Tailoring Titanium Carbide Clusters for New Materials: from Met-Cars to Carbon-Doped Superatoms.

Tailoring materials with prescribed properties and regular structures is a critical and challenging research topic. Early transition metals were found to form supermagic M8C12 metallocarbohedrenes (Met-Cars); however, stable metal carbides are not limited to this common stoichiometry. Utilizing self-developed deep-ultraviolet laser ionization mass spectrometry, here, we report a strategy to generate new titanium carbides by reacting pure Tin clusters with acetylene. Interestingly, two products corresponding to Ti17C2 and Ti19C10 exhibit superior abundances in addition to the Ti8C12 Met-Cars. Using global-minimum search, the structures of Ti17C2 and Ti19C10 are determined to be an ellipsoidal D4d and a rod-shaped D5h geometry, respectively, both with carbon-capped Ti4C moieties and superatomic features. We illustrate the electronic structures and bonding nature in these carbon-doped superatoms concerning their enhanced stability and local aromaticity, shedding light on a new class of metal-carbide nanomaterials with atomic precision.

Enhancing Solar Steam Generation of Hydrogels via Silver Nanoparticle-Doped Cellulose Nanofibers.

Solar steam generation (SSG) is regarded as an efficient approach for harnessing solar energy to purify polluted or saline water. Herein, we demonstrate a hydrogel composed of cellulose nanofibers (CNFs), polyethylenimine (PEI), and reduced graphene oxide (rGO) that functions as an independent solar steam generator, which shows enhanced solar water evaporation efficiency by incorporating silver nanoparticles (AgNPs). It presented that the presence of AgNPs increases the photothermal conversion efficiency and thermal conductivity of the evaporator and reduces the enthalpy of evaporation. As a result, an outstanding water evaporation rate of 3.62 kg m-2 h-1 and a photothermal conversion efficiency of 96.25% are successfully obtained under one sun illumination. Also, the resulting hydrogel exhibits exceptional mechanical properties, as well as outstanding desalination and salt-resistant abilities during prolonged seawater desalination. In oil/water mixtures, the evaporation of the hydrogel decreases to 2.94 kg m-2 h-1, owing to the oil layer barrier. This work paves a reference approach to produce easily addressed cellulose nanofiber (CNF)-based hydrogel evaporators with significantly enhanced evaporation rates.

Dehydrogenation of diborane on small Nbn+ clusters.

The reactivity of Nbn+ (1 ≤ n ≤ 21) clusters with B2H6 is studied by using a self-developed multiple-ion laminar flow tube reactor combined with a triple quadrupole mass spectrometer (MIFT-TQMS). The Nbn+ clusters were generated by a magnetron sputtering source and reacted with the B2H6 gas under fully thermalized conditions in the downstream flow tube where the reaction time was accurately controlled and adjustable. The complete and partial dehydrogenation products NbnB1-4+ and NbnB1-4H1,2,4+ were detected, indicative of the removal of H2 and likely BHx moieties. Interestingly, these NbnB1-4+ and NbnB1-4H1,2,4+ products are limited to 3 ≤ n ≤ 6, suggesting that the small Nbn+ clusters are relatively more reactive than the larger Nbn>6+ clusters under the same conditions. By varying the B2H6 gas concentrations and the reactant doses introduced into the flow tube, and by changing the reaction time, we performed a detailed analysis of the reaction dynamics in combination with the DFT-calculated thermodynamics. It is demonstrated that the lack of cooperative active sites on the Nb1+ cations accounts for the weakened dehydrogenation efficiency. Nb2+ forms partial dehydrogenation products at a faster rate. In contrast, the Nbn>6+ clusters are subject to more flexible vibrational relaxation which disperse the energy gain of B2H6-adsorption and thus are unable to overcome the energy barriers for subsequent hydrogen atom transfer and H2 release.

To What Extent Do Iodomethane and Bromomethane Undergo Analogous Reactions?

