Search Results (31)

Low-dimensional (0D/1D/2D) nanomaterials exhibit unique physical and chemical properties different from general bulk materials due to enhanced surface and interface contributions and quantum confinement effects, which strongly modulate electronic structures. Boron, with atomic number 5, can form multicenter bonds and enables the construction of structurally diverse nanomaterials across different dimensionalities. In this review, boron-based low-dimensional materials are systematically organized from 0D clusters to 1D nanostructures and 2D sheets, and their optical and electrical properties are discussed in relation to structural factors such as dimensionality. This review provides an integrated perspective on how dimensional expansion and structural design govern the optical and electrical properties of boron-based nanomaterials. Full article

In the oral environment, silicone (polysiloxane) supports healing by creating low-permeability interfaces that limit microleakage, whereas silicon/silica systems support healing via hydroxyapatite nucleation. We synthesized human evidence on intraoral healing associated with silicone and silicon/silica-based materials and assessed translational differences between preclinical models and clinical settings. A systematic review (1990-September 2025) identified 14 clinical studies of bioactive glass (BAG) that met the inclusion criteria. Periodontal outcomes included probing depth (PD), clinical attachment level (CAL), and radiographic fill; endodontic outcomes included the periapical index (PAI). Human BAG studies showed periodontal benefits versus controls in intrabony defects, with reduced PD, improved CAL, and greater radiographic fill. For endodontic healing, a multicenter randomized clinical trial reported improved PAI at 12 months in both the zinc-oxide-eugenol and silicone-sealer groups without a significant between-group difference. The literature supports a functional split: silicone primarily provides sealing and permissive healing, whereas silicon/silica-based materials support signaling, interfacial bonding, and regenerative healing. Clinically, BAG appears most relevant for contained periodontal intrabony defects, whereas silicone sealers should be viewed primarily as stable sealing adjuncts to well-executed root canal therapy. Full article

Phenothiazine is a heteroaromatic molecule capable of various noncovalent interactions, including halogen bonding and π-stacked association. Despite its broad use in functional materials and pharmaceutical ingredients, a systematic comparison of these interaction modes has been lacking. Here, we report a combined experimental and computational study of intermolecular interactions of phenothiazine with a prototypical halogen-bond (HaB) donor (tetrabromomethane), planar π-electron acceptors (tetracyanopyrazine and tetrafluoro-p-benzoquinone), and multifunctional species capable of both interaction types (iodo- and bromo-3,5-dinitrobenzenes). X-ray structural analysis revealed that CBr₄ forms exclusively C–Br···π halogen bonds with the aromatic rings of phenothiazine, whereas all π-acceptors yield alternating donor–acceptor stacks characterized by multiple short contacts indicative of multicenter interactions. Notably, co-crystals of iodo- and bromodinitrobenzenes with phenothiazine display only π-stacked architectures. Density-functional calculations showed that isolated HaB complexes involving N, S, or π sites of phenothiazine possess comparable binding energies (≈−3 kcal mol⁻¹), whereas π-stacked complexes are substantially stronger (≈−9–12 kcal mol⁻¹). QTAIM, NCI, NBO, and energy-decomposition analyses indicated that while amounts of charge transfer in halogen-bonded and π-stacked complexes are comparable, the enhanced stability of the latter originates primarily from a large dispersion contribution. These results rationalize the solid-state preference for π-stacking over halogen bonding in systems where both motifs are accessible and clarify the hierarchy and physical origin of noncovalent interactions involving phenothiazine, providing guidance for the design of supramolecular assemblies and functional materials based on this versatile electron donor. Full article

