Na2B6Si2: A Prototype Silico-boride with Closo (B6)2- Clusters.

The compound Na2B6Si2 was synthesized under high-pressure, high-temperature conditions at pressures ranging from 6 to 9.5 GPa and temperatures from 1070 to 1270 K before quenching to room temperature followed by slow decompression. The crystal structure was determined from microcrystals using precession-assisted electron diffraction tomography, validated by dynamical refinement and full-profile refinements using optimized coordinates from quantum chemical calculations (space group R3̅m, Pearson symbol hR30, a = 5.0735(1) Å and c = 16.0004(7) Å). The atomic arrangement consists of a unique framework formed by electron-precise octahedral closo (B6)2- clusters connected via ethane-like (Si2)0 dumbbells. The Na+ cations occupy cavities in the hierarchical variation of a Heusler-type framework. The balance (Na+)2([B6]2-)(Si0)2 reveals an electron precise Zintl-Wade phase, which is in line with electronic band structure calculations predicting semiconducting behavior.

A Borosilicide with Clathrate VIII Structure.

The high-pressure phase Na8BxSi46-x (3 < x < 5) is the first representative of a borosilicide crystallizing in the rarely occurring clathrate VIII type structure. Crystals with composition Na8B4Si42 (space group I43̅m; a = 9.7187(2) Å; Pearson symbol cI54) were obtained at 5-8 GPa and 1200 K. The clathrate I modification exists for the same composition at lower pressure with a larger cell volume (Pm3̅n; a = 9. 977(2) Å; cP54). Profound structural adaptions allow for a higher density of the clathrate VIII type than clathrate I, opening up the perspective of obtaining clathrate VIII type compounds as high-pressure forms of clathrate I.

The impact of boron atoms on clathrate-I silicides: composition range of the borosilicide K8-xBySi46-y.

The clathrate-I borosilicide K8-xBySi46-y (0.8 ≤x≤ 1.2 and 6.4 ≤y≤ 7.2; space group Pm3[combining macron]n) was prepared in sealed tantalum ampoules between 900 °C and 1000 °C. By high-pressure preparation at 8 GPa and 1000 °C, a higher boron content is achieved (x = 0.2, y = 7.8). Crystal structure and composition were established from X-ray diffraction data, chemical analysis, WDX spectroscopy, and confirmed by 11B and 29Si NMR, and magnetic susceptibility measurements. The compositions are electron-balanced according to the Zintl rule within one estimated standard deviation. The lattice parameter varies with composition from a = 9.905 Å for K7.85(2)B7.8(1)Si38.2(1) to a = 9.968(1) Å for K6.80(2)B6.4(5)Si39.6(5).

Cage Adaption by High-Pressure Synthesis: The Clathrate-I Borosilicide Rb8B8Si38.

Rb8B8Si38 forms under high-pressure, high-temperature conditions at p = 8 GPa and T = 1273 K. The new compound (space group Pm3̅n, a = 9.9583(1) Å) is the second example for a clathrate-I borosilicide. The phase is inert against strong acids and bases and thermally stable up to 1300 K at ambient pressure. (Rb+)8(B-)8(Si0)38 is electronically balanced, diamagnetic, and shows semiconducting behavior with moderate Seebeck coefficient below 300 K. Chemical bonding analysis by the electron localizability approach confirms the description of Rb8B8Si38 as Zintl phase.

Molecular Imaging of Smoke-Induced Changes in Nuclear Factor-Kappa B Expression in Murine Tissues Including the Lung.

Many inflammatory responses are mediated by activation of the transcription factor, nuclear factor-kappa B (NF-κB), and a wide variety of human diseases involve abnormal regulation of its expression. In this investigation, we evaluated the effect of smoke inhalation injury on NF-κB expression in lung using two strains of NF-κB reporter mice. Groups of reporter mice with viral thymidine kinase (TK) or "fire fly" luciferase (Luc) genes under control by the NF-κB promoter (TK/NF-κB mice and Luc/NF-κB mice) were subjected to nonlethal smoke inhalation injury. Sham-treated animals served as controls. Twenty-four hours (each animal was injected intravenously with either 9-(4-18F-fluoro-3-[hydroxymethyl]butyl)guanine (FHBG) (~ 1.0 mCi) or luciferin (1.0 mg). One hour later, the TK/NF-κB mice were studied by micro-positron emission tomography (µ-PET) imaging using a Concord P4 µ-PET camera, and the Luc/NF-κB mice were studied by bioluminescence imaging with a charge-coupled device camera. The µ-PET data demonstrated that smoke injury produced massive increases in NF-κB expression (FHBG-standardized uptake value: 3.1 vs 0.0) 24 hours after smoke inhalation, which was reduced 48 hours after smoke inhalation, but still significantly different than the control. Qualitative analysis of the bioluminescence data revealed a remarkably similar effect of burn NF-κB luciferase expression in vivo. Biodistribution studies of FHBG uptake and luciferase activity in lung tissue demonstrated a similar increase 24 hours after injury, which was reduced 48 hours later, but still significantly higher than the sham. The present data with these models providing longitudinal imaging data on the same mouse may prove useful in the examination of the factors producing lung injury by smoke inhalation, as well as the treatment(s) for the damage produced with and without burn injury.

