Unusual Stepwise Protonation and J-Aggregation ofmeso-Tetrakis(N-methylpyridinium-4-yl)porphine on Binding Poly(sodium vinylsulfonate)

Enhancement of the Rates for Insertion of Zinc(II) Ions into a Cationic Porphyrin Catalyzed by Poly(glutamate)

The self-assembly of porphyrins onto polyelectrolytes could lead to interesting changes in their reactivity with respect to the bulk solution. Here, we investigated the kinetics of Zn2+ incorporation into tetra-cationic water-soluble 5,10,15,20-tetrakis-(N-methylpyridinium-4-yl)porphyrin (TMpyP(4)) in the presence of poly(L-glutamic acid) (PGA) in a pH range from 4 to 6.5. Under these conditions, the porphyrin electrostatically interacted with the polymer, which gradually switched from an α-helical to a random coil structure. The profile of the logarithm of the observed rate constant (kobs) versus the pH was sigmoidal with an inflection point close to the pH of the conformation transition for PGA. At a pH of 5.4, when PGA was in its highly charged random coil conformation, an almost 1000-fold increase in the reaction rates was observed. An increase in the ionic strength of the bulk solution led to a decrease in the metal insertion rates. The role of the charged matrix was explained in terms of its ability to assemble both reagents in proximity, in agreement with the theory of counter-ion condensation around polyelectrolytes in an aqueous solution.

Kinetic Investigations on the Chiral Induction by Amino Acids in Porphyrin J-Aggregates

The self-assembling kinetics of the 5,10,15,20-tetrakis(4-sulfonato-phenyl)porphyrin (TPPS₄) into nano-tubular J-aggregates under strong acidic condition and in the presence of amino acids as templating chiral reagents have been investigated through UV/Vis spectroscopy. The ability of the chiral species to transfer its chiral information to the final J-aggregate has been measured through circular dichroism (CD) spectroscopy and compared to the spontaneous symmetry breaking process usually observed in these nano-aggregates. Under the experimental conditions here selected, including mixing protocol, we have observed a large difference in the observed aggregation rates for the various amino acids, those with a positively charged side group being the most effective. On the contrary, these species are less efficient in transferring their chirality, exhibiting a quite low or modest enhancement in the observed dissymmetry g-factors. On the other side, hydrophobic and some hydrophilic amino acids are revealed to be very active in inducing chirality with a discrete increase of intensity of the detected CD bands with respect to the spontaneous symmetry breaking.

Role of Cobalt(III) Cationic Complexes in the Self-Assembling Process of a Water Soluble Porphyrin

Under moderate acidic conditions, the cationic (+3) complexes ions tris(1,10-phenanthroline)cobalt(III), [Co(phen)₃]³⁺, and hexamminecobalt(III), [Co(NH₃)₆]³⁺, efficiently promote the self-assembling process of the diacid 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H₂TPPS₄) into J-aggregates. The growth kinetics have been analyzed according to a well-established autocatalytic model, in which the rate determining step is the initial formation of a nucleus containing m porphyrin units (in the range 2–3), followed by a stage whose rate constant k_c evolves as a power of time. The observed catalytic rate constants and the extent of J-aggregation increase on increasing the metal complex concentration, with the phen complex being the less active. The UV/Vis extinction spectra display quite broad envelops at the J-band, especially for the amino-complex, suggesting that electronic dipolar coupling between chromophores is operative in these species. The occurrence of spontaneous symmetry breaking has been revealed by circular dichroism and the measured dissymmetry g-factor decreases on increasing the aggregation rates. The role of these metal complexes on the growth and stabilization of porphyrin nano-assemblies is discussed in terms of the different degree of hydrophilicity and hydrogen bonding ability of the ligands present in the coordination sphere around the metal center.

Sulfobutylether-β-cyclodextrin/5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphine nanoassemblies with sustained antimicrobial phototherapeutic action

Nowadays, novel less-expensive nanoformulations for in situ-controlled and safe delivery of photosensitisers (PSs) against opportunistic pathogens in body-infections areas need to be developed. Antimicrobial photodynamic therapy (aPDT) is a promising approach to treat bacterial infections that are recalcitrant to antibiotics. In this paper, we propose the design and characterization of a novel nanophototherapeutic based on the trade cyclodextrin CAPTISOL® (sulfobutylether-beta-cyclodextrin, SBE-βCD) and 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphine tetrakis(p-toluenesulfonate) (TMPyP) to fabricate efficient biocompatible systems for aPDT. Spherical nanoassemblies of about 360 nm based on CAPTISOL®/TMPyP supramolecular complexes with 1:1 stoichiometry and apparent equilibrium binding constant (K_b ≅ 1.32 × 10⁵ M^-1) were prepared with entrapment efficiency of ≅ 100% by simple mixing in aqueous media and freeze-drying. These systems have been characterized by complementary spectroscopy and microscopy techniques. Time resolved fluorescence pointed out the strong interaction of porphyrin monomer within nanoassemblies (τ₂ ≅ 11 ns with an amount of ca 90%) and scarce self-aggregation of porphyrins have been observed. Singlet oxygen comparative determination (ϕ_{Δ CAPTISOL}®_/TMPyP = 0.58) assessed their photodynamic potential. Release and photostability studies have been carried out under physiological conditions pointing out the role of CAPTISOL® to sustain porphyrin release for more than 2 weeks and to protect PS from photodegradation. Finally, photoantimicrobial activity of nanoassemblies vs free porphyrin have been investigated against Gram-negative P. aeruginosa, E. coli and Gram-positive S. aureus. The proposed nanosystems were able to photokill both Gram-positive and -negative bacterial cells similarly to TMPyP at MBC₉₀ = 6 µM of TMPyP and at 42 J/cm² light dose. However, with respect to the less selective free TMPyP in biological sites, nanoassemblies exhibit sustained release properties and a higher photostability thus optimizing the PDT effect at the site of action. These results can open routes for in vivo translational studies on nano(photo)drugs and nanotheranostics based on less expensive formulations of CD and PS.

