A few-layer covalent network of fullerenes.

The two natural allotropes of carbon, diamond and graphite, are extended networks of sp3-hybridized and sp2-hybridized atoms, respectively1. By mixing different hybridizations and geometries of carbon, one could conceptually construct countless synthetic allotropes. Here we introduce graphullerene, a two-dimensional crystalline polymer of C60 that bridges the gulf between molecular and extended carbon materials. Its constituent fullerene subunits arrange hexagonally in a covalently interconnected molecular sheet. We report charge-neutral, purely carbon-based macroscopic crystals that are large enough to be mechanically exfoliated to produce molecularly thin flakes with clean interfaces-a critical requirement for the creation of heterostructures and optoelectronic devices2. The synthesis entails growing single crystals of layered polymeric (Mg4C60)∞ by chemical vapour transport and subsequently removing the magnesium with dilute acid. We explore the thermal conductivity of this material and find it to be much higher than that of molecular C60, which is a consequence of the in-plane covalent bonding. Furthermore, imaging few-layer graphullerene flakes using transmission electron microscopy and near-field nano-photoluminescence spectroscopy reveals the existence of moiré-like superlattices3. More broadly, the synthesis of extended carbon structures by polymerization of molecular precursors charts a clear path to the systematic design of materials for the construction of two-dimensional heterostructures with tunable optoelectronic properties.

Electrochemical Doping of Two-Dimensional Superatomic Materials.

We report an electrochemical method for doping two-dimensional (2D) superatomic semiconductor Re6Se8Cl2 that significantly improves the material's electrical transport while retaining the in-plane and stacking structures. The electrochemical reduction induces the complete dissociation of chloride anions from the surface of each superatomic nanosheet. After the material is dehalogenated, we observe the electrical conductivity (σ) increases by two orders of magnitude while the 3D electron carrier density (n3D) increases by three orders of magnitude. In addition, the thermal activation energy (Ea) and electron mobility (µe) decrease. We conclude that we have achieved effective electron-doping in 2D superatomic Re6Se8Cl2, which significantly improves the electrical transport properties. Our work sets the foundation for electrochemically doping and tuning the transport properties of other 2D superatomic materials.

Superatom Regiochemistry Dictates the Assembly and Surface Reactivity of a Two-Dimensional Material.

The area of two-dimensional (2D) materials research would benefit greatly from the development of synthetically tunable van der Waals (vdW) materials. While the bottom-up synthesis of 2D frameworks from nanoscale building blocks holds great promise in this quest, there are many remaining hurdles, including the design of building blocks that reliably produce 2D lattices and the growth of macroscopic crystals that can be exfoliated to produce 2D materials. Here we report the regioselective synthesis of the cluster [trans-Co6Se8(CN)4(CO)2]3-/4-, a "superatomic" building block designed to polymerize and assemble into a 2D cyanometalate lattice whose surfaces are chemically addressable. The resulting vdW material, [Co(py)4]2[trans-Co6Se8(CN)4(CO)2], grows as bulk single crystals that can be mechanically exfoliated to produce flakes as thin as bilayers, with photolabile CO ligands on the exfoliated surface. As a proof of concept, we show that these surface CO ligands can be replaced by 4-isocyanoazobenzene under blue light irradiation. This work demonstrates that the bottom-up assembly of layered vdW materials from superatoms is a promising and versatile approach to create 2D materials with tunable physical and chemical properties.

Aspm sustains postnatal cerebellar neurogenesis and medulloblastoma growth in mice.

Alterations in genes that regulate brain size may contribute to both microcephaly and brain tumor formation. Here, we report that Aspm, a gene that is mutated in familial microcephaly, regulates postnatal neurogenesis in the cerebellum and supports the growth of medulloblastoma, the most common malignant pediatric brain tumor. Cerebellar granule neuron progenitors (CGNPs) express Aspm when maintained in a proliferative state by sonic hedgehog (Shh) signaling, and Aspm is expressed in Shh-driven medulloblastoma in mice. Genetic deletion of Aspm reduces cerebellar growth, while paradoxically increasing the mitotic rate of CGNPs. Aspm-deficient CGNPs show impaired mitotic progression, altered patterns of division orientation and differentiation, and increased DNA damage, which causes progenitor attrition through apoptosis. Deletion of Aspm in mice with Smo-induced medulloblastoma reduces tumor growth and increases DNA damage. Co-deletion of Aspm and either of the apoptosis regulators Bax or Trp53 (also known as p53) rescues the survival of neural progenitors and reduces the growth restriction imposed by Aspm deletion. Our data show that Aspm functions to regulate mitosis and to mitigate DNA damage during CGNP cell division, causes microcephaly through progenitor apoptosis when mutated, and sustains tumor growth in medulloblastoma.