Boron is a trace element with multifaceted chemical and biological properties that underpin its emerging relevance in human health and medicinal chemistry. Although present in organisms at very low concentrations, boron participates in key physiological processes, including mineral metabolism, bone homeostasis, hormonal regulation, immune modulation, and redox balance. Its unique electronic structure—characterized by electron deficiency and the ability to form multi-center bonds—gives rise to diverse allotropic, cluster, and coordination chemistries, enabling the formation of biologically active complexes and therapeutic agents. Dietary boron, derived mainly from plant-based foods, is efficiently absorbed and predominantly excreted by the kidneys, showing a strong correlation between intake and urinary levels. Current evidence suggests beneficial effects of boron on bone mineral density, cognitive function, inflammation, antioxidant defenses, and metabolic regulation, although the precise molecular mechanisms remain partially understood. In medicinal chemistry, a broad spectrum of boron-containing compounds—including borates, boronic acids, boronated amino acids, carboranes, and metallacarboranes—has gained clinical and preclinical importance. These compounds serve as enzyme inhibitors, antimicrobial and anti-inflammatory agents, metabolic modulators, and critical boron carriers in boron neutron capture therapy (BNCT), which leverages the neutron-capture properties of ¹⁰B for targeted cancer treatment. Advances in synthesis, functionalization, and nanocarrier design have expanded the therapeutic potential of boron-based molecules. Ongoing research aims to optimize their selectivity, biodistribution, safety, and diagnostic integration. Overall, boron represents a versatile and rapidly developing component of modern biomedical science, with promising implications for oncology, infectious diseases, metabolic disorders, and precision medicine. Full article

Classical chemical bonding is typically categorized into primary, strong interactions, such as covalent, ionic, and metallic bonds, and secondary, weak interactions, such as van der Waals forces, the hydrogen bond, and their likes (halogen bond, chalcogen bond, etc.). However, other not-so-known bonding mechanisms also play a crucial role in chemical systems. Particularly important are the charge-shift bond (CSB) and the multicenter bonds, i.e., the electron-rich multicenter bond (ERMB), also known as hypervalent or three-center-four-electron (3c-4e) bond, and the electron-deficient multicenter bond (EDMB), also known as the three-center-two-electron (3c-2e) bond in molecules and, more recently, as the two-center-one-electron (2c-1e) bond in extended solids. We consider that these latter interactions have not yet received the proper attention of the scientific community, even though multicenter interactions were proposed in the early days of Quantum Mechanics. In this work, we aim at providing: (i) a concise historical overview of the two types of multicenter bonds; (ii) a short introduction to the recently proposed unified theory of multicenter bonding (UTMB), which elucidates the origin and mechanisms of formation of both ERMBs and EDMBs; and (iii) an extension of the UTMB to include CSBs, due to the strong relationship between ERMBs and CSBs. We hope that the integrated perspective of chemical bonding, the heartland of chemistry, offered by the UTMB (beyond traditional and historical assumptions) will help researchers to understand materials properties and will provide a framework allowing the development of advanced materials for enhanced technological applications. Full article

Background/Objectives: An elevated level of lipoprotein(a) [Lp(a)] is a genetically determined risk factor for cardiovascular disease. The atherogenic properties of Lp(a) include attribution to its role as a carrier of oxidized phospholipids (OxPL). Despite genetic control, Lp(a) levels increase with dietary saturated fat (SFA) reduction. However, little is known about the impact of dietary factors on Lp(a) risk properties. Methods: We assessed total Lp(a)-OxPL concentration, Lp(a)-OxPL subspecies abundance, and Lp(a) lipidomics in response to SFA reduction in two multicenter, randomized, controlled, crossover feeding trials, DELTA (Dietary Effects on Lipoproteins and Thrombogenic Activity) 1 (96 healthy individuals) and 2 (79 metabolically challenged individuals). In both trials, significant increases in Lp(a) levels were reported previously. Results: While no between-diet differences in the concentrations of total Lp(a)-OxPL and four major OxPL subspecies (ALDOPC, POVPC, PAzPC, and PGPC) were observed in DELTA 1, ALDOPC decreased significantly in DELTA 2 when SFA was replaced with carbohydrates (p = 0.014). Of 440 individual lipid species annotated in an untargeted analysis of the Lp(a) lipidome, 87 lipids differed significantly (p < 0.05 adjusted for multiplicity) between diets, with triacylglycerol species showing the most pronounced changes in both trials. For all intervention diets, triacylglycerol species with a higher average number of carbon atoms and double bonds increased the most in abundance with SFA reduction. Conclusions: In parallel with an increase in plasma Lp(a) levels, significant changes in Lp(a) lipid composition occurred. The findings demonstrate the dynamic nature of intraindividual Lp(a) lipid composition in response to diet interventions. Full article

