Adaptive Synthesis, Supramolecular Behavior, and Biological Properties of Amphiphilic Carbosilane-Phosphonium Dendrons with Tunable Structure

Here, we present a modular synthesis as well as physicochemical and biological evaluation of a new series of amphiphilic dendrons carrying triphenylphosphonium groups at their periphery. Within the series, the size and mutual balance of lipophilic and hydrophilic domains are systematically varied, changing the dendron shape from cylindrical to conical. In physiological solution, the dendrons exhibit very low critical micelle concentrations (2.6-4.9 μM) and form stable and uniform micelles 6-12 nm in diameter, depending on dendron shape; the results correlate well with molecular dynamics simulations. The compounds show relatively high cytotoxicity (IC50 1.2-21.0 μM) associated with micelle formation and inversely related to the size of assembled particles. Depending on their shape, the dendrons show promising results in terms of dendriplex formation and antibacterial activity. In addition to simple amphiphilic dendrons, a fluorescently labeled analogue was also prepared and utilized as an additive visualizing the dendron's cellular uptake.

Aggregation Behavior of CHR-bis(BODIPY) Bichromophores in THF-water Mixtures: Effect of Linking Positions and Aryl-spacer Substituents

Aggregation-caused quenching effect (ACQ) greatly limits the practical use of many organic luminophores in biomedicine, optics and electronics. The comparative analysis of aggregation characteristics of CHR-bis(BODIPY) bichromophores 1-6 with R = H, Ph, MeOPh and various linking positions (α,α-; α,β-; β,β- and β',β'-) in THF-water mixtures with different water fractions or dye concentrations is first presented in this article. Both the linking style 1-4 and the arylation of the spacer with phenyl (Ph-) 5 or methoxyphenyl (MeOPh-) 6 substituents strongly affect the formation of luminophore aggregated forms in binary THF-water mixtures. The α,α-and β,β-isomers (1 and 3) form non-fluorescent H-type aggregates in THF-water mixtures with fw > 70%. The α,β-; β',β'-isomers (2, 4) and the MeOPh-substituted β,β-bichromophore 6 are characterized by predominant formation fluorescent aggregates. All bichromophores are characterized by the presence of residual amounts of non-aggregated forms in binary mixtures with maximum water content. The results are useful for controlling the aggregation behavior and spectral characteristics of CHR-bis(BODIPY) bichromophores in aqueous-organic media, which is important in the development of biomarkers and PDT agents.

Enhancing Hybrid Photovoltaic-Thermal System Efficiency with Boron Dipyrromethene Dyes

A library of boron dipyrromethene (BODIPY) compounds was studied to assess their efficacy as components of a working liquid in hybrid photovoltaic-thermal (PVT) systems. Two series of BODIPY dyes were investigated: series I included alkylBODIPYs with varying substitution patterns, while series II included 1,3,5,7-tetramethyl-substituted BODIPYs featuring electron-rich aromatic groups in the meso position, such as naphthalene, anthracene, and carbazole. Series II dyes were designed to exhibit luminescence downshifting due to enhanced UV absorption (300-400 nm) and excited-state energy transfer, leading to visible-region fluorescence under UV excitation. Samples of PVT liquids based on decalin and containing each individual BODIPY dye were tested on a standard a-Si solar cell to evaluate their impact on solar energy conversion efficiency. The thermal behavior of the working liquid and the cell during the illumination cycle was monitored, alongside the cell's electrical characteristics. Energy conversion pathways and the overall effects of the dyes on the system performance were scrutinized. Results indicated that all BODIPY dyes enhanced both the electrical conversion efficiency (up to 2.41% increase) and thermal energy generation (up to 6.87%) compared to the solvent alone. These findings highlight the potential of BODIPY dyes to significantly improve the performance of PVT systems.

Evidence for a transfer-to-trap mechanism of fluorophore concentration quenching in lipid bilayers