Two-Dimensional Fullerene Assembly from an Exfoliated van der Waals Template.

Two-dimensional (2D) materials are commonly prepared by exfoliating bulk layered van der Waals crystals. The creation of synthetic 2D materials from bottom-up methods is an important challenge as their structural flexibility will enable chemists to tune the materials properties. A 2D material was assembled using C60 as a polymerizable monomer. The C60 building blocks are first assembled into a layered solid using a molecular cluster as structure director. The resulting hierarchical crystal is used as a template to polymerize its C60 monolayers, which can be exfoliated down to 2D crystalline nanosheets. Derived from the parent template, the 2D structure is composed of a layer of inorganic cluster, sandwiched between two monolayers of polymerized C60 . The nanosheets can be transferred onto solid substrates and depolymerized by heating. Electronic absorption spectroscopy reveals an optical gap of 0.25 eV, narrower than that of the bulk parent crystalline solid.

van der Waals Solids from Self-Assembled Nanoscale Building Blocks.

Traditional atomic van der Waals materials such as graphene, hexagonal boron-nitride, and transition metal dichalcogenides have received widespread attention due to the wealth of unusual physical and chemical behaviors that arise when charges, spins, and vibrations are confined to a plane. Though not as widespread as their atomic counterparts, molecule-based two-dimensional (2D) layered solids offer significant benefits; their structural flexibility will enable the development of materials with tunable properties. Here we describe a layered van der Waals solid self-assembled from a structure-directing building block and C60 fullerene. The resulting crystalline solid contains a corrugated monolayer of neutral fullerenes and can be mechanically exfoliated. The absorption spectrum of the bulk solid shows an optical gap of 390 ± 40 meV that is consistent with thermal activation energy obtained from electrical transport measurement. We find that the dimensional confinement of fullerenes significantly modulates the optical and electronic properties compared to the bulk solid.

Transition from Molecular Vibrations to Phonons in Atomically Precise Cadmium Selenide Quantum Dots.

We use micro-Raman spectroscopy to measure the vibrational structure of the atomically precise cadmium selenide quantum dots Cd35Se20X30L30, Cd56Se35X42L42, and Cd84Se56X56L56. These quantum dots have benzoate (X) and n-butylamine (L) ligands and tetrahedral (Td) shape with edges that range from 1.7 to 2.6 nm in length. Investigating this previously unexplored size regime allows us to identify the transition from molecular vibrations to bulk phonons in cadmium selenide quantum dots for the first time. Room-temperature Raman spectra have broad CdSe peaks at 175 and 200 cm-1. Density functional theory calculations assign these peaks to molecular surface and interior vibrational modes, respectively, and show that the interior, surface, and ligand atom motion is strongly coupled. The interior peak intensity increases relative to the surface peak as the cluster size increases due to the relative increase in the polarizability of interior modes with quantum dot size. The Raman spectra do not change with temperature for molecular Cd35Se20X30L30, while the interior peak narrows and shifts to higher energy as temperature decreases for Cd84Se56X56L56, a spectral evolution typical of a phonon. This result shows that the single bulk unit cell contained within Cd84Se56X56L56 is sufficient to apply a phonon confinement model, and that Cd56Se35X42L42, with its 2.1 nm edge length, marks the boundary between molecular vibrations and phonons.

Tonic activation of Bax primes neural progenitors for rapid apoptosis through a mechanism preserved in medulloblastoma.

