Enhanced Stability of Rhombic Dodecahedron Nb15- with Well-Organized Superatomic States

Well-resolved Nb_n^- clusters are produced and reacted with ethene and propene via a downstream flow tube reactor. Interestingly, the Nb_n^- clusters readily react with ethene and propene to form dehydrogenation products; however, Nb₁₅^- shows up in the mass spectra with prominent mass abundance indicating its inertness to react with olefins. For this cluster, we conduct photoelectron velocity map imaging (VMI) experiments and verify the stability of Nb₁₅^- within a highly symmetrical rhombic dodecahedron structure. Theoretical studies show that the stability of the Nb₁₅^- cluster is correlated with its superatomic nature pertaining to both geometric and electronic shell closures. Notably, the superatomic 1s orbital is dominated by the 5s electron of the central Nb atom, while the other superatomic orbitals are contributed by s-d hybridization, especially a remarkable contribution of s-d_z² hybridization. Apart from the closed shells, the highly symmetric geometry of Nb₁₅^- is associated with a regular polyhedral structure directed by all rhombus facets, embodying a magic number for body-centered dodecahedra, indicative of enhanced stability as a double magic cluster free of olefin adsorption.

Unraveling the flexible aromaticity of C13H9+/0/-: a 2D superatomic-molecule theory

Phenalenyl (C₁₃H₉) is the smallest triangular unit of a graphene nanosheet, and has been experimentally verified to be stable in radical (C₁₃H₉˙), cationic (C₁₃H₉⁺), and anionic (C₁₃H₉^-) states. All these three species feature high symmetry and stability as well as delocalized π electrons, a visible sign of aromaticity, but their aromatic origin remains a challenge. This work reports new chemical insights into the π electrons of C₁₃H₉^+/0/- and deciphers their aromaticity using a recently emerged two-dimensional (2D) superatomic-molecule theory. 12π-C₁₃H₉⁺, 13π-C₁₃H₉˙, and 14π-C₁₃H₉^- are seen as triangular 2D superatomic molecules ^◊O₃, ^◊O₃^-, and ^◊O₃^2-, respectively, where ^◊O denotes a 2D benzenoid superatom bearing 4 π electrons. Visualized superatomic Lewis structures show that each ^◊O can dynamically adjust its π electrons to satisfy the superatomic sextet rule of benzene via superatomic lone pairs and covalent bonds. C₁₃H₉^+/0/- are representatives of adaptive aromaticity in the 2D superatomic-molecule system, exhibiting flexible π electronic structures to achieve shell-closure. Moreover, we specially adopt a progressive methodology to study the evolution of 2D periodic materials, by applying this theory to the similar family of C₆H₃N₇, C₁₈H₆N₂₂ and graphitic carbon nitride (g-C₃N₄) crystals, and meanwhile accounting for the special stability of g-C₃N₄. This work enriches 2D superatomic bonding chemistry and provides a useful strategy to design new 2D functional nanostructured materials.

Planar σ-Aromaticity in Ga-Doped Au Clusters

Recently, the first example of Au-Ga clusters is synthesized and characterized, which can be described by the jellium model as a superatom with 8 valence electrons that come from the joint contribution of Au and Ga atoms, opening a whole new field for further research. Here, the structure features and stability of one Ga-doped Au cluster with magic number electrons (6 and 8) are analyzed in detail. Moreover, the valence electron fillings and chemical bonding of them are also further explored. It is found that Au₃Ga and Au₅Ga clusters present planar configurations, and they have higher stability than that of neighbor clusters. The AIMD simulations show that these two clusters still have a good thermal stability at 500 K. The molecular orbital analyses show that the Au₃Ga and Au₅Ga have three and one typical delocalization orbital throughout the whole planar spaces, respectively, following the planar σ-aromaticity rule. The ELF and LOL analyses are further performed, and the results are consistent with the molecular orbital analyses. The NICSzz-scan curves confirm that the Au₃Ga is more aromatic than the Au₅Ga, and the reason is that the former has more delocalized electrons than the latter. Our work opens up aromaticity studies in the Au-Ga clusters.

