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The design of boron-based molecular rotors stems from boron-carbon binary clusters containing multiple planar hypercoordinate carbons (phCs, such as C2B8). However, the design of boron-coordinated phCs is challenging due to boron's tendency to occupy hypercoordinate centers more than carbon. Although this challenge has been addressed, the designed clusters of interest have not exhibited dynamic fluxionality similar to that of the initial C2B8. To address this issue, we report a σ/π doubly aromatic CB2H5 + cluster, the first global minimum containing a boron-coordinated planar tetracoordinate carbon atom with dynamic fluxionality. Dynamics simulations show that two ligand H atoms exhibit alternate rotation, resulting in an intriguing dynamic fluxionality in this cluster. Electronic structure analysis reveals the flexible bonding positions of the ligand H atoms because they do not participate in π delocalized bonding nor bond to any other non-carbon atom, highlighting this rotational fluxionality. Unprecedentedly, the fluxional process involves not only the usual conversion of the number of bonding atoms, but also the type of bonding (3c π bonds â4c σ bonds), which is an uncommon fluxional mechanism. The cluster represents an effort to apply phC species to molecular machines.
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A 14-electron ternary anionic CBe2 H5 - cluster containing a planar tetracoordinate carbon (ptC) atom is designed herein. Remarkably, it can be stabilized by only two beryllium atoms with both π-acceptor/σ-donor properties and two hydrogen atoms, which means that the conversion from planar methane (transition state) to ptC species (global minimum) requires the substitution of only two hydrogen atoms. Moreover, two ligand H atoms exhibit alternate rotation, giving rise to interesting dynamic fluxionality in this cluster. The electronic structure analysis reveals the flexible bonding positions of ligand H atoms due to C-H localized bonds, highlighting the rotational fluxionality in the cluster, and two CBe2 3c-2e delocalized bonds endow its rare 2σ/2π double aromaticity. Unprecedentedly, the fluxional process exhibits a conversion in the type of bonding (σ bondâπ bond), which is an uncommon fluxional mechanism. The cluster can be seen as an attempt to apply planar hypercoordinate carbon species to molecular motors.
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Boron-based nanoclusters show unique geometric structures, nonclassical chemical bonding, and dynamic structural fluxionality. We report here on the theoretical prediction of a binary Pd3B26 cluster, which is composed of a triangular Pd3 core and a tubular double-ring B26 unit in a coaxial fashion, as identified through global structural searches and electronic structure calculations. Molecular dynamics simulations indicate that in the core-shell alloy cluster, the B26 double-ring unit can rotate freely around its Pd3 core at room temperature and beyond. The intramolecular rotation is virtually barrier free, thus giving rise to an antifriction bearing system (or ball bearing) at the nanoscale. The dimension of the dynamic system is only 0.66 nm. Chemical bonding analysis reveals that Pd3B26 cluster possesses double 14π/14σ aromaticity, following the (4n + 2) Hückel rule. Among 54 pairs of valence electrons in the cluster, the overwhelming majority are spatially isolated from each other and situated on either the B26 tube or the Pd3 core. Only one pair of electrons are primarily responsible for chemical bonding between the tube and the core, which greatly weaken the bonding within the Pd3 core and offers structural flexibility. This is a key mechanism that effectively diminishes the intramolecular rotation barrier and facilitates dynamic structural fluxionality of the system. The current work enriches the field of nanorotors and nanomachines.
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Achieving a planar hypercoordinate arrangement of s-block metals through covalent bonding with ligands is challenging due to the strong ionicity involved. Herein, we report the first case of a neutral binary global minimum containing a planar hexacoordinate beryllium atom. The central Be atom is coordinated by six active Be atoms, the latter in turn are enclosed by an equal number of more electronegative chlorine atoms in the periphery, forming a star-like phBe cluster (Be©Be6 Cl6 ). Importantly, the cluster exhibits dynamically stabilized stemming geometrically from the appropriate matching of metal-ligand size and electronically from adherence to the octet rule as well as possessing a 6σ/2π double aromaticity. Remarkably, energy decomposition analysis-natural orbitals for chemical valence (EDA-NOCV) analysis reveals a significant covalent interaction between the ligand and the central metal beryllium atoms, a fact further supported by a large Wiberg bond index. This cluster is a promising synthetic as its excellent electronic, dynamic and thermodynamic stability.
