Manganese porphyrins — Studies on their potential use for protein labeling

Organic-Inorganic Porphyrinoid Frameworks for Biomolecule Sensing

Porphyrinoids and their analogous compounds play an important role in biosensing applications on account of their unique and versatile catalytic, coordination, photophysical, and electrochemical properties. Their remarkable arrays of properties can be finely tuned by synthetically modifying the porphyrinoid ring and varying the various structural parameters such as peripheral functionalization, metal coordination, and covalent or physical conjugation with other organic or inorganic scaffolds such as nanoparticles, metal-organic frameworks, and polymers. Porphyrinoids and their organic-inorganic conjugates are not only used as responsive materials but also utilized for the immobilization and embedding of biomolecules for applications in wearable devices, fast sensing devices, and other functional materials. The present review delineates the impact of different porphyrinoid conjugates on their physicochemical properties and their specificity as biosensors in a range of applications. The newest porphyrinoid types and their synthesis, modification, and functionalization are presented along with their advantages and performance improvements.

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.

Porphyrins as Colorimetric and Photometric Biosensors in Modern Bioanalytical Systems

Advances in porphyrin chemistry have provided novel materials and exciting technologies for bioanalysis such as colorimetric sensor array (CSA), photo-electrochemical (PEC) biosensing, and nanocomposites as peroxidase mimetics for glucose detection. This review highlights selected recent advances in the construction of supramolecular assemblies based on the porphyrin macrocycle that provide recognition of various biologically important entities through the unique porphyrin properties associated with colorimetry, spectrophotometry, and photo-electrochemistry.

Electrochemical and spectroelectrochemical characterization of Cu(II) and Mn(III) tetrabutano- and tetrabenzoporphyrins containing sterically hindered meso -(2,6-difluorophenyl) substituents in nonaqueous media

Four tetrabutano and tetrabenzoporphyrins containing sterically hindered meso-(2,6-difluorophenyl) substituents and copper(II) or manganese(III) central metal ions were synthesized and characterized as to their electrochemical and spectroelectrochemical properties in nonaqueous media. The copper(II) derivatives exhibit the expected two one-electron reductions to give [Formula: see text]-anion radicals and dianions in CH2Cl2. Electrochemical and spectroelectrochemical data suggest that a Cu(II) phlorin anion is generated from the doubly reduced Cu(II) butanoporphyrin and it is this species which undergoes the third reduction in pyridine. The first one-electron reduction of the Mn(III) porphyrins is metal-centered to give a Mn(II) compound, while the second and third reductions are macrocycle-centered to give Mn(II) porphyrin [Formula: see text]-anion radicals and dianions in both CH2Cl2 and pyridine. A Mn(II) phlorin anion is also generated from the Mn(II) dianion on the spectroelectrochemical timescale under the given solution conditions. The [Formula: see text],[Formula: see text]-butano and benzo groups have a significant effect on the measured redox potentials. Steric hindrance of the meso-(2,6-difluorophenyl) substituents also has an effect on the potential separation between the first two oxidations of the benzoporphyrins.

Spectral, Electrochemical, and ESR Characterization of Manganese Tetraarylporphyrins Containing Four β,β'-Pyrrole Fused Butano and Benzo Groups in Nonaqueous Media

Two series of β,β'-pyrrole butano- and benzo-substituted mangenese(III) tetraarylporphyrins were synthesized and characterized with regard to their spectral and electrochemical properties. The investigated compounds have the general formula butano(Ar)₄PorMnCl and benzo(Ar)₄PorMnCl, where Por is the dianion of the porphyrin and Ar is a p-CH₃Ph, Ph or p-ClPh group on each of the four meso-positions of the macrocycle. Each manganese(III) butano- or benzoporphyrin was examined in CH₂Cl₂ and/or pyridine containing 0.1 M tetra- n-butylammonium perchlorate and the data then were compared to that of the parent tetraarylporphyrins having the same meso-substituents. Up to four reductions are observed for each compound, the first being metal-centered to generate a Mn(II) porphyrin, and the second and third being porphyrin ring-centered to give a Mn(II) porphyrin π-anion radical and dianion, respectively. The one-electron reduced manganese porphyrins have an ESR spectrum with signals at g_⊥= 5.6-5.8 and g_// = 2.0, indicating a mixture of the four- and five-coordinated Mn(II) complexes in a high-spin state (3d⁵, S = 5/2, I = 5/2). Data from cyclic voltammetry and spectroelectrochemistry both suggest that formation of the porphyrin dianion is followed by a chemical reaction at the electrode surface to give an electroactive phlorin anion. The effects of solvent and porphyrin substituents on ultraviolet-visible light (UV-vis) spectra, redox potentials, and electron transfer mechanisms are discussed.

Analytical characterization of IgG–cTpp and IgG–Mn-cTpp conjugates

Herein, the conjugation of carboxylated tetraphenylporphyrin or its derivative containing manganese cation and model protein — immunoglobulin G is presented. The obtained IgG–cTpp and IgG–Mn-cTpp conjugates were subsequently used for model immunoassays construction. The IgG–cTpp formation was confirmed using size-exclusion chromatography. Thanks to the unique properties of applied labels the assay analysis was carried out with both spectrophotometric and spectrofluorimetric detection. The assays were performed creating semi-quantitative detection system using 96-well plates. The incubation time, ensuring full saturation of the surface with secondary antibodies was also optimized. Moreover, in the case of IgG–Mn-cTpp conjugates we present the possibility of both direct and indirect determination of the label, the latter based on the catalytic activity of Mn-cTpp, which allows for amplification of the measured signal. We proved that both cTpp and Mn-cTpp may be successfully used for protein labeling and serve as universal tracers for various formats of affinity assays and sensors.

Tetraphenylporphyrin as a protein label for triple detection analytical systems

Porphyrins and metalloporphyrins are promising new protein labels that can be detected using multiple techniques; improving the reliability of the analysis and broadening the range of the linear response. Here, we investigate the potential of 5,10,15,20-tetraphenyl-21H,23H-porphyrin (Tpp) as a hybrid protein label. The electrochemical and optical properties of porphyrin conjugated with bovine serum albumin (BSA), chicken egg albumin (CEA) and immunoglobulin G (IgG) were determined and optimal conditions for Tpp-protein conjugation established. Model conjugates of carboxylated Tpp with BSA and short peptides were characterized using differential pulse voltammetry, UV-Vis spectrophotometry and spectrofluorimetry. These results reveal that Tpp is a promising molecule to be used in a triple detection protein labelling system.

Studies on potential use of tin(IV) porphyrin in a role of proteins' label

We present an electrochemical and optical characterization of 5,10,15,20-tetraphenylporphyrin tin(IV) dichloride (Sn-tpp) in terms of its potential use as a hybrid proteins' label. Our research comprised Sn-tpp and Sn-tpp in the presence of model proteins selected as to mimic a receptor or surface blocking agents: bovine serum albumin, ovalbumin, and immunoglobulin G. In the course of the study, we determined optimal conditions for analysis by means of differential pulse voltammetry, ultraviolet-visible spectrophotometry, and spectrofluorimetry. In electrochemical detection, the influence of the working electrode, solvent, and supporting electrolyte was examined. Displacements of the received signals along the potential axis (a shift of the potential) and changes in signal intensities due to the addition of proteins were observed and analyzed. Simultaneously, the suitability of Sn-tpp as a label in optical detection mode was assessed by using spectroscopic techniques. The obtained results prove Sn-tpp to be applicable in dual and triple detection systems. Such an approach will improve the reliability of the analysis and, at the same time, will allow for widening the range of the linear response with some overlapping ranges of concentrations.