Single hind limb burn injury to mice alters nuclear factor-κB expression and [¹8F] 2-fluoro-2-deoxy-D-glucose uptake.

Burn trauma to the extremities can produce marked systemic effects in mice. Burn injury to the dorsal surface of mice is also associated with changes in glucose metabolism ([18F] 2-fluoro-2-deoxy-D-glucose [18FDG] uptake) by brown adipose tissue (BAT) and nuclear factor (NF)-κB activity in several tissues including skeletal muscle. This study examined the effect of a single hind limb burn in mice on 18FDG uptake by NF-κB activity in vivo, and blood flow was determined by laser Doppler techniques. Male NF-κB luciferase reporter mice (28-30 g) were anesthetized, both legs were shaven, and the right leg was subjected to scald injury by immersion in 90°C water for 5 seconds. Sham-treated animals were used as controls. Each burned and sham mouse was resuscitated with saline (2 mL, i.p.). The individual animals were placed in wire bottom cages with no food and free access to water. After 24 hours, the animals were imaged with laser Doppler for measuring blood flow in the hind limb. The animals were then unanesthetized with 50 µCi of FDG or luciferin (1.0 mg, i.v.) via tail vein. Five minutes after luciferin injection, NF-κB mice were studied by bioluminescence imaging with a charge-coupled device camera. One hour after 18FDG injection, the animals were killed with carbon dioxide overdose, and 18FDG biodistribution was measured. Tissues were also analyzed for NF-κB luciferase activity. The scalding procedure used here produced a full-thickness burn injury to the leg with sharp margins. 18FDG uptake by the burned leg was lower than that in the contralateral limb. Similarly, luciferase activity and blood flow in the burned leg were lower than those in the contralateral leg. 18FDG uptake by BAT and heart increased, whereas that by brain decreased. In conclusion, the present study suggests that burn injury to a single leg decreased FDG uptake by skeletal muscle but increased 18FDG uptake by BAT. The injury to the leg reduced NF-κB expression compared with the contralateral leg and the uninjured skeletal muscle of the sham but activated NF-κB expression in a number of other organs. These findings are consistent with the hypothesis that burn trauma to the extremities can produce marked systemic effects, including activation of NF-κB expression and activation of 18FDG uptake by BAT.

BaRh2Si9--a new clathrate with a rhodium-silicon framework.

The semiconducting compound BaRh2Si9 is a new kind of intermetallic clathrate. It was obtained by reacting BaSi, Rh and Si at 950 °C. The crystal structure (space group C2/c; Pearson symbol mC48, a = 6.2221(5) Å, b = 21.399(2) Å, c = 6.2272(5) Å, ß = 90.306(7)°) displays a covalently bonded Rh-Si framework, in which four-connected Si atoms partly show unusually small bond angles. The Ba atoms are encapsulated in large polyhedral cages formed by 18 Si and 4 Rh atoms. The compound is a diamagnetic p-type semiconductor, which is in agreement with band structure calculations resulting in a band gap of 0.12 eV. Quantum chemical calculations reveal positively charged Ba atoms (Ba(+1.3)) and negatively charged Rh atoms (Rh(-1)). Si atoms with neighboring Rh atoms are positively charged, while those connected only with Si atoms are negatively charged.

Synthesis, crystal structure and physical properties of the clathrate-I phase Ba(8)Rh(x)Si(46-x-y□y).

The new clathrate-I phase Ba(8)Rh(x)Si(46-x-y□y) (2.36 < x < 2.74; y = 0.65 for x = 2.74), Pearson symbol cP54, space group Pm3[combining macron]n, was prepared as a single phase and characterized. For these compositions, the lattice parameter does not change significantly and was found to be a = 10.347(1) Å. Phase relations were investigated by means of metallographic and thermal analyses. The incongruently melting phase Ba(8)Rh(x)Si(46-x-y□y) was obtained by annealing a solidified melt of the stoichiometric composition at 1000 °C for five days. Below 850 °C, the clathrate phase slowly decomposes to BaSi(2), Si and the new compound BaRh(2)Si(9). Crystal structure and vacancy concentration were investigated by means of single crystal and powder X-ray diffraction and wavelength dispersive X-ray spectroscopy analyses. Quantum chemical calculations show that the Rh 4d states hybridize with Si 3p states so that the DOS structure cannot be simply deduced in a rigid band approach from that of the binary Ba(8)Si(46). Analysis of the chemical bonding applying the ELI-D approach yielded covalent two-center two-electron bonds between Rh and Si atoms. For the composition Ba(8)Rh(2.74)Si(42.61□0.65), a temperature dependent diamagnetic susceptibility and an almost temperature independent electrical resistivity (ρ≈ 5 µΩm) were observed. The magnitude of the negative Seebeck coefficient is increasing linearly with temperature from 0 µV K(-1) at 2 K to -35 µV K(-1) at 850 K indicating n-type electrical conductivity.

Gram-negative bacterial infection in thigh abscess can migrate to distant burn depending on burn depth.