The aromaticity of small boron clusters remains under scrutiny due to persistent inconsistencies between magnetic and electronic descriptors. Here, we reexamine B₃⁻, B₃⁺, B₄, B₄²⁺, and B₄²⁻ using a multidimensional approach that integrates Adaptive Natural Density Partitioning, Electron Density of Delocalized Bonds, magnetically induced current density, and the z-component of the induced magnetic field. We introduce a model in which σ-aromaticity arises from two distinct delocalization topologies: a radial 2e⁻ σ-pathway and a tangential multicenter circuit formed by alternating filled and vacant sp² orbitals. This framework accounts for the evolution of aromaticity upon oxidation or reduction, preserving coherence between electronic structure and magnetic response. B₃⁻ features cooperative radial and tangential σ-delocalization, together with a delocalized 2e⁻ π-bond, yielding robust double aromaticity. B₃⁺ retains σ- and π-aromaticity, but only via a tangential 6e⁻ σ-framework, leading to a more compact delocalization and slightly attenuated ring currents. In B₄, the presence of a radial 2e⁻ σ-bond and a 4c–2e π-bond confers partial aromatic character, while the tangential 8e⁻ σ-framework satisfies the 4n rule and induces a paratropic current. In contrast, B₄²⁺ lacks the radial σ-component but retains a tangential 8e⁻ σ-circuit and a 2e⁻ 4c–2e π-bond, leading to a σ-antiaromatic and π-aromatic configuration. Finally, B₄²⁻, exhibits delocalized π- and σ-circuits, yielding consistent diatropic ring currents, which confirms its fully doubly aromatic nature. Altogether, this analysis underscores the importance of resolving σ-framework topology and demonstrates that, when radial and tangential contributions are correctly distinguished, Hückel’s rule remains a powerful tool for interpreting aromaticity in small boron rings. Full article

Experimentally accessible stable polyhedral clusters of gallium differ from clusters of its lighter homologue boron by having sterically demanding external groups such as tBu₃Si, (Me₃Si)₃Si, (Me₃Si)₃C, (Me₃Si)₂N, and fluorenyl. This restricts closo deltahedral [Ga_nR_n]^z gallane chemistry to octahedral derivatives such as Ga₆R₆²⁻ (R = SiBuPh₂, SiBu^t₃) and Ga₆R₆ (R = SiMe(SiMe₃)₂) in which the bulky external silyl groups are spread out because of the relatively high local curvature of the degree 4 vertices of the central Ga₆ octahedron. The structures of larger gallium clusters are based on alternatives to closo deltahedra having exclusively high local curvature degree 4 vertices such as the 8-vertex square antiprismatic Ga₈R₈ (R = fluorenyl) or, more commonly, larger polyhedra or fused polyhedra with some bare gallium vertices. Some of the larger gallium clusters can be considered to be spherically aromatic systems with closed shells according to the jellium model. Examples include [Ga₁₃(SitBu₃)₆]⁻ with 8 cluster electrons corresponding to a filled 1S²1P⁶ shell as well as [Ga@Ga₁₈{C(SiMe₃)₃}₆]⁻ with 52 cluster electrons, Ga₂₂{E(SiMe₃)₃]₈, (E = C, Si) and Ga@Ga₁₁{GaN(SiMe₃)₂}₁₁ with 58 skeletal electrons, and [Ga₂₆{Si(SiMe₃)₃}₈]²⁻ with 72 cluster electrons. The 10-vertex species Ga₁₀{Si(SiMe₃)₃}₆, [Ga₁₀(SitBu₃)₆]⁻, and Ga₁₀(SitBu₃)₆ have structures consisting of a fusion of two polyhedra sharing bare gallium vertices with skeletal electron counts, suggesting a multicenter core bond in each of the two polyhedral cavities. Full article

