Boron Cluster Anions Research Articles

Enhancing Membrane Permeability of Fluorescein-Type Chromophore Through Covalent Attachment of Chlorinated Dodecaborate.

Anionic boron clusters, such as [B12X12]2- (X = Cl, Br, I), have attracted attention in pharmaceuticals due to their unique superchaotropic properties. In particular, [B12Br12]2- (1) has demonstrated strong interactions with biomolecules, facilitating cargo translocation across plasma membranes. In this study, we investigated the effect of covalently attaching chlorinated dodecaborate moiety [B12Cl11O-]2- to 6-carboxyfluorescein (6-FAM) (3) via a PEG3 linker to form conjugate (4). We compared the membrane permeability of this covalent conjugate with that of non-covalent interactions between 6-FAM (3) and [B12Cl12]2- (2). Live-cell fluorescence imaging revealed that the covalent conjugate exhibited enhanced membrane permeability and water solubility while maintaining low cytotoxicity. These results highlight the potential of covalent conjugation with boron clusters for improving the cellular uptake of hydrophilic cargos.

Electrochemically Gated Frustrated Lewis Pair Chemistry in Electric Double Layer.

The recent discovery of frustrated Lewis pairs (FLPs) during the activation of small molecules has inspired extensive research across the full span of chemical science. Owing to the nature of weak interactions, it is experimentally challenging to directly observe and modulate FLP at the molecular scale. Here we design a boron cluster anion building block (B10H82-) and organic amine cations ([NR4]+, R= -CH3, -C2H5) as the FLP to prove the feasibility of controlling their interaction in the electric double layer (EDL) via an electrochemical strategy. In situ single-molecule electrical measurements and Raman monitoring of B10H82--[NR4]+ FLP formed at the positively charged Au(111) electrode surface, in contrast to the free-standing B10H82- near or below the potential of zero charge (PZC). Furthermore, this FLP chemistry leads to a shift in the local density of states of boron clusters towards the EF for enhancing electron transport, providing a new prototype of a reversible single-cluster switch that digitally switches upon controlling FLP chemistry in the electric double layer.

Electrochemically Gated Frustrated Lewis Pair Chemistry in Electric Double Layer

AbstractThe recent discovery of frustrated Lewis pairs (FLPs) during the activation of small molecules has inspired extensive research across the full span of chemical science. Owing to the nature of weak interactions, it is experimentally challenging to directly observe and modulate FLP at the molecular scale. Here we design a boron cluster anion building block (B10H82−) and organic amine cations ([NR4]+, R=−CH3, −C2H5) as the FLP to prove the feasibility of controlling their interaction in the electric double layer (EDL) via an electrochemical strategy. In situ single‐molecule electrical measurements and Raman monitoring of B10H82−−[NR4]+ FLP formed at the positively charged Au(111) electrode surface, in contrast to the free‐standing B10H82− near or below the potential of zero charge (PZC). Furthermore, this FLP chemistry leads to a shift in the local density of states of boron clusters towards the EF for enhancing electron transport, providing a new prototype of a reversible single‐cluster switch that digitally switches upon controlling FLP chemistry in the electric double layer.

Boron Cluster Anions Dissolve En Masse in Lipids Causing Membrane Expansion and Thinning

AbstractBoron clusters are applied in medicinal chemistry because of their high stability in biological environments and intrinsic ability to capture neutrons. However, their intermolecular interactions with lipid membranes, which are critical for their cellular delivery and biocompatibility, have not been comprehensively investigated. In this study, we combine different experimental methods – Langmuir monolayer isotherms at the air–water interface, calorimetry (DSC, ITC), and scattering techniques (DLS, SAXS) – with MD simulations to evaluate the impact of closo‐dodecaborate clusters on model membranes of different lipid composition. The cluster anions interact strongly with zwitterionic membranes (POPC and DPPC) via the chaotropic effect and cause pronounced expansions of lipid monolayers. The resulting lipid membranes contain up to 33 mol % and up to 52 weight % of boron cluster anions even at low aqueous cluster concentrations (1 mM). They show high (μM) affinity to the hydrophilic‐hydrophobic interface, affecting the structuring of the lipid chains, and therefore triggering a sequence of characteristic effects: (i) an expansion of the surface area per lipid, (ii) an increase in membrane fluidity, and (iii) a reduction of bilayer thickness. These results aid the design of boron cluster derivatives as auxiliaries in drug design as well as transmembrane carriers and help rationalize potential toxicity effects.