It is important to understand the behaviors of fluorescent molecules because, firstly, they are often utilized as probes in biophysical experiments and, secondly, they are crucial cofactors in biological processes such as photosynthesis. A phenomenon called "fluorescence quenching" occurs when fluorophores are present at high concentrations, but the mechanisms for quenching are debated. Here, we used a technique called "in-membrane electrophoresis" to generate concentration gradients of fluorophores within a supported lipid bilayer, across which quenching was expected to occur. Fluorescence lifetime imaging microscopy (FLIM) provides images where the fluorescence intensity in each pixel is correlated to fluorescence lifetime: the intensity provides information about the location and concentration of fluorophores and the lifetime reveals the occurrence of energy-dissipative processes. FLIM was used to compare the quenching behavior of three commonly used fluorophores: Texas Red (TR), nitrobenzoaxadiazole (NBD), and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY). FLIM images provided evidence of quenching in regions where the fluorophores accumulated, but the degree of quenching varied between the different fluorophores. The relationship between quenching and concentration was quantified and the "critical radius for trap formation," representing the relative quenching strength, was calculated as 2.70, 2.02, and 1.14 nm, for BODIPY, TR, and NBD, respectively. The experimental data support the theory that quenching takes place via a "transfer-to-trap" mechanism which proposes, firstly, that excitation energy is transferred between fluorophores and may reach a "trap site," resulting in immediate energy dissipation, and, secondly, that trap sites are formed in a concentration-dependent manner. Some previous work suggested that quenching occurs only when fluorophores aggregate, or form long-lived dimers, but our data and this theory argue that traps may be "statistical pairs" of fluorophores that exist only transiently. Our findings should inspire future work to assess whether these traps can be charge-transfer states, excited-state dimers, or something else.

J-Aggregate Promoting NIR-II Emission for Fluorescence/Photoacoustic Imaging-Guided Phototherapy

J-aggregate is a promising strategy to enhance second near-infrared window (NIR-II) emission, while the controlled synthesis of J-aggregated NIR-II dyes is a huge challenge because of the lack of molecular design principle. Herein, bulk spiro[fluorene-9,9'-xanthene] functionalized benzobisthiadiazole-based NIR-II dyes (named BSFX-BBT and OSFX-BBT) are synthesized with different alkyl chains. The weak repulsion interaction between the donor and acceptor units and the S…N secondary interactions make the dyes to adopt a co-planar molecular conformation and display a peak absorption >880 nm in solution. Importantly, BSFX-BBT can form a desiring J-aggregate in the condensed state, and femtosecond transient absorption spectra reveal that the excited states of J-aggregate are the radiative states, and J-aggregate can facilitate stimulated emission. Consequently, the J-aggregated nanoparticles (NPs) display a peak emission at 1124 nm with a high relative quantum yield of 0.81%. The efficient NIR-II emission, good photothermal effect, and biocompatibility make the J-aggregated NPs demonstrate efficient antitumor efficacy via fluorescence/photoacoustic imaging-guided phototherapy. The paradigm illustrates that tuning the aggregate states of NIR-II dye via spiro-functionalized strategy is an effective approach to enhance photo-theranostic performance.

Multiple-stimuli fluorescent responsive metallo-organic helicated cage arising from monomer and excimer emission

Effectively regulating monomer and excimer emission in a singular supramolecular luminous platform is challenging due to high difficulty of precise control over its aggregation and dispersion behavior when subjected to external stimuli. Here, we show a metallo-cage (MTH) featuring a triple helical motif that displays a unique dual emission. It arises from both intramolecular monomer and intermolecular excimer, respectively. The distorted molecular conformation and the staggered stacking mode of MTH excimer are verified through single crystal X-ray diffraction analysis. These structural features facilitate the switch between monomer and excimer emission, which are induced by changes in concentration and temperature. Significantly, adjusting the equilibrium between these two states in MTH enables the production of vibrant white light emission in both solution and solid state. Moreover, when combined with a PMMA (polymethyl methacrylate) substrate, the resulting thin films can serve as straightforward fluorescence thermometer and thermally activated information encryption materials.

In vivo fluorescence imaging of nanocarriers in near-infrared window II based on aggregation-caused quenching

Accurate fluorescence imaging of nanocarriers in vivo remains a challenge owing to interference derived mainly from biological tissues and free probes. To address both issues, the current study explored fluorophores in the near-infrared (NIR)-II window with aggregation-caused quenching (ACQ) properties to improve imaging accuracy. Candidate fluorophores with NIR-II emission, ACQ984 (λem = 984 nm) and IR-1060 (λem = 1060 nm), from the aza-BODIPY and cyanine families, respectively, were compared with the commercial fluorophore ICG with NIR-II tail emission and the NIR-I fluorophore P2 from the aza-BODIPY family. ACQ984 demonstrates high water sensitivity with complete fluorescence quenching at a water fraction greater than 50%. Physically embedding the fluorophores illuminates various nanocarriers, while free fluorophores cause negligible interference owing to the ACQ effect. Imaging based on ACQ984 revealed fine structures in the vascular system at high resolution. Moreover, good in vivo and ex vivo correlations in the monitoring of blood nanocarriers can be established, enabling real-time noninvasive in situ investigation of blood pharmacokinetics and dynamic distribution in various tissues. IR-1060 also has a good ACQ effect, but the lack of sufficient photostability and steady post-labeling fluorescence undermines its potential for nanocarrier bioimaging. P2 has an excellent ACQ effect, but its NIR-I emission only provides nondiscriminative ambiguous images. The failure of the non-ACQ probe ICG to display the biodistribution details serves as counterevidence for the improved imaging accuracy by NIR-II ACQ probes. Taken together, it is concluded that fluorescence imaging of nanocarriers based on NIR-II ACQ probes enables accurate in vivo bioimaging and real-time in situ pharmacokinetic analysis.

