Hemin-Caged Ferritin Acting as a Peroxidase-like Nanozyme for the Selective Detection of Tumor Cells

Nanozyme is a class of artificial materials that possess enzyme-like activities and can overcome limitations of natural enzymes. However, controllability of the active sites, uniformity of the particles, and dispersion in the physiological media are still challenging for nanomaterial-based nanozymes. In this work, a protein-based nanozyme has been constructed by the encapsulation of hemin into the nanocavity of a recombinant human heavy chain ferritin (Ftn), generating a monodispersed peroxidase-mimetic nanozyme (hemin@Ftn). Hemin@Ftn possesses high peroxidase catalytic activity and high tolerance to the harsh environmental conditions, such as high temperature and chemical denaturant. Remarkably, hemin@Ftn can act as a colorimetric probe for the detection of tumor cells because it can selectively catalyze reactions in tumor cells. This protein-based nanozyme bridges the gap between natural enzymes and nanomaterial-based nanozymes by the incorporation of a catalytically active prosthetic group into a highly stable Ftn.

Porpholactone Chemistry: Shining New Light on an Old Cofactor

The emergence of porpholactone chemistry, discovered over 30 years ago, has significantly stimulated the development of biomimetic tetrapyrrole chemistry. It offers an opportunity, through modifications of non-pyrrolic building blocks, to clarify the relationship between chemical structure and excited-state properties, deciphering the structural code for the biological functions of life pigments. With intriguing photophysical properties in the red to near-infrared (NIR) regions, facile modulation of their electronic nature by fine-tuning chemical structures, and coordination ability with diverse metal ions, these novel porphyrinoids have favorable prospects in the fields of optical materials, bioimaging and therapy, and catalysis. In this Minireview, we summarize the brief history of porpholactone chemistry, and focus on the studies carried out in our group, particularly on the regioisomeric effect, NIR lanthanide luminescence, and metal catalysis. We outline the perspectives of these compounds in the construction of porpholactone-related biomedical applications and optical and energy materials, in order to inspire more interest and further advance bioinspired inorganic chemistry and lanthanide chemical biology.

Synthesis of Hangman Chlorins

Two complementary rational synthetic routes have been developed in order to synthesize hangman chlorins, which differ with regard to the order of the installation (pre- and post-formation of the chlorin macrocycle) and position of the xanthene backbone about the chlorin periphery. The versatility of the synthetic method is demonstrated with the preparation of ten new hangman chlorins bearing a xanthene backbone and a pendant carboxylic acid. Cyclic voltammograms of hangman chlorins exhibit a hangman effect derived from intermolecular proton transfer. This hangman effect is manifested in catalytic hydrogen evolution production.

Preparation and Characterization of Tadpole- and Sphere-Shaped Hemin Nanoparticles for Enhanced Solubility

Hemin is a potent iron supplement. A major limitation of the applicability of hemin is its extremely low aqueous solubility and bioavailability. The aim of this work is to prepare hemin nanoparticles with improved solubility. Transmission electron microscopic images showed that hemin nanoparticles with different initial concentrations of hemin (0.1 and 0.5 mg/mL) were tadpole-shaped (head of approximately 200 nm and tail of 100 nm) and sphere-shaped (50-100 nm), respectively. Moreover, hemin nanoparticles exhibited higher solubility than free hemin. The solubility of sphere-shaped nanoparticles was 308.2-fold higher than that of pure hemin at 25 °C. The hemin nanoparticles were stable in acidic conditions and displayed excellent thermal stability. These results suggested that hemin nanoparticles could serve as a potential iron supplement with potential applications in the food, biomedical, and photodynamic-photothermal therapy fields.

Aromaticity versus regioisomeric effect of β-substituents in porphyrinoids

Maximizing the regioisomeric effect of β-substituents on photophysical properties of porphyrinoids through disruption of TT-conjugation and reducing the aromaticity.

New molecular design for blue BODIPYs

Dihydro analogues of BODIPYs exhibit spectral features (Φ_f ∼ 0.4–0.9) resembling aminocoumarins and suggest applications for broad-band photosensitization or where large Stokes shifts are desired.

Annulated bacteriochlorins for near-infrared photophysical studies

Bacteriochlorins with phenaleno or benzo annulation absorb at 913 or 1033 nm and exhibit excited-state lifetimes of 150 or 7 ps, suggesting applications in photoacoustic imaging.

A Dipyrrin Programmed for Covalent Loading with Fullerenes

We describe here a di-(β,β'-sulfoleno)pyrrin programmed for efficient and specific β,β'-functionalization via [4+2] cycloaddition reactions. At 120 °C and in the presence of an excess of C60 -fullerene the di-(β,β'-sulfoleno)pyrrin decomposed cleanly, furnishing a di-(β,β'-fullereno)pyrrin and the corresponding monofullereno-dipyrrin in an overall yield of 96 %. Hence, relatively mild thermolysis of the di-(β,β'-sulfoleno)pyrrin induced stepwise extrusion of two equivalents of SO2 , producing highly reactive dipyrrin-β,β'-diene intermediates readily, providing a very effective path to [4+2]-cycloadducts. As presented here by the example of the covalent attachment of C60 -fullerene units, a convenient general methodology for the efficient synthesis of covalent dipyrrin β,β'-cycloadducts is made available.