Cationic porphyrins with large side arm substituents as resonance light scattering ratiometric probes for specific recognition of nucleic acid G-quadruplexes

Specific G-quadruplex-probing is crucial for both biological sciences and biosensing applications. Most reported probes are focused on fluorescent or colorimetric recognition of G-quadruplexes. Herein, for the first time, we reported a new specific G-quadruplex-probing technique-resonance light scattering (RLS)-based ratiometric recognition. To achieve the RLS probing of G-quadruplexes in the important physiological pH range of 7.4-6.0, four water soluble cationic porphyrin derivatives, including an unreported octa-cationic porphyrin, with large side arm substituents were synthesized and developed as RLS probes. These RLS probes were demonstrated to work well for ratiometric recognition of G-quadruplexes with high specificity against single- and double-stranded DNAs, including long double-stranded ones. The working mechanism was speculated to be based on the RLS signal changes caused by porphyrin protonation that was promoted by the end-stacking of porphyrins on G-quadruplexes. This work adds an important member in G-quadruplex probe family, thus providing a useful tool for studies on G-quadruplex-related events concerning G-quadruplex formation, destruction and changes in size, shape and aggregation. As a proof-of-concept example of applications, the RLS probes were demonstrated to work well for label-free and sequence-specific sensing of microRNA. This work also provides a simple and useful way for the preparation of cationic porphyrins with high charges.

Asymmetric Cationic Porphyrin as a New G-Quadruplex Probe with Wash-Free Cancer-Targeted Imaging Ability Under Acidic Microenvironments

Porphyrins are promising candidates for nucleic acid G-quadruplex-specific optical recognition. We previously demonstrated that G-quadruplex recognition specificity of porphyrins could be improved by introducing bulky side arm substituents, but the enhanced protonation tendency limits their applications in some cases, such as under acidic conditions. Here, we demonstrated that the protonation tendency of porphyrin derivatives could be efficiently overcome by increasing molecular asymmetry. To validate this, an asymmetric, water-soluble, cationic porphyrin FA-TMPipEOPP (5-{4-[2-[[(2 E)-3-[3-methoxy-4-[2-(1-methyl-1-piperidinyl)ethoxy]phenyl]-1-oxo-2-propenyl]oxy]ethoxy]phenyl},10,15,20-tri{4-[2-(1-methyl-1-piperidinyl)ethoxy]-phenyl}porphyrin) was synthesized by introducing a ferulic acid (FA) unit at one side arm, and its structure was well-characterized. Unlike its symmetric counterpart TMPipEOPP that has a tendency to protonate under acidic conditions, FA-TMPipEOPP remained in the unprotonated monomeric form under the pH range of 2.0-8.0. Correspondingly, FA-TMPipEOPP showed better G-quadruplex recognition specificity than TMPipEOPP and thus might be used as a specific optical probe for colorimetric and fluorescent recognition of G-quadruplexes under acidic conditions. The feasibility was demonstrated by two proof-of-concept studies: probing structural competition between G-quadruplexes and duplexes and label-free and wash-free cancer cell-targeted bioimaging under an acidic tumor microenvironment. As G-quadruplex optical probes, FA-TMPipEOPP works well under acidic conditions, whereas TMPipEOPP works well under neutral conditions. This finding provides useful information for G-quadruplex probe research. That is, porphyrin-based G-quadruplex probes suitable for different pH conditions might be obtained by adjusting the molecular symmetry.

Spectroscopic investigation on porphyrins nano-assemblies onto gold nanorods

The interaction between gold nanorods (Au NRs), synthesized by a conventional seeded growth protocol, and the anionic tetrakis-(4-sulfonatophenyl)porphyrin (TPPS₄) has been investigated through various spectroscopic techniques. At neutral pH, the formation of H-aggregates and the inclusion of porphyrin monomers in CTAB micelles covering the nanorods have been evidenced. Under mild acidic conditions (pH=3) a nano-hybrid assembly of porphyrin J-aggregates and Au NRs has been revealed. For the sake of comparison, Cu(II) and Zn(II) metal porphyrin derivatives as well as a cationic porphyrin have been studied in the same experimental conditions, showing that: i) CuTPPS₄ forms porphyrin H-dimers onto the Au NRs; ii) ZnTPPS₄ undergoes to demetallation, followed by acidification of the central core and eventually aggregation onto Au NRs; iii) cationic porphyrin does not interact with Au NRs.

Cooperative self-assembly of porphyrins with polymers possessing bioactive functions

This review covers recent research on design strategies for the cooperative self-assembly of porphyrins with polymers and its implementation as bioactive assembly.