Protein aggregation monitoring in cells under oxidative stress: a novel fluorescent probe based on a 7-azaindole-BODIPY derivative

The development of new fluorescent probes as molecular sensors is a critical step for the understanding of molecular mechanisms. BODIPY-based probes offer versatility due to their high fluorescence quantum yields, photostability, and tunable absorption/emission wavelengths. Here, we report the synthesis and evaluation of a novel 7-azaindole-BODIPY derivative to probe hydrophobic proteins as well as protein misfolding and aggregation. In organic solvents, this compound shows two efficiently interconverting emissive excited states. In aqueous environments, it forms molecular aggregates with unique photophysical properties. The complex photophysics of the 7-azaindole-BODIPY derivative was explored for sensing applications. In the presence of albumin, the compound is stabilized in hydrophobic protein regions, significantly increasing its fluorescence emission intensity and lifetime. Similar effects occur in the presence of protein aggregates but not with other macromolecules like pepsin, DNA, Ficoll 40, and coconut oil. Fluorescence lifetime imaging microscopy (FLIM) and two-photon fluorescence microscopy on breast (MCF-7) and lung (A549) cancer cells incubated with this compound display longer fluorescence lifetimes and higher emission intensity under oxidative stress. Synchrotron FTIR micro spectroscopy confirmed that the photophysical changes observed were due to protein misfolding and aggregation caused by the oxidative stress. These findings demonstrate that this compound can serve as a fluorescent probe to monitor protein misfolding and aggregation triggered by oxidative stress.

FRET-Sensing of Multivalent Protein Binding at the Interface of Biomimetic Microparticles Functionalized with Fluorescent Glycolipids

Cell adhesion is a central process in cellular communication and regulation. Adhesion sites are triggered by specific ligand-receptor interactions inducing the clustering of both partners at the contact point. Investigating cell adhesion using microscopy techniques requires targeted fluorescent particles with a signal sensitive to the clustering of receptors and ligands at the interface. Herein, we report on simple cell or bacterial mimics, based on liquid microparticles made of lipiodol functionalized with custom-designed fluorescent lipids. These lipids are targeted toward lectins or biotin membrane receptors, and the resulting particles can be specifically identified and internalized by cells, as demonstrated by their phagocytosis in primary murine bone marrow-derived macrophages. We also evidence the possibility to sense the binding of a multivalent lectin, concanavalin A, in solution by monitoring the energy transfer between two matching fluorescent lipids on the surface of the particles. We anticipate that these liquid particle-based sensors, which are able to report via Förster resonance energy transfer (FRET) on the movement of ligands on their interface upon protein binding, will provide a useful tool to study receptor binding and cooperation during adhesion processes such as phagocytosis.

BODIPY-fused uracil: synthesis, photophysical properties, and applications

Fluorescent nucleobase and nucleic acid analogs are important tools in chemical and molecular biology as fluorescent labelling of nucleobases has applications in cellular imaging and anti-tumor activity. Boron-dipyrromethene (BODIPY) dyes exhibiting high brightness and good photostability are extensively used as fluorescent labelling agents and as type II photosensitizers for photodynamic therapy. Thus, the combination of nucleobases and BODIPY to obtain new compounds with both anti-tumor activity and fluorescent imaging functions is the focus of our research. We synthesized two new nucleobase analogs 1 and 2 by fusing the BODIPY core directly with uracil which resulted in favorable photophysical properties and high emission quantum efficiencies particularly in organic solvents. Further, we explored the newly synthesized derivatives, which possessed good singlet oxygen generation efficiencies and bio-compatibility, as potential PDT agents and our results show that they exhibit in vitro anti-tumor activities.

Host-Guest Photosensitizer of a Cationic BODIPY Derivative and Cucurbit[7]uril for High-Efficiency Visible Light-Induced Photooxidation Reactions

In recent years, there has been a notable surge of interest in the fields of organic and pharmaceutical research about photocatalysts (PCs) and photosensitizers (PSs). In this study, a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) molecule adorned with quaternary ammonium (TMB) functionality was meticulously designed and synthesized. This compound has remarkable characteristics such as exceptional water solubility, great optical qualities, and commendable photostability. It can form a 1:1 complex (TMB-CB[7]) with cucurbit[7]uril (CB[7]) through host-guest interactions in the aqueous solution and shows obvious fluorescence enhancement. The reactive oxygen species (ROS) including superoxide anion radical (O2·-) and singlet oxygen (1O2) generation ability of TMB-CB[7] were promoted compared with that of TMB in the aqueous solution. More interestingly, the ROS generated from TMB-CB[7] can be used as PCs for aerobic cross dehydrogenation coupling reactions and photooxidation reactions in water with high yields of 89 and 95%, respectively. Therefore, the utilization of a host-guest PS presents a novel and environmentally friendly approach for conducting photocatalyzed organic processes under ambient conditions using visible light.

