Tuning the Cell Uptake and Subcellular Distribution in BODIPY–Carboranyl Dyads: An Experimental and Theoretical Study

Towards the Application of Purely Inorganic Icosahedral Boron Clusters in Emerging Nanomedicine

Traditionally, drugs were obtained by extraction from medicinal plants, but more recently also by organic synthesis. Today, medicinal chemistry continues to focus on organic compounds and the majority of commercially available drugs are organic molecules, which can incorporate nitrogen, oxygen, and halogens, as well as carbon and hydrogen. Aromatic organic compounds that play important roles in biochemistry find numerous applications ranging from drug delivery to nanotechnology or biomarkers. We achieved a major accomplishment by demonstrating experimentally/theoretically that boranes, carboranes, as well as metallabis(dicarbollides), exhibit global 3D aromaticity. Based on the stability-aromaticity relationship, as well as on the progress made in the synthesis of derivatized clusters, we have opened up new applications of boron icosahedral clusters as key components in the field of novel healthcare materials. In this brief review, we present the results obtained at the Laboratory of Inorganic Materials and Catalysis (LMI) of the Institut de Ciència de Materials de Barcelona (ICMAB-CSIC) with icosahedral boron clusters. These 3D geometric shape clusters, the semi-metallic nature of boron and the presence of exo-cluster hydrogen atoms that can interact with biomolecules through non-covalent hydrogen and dihydrogen bonds, play a key role in endowing these compounds with unique properties in largely unexplored (bio)materials.

BODIPY derivatives modified with carborane clusters: synthesis, characterization and DFT studies

An efficient approach for the preparation of 3,5-dicarborane-substituted BODIPY conjugates was developed via the functionalization of 3,5-dibromo-8-pentafluorophenyl-BODIPY with neutral and anionic carborane S-nucleophiles. It was found that 3,5-dicarborane-substituted BODIPYs could be easily modified with a third carborane cluster using S_NAr substitution reactions of the para-fluorine atom in the meso-pentafluorophenyl BODIPY substituent with the corresponding carborane S-nucleophile affording boron-enriched BODIPYs in good yields. The influence of bromine atom substitution with carborane moieties on the position of absorption and fluorescence bands and the fluorescence quantum yields of the prepared BODIPYs were analyzed. The crystal structures of BODIPYs 4 and 8 were investigated. Density functional theory methods (DFT wb97xd/6-31G* and wb97xd/lanl2dz) were performed to study the geometrical structures, electronic characteristics, the highest occupied and the lowest unoccupied molecular orbitals (HOMOs and LUMOs) and other chemical descriptors of the synthesized compounds.

BODIPY-Ethynylestradiol molecular rotors as fluorescent viscosity probes in endoplasmic reticulum

Due to their capability for sensing changes in viscosity, fluorescent molecular rotors (FMRs) have emerged as potential tools to develop several promising viscosity probes; most of them, however, localize non-selectively within cells, precluding changes in the viscosity of specific cellular microdomains to be studied by these means. Following previous reports on enhanced fluorophore uptake efficiency and selectivity by incorporation of biological submolecular fragments, here we report two potential BODIPY FMRs based on an ethynylestradiol spindle, a non-cytotoxic semisynthetic estrogen well recognized by human cells. A critical evaluation of the potential of these fluorophores for being employed as FMRs is presented, including the photophysical characterization of the probes, SXRD studies and TD-DFT computations, as well as confocal microscopy imaging in MCF-7 (breast cancer) cells.

Symmetry dual functional pyrimidine-BODIPY probes for imaging targeting and activity study

Nondestructive diagnosis of tumor has always been the goal of scientists. Fluorescent dyes have become the rising star in the field of cancer diagnosis because of their excellent characteristics. Therefore, in this work, fluorescence probes d-Y-B and dO-Y-B with anti-tumor activity were constructed by introducing pyrimidine groups with high anti-tumor activity using fluorescence dye BODIPY as parent nucleus. The modified BODIPY group in the structure had the advantage of fluorescent dye, ensuring the strong fluorescence and photosensitivity of the target compound. That ethylenediamine acts as a bridge with two -NH- groups to increase molecular hydrogen bonding, and can bind firmly to multiple proteins. Co-localization of the target compounds d-Y-B and dO-Y-B with the hoechst dye for labeling living cells showed that these compounds had high biocompatibility and photostability for localization to HeLa cells. In vivo imaging in mice can realize specific localization and real-time visualization of tumor cells. The results of cytotoxicity experiments in vitro and computer software simulating molecular docking confirmed the potential of the target compounds as an anticancer agents. The bifunctional probe realized visualization of cancer cells in mice, and can kill cancer cells by anti-proliferation, which may provide a direction for future anticancer drug development.