Commitment to survival or apoptosis within expanding progenitor populations poses distinct risks and benefits to the organism. We investigated whether specialized mechanisms regulate apoptosis in mouse neural progenitors and in the progenitor-derived brain tumor medulloblastoma. Here, we identified constitutive activation of proapoptotic Bax, maintained in check by Bcl-xL, as a mechanism for rapid cell death, common to postnatal neural progenitors and medulloblastoma. We found that tonic activation of Bax in cerebellar progenitors, along with sensitivity to DNA damage, was linked to differentiation state. In cerebellar progenitors, active Bax localized to mitochondria, where it was bound to Bcl-xL. Disruption of Bax:Bcl-xL binding by BH3-mimetic ABT 737 caused rapid apoptosis of cerebellar progenitors and primary murine medulloblastoma cells. Conditional deletion of Mcl-1, in contrast, did not cause death of cerebellar progenitors. Our findings identify a mechanism for the sensitivity of brain progenitors to typical anticancer therapies and reveal that this mechanism persists in medulloblastoma, a malignant brain tumor markedly sensitive to radiation and chemotherapy.

Ferromagnetic ordering in superatomic solids.

In order to realize significant benefits from the assembly of solid-state materials from molecular cluster superatomic building blocks, several criteria must be met. Reproducible syntheses must reliably produce macroscopic amounts of pure material; the cluster-assembled solids must show properties that are more than simply averages of those of the constituent subunits; and rational changes to the chemical structures of the subunits must result in predictable changes in the collective properties of the solid. In this report we show that we can meet these requirements. Using a combination of magnetometry and muon spin relaxation measurements, we demonstrate that crystallographically defined superatomic solids assembled from molecular nickel telluride clusters and fullerenes undergo a ferromagnetic phase transition at low temperatures. Moreover, we show that when we modify the constituent superatoms, the cooperative magnetic properties change in predictable ways.

A dose of our own therapy: using research findings to challenge mental health nurses to embrace contemporary practice realities.

This paper explores the effects of mental policy changes and the curtailment of mental health nursing education on the realities of working as a mental health nurse in rural and remote locations in New South Wales, Australia. Using the twin lenses of mental health nursing and the sociology of work and social change, the experiences of mental health nurses are explored and set in the context of the evolution of the mental health nurse into non-specialist mental health worker. At the same time, mental health nurses are challenged to adapt to new practice realities.

Sex-specific expression of distinct serotonin receptors mediates stress vulnerability of adult hippocampal neural stem cells in mice.

Women are more vulnerable to stress and have a higher likelihood of developing mood disorders. The serotonin (5HT) system has been highly implicated in stress response and mood regulation. However, sex-dependent mechanisms underlying serotonergic regulation of stress vulnerability remain poorly understood. Here, we report that adult hippocampal neural stem cells (NSCs) of the Ascl1 lineage (Ascl1-NSCs) in female mice express functional 5HT1A receptors (5HT1ARs), and selective deletion of 5HT1ARs in Ascl1-NSCs decreases the Ascl1-NSC pool only in females. Mechanistically, 5HT1AR deletion in Ascl1-NSCs of females leads to 5HT-induced depolarization mediated by upregulation of 5HT7Rs. Furthermore, repeated restraint stress (RRS) impairs Ascl1-NSC maintenance through a 5HT1AR-mediated mechanism. By contrast, Ascl1-NSCs in males express 5HT7R receptors (5HT7Rs) that are downregulated by RRS, thus maintaining the Ascl1-NSC pool. These findings suggest that sex-specific expression of distinct 5HTRs and their differential interactions with stress may underlie sex differences in stress vulnerability.

Anterior cingulate cortex projections to the dorsal medial striatum underlie insomnia associated with chronic pain.

Chronic pain often leads to the development of sleep disturbances. However, the precise neural circuit mechanisms responsible for sleep disorders in chronic pain have remained largely unknown. Here, we present compelling evidence that hyperactivity of pyramidal neurons (PNs) in the anterior cingulate cortex (ACC) drives insomnia in a mouse model of nerve-injury-induced chronic pain. After nerve injury, ACC PNs displayed spontaneous hyperactivity selectively in periods of insomnia. We then show that ACC PNs were both necessary for developing chronic-pain-induced insomnia and sufficient to mimic sleep loss in naive mice. Importantly, combining optogenetics and electrophysiological recordings, we found that the ACC projection to the dorsal medial striatum (DMS) underlies chronic-pain-induced insomnia through enhanced activity and plasticity of ACC-DMS dopamine D1R neuron synapses. Our findings shed light on the pivotal role of ACC PNs in developing chronic-pain-induced sleep disorders.