In house synthesized novel distyryl-BODIPY dye and polymer assembly as deep-red emitting probe for protamine detection

In this contribution, we designed and synthesized a deep-red emitting distyryl-BODIPY dye (dye 3) which is non-fluorescent in aqueous solution due to the formation of non-emissive aggregates. However, in presence of an amphiphilic polymer (polystyrene sulfonate, PSS), the aggregated dye molecules de-aggregate and form dye 3-PSS complex, which significantly modulates the optical features of the bound dye. Interestingly, the dye 3-PSS complex shows turn-on fluorescence response in deep-red region in presence of protamine (Pr) due to the formation of dye 3-PSS-Pr ternary complex. Such enhancement follows a linear trend in the dynamic range of 0-8.75 μM of Pr which has been utilized to determine Pr with limit of detection (LOD) of 15.04(±0.5) nM in phosphate buffer. Furthermore, excellent selectivity of the dye 3-PSS system towards Pr allows us to determine Pr even in complex biological matrix like 1% human serum. Thus, dye 3-PSS system can be applied as a very effective tool for the detection and quantification of Pr in deep-red region, overcoming several limitations encountered with the probes in the shorter wavelength region. This is the first report on BODIPY dye based supramolecular assembly for sensing and quantification of protamine.

Diiodo-BODIPY Sensitizing of the [Mo3S13]2- Cluster for Noble-Metal-Free Visible-Light-Driven Hydrogen Evolution within a Polyampholytic Matrix

We report on a photocatalytic setup that utilizes the organic photosensitizer (PS) diiodo-BODIPY and the non-precious-metal-based hydrogen evolution reaction (HER) catalyst (NH₄)₂[Mo₃S₁₃] together with a polyampholytic unimolecular matrix poly(dehydroalanine)-graft-poly(ethylene glycol) (PDha-g-PEG) in aqueous media. The system shows exceptionally high performance with turnover numbers (TON > 7300) and turnover frequencies (TOF > 450 h^-1) that are typical for noble-metal-containing systems. Excited-state absorption spectra reveal the formation of a long-lived triplet state of the PS in both aqueous and organic media. The system is a blueprint for developing noble-metal-free HER in water. Component optimization, e.g., by modification of the meso substituent of the PS and the composition of the HER catalyst, is further possible.

Chitosan Composites Containing Boron-Dipyrromethene Derivatives for Biomedical Applications

The work is devoted to preparing and characterizing the properties of photosensitive composites, based on chitosan proposed for photodynamic therapy. Chitosan films with a 5% addition of two BODIPY dyes were prepared by solution casting. These dyes are dipyrromethene boron derivatives with N-alkyl phthalimide substituent, differing in the presence of iodine atoms in positions 2 and 6 of the BODIPY core. The spectral properties of the obtained materials have been studied by infrared and UV-vis absorption spectroscopy and fluorescence, both in solutions and in a solid state. Surface properties were investigated using the contact angle measurement. The morphology of the sample has been characterized by Scanning Electron and Atomic Force Microscopy. Particular attention was paid to studying the protein absorption and kinetics of the dye release from the chitosan. Adding BODIPY to the chitosan matrix leads to a slight increase in hydrophilicity, higher structure heterogeneity, and roughness, than pure chitosan. The presence of iodine atoms in the BODIPY structure caused the bathochromic effect, but the emission quantum yield decreased in the composites. It has been found that BODIPY-doped chitosan interacts better with human serum albumin and acidic α-glycoprotein than unmodified chitosan. The release rate of dyes from films immersed in methanol depends on the iodine present in the structure.

Unconventional OFF-ON Response of a Mono(calix[4]arene)-Substituted BODIPY Sensor for Hg2+ through Dimerization Reversion

A new selective fluorogenic chemosensor for Hg²⁺, which combines a calixarene derivative with a BODIPY core as a fluorescent reporter, is described. The remarkable change in its fluorogenic properties in DMSO and CHCl₃ has been analyzed. A study of its spectral properties on dilution, along with molecular modeling studies, allowed us to explain that this behavior involves the formation of a J-dimer, as well as how the sensing mechanism of Hg²⁺ proceeds.

