A theta-shaped amphiphilic cobaltabisdicarbollide anion: transition from monolayer vesicles to micelles

Enhanced conductivity of sodium versus lithium salts measured by impedance spectroscopy. Sodium cobaltacarboranes as electrolytes of choice

Scheme of the proposed mechanism to explain the mobility of the cations through the monomers COSANE and TPB. While in COSANE the mechanism is through jumps (hopping mechanism) in TPB the ionic transport is vehicular.

Metallacarboranes as tunable redox potential electrochemical indicators for screening of gene mutation

The substitution of hydrogen with chlorine in the metallacarborane [3,3-Fe(1,2-closo-C2B9H11)2]- cluster modulates the formal potential of the Fe3+/Fe2+ redox couple, shifting it to a more positive value. Hence, very similar redox probes with a wide range of formal potentials, ranging from negative to positive values, are available. Thus, we have achieved the synthesis and studied the electrochemical behaviour of the sodium salt of [3,3-Fe(8,9,12-Cl3-1,2-closo-C2B9H8)2]- in aqueous media. This strategy allows tuning of the redox potential of the [3,3-Fe(1,2-closo-C2B9H11)2]- framework with a minor change in its shape and dimensions. We also describe the interaction of the prepared [3,3-Fe(8,9,12-Cl3-1,2-closo-C2B9H8)2]- and the pristine [3,3-Fe(1,2-closo-C2B9H11)2]- with DNA. These studies have been carried out not only with DNA in solution but also with DNA immobilized on screen-printed gold electrodes. The results obtained point to a strong interaction between the metallacarboranes and DNA, to a different extent with single stranded DNA (ssDNA) compared to double stranded DNA (dsDNA). This property makes them selective and wide-ranging potential electrochemical indicators of hybridization. The suitability of these new redox indicators for selective DNA biosensor development has been probed by the direct detection of two different mutations associated with cystic fibrosis in PCR amplicons extracted from blood cells.

Stealth Amphiphiles: Self-Assembly of Polyhedral Boron Clusters

This is the first experimental evidence that both self-assembly and surface activity are common features of all water-soluble boron cluster compounds. The solution behavior of anionic polyhedral boranes (sodium decaborate, sodium dodecaborate, and sodium mercaptododecaborate), carboranes (potassium 1-carba-dodecaborate), and metallacarboranes {sodium [cobalt bis(1,2-dicarbollide)]} was extensively studied, and it is evident that all the anionic boron clusters form multimolecular aggregates in water. However, the mechanism of aggregation is dependent on size and polarity. The series of studied clusters spans from a small hydrophilic decaborate-resembling hydrotrope to a bulky hydrophobic cobalt bis(dicarbollide) behaving like a classical surfactant. Despite their pristine structure resembling Platonic solids, the nature of anionic boron cluster compounds is inherently amphiphilic-they are stealth amphiphiles.

Cation-sensitive compartmentalization in metallacarborane containing polymer nanoparticles

The inner structure of hybrid nanoparticles based on metallacarborane complexation with diblock copolymer PEO–POX is sensitive to alkaline cations.

Phosphine-catalyzed cage carbon functionalization of o-carborane: facile synthesis of alkenylcarboranes

Phosphines can efficiently catalyze alkenylation of o-carborane with electron-deficient alkynes, which represents the first example of organocatalysis in o-carborane functionalization.

Cationic Micelles Based on Polyhedral Oligomeric Silsesquioxanes for Enhanced Gene Transfection

The synthesis and gene transfection efficiency of a series of amphiphilic copolymers, poly(2-(dimethylamino)ethyl methacrylate)-poly (methacrylate isobutyl polyhedral oligomeric silsesquioxane) (PDMAEMA-POSS) copolymers are reported. The hydrophobic POSS interior allows a cell-sensitizing drug such as paclitaxel to be incorporated, whereas the cationic and hydrophilic PDMAEMA corona allows the complexation of anionic DNA to form a nano-sized polyplex. These drug-encapsulated copolymers display excellent gene transfection efficiency compared with polyethylenimine or PDMAEMA homopolymers.

Palladium-Catalyzed Regioselective Diarylation of o-Carboranes By Direct Cage B-H Activation

Palladium-catalyzed intermolecular coupling of o-carborane with aromatics by direct cage B-H bond activation has been achieved, leading to the synthesis of a series of cage B(4,5)-diarylated-o-carboranes in high yields with excellent regioselectivity. Traceless directing group -COOH plays a crucial role for site- and di-selectivity of such intermolecular coupling reaction. A Pd(II)-Pd(IV)-Pd(II) catalytic cycle is proposed to be responsible for the stepwise arylation.

COSAN as a molecular imaging platform: synthesis and "in vivo" imaging

A labelling method for the covalent attachment of radioiodine to the boron-rich 8-I-cobaltabisdicarbollide (I-COSAN) and a bi-functional (iodine and PEG) COSAN derivative, [3,3'-Co(8-I-1,2-C2B9H10)(8'-(OCH2CH2)2COOC6H5-1',2'-C2B9H10)], is reported. Biodistribution studies in rodents using dissection/gamma counting and in vivo nuclear imaging have been performed. The general strategy reported here can be applied in the future to COSAN derivatives bearing a wide range of functionalities.