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Doping alkali metals into boron clusters can effectively compensate for the intrinsic electron deficiency of boron and lead to interesting boron-based binary clusters, owing to the small electronegativity of the former elements. We report on the computational design of a three-layered sandwich cluster, Na5B7, on the basis of global-minimum (GM) searches and electronic structure calculations. It is shown that the Na5B7 cluster can be described as a charge-transfer complex: [Na4]2+[B7]3-[Na]+. In this sandwich cluster, the [B7]3- core assumes a molecular wheel in shape and features in-plane hexagonal coordination. The magic 6π/6σ double aromaticity underlies the stability of the [B7]3- molecular wheel, following the (4n + 2) Hückel rule. The tetrahedral Na4 ligand in the sandwich has a [Na4]2+ charge-state, which is the simplest example of three-dimensional aromaticity, spherical aromaticity, or superatom. Its 2σ electron counting renders σ aromaticity for the ligand. Overall, the sandwich cluster has three-fold 6π/6σ/2σ aromaticity. Molecular dynamics simulation shows that the sandwich cluster is dynamically fluxional even at room temperature, with a negligible energy barrier for intramolecular twisting between the B7 wheel and the Na4 ligand. The Na5B7 cluster offers a new example for dynamic structural fluxionality in molecular systems.
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The transition-metal centered boron molecular wheels have attracted the attention of chemists. The highest deca-coordination number for central metal atoms was observed in D 10h Ta©B10 - and Nb©B10 - molecular wheels. Here, we report a theoretical study of La©B8C4 q (q = +1, 0, -1) clusters with the dodeca-coordinated La atom. The La©B8C4 q clusters adopt fascinating molecular wheel structures, showing a La atom enclosed by a perfect B8C4 monocyclic ring. The cationic La©B8C4 + cluster has a C 4v symmetry with the distinctly out-of-plane distortion of the La atom (0.70 Å), which is gradually flattened by the sequential reduction reaction. The distortion of the La atom from the plane in the neutral La©B8C4 cluster decreases to 0.46 Å. The La©B8C4 - species turns out to be perfectly planar. Chemical bonding analyses indicate that the neutral La©B8C4 and anionic La©B8C4 - possess 10σ and 9π/10π double aromaticity, respectively, obeying the principle of double aromaticity. However, the cationic La©B8C4 + has 10σ and 8π conflicting aromaticity, representing a counterexample in planar hyper-coordinated molecular wheels. The dodeca-coordination number in La©B8C4 q (q = +1, 0, -1) clusters is unprecedented, which provides a new idea and concept for searching planar hyper-coordinated systems.
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The beryllium-doped Be3B11- cluster has two nearly isoenergetic isomers, adopting the smallest trihedral spherical geometries with a boron single-chain skeleton. The B11 skeleton in the global minimum (C2v, 1A1) comprises three conjoined boron rings (one B8/two B7) on the waist, sharing two B3 equilateral triangles at the top and bottom, respectively. However, the local minimum (Cs, 1A') has one deformed B4 pyramid at the top. The drastic structural transformation of B11 skeletons from perfectly planar B11 clusters mainly profited from robust electrostatic interaction between Be atoms and B11 skeletons. The dynamic simulations suggest that two species can interconvert via a novel mechanism, that is "triangle-pyramid-triangle", which facilitates the free migration of boron atoms in the B11 skeleton, thereby showing the fascinating dynamic fluxionality. The chemical bonding analyses reveal that the B11 skeleton is covered by two types of delocalized π bonds in an orthogonal direction, which leads to its spherical aromaticity.