Iodomethane and bromomethane (CH3I/CH3Br) are common chemicals, but their chemistry on nanometals is not fully understood. Here, we analyze the reactivity of Rhn+ (n = 3-30) clusters with halomethanes and unveil the spin effect and concentration dependence in the C-H and C-X bond activation. It is found that the reactions under halomethane-rich conditions differ from those under metal-rich conditions. Both CH3I and CH3Br undergo similar dehydrogenation on the Rhn+ clusters in the presence of small quantity reactants; however, different reactions are observed in the presence of sufficient CH3I/CH3Br, showing dominant Rh(CH3Br)x+ (x = 1-4) products but a series of RhnCxHyIz+ species (x = 1-4, y = 1-12, and z = 1-5) pertaining to H2, HI, or CH4 removal. Density functional theory calculations reveal that the dehydrogenation and demethanation of CH3Br are relatively less exothermic and will be deactivated by sufficient gas collisions if helium cooling takes away energy immediately; instead, the successive adsorption of CH3Br gives rise to a series of Rh(CH3Br)x+ species with accidental C-Br bond dissociation.

Unusually High-Spin Fe12C12- Metallo-Carbohedrene Clusters.

Ferromagnets constructed from nanometals of atomic precision are important for innovative advances in information storage, energy conversion, and spintronic microdevices. Considerable success has been achieved in designing molecular magnets, which, however, are challenging in preparation and may suffer from drawbacks on the incompatibility of high stability and strong ferromagnetism. Utilizing a state-of-the-art self-developed mass spectrometer and a homemade laser vaporization source, we have achieved a highly efficient preparation of pure iron clusters, and here, we report the finding of a strongly ferromagnetic metal-carbon cluster, Fe12C12-, simply by reacting the Fen- clusters with acetylene in proper conditions. The unique stability of this ferromagnetic Fe12C12- cluster is rooted in a plumb-bob structure pertaining to Jahn-Teller distortion. We classify Fe12C12- as a new member of metallo-carbohedrenes and elucidate its structural stability mechanism as well as its soft-landing deposition and magnetization measurements, providing promise for the exploration of potential applications.

The s-p Nonhybrid Nature Causes Adaptive Superatomic States of Bismuth Clusters.

We report a joint experimental and theoretical study on the stability and reactivity of Bin + (n=5-33) clusters. The alternating odd-even effect on the reaction rates of Bin + clusters with NO is observed, and Bi7 + finds the most inertness. First-principles calculation results reveal that the lowest energy structures of Bi6-9 + exhibit quasi-spherical geometry pertaining to the jellium shell model; however, the Bin + (n≥10) clusters adopt assembly structures. The prominent stability of Bi7 + is associated with its highly symmetric structure and superatomic states with a magic number of 34e closed shell. For the first time, we demonstrate that the unique s-p nonhybrid feature in bismuth rationalizes the stability of Bi6-9 + clusters within the jellium model, by filling the 6s electrons into the superatomic orbitals (forming "s-band"). Interestingly, the stability of 18e "s-band" coincides with the compact structure for Bin + at n≤9 but assembly structures for n≥10, showing an accommodation of the s electrons to the geometric structure. The atomic p-orbitals also allow to form superatomic orbitals at higher energy levels, contributing to the preferable structures of tridentate binding units. We illustrate the s-p nonhybrid nature accommodates the structure and superatomic states of bismuth clusters.

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

Well-resolved Nbn- clusters are produced and reacted with ethene and propene via a downstream flow tube reactor. Interestingly, the Nbn- 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-dz2 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.

Design of Closed-Loop Control Schemes Based on the GA-PID and GA-RBF-PID Algorithms for Brain Dynamic Modulation.

