The Role of Electron-Donating Subunits in Cross-Linked BODIPY Polymer Films.

A new method for synthesizing cross-linked 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) using a radical-based thiol-ene click reaction is developed. This method is simple, efficient, and cost-effective, and it produces polymers with unique optical, electrochemical, and surface morphology properties. Significant blue shifts in absorption and photoinduced electron transfer in emissions are observed in the cross-linked BODIPY thin films. Cross-linking also leads to the restriction of conjugation, which results in the breakage of the terminal vinyl group, an increase in the oxidation potential, and a slight upshift in the HOMO position. As a result, the electrochemical band gap is widened from 1.88 to 1.94 eV for polymer bearing N,N-dimethylamino-BODIPY and from 1.97 to 2.02 eV for polymer bearing N,N-diphenylamino-BODIPY moieties. Monomer thin films form planar surfaces due to crystallinity, while amorphous cross-linked BODIPY polymers form more rough surfaces. Additionally, photopatterning on the film surface is successfully performed using different patterned masks. This new method for synthesizing cross-linked BODIPYs has the potential to be used in a variety of applications, including organic electronics, bioimaging, and photocatalysis.

Comparison of Antiaromatic Properties in a Series of Structurally Isomeric Naphthothiophene-Fused s-Indacenes.

Fusion of aromatic subunits to stabilize an antiaromatic core allows the isolation and study of otherwise unstable paratropic systems. A complete study of a series of six naphthothiophene-fused s-indacene isomers is herein described. Additionally, the structural modifications resulted in increased π-π overlap in the solid state, which was further explored through changing the sterically blocking mesityl group to (triisopropylsilyl)ethynyl in three derivatives. The computed antiaromaticity of the six isomers is compared to the observed physical properties, such as NMR chemical shift, UV-vis, and CV data. We find that the calculations predict the most antiaromatic isomer and give a general estimation of the relative degree of paratropicity for the remaining isomers, when compared to the experimental results.

Fused Indacene Dimers.

Polycyclic hydrocarbons consisting of two or more directly fused antiaromatic subunits are rare due to their high reactivity. However, it is important to understand how the interactions between the antiaromatic subunits influence the electronic properties of the fused structure. Herein, we present the synthesis of two fused indacene dimer isomers: s-indaceno[2,1-a]-s-indacene (s-ID) and as-indaceno[3,2-b]-as-indacene (as-ID), containing two fused antiaromatic s-indacene or as-indacene units, respectively. Their structures were confirmed by X-ray crystallographic analysis. 1 H NMR/ESR measurements and DFT calculations revealed that both s-ID and as-ID have an open-shell singlet ground state. However, while localized antiaromaticity was observed in s-ID, as-ID showed weak global aromaticity. Moreover, as-ID exhibited a larger diradical character and a smaller singlet-triplet gap than s-ID. All the differences can be attributed to their distinct quinoidal substructures.

Tetra-tert-butyl-s-indacene is a Bond-Localized C2h Structure and a Challenge for Computational Chemistry.

Whether tetra-tert-butyl-s-indacene is a symmetric D2h structure or a bond-alternating C2h structure remains a standing puzzle. Close agreement between experimental and computed proton chemical shifts based on minima structures optimized at the M06-2X, ωB97X-D, and M11 levels confirm a bond-localized C2h symmetry, which is consistent with the expected strong antiaromaticity of TtB-s-indacene.

BODIPYs in PDT: A Journey through the Most Interesting Molecules Produced in the Last 10 Years.

Over the past 30 years, photodynamic therapy (PDT) has shown great development. In the clinical setting the few approved molecules belong almost exclusively to the porphyrin family; but in the scientific field, in recent years many researchers have been interested in other families of photosensitizers, among which BODIPY has shown particular interest. BODIPY is the acronym for 4,4-difluoro-4-bora-3a, 4a-diaza-s-indacene, and is a family of molecules well-known for their properties in the field of imaging. In order for these molecules to be used in PDT, a structural modification is necessary which involves the introduction of heavy atoms, such as bromine and iodine, in the beta positions of the pyrrole ring; this change favors the intersystem crossing, and increases the 1O2 yield. This mini review focused on a series of structural changes made to BODIPYs to further increase 1O2 production and bioavailability by improving cell targeting or photoactivity efficiency.

