dyes. This research emphasizes the use of meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) as a photosensitizer for purifying water contaminated with rhodamine B. Investigations were conducted under homogeneous conditions using visible light irradiation, revealing the efficacy of the porphyrin in the decolorization of rhodamine B strongly depends on pH of the solution. This study demonstrated that within 120 min, the decolorization process rapidly removed about 95% of RhB at an initial pH of 3.0, while at pH 6.0, the removal rate was significantly lower, at only 12%. An extensive photophysical study of the TPPS was carried out at pH 6.0 and pH 3.0 including absorption and fluorescence spectra, fluorescence quantum yields, triplet absorption spectra, triplet lifetimes, triplet and singlet oxygen quantum yields in order to explain difference in the efficiency of RhB discoloration. A thorough investigation into mechanism revealed that neither reactive oxygen species nor singlet oxygen played a role in RhB decolorization within this system. Instead, the predominant route was found to be the electron transfer from photoexcited TPPS to RhB, followed by proton transfer at pH 3.0, leading to the generation of a colorless leuco form.

Porphyrin-Grafted Poly(ethylene terephthalate) as a Reusable and Highly Selective Colorimetric Probe for Mercuric Ion Contaminants in Aqueous Samples

Heavy metals are the most hazardous water pollutants, with severe health and environmental consequences. Among these, mercuric (Hg2+) ions are known to cause detrimental health issues in both humans and aquatic life. Due to this, several analytical techniques have been devised to detect and quantify the amount of this ion. However, most of these require advanced instrumentation, prolonged analysis time, and sample preparation. In this study, a low-cost and highly reusable colorimetric probe was developed by grafting porphyrin to poly(ethylene terephthalate) sheets using an oxazoline polymer as covalent adhesive. Upon exposure to trace amounts of Hg2+ in solution, the fabricated material visually transitioned from faint brownish pink to green by the complexation mechanism. Additionally, the transparency of this probe allowed the quantitative spectrophotometric determination of the Hg2+ concentration in aqueous samples. It was also shown that the material is highly stable, which can be reused for more than 50 times without significant decline in its performance, hence, making it suitable for the onsite monitoring of mercuric ion contamination in different bodies of water.

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)).

Molecular Photoacoustic Contrast Agents: Design Principles & Applications

Photoacoustic imaging (PAI) is a rapidly growing field which offers high spatial resolution and high contrast for deep-tissue imaging in vivo. PAI is nonionizing and noninvasive and combines the optical resolution of fluorescence imaging with the spatial resolution of ultrasound imaging. In particular, the development of exogenous PA contrast agents has gained significant momentum of late with a vastly expanding complexity of dye materials under investigation ranging from small molecules to macromolecular proteins, polymeric and inorganic nanoparticles. The goal of this review is to survey the current state of the art in molecular photoacoustic contrast agents (MPACs) for applications in biomedical imaging. The fundamental design principles of MPACs are presented and a review of prior reports spanning from early-to-current literature is put forth.

Porphyrin-Gold Nanomaterial for Efficient Drug Delivery to Cancerous Cells

With an aim to overcome multidrug resistance (MDR), nontargeted delivery, and drug toxicity, we developed a new nanochemotherapeutic system with tetrasodium salt of meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) armored on gold nanoparticles (TPPS-AuNPs). The nanocarrier is able to be selectively internalized within tumor cells than in normal cells followed by endocytosis and therefore delivers the antitumor drug doxorubicin (DOX) particularly to the nucleus of diseased cells. The embedment of TPPS on the gold nanosurface provides excellent stability and biocompatibility to the nanoparticles. Porphyrin interacts with the gold nanosurface through the coordination interaction between gold and pyrrolic nitrogen atoms of the porphyrin and forms a strong association complex. DOX-loaded nanocomposite (DOX@TPPS-AuNPs) demonstrated enhanced cellular uptake with significantly reduced drug efflux in MDR brain cancer cells, thereby increasing the retention time of the drug within tumor cells. It exhibited about 9 times greater potency for cellular apoptosis via triggered release commenced by acidic pH. DOX has been successfully loaded on the porphyrin-modified gold nanosurface noncovalently with high encapsulation efficacy (∼90%) and tightly associated under normal physiological conditions but capable of releasing ∼81% of drug in a low-pH environment. Subsequently, DOX-loaded TPPS-AuNPs exhibited higher inhibition of cellular metastasis, invasion, and angiogenesis, suggesting that TPPS-modified AuNPs could improve the therapeutic efficacy of the drug molecule. Unlike free DOX, drug-loaded TPPS-AuNPs did not show toxicity toward normal cells. Therefore, higher drug encapsulation efficacy with selective targeting potential and acidic-pH-mediated intracellular release of DOX at the nucleus make TPPS-AuNPs a "magic bullet" for implication in nanomedicine.

