Surface relief VCSELs at 670 nm with integrated polymer microlens for highly collimated fundamental-mode emission.

We demonstrate the integration of a wet-chemically etched surface relief on a vertical-cavity surface-emitting laser (VCSEL) emitting in the red spectral range for higher-order mode suppression. With this relief, fundamental-mode emission is achieved over the entire power range from threshold beyond thermal rollover. For collimation of the emitted beam, we implement polymer microlenses fabricated on-chip by a thermal reflow technique. We reduce the angle of divergence for all injected currents to a maximum of 2∘. By measuring high-resolution spectra, we show that Gaussian beam profiles correspond to pure fundamental-mode emission which is preserved after implementation of the polymer microlens onto the etched relief, proving the compatibility of the two processes.

Polyhedral Oligomeric Silsesquioxane D3h-(RSiO1.5)14.

While smaller polyhedral oligomeric silsesquioxanes TnRn (POSS) are readily accessible or even commercially available, unambiguously authenticated larger systems (n>12) have barely been reported. Synthesis and isolation procedures are lengthy, and yields are often very low. Herein, we present the surprisingly straightforward and high-yielding access to the phenyl-substituted derivative of a so far only postulated second D3h-symmetric T14 isomer and with that the largest crystallographically characterized POSS cage with organic substituents. Treatment of the commercially available incompletely condensed T7Ph7(OH)3 silsesquioxane with catalytic amounts of trifluoromethanesulfonic acid results in high yields of the T14Ph14 framework, which is isolated in crystalline form by a simple work-up. D3h-T14Ph14 was analyzed by single crystal X-ray diffraction, multinuclear NMR spectroscopy and thermal analysis. The relative energies of all four theoretically possible T14Ph14 isomers were determined by optimization of the corresponding structure using DFT methods.

Tetrylene-Functionalized Si7-Siliconoids.

The core expansion of metallic or metalloid clusters by the addition of further homo- or heteronuclear vertices is pivotal to the nucleation and growth of particles. The exohedral grafting of a low-valent functionality followed by endohedral incorporation have been identified as key steps. Following previous work on the Si6 series, we now report the synthesis and full characterization of the amidinatotetrylene-functionalized seven-vertex siliconoids Si7R5[E(NtBu)2CPh] (E = Si, Ge, Sn). In the case of the silylene derivative, the solid-state structure was determined by single crystal X-ray diffraction.

π-Complexes Derived from Non-classical Diboriranes: Side-on vs. End-on Carbonylative Ring Expansion.

Unlike cyclopropanes, the analogous B2C species, the diboriranes, tend to adopt non-classical Hückel-aromatic structures with bridging moieties R between the boron atoms. The coordination of the thus generated cyclic 2e- π-system to transition metals is completely unexplored. We here report that complexation of non-classical diboriranes cyclo-µ-RB2Dur2CPh (R = H, SnMe3; Dur = 2,3,5,6-tetramethylphenyl) to Fe(CO)3 fragments allows for the carbonylative ring expansion of the B2C ring to either four- or five-membered rings depending on the nature of the BRB 3-center-2-electron bond (3c2e): the H-bridged diborirane (R = H) initially reacts with Fe2(CO)9 to the allylic π-complex with an agostic BH/Fe interaction. Subsequent formal hydroboration of CO from excess Fe2(CO)9 results in the side-on ring expansion to a five-membered B2C2O ring, coordinated to the Fe(CO)3 moiety. In contrast, in case of the stannyl-bridged diborirane (R = SnMe3) under the same conditions, CO is added end-on to the B-B bond with the carbon terminus formally inserting into the B2Sn 3c2e-bond. The two carbonylative ring expansion products can also be described as nido and closo clusters, respectively, according to the Wade-Mingos rules.

σ,π-Conjugated Bis(germylene) Adducts with NHC and CAACs.