Antiaromatic 1,5-Diaza-s-indacenes.

s-Indacene is a classical non-alternant hydrocarbon that contains 12 π-electrons in a cyclic π-conjugation system. Herein, we report its nitrogen-doped analogue, 1,5-diaza-s-indacene. 1,5-Diaza-s-indacenes were readily prepared from commercially available 2,5-dichlorobenzene-1,4-diamine through a two-step transformation consisting of a palladium-catalyzed Larock cyclization with diaryl acetylenes followed by hydrogen abstraction. The thus obtained 1,5-diaza-s-indacenes exhibited distinct antiaromaticity, as manifested in clear bond-length alternation, a forbidden HOMO-LUMO transition, and a paratropic ring current. As compared to the parent s-indacene, the 1,5-diaza-s-indacenes showed higher electron-accepting ability owing to the presence of imine-type nitrogen atoms. The 1,5-diaza-s-indacene core is effectively conjugated with the peripheral aryl groups, which enables fine-tuning of the absorption spectra and redox properties. The two possible localized forms of 1,5-diaza-s-indacene were compared in terms of their energetic aspects.

A Tale of Two Isomers: Enhanced Antiaromaticity/Diradical Character versus Deleterious Ring-Opening of Benzofuran-fused s-Indacenes and Dicyclopenta[b,g]naphthalenes.

We examine the effects of fusing two benzofurans to s-indacene (indacenodibenzofurans, IDBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units. Synthesis via 3-functionalized benzofuran yields syn-IDBF and syn-IIDBF. syn-IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character for syn-IIDBF. In the case of the anti-isomers, synthesized via 2-substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring-opening reaction during the final dearomatization step. All the results are compared to the benzothiophene-fused analogues and show that the increased electronegativity of oxygen in the syn-fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity. For syn-IIDBF increased diradical character results from rearomati-zation of the core naphthalene unit in order to relieve this paratropicity.

NICS-XY-Scan Predictions of Local, Semi-Global, and Global Ring Currents in Annulated Pentalene and s-Indacene Cores Compared to First-Principles Current Density Maps.

The magnetic response of a set of 20 molecules, their dications and their dianions has been studied by the NICS-XY method, and the results have been compared with first principles current density maps. The molecules have been built from pentalene and s-indacene by single and double annulation of cyclobutadiene, benzene and benzocyclobutadiene in an alternate fashion on both sides of the molecules. The prediction of tropicities obtained by the NICS-XY method are overall consistent with the current density maps. A literal code, developed to give a compact description of the tropicities of currents flowing around rings and bonds cut by the scan trajectory shows that, in most cases, the NICS-XY method leads to an exact match with the current density analyses. Mismatches are generally due to small circulations out of the scan trajectory, and they do not correspond to misinterpretations of the overall tropicities. The dataset provides several cases where the prediction of the overall antiaromatic/aromatic response by the 4n/4n+2 count of π electrons fails.

Structure-Property Relationship Study of Donor and Acceptor 2,6-Disubstituted BODIPY Derivatives for High Performance Dye-Sensitized Solar Cells.