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Computational evidence is reported for the largest planar molecular wheel of the Y©B8C4 cluster, featuring an yttrium atom enclosed by a highly symmetric B8C4 ring. The B8C4 ring is viable in the -(BCB)4- form with double 9π/10σ aromaticity. The centered yttrium atom is dodeca-coordinated with the peripheral B8C4 ring, which sets a record coordination number for a planar structure in chemistry heretofore.
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BACKGROUND: Patients diagnosed with non-small-cell lung cancer with activated epidermal growth factor receptor mutations are more likely to develop leptomeningeal (LM) metastasis than other types of lung cancers and have a poor prognosis. Early diagnosis and effective treatment of leptomeningeal carcinoma can improve the prognosis. CASE SUMMARY: A 55-year-old female with a progressive headache and vomiting for one month was admitted to Peking University First Hospital. She was diagnosed with lung adenocarcinoma with osseous metastasis 10 months prior to admittance. epidermal growth factor receptor (EGFR) mutation was detected by genomic examination, so she was first treated with gefitinib for 10 months before acquiring resistance. Cell-free cerebrospinal fluid (CSF) circulating tumor DNA detection by next-generation sequencing was conducted and indicated the EGFR-Thr790Met mutation, while biopsy and cytology from the patient's CSF and the first enhanced cranial magnetic resonance imaging (MRI) showed no positive findings. A month later, the enhanced MRI showed linear leptomeningeal enhancement, and the cytology and biochemical examination in CSF remained negative. Therefore, osimertinib (80 mg/d) was initiated as a second-line treatment, resulting in a good response within a month. CONCLUSION: This report suggests clinical benefit of osimertinib in LM patients with positive detection of the EGFR-Thr790Met mutation in CSF and proposes that the positive findings of CSF circulating tumor DNA as a liquid biopsy technology based on the detection of cancer-associated gene mutations may appear earlier than the imaging and CSF findings and may thus be helpful for therapy. Moreover, the routine screening of chest CT with the novel coronavirus may provide unexpected benefits.
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Theoretical evidence is reported for a boron-based K6Be2B6H6 sandwich cluster, showing a perfectly D 6h B6H6 ring, being capped by two tetrahedral K3Be ligands. Due to the comfortable charge transfer, the sandwich is viable in [K3Be]3+[B6H6]6-[BeK3]3+ ionic complex in nature. The [B6H6]6- core with 6π aromaticity vividly imitates the benzene (C6H6), occurring as a real borozene. In contrast, the tetrahedral [K3Be]3+ ligand is 2σ three-dimensional aromatic, acting as the simple superatom. Thus, this complex possesses a collectively three-fold 2σ/6π/2σ aromaticity. The interlaminar interaction is governed by the robust electrostatic attraction. The unique chemical bonding gives rise to interesting dynamic fluxionality.
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Computational evidence is reported on a boron-based ternary Rb6Be2B6 cluster as the "Big Mac" sandwich on a subnanoscale with thickness of 0.58 nm. The core hexagonal B6 ring, occurring in the naked form due to double 6π/6σ aromaticity, is capped by two tetrahedral BeRb3 ligands. Such a B6 motif is scarce in boron clusters. The sandwich cluster has four-fold 2σ/6π/6σ/2σ aromaticity and its tetrahedral BeRb3 ligand is the simplest case of three-dimensional aromaticity (or spherical aromaticity). The sandwich can be formulated as a charge-transfer complex, [Rb3Be]3+[B6]6-[BeRb3]3+, whose components are held together by robust electrostatics, facilitating dual-mode dynamic fluxionality.