The nature of stability and adsorption interactions of binary Au-Li clusters with bridge adsorption structures

Earlier findings have confirmed that CO molecules have propensities to adsorb on low-coordinated gold atoms (top sites) of Au-based clusters, which can be treated by the Blyholder model wherein the σ donation and π-back donation take place. Here, the structural features and stability of (AuLi)_n (n = 1-9) clusters were first analyzed using the GA-DFT method. The new adsorption modes, vibration frequencies and electronic interactions for Au-Li clusters with CO were investigated in detail. More excitingly, we found that CO prefers to adsorb on the bridge sites of the Au-Li clusters rather than on the top sites, which are much lower in energies than the top adsorptions, and the C-O stretching frequencies are also red-shifted. AIMD simulations show that the adsorption structures still have good thermal stability at 500 K. The density of states reveals that the electronic structures of Au-Li clusters have excellent stability for the bridge adsorptions of CO molecules. The ETS-NOCV analysis and NPA charges show that the direction of charge flow is from Au-Li clusters → CO. Our study provides an idea to elucidate the new adsorption mechanism on Au-Li clusters and the connection between the geometries and reaction properties.

Dabrafenib and Trametinib Therapy for Advanced Anaplastic Thyroid Cancer - Real-World Outcomes From UK Centres

AIMS

Anaplastic thyroid cancer (ATC) is a rare but aggressive form of thyroid cancer with a median survival of 4 months. Recent advances in molecular profiling have shown that up to half of ATCs harbour the BRAF-V600E mutation. The aim of this study was to provide real-world data and experience on the use of combination therapy dabrafenib and trametinib in patients with BRAF-V600E-mutated advanced ATC.

MATERIALS AND METHODS

We retrospectively evaluated patients with confirmed BRAF-V600E-mutated ATC, defined as patients with locally advanced or metastatic ATC with no locoregional, radical treatment options. Outcomes measured were overall survival, progression-free survival, response rate, discontinuation rate, dose reduction rate and toxicity data.

RESULTS

Seventeen patients were evaluated and the mean age was 68 years. Ten patients died by the time of censoring. The median duration of follow-up was 12 months (3-43 months). The estimated median overall survival was 6.9 months (95% confidence interval 2.46 months - upper confidence interval not reached) and the median progression-free survival was 4.7 months (95% confidence interval 1.4-7.8 months). Dose interruptions and/or reductions were common, but none of the patients had to permanently discontinue treatment because of toxicities. Severe toxicities (grades 3 and 4) were uncommon.

CONCLUSIONS

This study supports the indication of dabrafenib and trametinib in BRAF-V600E-mutated ATC as an effective and well-tolerated treatment in an historically difficult to treat cancer.

[Characteristics and significance of outer retinal thickness changes in reticular macular disease]

Objective: To study the characteristics and significance of changes in the thickness of the outer retinal layer (ORL) outside the macula in patients with reticular macular disease (RMD). Methods: A cross-sectional study was conducted. The clinical data of patients who visited the Department of Ophthalmology of the First Affiliated Hospital of Guangzhou Medical University from February to September 2019 were retrospectively collected. Thirty-one patients with at least one eye (54 eyes in total) diagnosed with early/mid-stage age-related macular degeneration (AMD) were consecutively included in the AMD group, and 33 patients with at least one eye (64 eyes in total) showing subretinal wart-like deposits on optical coherence tomography images were consecutively included in the RMD group. Thirty-two volunteers aged between 50 to 90 years with a normal fundus in both eyes (64 eyes in total) were consecutively included in the healthy control (HC) group. Frequency domain optical coherence tomography was applied to examine and analyze the thickness features of the ORL, inner retinal layer and choroid at the macular fovea (F), 2 mm of the temporal edge (T), the nasal edge (N), the superior edge (S) and inferior edge (I) of the macular fovea in each group. The correlations of the thickness of ORL with the choroidal thickness and the blood flow density of the choriocapillaris layer in patients with RMD were also analyzed. Results: The thickness of ORL at the F, T, S and I sites in the RMD group was significantly thinner than that in the AMD and HC groups. The difference was most obvious at the F site [(90.27±8.93), (98.04±11.7) and (97.19±7.02)μm] in the RMD, AMD and HC groups, respectively; all P<0.01). In the logistic regression model with independent variables of the ORL thickness at the macular F site, gender and age, there was a significant association between the thickness of ORL at the F site and the incidence of RMD (odds ratio=0.926, P<0.05). The ORL and choroid in the eyes of patients with RMD were significantly thinner at the F site [(90.27±8.93) and (163.21±72.43) μm, respectively; both P<0.01] compared with the AMD [(98.04±11.7) and (235.34±64.15) μm, respectively] and HC [(97.19±7.02) and (240.08±62.27) μm, respectively] groups. However, the ORL and choroidal thickness did not show significant and strong linear correlations at multiple sites. In contrast, there was a significant linear correlation between the blood flow density of the choriocapillaris layer and the thickness of ORL at the F, T and S sites in patients with RMD (r=0.487, 0.722, 0.467, respectively; all P<0.05). Conclusions: The thickness of ORL outside the macula of eyes with RMD is thinner than that of healthy eyes and eyes with early/mid-stage AMD. The thinning of ORL outside the macula is related to the decrease in the blood flow density of the choriocapillaris layer in patients with RMD.