In situ ultra-fast heat deposition does not perturb the structure of serum albumin

MnTPPS is a metallic water soluble porphyrin with high potential to be used as a contrast agent in photoacoustic tomography. In order to fully understand the interaction between MnTPPS and serum albumin and to investigate the effect of the light induced fast in situ heat deposition by MnTPPS in the protein, we performed several experimental studies using fluorescence and circular dichroism spectroscopies, as well as photoacoustic calorimetry. To identify the possible binding site(s) of the metalloporphyrin in serum albumin and to help interpret the spectroscopic results, a molecular docking exercise was also carried out. The fluorescence data indicate a 1 : 1 stoichiometry for the complex BSA : MnTPPS. The molecular docking results suggest one binding site at the subdomain IB of albumin, where Trp-134 is found, as the main binding site for MnTPPS. The CD data indicate no significant conformational changes of the BSA secondary structure upon MnTPPS binding and even after several minutes of laser excitation of MnTPPS. TR-PAC results show that the in situ heat deposition from MnTPPS does not cause any significant transient conformational change to the BSA structure. In conclusion, this work demonstrates that MnTPPS, in addition to the necessary physical and chemical properties to be used as a contrast agent in photoacoustic tomography, can be effectively carried by albumin and that in situ heat release following light absorption does not cause any significant damage to the protein structure.

The singlet-oxygen-sensitized delayed fluorescence in mammalian cells: a time-resolved microscopy approach

Microsecond kinetics of singlet-oxygen-sensitized delayed fluorescence (SOSDF) have been detected from individual living fibroblast cells as a proof-of-concept. These provide valuable information about excited state lifetimes and their changes during PDT-like treatment.

Total Internal Reflection Fluorescence Spectroscopy for Investigating the Adsorption of a Porphyrin at the Glass/Water Interface in the Presence of a Cationic Surfactant Below the Critical Micelle Concentration

Total internal reflection fluorescence (TIRF) spectroscopy was used to investigate the adsorption behavior of meso-tetrakis(p-sulfonatophenyl)porphyrin (TPPS) at the glass/water interface in the presence of a cationic surfactant (cetyltrimethylammonium bromide, CTAB) far below the critical micelle concentration. The adsorption model of TPPS at the glass/water interface in the presence of low concentration of CTAB was proposed, which was different from the adsorption of TPPS in the presence of micelles of CTAB at the glass/water interface. TPPS and CTAB did not form stable complex at the interface in dilute system. The interfacial species of TPPS were analyzed by comparing the spectra of TPPS at the glass/water interface and in the aqueous phase. The influences of the TPPS concentration, the CTAB concentration, and the pH values on the interfacial fluorescence spectra and intensities were studied. It was demonstrated that electrostatic interaction and hydrophobicity performed an important role on the adsorption of TPPS in the presence of CTAB. The different effects of TPPS concentration on the adsorption behaviour of TPPS at different pH were observed for the first time. It was found that the adsorption isotherms of TPPS at glass/water interface could fit Freundlich equation at pH 7.1.

Labelling of manganese-based magnetic resonance imaging (MRI) contrast agents with the positron emitter 51Mn, as exemplified by manganese-tetraphenyl-porphin-sulfonate (MnTPPS4)

The potential tumor seeking MRI contrast agent MnTPPS(4) was labelled with the positron emitting nuclide (51)Mn in no-carrier-added (n.c.a.) form. The complex formation kinetics were investigated and the apparent rate constants were determined under pseudo-first-order conditions. The derived bimolecular rate constants gave the Arrhenius parameters E(A)=84 kJ mol(-1) and A=2 x 10(12)s(-1)M(-1). Optimum labelling conditions were derived (radiochemical yields >99% possible, effective yields about 32%). Separation and purification of n.c.a. (51)MnTPPS(4) were performed for potential human use. All impurities were <1%.