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The typical electron-deficiency of the boron element renders fascinating architectures and chemical bonding to boron-based nanoclusters. We theoretically predict two di-Ca-doped boron clusters, B6Ca2 (D2h, 1Ag) and B8Ca2 (D8h, 1A1g), and both adopt interesting inverse sandwich geometries, showing an elongated D2h B6 or perfectly planar D8h B8 ring being sandwiched by two Ca atoms only, respectively. Natural atomic charge analyses indicate that the Ca atoms donate nearly all the 4s electrons to the B6 (or B8) ring, forming [Ca]2+[B6]4-[Ca]2+ and [Ca]2+[B8]4-[Ca]2+ charge transfer complexes. The interaction between the two Ca atoms and the boron rings is governed by robust electrostatics albeit by weaker B-Ca covalent interaction. Chemical bonding analyses show that B6Ca2 has 4σ and 6π delocalized electrons on the elongated B6 ring, leading to a conflicting aromatic system. B8Ca2, possessing 6σ and 6π delocalized electrons on the B8 ring, is doubly aromatic. Additionally, the B6Ca2 and B8Ca2 clusters show noticeable structural and electronic transmutation relative to their equivalent electronic B6Be2 and B8Mg2 clusters, respectively. The intrinsic reasons behind the transmutations are elucidated via in-depth bonding analyses.
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Boron-based clusters possess unusual structural and bonding properties owing to boron's electron-deficiency. We report on the theoretical prediction of two binary B-Na clusters, Na6B7- and Na8B7+, which assume unique sandwich geometries, featuring a perfectly planar B7 wheel and two triangular Na3 or quasi-tetrahedral Na4 ligands. Despite distinct electronegativities of B/Na, the B-Na clusters do not form typical salts. Both sandwich species are dynamically fluxional at 300 K and beyond. Two dynamic modes are observed: an in-plane rotation of the B7 wheel versus twisting of the two Na3/Na4 ligands. Their energy barriers are negligibly small. Natural bond orbital calculations show that the clusters are charge-transfer complexes [Na3]+[B7]3-[Na3]+ and [Na4]2+[B7]3-[Na4]2+, respectively. Chemical bonding analyses indicate that the B7 wheel in the clusters has 6π/6σ double aromaticity and the Na3/Na4 ligands are 2σ aromatic, collectively leading to four-fold π/σ aromaticity. The quasi-tetrahedral Na4 ligand is the simplest example of spherical aromaticity and can also be considered a superatom. Interlayer bonding in the sandwiches is greater than 20 eV, due to electrostatics, which should not be confused with weakly bound species. Four-fold π/σ aromaticity and robust interlayer ionic bonding offer uniform and dilute electron clouds over the sandwiches, facilitating their dual-mode dynamic fluxionality. The Na8B7+ cluster is also a superalkali cation.
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Typical salts are composed of positive and negative ions that appear alternatively, whereas decorated layered materials normally have ions anchored on the polygonal sites. In this way, the ions are spatially fixed and the system is stabilized on electrostatic grounds. Here we report on a unique boron-lithium cluster, B7 Li4 - , which contains a disk-like B7 core, being sandwiched by a Li3 ring and an isolated Li atom. All Li centers are stacked exactly on the B atoms from top or bottom, rather than being anchored on triangular B3 sites. The cluster shows dynamic fluxionality, whose Li3 ring rotates freely on the B7 disk even at below room temperature (200â K), akin to a subnanoscale propeller. The rotation barrier is only 0.37â kcal mol-1 at the single-point CCSD(T) level. The sandwich shape facilitates intramolecular charge-transfers, leading to a [Li3 ]+ [B7 ]3- [Li]+ salt complex. The [Li3 ]+ layer has 2σ aromaticity, while [B7 ]3- core is robust with both π and σ sextets. Three-fold π/σ aromaticity collectively stabilizes the system, as well as underlies its dynamic fluxionality. The interlayer bonding turns out to be strong, dominated by ionic interactions (of the order of 3-4â eV per Li3 /Li unit). The work demonstrates a propeller at the subnanoscale, which is dynamically fluxional despite strong covalent and ionic bonding.