Boron Cluster Anions Dissolve En Masse in Lipids Causing Membrane Expansion and Thinning.

Boron clusters are applied in medicinal chemistry because of their high stability in biological environments and intrinsic ability to capture neutrons. However, their intermolecular interactions with lipid membranes, which are critical for their cellular delivery and biocompatibility, have not been comprehensively investigated. In this study, we combine different experimental methods - Langmuir monolayer isotherms at the air-water interface, calorimetry (DSC, ITC), and scattering techniques (DLS, SAXS) - with MD simulations to evaluate the impact of closo-dodecaborate clusters on model membranes of different lipid composition. The cluster anions interact strongly with zwitterionic membranes (POPC and DPPC) via the chaotropic effect and cause pronounced expansions of lipid monolayers. The resulting lipid membranes contain up to 33 mol % and up to 52 weight % of boron cluster anions even at low aqueous cluster concentrations (1 mM). They show high (μM) affinity to the hydrophilic-hydrophobic interface, affecting the structuring of the lipid chains, and therefore triggering a sequence of characteristic effects: (i) an expansion of the surface area per lipid, (ii) an increase in membrane fluidity, and (iii) a reduction of bilayer thickness. These results aid the design of boron cluster derivatives as auxiliaries in drug design as well as transmembrane carriers and help rationalize potential toxicity effects.

A small-molecule carrier for the intracellular delivery of a membrane-impermeable protein with retained bioactivity.

Intracellular protein delivery has the potential to revolutionize cell-biological research and medicinal therapy, with broad applications in bioimaging, disease treatment, and genome editing. Herein, we demonstrate successful delivery of a functional protein, cytochrome c (CYC), by using a boron cluster anion as molecular carrier of the superchaotropic anion type (B12Br11OPr2-). CYC was delivered into lipid bilayer vesicles as well as living cells, with a cellular uptake ratio approaching 90%. Mechanistic studies showed that CYC was internalized into cells through a permeation pathway directly into the cytoplasm, bypassing endosomal entrapment. Upon carrier-assisted internalization, CYC retained its bioactivity, as reflected by an induced cell apoptosis rate of 25% at low dose (1 µM). This study furbishes a direct protein delivery method by a molecular carrier with high efficiency, confirming the potential of inorganic cluster ions as protein transport vehicles with an extensive range of future cell-biological or biomedical applications.

Silver(I) complexation with N-donor heterocyclic ligands in the presence of boron cluster anions: Synthesis and coordination features

Silver(I) complexation with boron cluster anions [BnHn]2− (n = 10, 12) and chelating 1-substituted-2-aldiminebenzimidazoles 1-(1-methylbenzimidazol-2-yl)-N-phenylmetanimine (L1) and 1-(1-benzylbenzimidazol-2-yl)-N-cyclohexylmethanimine (L2) in systems AgNO3/[BnHn]2−/L and {Ag2[BnHn]}m/L, as well as with azaheterocyclic ligands 2,2ʹ-bipyridine (bipy) or 1,10-phenanthroline (phen) in the system AgNO3/[BnHn]2−/L has been first studied. The effect of the organic ligand on the composition and structures of the resulting compounds has been shown. As a result, binuclear complexes [Ag2L2[μ–BnHn]] with bridging boron cluster anions with various combinations of coordination modes (edge-edge and edge-face for the [B10H10]2− anion, edge–atom and nontrivial asymmetric for the [B12H12]2− anion) have been synthesized and structurally characterized for benzimidazole derivatives L1 and L2. When using bipy or phen as ligands, polymeric complexes {Ag2L[B10H10]}m or {Ag2L2[μ-B12H12]}m have been obtained.

Controlling Protein Assembly with Superchaotropic Nano-Ions.