Seven donor and acceptor 2,6-disubstituted 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyes have been synthesized and characterized. Including MPBTCA, which is a known compound, the seven BODIPY dyes have been characterized by varied physical methods, such as UV/Visible absorption spectroscopy, low energy photo-electron spectroscopy (AC-2), and HOMO-LUMO DFT/TDDFT calculation. All seven BODIPY dyes have absorption λmax around 535-545 nm, which is significantly longer than 499 nm of 4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene (PM 546). Having structural variation on donor group, acceptor group, donor π-spacer, acceptor π-spacer, and the substituent on boron, some BODIPY dyes exhibit small extinction coefficients or spectral integrals in solution (MPCtBTCA, MPBT-pyO, MPBTT-pyO, MTBTCA), broadening absorption spectral profile (MTBTCA), weak intramolecular charge transfer characteristics (MPBT-pyO, MPBTT-pyO, MTBTCA), too low LUMO energy level (PPBTCA), or insufficient dye-uptake by TiO2 FTO (MPBT-pyO, MPBTT-pyO, MTBTCA). Two of the seven BODIPY dyes, MPBTCA and MPBTTCA, do not show the adverse properties like other BODIPY dyes. With our improved TiO2 FTO (fluorine doped tin oxide) dyeing method, namely a solution dropping method, high performance dye-sensitized solar cells (DSCs) have been realized by MPBTCA and MPBTTCA photosensitizers. Power conversion efficiencies of 6.3 and 6.4 % have been achieved by MPBTCA and MPBTTCA DSCs, respectively. To the best of our knowledge, MPBTCA and MPBTTCA are the most efficient dyes for the donor and acceptor 2,6-disubstituted BODIPY DSCs so far.

Simultaneous monitoring of intra- and extracellular nitric oxide in living cells by means of dual-color fluorescence imaging.

A dual-color fluorescence imaging method for simultaneous monitoring of intra- and extracellular nitric oxide (NO) was developed. Assisted by confocal laser scanning microscope, the intra- and extracellular NO can be successfully visualized by using two selected probes, 4,4-difluoro-8-(3,4-diaminophenyl)-3,5-bis(4-methoxyphenyl)-4-bora-3a,4a-diaza-s-indacene (p-MOPB) and disodium 2,6-disulfonate-1,3-dimethyl-5-hexadecyl-8-(3,4-diaminophenyl)-4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene (DSDMHDAB), which display distinct membrane permeability and show different colors of fluorescence after reaction with NO. Results indicated that intra- and extracellular NO could be fluorometrically detected without mutual interference. The applicability of the proposed method was validated by dual-color imaging of NO on both sides of the plasma membrane in RAW 264.7 murine macrophages and human vascular endothelial (ECV-304) cells. This multi-labeling approach using multi-laser excitation and multi-color fluorescence detection holds great promise for simultaneous analysis of NO as well as other gasotransmitters in living cells with subcellular resolution.

A CE-LIF method based on long wavelength fluorescence labeling for the analysis of thiols in human urine.

A rapid and robust CE method using a long wavelength fluorescent reagent 1,7-dimethyl-3,5-distyryl-8-phenyl-(2-maleimide)difluoroboradiaza-s-indacene as the labeling reagent has been developed for the simultaneous determination of thiols, including glutathione, cysteine, homocysteine, N-acetylcysteine, cysteinylglycine, and penicillamine. The derivatization reaction was carried out in 14 mmol/L pH 8.5 borate buffer at 30°C for 6 min and the labeled thiols derivatives were separated with the running buffer containing 30 mmol/L pH 7.4 phosphate, 30% v/v acetonitrile and 8 mmol/L SDS within 12 min. Detection limits ranged from 0.4 to 2.4 nmol/L. To demonstrate the capability of this method, it was applied to the analysis of thiols in human urine with recoveries of 92.4-105.6%. The derivatization reaction was much faster at milder conditions, and the analysis was rapider. Moreover, with excitation wavelength at long wavelength region, background interference from samples was reduced effectively. The present method seems to be a potential choice for quantifying thiols in human urine.

Maytansinoid-BODIPY Conjugates: Application to Microscale Determination of Drug Extinction Coefficients and for Quantification of Maytansinoid Analytes.