Surfactant mediated suppression of aggregation and excited state ring puckering process in Pyrromethene 597-Application in water based dye laser

Water is being considered as an economical, safe and environmental friendly alternative solvent for dye lasers. However, the use of water in dye laser is restricted due to the formation of non-emissive aggregates of dye molecules. In the present study we have explored the possibility of the use of commercially available surfactant molecules for the water based laser of Pyrromethene 597 (PM597) dye, which has emerged as an alternative for more commonly used Rhodamine dyes in dye laser systems. Our studies show that in water, PM597 forms non-emissive aggregates which can be dissociated into monomeric dye molecules by adding common surfactants. Further, the high microviscosity in the micellar media retarded energy wasting ring puckering process in the excited state of the dye leading to the increase in its emission yield and excited state lifetime to a significant extent. It has been demonstrated that the emission yield and excited state lifetime in surfactant solution is relatively higher than in ethanol, the most commonly used organic solvent for dye lasers. Lasing action has been demonstrated in the aqueous solution of dye and lasing efficiency is found to be comparable to ethanol.

Semi-Empirical Calculation of Bodipy Aggregate Spectroscopic Properties through Direct Sampling of Configurational Ensembles

Efficient prediction of the aggregation-induced callback of organic chromophores for utilization in molecular sensorics is a desirable development goal in modern computational chemistry. Dye aggregates are complicated to study when utilizing conventional quantum chemistry approaches, since they are usually composed of too many atoms to be effectively analyzed, even with high-throughput parallel systems. Here, we present a successful attempt to develop a protocol to assess the spectroscopic changes happening in BODIPY dyes upon aggregation from the first principles utilizing extended tight-binding (XTB) and Zerner's intermediate neglect of differential overlap (ZINDO) Hamiltonians. The developed sampling technique for aggregate configurational space scanning was found to be sufficient to both reproduce peculiarities and justify experimental data on the spectroscopic behavior of chromophore aggregates. The sTDA, sTD-DFT (GFN2-XTB) and CIS (ZINDO) approaches were assessed, and then sources of errors and benefits were outlined. Importantly, our goal was to keep any of the mentioned calculations within a computational cost feasible for a single workstation, whereas scaling was possible at any point in time. Finally, several aggregate structures were investigated in the external field to try to achieve distributions similar to the ones observed in the electrostatic potential of the air-water interface to assess the borderlines of practical applicability of the suggested scheme.

Sensing lysozyme fibrils by salicylaldimine substituted BODIPY dyes - A correlation with molecular structure

Quick and efficient detection of protein fibrils has enormous impact on the diagnosis and treatment of amyloid related neurological diseases. Among several methods, fluorescence based techniques have garnered most importance in the detection of amyloid fibrils due to its high sensitivity and extreme simplicity. Among other classes of molecular probes, BODIPY derivatives have been employed extensively for the detection of amyloid fibrils. However, there are very few studies on the relationship between the molecular structure of BODIPY dyes and their amyloid sensing activity. Here in a BODIPY based salicylaldimine Schiff base and its corresponding boron complex have been evaluated for their ability to sense amyloid fibrils from hen-egg white lysozyme using steady state and time-resolved spectroscopic techniques. Both dyes show fluorescence enhancement as well as increase in their excited state lifetime upon their binding with lysozyme fibrils. However, the BODIPY derivative which shows more emission enhancement in fibrillar solution has much lower affinity towards amyloid fibrils as compared to other derivative. This contrasting behaviour in the emission enhancement and binding affinity has been explained on the basis of differences in their photophysical properties in water and amyloid fibril originating from the difference in their molecular structure. Such correlation between the amyloid sensitivity and the molecular structure of the probe can open up a new strategy for designing new efficient amyloid probes.

Application of meso-CF3-Fluorophore BODIPY with Phenyl and Pyrazolyl Substituents for Lifetime Visualization of Lysosomes

A bright far-red emitting unsymmetrical meso-CF₃-BODIPY fluorescent dye with phenyl and pyrazolyl substituents was synthesized by condensation of trifluoropyrrolylethanol with pyrazolyl-pyrrole, with subsequent oxidation and complexation of the formed dipyrromethane. This BODIPY dye exhibits optical absorption at λ_ab ≈ 610-620 nm and emission at λ_em ≈ 640-650 nm. The BODIPY was studied on Ehrlich carcinoma cells as a lysosome-specific fluorescent dye that allows intravital staining of cell structures with subsequent real-time monitoring of changes occurring in the cells. It was also shown that the rate of uptake by cells, the rate of intracellular transport into lysosomes, and the rate of saturation of cells with the dye depend on its concentration in the culture medium. A concentration of 5 μM was chosen as the most suitable BODIPY concentration for fluorescent staining of living cell lysosomes, while a concentration of 100 μM was found to be toxic to Ehrlich carcinoma cells.