Heavier tetrylenes attract attention for their potential in synthesis, catalysis and small molecule activation. The coordination by N-heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (CAACs) results in substantial structural and electronic differences although typically only one of these yields stable derivatives for one and the same tetrylene. We now report both NHC- and CAAC-coordination to a bridged bis(germylene) motif. The NHC-coordinated bis(germylene) exhibits pyramidal germanium centers with lone pairs of electrons, while with CAAC an unprecedented stable bis(germene) with two Ge=C bonds is isolated. Spectroscopic and crystallographic evidence as well as DFT calculations confirm the effects of σ,π-conjugation between the two germanium centers in both cases. The coordination of NHC is reversible as the reaction with BPh3 liberates the transient bis(germylene) and thus provides an alternative low-temperature route towards polymers with Ge=Ge bonds.

Siliconoid Expansion by a Single Germanium Atom through Isolated Intermediates.

The growth of (semi-)metal clusters is pivotal for nucleation processes in gaseous and condensed phases. We now report the isolation of intermediates during the expansion of a stable unsaturated silicon cluster (siliconoid) by a single germanium atom through a sequence of substitution, rearrangement and reduction. The reaction of ligato-lithiated hexasilabenzpolarene LiSi6 Tip5 (1Li⋅(thf)2 , Tip=2,4,6-triisopropylphenyl) with GeCl2 ⋅NHC (NHC=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) initially yields the product with exohedral germanium(II) functionality, which then inserts into an Si-Si bond of the Si6 scaffold. The concomitant transfer of the chloro functionality from germanium to an adjacent silicon preserves the electron-precise nature of the formed endohedral germylene. Full incorporation of the germanium heteroatom to the Si6 Ge cluster core is finally achieved either by reduction under loss of the coordinating NHC or directly by reaction of 1Li⋅(thf)2 with GeCl2 ⋅1,4-dioxane.

Transition-Metal Complexes of Heavier Cyclopropenes: Non-Dewar-Chatt-Duncanson Coordination and Facile Si═Ge Functionalization.

Transition-metal complexes of cyclopropenes occur as fleeting intermediates of numerous metal-catalyzed organic transformations. A heavier analogue has now been obtained from the reaction of an NHC-stabilized silagermenylidene, bis(1,5-cyclooctadiene)nickel(0), and 1 equiv of N-heterocyclic carbene (NHC). The residual chloro functionality at the germanium end of the coordinated Ge═Si moiety of the thus formed 1H-disilagermirene is easily exchanged by treatment with anionic nucleophiles, which provides access to a series of differently substituted Si2Ge-cyclopropenes as nickel complexes in excellent yields. NMR spectroscopic data, X-ray crystallographic analysis, and DFT calculations indicate a coordination mode different from the metallacyclopropane and π-complex extremes of the Dewar-Chatt-Duncanson model: the σ-component of the Ge═Si double bond acts as donor and acceptor, leaving behind a nearly unsupported Si-Ge π-bond.

Transition Metal Complexes of Heavier Vinylidenes: Allylic Coordination vs Vinylidene-Alkyne Rearrangement at Nickel.

Transition metal π-allyl complexes are key reagents/intermediates of various catalytic and stoichiometric allylation reactions. We now report the first transition metal complex of a heavier allylic π-system. The η3-Si2Ge allyl nickel complex is formally obtained by the oxidative addition of the Si-Cl bond of the heavier vinylidene [R2(Cl)Si-(R)Si═(NHC)Ge:] to [Ni(COD)2] (R = 2,4,6-triisopropylphenyl; NHC = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; COD = 1,5-cyclooctadiene). Due to geometric constraints, the coordination to the Ni(II) center occurs through the formal Si═Ge double bond instead of the residual lone pair of electrons at germanium. In contrast, the Si-N bond of the analogous vinylidene [R2(Me2N)Si-(R)Si═(NHC)Ge:] (obtained by nucleophilic substitution of Cl by NMe2) does not oxidatively add to Ni(0), and a hydridosilagermene-η2-nickel complex is obtained instead. The formation of this complex necessarily implies the isomerization of the heavier vinylidene to the corresponding heteroalkyne with the Si≡Ge triple bond in the coordination sphere of nickel followed by the activation of a C-H bond of one of the isopropyl groups of an N-heterocyclic carbene (NHC) ligand.