Superatomic Three-Center Bond in a Tri-Icosahedral Au36Ag2(SR)18 Cluster: Analogue of 3c-2e Bond in Molecules

Probing the nature of electronic stability for ligand-protected gold clusters is important in gold chemistry. A thermally stable Au₃₆Ag₂(SR)₁₈ nanocluster was synthesized recently. It has a D_3h tri-icosahedral [Au₃₀Ag₂]¹²⁺ core with 20 valence electrons, which does not follow the magic number of gold superatoms. Herein, we propose a superatomic three-center bond to unveil its electronic stability. The [Au₃₀Ag₂]¹²⁺ core is viewed as a union of three face-fused superatoms, and chemical bonding analysis suggests a three-superatom-center two-electron (3sc-2e) bond for the octet rule of each superatom, which mimics the bonding framework of the D_3h O₃^2- molecule. Moreover, a liganded tri-icosahedral [Au₂₇Pt₃Ag₂]¹¹⁺ core with 18 valence electrons is predicted, and three 2sc-2e bonds are formed between each of two superatoms to satisfy the octet rule (analogue of D_3h O₃), indicating the flexibility of superatomic bonding. Such a superatomic three-center bond extends the community of superatomic bonding and gives a new perspective for superatom assembling.

Sodium Cationization Enables Exotic Deprotonation Sites on Gaseous Mononucleotides

We report observation and photoelectron spectroscopic characterization of sodium cationization on four doubly deprotonated mononucleotide dianions Na⁺·[dNMP-2H]^2- (N = A, G, C, or T) in the gas phase. Multiple tautomers with distinct deprotonated sites are identified, in which Na⁺ enables novel double deprotonation patterns and folds the resultant mononucleotide dianions. The most stable isomer for the whole family is derived from detaching one proton from the phosphate and the other from the nucleobase (amino group for N = A, G, and C, but nitrogen atom for T), whereas high-lying isomers with protons detached separately from the phosphate and the hydroxy group of sugar coexist. Particularly, an exotic deprotomer with both protons deprived from guanosine is populated as well. This work thus displays a remarkably diverse binding landscape enabled by sodium cationization, a potentially critical element in developing a general formulism to better model metal cation and nucleotide interactions.

A unified superatomic-molecule theory for local aromaticity in π-conjugated systems

Aromaticity is one of the most important concepts in chemistry. However, there is still no unified chemical insight for various systems with conjugated sp2 carbon. Herein, we proposed a superatomic-molecule theory to build a generalized electron-rule for polycyclic conjugated hydrocarbons, fullerenes and 2D periodic materials. Taking benzenoid units as 2D superatoms, polycyclic conjugated hydrocarbons and C60 can be seen as superatomic molecules consisting of bonded superatoms, resulting in local aromaticity. In superatomic molecules, π electrons are not totally delocalized, but localized in a single superatom forming superatomic lone pairs or shared by two atoms forming a superatomic bond, mimicking rules in classical valence bond theory. Moreover, two 2D superatomic crystals (C18H6 and C54H18) are predicted to have fairly large band gaps (∼1.8 eV), although the π electrons are conjugated and delocalized. The proposed superatomic-molecule theory provides generalized chemical insights into the nature of local aromaticity, which can be qualitatively evaluated by the chemical intuition given by superatomic Lewis structures.