Electronic transitions in noncovalent BODIPY dimers: TD-DFT study

Theoretical computations have been performed on the absorption spectra of (8-R-TMB)₂ dimers with varying character of substituents at the 8 position (meso) at monomers units (R = NH₂, OH, CH₃, H, COH, CF₃, CN). The obtained results (TD-CAM-B3LYP) show that the first four lower transitions of studied dimers (S₀ → S_i, i = 1-4) are intrinsically linked with delocalized HOMO and LUMO orbitals of the two monomers, which constitute a dimer. For all the dimers, S₀ → S₁ and S₀ → S₃ transitions are strongly forbidden, whereas S₀ → S₂ and S₀ → S₄ are allowed. There is a good agreement between the TD-CAM-B3LYP theory and the simple model of exciton coupling for two identical chromophores with the planes of two moieties, which are stacked upon each other. Intensities of the allowed transitions depend strongly on the nature of the substituent at the meso position. For the dimers with monomer units bearing electron-donor groups, S₀ → S₂ transitions are more intense compared with S₀ → S₄ ones. As the donor properties of the meso substituents diminish and electron acceptor properties enlarge, the intensity of these transitions becomes lower, whereas that of S₀ → S₄ transitions becomes higher. For the dimers with NH₂ and CN substituents, the almost inverse ratio of intensities of the transitions discussed is observed (for example, f = 0.80 and 0.06 (in the case of NH₂) and f = 0.09 and 0.72 (CN) for S₀ → S₂ and S₀ → S₄, respectively). Protonation of the tertiary amine function drastically 'switches off' its electron-donating properties. As a result, the red shift of the bands and redistribution of intensities of the allowed S₀ → S₂ and S₀ → S₄ transitions is predicted for protonated forms of the (8-NH₂-TMB)₂ dimer. This peculiarity can be of especial importance for the design of dimers with a sensor function.

Exploring BODIPY-Based Sensor for Imaging of Intracellular Microviscosity in Human Breast Cancer Cells

BODIPY-based molecular rotors are highly attractive imaging tools for imaging intracellular microviscosity in living cells. In our study, we investigated the ability to detect the microviscosity of biological objects by using BDP-NO₂ and BDP-H molecular rotors. We describe in detail the optical properties of BDP-NO₂ and BDP-H molecular rotors in aqueous media with and without proteins, together with their accumulation dynamics and localization in live and fixed human breast cancer cells. Furthermore, we investigate the applicability of these molecules to monitor microviscosity in the organelles of human breast cancer cells by fluorescence lifetime imaging microscopy (FLIM). We demonstrate that the BDP-NO₂ molecular rotor aggregates in aqueous media and is incompatible with live cell imaging. The opposite effect is observed with BDP-H which preserves its stability in aqueous media, diffuses through the plasma membrane and accumulates in lipid droplets (LDs) and the cytosol of both live and fixed MCF-7 and MDA-MB-231 cancer cells. Finally, by utilizing BDP-H we demonstrate that LD microviscosity is significantly elevated in more malignant MDA-MB-231 human breast cancer cells, as compared to MCF-7 breast cancer cells. Our findings demonstrate that BDP-H is a water-compatible probe that can be successfully applied to measure microviscosity in the LDs of living cells.

A BODIPY-Based Probe Enables Fluorogenicity via Thiol-Dependent Modulation of Fluorophore Aggregation

Given the popular usage of BODIPY fluorophores in biological research, their propensity to aggregate in aqueous solution and impact their spectroscopic properties arguably warrants more attention. The probe under study herein serves as a case in point. A para-maleimide-substituted meso-phenyl BODIPY (p-MB) had previously been characterized in organic media, where its inherently high fluorescence ruled out its fluorogenic potential. Here, we have found that in aqueous solution, p-MB behaves differently, exhibiting a much-reduced fluorescence as a result of aggregation-caused quenching (ACQ). Additionally, p-MB is capable of responding to complementarily reactive substrates, including thiols and TCEP, to generate a substantial turn-on signal. The fluorescence restoration is largest when it reacts with those containing adjacent ionizable groups. By being part of a polar conjugate, p-MB assumes a disaggregated form, circumventing ACQ and unleashing up to ~1000-fold fluorescence enhancement through apparent disaggregation-induced emission (DIE). While our results support DIE as the turn-on mechanism, we found that the reactivity of the probe is much lower when it is given time to form stable aggregates. Therefore, contrary to the conventional depiction that a DIE probe works by dispersing from preformed aggregates to react with the target, our results suggest that it functions via a target-mediated inhibition of probe aggregation. Altogether, our work highlights the aggregation issue often faced by BODIPY-based probes and demonstrates how that can be exploited for turn-on sensing application. Furthermore, it reconstructs a different pathway for the DIE mechanism.