In living systems, protein assemblies have essential functions, serving as structural supports, transport highways for molecular cargo, and containers of genetic material. The construction of protein assemblies, which involves control over space and time, remains a significant challenge in biotechnology. Here, we show that anionic boron clusters, 3,3'-commo-bis[closo-1,2-dicarba-3-cobaltadodecaborane] (COSAN-), and halogenated closo-dodecarboranes (B12X12 2-, X=H, Cl, or I), described as super-chaotropic nano-ions, induce the formation of 2D assemblies of model proteins, myoglobin, carbonic anhydrase, and trypsin inhibitor. We found that the nano-ion concentration reversibly controls the size of the protein assemblies. Furthermore, the secondary structures of the proteins are only slightly affected by assembly formation. For myoglobin, the formation of these assemblies even prevents temperature denaturation, highlighting a preservation effect of nano-ions. Our study reveals that inorganic boron-based nano-ions act as a reversible molecular glue for proteins, providing a potential starting point for the further development of controlled protein assemblies.

Controlling Protein Assembly with Superchaotropic Nano‐Ions.

In living systems, protein assemblies have essential functions, serving as structural supports, transport highways for molecular cargo, and containers of genetic material. The construction of protein assemblies, which involves control over space and time, remains a significant challenge in biotechnology. Here, we show that anionic boron clusters, 3,3’‐commo‐bis[closo‐1,2‐dicarba‐3‐cobaltadodecaborane] (COSAN‐), and halogenated closo‐dodecarboranes (B12X122‐, X = Η, Cl or I), described as super‐chaotropic nano‐ions, induce the formation of 2D assemblies of model proteins, myoglobin, carbonic anhydrase, and trypsin inhibitor. We found that the nano‐ion concentration reversibly controls the size of the protein assemblies. Furthermore, the secondary structures of the proteins are only slightly affected by assembly formation. For myoglobin, the formation of these assemblies even prevents temperature denaturation, highlighting a preservation effect of nano‐ions. Our study reveals that inorganic boron‐based nano‐ions act as a reversible molecular glue for proteins, providing a potential starting point for the further development of controlled protein assemblies.

Probing the Structural and Electronic Properties of the Anionic and Neutral Tellurium-Doped Boron Clusters TeBnq (n = 3-16, q = 0, -1).

In this study, we employ density functional theory along with the artificial bee colony algorithm for cluster global optimization to explore the low-lying structures of TeBnq (n = 3-16, q = 0, -1). The primary focus is on reporting the structural properties of these clusters. The results reveal a consistent doping pattern of the tellurium atom onto the in-plane edges of planar or quasi-planar boron clusters in the most energetically stable isomers. Additionally, we simulate the photoelectron spectra of the cluster anions. Through relative stability analysis, we identify three clusters with magic numbers -TeB7-, TeB10, and TeB12. The aromaticity of these clusters is elucidated using adaptive natural density partitioning (AdNDP) and magnetic properties analysis. Notably, TeB7- exhibits a perfect σ-π doubly aromatic structure, while TeB12 demonstrates strong island aromaticity. These findings significantly contribute to our understanding of the structural and electronic properties of these clusters.

A novel hydrophobic carborane-hybrid microporous material for reversed C2H6 adsorption and efficient C2H4/C2H6 separation under humid conditions.

Since ethylene (C2H4) is important feedstock in the chemical industry, developing economical and energy-efficient adsorption separation techniques based on ethane (C2H6)-selective adsorbents to replace the energy-intensive cryogenic distillation is highly demanded, which however remains a daunting challenge. While previous anionic boron cluster hybrid microporous materials display C2H4-selective features, we herein reported that the incorporation of a neutral para-carborane backbone and aliphatic 1,4-diazabicyclo[2.2.2]octane (DABCO) enables the reversed adsorption of C2H6 over C2H4. The generated carborane-hybrid microporous material ZNU-10 (ZNU = Zhejiang Normal University) is highly stable in humid air and maintains good C2H6/C2H4 separation performance under high humidity. Gas loaded single crystal structure and density-functional theory (DFT) calculations revealed that the weakly polarized carborane and DABCO within ZNU-10 induce more specific C-Hδ+⋯Hδ--B dihydrogen bonds and other van der Waals interactions with C2H6, while the suitable pore space allows the high C2H6 uptake. Approximately 14.5 L kg-1 of polymer grade C2H4 can be produced from simulated C2H6/C2H4 (v/v 10/90) mixtures under ambient conditions in a single step, comparable to those of many popular materials.

