A Green BODIPY-Based, Super-Fluorogenic, Protein-Specific Labelling Agent

Phosphorogenic Iridium(III) bis-Tetrazine Complexes for Bioorthogonal Peptide Stapling, Bioimaging, Photocytotoxic Applications, and the Construction of Nanosized Hydrogels

The dual functionality of 1,2,4,5-tetrazine as a bioorthogonal reactive unit and a luminescence quencher has shaped tetrazine-based probes as attractive candidates for luminogenic labeling of biomolecules in living systems. In this work, three cyclometalated iridium(III) complexes featuring two tetrazine units were synthesized and characterized. Upon photoexcitation, the complexes were non-emissive but displayed up to 3900-fold emission enhancement upon the inverse electron-demand Diels-Alder (IEDDA) [4+2] cycloaddition with (1R,8S,9s)-bicyclo[6.1.0]non-4-yne (BCN) substrates. The rapid reaction kinetics (k₂ up to 1.47×10⁴  M^-1  s^-1 ) of the complexes toward BCN substrates allowed effective peptide labeling. The complexes were also applied as live cell bioimaging reagents and photocytotoxic agents. One of the complexes was utilized in the preparation of luminescent nanosized hydrogels that exhibited interesting cargo delivery properties.

Wavelength dependent photochemistry of BODIPY-phenols and their applications in the fluorescent labeling of proteins

A series of BODIPY dyes were synthesized, that were at the 3, or 3 and 5 positions, substituted by photochemically reactive quinone methide (QM) precursor moieties. Fluorescence properties of the molecules were investigated and we demonstrated that the molecules undergo wavelength dependent photochemistry. Photodeamination to deliver QMs takes place only upon excitation to higher excited singlet states, showing unusual anti-Kasha photochemical reactivity. The findings were corroborated by TD-DFT computations. Laser flash photolysis experiments could not reveal QMs due to the low efficiency of their formation, but enabled the detection of phenoxyl radicals. The applicability of the molecules for the fluorescent labeling of bovine serum albumin as a model protein upon photoexcitation at 350 nm was demonstrated.

A Protein-Binding Molecular Photothermal Agent for Tumor Ablation

Photothermal therapy usually requires a high power density to activate photothermal agent for effective treatment, which inevitably leads to damage to normal tissues and inflammation in tumor tissues. Herein, we rationally design a protein-binding strategy to build a molecular photothermal agent for photothermal ablation of tumor. The synthesized photothermal agent can covalently bind to the thiol groups on the intracellular proteins. The heat generated by the photothermal agent directly destroyed the bioactive proteins in the cells, effectively reducing the heat loss and the molecular leakage. Under a low power density of 0.2 W cm^-2 , the temperature produced by the photothermal agent was sufficient to induce apoptosis. In vitro and in vivo experiments showed that the therapeutic effect of photothermal therapy can be efficiently improved with the protein-binding strategy.

Theoretical predictions of the spectroscopic properties of BODIPY dyes: Effects of the fused aromatic and heteroaromatic rings at the b, g bonds

The fusion of aryl and heteroaryl moieties in the BODIPY skeleton is the important route to design BODIPYs exhibiting absorption and fluorescence in red or near infra-red regions. Despite the importance of this approach, little is known about the influence of aryl and heteroaryl rings on the position of the energy levels of the lower electronic states of such dyes. In this paper, the influence of benzene (B), thiophene (T) and furan (F) rings fused in the BODIPY core (b) at both b and g bonds on the optical properties of the symmetric BbB, TbT and FbF and asymmetric TbF, BbF and BbT dyes have been investigated by TD-CAM-B3LYP and RI-CC2 calculations. We have shown that in contrast to the locally excited (LE0-type) main vertical state, energy of which is nearly the same for all the substituents at the b and g bonds, energy of the next two states of the LE1- and LE2-type for the symmetric dyes or the charge transfer (CT1- and CT2-type) for the asymmetric dyes depends strongly on the nature of the rings at the b and g bonds. The benzene-fused dyes (BbF, BbT, BbB) have the lowest energy of the excited levels of the LE-type (or CT1-type) states, and inversion with LE0-type levels occurs. As a result, the dramatic decrease of the fluorescence quantum yield is expected in these cases. The identification of these effects provides a quality framework for understanding of how fused substituents regulate photophysical processes of BODIPYs.

Labeling of Proteins by BODIPY-Quinone Methides Utilizing Anti-Kasha Photochemistry

A novel approach for the photolabeling of proteins by a BODIPY fluorophore is reported that is based on an anti-Kasha photochemical reaction from an upper singlet excited state (S_n) leading to the deamination of the BODIPY quinone methide precursor. On the other hand, the high photochemical stability of the dye upon excitation by visible light to S₁ allows for the selective fluorescence detection from the dye or dye-protein adduct, without concomitant bleaching or hydrolysis of the protein-dye adduct. Therefore, photolabeling and fluorescence monitoring can be uncoupled by using different excitation wavelengths. Combined theoretical and experimental studies by preparative irradiations, fluorescence, and laser flash photolysis fully disclose the photophysical properties of the dye and its anti-Kasha photochemical reactivity. The application of the dye was demonstrated on photolabeling of bovine serum albumin.

A Near-Infrared Photoswitchable Protein-Fluorophore Tag for No-Wash Live Cell Imaging

FR-1V, a fluorene-based aldehydic chromophore, binds its target protein as an imine to yield a highly bathochromic pigment, CF-2, a prototypic protein-dye tagging system whose NIR emission can be spatiotemporally switched ON by rapid UV-light activation. This is achieved through photoisomerization of the imine and its subsequent protonation. We demonstrate a no-wash protocol for live cell imaging of subcellular compartments in a variety of mammalian cell lines with minimal fluorescence background.