Neurostimulation can be used to modulate brain dynamics of patients with neuropsychiatric disorders to make abnormal neural oscillations restore to normal. The control schemes proposed on the bases of neural computational models can predict the mechanism of neural oscillations induced by neurostimulation, and then make clinical decisions that are suitable for the patient's condition to ensure better treatment outcomes. The present work proposes two closed-loop control schemes based on the improved incremental proportional integral derivative (PID) algorithms to modulate brain dynamics simulated by Wendling-type coupled neural mass models. The introduction of the genetic algorithm (GA) in traditional incremental PID algorithm aims to overcome the disadvantage that the selection of control parameters depends on the designer's experience, so as to ensure control accuracy. The introduction of the radial basis function (RBF) neural network aims to improve the dynamic performance and stability of the control scheme by adaptively adjusting control parameters. The simulation results show the high accuracy of the closed-loop control schemes based on GA-PID and GA-RBF-PID algorithms for modulation of brain dynamics, and also confirm the superiority of the scheme based on the GA-RBF-PID algorithm in terms of the dynamic performance and stability. This research of making hypotheses and predictions according to model data is expected to improve and perfect the equipment of early intervention and rehabilitation treatment for neuropsychiatric disorders in the biomedical engineering field.

Plasma-Assisted Dinitrogen Activation on Small Cobalt Clusters: Co4 N9 + with Enhanced Stability.

We have performed a study on the accommodation of nitrogen doping toward superatomic states of transition metal clusters. By reacting cobalt clusters with N2 in the presence of plasma radiation, a large number of odd-nitrogen clusters were observed, typically Co3 N2m-1 + (m=1-5) and Co4 N2m-1 + (m=1-6) series, showing N≡N bond cleavage in the mild plasma atmosphere. Interestingly, the Co3 N7 + , Co4 N9 + , and Co5 N9 + clusters exhibit prominent mass abundances. First-principles calculation results elucidate the stability of the diverse cobalt nitride clusters and find unique stability of Co4 N9 + with a swallow-kite structure of which four coordinated N2 molecules causes a significantly enlarged HOMO-LUMO gap, while the single N atom doping gives rise to superatomic states of 1S2 1P3 ||1D0 . We reveal an efficient dinitrogen activation strategy by reacting multiple N2 molecules with cobalt clusters under a plasma atmosphere.

An oxygen-passivated vanadium cluster [V@V10O15]- with metal-metal coordination produced by reacting Vn- with O2.

Vanadium cluster anions are highly reactive making the preparation of pure Vn- and the observation of their reactivity extremely challenging. Herein, well-resolved anionic Vn- clusters are prepared enabling an in-depth study on their reactions with O2 in the gas phase. While pure metal clusters of a magic number are not identified due to the strong V-O bonding, interestingly an unexpected oxide V11O15- was experimentally observed in surviving O2 etching reactions. First-principles theory calculations indicate that V11O15- possesses a body-centered pentagonal prism structure (D5h, ), with the V@V10 core fully protected by 15 oxygen bridges. Such an oxygen-protected metal cluster [V@V10O15]- exhibits typical superatom orbital features pertaining to the V@V10 core which shows effective metal-metal coordination bonding. Meanwhile, the high stability of [V@V10O15]- is reinforced by the V-O-V conjugation interactions which help to maintain the structural integrity, resulting in 3D inorganic aromaticity. This finding of such an oxygen-passivated superatom cluster sheds light on the bonding nature in ligand-protected metal clusters via wet synthesis.

Cyclotrimerization of Acetylene on Clusters Con+/Fen+/Nin+(n = 1-16).

Cyclotrimerization of acetylene to benzene has attracted significant interest, but the role of geometric and electronic effects on catalytic chemistry remains unclear. To fully elucidate the mechanism of catalytic acetylene-to-benzene conversion, we have performed a gas-phase reaction study of the Fen+, Con+, and Nin+ (n = 1-16) clusters with acetylene utilizing a customized mass spectrometer. It is found that their reactions with acetylene are initiated by C2H2 molecular adsorption and allow for dominant dehydrogenation with the relatively low partial pressure of the acetylene gas. However, at high acetylene concentrations, the cyclotrimerization in Mn+ + 3C2H2 (M = Fe, Co, Ni) becomes the dominant reaction channel. We demonstrate theoretically the favorable thermodynamics and reaction dynamics leading to the formation of the M+(C6H6) products. The results are discussed in terms of a cluster-catalyzed multimolecule synergistic effect and the cation-π interactions.

