Synthesis of Fullerenes from a Nonaromatic Chloroform through a Newly Developed Ultrahigh-Temperature Flash Vacuum Pyrolysis Apparatus.

The flash vacuum pyrolysis (FVP) technique is useful for preparing curved polycyclic aromatic compounds (PAHs) and caged nanocarbon molecules, such as the well-known corannulene and fullerene C60. However, the operating temperature of the traditional FVP apparatus is limited to ~1250 °C, which is not sufficient to overcome the high energy barriers of some reactions. Herein, we report an ultrahigh-temperature FVP (UT-FVP) apparatus with a controllable operating temperature of up to 2500 °C to synthesize fullerene C60 from a nonaromatic single carbon reactant, i.e., chloroform, at 1350 °C or above. Fullerene C60 cannot be obtained from CHCl3 using the traditional FVP apparatus because of the limitation of the reaction temperature. The significant improvements in the UT-FVP apparatus, compared to the traditional FVP apparatus, were the replacement of the quartz tube with a graphite tube and the direct heating of the graphite tube by impedance heating instead of indirect heating of the quartz tube using an electric furnace. Because of the higher temperature range, UT-FVP can not only synthesize fullerene C60 from single carbon nonaromatic reactants but sublimate some high-molecular-weight compounds to synthesize larger curved PAHs in the future.

Highly Robust but Surface-Active: An N-Heterocyclic Carbene-Stabilized Au25 Nanocluster.

Surface organic ligands play a critical role in stabilizing atomically precise metal nanoclusters in solutions. However, it is still challenging to prepare highly robust ligated metal nanoclusters that are surface-active for liquid-phase catalysis without any pre-treatment. Now, an N-heterocyclic carbene-stabilized Au25 nanocluster with high thermal and air stabilities is presented as a homogenous catalyst for cycloisomerization of alkynyl amines to indoles. The nanocluster, characterized as [Au25 (i Pr2 -bimy)10 Br7 ]2+ (i Pr2 -bimy=1,3-diisopropylbenzimidazolin-2-ylidene) (1), was synthesized by direct reduction of AuSMe2 Cl and i Pr2 -bimyAuBr with NaBH4 in one pot. X-ray crystallization analysis revealed that the cluster comprises two centered Au13 icosahedra sharing a vertex. Cluster 1 is highly stable and can survive in solution at 80 °C for 12 h, which is superior to Au25 nanoclusters passivated with phosphines or thiols. DFT computations reveal the origins of both electronic and thermal stability of 1 and point to the probable catalytic sites. This work provides new insights into the bonding capability of N-heterocyclic carbene to Au in a cluster, and offers an opportunity to probe the catalytic mechanism at the atomic level.

Assembly of a Wheel-Like Eu24 Ti8 Cluster under the Guidance of High-Resolution Electrospray Ionization Mass Spectrometry.

A building blocks strategy is an effective approach for constructing the large molecular systems. Herein, we demonstrate that high-resolution electro-spray ionization mass spectrometry (HRESI-MS) provides an effective chance to insight the assemble process of the building blocks and guides the construction of high-nuclearity metal clusters on the basis of the reaction of Ti(Oi Pr)4 , Eu(acac)3 , and salicylic acid. The time-dependent HRESI-MS indicates that not only a Eu3 Ti building block can be formed, but that it can further assemble into a Eu24 Ti8 compound. Temperature-dependent HRESI-MS reveals that increase of the reaction temperature favors the formation and crystallization of the stable Eu24 Ti8 structure. Single-crystal structural analysis demonstrates that the Eu24 Ti8 has a wheel-like structure with diameter of ca. 4.1 nm and is the highest nuclearity lanthanide-titanium oxo cluster reported to date.

Highly Sensitive and Automated Surface Enhanced Raman Scattering-based Immunoassay for H5N1 Detection with Digital Microfluidics.