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OBJECTIVES: To assess the predictive significance of quantitative perfusion parameters from contrast-enhanced ultrasound (CEUS) for the therapeutic response to high-intensity focused ultrasound (HIFU) ablation in patients with uterine fibroids. METHODS: A total of 263 patients with single uterine fibroids were treated with HIFU ablation under ultrasound guidance. The arrival time, peak time, enhancement time, enhancement intensity, and enhancement rate were evaluated with pretreatment CEUS. According to a nonperfused volume ratio evaluation by posttreatment magnetic resonance imaging, all patients were assigned to groups with volume ratios of 70% or higher and lower than 70%. Then the predictive performances of different parameters for ablation efficacy were studied. RESULTS: The arrival time, peak time, and enhancement time in the group with a nonperfused volume ratio of 70% or higher were longer than those in the group with a volume ratio lower than 70% (mean ± SD, 16.7 ± 3.5, 26.5 ± 4.9, and 10.2 ± 2.6 seconds, respectively, versus 13.3 ± 4.2, 20.8 ± 5.4, and 7.6 ± 2.3 seconds), whereas patients with a volume ratio of 70% or higher had a lower mean enhancement intensity and enhancement rate than those with a volume ratio lower than 70% (29.7 ± 16.7 dB and 3.2 ± 1.5 dB/s versus 63.2 ± 26.3 dB and 8.6 ± 4.3 dB/s; P < .05). The nonperfused volume ratio was negatively correlated with the enhancement intensity and enhancement rate (r = -0.631 and -0.712) but positively correlated with the arrival time, peak time, and enhancement time (r = 0.322, 0.456, and 0.477; P < .05). The areas under the receiver operating characteristic curve for the enhancement time, enhancement intensity, and enhancement rate were 0.73, 0.79, and 0.81 (P < .05). CONCLUSIONS: Quantitative parameters from CEUS are potentially useful for evaluating the therapeutic effect of HIFU ablation for uterine fibroids.
Assuntos
Meios de Contraste , Ablação por Ultrassom Focalizado de Alta Intensidade/métodos , Aumento da Imagem/métodos , Leiomioma/diagnóstico por imagem , Ultrassonografia/métodos , Neoplasias Uterinas/diagnóstico por imagem , Adulto , Estudos de Avaliação como Assunto , Feminino , Humanos , Leiomioma/irrigação sanguínea , Leiomioma/cirurgia , Masculino , Valor Preditivo dos Testes , Resultado do Tratamento , Neoplasias Uterinas/irrigação sanguínea , Neoplasias Uterinas/cirurgia , Útero/irrigação sanguínea , Útero/diagnóstico por imagem , Útero/cirurgiaRESUMO
Alloying an elongated B10 cluster with Ca is shown to give rise to a dynamically fluxional B10Ca cluster, the latter behaving like a tank tread at the subnanoscale. Computer global search identifies the B10Ca C 2 (1A) global-minimum structure, which is chiral in nature and retains the quasi-planar moiety of bare B10 cluster with Ca capped at one side, forming a half-sandwich. The rotation barrier of B10Ca cluster is reduced with respect to B10 by one order of magnitude, down to 1 kcal mol-1 at the PBE0/6-311+G* level, which demonstrates structural fluxionality at 600 K and beyond via molecular dynamics simulations. Structurewise, the Ca alloying in B10Ca cluster generates rhombic defect holes, preactivating the species and making it flexible against deformation. Chemical bonding analyses indicate that the B10Ca cluster is a charge-transfer [B10]2-[Ca]2+ complex, being doubly π/σ aromatic with the 6π and 10σ electron-counting. Such a pattern offers ideal π/σ delocalization and facilitates fluxionality. In contrast, bare B10 cluster has conflicting aromaticity with 6π and 8σ electrons, which is nonfluxional with a barrier of 12 kcal mol-1. Double π/σ aromaticity versus conflicting aromaticity is a key mechanism that distinguishes between fluxional B10Ca and nonfluxional B10 clusters, offering a compelling example that the concept of aromaticity (and double aromaticity) can be exploited to design dynamically fluxional nanosystems.