Synthesis of New Iminium Derivatives of Sulphonio-сloso-Decaborate Anion (Bu4N)[2-B10H9SC(NH2)R] (R = –CH3, –CH2CH3, –CH(CH3)2, –Ph, –PhCH3)

New iminium derivatives of the sulfonio-closo-decaborate anion have been obtained in the form of tetrabutylammonium salts (Bu4N)[2-B10H9SC(NH2)R] (R = –CH3, –CH2CH3, –CH(CH3)2, –Ph, –PhCH3), in which the iminium group acts as a protective group and allows further modification of the boron cluster anion without acting the sulfonium group. The compounds have been studied by elemental analysis, IR and 11B, 1H, 13C NMR spectroscopies. The structure of compounds (Bu4N)[2-B10H9SC(NH2)CH3] and (Bu4N)[2-B10H9SC(NH2)Ph] has been confirmed by X-ray diffraction analysis. The yield of final compounds is 80%.

Boron cluster anions [BnHn]2– (n = 10, 12) in design of polynuclear silver(I) and copper(II) complexes

The role of boron cluster anions [BnHn]2– (n = 10, 12) in the stabilization of polynuclear compounds was shown. Tetranuclear silver(I) complex [Ag4(bipy)4[B12H12]2] (1) (bipy is 2,2ʹ-bipiridyl) and hexanuclear copper(II) complex [[CuII2(bipy)4(μ–CO3)]2[(CuII2(bipy)2(μ–OH)2]][Ag[B10H10]2]2∙5DMF (2∙5DMF) stabilized by first complex trianion [Ag[B10H10]2]3– were isolated and their structures were determined by single crystal X-ray diffraction. Based on the data of physicochemical methods of analysis (IR, Raman spectroscopy, as well as X-ray diffraction data for the polymer complex {[Ag(CH3CN)3][Ag[B10H10]]}n (3) possible mechanisms for the formation of polynuclear complexes were proposed.

Features of Cadmium(II) Complexation with N-Donor Heterocyclic Ligands in the Presence of the Octadecahydroeicosaborate Anion

The process of cadmium(II) complexation with 1-ethyl-2-(4-methoxyphenyl)azobenzimidazole (L1), 2,2′-bipyridyl (L2), and 1,10-phenanthroline (L3) in the presence of the [trans-B20H18]2– anion has been studied. It has been found that the nature of the organic ligand affects the composition and structures of the resulting compounds. Complexation with ligand L1, a benzimidazole derivative, has yielded binuclear complex [CdL12NO3(μ-NO3)CdL1(NO3)2] (1), which contains no boron cluster anion. In the case of azaheterocyclic ligands L2 and L3, depending on the Cd : L ratio, heteroleptic complexes [CdL2NO3]2[trans-B20H18] (L = L2 (2); L3 (3)) with coordinated nitrate ions (Cd : L = 1 : 2) or tris-chelate complexes [CdL3][trans-B20H18] (L = L2 (4); L3 (5)) with the boron cluster anion as a counterion (Cd : L = 1 : 3) have been isolated. The structures of complexes [CdL12NO3(μ-NO3)CdL1(NO3)2] (1) and [Cd(L2)2NO3]2[trans-B20H18] (2) have been determined by X-ray diffraction.

Geometric and electronic structures of medium-sized boron clusters doped with plutonium

Doping metal heteroatoms is an effective strategy to regulate the geometric and electronic structure of boron based nanoclusters. However, the exploration of the ground state structures of metal-boron-based nanoclusters is still a challenge duo to the complexity of the bonding interactions between heterogeneous atoms and boron cluster and the number of isomers on the potential energy surface increases exponentially with cluster size. Here, we use the CALYPSO cluster structural search method in combination with density functional theory calculations to study the geometries and electronic properties of anionic boron clusters doped with plutonium (PuB, n = 10–20). Our results show that the medium-sized PuB cluster exhibits excellent stability with highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap of 2.30 eV. The remarkable stability of the anionic PuB cluster is due to the robust interactions between the Pu metal and the B14 skeleton, along with the strong covalent interactions between the B atoms. These findings enrich the geometric structure database of metal doped clusters and provide valuable insights for the future synthesis of boron based nanomaterials.