Assembling Au4 Tetrahedra to 2D and 3D Superatomic Crystals Based on Superatomic-Network Model

Thiolate-protected gold nanoclusters (denoted as Au _m (SR) _n or Au _n L _m ) have received extensive attention both experimentally and theoretically. Understanding the growth mode of the Au₄ unit in Au _m (SR) _n is of great significance for experimental synthesis and the search for new gold clusters. In this work, we first build six clusters of Au₇(AuCl₂)₃, Au₁₂(AuCl₂)₄, Au₁₆(AuCl₂)₆, Au₂₂(AuCl₂)₆, and Au₃₀(AuCl₂)₆ with the Au₄ unit as the basic building blocks. Density functional theory (DFT) calculations show that these newly designed clusters have high structural and electronic stabilities. Based on chemical bonding analysis, the electronic structures of these clusters follow the superatom network (SAN) model. Inspired by the cluster structures, we further predicted an Au₄ two-dimensional (2D) monolayer and a three-dimensional (3D) crystal using graphene and diamond as templates, respectively. The computational results demonstrate that the two structures have high dynamic, thermal, and mechanical stabilities, and both structures exhibit metallic properties according to the band structures calculated at the HSE06 level. The chemical bonding analysis by the solid-state natural density partitioning (SSAdNDP) method indicates that they are superatomic crystals assembled by two electron Au₄ ^- superatoms. With this construction strategy, the new bonding pattern and properties of Au _n L _m are studied and the structure types of gold are enriched.

Theoretical study on L-H+-L with identical donors: short strong hydrogen bond or not?

Short strong hydrogen bonds (SSHBs) play crucial role in many chemical processes. Recently, as the representative of SSHBs, [F-H-F]- was experimentally observed. [F-H-F]- has a symmetric structure, which can be described as a H+ acid shared by two terminal F- donors (F--H+-F-). To explore whether two identical donors are bound to result in SSHBs, we performed theoretical studies on a series of compounds (L-H+-L) with two identical electron donors (L corresponds to donors containing group 14, 15, 16 and 17 elements). The results show that identical donors do not definitely lead to SSHBs. Instead, typical hydrogen bonds also exist. We found that both electronegativity and basicity contribute to the patterns of hydrogen bonds, where more electronegative and weaker donors benefit to SSHBs. Besides, it was found that zero-point energies also respond to the hydrogen bonding systems. This systemic work is expected to provide more insights into SSHBs.

New insight into the electronic structure of SiF4: synergistic back-donation and the eighteen-electron rule

SiF₄ demonstrated high thermal stability in dry air or vacuum, and a Si-F bond length of 1.554 Å is close to the second period element C-C bond length (1.54 Å) of C₂H₆. To determine which factors confer this property of SiF₄, here we conduct a comparative study of a series of molecules SiH_nF_4-n (n = 0, 1, 2, 3), SiX₄ (X = Cl, Br, I), CF₄ and TiF₄ in terms of bond length and energy, molecular orbitals, and adaptive natural density partitioning (AdNDP) analysis. The AdNDP analysis shows that there are five 5c-2c bonds in SiF₄, here named synergistic back-donation (SBD) bonds. These SBD bonds together with the Si-F σ bonds and the eighteen-electron rule are demonstrated as the main factors contributing to the short Si-F bond length and the high thermal stability of SiF₄ in dry air or vacuum. Moreover, the SBD bonds exist widely in other isoelectronic species of SiF₄ such as ClO₄^-, SO₄^2-, PO₄^3- and XeO₄.

P-606 Androgen receptor splice variant lead to PCOS with insulin resistance via IRS1/AKT signaling pathway in mice

Study question

How does the androgen receptor splice variant (ARSV) contribute to insulin resistance in polycystic ovary syndrome (PCOS) patients?

Summary answer

ARSV inhibited the intracellular signaling pathway of insulin, resulting in decreased glucose transporter type 4 (GLUT4) translocation, impaired cellular glucose uptake, and insulin resistance.