Determining drug to antibody ratios (DAR) for antibody-drug conjugates (ADCs) in early research and development can be hampered by difficulties in accurate weighing of the effector payload and subsequent determination of its extinction coefficient. Two maytansinoids, DM1 and DM4, potent antimitotic agents used in clinical ADCs, were derivatized with the compact fluorophore BODIPY FL using two different linker designs. We identified DM1-mal-BODIPY as a conjugate with little through-space interaction between the maytansinoid and BODIPY chromophores. The 1:1 stoichiometry between the maytansinoid and BODIPY makes the molar concentration of both components equal and the extinction coefficient of the maytansinoid in proportion with the known BODIPY chromophore according to Beer's Law. By only derivatizing 50 µg of unpurified DM1 and analyzing about 25 µg of DM1-mal-BODIPY by UV-vis, we determined εDM1 252 nm and εDM1 280 nm as 26 355 ± 360 and 5230 ± 160 cm(-1) M(-1), respectively. These values are nearly identical to those accepted for DM1 based on weighing >100 mg of pure sample. Surprisingly, some of the maytansinoid-BODIPY conjugates that were synthesized were partially or completely fluorescence-quenched. The green fluorescence of quenched DM4-acetamide-BODIPY could be fully restored in the presence of an antibody designed to tightly bind maytansine. We exploited this observation to develop a simple "mix and read" fluorogenic immunoassay for detection of nanogram quantities of maytansinoids.

Phase diagram of a 4-component lipid mixture: DSPC/DOPC/POPC/chol.

We report the first 4-component phase diagram for the lipid bilayer mixture, DSPC/DOPC/POPC/chol (distearoylphosphatidylcholine/dioleoylphosphatidylcholine/1-palmitoyl, 2-oleoylphosphatidylcholine/cholesterol). This phase diagram, which has macroscopic Ld+Lo phase domains, clearly shows that all phase boundaries determined for the 3-component mixture containing DOPC transition smoothly into the boundaries for the 3-component mixture containing POPC, which has nanoscopic phase domains of Ld+Lo. Our studies start from two published ternary phase diagrams, and show how these can be combined into a quaternary phase diagram by study of a few hundred samples of intermediate compositions.

Development of a potential method based on microchip electrophoresis with fluorescence detection for the sensitive determination of intracellular thiols in RAW264.7 cells.

This paper, for the first time, reported the development of a simple, rapid, and reliable method for the separation and sensitive determination of four thiol compounds including homocysteine, cysteine, glutathione, and N-acetylcysteine based on glass MCE with fluorescence detection using a highly reactive fluorogenic probe, 1,3,5,7-tetramethyl-8-phenyl-(2-maleimide)-difluoroboradiaza-s-indacene (TMPAB-o-M), as the labeling reagent. TMPAB-o-M reacted selectively with thiols to produce highly fluorescent derivatives and the highest derivatization efficiency was achieved within 6 min in physiological conditions. After the optimization of separation conditions, a baseline separation of the four thiol compounds was achieved with the detection limits ranging from 2 nM for glutathione to 4 nM for cysteine (S/N = 3) and RSDs (n = 5) in the range of 3.2-3.8%. The proposed method was significantly sensitive compared to those using electrochemical or even LIF detection in MCE-based setup reported previously, and applied to the determination of intracellular thiols in macrophage RAW264.7 cells.

Rapid and sensitive determination of free thiols by capillary zone electrophoresis with near-infrared laser-induced fluorescence detection using a new BODIPY-based probe as labeling reagent.