Multi-photon absorption organotin complex for bioimaging and promoting ROS generation

Compared to general fluorescent dyes, multi-photon fluorescent dyes exhibit deeper tissue penetration and lower auto-fluorescence in the bio-imaging field. Therefore, it is necessary to develop an efficient multiphoton imaging agent for deep tissue imaging. In this work, an organotin derivative (HSnBu₃) has been designed and synthesized, which shows multiphoton absorption activity. In constrast to the ignorable three-photon activity of the ligand, the complex (HSnBu₃) exhibits three-photon activity under NIR excitation (1500 nm). Results of chemical and biological tests confirmed that HSnBu₃ was more easily activated by oxygen resulting in a higher level of ¹O₂, which could induce a decrease in mitochondrial membrane potential in HepG2 cells. It suggests that HSnBu₃ has potential in photodynamic therapy.

Synthesis and Properties of BODIPY Appended Tetraphenylethylene Scaffolds as Photoactive Arrays

Tetraphenylethylene (TPE) and its derivatives exhibit excellent aggregation-induced emission (AIE) properties. The TPE unit is easily accessible, and many functional groups can be introduced in a facile manner to yield effective luminescent materials in both solution and the solid-state. It is because of this, several TPE-based compounds have been developed and applied in many areas, such as OLEDs and chemical sensors. Boron dipyrromethenes (BODIPYs) are a class of pyrrolic fluorophore of great interest with myriad application in both material science and biomedical applications. Through the combination of Pd-catalyzed cross-coupling reactions and traditional dipyrromethene chemistry, we present the syntheses of novel tetra-BODIPY-appended TPE derivatives with different distances between the TPE and BODIPY cores. The TPE-BODIPY arrays 6 and 9 show vastly differing AIE properties in THF/H2O systems, with 9 exhibiting dual-AIE, along with both conjugates being found to produce singlet oxygen (1O2). We presume the synthesized BODIPY-appended TPE scaffolds to be utilized for potential applications in the fields of light-emitting systems and theranostics.

New insights into quantifying the solvatochromism of BODIPY based fluorescent probes

A simple semiempiric phenomenological approach is developed for quantifying the solvent effect on the absorption and emission properties of BODIPYs. It is based on a new rule describing the linear relationship between the difference (Stokes shift) and the sum (double Gibbs free energy of electron transfer) for absorption and emission wavenumbers derived from a combination of solvent functions of Liptay theory. This rule is correspondent to changes of dipole moments in the ground and excited states. High reliability and advantages of the developed approach in comparison with traditional methods of the analysis of the solvatochromism based on Dimroth-Reichard and Lippert-Mataga solvent scales are illustrated for selected BODIPYs exhibiting positive, negative, and near-zero solvatochromism.

Antioxidant and antimicrobial material by grafting of L-arginine onto enzymatic poly(gallic acid)

Microwave-mediated grafting of L-Arg onto naturally derived and stable multiradical poly(gallic acid) (PGAL) in aqueous media has been successfully achieved. This polymeric material has no adverse effect in human cells as there is no hemolytic activity upon MTT and Neutral Red assays. The analytical and computational characterization studies carried out in this study describe a helical molecular structure with random incorporation of L-Arginine pendant groups from PGAL's backbone. The antioxidant properties of the precursor polymer are preserved as proved by the elimination of stable DPPH and hydroxyl radical scavenging, as well as the FRAP and ORAC assays. Regarding the latter, the oxygen radical inhibition is enhanced compared to PGAL, which is attributed to the guanidyl moieties. PGAL-g-L-Arg displays antimicrobial activity against Gram (+) Listeria monocytogenes and Staphylococcus aureus strains with a MIC of 0.8 g/L and a bacteriostatic effect against Gram (-) Escherichia coli. Additionally, scanning electron and confocal fluorescence microscopies as well as crystal violet colorimetric assay demonstrate that the mechanism involved in the bacterial inhibition is related to the formation of porous channels on the membrane, which is discussed according to the helical secondary structure of the polymer and the amino acid guanidyl moieties interacting to bacterial membranes.