What is known already

PCOS is the most common endocrine disorder in women of reproductive age and characterized by hyperandrogenism, ovulation dysfunction, and ovarian polycystic changes. In addition, a significant proportion of PCOS patients will experience insulin resistance. Our previous study identified an ARSV in granulosa cells from PCOS patients, which may be associated with higher insulin levels in follicular fluid.

Study design, size, duration

/

Participants/materials, setting, methods

Glucose metabolism of a mouse model presenting ARSV by CRISPR-Cas9 was measured by glucose tolerance test and insulin tolerance test. Body composition was measured by a nuclear magnetic resonance system. KGN cell lines stably overexpressing wild type androgen receptor (AR group) or ARSV (ARSV group) were successfully constructed by lentivirus infection. The process of glucose uptake by GLUT4, and the expression of target genes in the glucose uptake pathway were detected in cells.

Main results and the role of chance

The mice expressing ARSV had higher body weight and body fat content than the wild type mice, while the muscle content was equivalent.ARSV mice displayed diabetes with impaired glucose tolerance and insulin tolerance at 48 week-age. The levels of fasting glucose and insulin levels were significantly higher in ARSV mice. The basal and insulin-stimulated glucose uptake capacity were also found impaired in ARSV group. Immunofluorescence demonstrated that under insulin stimulation, GLUT4 protein was less expressed in the membrane and more expressed in the cytoplasm in ARSV group. Similar results were obtained by detecting the expression of GLUT4 protein after separating the cell membrane and cytoplasmic proteins. Further detection of the upstream signaling molecules of GLUT4 revealed that the phosphorylation levels of insulin receptor substrate 1 (IRS1) at Ser1101 were slightly increased in ARSV group, after stimulation with insulin and DHT. Besides, the phosphorylation levels of protein kinase B (AKT) were also found significantly decreased at Thr308 and slightly decreased at Ser473 in ARSV group. ARSV inhibited the intracellular signaling pathway of insulin by altering the phosphorylation level of IRS1/AKT signaling, resulting in decreased GLUT4 translocation, impaired cellular glucose uptake, and insulin resistance.

Limitations, reasons for caution

In this study, we failed to obtain clinical samples of PCOS to prospectively verify the association between ARSV and glucose uptake, insulin resistance, and subsequent onset diabetes.

Wider implications of the findings

This transgenic animal model can simulate the reproductive and metabolic phenotypes of PCOS patients, providing a model for future PCOS research. PCOS patients with ARSV should delay the onset of insulin resistance through lifestyle intervention, exercise, and drug therapy as early as possible.

Trial registration number

NA

Properties of Daily Helium Fluxes

We present the precision measurement of 2824 daily helium fluxes in cosmic rays from May 20, 2011 to October 29, 2019 in the rigidity interval from 1.71 to 100 GV based on 7.6×10^{8} helium nuclei collected with the Alpha Magnetic Spectrometer (AMS) aboard the International Space Station. The helium flux and the helium to proton flux ratio exhibit variations on multiple timescales. In nearly all the time intervals from 2014 to 2018, we observed recurrent helium flux variations with a period of 27 days. Shorter periods of 9 days and 13.5 days are observed in 2016. The strength of all three periodicities changes with time and rigidity. In the entire time period, we found that below ∼7  GV the helium flux exhibits larger time variations than the proton flux, and above ∼7  GV the helium to proton flux ratio is time independent. Remarkably, below 2.4 GV a hysteresis between the helium to proton flux ratio and the helium flux was observed at greater than the 7σ level. This shows that at low rigidity the modulation of the helium to proton flux ratio is different before and after the solar maximum in 2014.

FeP2 monolayer: isoelectronic analogue of MoS2 with excellent electronic and optical properties

Two-dimensional semiconductors with suitable indirect band gaps, excellent light absorption capacity, and oxidation resistance are particularly suitable for material applications. Here based on first-principle calculations, we report that the FeP₂ monolayer, which is isoelectronic with MoS₂, has novel electronic properties and an ultra-low diffusion energy barrier of K on the surface, indicating its potential as an anode material of K-ion batteries. The calculated phonon dispersion curves, molecular dynamics, and elastic constants showed that it has high structural stability and oxidation resistance. The monolayer was a semiconductor with an indirect band gap of 0.68 eV. In addition, the FeP₂ monolayer had obvious light absorption in the infrared, visible, and ultraviolet regions, which can be widely used in optoelectronic devices. Bonding analysis showed that there were multicenter bonds inside every hexagonal ring. As the anode material of K-ion batteries, the FeP₂ monolayer had a capacity of 456.84 mA h g^-1, low diffusion energy barrier, and open-circuit voltage. All these characteristics suggest that the FeP₂ monolayer is a potential anode material for K-ion batteries, which needs to be further verified by experiments.