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Boron-based binary cluster Mg2 B8 is shown to adopt a compass-like structure via computational global searches, featuring an Mg2 dimer as the needle and a disk-shaped B8 molecular wheel as baseplate. The nanocompass has a diameter of 0.35â nm. Born-Oppenheimer molecular dynamics simulations indicate that Mg2 B8 is structurally fluxional with the needle rotating freely on the baseplate, analogous to a functioning compass. The dynamics is readily initiated via a ultrasoft vibrational mode. The rotational barrier is only 0.1â kcal mol-1 at the single-point CCSD(T) level. Chemical bonding analysis suggests that the cluster compass can be formulated as [Mg2 ]2+ [B8 ]2- ; that is, the baseplate and the needle are held together primarily through ionic interactions. The baseplate is doubly aromatic with π and σ sextets. The bonding pattern provides a dilute, continuous, and delocalized electron cloud, which underlies the dynamics of the nanocompass.
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Two low-lying structures are unveiled for the Be6 B11- nanocluster system that are virtually isoenergetic. The first, triple-layered cluster has a peripheral B11 ring as central layer, being sandwiched by two Be3 rings in a coaxial fashion, albeit with no discernible interlayer Be-Be bonding. The B11 ring revolves like a flexible chain even at room temperature, gliding freely around the Be6 prism. At elevated temperatures (1000â K), the Be6 core itself also rotates; that is, two Be3 rings undergo relative rotation or twisting with respect to each other. Bonding analyses suggest four-fold (π and σ) aromaticity, offering a dilute and fluxional electron cloud that lubricates the dynamics. The second, helix-type cluster contains a B11 helical skeleton encompassing a distorted Be6 prism. It is chiral and is the first nanosystem with a boron helix. Molecular dynamics also shows that at high temperature the helix cluster readily converts into the triple-layered one.
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Planar boron clusters form dynamic rotors, either as molecular Wankel motors or subnanoscale tank treads, the latter being exemplified by an elongated B11- cluster. For an in-depth mechanistic understanding of the rotors, we investigate herein a doped boron cluster, B10C, in which a C atom isovalently substitutes B- in the B11- tank tread. Two critical structures are achieved: the Cs (1A') global minimum (GM) with C positioned in the peripheral ring and the C2v (1A1) local minimum (LM) with C in the diatomic core. In the GM the C atom completely halts the rotation of B10C, whereas in the LM the dynamic fluxionality remains. The energy barriers for in-plane rotation differ markedly: 12.93/18.31 kcal mol-1 for GM versus 1.84 kcal mol-1 for LM at the single-point CCSD(T) level. The GM rotates via two transition states (TS), compared to one for the LM. Chemical bonding in the structures is elucidated via canonical molecular orbital (CMO) analysis, adaptive natural density partitioning (AdNDP), electron localization functions (ELFs), and Wiberg bond indices (WBI). Electron delocalization is shown to be essential for structural fluxionality. In particular, the variation of WBI from the GM or LM geometries to their TS structures correlates positively with the energy barrier, which offers a quasi-quantitative measure of the barrier height and hence controls the dynamics. This finding may be extended to all molecular rotors. It also helps rationalize why a strongly covalently bound system can behave dynamically in a manner similar to a weakly bound one; it is the latter that is generally anticipated to be structurally fluxional.
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Planar boron clusters B11-, B13+, B15+, and B19- have been introduced recently as molecular Wankel motors or tank treads. Here we present a universal mechanism for these dynamically fluxional clusters; that is, they are molecular rotors with inner wheels that rotate almost freely in pseudo-rotating outer bearings, analogous to rotating molecules trapped in pseudo-rotating cages. This mechanism has significant quantum mechanical consequences: the global-minimum structures of the clusters have C2v symmetry, whereas the wheels rotating in pseudo-rotating bearings generate rosette-type shapes with D9h, D10h, D11h, and D13h symmetries. The related rotational/pseudo-rotational energies appear with characteristic band structures, effecting the dynamics.