The impact of the COVID-19 pandemic on people with rheumatic and musculoskeletal diseases: insights from patient-generated data on social media.

OBJECTIVES: During the COVID-19 pandemic, much communication occurred online, through social media. This study aimed to provide patient perspective data on how the COVID-19 pandemic impacted people with rheumatic and musculoskeletal diseases (RMDs), using Twitter-based patient-generated health data (PGHD). METHODS: A convenience sample of Twitter messages in English posted by people with RMDs was extracted between 1 March and 12 July 2020 and examined using thematic analysis. Included were Twitter messages that mentioned keywords and hashtags related to both COVID-19 (or SARS-CoV-2) and select RMDs. The RMDs monitored included inflammatory-driven (joint) conditions (ankylosing spondylitis, RA, PsA, lupus/SLE and gout). RESULTS: The analysis included 569 tweets by 375 Twitter users with RMDs across several countries. Eight themes emerged regarding the impact of the COVID-19 pandemic on people with RMDs: (i) lack of understanding of SARS-CoV-2/COVID-19; (ii) critical changes in health behaviour; (iii) challenges in healthcare practice and communication with healthcare professionals; (iv) difficulties with access to medical care; (v) negative impact on physical and mental health, coping strategies; (vi) issues around work participation; (vii) negative effects of the media; and (viii) awareness-raising. CONCLUSION: The findings show that Twitter serves as a real-time data source to understand the impact of the COVID-19 pandemic on people with RMDs. The platform provided 'early signals' of potentially critical health behaviour changes. Future epidemics might benefit from the real-time use of Twitter-based PGHD to identify emerging health needs, facilitate communication and inform clinical practice decisions.

Diphosphanylmetallocenes of Main-Group Elements.

Several 1,1'-diphosphanyl-substituted metallocenes of magnesium (magnesocenes) were synthesized, structurally characterized, and their reactivity and coordination chemistry were investigated. Transmetalation of these magnesocenes gives access to group 14 metallocenes (tetrelocenes), as well as to group 15 stibonocenes. These s- and p-block metallocenes represent a novel class of bis(phosphanyl) ligands, exhibiting Lewis-amphiphilic character. Their coordination chemistry towards different transition-metal and main-group fragments was investigated and different complexes are presented.

Re-evaluating standards of human subjects protection for sensitive health data in social media networks.

This study addresses ethical questions about conducting health science research using network data from social media platforms. We provide examples of ethically problematic areas related to participant consent, expectation of privacy, and social media networks. Further, to illustrate how researchers can maintain ethical integrity while leveraging social media networks, we describe a study that demonstrates the ability to use social media to identify individuals affected by cancer. We discuss best practices and ethical guidelines for studying social media network data, including data collection, analysis, and reporting.

Arid1a Loss Drives Nonalcoholic Steatohepatitis in Mice Through Epigenetic Dysregulation of Hepatic Lipogenesis and Fatty Acid Oxidation.