A CZE with near-infrared (NIR) LIF detection method has been developed for the analysis of six low molecular weight thiols including glutathione, homocysteine, cysteine, γ-glutamylcysteine, cysteinylglycine, and N-acetylcysteine. For this purpose, a new NIR fluorescent probe, 1,7-dimethyl-3,5-distyryl-8-phenyl-(4'-iodoacetamido)difluoroboradiaza-s-indacene was utilized as the labeling reagent, whose excitation wavelength matches the commercially available NIR laser line of 635 nm. The optimum procedure included a derivatization step of the free thiols at 45°C for 25 min and CZE analysis conducted within 14 min in the running buffer containing 16 mmol/L pH 7.0 sodium citrate and 60% v/v ACN. The LODs (S/N = 3) ranged from 0.11 nmol/L for N-acetylcysteine to 0.31 nmol/L for γ-glutamylcysteine, which are better than or comparable to those reported with other derivatization-based CE-LIF methods. As the first trial of NIR CE-LIF method for thiol determination, the practical application of the proposed method has been validated by detecting thiols in cucumber and tomato samples with recoveries of 96.5-104.3%.

Involvement of apoptosis and autophagy in the death of RPMI 8226 multiple myeloma cells by two enantiomeric sigma receptor ligands.

Over-expression of σ receptors by many tumor cell lines makes ligands for these receptors attractive as potential chemotherapeutic drugs. Enantiomeric piperazines (S)-4 and (R)-4 were prepared as potential σ-receptor ligands in a chiral pool synthesis starting from (S)- and (R)-aspartate. Both compounds showed high affinities for the σ1 and σ2 receptors. In the human multiple myeloma cell line RPMI 8226, a line expressing high levels of σ receptors, both compounds inhibited cell proliferation with IC50 values in the low µM range. No chiral differentiation between either the σ receptor binding affinity or the cytotoxicity of the two enantiomers was observed. Both compounds induced apoptosis, which was evidenced by nuclear condensation, binding of annexin-V to phosphatidylserine in the outer leaf of the cell membrane, cleavage products of poly(ADP-ribose) polymerase-1 (PARP-1) and caspase-8 as well as the expression of bcl2 family members bax, bad and bid. However, apoptosis appeared to be caspase independent. Increased levels of the phosphorylated form of the microtubule associated protein light chain 3-II (LC3-II), an autophagosome marker, gave evidence that both compounds induced autophagy. However, further data (e.g., treatment with wortmannin) indicate that autophagy is incomplete and not cytoprotective. Lipid peroxidation (LPO) was observed in RPMI 8226 cells treated with the two compounds, and the lipid antioxidant α-tocopherol attenuated LPO. Interestingly, α-tocopherol reduced significantly both apoptosis and autophagy induced by the compounds. These results provide evidence that, by initiating LPO and changes in mitochondrial membrane potential, both compounds induce apoptosis and autophagy in RPMI 8226 cells.

Galactose conjugated boron dipyrromethene and hydrogen bonding promoted J-aggregates for efficiently targeted NIR-II fluorescence assistant photothermal therapy.

It is essential to develop novel multifunctional and easily synthesized stable NIR-II fluorescent probes to guide photothermal therapy for tumors. Here, we propose a new strategy to construct boron dipyrromethene (BODIPY) J-aggregates by intermolecular hydrogen bonding (H-bond) and π-π stacking interactions to achieve fluorescence emission in the second near-infrared window (NIR-II, 1000-1700 nm). A novel meso-benzamide galactose hexanoate-BODIPY (Gal-OH-BDP) amphiphilic small molecular dye was synthesized and it formed nanoparticles spontaneously in aqueous solution with a maximum emission wavelength near 1060 nm, which works as a smart nanomedicine for targeting NIR-II imaging-guided photothermal therapy (PTT) of hepatocellular carcinoma. Galactose not only provided hydrogen bonds to regulate the aggregation pattern of the molecules but also effectively targeted hepatocellular carcinoma cells and promoted the formation of well-dispersed nanoparticles of dye molecules due to their hydrophilicity. Moreover, due to high photothermal conversion efficiency (PCE = 55%), Gal-OH-BDP NPs achieve galactose-targeted NIR-II imaging and PTT, which is important for the precise diagnosis and treatment of tumors (Scheme 1). In the present research work, H-bond was introduced for the first time into BODIPY for building J-aggregates to achieve the NIR-II fluorescence.