Reactivity of Cobalt Clusters Con±/0 with Dinitrogen: Superatom Co6+ and Superatomic Complex Co5N6.

We report a joint experimental and theoretical study on the reactions of cobalt clusters (Con±/0) with nitrogen using the customized reflection time-of-flight mass spectrometer combined with a 177.3 nm deep-ultraviolet laser. Comparing to the behaviors of neutral Con (n = 2-30) and anionic Con- clusters (n = 7-53) which are relatively inert in reacting with nitrogen in the fast-flow tube, Con+ clusters readily react with nitrogen resulting in adducts of one or multiple N2 except Co6+ which stands firm in the reaction with nitrogen. Detailed quantum chemistry calculations, including the energetics, electron occupancy, and orbital analysis, well-explained the reasonable reactivity of Con+ clusters with nitrogen and unveiled the open-shell superatomic stability of Co6+ within a highly symmetric (D3d) structure. The D3d Co6+ bears an electron configuration of a half-filled superatomic 1P orbital (i.e., 1S21P3||1D0), a large α-highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, symmetric multicenter bonds, and reasonable electron delocalization pertaining to metallic aromaticity. Topology analysis by atom-in-molecule illustrates the interactions between Con+ and N2 corresponding to covalent bonds, but the Co-N interactions in cationic Co2+N2 and Co6+N2 clusters are apparently weaker than those in the other systems. In addition, we identify a superatomic complex Co5N6+ which exhibits similar frontier orbitals as the naked Co5+ cluster, but the alpha HOMO-LUMO gap is nearly double-magnified, which is consistent with the high-abundance peak of Co5N6+ in the experimental observation. The enhanced stability of such a ligand-coordinated superatomic complex Co5N6+, along with the superatom Co6+ with aromaticity, sheds light on special and general superatoms.

Healable, Phase-Selective, and White-Light-Emitting Titania Based Hybrid Lanthanide-Doped Metallogels.

Self-healing and tough gels with intriguing white-light emission, prepared by lanthanide metal ions, are highly desirable and remain a challenging topic. In this study, we present the preparation of a hybrid gel that contains poly(methyl methacrylate)/polyacrylic acid (PMMA/PAA) as the organic network and titania as the inorganic network, which are interpenetrating and linked by lanthanide metal ions. Interestingly, the gelation process for the organic phase allows for the efficient phase separation of the water-THF mixture (separation efficiency: >88%), either by the heating-cooling process or by the room temperature gelation that originated from xerogels. The as-prepared gels are self-healing and robust, based on the hybrid networks and dynamic coordination interactions. Specifically, the hybrid gels exhibit various colors of luminescence, depending on either the stoichiometric ratio of Eu3+ and Tb3+ or the excitation wavelengths. Upon excitation by the 365 nm light, the hybrid gel with Eu3+/Tb3+ ions (molar ratio 1:30) demonstrates a white-light emission color. The results also show that the gels prepared by only Eu3+ and Tb3+ possess different morphologies, surface areas, and contact angles. This work presents, for the first time, the crucial role of lanthanide ions for preparing a robust, self-healing hybrid gel with interpenetrating networks in the polymerization process, and the resulting hydrophobic surfaces are related to the phase-selective ability of the gels.

Reactivity of Cobalt Clusters Con±/0 with Ammonia: Co3+ Cluster Catalysis for NH3 Dehydrogenation.