Furan- and Thiophene-Based Auxochromes Red-shift Chlorin Absorptions and Enable Oxidative Chlorin Polymerizations

The de novo syntheses of chemically stable chlorins with five-membered heterocyclic (furane, thiophene, formylfurane and formylthiophene) substituents in selected meso- and β-positions are reported. Heterocycle incorporation in the 3- and 13-positions shifted the chlorin absorption and emission to the red (up to λem =680 nm), thus these readily incorporated substituents function analogously to auxochromes present in chlorophylls, for example, formyl and vinyl groups. Photophysical, theoretical and X-ray crystallographic experiments revealed small but significant differences between the behavior of the furan- and the thiophene-based auxochromes. Four regioisomeric bis-thienylchlorins (3,10; 3,13, 3,15 and 10,15) were oxidatively electropolymerized; the chlorin monomer geometry had a profound impact on the polymerization efficiency and the electrochemical properties of the resulting material. Chemical co-polymerization of 3,13-bis-thienylchlorin with 3-hexylthiophene yielded an organic-soluble red-emitting polymer.

Synthesis and photophysical characterization of bacteriochlorins equipped with integral swallowtail substituents

The two pyrroline units of bacteriochlorins can now bear gem-dialkyl or diaryl groups (L), which project above and below the macrocycle plane, whereas dimethyl groups generally have been accessible previously.

Directly linked hydroporphyrin dimers

The synthesis and chemical, photophysical and electrochemical characterisation of directly meso–meso- or meso-β-linked hydroporphyrin (chlorin) dimers is reported.

Bioinspired nanophotosensitizers: synthesis and characterization of porphyrin–noble metal nanoparticle conjugates

Conjugatable and compact porphyrinic photosensitizer nanoparticle conjugates were developed through rational synthesis followed by conjugation with noble metal nanoparticles.

Progress Towards Synthetic Chlorins with Graded Polarity, Conjugatable Substituents, and Wavelength Tunability

Advances in chlorin synthetic chemistry now enable the de novo preparation of diverse chlorin-containing molecular architectures. Five distinct molecular designs have been explored here, including hydrophobic bioconjugatable (oxo)chlorins; a hydrophilic bioconjugatable chlorin; a trans-ethynyl/iodochlorin building block; a set of chlorins bearing electron-rich (methoxy, dimethylamino, methylthio) groups at the 3-position; and a set of ten 3,13-disubstituted chlorins chiefly bearing groups with extended π-moieties. Altogether 23 new chlorins (17 targets, 6 intermediates) have been prepared. The challenge associated with molecular designs that encompass the combination of "hydrophilic, bioconjugatable and wavelength-tunable" chiefly resides in the nature of the hydrophilic unit.

Effects of substituents on synthetic analogs of chlorophylls. Part 4: How formyl group location dictates the spectral properties of chlorophylls b, d and f

Photosynthetic organisms are adapted to light characteristics in their habitat in part via the spectral characteristics of the associated chlorophyll pigments, which differ in the position of a formyl group around the chlorin macrocycle (chlorophylls b, d, f) or no formyl group (chlorophyll a). To probe the origin of this spectral tuning, the photophysical and electronic structural properties of a new set of synthetic chlorins are reported. The zinc and free base chlorins have a formyl group at either the 2- or 3-position. The four compounds have fluorescence yields in the range 0.19-0.28 and singlet excited-state lifetimes of ca 4 ns for zinc chelates and ca 8 ns for the free base forms. The photophysical properties of the 2- and 3-formyl zinc chlorins are similar to those observed previously for 13-formyl or 3,13-diformyl chlorins, but differ markedly from those for 7-formyl analogs. Molecular-orbital characteristics obtained from density functional theory (DFT) calculations were used as input to spectral simulations employing the four-orbital model. The analysis has uncovered the key changes in electronic structure engendered by the presence/location of a formyl group at various macrocycle positions, which is relevant to understanding the distinct spectral properties of the natural chlorophylls a, b, d and f.

In vitro conversion of vinyl to formyl groups in naturally occurring chlorophylls

The chemical structural differences distinguishing chlorophylls in oxygenic photosynthetic organisms are either formyl substitution (chlorophyll b, d, and f) or the degree of unsaturation (8-vinyl chlorophyll a and b) of a side chain of the macrocycle compared with chlorophyll a. We conducted an investigation of the conversion of vinyl to formyl groups among naturally occurring chlorophylls. We demonstrated the in vitro oxidative cleavage of vinyl side groups to yield formyl groups through the aid of a thiol-containing compound in aqueous reaction mixture at room temperature. Heme is required as a catalyst in aqueous solution but is not required in methanolic reaction mixture. The conversion of vinyl- to formyl- groups is independent of their position on the macrocycle, as we observed oxidative cleavages of both 3-vinyl and 8-vinyl side chains to yield formyl groups. Three new chlorophyll derivatives were synthesised using 8-vinyl chlorophyll a as substrate: 8-vinyl chlorophyll d, [8-formyl]-chlorophyll a, and [3,8-diformyl]-chlorophyll a. The structural and spectral properties will provide a signature that may aid in identification of the novel chlorophyll derivatives in natural systems. The ease of conversion of vinyl- to formyl- in chlorophylls demonstrated here has implications regarding the biosynthetic mechanism of chlorophyll din vivo.