Digital microfluidics (DMF) is a powerful platform for a broad range of applications, especially immunoassays having multiple steps, due to the advantages of low reagent consumption and high automatization. Surface enhanced Raman scattering (SERS) has been proven as an attractive method for highly sensitive and multiplex detection, because of its remarkable signal amplification and excellent spatial resolution. Here we propose a SERS-based immunoassay with DMF for rapid, automated, and sensitive detection of disease biomarkers. SERS tags labeled with Raman reporter 4-mercaptobenzoic acid (4-MBA) were synthesized with a core@shell nanostructure and showed strong signals, good uniformity, and high stability. A sandwich immunoassay was designed, in which magnetic beads coated with antibodies were used as solid support to capture antigens from samples to form a beads-antibody-antigen immunocomplex. By labeling the immunocomplex with a detection antibody-functionalized SERS tag, antigen can be sensitively detected through the strong SERS signal. The automation capability of DMF can greatly simplify the assay procedure while reducing the risk of exposure to hazardous samples. Quantitative detection of avian influenza virus H5N1 in buffer and human serum was implemented to demonstrate the utility of the DMF-SERS method. The DMF-SERS method shows excellent sensitivity (LOD of 74 pg/mL) and selectivity for H5N1 detection with less assay time (<1 h) and lower reagent consumption (∼30 µL) compared to the standard ELISA method. Therefore, this DMF-SERS method holds great potentials for automated and sensitive detection of a variety of infectious diseases.

Sniffing with mass spectrometry.

Gaseous compounds are usually on-line detectable on sensors. The limitations of conventional sensors are suffering from incapability for exactly identifying multiple components as well as incompatibility to possible toxicants in every odor sample. Herein, we discuss an inlet modification to the laboratory standard mass spectrometer, inspired by the sensitive olfactory systems of animals, for direct sniffing, established by connecting a mini pump to the nebulizer gas tubing. The modified mass spectrometry method-sniffing-mass spectrometry (sniffing-MS)-can acquire detailed fingerprint spectra of mixed odors and shows high tolerance to toxicants. Furthermore, the method has a low limit of detection in the order of parts per trillion and is a 'sampling-free' technique for analyzing various gaseous compounds simultaneously, thus offering versatility for smelling daily commodities, tracking diffusion, and locating position of odors. Sniffing-MS can mimic or even surpass the olfaction of animals and is applicable for analyzing gaseous/volatile compounds, especially those polar compounds, in a simple manner depending on the intrinsic molecular mass-to-charge ratio.

Assembly of silver Trigons into a buckyball-like Ag180 nanocage.

Buckminsterfullerene (C60) represents a perfect combination of geometry and molecular structural chemistry. It has inspired many creative ideas for building fullerene-like nanopolyhedra. These include other fullerenes, virus capsids, polyhedra based on DNA, and synthetic polynuclear metal clusters and cages. Indeed, the regular organization of large numbers of metal atoms into one highly complex structure remains one of the foremost challenges in supramolecular chemistry. Here we describe the design, synthesis, and characterization of a Ag180 nanocage with 180 Ag atoms as 4-valent vertices (V), 360 edges (E), and 182 faces (F)--sixty 3-gons, ninety 4-gons, twelve 5-gons, and twenty 6-gons--in agreement with Euler's rule V - E + F = 2. If each 3-gon (or silver Trigon) were replaced with a carbon atom linked by edges along the 4-gons, the result would be like C60, topologically a truncated icosahedron, an Archimedean solid with icosahedral (Ih) point-group symmetry. If C60 can be described mathematically as a curling up of a 6.6.6 Platonic tiling, the Ag180 cage can be described as a curling up of a 3.4.6.4 Archimedean tiling. High-resolution electrospray ionization mass spectrometry reveals that {Ag3}n subunits coexist with the Ag180 species in the assembly system before the final crystallization of Ag180, suggesting that the silver Trigon is the smallest building block in assembly of the final cage. Thus, we assign the underlying growth mechanism of Ag180 to the Silver-Trigon Assembly Road (STAR), an assembly path that might be further employed to fabricate larger, elegant silver cages.

Multifunctional Triple-Decker Inverse 12-Metallacrown-4 Sandwiching Halides.