BODIPY derivatives as fluorescent reporters of molecular activities in living cells

Fluorescent compounds have become indispensable tools for imaging molecular activities in the living cell. 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is currently one of the most popular fluorescent reporters due to its unique photophysical properties. This review provides a general survey and presents a summary of recent advances in the development of new BODIPY-based cellular biomarkers and biosensors. The review starts with the consideration of the properties of BODIPY derivatives required for their application as cellular reporters. Then review provides examples of the design of sensors for different biologically important molecules, ions, membrane potential, temperature and viscosity defining the live cell status. Special attention is payed to BODPY-based phototransformable reporters.

The bibliography includes 339 references.

8-[4-(2-Hydroxypropane-2-yl)phenyl]-1,3,4,4,5,7-hexamethyl-4-boron-3a,4a-diaza-S-indacene

During recent years, the BODIPY core became a popular scaffold for designing photoremovable protecting groups (PPG). In this paper, we report the synthesis of a new molecule—8-[4-(2-hydroxypropane-2-yl)phenyl]-1,3,4,4,5,7-hexamethyl-4-boron-3a,4a-diaza-S-indacene—by the treatment of meso-(4-CO2Me-phenyl)-BODIPY with excess of MeMgI. The product was characterized by 1H, 13C NMR and HRMS. The combination of BODIPY core with tertiary benzilyc alcohol might be promising for utilizing this molecule as visible light removable PPG.

Photoinduced and Classical Sol-Gel Synthesis: Spectral and Photophysical Behavior of Silica Matrix Doped by Novel Fluorescent Dye Based on Boron Difluoride Complex

The boron difluoride complex is known as an extraordinary class of fluorescent dyes, which has attracted research interest because of its excellent properties. This article reports the optical properties such as absorption, fluorescence, molar absorptivity, and photo-physical parameters like dipole moment, and oscillator strength of new fluorescent organic dye based on boron difluoride complex 2-(1-(difluoroboraneyl)-1,2-dihydroquinolin-2-yl)-2-(1-methylquinoxalin-2-ylidene) acetonitrile (DBDMA). The spectral characterization of the dye was measured in sol-gel glass, photosol-gel, and organic-inorganic matrices. The absorption and fluorescence properties of DBDMA in sol-gel glass matrices were compared with each other. Compared with the classical sol-gel, it was noticed that the photosol-gel matrix is the best one with immobilized DBDMA. In the latter, a large stokes shift was obtained (97 nm) and a high fluorescence quantum yield of 0.5. Special attention was paid to the addition of gold NPs into the hybrid material. The fluorescence emission intensity of the DBDMA with and without gold nanoparticles in different solid media is described, and that displayed organic-inorganic matrix behavior is the best host.

A Concise Route to Water-Soluble 2,6-Disubstituted BODIPY-Carbohydrate Fluorophores by Direct Ferrier-Type C-Glycosylation

Novel, linker-free, BODIPY-carbohydrate derivatives containing sugar residues at positions C2 and C6 are efficiently obtained by, hitherto unreported, Ferrier-type C-glycosylation of 8-aryl-1,3,5,7-tetramethyl BODIPYs with commercially available tri-O-acetyl-d-glucal followed by saponification. This transformation, which involves the electrophilic aromatic substitution (S_EAr) of the dipyrrin framework with an allylic oxocarbenium ion, provides easy access to BODIPY-carbohydrate hybrids with excellent photophysical properties and a weaker tendency to aggregate in concentrated water solutions.

GlycoBODIPYs: Sugars Serving as a Natural Stock for Water-soluble Fluorescent Probes of Complex Chiral Morphology

A range of unprocessed, reducing sugar substrates (mono-, di-, and trisaccharides) is shown to take part in a straightforward four-step synthetic route to water-soluble, uncharged BODIPY derivatives with unimpaired chiral integrity and high fluorescence efficiency. A wide compatibility with several postfunctionalizations is demonstrated, thus suggesting a universal utility of the multifunctional glycoconjugates, which we call GlycoBODIPYs. Knoevenagel condensations are able to promote a red-shift in the spectra, thereby furnishing strongly fluorescent red and far-red glycoconjugates of high hydrophilicity. The synthetic outcome was studied by X-ray crystallography and by comprehensive photophysical investigations in several solvent systems. Furthermore, cell experiments illustrate efficient cell uptake and demonstrate differential cell targeting as a function of the integrated chiral information.