The concept of superhalogen was proposed for more than 40 years, and it has never been associated with planar tetracoordinate fluorine (ptF) species. In this work, using Li as the ligands and Cl, Br, I as the auxiliary atoms, we have designed the star-like D_4h FLi₄X₄⁻ (X = Cl, Br, I) clusters, which contain the ptF at the centers. They are all global minima (GMs) based on unbiased searches on the potential energy surfaces. Born–Oppenheimer molecular dynamics (BOMD) simulations suggest that these ptF structures are robust against dissociation at room temperature. Chemical bonding analyses indicate that there are four lone pairs (LPs) for ptF, three LPs for each X atom, and four 3c-2e Li–X–Li σ bonds. The stabilities of these ptF clusters are dominated by multicenter ionic bonding, rather than the σ aromaticity. Interestingly, these ptF species have large first vertical detachment energies (7.37, 6.94, and 6.30 eV). According to the definition of superhalogen, they can be viewed as superhalogen anions. The current work builds an important link between superhalogen and ptF chemistry. Full article

Among the known planar pentacoordinate atoms, chlorine is missing due to its large radius and high electronegativity. Herein, we report the first star-like superhalogen anion D_5h Cl©Li₅Cl₅⁻ (1), which contains a planar pentacoordinate chlorine (ppCl) at the center. Computer structural searches and high-level calculations reveal that 1 is a true global minimum (GM) on the potential energy surfaces. Molecular dynamics simulations indicate it is kinetically stable against isomerization or decomposition. Although detailed chemical bonding analyses reveal one delocalized 6c-2e σ bond over the Cl©Li₅ central unit and five delocalized 3c-2e σ bonds along the periphery, while aromaticity has very little beneficial effect on stability, instead, ionic interaction dominates the stability of the system. More encouragingly, with the large HOMO–LUMO energy gap of 7.66 eV and vertical detachment energy of 7.87 eV, the highly chemically inert 1 can be viewed as a typical superhalogen anion and is possible to be synthesized and characterized in future experiments. Full article

Boron, the neighbor element to carbon in the periodic table, is characterized by unique electron deficiency that fosters multicenter delocalized bonding, contributing to its diverse chemistry. Unlike carbon cages (fullerenes), which preserve their structural integrity under endohedral or exohedral doping, larger boron cages (borospherenes) exhibit diverse structural configurations. These configurations can differ from those of pure boron cages and are stabilized by various metals through unique metal–boron bonding, resulting in a variety of metalloborospherenes. Due to boron’s electron deficiency, metalloborospherenes exhibit fascinating chemical bonding patterns that vary with cluster size and the type of metal dopants. This review paper highlights recent advancements in metalloborospherene research, drawing comparisons with metallofullerenes, and focuses on the use of transition metals, lanthanides, and actinides as dopants across various cage dimensions. Full article

4-Nitroquinoline-N-oxide (NQO) and 4-nitropyridine-N-oxide (NPO) are important precursors for the synthesis of substituted heterocycles while NQO is a popular model mutagen and carcinogen broadly used in cancer research; intermolecular interactions are critical for their reactions or functioning in vivo. Herein, the effects of the coordination of N-oxide’s oxygen atom to Lewis acids on multicenter donor–acceptor bonding were explored via a combination of experimental and computational studies of the complexes of NQO and NPO with a typical π-electron donor, pyrene. Coordination with ZnCl₂ increased the positive electrostatic potentials on the surfaces of these π-acceptors and lowered the energy of their LUMO. Analogous effects were observed upon the protonation of the N-oxides’ oxygen or bonding with boron trifluoride. The interaction of ZnCl₂, NPO, or NQO and pyrene resulted in the formation of dark co-crystals comprising π-stacked Zn-coordinated N-oxides and pyrene similar to that found with protonated or (reported earlier) BF₃-bonded N-oxides. Computational studies indicated that the coordination of N-oxides to zinc(II), BF₃, or protonation led to the strengthening of the multicenter bonding of the nitro-heterocycle with pyrene, and this effect was related both to the increased electrostatic attraction and molecular–orbital interactions in their complexes. Full article