Binding mode analysis of ABCA7 for the prediction of novel Alzheimer's disease therapeutics.

The adenosine-triphosphate-(ATP)-binding cassette (ABC) transporter ABCA7 is a genetic risk factor for Alzheimer's disease (AD). Defective ABCA7 promotes AD development and/or progression. Unfortunately, ABCA7 belongs to the group of 'under-studied' ABC transporters that cannot be addressed by small-molecules. However, such small-molecules would allow for the exploration of ABCA7 as pharmacological target for the development of new AD diagnostics and therapeutics. Pan-ABC transporter modulators inherit the potential to explore under-studied ABC transporters as novel pharmacological targets by potentially binding to the proposed 'multitarget binding site'. Using the recently reported cryogenic-electron microscopy (cryo-EM) structures of ABCA1 and ABCA4, a homology model of ABCA7 has been generated. A set of novel, diverse, and potent pan-ABC transporter inhibitors has been docked to this ABCA7 homology model for the discovery of the multitarget binding site. Subsequently, application of pharmacophore modelling identified the essential pharmacophore features of these compounds that may support the rational drug design of innovative diagnostics and therapeutics against AD.

The impact of tunnel mutations on enzymatic catalysis depends on the tunnel-substrate complementarity and the rate-limiting step.

Transport of ligands between bulk solvent and the buried active sites is a critical event in the catalytic cycle of many enzymes. The rational design of transport pathways is far from trivial due to the lack of knowledge about the effect of mutations on ligand transport. The main and an auxiliary tunnel of haloalkane dehalogenase LinB have been previously engineered for improved dehalogenation of 1,2-dibromoethane (DBE). The first chemical step of DBE conversion was enhanced by L177W mutation in the main tunnel, but the rate-limiting product release was slowed down because the mutation blocked the main access tunnel and hindered protein dynamics. Three additional mutations W140A + F143L + I211L opened-up the auxiliary tunnel and enhanced the product release, making this four-point variant the most efficient catalyst with DBE. Here we study the impact of these mutations on the catalysis of bulky aromatic substrates, 4-(bromomethyl)-6,7-dimethoxycoumarin (COU) and 8-chloromethyl-4,4'-difluoro-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (BDP). The rate-limiting step of DBE conversion is the product release, whereas the catalysis of COU and BDP is limited by the chemical step. The catalysis of COU is mainly impaired by the mutation L177W, whereas the conversion of BDP is affected primarily by the mutations W140A + F143L + I211L. The combined computational and kinetic analyses explain the differences in activities between the enzyme-substrate pairs. The effect of tunnel mutations on catalysis depends on the rate-limiting step, the complementarity of the tunnels with the substrates and is clearly specific for each enzyme-substrate pair.

BODIPY-based Carbonaceous Materials for High Performance Electrical Capacitive Energy Storage.

Incorporation of heteroatoms into carbon materials is crucial to tailor carbon materials' donor-acceptor properties and consequently tune their chemical and electrical performance. However, doping carbon materials with multi-heteroatoms (three or more, especially the light elements) has been rarely payed attention until now. In this work, we develop a porous organic polymer containing boron, nitrogen, fluorine elements and realize its corresponding carbonaceous materials by subsequent carbonation or KOH activation process. Electrochemical measurements results reveal that KOH activation sample (BPOP-700A) is endowed with excellent specific capacitance of 408 F g-1 in three-electrode system and an energy density over 19.2 Wh kg-1 in two-electrode system at aqueous electrolyte, which can be attributed to multi light elements (boron, nitrogen and trace fluorine) doping, favorable morphology and rational pore size distribution architecture. In addition, BPOP-700A displays well rate ability and outstanding cycle performance (10 A g-1 , 10 000 cycles, 95 % retention). Our work might give some hints in designing multi light element doping carbon materials in supercapacitor applications.