A family of six triple-decker complexes, {(MX)2[(pz)4]3} (Hpz = 4-nitropyrazole, MX = NaCl, 1; NaBr, 2; NaI, 3; KCl, 4; KBr, 5, and KI, 6), exhibiting inclusion of halides into inverse 12-metallacrown-4 [inv-(12-MCCu(I),pz-4)] array has been realized. Single-crystal X-ray crystallography of each compound reveals a common structural feature consisting of four CuI ions bonded by four pz to form a square metallomacrocycle comprising four metal centers and eight N atoms, thus giving an inv-[12-MCCu(I),pz-4] motif. Two halides are sandwiched by three inv-[12-MCCu(I),pz-4] to form triple-deckers that are further extended in an offset stacking mode by ligand-unsupported cuprophilicity interactions to form a one-dimensional chain structure. Halides are attached to six CuI centers with weak CuI···halogen interaction, resembling anion templates. High-resolution electrospray ionization mass spectrometry reveals that the predominant fragments corresponding to a half of the triple-decker structures of 1-3 exist in solution. Compounds 4, 5, and 6 showed excellent electrocatalytic activities toward the reduction of nitrite and can also be used as selective "turn-off" sensors for Ag(I) in water. The present results will be helpful for the future design and synthesis of functional inverse metallacrowns and their multiple-decker complexes.

High-Nuclear Organometallic Copper(I)-Alkynide Clusters: Thermochromic Near-Infrared Luminescence and Solution Stability.

Cu(CF3 COO)2 reacts with tert-butylacetylene (tBuC≡CH) in methanol in the presence of metallic copper powder to give two air-stable clusters, [CuI15 (tBuC≡C)10 (CF3 COO)5 ]⋅tBuC≡CH (1) and [CuI16 (tBuC≡C)12 (CF3 COO)4 (CH3 OH)2 ] (2). The assembly process involves in situ comproportionation reaction between Cu2+ and Cu0 and the formation of two different clusters is controlled by reactants concentration. The clusters consist of Cu15 and Cu16 cores co-stabilized by strong by σ- and π-bonded tert-butylethynide and CF3 COO- (together with methanol molecule in 2). Their stabilities in solution were confirmed using electrospray ionization mass spectrometry in which the cluster core remains intact for 1 in chloroform and acetone, and for 2 in acetonitrile. Strong thermochromic luminescence in the near infrared (NIR) region was observed in the solid-state. Of particular interest, the emission maximum of 1 is red-shifted from 710 nm at 298 K to 793 nm at 93 K, along with a 17-fold fluorescence enhancement. In contrast, 2 exhibits red shift from 298 to 123 K followed by blue shift from 123 to 93 K. The emission wavelength was correlated with the structural parameters using variable-temperature X-ray single-crystal analyses. The rich cuprophilic interaction plays a significant role in the formation of 3 LMCT (tBuC≡C→Cux ) excited state mixed with cluster-centered (3 CC) characters, which can be considerably influenced by temperature, leading to thermochromic luminescence. The present work provides 1) a new synthetic protocol for the high-nuclear CuI -alkynyl clusters; 2) a comprehensive insight into the mechanism of thermochromic luminescence; 3) unusual emissive materials with the characters of NIR and thermochromic luminescence simultaneously.

Studying mass spectrometric behaviors of {Au6 Ag2 (C)[PPh2 (4-CH3 -Py)]6 }(BF4 )4 and {Au8 [(PPh3 )2 O]3 (PPh3 )2 }(NO3 )2 by electrospray time-of-flight mass spectrometry and electrospray ion trap mass spectrometry.