POS0562 AUTOANTIBODIES TO JOINT PROTEINS AS NOVEL BIOMARKERS FOR THE DIAGNOSIS OF UNTREATED EARLY RHEUMATOID ARTHRITIS

Background

Autoantibodies to citrullinated protein (ACPA; measured as anti-CCP; aCCP) and rheumatoid factor (RF) appear years before clinical onset of RA and are essential tools in today’s classification criteria for RA. In animal models, antibodies to joint specific proteins (JP) can induce arthritis, and they are also present at onset of RA [1]. As there is a need for increased precision for early diagnosis of RA as well as identification of different subtypes of the disease, we aim to assess whether autoantibodies to native or modified JP can be used for early and precise diagnosis of RA.

Objectives

To study whether antibodies to JP, alone or in combination with ACPA/RF, could increase the diagnostic sensitivity and specificity in untreated early (ue)RA patients.

Methods

Antibodies to JP were analysed in serum from patients in three independent ueRA cohorts as well as from population controls without rheumatic diseases (WINGA, Gothenburg and MFM-ÅUS, Malmö n=1062). ERAp (n=66), the smallest and most recent cohort was chosen for screening, and BARFOT and TIRA-2 (n=1939) for validation. We have developed a bead-based multianalyte flow immunoassay [2] and screened approx. 350 peptides derived from JPs of interest. We included monoclonal antibodies as assay calibrators and determined limit of detection (LoD). To assess positivity for autoantibodies to JP of interest above LoD, we used 5MAD (median absolute deviation) of the control populations as the cut-off.

Results

In the ERAp cohort, 5 autoantibodies discriminated RA patients from controls with 81% sensitivity and 100% specificity (Table 1). The same autoantibodies had 68% sensitivity and 98% specificity in the combined BARFOT and TIRA-2 cohorts. Together with RF and aCCP, only 2 of the 5 autoantibodies added statistically significant diagnostic value, increasing the sensitivity from 48% to 61% with 99% specificity. In aCCP- and RF-negative ueRA patients (n=536), the novel biomarkers identified 22.5% of the patients with 99% specificity compared to controls.

Table 1.

Diagnostic capacity of the joint-specific antibodies

Test panelPerformanceGroup of patientsaCCP+RF+JP+SensitivitySpecificityAUC(ROC)ERApAll patients (n=66)--X81%100%89%RF and aCCP-neg patients (n=7)1------BARFOT and TIRA-2, combined dataAll patients (N=1939)--X68%98%86%All patients (N=1939)X--58%99%78%All patients (N=1939)2XX-48%100%84%All patients (N=1939)2, 3XXX61%99%86%RF and/or aCCP-pos patients (N=1403)--X84%99%93%RF and aCCP-neg patients (N=536)--X22%99%67%RA, literature valuesAnti-CCP testXN/AN/A53–71%95–96%N/A

1Not analysed due to lack of power

2This patient population is both aCCP+ and RF+

3Only 2 of the 5 autoantibodies added statistically significant to the diagnostic value

AUC, Area under the curve; ROC, receiver operating characteristic curve; N/A, not applicable. Controls without rheumatic diseases: N=935 for BARFOT / TIRA-2 and N=27 for ERAp.

Conclusion

Autoantibodies to JP discriminate ueRA patients better then aCCP and RF alone and add an increased diagnostic value in particular for seronegative patients.

References

[1]Holmdahl, R., V. Malmstrom, and H. Burkhardt, Autoimmune priming, tissue attack and chronic inflammation - the three stages of rheumatoid arthritis. Eur J Immunol, 2014. 44(6): p. 1593-9.