BODIPY dimers: structure, interaction, and absorption spectrum

The object of the present study are BODIPY molecules obtained previously by Piskorz et al. (Dyes Pigm. 178:108322, 2020) for their antimicrobial activity. Structural analysis of the BODIPY dimers is presented in context of the aggregation influence on the photophysical properties. The thorough investigation of the nature of intermolecular interaction in the representative BODIPY dimers is provided together with the decomposition of the interaction energy into the components of well-defined origin according to SAPT procedure. For the model BODIPY systems the careful examination of the interaction nature for the dimer structure based on experimental crystal study as well as fully optimized is given. The tendencies observed in the model dimers are further on investigated for two pairs of BODIPY systems designed for biomedical application. The analyzed molecules are shown to maximize the mutual interaction by the optimization of the stacking dispersion contacts between the aromatic rings of the molecules, therefore producing stable dimers. The estimation of SAPT0 interaction energy components confirms the dominating dispersion character arising from mutual BODIPY core contacts. The influence of the dimerization process on the photophysical properties of the systems studied theoretically depends to the high extend on the dimerization mode and is significant for parallel and antiparallel dispersion-governed dimers.

A modular approach toward producing nanotherapeutics targeting the innate immune system

Immunotherapies controlling the adaptive immune system are firmly established, but regulating the innate immune system remains much less explored. The intrinsic interactions between nanoparticles and phagocytic myeloid cells make these materials especially suited for engaging the innate immune system. However, developing nanotherapeutics is an elaborate process. Here, we demonstrate a modular approach that facilitates efficiently incorporating a broad variety of drugs in a nanobiologic platform. Using a microfluidic formulation strategy, we produced apolipoprotein A1-based nanobiologics with favorable innate immune system-engaging properties as evaluated by in vivo screening. Subsequently, rapamycin and three small-molecule inhibitors were derivatized with lipophilic promoieties, ensuring their seamless incorporation and efficient retention in nanobiologics. A short regimen of intravenously administered rapamycin-loaded nanobiologics (mTORi-NBs) significantly prolonged allograft survival in a heart transplantation mouse model. Last, we studied mTORi-NB biodistribution in nonhuman primates by PET/MR imaging and evaluated its safety, paving the way for clinical translation.

Modulating the Optical Properties of BODIPY Dyes by Noncovalent Dimerization within a Flexible Coordination Cage

Aggregation of organic molecules can drastically affect their physicochemical properties. For instance, the optical properties of BODIPY dyes are inherently related to the degree of aggregation and the mutual orientation of BODIPY units within these aggregates. Whereas the noncovalent aggregation of various BODIPY dyes has been studied in diverse media, the ill-defined nature of these aggregates has made it difficult to elucidate the structure-property relationships. Here, we studied the encapsulation of three structurally simple BODIPY derivatives within the hydrophobic cavity of a water-soluble, flexible PdII6L4 coordination cage. The cavity size allowed for the selective encapsulation of two dye molecules, irrespective of the substitution pattern on the BODIPY core. Working with a model, a pentamethyl-substituted derivative, we found that the mutual orientation of two BODIPY units in the cage's cavity was remarkably similar to that in the crystalline state of the free dye, allowing us to isolate and characterize the smallest possible noncovalent H-type BODIPY aggregate, namely, an H-dimer. Interestingly, a CF3-substituted BODIPY, known for forming J-type aggregates, was also encapsulated as an H-dimer. Taking advantage of the dynamic nature of encapsulation, we developed a system in which reversible switching between H- and J-aggregates can be induced for multiple cycles simply by addition and subsequent destruction of the cage. We expect that the ability to rapidly and reversibly manipulate the optical properties of supramolecular inclusion complexes in aqueous media will open up avenues for developing detection systems that operate within biological environments.

Restricted suitability of BODIPY for caging in biological applications based on singlet oxygen generation

Recent studies report the boron-dipyrromethene (BODIPY) moiety to be interesting for caging applications in photopharmacology based on its response to irradiation with wavelengths in the biooptical window. Thus, in a model study, we investigated the meso-methyl-BODIPY caged CDK2 inhibitor AZD5438 and aimed to assess the usability of BODIPY as a photoremovable protecting group in photoresponsive kinase inhibitor applications. Photochemical analysis and biological characterisation in vitro revealed significant limitations of the BODIPY-caged inhibitor concept regarding solubility and uncaging in aqueous solution. Notably, we provide evidence for BODIPY-caged compounds generating singlet oxygen/radicals upon irradiation, followed by photodegradation of the caged compound system. Consequently, instead of caging, a non-specific induction of necrosis in cells suggests the potential usage of BODIPY derivatives for photodynamic approaches.