Composites and Materials Prepared from Boron Cluster Anions and Carboranes.

Here, we present composites and materials that can be prepared starting with boron hydride cluster compounds (decaborane, decahydro-closo-decaborate and dodecahydro-closo-dodecaborate anions and carboranes). Recent examples of their utilization as boron protective coatings including using them to synthesize boron carbide, boron nitride, metal borides, metal-containing composites, and neutron shielding materials are discussed. The data are generalized demonstrate the versatile application of materials based on boron cluster anions and carboranes in various fields.

Closo-[B12H12]2- derivatives with polar groups as promising building blocks in MOFs for gas separation.

Engineering design of metal organic frameworks (MOFs) for gas separation applications is nowadays a thriving field of investigation. Based on the recent experimental studies of dodecaborate-hybrid MOFs as potential materials to separate industry-relevant gas mixtures, we herein present a systematic theoretical study on the derivatives of the closo-dodecaborate anion [B12H12]2-, which can serve as the building blocks for MOFs. We discover that amino functionalization can impart a greater ability to selectively capture carbon dioxide from its mixtures with other gases such as nitrogen, ethylene and acetylene. The main origin lies in the polarization effect induced by amino group, which favors the localization of the negative charges on the boron-cluster anion and offers a nucleophilic anchoring site to accommodate the carbon atom in carbon dioxide. This work suggests an appealing strategy of polar functionalization to optimize the molecule discrimination ability via preferential adsorption.

Hydroxy-substituted closo-dodecaborate anion [B12H11OH]2– in silver(I) and lead(II) complexation in the presence of azaheterocyclic ligands L

A systematic study of the reactivity of the hydroxy-substituted derivative of the closo-dodecaborate anion [B12H11OH]2– has been carried out in silver(I) and lead(II) complexation, including the presence of organic ligands 2,2ʹ-bipyridyl (bipy), 1,10-phenanthroline (phen) and 2,2′-bipyridylamine (bpa). A number of salts and silver(I) and lead(II) complexes of various composition and structures have been synthesized and characterized. The structures of polymeric {Ag2(bipy)2[B12H11OH]}n and binuclear [Ag2(bpa)2[μ-B12H11OH]] silver(I) complexes, dimeric binuclear lead(II) complex [Pb(bipy)2[μ-B12H11OH]]2, as well as salts CsNO3∙Cs2[B12H11OH] and (Hbpa)2[B12H11OH] have been determined by X-ray diffraction. It has been found that in the complexes obtained, the coordination of the boron cluster anion by metal atoms is realized both due to the formation of three-center two-electron MHB bonds with the BH groups of the polyhedron and with the participation of the oxygen atom of the substituent in metal coordination; cocrystallization of several bond and positional isomers is observed in the structures of silver(I) complexes.

Features of Copper(I) Complexation with Benzimidazole Derivatives in the Presence of the closo-Dodecaborate Anion

The process of copper(I) complexation with organic ligands as luminophores 1-(1-methylbenzimidazol-2-yl)-N-phenylmethanimine (L1), 1-ethyl-2-(4-methoxyphenyl)azobenzimidazole (L2), and 1-(1-benzylbenzimidazol-2-yl)-N-cyclohexylmethanimine (L3) in the presence of the closo-dodecaborate anion [B12H12]2– has been studied. It has been shown that in acetonitrile, a redox reaction proceeds to form copper(II) tris-chelate complexes [CuIIL3][B12H12]. Using diiodomethane as a solvent, we have succeeded in stabilizing copper in the +1 oxidation state; as a result, mixed-ligand binuclear complexes [CuI2L2(μ-I)2] containing no boron cluster anion have been isolated. The structures of complexes [CuII(L1)3][B12H12] and [CuI2(L3)2(μ‑I)2] have been determined by X-ray diffraction.

Spin Crossover in Iron(II) Complexes with Polynitrogen Heterocyclic Ligands and Outer-Sphere Boron Cluster Anions (Review)

Spin Crossover in Iron(II) Complexes with Polynitrogen Heterocyclic Ligands and Outer-Sphere Boron Cluster Anions (Review)