A customized reflection time-of-flight (Re-TOF) mass spectrometer combined with a 177 nm deep-ultraviolet laser has enabled us to observe well-resolved cobalt clusters Con±/0 and perform a comprehensive study of their reactivity with ammonia (NH3). The anions Con- are found to be inert, the neutrals allow the adsorption of multiple NH3 molecules, while the cationic Con+ clusters readily react with NH3 giving rise to dehydrogenation. However, incidental dehydrogenation of NH3 on Con+ is only observed for n ≥ 3. The dramatic charge- and size-dependent reactivities of Con±/0 clusters with NH3 are studied by the density functional theory (DFT)-calculation results of energetics, density of states, orbital interactions, and reaction dynamics. We illustrate the dehydrogenation from two NH3 molecules, where a significantly reduced transition-state energy barrier is found pertaining to the dimolecular co-catalysis effect. The reactivity of Co3+ with NH3 is illustrated showing effective catalysis for N-H dissociation to produce hydrogen applicable for designing ammonia fuel cells.

Furthering the reaction mechanism of cationic vanadium clusters towards oxygen.

Vanadium is a polyvalent metallic element. The fact that V-O bears a much larger bond energy than the V-V metal bond challenges the preparation of pure vanadium clusters and the observation of their reactions with oxygen-containing chemicals. Utilizing a customized reflection time-of-flight mass spectrometer (Re-TOFMS), here we have prepared well-resolved small and large cationic vanadium clusters Vn+ (n < 30), and we conducted a comprehensive study on their reactivity with oxygen. It is illustrated that cationic Vn+ clusters readily react with oxygen leading to the production of both etched building blocks and oxygen-rich VnOm+ (n < m) species profiting from the ion-molecule attraction and hence increased collisional cross section. Furthermore, DFT-based energy calculations reveal that the oxygen-addition reactions are thermodynamically and kinetically favorable pathways. Also the generalized charge decomposition analysis (GCDA) illustrates that the ion-molecule charge-transfer interactions initiate the incorporation of vanadium oxides. This finding of synchronous channels of both etching and growth of vanadium clusters clarifies the reactivity of Vn+ clusters with oxygen, interprets the readily formed VnOm+ clusters within the classification of the CxAyBz series (A = VO2, B = VO3, C = VO), and enriches the understanding of the industrial chemistry of vanadium.

Correlation between serum interleukin-6 level and type 1 diabetes mellitus: A systematic review and meta-analysis.

OBJECTIVE: This report aimed to explore the association between the change of circulating interleukin-6 (IL-6) in patients and the development of type 1 diabetes mellitus (T1DM). METHODS: Four databases (PubMed, CNKI, WanFang and Civip) were used to search and list all clinical case-control studies about serum IL-6 level in T1DM patients between Jan 1, 2000 and Aug 31, 2016. RESULTS: A total of 20 case-control studies with 1238 T1DM patients and 742 healthy controls were included in this study. Compared to healthy controls, the serum content of IL-6 in patients with T1DM was significantly greater (overall: SMD, 1.49; 95% CI, 1.04 to 1.93; p<0.001), and notably increased in all subgroup with different age, ethnic and disease duration (all p<0.001). Furthermore, the analysis in subgroup exhibited that serum levels of IL-6 in the age greater than 20-year old (SMD, 1.64; 95% CI, 0.57-2.71; p<0.001), the diseased duration among 0-10years (SMD, 2.43; 95% CI, 1.42-3.44; p<0.001) and the sorted American group (SMD, 1.68; 95% CI, 0.85-2.51; p<0.001) were higher than those in control groups. CONCLUSIONS: Patients with T1DM were found to be linked to elevated level of serum IL-6, which the age, ethnic and disease durations in T1DM patients had no effect on the serum IL-6 levels for promoting diabetes mellitus.

Cyclodextrin-Assisted Two-Component Sonogel for Visual Humidity Sensing.