In the last few years, a controversy has been raised regarding the nature of the chemical bonding present in phase change materials (PCMs), many of which are minerals such as galena (PbS), clausthalite (PbSe), and altaite (PbTe). Two opposite bonding models have claimed to be able to explain the extraordinary properties of PCMs in the last decade: the hypervalent (electron-rich multicenter) bonding model and the metavalent (electron-deficient) bonding model. In this context, a third bonding model, the electron-deficient multicenter bonding model, has been recently added. In this work, we comment on the pros and cons of the hypervalent and metavalent bonding models and briefly review the three approaches. We suggest that both hypervalent and metavalent bonding models can be reconciled with the third way, which considers that PCMs are governed by electron-deficient multicenter bonds. To help supporters of the metavalent and hypervalent bonding model to change their minds, we have commented on the chemical bonding in GeSe and SnSe under pressure and in several polyiodides with different sizes and geometries. Full article

Tri-metallofullerenes, specifically ${\mathrm{M}}_3@{\mathrm{C}}_{80}$ where M denotes rare-earth metal elements, are molecules that possess intriguing magnetic properties. Typically, only one metal element is involved in a given tri-metallofullerene molecule. However, mixed tri-metallofullerenes, denoted as M1_xM2_3-x@C₈₀ (x = 1 or 2, M1 and M2 denote different metal elements), have not been previously discovered. The investigation of such mixed tri-metallofullerenes is of interest due to the potential introduction of distinct properties resulting from the interaction between different metal atoms. This paper presents the preparation and theoretical analysis of mixed rare-earth tri-metallofullerenes, specifically Y_xDy_3−x@C₈₀ (x = 1 or 2). Through chemical oxidation of the arc-discharge produced soot, the formation of tri-metallofullerene cations, namely ${\mathrm{Y}}_2\mathrm{D}\mathrm{y}@{\mathrm{C}}_{80}^{+}$ and ${\mathrm{Y}\mathrm{D}\mathrm{y}}_2@{\mathrm{C}}_{80}^{+}$, has been observed. Density functional theory (DFT) calculations have revealed that the tri-metallofullerenes Y_xDy_3−x@C₈₀ (x = 1 or 2) exhibit a low oxidation potential, significantly lower than other fullerenes such as C₆₀ and C₇₀. This low oxidation potential can be attributed to the relatively high energy level of a singly occupied orbital. Additionally, the oxidized species demonstrate a large HOMO-LUMO gap similar to that of Y_xDy_3−xN@C₈₀, underscoring their high chemical stability. Theoretical investigations have uncovered the presence of a three-center two-electron metal–metal bond at the center of ${\mathrm{Y}}_2\mathrm{D}\mathrm{Y}@{\mathrm{C}}_{80}^{+}$ and ${\mathrm{Y}\mathrm{D}\mathrm{y}}_2@{\mathrm{C}}_{80}^{+}$. This unique multi-center bond assists in alleviating the electrostatic repulsion between the metal ions, thereby contributing to the overall stability of the cations. These mixed rare-earth tri-metallofullerenes hold promise as potential candidates for single-molecule magnets. Full article

In the search for common bonding patterns in pure and mixed clusters of beryllium and magnesium derivatives, the most stable dimers and trimers involving BeX₂ and MgX₂ (X = H, F, Cl) have been studied in the gas phase using B3LYP and M06-2X DFT methods and the G4 ab initio composite procedure. To obtain some insight into their structure, stability, and bonding characteristics, we have used two different energy decomposition formalisms, namely MBIE and LMO-EDA, in parallel with the analysis of the electron density with the help of QTAIM, ELF, NCIPLOT, and AdNDP approaches. Some interesting differences are already observed in the dimers, where the stability sequence observed for the hydrides differs entirely from that of the fluorides and chlorides. Trimers also show some peculiarities associated with the presence of compact trigonal cyclic structures that compete in stability with the more conventional hexagonal and linear forms. As observed for dimers, the stability of the trimers changes significantly from hydrides to fluorides or chlorides. Although some of these clusters were previously explored in the literature, the novelty of this work is to provide a holistic approach to the entire series of compounds by using chemical bonding tools, allowing us to understand the stability trends in detail and providing insights for a significant number of new, unexplored structures. Full article