Sepsis remains the major cause of death in patients with major burn injuries. In the present investigation we evaluated the interaction between burn injuries of varying severity and preexisting distant infection. We used Gram-negative bacteria (Pseudomonas aeruginosa and Proteus mirabilis) that were genetically engineered to be bioluminescent, which allowed for noninvasive, sequential optical imaging of the extent and severity of the infection. The bioluminescent bacteria migrated from subcutaneous abscesses in the leg to distant burn wounds on the back depending on the severity of the burn injury, and this migration led to increased mortality of the mice. Treatment with ciprofloxacin, injected either in the leg with the bacterial infection or into the burn eschar, prevented this colonization of the wound and decreased mortality. The present data suggest that burn wounds can readily become colonized by infections distant from the wound itself.

In vivo molecular imaging of murine embryonic stem cells delivered to a burn wound surface via Integra® scaffolding.

It has been demonstrated that restoration of function to compromised tissue can be accomplished by transplantation of bone marrow stem cells and/or embryonic stem cells (ESCs). One limitation to this approach has been the lack of noninvasive techniques to longitudinally monitor stem cell attachment and proliferation. Recently, murine ESC lines that express green fluorescent protein (GFP), luciferase (LV), and herpes simplex thymidine kinase (HVTK) were developed for detection of actively growing cells in vivo by imaging. In this study, the authors investigated the use of these ESC lines in a burned mouse model using Integra® as a delivery scaffolding/matrix. Two different cell lines were used: one expressing GFP and LV and the other expressing GFP, LV, and HVTK. Burn wounds were produced by application of a brass block (2 × 2 cm kept in boiling water before application) to the dorsal surface of SV129 mice for 10 seconds. Twenty-four hours after injury, Integra® with adherent stem cells was engrafted onto a burn wound immediately after excision of eschar. The stem cells were monitored in vivo by measuring bioluminescence with a charge-coupled device camera and immunocytochemistry of excised tissue. Bioluminescence progressively increased in intensity over the time course of the study, and GFP-positive cells growing into the Integra® were detected. These studies demonstrate the feasibility of using Integra® as a scaffolding, or matrix, for the delivery of stem cells to burn wounds as well as the utility of bioluminescence for monitoring in vivo cellular tracking of stably transfected ESC cells.

Effects of burn injury, cold stress and cutaneous wound injury on the morphology and energy metabolism of murine brown adipose tissue (BAT) in vivo.

AIMS: Cold stress has been shown to produce dramatic increases in 2-fluoro-2-deoxy-D-Glucose ((18)FDG) accumulation by brown adipose tissue (BAT) in rodents. However, neither the effects of other types of stress on (18)FDG accumulation nor the effects of stressors on the accumulation of tracers of other aspects of energy metabolism have been evaluated. In this report we studied the effects of cold stress, burn injury and cutaneous wounds on murine BAT at the macroscopic, microscopic and metabolic level. MAIN METHODS: Glucose metabolism was studied with (18)FDG, fatty acid accumulation was evaluated with trans-9(RS)-(18)F-fluoro-3,4(RS,RS)-methyleneheptadecanoic acid (FCPHA) and tricarboxcylic acid cycle (TCA) activity was evaluated with (3)H acetate. KEY FINDINGS: All three stressors produced dramatic changes in BAT at the macroscopic and microscopic level. Macroscopically, BAT from the stressed animals appeared to be a much darker brown in color. Microscopically BAT of stressed animals demonstrated significantly fewer lipid droplets and an overall decrease in lipid content. Accumulation of (18)FDG by BAT was significantly (p<0.01) increased by all 3 treatments (Cold: ~16 fold, burn ~7 Fold and cutaneous wound ~14 fold) whereas uptake of FDG by white fat was unchanged. This effect was also demonstrated non invasively by µPET imaging. Although less prominent than with (18)FDG, BAT uptake of FCPHA and acetate were also significantly increased by all three treatments. These findings suggest that in addition to cold stress, burn injury and cutaneous wounds produce BAT activation in mice. SIGNIFICANCE: This study demonstrates brown fat activated by several stressors leads to increased uptake of various substrates.

Inhibition of JNK activation prolongs survival after smoke inhalation from fires.

Initial injury from smoke inhalation is mainly to the trachea and bronchi and is characterized by mucosal hyperemia and increased microvascular permeability, exfoliation of epithelial lining, mucous secretion, mucous plugging, and an acute inflammatory cell influx. In this study, we explore the role of the c-Jun N-terminal protein kinase (JNK) pathway in smoke inhalation lung injury using a rat model of exposure to smoke from burning cotton. Male Sprague-Dawley rats were exposed to smoke from burning cotton for 15 min, and 1 h after injury a JNK inhibitor (SP-600125) or vehicle was injected. We measured neutrophil influx, cytokine release, percent of apoptotic cells, airway plugging, and survival. Administration of a JNK inhibitor 1 h after smoke inhalation decreased airway apoptosis, mucous plugging, influx of inflammatory cells, and the release of cytokines and significantly prolonged animal survival (P < 0.05). These in vivo data show that the JNK pathway plays a critical role in smoke-induced lung injury and offer an attractive therapeutic approach for this injury.