Nonalcoholic steatohepatitis (NASH) is a rapidly growing cause of chronic liver damage, cirrhosis, and hepatocellular carcinoma. How fatty liver pathogenesis is subject to epigenetic regulation is unknown. We hypothesized that chromatin remodeling is important for the pathogenesis of fatty liver disease. AT-rich interactive domain-containing protein 1A (ARID1A), a DNA-binding component of the SWItch/sucrose nonfermentable adenosine triphosphate-dependent chromatin-remodeling complex, contributes to nucleosome repositioning and access by transcriptional regulators. Liver-specific deletion of Arid1a (Arid1a liver knockout [LKO]) caused the development of age-dependent fatty liver disease in mice. Transcriptome analysis revealed up-regulation of lipogenesis and down-regulation of fatty acid oxidation genes. As evidence of direct regulation, ARID1A demonstrated direct binding to the promoters of many of these differentially regulated genes. Additionally, Arid1a LKO mice were more susceptible to high-fat diet-induced liver steatosis and fibrosis. We deleted Pten in combination with Arid1a to synergistically drive fatty liver progression. Inhibition of lipogenesis using CAT-2003, a potent sterol regulatory element-binding protein inhibitor, mediated improvements in markers of fatty liver disease progression in this Arid1a/Pten double knockout model. Conclusion: ARID1A plays a role in the epigenetic regulation of hepatic lipid homeostasis, and its suppression contributes to fatty liver pathogenesis. Combined Arid1a and Pten deletion shows accelerated fatty liver disease progression and is a useful mouse model for studying therapeutic strategies for NASH.

Gaussian-like transverse-mode profile characteristics of high-power large-area red-emitting VCSELs.

We demonstrate a large-area red-emitting vertical-cavity surface-emitting laser (VCSEL) structure with significant improvement in the uniformity of charge carrier distribution by adopting a Si-doped $ {{\rm Al}_{0.20}}{\rm GaInP} $Al0.20GaInP current spreading layer and a bottom disk contact. The new structure emitting at 670 nm with a bottom disk contact diameter of 20 µm was compared with the conventional oxide-confined top-emitting structure with a similar aperture size. The maximum output peak power increased from 8.8 mW to 22.5 mW under pulsed-mode operation at room temperature. The far field improved from a strong multiple-mode pattern to a Gaussian-like profile. The corresponding divergence angle of the far-field pattern at $ 2{\rm {I}}_{\rm{th}} $2Ith injection current reduced from 16.2° to 10.9°.

Chalcogen-Expanded Unsaturated Silicon Clusters: Thia-, Selena-, and Tellurasiliconoids.

Reactions of silylenes with heavier chalcogens (E) typically result in Si=E double bonds or their π-addition products. In contrast, the oxidation of a silylene-functionalized unsaturated silicon cluster (siliconoid) with Group 16 elements selectively yields cluster expanded siliconoids Si7 E (E=S, Se, Te) fully preserving the unsaturated nature of the cluster scaffold as evident from the NMR signatures of the products. Mechanistic considerations by DFT calculations suggest the intermediacy of a Si6 siliconoid with exohedral Si=E functionality. The reaction thus may serve as model system for the oxidation of surface-bonded silylenes at Si(100) by chalcogens and their diffusion into the silicon bulk.

Magnesocenophane-Catalyzed Amine Borane Dehydrocoupling.

The Lewis acidities of a series of [n]magnesocenophanes (1 a-d) have been investigated computationally and found to be a function of the tilt of the cyclopentadienyl moieties. Their catalytic abilities in amine borane dehydrogenation/dehydrocoupling reactions have been probed, and C[1]magnesocenophane (1 a) has been shown to effectively catalyze the dehydrogenation/dehydrocoupling of dimethylamine borane (2 a) and diisopropylamine borane (2 b) under ambient conditions. Furthermore, the mechanism of the reaction with 2 a has been investigated experimentally and computationally, and the results imply a ligand-assisted mechanism involving stepwise proton and hydride transfer, with dimethylaminoborane as the key intermediate.

Indirect and Direct Grafting of Transition Metals to Siliconoids.

Unsaturated charge-neutral silicon clusters (siliconoids) are important as gas-phase intermediates between molecules and the elemental bulk. With stable zirconocene- and hafnocene-substituted derivatives, we here report the first examples containing directly bonded transition-metal fragments that are readily accessible from the ligato-lithiated Si6 siliconoid (1Li) and Cp2 MCl2 (M=Zr, Hf). Charge-neutral siliconoid ligands with pending tetrylene functionality were prepared by the reaction of amidinato chloro tetrylenes [PhC(NtBu)2 ]ECl (E=Si, Ge, Sn) with 1Li, thus confirming the principal compatibility of such low-valent functionalities with the unsaturated Si6 cluster scaffold. The pronounced donor properties of the tetrylene/siliconoid hybrids allow for their coordination to the Fe(CO)4 fragment.