[2]Viljanen, J., et al., Synthesis of an Array of Triple-Helical Peptides from Type II Collagen for Multiplex Analysis of Autoantibodies in Rheumatoid Arthritis. ACS Chem Biol, 2020. 15(9): p. 2605-2615. Correction: ACS Chem Biol, 2020. 15(11): p. 3072

Acknowledgements

BARFOT study group.

Disclosure of Interests

Erik Lönnblom: None declared, Monica Leu Agelii: None declared, Outi Sareila Employee of: Part time employee in Vacara AB, Ingiäld Hafström: None declared, Maria Andersson: None declared, Lei Cheng: None declared, Göran Bergström: None declared, Anna-Karin H Ekwall: None declared, Anna Rudin: None declared, Alf Kastbom: None declared, Christopher Sjowall: None declared, Bingze Xu: None declared, Lennart T.H. Jacobsson: None declared, Johan Viljanen: None declared, Jan Kihlberg: None declared, Inger Gjertsson: None declared, Rikard Holmdahl Shareholder of: Rikard Holmdahl the founder of Vacara AB.

Adsorption properties of pyramidal superatomic molecules based on the structural framework of the Au20 cluster

The pyramidal Au₂₀ cluster is a highly inert and stable superatomic molecule, but it is not suitable as a potential catalyst for covalent bond activations, e.g., CO oxidation reaction. Herein, the adsorption and electronic properties of CO molecules on various pyramidal clusters based on the structural framework of Au₂₀ are investigated using density functional theory. According to the SVB model, we constructed isoelectronic superatomic molecules with different pyramid configurations by replacing the vertex atoms of the Au₂₀ using metal M atoms (M = Li, Be, Ni, Cu, and Zn group atoms). After the CO molecules are adsorbed on the vertex atoms of these metal clusters, we analyzed the CO adsorption energies, C-O bond stretching frequencies, and electronic properties of the adsorption structures. It was found that the adsorption of CO molecules results in minimal changes in the parent geometries of the pyramidal clusters, and most adsorption structures are consistent with the geometry of CO adsorption at the vertex site of the Au₂₀ cluster. There are significant red shifts when CO molecules are adsorbed on the Ni/Pd/Pt atoms of the clusters, and their CO adsorption energies were also greater. The molecular orbitals and density of states reveal that there are overlaps between the frontier orbitals of the clusters and CO, and the electronic structure of NiAu₁₉^- is not sensitive to CO. The ETS-NOCV analysis shows that the increase in the density of the bonding area caused by the orbital interactions between the fragments is higher than the decrease in the density of the bonding area caused by Pauli repulsion, presenting that the direction of charge flow in the deformation density is from CO → clusters. From energy decomposition analysis (EDA) and NPA charge, we find a predominant covalent nature of the contributions in CO⋯M interactions (σ-donation). Our study indicates that the SVB model provides a new direction to expand the superatomic catalysts from the superatom clusters, which also provides inference for the extension of the single atom catalysis.

Exoergic pathways triggered by O/H radicals in different metallic carbohydrazide perchlorates (M2+ = Mn2+, Fe2+, Co2+, Ni2+, Zn2+ and Cd2+)

Metallic carbohydrazide perchlorates (M[(N₂H₃)₂C = O](ClO₄)₂, M²⁺ = Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺ and Cd²⁺, simplified as MCPs) are a series of energetic primary explosives, among which ZnCP and CdCP are already applied in civilian/military fields. The six MCPs possess similar structures but demonstrate different energetic performances in their decomposition, which are obviously determined by their different central metals. Here, we apply DFT and Car-Parrinello molecular dynamics (CPMD) to understand the electronic structures and decomposition pathways of the MCPs. Based on the results, the crystal MCPs with larger electronic band gaps show lower impact sensitivity. However, the friction sensitivity of MCPs is dominated by the strength of their intermolecular O⋯H interactions. In the CPMD simulations, we obtained a different conclusion from the traditional viewpoint, where the decomposition is spontaneous from the cleavage of M-N bonds. Indeed, there are two stages in the decomposition of the MCPs, based on our calculations: (I) nonspontaneous 3-step departure of the CHZ groups and (II) spontaneous exoergic decomposition pathways of the CHZ groups triggered by the transfer of O/H radicals. Our study provides a systematic study of the MCP family, which also affords a new route for understanding the relationship between the energetic properties and electronic structures of energetic metal complexes.