R6G on graphene: high Raman detection sensitivity, yet decreased Raman cross-section.

Several recent studies have demonstrated the use of single and few-layer graphene as a substrate for the enhancement of Raman scattering by adsorbed molecules in a method termed graphene-enhanced Raman spectroscopy (GERS). Here we determine the resonance Raman scattering cross-section for the dye molecule rhodamine 6G (R6G) adsorbed on bilayer graphene. For the 1650 cm(-1) R6G mode, we obtain a cross-section of 5.1 × 10(-24) cm(2)·molecule(-1), a greater than 3-fold reduction from the previously reported solution value. We show that the absorption spectrum of adsorbed R6G can be measured using micro-optical contrast spectroscopy, and we find that detuning of the molecular resonance explains the decreased Raman scattering cross-section. We find no evidence for a graphene Raman enhancement process. We also study the graphene thickness dependence of the adsorbed R6G Raman signal and show that a model incorporating electromagnetic interference effects can qualitatively explain the decrease in signal with increasing graphene thickness.

Long-term optical imaging of the spinal cord in awake, behaving animals.

Advances in optical imaging approaches and fluorescent biosensors have enabled an understanding of the spatiotemporal and long-term neural dynamics in the brain of awake animals. However, methodological difficulties and the persistence of post-laminectomy fibrosis have greatly limited similar advances in the spinal cord. To overcome these technical obstacles, we combined in vivo application of fluoropolymer membranes that inhibit fibrosis; a redesigned, cost-effective implantable spinal imaging chamber; and improved motion correction methods that together permit imaging of the spinal cord in awake, behaving mice, for months to over a year. We also demonstrate a robust ability to monitor axons, identify a spinal cord somatotopic map, conduct Ca2+ imaging of neural dynamics in behaving animals responding to pain-provoking stimuli, and observe persistent microglial changes after nerve injury. The ability to couple neural activity and behavior at the spinal cord level will drive insights not previously possible at a key location for somatosensory transmission to the brain.

Synthesis of graded CdS1-xSex nanoplatelet alloys and heterostructures from pairs of chalcogenoureas with tailored conversion reactivity.

A mixture of N,N,N'-trisubstituted thiourea and cyclic N,N,N',N'-tetrasubstituted selenourea precursors were used to synthesize three monolayer thick CdS1-xSex nanoplatelets in a single synthetic step. The microstructure of the nanoplatelets could be tuned from homogeneous alloys, to graded alloys to core/crown heterostructures depending on the relative conversion reactivity of the sulfur and selenium precursors. UV-visible absorption and photoluminescence spectroscopy and scanning transmission electron microscopy electron energy loss spectroscopy (STEM-EELS) images demonstrate that the elemental distribution is governed by the relative precursor conversion kinetics. Slow conversion kinetics produced nanoplatelets with larger lateral dimensions, behavior that is characteristic of precursor conversion limited growth kinetics. Across a 10-fold range of reactivity, CdS nanoplatelets have 4× smaller lateral dimensions than CdSe nanoplatelets grown under identical conversion kinetics. The difference in size is consistent with a rate of CdSe growth that is 4× greater than the rate of CdS. The influence of the relative sulfide and selenide growth rates, the duration of the nucleation phase, and the solute composition on the nanoplatelet microstructure are discussed.

Realities of mental health nursing practice in rural Australia.

Mental health nursing as a distinct speciality has been in decline in New South Wales (NSW), Australia, for two decades. Arguably, this decline has worsened both consumer outcomes and the workplace experiences of mental health nurses. This article reports on a study designed to ascertain the nature of contemporary mental health nursing practice in New South Wales. The study utilised focus group research methodology, with participants recounting the realities of their day-to-day professional practice and perceptions of their professional identity. The findings indicate a contracting, if not moribund, profession; a decrease in the value attached to mental health nursing; and a pattern of persistent underfunding by successive governments of mental health services. An analysis of present and historical trends reveals there is a pressing need for a restructure and re-formation of mental health nursing in rural areas. This article links the shortage of mental health nurses in NSW to the closure of the mental health nursing register, a shift to comprehensive/generalist nurse education models, a perceived lack of nurses' professional standing, and natural attrition without suitably qualified replacements. Mental health nurses in this study perceived that they were not valued by other health professionals or by their own managers. Participants in this study reported mental health nursing in rural areas was an unattractive career choice. These findings are important to the understanding of recruitment and retention issues in rural mental health nursing in Australia.