RATIONALE: Mass spectrometry (MS) has been recognized as a powerful technique to detect accurate chemical information about metal clusters. Maintaining metal clusters intact, which is a great challenge in MS analysis, was achieved in this work by choosing a suitable mass analyzer and carefully optimizing analysis parameters. METHODS: Electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) and electrospray ion trap mass spectrometry (ESI-IT-MS) were applied to characterize the synthesized ligand-protected metal clusters [Au6 Ag2 (C)(L(1) )6 ](BF4 )4 (L(1)  = 2-diphenylphosphanyl-4-methylpyridine) (1) and [Au8 (L(2) )3 (L(3) )2 ](NO3 )2 (L(2)  = bis(2-diphenylphosphinophenyl)ether, L(3)  = triphenyl-phosphane) (2). Three kinds of buffer gas (helium, mass: 2; nitrogen, mass: 28; argon, mass: 40) and various radiofrequency (RF) amplitudes (from 70 to 330) were chosen to study the fragmentation rate during the "collision cooling" process in the ion trap analyzer. RESULTS: In the ESI-TOF-MS analysis, metal clusters 1 and 2 were mainly observed as intact clusters, which were Au6 Ag2 (C)(L(1) )6 (BF4 )2 (2+) , Au6 Ag2 (C)(L(1) )6 (BF4 )(3+) , Au6 Ag2 (C)(L(1) )6 (4+) for 1 and Au8 (L(2) )3 (L(3) )2 (2+) for 2. While, in the ESI-IT-MS analysis, only fragments could be found, such as Au6 Ag(C)(L(1) )6 (BF4 )(2+) , Au6 (C)(L(1) )6 (2+) , Au5 Ag(C)(L(1) )4 (2+) , Au6 Ag(C)(L(1) )6 (3+) , Au(L(1) )(+) for 1 and Au8 (L(2) )3 (L(3) )(2+) , Au8 (L(2) )3 (2+) , Au6 (L(2) )3 (2+) for 2. It is obvious that the two kinds of mass analyzers caused different MS behaviors of metal clusters. In the ion trap (IT) mass analyzer, particularly, "collision cooling" was contributing to further dissociation of fragile compounds, in which a higher RF amplitude and a larger mass buffer gas led to more fragmentation. CONCLUSION: In this work, intact metal clusters were obtained in ESI-TOF-MS, instead of ESI-IT-MS, in which the "collision cooling" process caused more cluster dissociation. It was concluded that the analyzer in ESI-TOF-MS is "softer" than that in ESI-IT-MS for metal clusters. Copyright © 2016 John Wiley & Sons, Ltd.

Hierarchical Assembly of a {Mn(II)15Mn(III)4} Brucite Disc: Step-by-Step Formation and Ferrimagnetism.

In search of functional molecular materials and the study of their formation mechanism, we report the elucidation of a hierarchical step-by-step formation from monomer (Mn) to heptamer (Mn7) to nonadecamer (Mn19) satisfying the relation 1 + Σn6n, where n is the ring number of the Brucite structure using high-resolution electrospray ionization mass spectrometry (HRESI-MS). Three intermediate clusters, Mn10, Mn12, and Mn14, were identified. Furthermore, the Mn19 disc remains intact when dissolved in acetonitrile with a well-resolved general formula of [Mn19(L)x(OH)y(N3)36-x-y](2+) (x = 18, 17, 16; y = 8, 7, 6; HL = 1-(hydroxymethyl)-3,5-dimethylpyrazole) indicating progressive exchange of N3(-) for OH(-). The high symmetry (R-3) Mn19 crystal structure consists of a well-ordered discotic motif where the peripheral organic ligands form a double calix housing the anions and solvent molecules. From the formula and valence bond sums, the charge state is mixed-valent, [Mn(II)15Mn(III)4]. Its magnetic properties and electrochemistry have been studied. It behaves as a ferrimagnet below 40 K and has a coercive field of 2.7 kOe at 1.8 K, which can be possible by either weak exchange between clusters through the anions and solvents or through dipolar interaction through space as confirmed by the lack of ordering in frozen CH3CN. The moment of nearly 50 NµB suggests Mn(II)-Mn(II) and Mn(III)-Mn(III) are ferromagnetically coupled while Mn(II)-Mn(III) is antiferromagnetic which is likely if the Mn(III) are centrally placed in the cluster. This compound displays the rare occurrence of magnetic ordering from nonconnected high-spin molecules.

Probing hydrogen bond energies by mass spectrometry.

Mass spectrometry with desorption electrospray ionization (DESI) is demonstrated to be useful for probing the strength of hydrogen bonding, exemplified by various complexes of benzothiazoles and carboxylic acids in the solid state. Efficiencies for fragmentation of the complexes, quantified by collision-induced dissociation (CID) technology, correspond well with energies of the hydrogen bonds of O-H···N and N-H···O bridging each pair of benzothiazole and carboxylic acid. Linear correlations (with correlation factors of 0.8953 and 0.9928) have been established for the calibration curves of normalized collision energy at 100% fragmentation rate vs the length between donor and acceptor (in the hydrogen bond of O-H···N) as well as the slope of the fragmentation efficiency curve vs the average length difference between O-H···N and N-H···O in the complex. The mechanism responsible for determination of the hydrogen bonds is proposed on the basis of the experiments starting from the mixtures of the complexes as well as labeling with deuterium. As a complement of previously available methods (e.g., X-ray diffraction analysis), expectably, the proposed mass spectrometric method seems to be versatile for probing hydrogen bond energies.