Carboranes in the chemist's toolbox

Once seldom encountered outside of a few laboratories, carboranes are now everywhere, playing a role in the development of a broad range of technologies encompassing organic synthesis, radionuclide handling, drug design, heat-resistant polymers, cancer therapy, nanomaterials, catalysis, metal-organic frameworks, molecular machines, batteries, electronic devices, and more. This perspective highlights selected examples in which the special attributes of carboranes and metallacarboranes are being exploited for targeted purposes in the laboratory and in the wider world.

Palladium-catalyzed regioselective intramolecular coupling of o-carborane with aromatics via direct cage B-H activation

Palladium-catalyzed intramolecular coupling of o-carborane with aromatics via direct cage B-H bond activation has been achieved, leading to the synthesis of a series of o-carborane-functionalized aromatics in high yields with excellent regioselectivity. In addition, the site selectivity can also be tuned by the substituents on cage carbon atom.

Surface activity and molecular organization of metallacarboranes at the air-water interface revealed by nonlinear optics

Because of their amphiphilic structure, surfactants adsorb at the water-air interface with their hydrophobic tails pointing out of the water and their polar heads plunging into the liquid phase. Unlike classical surfactants, metallabisdicarbollides (MCs) do not have a well-defined amphiphilic structure. They are nanometer-sized inorganic anions with an ellipsoidal shape composed of two carborane semicages sandwiching a metal ion. However, MCs have been shown to share many properties with surfactants, such as self-assembly in water (formation of micelles and vesicles), formation of lamellar lyotropic phases, and surface activity. By combining second harmonic generation and surface tension measurement, we show here that cobaltabis(dicarbollide) anion {[(C2B9H11)2Co](-) also named [COSAN](-)} with H(+) as a counterion, the most representative metallacarborane, adsorbs vertically at the water surface with its long axis normal to the surface. This vertical molecular orientation facilitates the formation of intermolecular and nonconventional dihydrogen bonds such as the B-H(δ-)···(δ+)H-C bond that has recently been proven to be at the origin of the self-assembly of MCs in water. Therefore, it appears here that lateral dihydrogen bonds are also involved in the surface activity of MCs.

Biological interaction of living cells with COSAN-based synthetic vesicles

Cobaltabisdicarbollide (COSAN) [3,3'-Co(1,2-C2B9H11)2](-), is a complex boron-based anion that has the unusual property of self-assembly into membranes and vesicles. These membranes have similar dimensions to biological membranes found in cells, and previously COSAN has been shown to pass through synthetic lipid membranes and those of living cells without causing breakdown of membrane barrier properties. Here, we investigate the interaction of this inorganic membrane system with living cells. We show that COSAN has no immediate effect on cell viability, and cells fully recover when COSAN is removed following exposure for hours to days. COSAN elicits a range of cell biological effects, including altered cell morphology, inhibition of cell growth and, in some cases, apoptosis. These observations reveal a new biology at the interface between inorganic, synthetic COSAN membranes and naturally occurring biological membranes.

Synthesis and in vitro study of new highly boronated phthalocyanine

A new highly boronated Zn ( II )-phthalocyanine with eight cobalt bis(dicarbollide) units (144 boron atoms) was prepared and its intracellular accumulation and distribution in GL6 human glioblastoma cells were studied. It was found that the boronated phthalocyanine undergoes strong aggregation in intracellular environment.

Supramolecular colloidosomes based on tri(dodecyltrimethylammonium) phosphotungstate: a bottom-up approach

Hybrid tri(dodecyldimethylammonium) phosphotungstate ([C12]3[PW12O40]) amphiphilic nanoparticles self-assemble in situ at the water/toluene interface to form stable water-in-oil (W/O) Pickering emulsions (droplet size ≈ 20 μm). These emulsions are used as a template for the preparation of colloidosomes (ϕ ≈ 5 μm), which are produced solely through the self-assembly properties of the [C12]3[PW12O40] nanoparticles into a "fused" phase on the water-drop surface in contact with toluene. The structure of the emulsions has been determined using optical and cross-polarized light microscopy, while the colloidosomes have been characterized by scanning electron microscopy (SEM). The structure as well as the aggregation behavior of these nanoparticles has been investigated. Small- and wide-angle X-ray scattering (SWAXS) and transmission electron microscopy (TEM) experiments have revealed a lamellar organization of the inorganic polyoxometalate anions because of the van der Waals interactions between the alkyl chains of the organic cations. According to the solvent, the internal molecular arrangement inside the nanoparticles can be modified: in water, the nanoparticles tend to aggregate in a lamellar structure, whereas in toluene, the nanoparticles are "fused" or coagulated.

Imaging in living cells using νB–H Raman spectroscopy: monitoring COSAN uptake

The boron cluster containing molecules, COSAN and I2-COSAN, accumulate within living cells, and can be visualised by νB–H Raman microspectroscopy. This offers an unexplored means of cell labelling.

Uni-molecular hollow micelles from amphiphilic homopolymer poly(2-(4-vinylphenyl)pyridine)

Amphiphilic homopolymer poly(2-(4-vinylphenyl)pyridine) (PVPPy) forms hollow micelles with uni-molecular thickness in a tetrahydrofuran/water (95/5 v/v) azeotropic solvent. Depending on the pH of the media, the micelles may be transformed to vesicles.