Superatomic solid solutions.

In atomic solids, substitutional doping of atoms into the lattice of a material to form solid solutions is one of the most powerful approaches to modulating its properties and has led to the discovery of various metal alloys and semiconductors. Herein we have prepared solid solutions in hierarchical solids that are built from atomically precise clusters. Two geometrically similar metal chalcogenide clusters, Co6Se8(PEt3)6 and Cr6Te8(PEt3)6, were combined as random substitutional mixture, in three different ratios, in a crystal lattice together with fullerenes. This does not alter the underlying crystalline structure of the [cluster][C60]2 material, but it influences its electronic and magnetic properties. All three solid solutions showed increased electrical conductivities compared with either the Co- or Cr-based parent material, substantially so for two of the Co:Cr ratios (up to 100-fold), and lowered activation barriers for electron transport. We attribute this to the existence of additional energy states arising from the materials' structural heterogeneity, which effectively narrow transport gaps.

Ultrafast observation of isomerization and complexation in the photolysis of bromoform in solution.

Ultrafast photolysis of bromoform (CHBr(3)) with a 267 nm pulse of light followed by broadband transient electronic absorption identifies the photoproducts and follows their evolution in both neat bromoform and cyclohexane solutions. In neat bromoform, a species absorbing at 390 nm appears promptly and decays with a time constant of 13 ps as another species absorbing at 495 nm appears. The wavelength and time evolution of the first absorption is consistent with the formation of iso-bromoform (CHBr(2)-Br) by recombination of the fragment radicals within the solvent cage. The presence of an isosbestic point in the transient spectra indicates that this isomer is the precursor of the second absorber. The excess internal energy remaining in iso-bromoform permits release of the weakly bound Br atom to form a complex, CHBr(3)-Br, with other bromoform molecules. The features in the transient spectra are qualitatively similar in cyclohexane solutions of bromoform. The wavelength of the transition of iso-bromoform does not change upon dilution, but that of the CHBr(3)-Br complex systematically decreases with addition of cyclohexane. This trend agrees with the predicted dependence of the energy of a charge-transfer transition on the dielectric constant of the medium. Vibrational relaxation is likely to be the controlling feature of the evolution of the initially formed iso-bromoform.

Time-resolved studies of the reactions of CN radical complexes with alkanes, alcohols, and chloroalkanes.

Ultrafast transient absorption experiments monitor the reaction of CN radicals with 16 different alkane, alcohol, and chloroalkane solutes in CH(2)Cl(2) and with a smaller number of representative solutes in CHCl(3) and CH(3)CCl(3). In these experiments, 267-nm photolysis generates CN radicals, and transient electronic absorption at 400 nm probes their time evolution. A crucial feature of the reactions of CN radicals is their rapid formation of two different types of complexes with the solvent that have different stabilities and reactivities. The signature of the formation of these complexes is the CN transient absorption disappearing more slowly than the infrared transient absorption of the HCN product appears. Studying both the growth of HCN and the decay of the CN-solvent complexes in the reaction of CN with pentane in CH(2)Cl(2) and CHCl(3) solutions provides the information needed to build a kinetic model that accounts for the reaction of both complexes. This model permits analysis of the reaction of each of the 16 different solutes using only the decay of the CN transient absorption. The reaction of CN-solvent complexes with alkanes and chloroalkanes is slower than the corresponding reactions of Cl. However, the reactions of alcohols with both CN and Cl occur at about the same rate, likely reflecting additional complexation of the CN radical or its ICN precursor by the alcohol. The rates for the reactions of CN with the chloroalkanes decrease with increasing Cl content of the solute, in keeping with previous observations for the reactions of Cl in both gases and liquids.