In this work, two naphthalimide-based compounds, 1a and 1b, have been designed and synthesized. Both compounds can form stable two-component gels in n-propanol or n-butanol upon addition of α-cyclodextrin (α-CD) followed by sonication at room temperature. Interestingly, the 1a/α-CD gel is thixotropic and very sensitive to water. Addition of a small amount of water induces rapid gel collapse, allowing further development of the gel as a visual relative humidity sensor. Specificity of the sensor has been confirmed using several approaches, such as scanning electron microscopy and fluorescence, Fourier transform infrared, and 1H NMR spectroscopy experiments. The results show that α-CD acts as a junction for the assembly of 1a or 1b through hydrogen bonding between hydroxyl and amide groups. Upon addition of water, α-CD interacts with the adamantane group of 1a via an incomplete host-guest encapsulation, resulting in the dissociation of the hydrogen-bonding-assisted two-component assembly, accompanied by gel collapse.

Fluorescent and Electrochemical Supramolecular Coordination Polymer Hydrogels Formed from Ion-Tuned Self-Assembly of Small Bis-Terpyridine Monomer.

Herein, ditopic ligand DTA comprised of terpyridine and acetylene segments with only one aromatic π-conjugated building block was designed and synthesized. Driven by metal-ligand coordination interactions, we presented that the use of metal salts can direct the self-assembly of DTA in the generation of fluorescent and electrochemical polymers that entrapped water to form ambidextrous hydrogels. These were characterized by several approaches including fluorescent titrations, UV-vis, circular dichroism, and X-ray diffraction spectra as well as scanning electron microscopy and transmission electron microscopy experiments. DTA can selectively recognize Zn2+ ions and gelate water in the presence of ZnC6H10O6 (zinc lactate), giving Zn2+-specific fluorescent metallogels. Otherwise, DTA/Cu(OAc)2 forms nonfluorescent, electrochemical, and chiral hydrogel that responds to multiple stimuli such as heat, light, shearing, electrolysis, and reducer. The ion-controlled gelation approach, morphology, rheology, as well as fluorescent and chiroptical properties of DTA was studied in detail. Hence, our work demonstrated for the first time the crucial role of metal salts in the supramolecular polymerization and corresponding properties, in which symmetry breaking played an important role for the dynamic assembly difference.

Tunable multicolor emissions in a monocomponent gel system by varying the solvent, temperature and fluoride anion.

The facile tuning of the fluorescent properties of organogels is highly desirable for optical switches, light-emitting diodes, chemosensors and bioprobes. The design of organic molecules with multiple emission colors but only one molecular platform remains challenging. Herein, a new cholesterol-based organogelator N1 containing D-A pairs (salicylaldehyde and naphthalimide units) was designed. We successfully obtained multiple solvent-tuned emission colors in both the solution and gel states using a unimolecular platform. Moreover, the effects of the solvent on the gel morphology, rheology and anion-responsive properties were studied. Finally, we showed that the gel in benzene displayed reversible thermochromic properties with changes in emission color from yellow-green to red. Several experiments suggested that a short-distance and ordered array of the D-A pairs facilitated the efficient intermolecular electron transfer of the fluorophores.

Selective and visual Ca(2+) ion recognition in solution and in a self-assembly organogel of the terpyridine-based derivative triggered by ultrasound.

A new kind of terpyridine-based Ca(2+) sensor TS was designed and studied based on the internal charge transfer (ICT). In the diluted solution state, TS sensed Ca(2+) and Mg(2+) ions among test ions via an "off-on" approach as seen from fluorescence spectra of test ions. Moreover, TS was able to form stable fluorescent gels in organic solvents accelerated by ultrasound, indicating the ultrasound responsive properties of TS molecules. The S-gel of TS could be successfully used to selectively recognize Ca(2+) through fluorescent emission color and morphological changes, which was different from that of the solution state. It was predicated that the competition between the self-assembly of TS molecules and the host­guest interaction of TS with Ca(2+) or Mg(2+) was responsible for the sensing properties. To the best of our knowledge, this is the first example that organogels could selectively sense Ca2+ ions.