Pentagon-fused hollow fullerene in C78 family retrieved by chlorination.

C(78) is one of the most widely investigated higher fullerenes. Among its huge isomer family, only one non-IPR (IPR = isolated pentagon ring) cage, the C(2)-symmetric (#22010)C(78), was previously stabilized by endohedral derivatization. Here we report a new C(1)-symmetric non-IPR hollow isomer, (#23863)C(78), which was captured as (#23863)C(78)Cl(8) and then subjected to a regioselective substitution reaction with benzyl hydroperoxide to form (#23863)C(78)(OOCH(2)C(6)H(5))Cl(7). The structural connectivity of (#23863)C(78), which contains a pair of fused pentagons, was confirmed by single-crystal X-ray diffraction analysis of the (#23863)C(78)(OOCH(2)C(6)H(5))Cl(7) molecule, which shares the same fullerene core with (#23863)C(78)Cl(8); support for the structure is provided by comparable IR measurements and computation. Theoretical studies suggest that the differences in C-Cl bond length, intermediate stability, and steric effects of the involved molecules account for the chemical regioselectivity of the substitution reaction.

Desorption electrospray ionization mass spectrometry for monitoring the kinetics of Baeyer-Villiger solid-state organic reactions.

Desorption electrospray ionization mass spectrometry (DESI-MS) has been used for monitoring solid-state organic reaction in ambient air, specifically the Baeyer-Villiger (BV) type reaction involving the oxidation of ketones (benzophenone or deoxybenzoin) by m-chloroperbenzoic acid (m-CPBA) in solid-state. The DESI mass spectra obtained at regular intervals during the BV reaction processes are featured, with the amount of ester products increasing as those of ketone reactants decrease. Quantitative analyses of relative intensities of the product, made to quantify the reaction degree of typical solid-state organic reaction (SSOR), show a precision with RSDs of around 5% to 12%, though the RSDs for direct analysis of intensities of the reactant or the product in the solid-state are obviously larger. The kinetics of the Baeyer-Villiger type reactions in solid-state are shown to be dramatically different, in reaction rate, kinetic curve, as well as concentration dependence, from those of the same reactions taking place in solution.

Tailoring the optical property by a three-dimensional epitaxial heterostructure: a case of ZnO/SnO2.

Epitaxial growth, as a best strategy to attain a heterostructure with a well-defined and clean interface, usually takes place on a planar substrate. In this paper, using a ZnO/SnO2 core-shell heterostructure as an example, we demonstrate the possibility of establishing a three-dimensional epitaxial interface between two materials with different crystal systems for the first time and show possible tailoring optical properties by building the heteroepitaxial crystal interface. The characterization results of element mapping, high-resolution transmission electron microscopy, and selected area electric diffraction reveal that the as-prepared ZnO/SnO2 heterostructure has a tetrapod-like ZnO core and a SnO2 shell with 15-30 nm, and their special epitaxial relation is (010)SnO2//(010)ZnO and [100]SnO2//[0001]ZnO. Such three-dimensional epitaxy between the ZnO core and SnO2 shell is quite different from the usual planar epitaxy or three-dimensional epitaxy between materials having the same crystal structure. A rational model of such complicated epitaxy has been proposed through investigating the certain structural comparability between the wurtzite ZnO and rutile SnO2 crystals. The as-prepared T-ZnO/SnO2 epitaxial heterostructure exhibits unique luminescence properties in contrast with individual tetrapod ZnO and SnO2 nanostructures, in which the epitaxial interface induces new luminescence properties. This result may inspire great interest in exploring other complicated epitaxy systems and their potential applications in laser, gas sensor, solar energy conversion, photo catalysis, and nanodevices in the future.

Glow discharge growth of SnO2 nano-needles from SnH4.

Single crystalline SnO(2) nano-needles with length up to 6-7 microm and diameter less than 300 nm are synthesized on an Au-coating porous silicon substrate from SnH(4) source via a glow discharge process.