Equilibrium Formation of Stable All-Silicon Versions of 1,3-Cyclobutanediyl.

Main group analogues of cyclobutane-1,3-diyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of all-silicon 1,3-cyclobutanediyls as stable closed-shell singlet species from the reversible reactions of cyclotrisilene c-Si3 Tip4 (Tip=2,4,6-triisopropylphenyl) with the N-heterocyclic silylenes c-[(CR2 CH2 )(NtBu)2 ]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated N-heterocyclic silylene c-(CH)2 (NtBu)2 Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3-cyclobutanediyl intermediate.

Boron and Phosphorus Containing Heterosiliconoids: Stable p- and n-Doped Unsaturated Silicon Clusters.

Unsaturated silicon clusters (siliconoids) are short-lived intermediates during the transition from molecules to the elemental bulk; stable representatives reiterate surface features of silicon materials. The incorporation of suitable heteroatoms into the cluster scaffold of stable siliconoids extends this analogy to the technological process of silicon doping. Here, we report boron- and phosphorus-containing heterosiliconoids with BSi5 and PSi5 core based on the global minimum Si6R6 platform (dubbed benzpolarene for its relationship to benzene). The reductive cleavage of an SiR2 moiety (R = 2,4,6-iPr3C6H2) from Si6R6 selectively yields a dianionic Si5R42- cluster as its lithium salt. Treatment with Me3SiCl affords the corresponding trimethylsilyl-substituted (Me3Si)2Si5R4. Reaction of Si5R42- with iPr2NECl2 (E = B, P) yields the unprecedented p- and n-doped heterosiliconoids iPr2NESi5R4. Their peculiar electronic features are compared to those of the hexasilabenzpolarene starting material on grounds of NMR spectroscopy, X-ray diffraction, and DFT calculations.

Persistent Digermenes with Acyl and α-Chlorosilyl Functionalities.

We report the preparation of α-chlorosilyl- and acyl-substituted digermenes. Unlike the corresponding transient disilenes, these species with a Ge=Ge double bond show an unexpectedly low tendency for cyclization, but in turn are prone to thermal Ge=Ge bond cleavage. Triphenylsilyldigermene has been isolated as a crystalline model compound, and is the first fully characterized example of a neutral digermene with an A2 GeGeAB substitution pattern. Spectroscopic and computational evidence prove the constitution of 1-adamantoyldigermene as a first persistent species with a heavy double bond conjugated with a carbonyl moiety.

Equilibrium Coordination of NHCs to Si(IV) Species and Donor Exchange in Donor-Acceptor Stabilized Si(II) and Ge(II) Compounds.

We report the reversible coordination of the N-heterocyclic carbene (NHC), NHC iPr2Me2 (NHC iPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene), to silicon(IV)-halides, SiCl4, MeSiCl3, Me2SiCl2, and Me3SiCl. Predicted as well as experimentally determined thermodynamic parameters of these equilibria confirm that the complexation constant increases with the Lewis acidity of the silicon halides. In contrast, the more σ-donating N-heterocyclic carbene, NHCMe4 (NHCMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene), does not show any signs of dissociation from the corresponding SiCl4 and Me2SiCl2 adducts even at higher temperatures. As a consequence, NHC iPr2Me2 in donor-acceptor stabilized Si(II)- and Ge(II)-dimethyl complexes, NHC iPr2Me2·GeMe2·Fe(CO)4 and NHC iPr2Me2·SiMe2·Fe(CO)4, is readily replaced by NHCMe4.